niosh case msd
TRANSCRIPT
Musculoskeletal Disorders andWorkplace Factors
A Critical Review of Epidemiologic Evidence forWork-Related Musculoskeletal Disorders of the Neck,Upper Extremity, and Low Back
Edited by:Bruce P. Bernard, M.D., M.P.H.
Contributors:Vern Putz-Anderson, Ph.D.Bruce P. Bernard, M.D., M.P.H.Susan E. BurtLibby L. Cole, Ph.D.Cheryl Fairfield-EstillLawrence J. Fine, M.D., Dr.P.H.Katharyn A. Grant, Ph.D.Christopher GjessingLynn JenkinsJoseph J. Hurrell Jr., Ph.D.Nancy Nelson, Ph.D.Donna PfirmanRobert RobertsDiana Stetson, Ph.D.Marie Haring-Sweeney, Ph.D.Shiro Tanaka, M.D.
U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICESPublic Health Service
Centers for Disease Control and PreventionNational Institute for Occupational Safety and Health
July 1997
ii
This document is in the public domain and may be freely copied or reprinted.
DISCLAIMER
Mention of any company name or product does not constitute endorsement by theNational Institute for Occupational Safety and Health.
Copies of this and other NIOSH documents are available from
National Institute for Occupational Safety and HealthPublications Dissemination4676 Columbia Parkway
Cincinnati, OH 45226–1998
Telephone number: 1–800–35–NIOSH (1–800–356–4674)Fax number: (513) 533–8573
E-mail: [email protected]
To receive other information about occupational safety and health problems, call 1–800–35–NIOSH(1–800–356–4674), or visit the NIOSH Home Page on the World Wide Web at
http://www.cdc.gov/niosh
This publication is also available from theNational Technical Information Service for $60.00 plus $4.00 handling.
Please call (703) 487–4650 and ask for PB97–178628.
DHHS (NIOSH) Publication No. 97BB141
iii
FOREWORD
Musculoskeletal disorders (MSDs) were recognized as having occupational etiologic factors as early asthe beginning of the 18th century. However, it was not until the 1970s that occupational factors wereexamined using epidemiologic methods, and the work-relatedness of these conditions began appearingregularly in the international scientific literature. Since then the literature has increased dramatically;more than six thousand scientific articles addressing ergonomics in the workplace have been published.Yet, the relationship between MSDs and work-related factors remains the subject of considerabledebate.
Musculoskeletal Disorders and Workplace Factors: A Critical Review of Epidemiologic Evidencefor Work-Related Musculoskeletal Disorders of the Neck, Upper Extremity, and Low Back willprovide answers to many of the questions that have arisen on this topic over the last decade. Thisdocument is the most comprehensive compilation to date of the epidemiologic research on the relationbetween selected MSDs and exposure to physical factors at work. On the basis of our review of theliterature, NIOSH concludes that a large body of credible epidemiologic research exists that shows aconsistent relationship between MSDs and certain physical factors, especially at higher exposure levels.
This document, combined with other NIOSH efforts in this area, will assist us in our continued efforts toaddress these inherently preventable disorders.
Linda Rosenstock, M.D., M.P.H.Director, National Institute for Occupational Safety and HealthCenters for Disease Control and Prevention
iv
v
NOTE TO THE READER
This second printing of Musculoskeletal Disorders and Workplace Factors: A Critical Review ofEpidemiologic Evidence for Work-Related Musculoskeletal Disorders of the Neck, UpperExtremity, and Low Back incorporates a number of editorial changes, including grammar, formatting,and consistency issues that were identified in the first printing. In addition, the notation of Dr. LawrenceFine as co-editor was inadvertently omitted in the first printing and has been re-inserted.
The conclusions of the document in terms of decisions regarding the weight of the existing epidemiologicevidence for the relationship between workplace factors and musculoskeletal disorders remainunchanged. The following technical inconsistencies or errors were corrected:
Page 2-14: Text was corrected to reflect that five studies (as opposed to three) examined therelationship between force and musculoskeletal disorders of the neck.
Page 2-28: For Viikari-Juntura [1994], the “NR” entry in the Risk Indicator column was replaced withthe value 3.0.
Page 2-34: Bergqvist [1995a] was changed to Bergqvist [1994]. The Risk Indicator entry for thisstudy was changed from 4.4 to 3.7 (both noted as statistically significant), the entry for PhysicalExamination was changed from “Yes” to “No,” and the entry for Basis for Assessing Exposure waschanged from “job titles or self-reports” to “observation or measurements.”
Page 3-3: Text was corrected to reflect that four studies (as opposed to three) met all four evaluationcriteria. A description of Kilbom and Persson [1987] was moved forward in the chapter to this sectionand includes a clarification that health outcome in their study was based on symptoms and physicalfindings.
Page 3-32: The confidence interval depicted for Ohlsson [1994] was corrected to show a range from3.5 to 5.9.
Page 3-69: Schibye et al. [1995] was added to Table 3-5.
Page 4-25: Dimberg [1989] was changed to Dimberg [1987].
vi
Page 5a-3: Text was corrected to reflect that nineteen studies (as opposed to fifteen) reported resultson the association between repetition and carpal tunnel syndrome (CTS). Text was also corrected toreflect that five studies (as opposed to four) met the four evaluation criteria for addressing repetitivenessand CTS. A description of Osorio et al. [1994] was moved forward in the chapter to this section.
Page 5a-15: Text was corrected to reflect that eleven studies (as opposed to ten) reported results onthe association between force and CTS and that four (as opposed to three) met all four evaluationcriteria. Descriptions of Moore and Garg [1994] and Osorio et al. [1994] were moved forward in thechapter to this section.
Page 5a-19 : The discussion (strength of association, temporality, consistency of association, coherenceof evidence, and exposure-response relationship) of force and CTS was inadvertently omitted in thefirst printing and has been re-inserted.
Page 5a-27: The Risk Indicator for Osorio et al. [1994] was changed from 4.6 to 6.7, and for Nathan[1992], the “No association” entry under Risk Indicator was changed to a value of 1.0.
Page 5a-29: Stetson et al. [1993] was moved to the bottom of the table, and entries for Nathan et al. [1992] and McCormack et al. [1990] were added.
Page 5a-31: This table was modified to more accurately reflect the text.
Page 5a-33: For Koskimies et al. [1990], the entry for Basis for Assessing Exposure was changedfrom “observation or measurements” to “job titles or self-reports.”
Page 5b-1: Text was corrected to reflect that seven studies (as opposed to eight) are referenced onTable 5b-1.
Page 5c-4: Text was corrected to reflect that five studies (as opposed to four) met three of the criteria. A brief description of Kivekäs et al. [1994] was added to this section.
A number of references were clarified, and full references for studies that were cited in the text of thefirst printing but were inadvertently omitted from the reference list were added.
Appendix C was added to the document to provide a concise overview of the studies reviewed relativeto the evaluation criteria, risk factors addressed, and other issues.
vii
CONTENTS
Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iiiNote to the Reader . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vExecutive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xAcknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvi
Chapter 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1
Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1Scope and Magnitude of the Problem. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1Cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6Defining Health Outcomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7Exposure Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8Information Retrieval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9Selection of Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9Methods for Analyzing or Synthesizing Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-10Criteria for Causality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-11Categories Used to Classify the Evidence of Work-Relatedness . . . . . . . . . . . . . . 1-13Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-14Description of Tables, Figures, and Appendices . . . . . . . . . . . . . . . . . . . . . . . . . . 1-14
Chapter 2. Neck Musculoskeletal Disorders: Evidence forWork-Relatedness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2Repetition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-12Posture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-16Vibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-21Neck or Neck/Shoulder MSDs and the Role of Confounders . . . . . . . . . . . . . . . . 2-21Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-22Tables and Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-24
viii
Chapter 3. Shoulder Musculoskeletal Disorders: Evidence forWork-Relatedness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1Repetition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-9Posture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14Vibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-23Role of Confounders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-25Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-25Tables and Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-27
Chapter 4. Elbow Musculoskeletal Disorders (Epicondylitis):Evidence for Work-Relatedness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2Repetition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6Posture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-16Epicondylitis and the Role of Confounders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-17Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-18Tables and Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-20
Chapter 5. Hand/Wrist Musculoskeletal Disorders (Carpal TunnelSyndrome, Hand/Wrist Tendinitis, and Hand-ArmVibration Syndrome): Evidence for Work-Relatedness . . . . . . . . . . 5-1
Chapter 5a. Carpal Tunnel Syndrome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5a-1
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5a-1Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5a-1Outcome and Exposure Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5a-2Repetition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5a-3Force and CTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5a-14Posture and CTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5a-22Vibration and CTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5a-25Confounding and CTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5a-27Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5a-28Tables and Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5a-29
Chapter 5b. Hand/Wrist Tendinitis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5b-1
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5b-1
ix
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5b-1Repetition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5b-2Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5b-9Posture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5b-13Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5b-17Tables and Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5b-18
Chapter 5c. Hand-Arm Vibration Syndrome . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5c-1
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5c-1Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5c-1Evidence for the Work-Relatedness of HAVS . . . . . . . . . . . . . . . . . . . . . . . . . . . 5c-2Tables and Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5c-10
Chapter 6. Low-Back Musculoskeletal Disorders: Evidence forWork-Relatedness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2Heavy Physical Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4Lifting and Forceful Movements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-13Bending and Twisting (Awkward Postures) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-21Whole Body Vibration (WBV) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-26Static Work Postures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-34Role of Confounders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-38Tables and Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-39
Chapter 7. Work-Related Musculoskeletal Disorders andPsychosocial Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1
Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1Psychosocial Pathways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2Upper-Extremity Disorders (Neck, Shoulder, Elbow, Hand, and Wrist) . . . . . . . . . 7-3Back Disorders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-7Tables and Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-11
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R-1
Appendices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1
A. Epidemiologic Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1B. Individual Factors Associated with Work-Related Musculoskeletal
Disorders (MSDs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1C. Summary Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-1
x
EXECUTIVE SUMMARY
The term musculoskeletal disorders (MSDs) refers to conditions that involve the nerves, tendons,muscles, and supporting structures of the body. The purpose of this NIOSH document is to examinethe epidemiologic evidence of the relationship between selected MSDs of the upper extremity and thelow back and exposure to physical factors at work. Specific attention is given to analyzing the weight ofthe evidence for the strength of the association between these disorders and work factors.
Because the relationship between exposure to physical work factors and the development andprognosis of a particular disorder may be modified by psychosocial factors, the literature aboutpsychosocial factors and the presence of musculoskeletal symptoms or disorders is also reviewed.Understanding these associations and relating them to the cause of disease is critical for identifyingexposures amenable to preventive and therapeutic interventions.
MAGNITUDE OF THE PROBLEMThe only routinely collected national source of information about occupational injuries and illnesses ofU.S. workers is the Annual Survey of Occupational Injuries and Illnesses conducted by the Bureau ofLabor Statistics (BLS) of the U.S. Department of Labor. The survey, which BLS has conducted for thepast 25 years, is a random sample of about 250,000 private sector establishments and providesestimates of workplace injuries and illnesses on the basis of information provided by employers fromtheir OSHA Form 200 log of recordable injuries and illnesses.
For cases involving days away from work, BLS reports that in 1994 (the last year of data available atthe time this report was prepared), approximately 705,800 cases (32%) were the result of overexertionor repetitive motion. Specifically, there were
C 367,424 injuries due to overexertion in lifting (65% affected the back); 93,325 injuries due tooverexertion in pushing or pulling objects (52% affected the back); 68,992 injuries due tooverexertion in holding, carrying, or turning objects (58% affected the back). Totaled acrossthese three categories, 47,861 disorders affected the shoulder.
C 83,483 injuries or illnesses in other and unspecified overexertion events.
xi
C 92,576 injuries or illnesses due to repetitive motion, including typing or key entry, repetitive use oftools, and repetitive placing, grasping, or moving of objects other than tools. Of these injuries orillnesses, 55% affected the wrist, 7% affected the shoulder, and 6% affected the back.
Data for 1992 to 1995 indicate that injuries and illnesses requiring days away from work declined 19%for overexertion and 14% for repetitive motion. The incidence rate of overexertion (in lifting) declinedfrom 52.1 per 10,000 workers in 1992 to 41.1 in 1995; the incidence rate for repetitive motiondisorders declined from 11.8 per 10,000 workers in 1992 to 10.1 in 1995. These declines are similarto those seen for cases involving days away from work from all causes of injury and illness.
The reasons for these declines are unclear but may include: a smaller number of disorders could beoccurring because of more intensive efforts to prevent them; more effective prevention and treatmentprograms could be reducing days away from work; employers or employees may be more reluctant toreport or record disorders; or the criteria used by health care providers to diagnose these conditionscould be changing.
IDENTIFICATION AND SELECTION OF STUDIESThe goal of epidemiologic studies is to identify factors that are associated (positively or negatively) withthe development or recurrence of adverse medical conditions. This evaluation and summary of theepidemiologic evidence focuses chiefly on disorders that affect the neck and the upper extremity,including tension neck syndrome, shoulder tendinitis, epicondylitis, carpal tunnel syndrome, and hand-arm vibration syndrome, which have been the most extensively studied in the epidemiologic literature.The document also reviews studies that have dealt with work-related back pain and that address theway work organizational and psychosocial factors influence the relationship between exposure tophysical factors and work-related MSDs. The literature about disorders of the lower extremity isoutside the scope of the present review.
A search strategy of bibliographic databases identified more than 2,000 studies. Because of the focuson the epidemiology literature, studies that were laboratory-based or that focused on MSDs from abiomechanical standpoint, dealt with clinical treatment of MSDs, or had other nonepidemiologic orientation were eliminated from further consideration for this document. Over 600studies were included in the detailed review process.
METHODS FOR SYNTHESIZING STUDIESFor the upper extremity studies included in this review, those which used specific diagnostic criteria,including physical examination techniques, were given greater consideration than studies that used lessspecific methods to define health outcomes. The review focused most strongly on observational studieswhose health outcomes were based on recognized symptoms and standard methods of clinicalexamination. For completeness, those epidemiologic studies that based their health outcomes onreported symptoms alone were also reviewed. For the low-back studies included in this review, thosewhich had objective exposure measurements were given greater consideration than those which used
xii
self-reports or other measures. For the psychosocial section, any studies which included measurementor discussion of psychosocial factors and MSDs were included.
No single epidemiologic study will fulfill all criteria to answer the question of causality. However, resultsfrom epidemiologic studies can contribute to the evidence of causality in the relationship betweenworkplace risk factors and MSDs. The framework for evaluating evidence for causality in this reviewincluded strength of association, consistency, temporality, exposure-response relationship, andcoherence of evidence.
Using this framework, the evidence for a relationship between workplace factors and the developmentof MSDs from epidemiologic studies is classified into one of the following categories:
Strong evidence of work-relatedness (+++). A causal relationship is shown to be very likelybetween intense or long-duration exposure to the specific risk factor(s) and MSD when theepidemiologic criteria of causality are used. A positive relationship has been observed betweenexposure to the specific risk factor and MSD in studies in which chance, bias, and confoundingfactors could be ruled out with reasonable confidence in at least several studies.
Evidence of work-relatedness (++). Some convincing epidemiologic evidence shows a causalrelationship when the epidemiologic criteria of causality for intense or long-duration exposure tothe specific risk factor(s) and MSD are used. A positive relationship has been observed betweenexposure to the specific risk factor and MSD in studies in which chance, bias, and confoundingfactors are not the likely explanation.
Insufficient evidence of work-relatedness (+/0). The available studies are of insufficientnumber, quality, consistency, or statistical power to permit a conclusion regarding the presence orabsence of a causal association. Some studies suggest a relationship to specific risk factors, butchance, bias, or confounding may explain the association.
Evidence of no effect of work factors (-). Adequate studies consistently show that the specificworkplace risk factor(s) is not related to development of MSD.
The classification of results in this review by body part and specific risk factor is summarized in Table 1.
xiii
Table 1. Evidence for causal relationship between physical work factors and MSDs
Body part Risk factor
Strongevidence
(+++)Evidence
(++)
Insufficientevidence
(+/0)
Evidenceof no effect
(-)
Neck and Neck/shoulder Repetition Force Posture Vibration
T
TT
T
Shoulder Posture Force Repetition Vibration
T
T T
T
Elbow Repetition Force Posture Combination T
T T
T
Hand/wrist Carpal tunnel syndrome Repetition Force Posture Vibration Combination T
TT
TT
Tendinitis Repetition Force Posture Combination T
TTT
Hand-arm vibration syndrome Vibration T
Back Lifting/forceful movement Awkward posture Heavy physical work Whole body vibration Static work posture
T
T
T
T
T
xiv
CONCLUSIONSA substantial body of credible epidemiologic research provides strong evidence of an associationbetween MSDs and certain work-related physical factors when there are high levels of exposure andespecially in combination with exposure to more than one physical factor (e.g., repetitive lifting of heavyobjects in extreme or awkward postures [Table 1]).
The strength of the associations reported in the various studies for specific risk factors after adjustmentsfor other factors varies from modest to strong. The largest increases in risk are generally observed instudies with a wide range of exposure conditions and careful observation or measurement of exposures.
The consistently positive findings from a large number of cross-sectional studies, strengthened by thelimited number of prospective studies, provides strong evidence (+++) for increased risk of work-related MSDs for some body parts. This evidence can be seen from the strength of the associations,lack of ambiguity in temporal relationships from the prospective studies, the consistency of the results inthese studies, and adequate control or adjustment for likely confounders. For some body parts and riskfactors, there is some epidemiologic evidence (++) for a causal relationship. For still other body partsand risk factors, there is either an insufficient number of studies from which to draw conclusions or theoverall conclusion from the studies is equivocal. The absence of existing epidemiologic evidence shouldnot be interpreted to mean there is no association between work factors and MSDs.
In general, there is limited detailed quantitative information about exposure-disorder relationshipsbetween risk factors and MSDs. The risk of each exposure depends on a variety of factors such as thefrequency, duration, and intensity of physical workplace exposures. Most of the specific exposuresassociated with the strong evidence (+++) involved daily whole-shift exposure to the factors underinvestigation.
Individual factors may also influence the degree of risk from specific exposures. There is evidence thatsome individual risk factors influence the occurrence of MSDs (e.g., elevated body mass index andcarpal tunnel syndrome or a history of past back pain and current episodes of low-back pain). There islittle evidence, however, that these individual factors interact synergistically with physical factors. All ofthese disorders can also be caused by nonwork exposures. The majority of epidemiologic studiesinvolve health outcomes that range in severity from mild (the workers reporting these disorders continueto perform their routine duties) to more severe disorders (workers are absent from the workplace forvarying periods of time). The milder disorders are more common. A limited number of studiesinvestigate the natural history of these disorders and attempt to determine whether continued exposureto physical factors alters their prognosis.
The number of jobs in which workers routinely lift heavy objects, are exposed on a daily basis towhole-body vibration, routinely perform overhead work, work with their necks in chronic flexionposition, or perform repetitive forceful tasks is unknown. While these exposures do not occur in mostjobs, a large number of workers may indeed work under these conditions. The BLS data indicate that
xv
the total employment is over three million in the industries with the highest incidence rates of casesinvolving days away from work from overexertion in lifting and repetitive motion. Within the highest riskindustries, however, it is likely that the range of risk is substantial depending on the specific nature of thephysical exposures experienced by workers in various occupations within that industry.
This critical review of the epidemiologic literature identified a number of specific physical exposuresstrongly associated with specific MSDs when exposures are intense, prolonged, and particularly whenworkers are exposed to several risk factors simultaneously. This scientific knowledge is being applied inpreventive programs in a number of diverse work settings. While this review has summarized animpressive body of epidemiologic research, it is recognized that additional research would be quitevaluable. The MSD components of the National Occupational Research Agenda efforts are principallydirected toward stimulation of greater research on MSDs and occupational factors, both physical andpsychosocial. Research efforts can be guided by the existing literature, reviewed here, as well as bydata on the magnitude of various MSDs among U.S. workers.
xvi
ACKNOWLEDGMENTS
In addition to the other contributors, the following staff members of the National Institute forOccupational Safety and Health are acknowledged for their support, assistance, and advice inpreparing this document:
Penny ArthurVanessa BecksDonna BiaginiJenise BrassellKaren BrewerCarol BurnettSue CairelliDick CarlsonShirley CarrDave CaseSharon CheesmanAlexander Cohen, Ph.D.Marian ColemanBarb CromerJudy CurlessDavid DankovicJohn DietherClayton DoakKaren DragonSue FeldmannJerry FleschLarry FosterSean GallagherLytt Gardner, Ph.D.Pamela GraydonDaniel Habes
Rose HagedornWilliam Halperin, M.D., Sc.D.Anne HamiltonDenise HillSuzanne HoganHongwei Hsiao, Ph.D.Lore JacksonLaurel JonesSusan KaelinSandy KasperAileen KielDiana KleinwachterNina LalichLeslie MacDonaldCharlene MaloneyDiane ManningJames McGlothlin, Ph.D.Patricia McGrawAlma McLemoreJudy MeeseMatthew MillerKathleen MitchellVivian MorganLeela MurthyRick NiemeierAndrea Okun
Marty PetersenDonna PfirmanLinda PlybonFaye RiceCindy RiddleKris RoyerWalt RuchSteven Sauter, Ph.D.Lucy SchoolfieldMitch Singal, M.D.Paul SchulteBecky SpryAnne StirnkorbNaomi Swanson, Ph.D.Rodger TatkenAllison Tepper, Ph.D.Julie TisdaleAnne VotawDavid VotawThomas Waters, Ph.D.Jane WeberJoann WessCindy WheelerKellie WilsonRalph Zumwalde
xvii
We also thank the following reviewers for their thoughtful comments on an earlier draft of thisdocument:
Gunnar B.J. Andersson, M.D., Ph.D. Robert Harrison, M.D., M.P.H.Rush-Presbyterian-St. Luke’s University of California at San Francisco Medical Center
Mohammed M. Ayoub, Ph.D., P.E., C.P.E. William S. Marras, Ph.D.Texas Tech University The Ohio State University
Sidney J. Blair, M.D., F.A.C.S. J. Steven Moore, M.D., M.P.H., C.I.H., C.P.E.Loyola Chicago University University of Texas Health Center at Tyler
Vance C. Calvez, M.S., C.P.E. Margareta Nordin, Dr. Med. Sc.The Joyce Institute New York University
Don B. Chaffin, Ph.D. Donald C. Olsen, Jr., C.S.P., C.P.E.University of Michigan ERGOSH
Jerome J. Congleton, Ph.D., P.E., C.P.E. Thomas Owens, C.I.H., P.E.Texas A&M University IBM Corporation
Thomas Cook, Ph.D., P.T. Malcolm H. Pope, Dr. Med. Sc., Ph.D.University of Iowa The University of Iowa
Theodore Courtney Laura Punnett, Sc.D.Liberty Mutual University of Massachusetts
Michael Feuerstein, Ph.D. Robert G. Radwin, Ph.D.Uniformed Services University University of Wisconsin-Madison of the Health Sciences
Eric Frumin David Rempel, M.D.Union of Needle Trades, Industrial, University of California, San Francisco and Textile Employees (UNITE)
Michael Gauf Suzanne H. Rodgers, Ph.D.CTD News Consultant in Ergonomics
Fred Gerr, M.D. C. Jivan SaranEmory University Central Missouri State University
Lawrence P. Hanrahan, Ph.D., M.S. Scott Schneider, C.I.H.Wisconsin Division of Health The Center to Protect Workers’ Rights
Barbara Silverstein, Ph.D., M.P.H., C.P.E.State of Washington Department of Labor and Industries
1-1
CHAPTER 1
Introduction
PURPOSE This document examines the epidemiologicevidence that associates selectedmusculoskeletal disorders (MSDs) of the upperextremity and the low back with exposure tophysical factors at work. The authors have paidparticular attention to analyzing the strength ofthe association between MSDs and workfactors. Because the development of an MSDmay be modified by psychosocial factors, theauthors have also reviewed the literature on therelationship of these factors to the presence ofmusculoskeletal symptoms or disorders.Understanding these associations and relatingthem to disease etiology is critical to identifyingworkplace exposures that can be reduced orprevented.
BACKGROUNDThe World Health Organization hascharacterized “work-related” diseases asmultifactorial to indicate that a number of riskfactors (e.g., physical, work organizational,psychosocial, individual, and sociocultural)contribute to causing these diseases [WHO1985]. One important reason for thecontroversy surrounding work-related MSDs istheir multifactorial nature. The disagreementcenters on the relative importance of multipleand individual factors in the development ofdisease. The same controversy has been anissue with other medical conditions such ascertain cancers and lung disorders—both ofwhich have multiple causal factors(occupational and nonoccupational).
The goal of epidemiologic studies is to identifyfactors (such as physical, work organizational,psychosocial, individual, and socioculturalfactors) that are associated positively ornegatively with the development or recurrenceof adverse medical conditions. This documentaddresses and evaluates the literature withregard to these issues for work-related MSDs.
This document reviews the epidemiologicevidence regarding the role of physical factorsin the development of MSDs for the followingbody areas: the neck, shoulder, elbow,hand/wrist, and back. The document alsoaddresses the influence of work organizationaland psychosocial factors on the association ofphysical factors with work-related MSDs. Thisevaluation and summary of the epidemiologicevidence focuses chiefly on disorders affectingthe neck and the upper extremity—includingtension neck syndrome, shoulder tendinitis,epicondylitis, carpal tunnel syndrome, andhand-arm vibration syndrome, which have beenthe most extensively studied in theepidemiologic literature. This document alsoconcentrates on studies that have dealt with theissue of work-related back pain and sciatica.The literature on disorders of the lowerextremities is beyond the scope of this review.
SCOPE AND MAGNITUDE OF THEPROBLEMThe only routinely published, national source ofinformation about occupational injuries andillnesses in U.S. workers is the Annual Surveyof Occupational Injuries and Illnesses (ASOII)
1-2
conducted by the Bureau of Labor Statistics(BLS) of the U.S. Department of Labor. Thissurvey is a random sample of about 250,000private-sector establishments, but it excludesself-employed workers, farms with fewer than11 employees, private households, and allgovernment agencies. The ASOII providesestimates of workplace injuries and illnessesfrom information that employers provide toBLS from their OSHA Form 200 log ofrecordable injuries and illnesses.
BLS has conducted this annual survey since1972 and has thus provided basic informationabout cases of occupational injury or illness thatrequired more than first-aid (including medicaltreatment, restricted work activity, or daysaway from work). This information includes thetotal number of cases categorized on theOSHA Form 200 log as either an injury or anillness. The illness data are separated into sixsubcategories; the category that contains most(but not all) musculoskeletal conditions isdisorders associated with repeated trauma.This illness category also includes illnessesassociated with noise-induced hearing loss,but MSDs account for the largest proportion ofthese cases, especially in recent years. All backdisorders or injuries are placed in the single,broad injury category, which also includes allother types of injuries such as lacerations,fractures, and burns.
From this part of the ASOII, BLS reports thatin 1995, 308,000 (or 62%) of all illness caseswere due to disorders associated with repeatedtrauma (excluding low-back disorders, whichare listed as injuries). The number of repeatedtrauma cases increased dramatically, risingsteadily from 23,800 in 1972 to 332,000 in1994—a 14-fold increase. In 1995, the
number of cases decreased by 7% to 308,000reported cases; but this number still exceeds thenumber of cases in any year before 1994.
Because these summary data did notadequately describe the nature of occupationalinjuries and illnesses and the related riskfactors, the ASOII was redesigned in 1992 tocapture more detailed information about injuryand illness cases requiring days away fromwork. This redesigned survey capturesdemographic information about injured workersas well as the following characteristics of theinjury or illness: (1) the employer’s descriptionof the nature of the injury or illness, such assprain or carpal tunnel syndrome; (2) the partof the body affected by the specifiedcondition, such as back or wrist; (3) the sourceof the injury or illness that directly producedthe disabling condition, such as a crate, heavybox, or a nursing home patient; and (4) theevent or exposure that describes the manner inwhich the injury or illness was inflicted, such asoverexertion during lifting or repetitive motion.The BLS data are based on informationprovided by employers from their records ofwork-related injuries and illnesses and thencoded into these categories.
For injury and illness cases involving days awayfrom work, BLS reports that in 1994 (the lastyear for which the detailed data were completewhen this report was prepared), approximately705,800 cases (32%) resulted fromoverexertion or repetitive motion. Specifically:C 367,424 injuries were due to overexertion in
lifting; 65% affected the back. Another93,325 injuries were due to overexertion inpushing or pulling objects; 52% affected theback. In addition, 68,992 injuries were dueto overexertion in holding, carrying, or turning
1-3
objects; 58% affected the back. Totaledacross these three categories, 47,861disorders affected the shoulder. The mediantime away from work from overexertioninjuries was 6 days for lifting, 7 days forpushing/pulling, and
6 days for holding/carrying/turning.
C 83,483 injuries or illnesses occurred in otherand unspecified overexertion events.
C 92,576 injuries or illnesses occurred as aresult of repetitive motion, including typing orkey entry, repetitive use of tools, andrepetitive placing, grasping, or moving ofobjects other than tools. Of these repetitivemotion injuries, 55% affected the wrist, 7%affected the shoulder, and 6% affected theback. The median time away from work was18 days as a result of injury or illness fromrepetitive motion.
The highest incidence rates (IRs) of work-related injuries and illnesses from over- exertionoccur among workers in nursing and personalcare facilities, scheduled air transportation, andmanufacturing of travel trailers and campers. AsTable 1–1 indicates, these industries have ratesof overexertion disorders four times higher thanthe average rate for all private industry. Morethan 2 million workers are employed in thethree highest-risk industries alone. However,rates are not available by occupation withinthese industries, and not all workers within ahigh-risk industry will be at equal risk ofdeveloping a work-related MSD.
Industries with the highest IRs of work-relatedinjuries and illnesses from repetitive motioninclude a number of garment manufacturingsectors such as knit underwear mills, men’s and
boy’s work clothes, and hats, caps, andmillinery; these industries also includemanufacturing sectors such as textile bags,potato chip and similar snacks, motor vehicles,and meat packing plants (Table 1–2). Theseindustries have IRs that are more than eighttimes the rate for all private industry.
Not all workers in these high-risk industries areexposed to the working conditions associatedwith these clearly elevated rates of illnesses andinjuries from overexertion and repetitivemotion; however, smaller proportions ofworkers in other industries may be similarlyexposed. For example, trucking and courierservices, an industry employing over 1.6 millionpeople, had IRs for overexertion disorders thatwere almost three times higher than the averagerate for all private industries. Thus, theseemployment estimates provide a conservativeapproximation of the number of workers withheavy exposures to high-risk conditions.
The BLS data are surveillance information thatmight contain misclassifications of bothexposure and health outcomes. However, someindustries have notably and consistentlyelevated rates of musculoskeletal injuries anddisorders that are not likely to be attributable todata collection or coding. Note that decisionsabout the event or exposure that resulted in aninjury or illness are associations rather thancausal inferences. Nevertheless, they providesome perspective on the magnitude of work-related MSDs.
Table 1-1. Private sector industries with the highest incidence rates of injuries and illnesses from overexertion resulting in days away from work, 1994
Industry* SIC code†
1994 annualaverage
employment‡ (in thousands)
Incidence rate (per 10,000workers)
95% confidenceinterval
(rate per 10,000) Number of casesNursing and personal care facilities 805 1,648 318.0 (286, 350) 41,884 Air transportation, scheduled 451 607 306.7 (276, 337) 16,309
Travel trailers and campers (manufacturing) 3792 22 303.7 (206, 401) 635
Food products machinery (manufacturing) 3556 24 260.1 (142, 378) 620 Bottled and canned soft drinks (manufacturing) 2086 95 255.6 (224, 287) 2,512
Beer, wine, and distilled beverages (wholesale) 518 150 254.6 (189, 321) 3,750 Coal mining 12 112 235.6 not available 2,609
Mattresses and bedsprings (manufacturing) 2515 31 233.5 (172, 295) 719 Comparison Industries:
All manufacturing 2, 3 18,319 83.00 (81.4, 84.6) 151,794 All private industry§ 94,146 76.00 (75.7, 76.3) 613,251
Finance, insurance, and real estate 6 6,707 17.90 (16.5, 19.3) 11,191
Source: Bureau of Labor Statistics, U.S. Department of Labor, Annual Survey of Occupational Injuries and Illnesses, 1994 Case and Demographic Resource Tables (ftp://stats.bls.gov/pub/special.requests/ocwc/osh/c_d_data).*High rate industries were those having an incidence rate greater than three times the rate for all private industry, at the most detailed or lowest SIC level at which rates are published. Generally, manufacturing industries are published at the 4-digit code level and the remaining industries at the 3-digit level.†Standard Industrial Classification Manual, 1987 edition.‡Annual average employment from the BLS Covered Employment and Wages (ES-202) Survey.§Excludes farms with fewer than 11 employees.
1-4
Table 1-2. Private sector industries with the highest incidence rates of injuries and illnesses from repetitive motion resulting in days away from work, 1994
Industry* SIC
code†
1994 annualaverage
employment‡ (in thousands)
Incidence rate(per 10,000workers)
95% confidenceinterval
(rate per 10,000) Number of casesKnit underwear mills (manufacturing) 2254 25 165.6 (145, 187) 370
House slippers (manufacturing) 3142 3
146.3 (92, 201) 48
Men’s and boy’s work clothes (manufacturing) 2326 42 117.2 (97, 137) 463 Textile bags (manufacturing) 2393 11 115.7 (60, 171) 117
Potato chips and similar snacks (manufacturing) 2096 35 115.2 (95, 135) 406 Motor vehicles and car bodies (manufacturing) 3711 335 113.9 (99, 129) 4,058
Hats, caps, and millinery (manufacturing) 235 21 103.9 (79, 129) 202
Meat packing plants (manufacturing) 2011 138 98.5 (76, 121) 1,402 Bras, girdles, and allied garments (manufacturing) 2342 12 96.2 (73, 119) 111
Wood products, not elsewhere classified (manufacturing) 2499 58 92.8 (69, 117) 515 Men’s and boy’s suits and coats (manufacturing) 231 40 89.1 (74, 104) 320
Electronic coils and transfers (manufacturing) 3677 17 87.0 (52, 122) 142 Men’s footwear (excluding athletic) 3143 28 84.9 (64, 106) 221
Comparison Industries:
All manufacturing 2, 3 18,319 27.0 (26.4, 27.6) 49,278 All private industry§ 94,146 11.5 (11.4, 11.6) 92,576
Finance, insurance, and real estate 6 6,707 8.1 (7.4, 8.8) 5,046
Source: Bureau of Labor Statistics, U.S. Department of Labor, Annual Survey of Occupational Injuries and Illnesses, 1994 Case and Demographic Resource Tables (ftp://stats.bls.gov/pub/special.requests/ocwc/osh/c_d_data).*High rate industries were those having an incidence rate greater than three times the rate for all manufacturing workers at the most detailed or lowest SIC level at which rates are published. Generally, manufacturing industries are published at the 4-digit code level and the remaining industries at the 3-digit level.†Standard Industrial Classification Manual, 1987 edition.‡Annual average employment from the BLS Covered Employment and Wages (ES-202) Survey.§Excludes farms with fewer than 11 employees.
1-5
1-6
The large number of work-related low-backinjuries or illnesses reported in the BLS data isconsistent with the results of two representativesurveillance studies in the United States andOntario. In the U.S. study, about 52% of theback pain reports were attributed by theworker to repetitive events at work, and anadditional 16% were attributed to discrete,acute events at work; 33% were associatedwith both types of exposures [Guo et al. 1995].
Although workers often consider MSDs to bework-related, their reports of back pain do notappear to affect the reliability of their selfreports about exposure to physical work. In theOntario study [Liira et al. 1996], 24% of thelong-term back disorders were related tobending and lifting, working with vibratingmachines, and working in awkward postures.Interestingly, 8% of the population wereexposed to at least two of these three factors,and an additional 3% were exposed to all three.
The impact of work-relatedness isdemonstrated by the elevated MSD rates forcertain industries in workers’ compensationdata as well as the BLS data. For example, inthe State of Washington workers’compensation system, the overall IR of work-related MSDs was 3.87/100 workers in 1992,3.72 in 1993, and 3.52 in 1994. Work-relatedMSDs in this study were defined as injuries andillnesses involving sprains/strains, jointinflammation, low-back pain, and nerve-compression syndromes. Four industries hadrates at least four times the 1992–94 averagerate: wallboard installation (23.6/100 workersper year), temporary help-assembly (23.6),roofing (19.9), and moving companies (18)[Washington State Department of Labor andIndustries 1996].
COSTThe precise cost of occupational MSDs is notknown. Estimates vary depending on themethod used. A conservative estimatepreviously published by NIOSH is$13 billion annually [NIOSH 1996]. Othershave estimated the cost at $20 billion annually[AFL-CIO 1997]. Regardless of the estimateused, the problem is large both in health andeconomic terms.
Work-related MSDs are a major component ofthe cost of work-related illness in the UnitedStates. The California Workers’ CompensationInstitute (a non-profit research institute)estimates that upper-extremity MSD claims byworkers average $21,453 each [CWCI 1993].Back pain is by far the most prevalent andcostly MSD among U.S. industries today.Recent analysis of the 1988 OccupationalHealth Supplement of the National HealthInterview Survey (an ongoing household-basedsurvey) shows that the overall prevalence ofself-reported back pain from repeated activitieson the most recent job was 4.5%, or 4.75million U.S. workers [Behrens et al. 1994]. Themean cost per case of compensable low-backpain was reported to be $8,321 in 1989[Webster and Snook 1994b].
Webster and Snook [1994a] estimated that themean compensation cost per case of upper-extremity, work-related MSD was $8,070 in1993; the total U.S. compensable cost forupper extremity, work-related MSDs was$563 million in 1993. For example, the State ofWashington averaged 44,648 work-relatedMSD claims, with an average total cost of$166.8 million/year for the period 1992–94.The State of Washington has a workingpopulation that is 2% that of the U.S.workforce. The compensable cost is limited tothe medical expenses and indemnity costs (lost
1-7
wages). When other expenses such as the fulllost wages, lost production, cost of recruitingand training replacement workers, cost ofrehabilitating the affected workers, etc. areconsidered, the total cost to the nationaleconomy becomes much greater.
DEFINING HEALTH OUTCOMESWork-related MSDs are defined differently indifferent studies; thus, it is not surprising thatcontroversy has arisen about the relativeimportance of various risk factors in theetiology of these disorders. Some investigatorsrestrict themselves to case definitions based onclinical pathology, some to the presence ofsymptoms, some to “objectively” demonstrablepathological processes, and some to workdisability (such as lost work-time status).
The most common health outcome has been theoccurrence of pain, which is assumed to be theprecursor of more severe disease [Riihimäki1995] or (as in the case of back pain) thedisorder itself. Different MSD health outcomeshave been assessed by investigators dependingon the particular concern or nature of the study.The specific health outcomes studied varydepending on (a) the purpose of the study, (b)the composition of the study population, (c) therarity or prevalence of the health outcome in thepopulation, (d) the need to limit specific biases,and (e) the decisions of the investigators.
Different epidemiologic measures and timescales have also been used to quantify MSDs ingroups of people (lifetime prevalence, periodprevalence, point prevalence, IR, incidenceratio, etc.). Similarly, some studies haveincluded chronic cases, whereas others havestudied acute or subacute cases or both.Cross-sectional studies usually employ casedefinitions that take into account prevalentcases at different stages of the disease
process—such as incipient disease or residualsigns of a MSD that was once clinicallyapparent. Because of the multifactorial natureof MSDs, it has been necessary to look at abroad spectrum of outcome measures to assessthe effects of these factors.
Certain authors have noted the scarcity ofobjective measures (including physicalexamination techniques) to define work-relatedMSDs, and the lack of standardized criteria fordefining MSD cases. Such insufficienciessometimes make study comparisons difficult[Gerr et al. 1991; Moore 1992; Frank et al.1995; Riihimäki 1995; Hadler 1997]. It wouldbe useful to have a concise pathophysiologicaldefinition and corresponding objective clinicaltest for each work-related MSD to translate thedegree of tissue damage or dysfunction into anestimate of current or future disability andprognosis. Such definitions and tests do not yetexist. Clinically defined work-related MSDsoften have no clearly delineatedpathophysiological mechanisms for pathologicalprocesses. In cases where some criteria exist(such as carpal tunnel syndrome [CTS]), thestandard of accuracy is relatively expensive,elaborate, and subject to interpretation. Forexample, the overlap between symptoms andpresence of abnormalities in nerve conductionstudies is not great [Stetson et al. 1993];furthermore, abnormalities in nerve conductionstudies cannot be reliably used to predict thefuture onset of CTS symptoms [Werner et al.1997]. Thus, in the interest of feasibility,expense, and utility, simpler tests and lessspecific case definitions may have been used insome studies, thereby introducing some risk ofmisclassification for specific
diagnostic entities.
For upper-extremity studies in this review,
1-8
those with specific diagnostic criteria (includingphysical examination techniques) were givengreater consideration than studies that usedless-specific methods to define healthoutcomes. The review focused on observationalstudies whose health outcomes were based onthe constellation of recognized symptoms andstandard methods of clinical examination. Forcompleteness, those epidemiologic studies thatbased their health outcomes on reportedsymptoms alone were also reviewed.
Therefore, this document focuses on the upper-extremity MSDs that have commonly useddiagnostic symptoms and physical examinationabnormality criteria. Specifically, these MSDsare (1) tension-neck syndrome, (2) rotator cufftendinitis and impingement syndrome in theshoulder, (3) epicondylitis in the elbow, (4)CTS,(5) wrist tendinitis, and (6) hand-arm vibration(HAV) syndrome. Generally, the physicalexamination techniques used to define theseMSD cases of the upper extremity have beensimilar from study to study and involve standardexamination techniques recognized by theAmerican Academy of Orthopedic Surgeons,the American College of Physicians, or theInternational Labor OrganizationMusculoskeletal Task Force (thus increasingthe reliability of comparisons between studies).Although physical examination techniques havenot been commonly used in epidemiologicstudies of low-back disorders, this documentalso reviews those epidemiologic studies thataddress low-back pain.
EXPOSURE MEASUREMENTSExposure measurements used in work-relatedMSD studies range from very crude
measures (e.g., occupational title) to complexanalytical techniques (e.g., spectral analysis ofelectrogoniometer measurements of jointmotions). Some studies have relied on self-
assessment of physical workload by the studysubjects.
The accuracy of such self-assessment has beendebated (both for under-estimation and over-estimation). Uhl et al. [1987] found thatworkers reported performing more physicalwork than observational data could support.Armstrong et al. [1989] found that workers can(on average) distinguish among levels ofexposure, but workers’ ratings may notcorrespond with objective measurements.Bernard et al. [1994] found that video displayterminal (VDT) operators (those with and thosewithout symptoms of work-related MSDs)reported that the average time they spent typingdaily in the last year was twice that noted byindependent observers in a single work day(although the 1-day observation period mayhave been insufficient to capture an averageday of typing time). Similarly, Stubbs [1986]found large and significant differences betweensubjective and observed estimates of time spentworking in specified postures. Fransson-Hall etal. [1995], on the other hand, found thatworkers tended to underestimate theirexposures to contact stress of the handcompared with observation. Thisunderestimation may be because workers tendto monitor discomfort from direct contactpressure—not the time spent with directcontact. Katz et al. [1996] found evidence ofthe validity of self-reported symptoms andfunctional status, and analysis of their datayielded evidence that variability in self-reportsis not influenced by potential secondary gain.
As Riihimäki [1995] pointed out, it is difficult toassess current exposure, but it is even moredifficult to assess cumulative past exposureretrospectively. Accurate retrospective data areusually not available; thus the exposureassessment is often based on self-reports, and
1-9
the assessment may incur information bias.
A few studies have used observational methodsto estimate exposures to workplace physicalhazards more accurately and reliably. Becausestudies that directly observe or assess physicalexposure factors are less likely to misclassifyexposure status, these studies are given greaterweight in this review.
Despite the noted limitations, occupationsclassified as “high-risk” in several studies sharea number of workplace exposures associatedwith work-related MSDs. These workplaceexposures occur in various combinations(singly, simultaneously, or sequentially) atdifferent levels for different durations. Theseexposures have not been routinely brokendown into task variables and quantified, withthe mechanical or physiological loads definedand measured.
INFORMATION RETRIEVALThis document examines scientific peer-reviewed epidemiologic journal articles,including recent publications addressing MSDrisk factors, conference proceedings, andabstracts dealing with upper-extremity or backMSDs, recent textbooks, internally reviewedgovernment reports or studies conducted byNIOSH, and other documents. Reports ofepidemiologic studies were acquired using bothCD-ROM and online commercial andgovernmental databases. Searches werecarried out on computer-based bibliographicdatabases: Grateful Med® (which includesMedline® and Toxline®), NIOSHTIC® (aNIOSH database), and CIS (the InternationalLabour Organization occupational healthdatabase). The search strategy included thefollowing key terms: occupation, repetition,force, posture, vibration, cold, psychosocial,psychological, physiological, repetition strain
injury, repetitive strain injury, epidemiology,etiology, cumulative trauma disorders, MSDs(neck, tension neck syndrome, shoulder,rotator cuff, elbow, epicondylitis, tendinitis,tenosynovitis, carpal tunnel, de Quervain's,nerve entrapment syndrome, vibration, backpain and sciatica, manual materials handling).Bibliographies of relevant articles werereviewed. Relevant foreign literature citations inEnglish and included in the databases wereincluded in this review along with literature fromthe personal files of the contributors. Thissearch strategy identified more than 2,000studies. Because of the focus on theepidemiology literature, a number of thesestudies that were laboratory-based or focusedon MSDs from a biomechanical standpoint thatdealt with clinical treatment of MSDs or othernon-epidemiologic orientations were eliminatedfrom further consideration for the presentdocument. Over 600 studies were included inthe detailed review process.
SELECTION OF STUDIESThe studies that were chosen for more detailedreview specifically concerned the work-relatedness of MSDs, musculoskeletalproblems of the neck, upper limbs, or back,and/or occupational and nonoccupational riskfactors. The following inclusion criteria wereused to select studies for the review:
Population: Studies were included if theexposed and referent populations were welldefined.
Health outcome: Studies were included if theyinvolved neck, upper-extremity, and low-backMSDs measured by well-defined, explicitcriteria determined before the study. Studieswhose primary outcomes were clinicallyrelevant diagnostic entities generally had lessmisclassification and were likely to involve
1-10
more severe cases. Studies whose primaryoutcomes were the reporting of symptomsgenerally had more misclassification of healthstatus and a wider spectrum of severity.
Exposure: Studies were included if theyevaluated exposure so that some inferencecould be drawn regarding repetition, force,extreme joint position, static loading orvibration, and lifting tasks. Studies in whichexposure was measured or observed andrecorded for the body part of concern wereconsidered superior to studies that used self-reports or occupational/job titles as surrogatesfor exposure.
Study design: Population-based studies ofMSDs, case-control studies, cross-sectionalstudies, longitudinal cohort studies, and caseseries were included.
METHODS FOR ANALYZING ORSYNTHESIZING STUDIESThe first step in the analytical process was toclassify the epidemiologic studies by thefollowing criteria:
1. The participation rate was $70%. Thiscriterion limits the degree of selection biasin the study.
2. The health outcome was defined bysymptoms and physical examination. Thiscriterion reflects the preference of mostreviewers to have health outcomes thatare defined by objective criteria.
3. The investigators were blinded to healthor exposure status when assessing healthor exposure status. This criterion limitsobserver bias in classifying exposure ordisease.
4. The joint under discussion was subjectedto an independent exposure assessment,with characterization of the independentvariable of interest (such as repetition orrepetitive work). This criterion indicateswhether the exposure assessment wasconducted on the joint of interest andinvolved the type of exposure beingexamined— such as repetitive work,forceful exertion, extreme posture, orvibration. This criterion indicates whetherthe exposure was measuredindependently or in combination withother types of exposures. Exposure wasalso characterized by the method used tomeasure the level of exposure. Studiesthat used either direct observation oractual measurements of exposure wereconsidered to have a more accurateexposure classification scheme, whereasstudies that exclusively used job titles,interviews, or questionnaire informationwere assumed to have less accurateexposure information.
During review of the studies, the greatestqualitative weight was given to studies that hadobjective exposure assessments, highparticipation rates, physical examinations, andblinded assessment of health and exposurestatus. The chapters dealing with the differentbody regions—neck (including neck-shoulder),shoulder, elbow, hand/wrist, and low-back—summarize these characteristics for eachstudy reviewed on the criteria table.
The second step of the analytical process wasto divide the studies into those with statisticallysignificant associations between exposures andhealth outcomes and those without statisticallysignificant associations. The associations werethen examined to determine whether they were
1-11
likely to be substantially influenced byconfounding or other selection bias (such assurvivor bias or other epidemiologic pitfalls thatmight have a major influence on theinterpretation of the findings). These include theabsence of nonrespondent bias andcomparability of study and comparison groups.There are also tables that summarizeinformation about confounders andepidemiologic pitfalls for each study reviewedat the end of each body region chapter.
The third step of the analytical process was toreview and summarize studies with regard tostrength of association, consistency inassociation, temporal association, andexposure-response relationship. Each of thesefactors is discussed in greater detail in the nextsection (Criteria for Causality). Each studyexamined (those with negative, positive, orequivocal findings) contributed to the pool ofdata for determining the strength ofwork-relatedness using causal inference. Theexposures examined for the neck and upperextremity were repetition, force, extremeposture, and segmental vibration. Theexposures examined for the low back wereheavy physical work, lifting, bending/twisting,whole-body vibration, and static postures.
Care should be taken when interpreting somestudy results regarding individual workplacefactors of repetition, force, extreme or staticpostures, and vibration. As Kilbom [1994]stated, these factors occur simultaneously orduring alternating tasks
within the same work, and their effects concurand interact. A single odds ratio (OR) for anindividual risk factor may not accurately reflectthe actual association, as not all of the studiesderived ORs for simultaneously occurringfactors. Thus these studies were not only
viewed individually (taking into account goodepidemiologic principles) but together as abody of evidence for making broaderinterpretations about epidemiologic causality.Many investigators did not examine each riskfactor separately but selected study andcomparison groups based on combinations ofrisk factors (such as workers in jobs involvinghigh force and repetition compared withworkers having no exposure to high force andrepetition).
CRITERIA FOR CAUSALITYNo single epidemiologic study will fulfill allcriteria for causality. However, the results ofmany epidemiologic studies can contribute tothe evidence of causality in the relationshipbetween workplace risk factors and MSDs.Rothman [1986] defined a cause as “an event,condition, or characteristic that plays anessential role in producing an occurrence of thedisease.”
This document uses the following framework ofcriteria to evaluate evidence for causality. Theframework was proposed by Hill [1966; 1971]and modified by Susser [1991] and Rothman[1986].
Strength of AssociationThe ORs and prevalence rate ratios (PRRs)from the reviewed studies were used toexamine the strength of the association betweenexposure to workplace risk factors and MSDs,with the higher values indicating strongerassociation. The greater the magnitude of therelative risk (RR) or the
OR, the less likely the association is to bespurious [Cornfield et al. 1959; Bross 1966;Schlesselman 1978]. Weaker associations aremore likely to be explained by undetectedbiases.
1-12
Debate is ongoing in the epidemiologicliterature about studies with small sample sizesthat find increased ORs or PRRs but haveconfidence intervals (CIs) that include 1.0. Thequestion is whether such studies simply showno significant association or can be seen asuseful estimates of associated risk.Nonetheless, it is useful to identify trends acrosssuch studies and consider whether they havevaluable information after taking into accountother epidemiologic principles. If the studieswith and without significant findings both havesimilarly elevated ORs or PRRs, thisinformation is useful in estimating the overalllevel of risk associated with exposure.
Consistency Consistency refers to the repeated observationof an association in independent studies.Multiple studies yielding similar associationssupport the plausibility of a causalinterpretation. Finding the same associationwith different and valid ways of measuringexposure and disease may show that theassociation is not dependent on measurementtools. Similar studies that yield diverse resultsweaken a causal interpretation.
Specificity of Effect or AssociationThis criterion refers to the association of asingle risk factor with a specific health effect.We have not emphasized this criterion becauseof the different views of its utility in determiningcausality. If this criterion is interpreted to meanthat a single stressor can be related to a specificoutcome (e.g., that forceful exertion alone canbe related to hand/wrist tendinitis) it becomesan important criterion for MSDs. However, thiscriterion can be interpreted and applied toosimplistically. Schlesselman [1982] noted thatthe concept of specificity is that is generally toosimplistic and that multiple causes and effectswere more often the rule than the exception.
Rothman [1986] referred to specificity of effectas “useless and misleading” as a criterion forcausality.
TemporalityTemporality refers to documentation that thecause precedes the effect in time. Prospectivelydesigned studies ensure that this criterion isstrictly adhered to—that is, that exposureprecedes adverse health outcome. But cross-sectional studies are not designed to allow strictadherence to this criterion because bothexposure information and adverse healthoutcome are obtained at the same point in time.
Even though the cross-sectional study designprecludes strict establishment of cause andeffect, additional information can be used tomake reasonable assumptions that exposurepreceded the health effect—particularly whenthe relationship between physical exposures ismeasured by observation or directmeasurement and by MSD-related healthoutcomes. If the exposure was directlymeasured or observed, it is also unlikely thatthe measurement was influenced by thepresence or absence of the MSD in theemployee. Rothman [1986] stated that it isimportant to realize that cause and effect in anepidemiologic study or epidemiologic datacannot be evaluated without making someassumptions (explicit or implicit) about thetiming between exposure and disease. Forexample, from a cross-sectional study ofhand/wrist tendinitis and highly forceful,repetitive jobs, a researcher can determinewhen exposure began from recorded workhistories or from interviews. The researcher canalso reasonably determine the time of tendinitisonset by interviews. Kleinbaum et al. [1982]said that in cross-sectional studies, risk factorsand prognostic factors cannot be distinguishedempirically without additional information.
1-13
With additional information (e.g., laboratoryexperiments or biomechanical findings), aninvestigator can deduce that the adverse healthoutcome followed exposure. For example,taking other confounders into account, it isunreasonable to deduce that persons withhand/wrist tendinitis are likely to seekemployment in jobs that require highly forceful,repetitive exertion of the hand/wrist area.
Exposure-Response RelationshipThe exposure-response relationship relatesdisease occurrence with the intensity,frequency, or duration of an exposure (or acombination of these factors). For example, iflong-duration, forceful, repetitive work usingthe hands and wrists is associated with anincreased prevalence of hand/wrist tendinitis,this association would tend to support a causalinterpretation. Some have challenged theimportance of physical factors as causal agents,but prospective studies have shown thatreduced exposures result in a decreaseddisease [Bigos et al. 1991b]. In occupationalhealth, important and effective preventiveactions have been initiated without prospectivedemonstration that reduced exposure decreasesthe incidence of disease.
Coherence of EvidenceCoherence of evidence means that anassociation is consistent with the natural historyand biology of disease. For example, anobserved association between repetitive wristmotion and CTS (defined by nerve conductioncriteria) must be supported by biologicalplausibility: repeated wrist movement can causeswelling of tissue in the carpal tunnel, resultingin injury to nerves. It is important to remember,however, that epidemiologic studies can identifynew associations for further study.
CATEGORIES USED TO CLASSIFY
THE EVIDENCE OF WORK-RELATEDNESSAfter assessing the quality of individualepidemiologic studies, NIOSH investigatorsjudged whether the evidence was strongenough to relate the risk factor to the MSD. Inmaking this judgement, the investigatorsconsidered the criteria for causality. Studieswhich met all four evaluation criteria were givenmore weight than those which met at least oneof the criteria.
The evidence of work-relatedness fromepidemiologic studies is classified into one ofthe following categories: strong evidence ofwork-relatedness (+++), evidence of work-relatedness (++), inadequate evidence ofwork-relatedness (+/0), and evidence of noeffect of work factors (-).
Strong Evidence of Work-Relatedness (+++)A causal relationship is very likely betweenintense and/or long duration exposure to aspecific risk factor(s) and an MSD when usingthe epidemiologic criteria of causality. Apositive relationship has been observedbetween exposure to the risk factor and theMSD in at least several studies in whichchance, bias, and confounding could be ruledout with reasonable confidence. Evidence of Work-Relatedness (++) Some convincing epidemiolgic evidence existsfor a causal relationship using the epidemiologiccriteria of causality forintense and/or long-duration exposure to aspecific risk factor(s) and an MSD. A positiverelationship has been observed betweenexposure to the risk factor and the MSD instudies in which chance, bias, and confoundingare not the likely explanation.
1-14
Insufficient Evidence of Work-Relatedness (+/0) The available studies are of insufficient quality,consistency, or statistical power to permit aconclusion regarding the presence or absenceof a causal association. Some studies suggest arelationship to specific risk factors but chance,bias, or confounding may explain theassociation.
Evidence of No Effect of Work Factors (-) Adequate studies consistently and stronglyshow that the specific risk factor is not relatedto MSDs.
SUMMARYThis document critically reviews the evidenceregarding work-related risk factors and theirrelationship to MSDs of the neck, shoulder,elbow, hand/wrist, and low back. Thedocument represents a first step in assessing thework-relatedness of MSDs. This step involvesexamination of relevant epidemiologicinformation to assess the strength of theavailable evidence that, under certain conditionsof exposure, specific risk factors could increasethe risk of MSDs or increase the likelihood ofimpairment or disability from MSDs. Thesecond step would involve quantitative riskestimates that are beyond the purpose andscope of this document. This review of theepidemiologic literature may assist national andinternational authorities, academics, and policymakers in assessing risk and formulating decisions about future research ornecessary preventive measures.
This document does not necessarily cite all ofthe literature on a particular MSD. Included arearticles considered relevant by NIOSHinvestigators and internal and external reviewersof the draft document. Only reports that havebeen published or accepted for publication inthe openly available scientific literature havebeen reviewed by the authors. In certaininstances, they have included government
agency reports that have undergone peerreview and are widely available.
DESCRIPTION OF TABLES,FIGURES, AND APPENDICESIn each chapter on neck, shoulder, elbow,hand/wrist, and low back disorders, there aretables summarizing the risk indicators andepidemiologic criteria used in examining studiesrelevant to each body part. For each of thesecriteria tables there are corresponding figureswhich depict ORs, PRRs, or IRs, along withtheir associated CIs, if available.
In a separate table for each chapter, moreextensive descriptions of studies, whether ornot they contributed to decisions regardingcausal inference, are provided for each bodypart. These tables include information fromeach study about their design, population,outcome, and exposure measures, as well asreported MSD prevalence. Some studies areincluded in the tables that may not bementioned in the text. These additional studiesare for information purposes only.
Appendix A, Epidemiologic Review, is a briefprimer on occupational epidemiologic methods.Appendix B, Individual Factors Associatedwith Work-Related Mus-culoskeletalDisorders (MSDs), discusses individual factors(age, gender, etc.) and their association withwork-related MSDs. Appendix C, SummaryTables, provides a concise overview of thestudies reviewed relative to the evaluationcriteria, risk factors addressed, and otherissues.
2-1
CHAPTER 2Neck Musculoskeletal Disorders: Evidencefor Work-Relatedness
SUMMARY Over 40 epidemiologic studies have examined physical workplace factors and their relationship to neck andneck/shoulder musculoskeletal disorders (MSDs). Among these studies are those which fulfill rigorousepidemiologic criteria and appropriately address important issues so that causal inferences can be made.The majority of studies involved working groups with a combination of interacting work factors, but certainstudies assessed specific work factors. Each of the studies we examined (those with negative, positive, orequivocal findings) contributed to the overall pool of data for us to use in assessing the strength of the work-relatedness using causal inference.
There is evidence for a causal relationship between highly repetitive work and neck and neck/shoulderMSDs. Most of the epidemiologic studies reviewed defined “repetitive work” for the neck as work activitieswhich involve continuous arm or hand movements which affect the neck/shoulder musculature and generateloads on the neck/shoulder area; fewer studies examined relationships based on actual repetitive neckmovements. The two studies which measured repetitive neck movements by measuring head position(using frequency and duration of movements) fulfilled the most stringent epidemiologic criteria, showingstrong associations with neck/shoulder MSDs. In those studies defining repetitive work involving continuousarm or hand movements affecting the neck/shoulder, nine studies were statistically significant and hadodds ratios (ORs) greater than 3.0.; eight studies fulfilled all the epidemiologic criteria except theexposure criteria, and measured repetition for the hand/wrist and not for the neck. Of these, threewere statistically significant and had ORs greater than 3, five had nonsignificant ORs, all under 2.0.
There is also evidence for forceful exertion and the occurrence of neck MSDs in the epidemiologicliterature. Most of the epidemiologic studies reviewed defined “forceful work” for the neck/shoulder as workactivities which involve forceful arm or hand movements, which generate loads to the neck/shoulder area; nostudy examined a relationship based on actual forceful neck movements. Of the 17 studies addressingforce as one of the exposure factors, five studies found statistically significant associations, but did notderive ORs; two studies found ORs greater than 3.0, seven studies from 1 to 3.0, and two studies with ORsless than 1.0. Many of the studies relating measured force (as workload, etc.) to MSDs are in thebiomechanical and ergonomic literature.
There is strong evidence that working groups with high levels of static contraction, prolonged static loads,or extreme working postures involving the neck/shoulder muscles are at increased risk for neck/shoulderMSDs. Consistently high ORs were found (twelve statistically significant studies with ORs over 3.0)providing evidence linking tension-neck syndrome with static postures or static loads.
The epidemiologic data were insufficient to provide support for the relationship of vibration to neckdisorders. At this time, further studies must be done before a decision regarding causal inference is made.The few prospective studies which have included interventions to decrease workplace exposures thatinclude decreasing repetitive work and less extreme working postures showed a decrease in the incidenceof neck MSDs and an improvement in symptoms among affected workers. The data on intervention provideadditional evidence that these disorders are related to workplace risk factors.
2-2
INTRODUCTION
Studies from the United States have generallyclassified neck disorders separately fromshoulder disorders when evaluating work-related risk factors. Scandinavian studiesexamining work-related factors, on the otherhand, have often combined neck and shoulderMSDs into one health outcome variable. Thiswas based on the concept that several musclesact on both the shoulder girdle and the upperspine together. We have divided our reviews ofthe neck and shoulder MSDs into twochapters: Chapter 2 addresses neck andneck/shoulder MSDs and Chapter 3 addressesshoulder MSDs.
Our discussion of the evidence for work-relatedness of the neck will include criteriaTables 2-1 through 2-6 and Figures 2-1through 2-6. Shoulder MSDs will be discussedin the next chapter.
Epidemiologic studies have defined neckMSDs in one of two ways: (a) by symptomsoccurring in the neck (usually with regard to aspecific duration, frequency, or intensity), or (b)by using both symptoms and physicalexamination findings.
The prevalence of reported MSDs is generallylower when they are defined using bothsymptoms and physical examination results thanwhen defined using symptoms alone. Forexample, the prevalence rate of tension necksyndrome (TNS) among male industrialworkers in the United States was reported tobe 4.9% from interview data and 1.4% whencase definitions included physical exam findings[Hagberg and Wegman 1987]. The percent ofwork-related MSD cases defined by physicalexamination findings to those defined solely by
symptoms has ranged from approximately 50%(Silverstein et al. [1987]; Blåder et al. [1991];Bernard et al. [1993]; Hales et al. 1994]) toabout 85% (Andersen and Gaardboe[1993b]). Forty-seven of the listed studiesreferenced included physical examinationfindings in their health outcome assessmentcriteria.
Many of the neck and neck/shoulder MSDstudies referenced in the tables were part oflarger studies that inquired aboutmusculoskeletal symptoms and physical findingsin multiple body sites. In most of these studies,there were no separate ergonomic exposureobservations or measurements made thatpertained to the neck region (e.g., there wereno neck posture observations, neck anglemeasurements, neck work-load assessment,trapezius electromyographic testing, etc.). Inthese studies, the primary interest andmeasurement strategies focused on the handand wrist region (e.g., Kuorinka and Koskinen[1979]; Ohlsson et al. [1989]; Hales et al.[1989]; Kiken et al. [1990]; Baron et al.[1991]). In the studies, workers werecategorized only by hand/wrist exposures.Hand/wrist categorization will not reflectexposures of the neck region (or othermusculoskeletal sites). For example, workerswho may have frequent and rapid awkwardpostures of the neck but less frequent orextreme postures of the hand and wrist regionmay be misclassified as low risk if classificationdepends only on hand/wrist exposure. Ingeneral, we have given these studies less weightbecause of a significant potential formisclassification.
The text of this section on neck andneck/shoulder MSDs is organized by work-
2-3
related exposure factor. The discussion withineach factor is organized according to thecriteria for evaluating evidence for work-relatedness in epidemiologic studies using thestrength of association, the consistency ofassociation, temporal relationships, exposure-response relationship, and coherence ofevidence. Conclusions are presented withrespect to neck and neck/shoulder MSDs as asingle disorder for each exposure factor.Summary information relevant to the criteriaused to evaluate study quality is presented inTables 2-1 through 2-6. A more extensive summary, whichincludes information on health outcome,covariates, and exposure measures, ispresented at the end of this chapter.
Studies Included in NeckMSDs Tables
Forty-six epidemiologic studies dealing withneck MSDs and 23 dealing with neck/shoulderMSDs appear in the summary tables. Of thestudies, 38 were cross-sectional, 2 were case-control studies, and 6 were prospective studies.Among all the studies pertaining to the neck orneck/shoulder area, 35 had participation ratesof over 70%, 3 had less than 70%, and 8 didnot report their participation rates.
REPETITION
Definition of Repetition for Neck andNeck/Shoulder MSDs
For our review of the neck or neck/shoulderregion, we chose those epidemiologic studiesthat examined repetition or repetitive workactivities and MSDs. Studies generally addressrepetition as cyclical work activities thatinvolved either: (1) repetitive neck movements(e.g., the frequency of different head positions
during a cycle), or
(2) repeated arm or shoulder motions thatgenerate loads to the neck/shoulder area (e.g.,trapezius muscle). Most of the studies thatexamined repetition or repetitive work as apotential risk factor for neck or neck/shoulderMSDs had several concurrent or interactingphysical workplace factors that were beingevaluated. Therefore, repetitive work was notnecessarily considered the primary exposurefactor but was considered along with the otherwork factors.
Studies Reporting on the Associationof Repetition as a Work Factor forNeck and Neck/ShoulderMSDs
Either the risk factor “repetition” or “repetitivework” was included in 26 studies as a factorfor selection of the study population in theirexamination of neck and neck/shoulder MSDsin the workplace. However, only a handful ofthese studies examined repetitive movements ofthe neck. Few of these studies observed ormeasured: (a) the frequency or duration oftasks pertaining to the neck, (b) the ratio ofwork-time-to-recovery time for neck orneck/shoulder involvement, or (c) thepercentage of the workday spent on repetitiveactivities involving the neck. Instead, studiestended to compare and contrast theprevalences of neck symptoms and/or physicalfindings in workers in occupations requiring acombination of forceful, repetitive movementsand extreme postures of the upper extremities(mainly of the hand/wrist) to workers inoccupations without those requirements.
Twenty studies that mentioned repetitive work
2-4
or repetitive movements found a
statistically significant positive associationbetween repetition and neck or neck/shoulderMSDs; 6 others had non-significant findings(Tables 2-1 and 2-2, Figures 2-1 and 2-2). Interms of magnitude of the association, 11studies had ORs greater than 3.0, 11 had ORsbetween 1.0 and 3.0, and none had an OR lessthan 1.0. Four studies did not report theirresults in terms of ORs or Prevalence RateRatio (PRRs), although all of these foundsignificant associations (p<0.05).
Studies Meeting the Four Evaluation Criteria
Of the 27 investigations (see Tables 2-1 and 2-2), 2 fulfilled all four evaluation criteria outlinedearlier in the introduction section [Ohlsson et al.1995; Jonsson et al. 1988]. Only the Ohlssonstudy reported ORs. The investigationsassessed repetitive work as an independentvariable in terms of frequency and duration ofneck movements.
In the cross-sectional study by Ohlsson et al.[1995], female industrial assembly-line workersexposed to repetitive tasks with short (<30seconds) cycles were compared to 2 referentgroups: 68 former assembly workers and 64other workers with no repetitive exposure attheir current jobs. Industrial workers had toperform tasks with a posture requiring anintermittently flexed neck and elevated arms,which were abducted intermittently. Workersand referents reported neck/shouldersymptom(s) and had physical exams performedby a single examiner. The examiner was blindedto exposure status but not completely to groupstatus. Ergonomic exposure assessment wasextensive. It included videotaping, observation,and analysis of postures, including
measurements of critical
angles (15E and 30E) of flexion of the neck.Two independent readers determinedfrequency, duration, and critical angles ofmovement for each variable by taking theaverage of the two readings. Weekly workingtime, work rotation, patterns of breaks, andindividual performance rate (piece rate) wererecorded and used in the analysis. The studycontrolled for age, gender (only females wereincluded), and psychosocial variables(“tendency for stress” and “worry”).
The other study that fulfilled the four criteriaconcerned a 3-year prospective study writtenup in a series of articles by Kilbom et al.[1986], Kilbom and Persson [1987], andJonsson et al. 1988]. Female electronicworkers in highly repetitive tasks with staticpostural loads to the neck and shoulder areaswere followed over a 3-year period. In thesecond year, some of the employees hadworkplace interventions that decreased thenumber of repetitive tasks involving extremeneck and shoulder postures, while otherscontinued to work at unaltered tasks. Threeseparate physical exams were carried out atyearly intervals, the first one initially assessingtenderness on palpation and pain or restrictionwith active and passive movements. Ergonomicassessments occurred at the outset of the studyand included video analysis of postures andmovements of the head, shoulder, and upperarm. The evaluation recorded work-cycle timeand number of cycles per hour; time at rest forthe arm, shoulder, and head; total number ofrest periods; and average and total duration perwork cycle and hour. (The method wasdesigned to study short-cycle repetitive workunder visual control.) The mean number of
2-5
neck forward flexions >20E per hour was 728 (standard deviation[s.d.] 365) in the initial 96 workers. Theparticipation rate of the study was 72% after 3years; the investigators analyzed severalvariables separately for dropouts and found nosignificant differences with regards to medicalstatus, physiologic capacity, working technique,or work history. The investigators performedstep-wise logistic regression with deteriorationof disorders or remaining healthy in the differentlocations (neck and neck/shoulder) as the twodependent variables. Age, muscle strength, jobsatisfaction, and high productivity wereincluded in the logistic regression analyses ofthese studies. Video analysis and observationwere used to assess repetitive exposure on allsubjects, using work cycle time, number ofcycles per hour, as well as number of neckflexions per hour as criteria. Work cycle timevaried between 4.6 and 9.1 min, with a meanvalue of 6.6 min.
Strength of Association forRepetition
In the Ohlsson et al. [1995] study, the OR forthe association between repetitive work relatedto the neck and any neck/shoulder diagnoseswas 4.6; for a diagnosis of tension necksyndrome, it was 3.6.
For the cohort study carried out by Kilbom etal. [1986], at the 2-year followup, the numberof neck flexions per hour appeared as a strongpredictor for deterioration to severe disordersof the neck. Improvement to a “healthy status”classification fromYear I to Year II was seen with reallocatingworkers to more varied work tasks (whichrequired a reorganization of monotonous andrepetitive work tasks). The new tasks werecharacterized as more dynamic and varied and
included only occasional sitting tasks,caretaking work, surveillance of machinery, orassembling of bigger and heavier equipment.The article documenting the last phase of thecohort study by Jonsson et al. [1988] did notspecifically address the neck but broadened thehealth outcome definition to include theneck/shoulder area and the rest of the upperextremity using “cervicobrachial region” as thehealth outcome of interest. A significantassociation between deterioration of healthstatus of the cervicobrachial region betweenYear II and Year III of the study and “workcycle, total time” at the p<0.05 level was found(ORs were not given).
Studies Meeting at Least One of the FourCriteria—Strength of Association
Of the studies that found significant ORs over3.0 but did not mention or fulfill all of thecriteria, almost all focused on working groupswith a combination of repetitive and forcefulwork and compared them to either populationreferents or groups in occupations with lowerexposure. Almost all were cross-sectionalsurveys. These studies used health outcomesfrom symptom surveys and self-reportedworkplace exposure (no direct observations)and either compared symptomatic workers(neck MSD cases) to asymptomatic workers inthe same workforce (e.g., Yu and Wong [1996]; Bergqvist et al. [1995a]; Schibye et al.[1995]; Hünting et al. [1981]) or in otheroccupations (e.g., Liss et al. [1995]; Andersenand Gaardboe [1993b]; Milerad and Ekenvall[1990]; Onishi et al. [1976]). Onishi et al.[1976] found significant differences inneck/shoulder MSDs (OR 3.8) betweengroups involved in repetitive upper limboperations and office workers. They foundworkers involved in repetitive activity had 10%to 30% maximum voluntary contraction (MVC)
2-6
of the trapezius muscle. They concluded thathabitual neck or shoulder muscle fatigue is
caused by repetitive tasks that result inlocalized tenderness and may be a precursor tochronic MSDs.
Andersen and Gaardboe [1993a] used across-sectional design to compare sewingmachine operators with a random sample ofwomen from the general population of the sameregion. A neck case required a strictpredetermined symptom and physicalexamination definition. Exposure was assessedthrough observation and categorization of jobs,based on the authors’ experience andjudgements. However, the main interest forexposure assessment was duration of exposureas a sewing machine operator. Statisticalmodeling controlled for age, having children,not doing leisure exercise, smoking, andsocioeconomic status found a significant trendfor “neck/shoulder syndrome” in relation toyears of exposure as a sewing machineoperator, with ORs from 3.2 to 36.74. The ORfor the lowest exposure category, 0-7 years,was not statistically significant, although thehigher exposure levels were. For this study, theexposure classification scheme does not allowseparation of the effects of repetition fromthose of force, and there was no precisemeasure of repetitiveness.
Baron et al. [1991] studied neck MSDs in 124grocery store checkers and 157 other grocerystore workers who were not checkers. Theneck MSD case definition met predeterminedsymptom and physical exam criteria. Physicalexaminations had higher participation ratesamong the checkers (85%) than among thereferents (55%). Telephone interviews to non-checkers resulted in questionnaire completionby 85% of the non-checkers. The OR for neck
disorders among checkers was 2.0 (95%confidence interval [CI] 0.6–6.7), in a modelthat included age, hobbies, second jobs,systemic disease, and obesity.
Bergqvist et al. [1995a] carried out a studycomparing office workers using video displayterminals (VDTs) to those who did not. Aphysiotherapist’s diagnosis of tension-necksyndrome was used to define a case. Exposureassessment was based on both self-reports andthe investigators’ observation of work postures,movements, and measurements of heights ofwork-station equipment in conjunction with theuser. Statistical modeling included severalindividual factors, organizational factors, andergonomic factors. For “tension neck”syndrome, no factor related to repetitive workwas found to be significantly related.
Blåder et al. [1991] surveyed 199 sewingmachine operators from 4 plants. Of the 155who reported shoulder or neck pain, 131 wereexamined. Exposure assessment was byquestionnaire and addressed employmentduration and hours per week. Authors statedthat the study involved a control group andtook into account psychosocial factors, but theresults were not included in the article. Bothemployment duration and working more than30 hours per week were found to bestatistically significant at the p<0.05 levels. Forthis study, the exposure as duration of work(per week and per years) does not allowseparation of the effects of repetition fromthose of force. There was no direct measure ofrepetitiveness. Ekberg et al. [1994] carried out a case-controlstudy involving cases from a semi-ruralcommunity in southern Sweden who hadconsulted a community physician for MSDs ofthe neck, shoulder, arm, or upper thorax.
2-7
Cases had to have been ill immediately prior tophysician visit and
have been on sick leave less than 4 weeks.Cases were excluded for trauma, infectiouscauses, accident, malignancy, rheumaticdisease, abuse, or pregnancy. Controls wererandomly selected from the Swedish insuranceregistry. Exposure was obtained byquestionnaire. The analysis showed that forneck disorders with precise repetitivemovements the OR was 3.8 for mediumexposure and 15.6 for high exposurecomparing jobs with low force and lowrepetition. Gender, immigrant status, workpace, and current smoking were also analyzedin the logistic model.
Ekberg et al. [1995] surveyed 637 Swedishresidents for the presence of neck symptoms inthe past six months. Exposure was based onquestionnaire responses. Twenty questionnaireitems on physical work conditions were factoranalyzed. Age, smoking, exercise habits, andfamily situation with preschool children werenot significantly associated with symptoms.Repetitive movements demanding precisionwas found to have an OR of 1.2 for neck pain.
Hales and Fine [1989] compared 89 femaleworkers in 7 high exposure jobs to 25 femalepoultry workers in low exposure jobsemployed in poultry processing. Neck casedefinition required symptoms and physicalexamination findings that met predeterminedcriteria. Exposure assessment was based onhand/wrist assessment of forceful and repetitivejobs. No assessment of neck repetition wasperformed. Twelve percent of workers in highrisk jobs versus none in low risk jobs were foundto have neck MSDS.
In a study of VDT users in a range of jobs
(data entry to “conversational” VDT use),Hünting et al. [1981] used a case definitionrequiring symptoms and physical exams and anextensive exposure assessment usingquestionnaire, observation, and measurementsof workstations, and body posturemeasurements using a prescribed method. Dataentry terminal users, whose tasks requiredmore extensive repetitive work than traditionaloffice workers, found an OR of 9.9 with thecomparison. There were no adjustments forconfounders in this analysis.
Kamwendo et al. [1991] compared 420medical secretaries with frequent, significantneck pain to those with few episodes based onquestionnaire responses. Exposure was alsoquestionnaire based. The analysis wascontrolled for age and length of employment. Asurrogate for repetitive work consisted of hourssitting or working with office machines with highexposure equal to 5 hrs or more/day.
Kiken et al. [1990] also studied poultryworkers at two plants with exposure to highlyforceful, highly repetitive jobs and comparedthem to other poultry workers with lessexposure. Neck case definition requiredsymptoms and physical examination findingsthat met predetermined criteria. Exposureassessment was based on hand/wristassessment of forceful and repetitive jobs. Noassessment of neck repetition was performed.Job turnover was around 50% at plant 1 and70% at plant 2 making survivor bias a strongpossibility.
Kuorinka and Koskinen [1979] studiedoccupational rheumatic diseases and upper limbstrain among 93 scissor makers and comparedthem to the same group of department storeassistants (n=143) that Luopajärvi et al. [1979]used as a comparison group. Temporary
2-8
workers and
those with recent trauma were excluded fromthe scissor makers group. Exposure assessmentincluded videotape analysis of scissor makertasks, however exposure assessed for the handand wrist region and not the neck. No formalexposure assessment was conducted on theshop assistants. Health assessment involved aninterview and physical examination by aphysiotherapist following a standard protocol.Diagnoses of tension neck syndrome weredetermined using predetermined criteria [Wariset al. 1979]. In problem cases, orthopedic andphysiatric teams determined case status. It isunclear whether cashiers were excluded fromthe comparison group in this study as they werein the Luopajärvi et al. [1979] study. The studygroup was 99% female.
Luopajärvi et al. [1979] compared theprevalence of neck/shoulder disorders among152 female assembly line packers in a foodproduction factory to 133 female shopassistants in a department store. Exposure torepetitive work, awkward hand/arm postures,and static work was assessed by observationand videotape analysis of factory workers. Noformal exposure assessment was conducted onthe department store workers; their job taskswere described as variable. Cashiers wereexcluded, presumably because their work wasrepetitive. No formal assessment occurred forneck/shoulder repetition. The health assessmentconsisted of interviews and physicalexaminations conducted by a physiotherapist,and diagnoses of tension neck syndrome werelater determined by medical specialists usingthese findings and predetermined criteria (95%CI 2.63–6.49). Age, hobbies, and houseworkwere considered in the analysis.
Milerad and Ekenvall [1990] compared theself-reported neck and neck/shouldersymptoms between dentists and pharmacists.Dentists had been considered the high riskgroup because of awkward postures andrepetitive use of small handtools. Exposure wasbased on self-reports. The authors examinedseveral covariates and stratified by gender fortheir analysis. No difference between groups inleisure time, smoking, systemic disease, andexposure to vibration.
Ohlsson et al. [1989] studied 148 electricalequipment and automobile assemblers,76 former female assembly workers who quitwithin 4 years and compared these two groupsto 60 randomly sampled females from thegeneral population. A case was determined byquestionnaire; exposure was based on jobcategorization and questionnaire responses.Repetitive exposure was based upon thenumber of items completed per hour. The workpace was divided into four classes: (1) Slow:<100 items/hr; (2) Medium: 100 to 199items/hr; (3) Fast: 200 to 700 items/hr;(4) Very Fast: >700 items/hour. The ORincreased with increasing work pace, except atvery high paces, where there was a decrease.This was attributed to “selective quitting ofsubjects with complaints, only the healthiestbeing left in the assembly work.”
Onishi et al. [1976] compared several groupsof workers with varying exposure to repetitivetasks. Health outcome was based on symptomsof shoulder stiffness, dullness, pain, numbness;pressure measured by strain transducer atwhich a subject felt pain; and a physical exam.Observation and measurements of some jobtasks, including some measures of repetition,were performed then job categorization wasdone. Based on job
2-9
categorization and job analysis, and taking intoaccount shift length, activities, number ofbreaks, repetitive movements of the hands, armmanipulations, and length of employment, therewas not a difference between workers withtenderness threshold above 1.5 kg/cm² andthose below with respect to age, height, weight,skinfold thickness, grip strength, upper armabduction strength, and back muscle strength.
Punnett et al. [1985] compared neck/shoulderMSDs based on symptom reporting alone in162 women garment workers and 76 womenhospital workers such as nurses, laboratorytechnicians, and laundry workers. There was alow participation rate among the hospitalworkers. Eighty-six percent of the garmentworkers were sewing machine operators andfinishers (sewing and trimming by hand). Thesewing machine operators were described asusing highly repetitive, low force wrist andfinger motions, while the finishers had shoulderand elbow motions as well. The exposedgarment workers likely had more repetitivejobs than most of the hospital workers. Theneck/shoulder cases were found to lift both the“typical” and “heaviest” loads with greaterfrequency than non-cases.
Sakakibara et al. [1995] found among orchardworkers that neck shoulder MSDs based onsymptom and physical findings weresignificantly higher when performing pearbagging than when apple bagging. Exposurewas based on measurements of specific anglesof the neck and shoulder and job tasks in arepresentative worker. ORs were not derivedin this study. Confounders were not checkedfor in this study.
Sakakibara et al. [1987] did not include
physical exam findings in the case definition ofneck and neck/shoulder MSDs whencomparing workers bagging pears versusapples. Exposure was again based onmeasurements of job tasks by a representativeworker.
Schibye et al. [1995] followed up 303 sewingmachine operators at nine factories representingdifferent technology levels who completed aquestionnaire in 1985. In April 1991, 241 of279 traced workers responded to the same1985 questionnaire. Operators still workingwere compared to those who moved to otheremployment in 1991. Exposure was assessedthrough a questionnaire asking type of machineoperated, work organization factors,workplace design factors, units produced perday, the payment system, and the duration ofemployment as a sewing machine operator.Although the authors state that the analysis didnot show that neck symptoms among workerswho had worked as a sewing machine operatorto be significantly related to exposure, exposuretime, or age, there was a significant drop-outrate of those above 35 years.
Rossignol et al. [1987] chose 38 random sitesfrom Massachusetts workers with more than 50 employees, and selected 191 workers from computer and dataprocessing services, and public utilitiesand the Commonwealth Government. Subjectswere selected after the observation of the worksite. A self-administered questionnaire case definition wasused for neck MSD. Exposure was also basedupon self-reports of number of hours workedeach day with a keyboard machine with aVDT. Analysis controlled for the
following confounding factors: age, cigarette
2-10
smoking, industry, and educational VDTtraining.
Yu and Wong [1996] chose to compare 90data entry, data processing, and computerprogrammers from an International Bank inHong Kong and 61 infrequent users of VDTs.Both neck MSD case definition and exposureassessment were based on symptom data.Analysis controlled for “age and gender, andother covariates” (as stated in the paper). Forfrequent VDT use an OR of 28.9 was found.
Kuorinka and Koskinen [1979] found asignificant difference in neck MSDs betweenscissor makers (an occupation chosen for studybecause of its assembly-line repetitive handtasks) and shop assistants (non-stereotypic,non-repetitive jobs) with an OR of 4.1. In thesame study, comparing the differentstereotypic, repetitive jobs in scissor-making,those in short-cycled tasks (2–9.5 sec) had nosignificantly different prevalence of neckdisorders than workers in longer-cycled tasks(7.3–26 sec) (OR 1.6, 95% CI 0.7– 3.8). It isimportant to note that both the longer-cycledtasks and short-cycled tasks in Kuorinka’sstudy would have been classified as “highlyrepetitive” in most other ergonomic studies[Silverstein et al. 1987; Chiang et al. 1993;Viikari-Juntura et al. 1991a; Kurppa et al.1991]. When comparing two groups in whichthe level of repetitive exposure may not differby much (in this case, where both groups havehighly repetitive tasks), it is unlikely that one willfind a significant difference because there is notenough variance between the exposures. Three studies [Ekberg et al. 1994, 1995;Milerad and Ekenvall 1990] used healthoutcomes and exposure assessments based onself-reports and found significant associations
between symptoms and repetitive work. TheEkberg studies specifically asked about“precise repetitive movements” in theirquestionnaire and controlled for confoundersand effect modifiers (age, gender, having pre-school children) in their analyses. Milerad andEkenvall [1990] compared dentists andpharmacists, stratified by gender, and found noassociation between neck or neck/shoulderMSDs with metabolic disease, smoking, leisuretime, exposure, or vibration. Significant ORs of2.0 to 2.6. for neck MSDs were reported fordentists compared to pharmacists.
Of those studies reporting no significantassociation between repetition and neck orneck/shoulder MSDs, none included exposureassessment or observations of the neck orneck/shoulder area that were both objectiveand independent of the hand/wrist. Several ofthese studies [Baron et al. 1991; Kiken et al.1990; Hales et al. 1989; Ohlsson et al. 1989;Luopajärvi et al. 1979] categorized workersinto high and low exposure groups basedstrictly on hand/wrist exposure and not arm,shoulder, or neck exposure. All of these studiesreported ORs below 2.0.
In the study of VDT users by Bergqvist et al.[1995a], exposure was based on self-reportsof “the presence of repeated work movements”for all work tasks and not specifically focusedon the neck or neck/shoulder area. They foundno significant association with neck/shoulderMSDs when the variable “repeated workmovements” was analyzed in the logistic modelalone, but found a significant relationship with acombination of variables: (1) workers wearingglasses, (2) who reported VDT use, and (3)VDT use for more than 20 hours/week. In thiscase, it was the combination of variables athigher levels of exposure (VDT use more than
2-11
20 hours per week) that was found to bestatistically significant.
Temporal Relationship—Repetitionand Neck/Shoulder MSDs
Of the prospective studies of neck MSDs thatcan be used to establish a temporal relationshipbetween exposure to repetitive work and neckor neck/shoulder disorders, the study byJonsson et al. [1988] fulfills all the four studycriteria. Jonsson’s study was a followup of thecohort studied by Kilbom et al. [1986],electronic workers who entered the studywithout MSDs. Exposure assessment pertainingspecifically to the neck/shoulder area wascompleted three times over 3 years.
In the longitudinal study by Ohara et al. [1976],the authors attributed the increase in necksymptoms in cash register operators to theintroduction of new electronic cash registersplaced at unsuitable heights. They noted anincrease in repetitiveness and an increase inawkward and static postures by cash registeroperators using the new registers. The authorsreported a relationship between static loadingand MSDs and found that a subsequentreduction in exposure to static loading resultedin less worker disability (sick leave).
Although temporality cannot be obtained fromcross-sectional studies, several studiesattempted to insure that disorders developedfollowing the exposure being studied. In certainstudies [Baron et al. 1991; Kiken et al. 1990;Hales et al. 1994; Hoekstra et al. 1994], thehealth outcome definition excluded personsreporting symptoms prior to the job orreporting acute injury thought to be unrelated towork, insuring that exposure preceded MSDoccurrence. Other studies excluded participants
with less than 6 months (or even longer) of jobexperience, thereby omitting from their studyworkers who may have developed their MSDsprior to working at the job of interest, or whohad experienced discomfort or fatigue due tonew activities or a “break-in period” at work. Itis reasonable to assume that in those studies,given the exclusions required by the casedefinitions, the onset of exposure was prior tothe onset of neck/shoulder MSDs in themajority of participants.
Consistency in Association forRepetition and Neck/Shoulder MSDs
In the studies fulfilling the four criteria [Ohlssonet al. 1995; Jonsson et al. 1988; Kilbom et al.1986], significantly positive associationsbetween neck MSDs and repetitive work werefound. Many more studies involved workers inrepetitive work from a range of industries(VDT workers, dentists, electronic assembly,sewing machine operators, etc.), comparingsymptom prevalences to those in less repetitivejobs. There was also significant associationbetween neck and neck/shoulder MSDs andjobs with repetitive tasks, with ORs between1.6 and 5.9 [Onishi et al. 1976; Kuorinka andKoskinen 1979; Rossignol et al. 1987; Vihmaet al. 1982; Kamwendo et al. 1991; Andersenand Gaardboe et al. 1993b; Ekberg et al.1994, 1995; Schibye et al. 1995] indicatingthat workers exposed to higher levels of workrisk factors have greater rates of neck andneck/shoulder symptoms. None of the studiesthat failed to find significant associations carriedout exposure assessment of the neck orneck/shoulder.
Coherence of Evidence forRepetition
2-12
Studies outside the epidemiologic literature givesupportive evidence that repetitive work isrelated to neck/shoulder disorders. Stevens etal. [1966] found that the neck injuries amongfork-lift truck drivers were from repetitive,extreme head rotations needed for theoperation of fork lift trucks and introduced thesideways-sitting driver forklift. Eklund et al.[1994] reported following up on a “sideways-sitting” forklift (in an unpublished study); thesedrivers experienced neck pain three times asoften as other drivers on traditionalforklifts—indicating that moderate headrotations during long periods of time can bemore risky than short term and extensive headrotations. Nicholas [1990] reported in hisdiscussion on pathophysiologic mechanisms ofsports injuries that a low-load force with highrepetition results in a gradual deterioration oftissue strength from strain to fatigue todeformation, with prefailure symptoms, such aspain on use, a common clinical sign of earlyinflammation from overuse.
Exposure-Response Relationship forRepetition
There were no studies reviewed that showed aclear dose-response relationship betweenrepetition and neck and neck/shoulder MSDs.
Conclusions Regarding RepetitionThe association between neck orneck/shoulder MSDs and repetitive work
was found to be statistically significant in 19studies using different epidemiologicapproaches and under different circumstancesof exposure. Twenty-seven studies found ORsabove one; of these, 13 were above 3.0.Almost all the studies (6 of 8) with non-significant associations used hand/wrist
exposure assessments for their analyses and didnot conduct specific neck, shoulder, or upperextremity (apart from hand/wrist) exposureassessment. (Only one of the studies findingsignificant associations did so using hand/wristexposure assessment.) The possibility ofmisclassification affecting the results must be aconsideration.
FORCE
Definition of Force for Neck andNeck/Shoulder MSDs
For our review, we included studies thatexamined force or forceful work or heavy loadsto the neck and neck/shoulder, or describedexposure as strenuous work involving the upperextremity that generates loads to the trapeziusmuscles. Most of the studies that examinedforce or forceful work as a risk factor forneck/shoulder had several concurrent orinteracting physical work load factors.
Force has generally been defined as: (1) eitherexternally as a load or internally as a force on abody structure, or (2) a force magnitudeexpressed in newtons or pounds or as aproportion of an individual’s strength capacity,that is, of a person’s MVC, usually measuredby EMG. Most studies that have dealt withforce loading of the neck or stress generated onthe neck structures are from biomechanicalstudies performed in the laboratory. Thesestudies are not included in this document. In theepidemiologic studies reviewed, force is usuallyestimated by either questionnaire,biomechanical models, in terms of weight lifted,electromyographic activity, or the variable, “heavy physical workload.”
Seventeen studies reported results on theassociation between force or forceful work (in
2-13
combination with repetition) and neck andneck/shoulder MSDs. Of the 17 studies offorce and neck MSDs, 11 found a statisticallysignificant positive association between forceand neck or neck/shoulder MSDs; six othershad non-significant findings. In terms ofmagnitude of the association, two studies hadORs greater than 3.0, seven were between 1.0and 3.0, and two were less than 1.0. Sixstudies did not report their results in terms ofORs or prevalence rate ratios (PRRs) butreported that the findings were statisticallysignificant at the p<0.05 level.
Studies Meeting the Four Criteria forForce and Neck/Shoulder MSDs
There were no studies that met the fourepidemiologic evaluation criteria for forcefulexertion of the neck.
Studies Not Meeting the Four Criteriafor Force and Neck/Shoulder MSDs
Åaras [1994] carried out a cohort study of fourgroups, 15 female assembly workers makingtelephone exchanges, 27 female VDT users, 25female data entry operators, and 29 male VDTusers. Case definition for neck MSD wasbased on self-reports. However,musculoskeletal sick leave per man-labor yearswas also used as an endpoint. For forceestimate the load on the
trapezius was measured by electromyography(EMG).
Quantification of the muscle load was done byranking the interval estimate (0.1 s) to producean amplitude probability distribution function.Both the total duration and number of periodsper minute when muscle activity was below 1%
maximum voluntary contraction (MVC) werecalculated. Post-intervention (which involvedchanges to the workstation, tools, andorganization of work)—see Table 2-4 at theend of the chapter for further explanation, themean static trapezius load in assemblers wasreduced from 4.3% MVC to 1.4%, the meanstatic trapezius load in VDT users reducedfrom 2.7% MVC to 1.6% MVC (post-intervention). Sick leave also decreasedconsiderably. Because so many interventionswere involved in this study, it is not clear towhat intervention changes the decrease in sick-leave per man-labor years might be attributed.
Bjelle et al. [1981] compared 13 workers of anindustrial plant consecutively seen at a healthclinic with acute, nontraumatic shoulder-neckpain not due to causative disease ormalformation compared to 26 controls,matched on age, gender and place of work.
In another cohort study, Veiersted andWestgaard [1994] followed 30 femalechocolate manufacturing workers, 17 of whomcontracted trapezius myalgia within 6 to51 weeks compared to those workers who didnot. Diagnosis was based on both symptomsand physical exam. There were prospectiveinterviews every 10 weeks to detect symptomsof muscle pain. Daily “pain diaries” were alsokept by subjects.
Exposure assessment consisted of measuredstatic muscle tension recorded by EMG.Interviews concerning exposure at work werealso conducted prospectively every 10 weeksfor 1 year. Only 55% of the subjects wereretained during the full study; however, the‘drop-outs’ were follow-up subjects and hadno significant differences in static muscle tensioncompared to the participants.
2-14
Viikari-Juntura et al. [1994] , the thirdlongitudinal study discussed under force andneck and neck/shoulder MSDs, usedquestionnaire to assess neck symptoms andbased exposure on job category, comparing688 machine operators, 553 carpenters, and591 office workers. For the initial evaluation,observation of work sites were performed. Inmultivariate analysis occupation, age, andcurrent smoking were significant predictors inchange from no neck trouble to severe necktrouble (ORs were not given for logisticmodel.)
Wells et al. [1983] evaluated letter carriers withan increased load on the shoulder from amailbag. Letter carriers were compared to gasmeter readers (without heavy loads) and postalclerks. A telephone survey was used to obtainboth symptoms and exposure. This analysiswas adjusted for age, number of years on thejob, quetelet (body mass) ratio and previouswork experience.
Of the studies in the tables, five (that did notfulfill all the inclusion criteria) examined the riskfactor, force, either as trapezius muscle load(using EMG), or as forceful work incombination with other risk factors [Aåras1994; Wells et al. 1983; Onishi et al. 1976;Andersen and Gaardboe 1993a; Punnett1991]. Wells et al. [1983] found a significantdifference (p<0.05) in reported neck painbetween letter carriers and postal clerks andattributed it to weight from carrying heavy mailbags on shoulder straps. In the Wells study,confounding due to age, number of years on thejob, previous work experience, or queteletratios was ruled out. As noted above, Onishi etal. [1976] reported that the operations studiedrequired continuous contraction of the trapeziusmuscle to sustain the arms, estimated to be
about 10 to 30% of the maximum contractionof the trapezius. This level, 10 to 30% of themaximum contraction, was found by Tanii et al.[1972] to induce static fatigue significantenough to produce electromyographic changes.Hales et al. [1989] and Kuorinka andKoskinen [1979] reported statisticallysignificant ORs (1.6 and 4.1, respectively) forthe association between neck MSDs and highlevels of force combined with high levels ofrepetition estimated for the hand/wrist areas.There were no separate force measurementsfor the neck area. Both studies controlled forage, gender, and length of employment in thecurrent job. Two of the four studies that usedestimated hand and wrist exposuremeasurement combinations of force andrepetition (but carried out no neck, shoulder, orupper extremity exposure measurements) foundnon-significant associations between neckMSDs and force/repetition exposure [Baron etal. 1991; Kiken et al. 1990].
Temporal Relationship—Force andNeck/Shoulder MSDs
See temporal relationship above in Repetitionand Neck/Shoulder MSDs.
Consistency in Association for Forceand Neck/Shoulder MSDs
Both Kilbom et al. [1986] in their cross-sectional study and Jonsson et al. [1988] intheir follow-up cohort studies found that
“time spent in physically heavy work before thepresent employment” appeared as a strong riskfactor for deterioration of health of theneck/shoulder area (specifically, the healthoutcome was for the cervicobrachial region inthe Jonsson study). Jonsson et al. [1988] notedthat the physical demands of the previous jobs
2-15
had only been assessed at the initial interviewand constituted a subjective estimate.However, the relationship was strengthened bythe consistency of findings in the prospectiveand cross-sectional studies.
Coherence of Evidence for Force
There is coherence with the biologicalmechanisms proposed by Hagberg [1984] foroccupational muscle-related disorders, such astension neck syndrome. The first mechanismconcerns stress on the trapezius andsurrounding muscles of the neck from heavyphysical exertion that causes rupture of themuscle’s z-discs, and an outflow of metabolitesfrom the muscle fibers, and activation of painreceptors through edema or other mechanisms.This temporary high, local stress involvingeccentric contractions in the shouldersimproves with time through a re-orientation ofcollagen in the muscles. This mechanism isoffered as an explanation for MSDs in workersunaccustomed to the work. The secondmechanism is from local decreased blood flow(ischemia), as seen in assembly workers whosetasks involved dynamic, frequent contractionsabove 10 to 20% of the MVC and few restbreaks. Reduced blood flow was found to becorrelated with myalgia (muscle pain) andragged red fibers in 17 patients with chronicmyalgia thought to be associated with staticload during repetitive assembly work [Larssonet al. 1990]. The third pathophysiologicmechanism for muscle pain deals with energymetabolism disturbance, caused by long-termstatic contractions of the muscles. Supportingthis theory was a study finding a correlationbetween muscle tension and plasma myoglobinamong patients with regional muscle tendernessand pain [Dammeskiold-Samsøe et al. 1982].
Other laboratory studies have examined muscledamage that may arise during static musclecontractions used to maintain static postures.Hägg et al. [1990] proposed that whilemaintaining static postures (that have low forcelevels), the same low-threshold motor units arecontracted repeatedly for prolonged periods,during which time they work close to theirmaximal capacity. This may lead to injury ofthese units, despite the fact that the totalworkload is low. This hypothesis was recentlysupported by a longitudinal study by Veierstedet al. [1993] who investigated the number ofrest-pauses during muscle fiber activity usingEMG recording from neck and shouldermuscles. Among subjects performing machine-paced repetitive packing work, those withsymptoms had fewer rest-pauses (0.9 versus8.4 per minute) and a tendency toward shortertotal duration of rest-pauses in the muscle fiberactivity of their trapezius muscle whencompared with those without symptoms. Thesemechanisms of decreased blood flow,increased metabolite concentration, andprolonged activation of certain small units atnear maximum capacity may explain the chronicmyofascial shoulder pain seen in workersperforming repetitive assembly work with staticloading of the trapezius muscles [Hagberg andKvarnström 1984; Larsson et al. 1988].
Exposure-Response Relationshipfor Force
Åaras [1994] reported that by reducing staticmuscle loading (an indication of forcemeasurement) through equipment changesamong VDT users, as well as improvingworkplace organization, he was able todecrease the prevalence of neck pain, decreasethe number of sick days taken, and cause asignificant reduction in trapezius load measured
2-16
by EMG in VDT operators.
Conclusions Regarding Force
There is evidence for forceful exertion andneck MSDs in the epidemiologic literature.Most of the epidemiologic studies revieweddefined “forceful work” for the neck/shoulderas work activities that involve forceful arm orhand movements that, in turn, generate theloads to the neck/shoulder area; no studyexamined a relationship based on actualforceful neck movements. Of the 17 studiesaddressing force as one of the exposurefactors, 5 found statistically significantassociations but did not derive ORs; 2 foundORs greater than 3.0, 7 found ORs from 1 to3.0, and 2 studies showed ORs less than 1.0.Many of the studies regarding measured force(as workload, etc.) and MSDs are in thebiomechanical and ergonomic literature.
POSTURE
Definition of Posture for Neck andNeck/Shoulder MSDs
We included those articles that mentioned neckor head postures, adverse or extreme head orneck postures, or static postures of the headand/or neck.
Studies Reporting on Posture as aWork Factor for Neck andNeck/Shoulder MusculoskeletalDisorders
We included 31 studies of the associationbetween extreme or static posture and neckand neck/shoulder MSDs, including TNS.Studies usually focused on the different
prevalences of neck symptoms and/or physicalfindings in workers in occupations or tasksrequiring some combination of forceful,repetitive movements, and extreme or staticpostures of the upper extremity, and comparedthem to workers in occupations without thoserequirements.
Twenty-seven studies that considered extremeor static posture found a statistically significantpositive association between posture and neckor neck/shoulder MSDs; three had non-significant findings (Table 2-1. Overall, in terms of magnitude of theassociation, looking at both significant and non-significant findings, 13 studies had estimationsof risk (ORs or PRRs) greater than 3.0, 9 hadrisk estimates between 1 and 3, and none had an estimate less than 1.0.Eleven studies did not report their results interms of ORs or PRRs; of these, all but onefound a significant relationship.
Studies Meeting the Four Evaluation Criteria
Of the 31 studies evaluating neck postures andneck MSDs, the four investigations mentionedabove [Ohlsson et al. 1995; Jonsson et al.1988; Kilbom and Persson 1987; Kilbom et al.1986] fulfilled the four evaluation criteria. Threeof these studies [Jonsson et al. 1988; Kilbom etal. 1986; Kilbom and Persson 1987], dealtwith the same cohort; female electronicsworkers
followed for 3 successive years. These studiesfound significant association between posturevariables and neck MSDs; however, none usedmethods that reported ORs.
2-17
Studies Not Meeting the Four Criteria forPosture and Neck/Shoulder MSDsBernard et al. [1993] carried out a cross-sectional study of 894 newspaper employeesusing a questionnaire survey for case definitionbased on frequency, duration, and intensity ofsymptoms in the neck. Exposure was basedupon both questionnaire and job analysis. Timespent on the telephone was associated with anincreased prevalence of neck MSDs, with aslightly elevated OR of 1.4. Analysis wascontrolled for age, gender, height, psychosocialfactors, and medical conditions.
Kukkonen et al. [1983] compared 104 dataentry operators with 57 female workers invarying office tasks. Neck MSD was based onpre-determined symptom and physical exam.Exposure was based on observation ofposture, movements and working techniques,assessment of equipment, interview withworkers and supervisors. An interventionconsisting of adjustment of office furniture andequipment was carried out. The study groupwas given a short course of basic training onpertinent aspects of ergonomics. Four lessonson relaxation was given by means of exercises.There was no controlling of confounders. Therewas a significant decrease in tension necksyndrome among the cases involved in theintervention compared to those workers whohad no change.
Linton and Kamwendo [1989] surveyed22,180 employees undergoing screeningexaminations at their occupational health careservice in Sweden. Neck cases defined fromquestionnaire responses as those personsreporting “yes” to having seen a health careprofessional for neck pain in the last year.Cases were compared to “non-cases” definedby outcome (neck pain). Exposure was based
on questionnaire responses regarding heavylifting, monotonous or assembly line work,sitting, uncomfortable work postures (bendingand twisting), and vibration. The psychosocialwork environment was also studied; theanalysis was stratified for age and gender.
As part of a longitudinal study, Viikari-Junturaet al. [1994] studied 154 subjects fromHelsinki, Finland that originally entered thestudy in 1955, and had repeated cross-sectional exams from 1961 to 1963. Duringthat time, 1084 subjects underwent cross-sectional examination. In 1985, a questionnairewas sent to all subjects; 801 (74%) responded.Of the respondents, 180 lived in the Helsinkiarea. It was from this group that 162responded. Eight were excluded due toillnesses. Outcome was based on questionnairedata for this study — because of small numberof abnormal physical findings, the physicalexam was eliminated from analysis. Exposurewas also based on survey, asking the amount ofwork with hands overhead, work in forwardbent position, and work in twisted or bentposition. This analysis was controlled forphysical and creative hobbies, with nointeractions seen.
In a cross-sectional study of machineoperators, carpenters were compared to officeworkers by Tola et al. [1988], who used apostal questionnaire to obtain both healthoutcome and exposure information. Analysisused “occupation” to examine relationships.Pain Drawing Diagrams were used todistinguish body areas. For the logisticregression model a 12 month prevalence ofneck and shoulder symptoms on 8 days ormore was used. The logistic regression modelswere adjusted for years working in anoccupation and age.
2-18
Welch et al. [1995] examined 39 electricians ata screening convention using surveys to collectinformation on symptoms and exposures. Thequestionnaire included questions concerning thefrequency of tasks performed, including thepercent of time spent hanging duct work. Theanalysis did not control for confounders exceptfor length of employment.
Strength of Association for Posture
Ohlsson et al.'s [1995] study, discussedpreviously, compared female industrial workersperforming repetitive tasks to referents withoutsuch exposure and found significantassociations (p<0.05) between (1) neck andneck/shoulder diagnoses with time spent inneck flexion, with critical angles greater than15E; and (2) neck/shoulder diagnoses and timespent with upper arm abduction greater than60E.
Kilbom et al. [1986], in the initial paperconcerning the electronic workers, reportedtwo findings: (1) that the more dynamic theworking technique, the fewer neck symptomsexperienced by electronic workers; and (2) thatthe greater the average time per work cyclespent in neck flexion, the greater the associationwith symptoms in the neck and neck/shoulderangle. A statistically significant association(p<0.05) was also obtained from the jobanalysis variables describing neck forwardflexion and upper arm elevation and neck andneck/shoulder disorders. Jonsson et al. [1988],in the follow-up study, performed an analysisthat grouped the different parts of the neck andupper extremity into a health outcome labeled“cervicobrachial disorder” (unlike the cross-sectional study by Kilbom et al. [1986] thatused “neck” and shoulder”). They found thatthe relationships between MSDs and neck
forward flexion, upper arm elevation, andcervicobrachial disorders weakened(compared with the results that Kilbom et al.[1986] had found), but that the results stillremained statistically significant in some of themultifactorial analyses (no numerical resultswere reported). The most important finding,according to the authors, was that reallocationto more varied work tasks was a strongpredictor of improvement over the secondyear. This change would have decreased staticloading and increased the dynamic pattern ofmovements of the workers.
Of those studies not fulfilling the four criteria,results regarding extreme or static posture weresimilar to those of the studies which did fulfillthem. Sakakibara et al. [1995] found asignificant difference in the prevalence of neckMSDs when they examined orchard workerswho picked and bagged pears and two monthslater picked and bagged apples. Exposure wasassessed by job analysis and posturemeasurements of two representative workers.Arm and neck elevation was significantlygreater for bagging pears (more than 90E for75% of the time) than for bagging apples (lessthan 40% of the time). The same authors foundsimilar results in 1987 when only the symptomsof orchard workers were studied. They foundsignificant a positive association betweenposture and neck MSDs, reporting histograms(not ORs) in their article.
Although they did not mention the participationrates in their methods, Aåras [1994], Veierstedand Westgaard [1994], and Bjelle et al. [1981]found significant relationships between posturesand neck MSDs (they fulfilled the other threecriteria). Veiersted and Westgaard [1994]found an association between “perceived
2-19
strenuous postures” and neck MSDs (OR 7.2),but found that these perceived postures werenot reflected in any of the conventional EMGparameters (static, median or peak loads)measured in the participants. One explanationfor these results may be information bias, if thedata concerning perceived strenuous postureare from questionnaires. Another explanationmay be that EMG testing results reflectparameters for a single day, whereas symptomswere asked about concerning the entireprevious year.
Several studies that carried out no independentassessment of ergonomic factors, but relied onself-reported exposure found significantrelationships between posture variables andneck disorders. Ekberg et al. [1994] found anOR of 4.8 for the variable “work with liftedarms,” and an OR of 3.6 for “uncomfortablesitting position” and neck MSDs. Hales et al.[1994] found that “use of bifocals” (OR 3.8) inVDT users was significantly associated withneck MSDs; this variable was interpreted to bea surrogate for neck posture, as bifocalsrequire either neck flexion or extension for eyeaccommodation when viewing a VDT screen.Bernard et al. [1994] reported that as workers’time spent on the telephone increased, so didthe ORs for neck symptoms, and interpretedthis variable as a surrogate for static posturerequiring neck deviation to cradle the telephonereceiver. Holmström et al. [1992] found thatthe odds of workers with neck MSDs reportingworking with hands above their shoulders forgreater than 4 hrs/day compared with thosereporting less than 1 hr/day was 2.0, astatistically significant finding. Bergqvist et al.[1995a] reported an OR of 4.4 for workersusing highly placed keyboards in their logisticmodeling of neck MSDs. Kuorinka andKoskinen [1979] found an increased OR (4.1)
of neck MSDs for scissor makers (chosen fortheir stereotypic, repetitive work using extremepostures) compared to shop assistants,although no quantitative measurements orobservations of neck posture were reported.One study by Hünting et al. [1981] showed afairly strong association (OR 4.9) withconstrained postures and neck MSDs in thoseworkers having neck flexion of more than 56Eand an OR of 9.9 from the comparison ofgroups. Several articles with significant postureand neck MSD associations dealt withcomparisons of workers in occupations chosenfor higher observed combinations of exposurefactors and compared them to workers withfewer observed exposure stressors: Viikari-Juntura et al. [1994], OR 3.9 to 4.2; Mileradand Ekenvall [1990], OR 2.6; and Wells et al.[1983], OR 2.57.
For those studies that did not find a significantrelationship, 2 out of the 3 did not carry outobservation or measurement (ergonomicassessment) of the neck or upper extremitypostures. Ferguson [1976] stated that sevenbody dimensions were measured in thetelephonists studied, but that neither discomfortnor aching were linked with any of these bodypostures. The article does not mention the bodypostures that were measured. Ferguson’sconclusion, that “physical complaints intelephonists are probably due to static load onjoints and muscles occasioned by the fixedforward bent position determined by visual,auditory
and manipulative tasks.” Ferguson's data arecontrary to the conclusions presented. Theseconclusions may then only be speculative.
2-20
Temporality for Extreme or StaticPostures
The prospective study by Veiersted andWestgaard [1994] followed the developmentof trapezius myalgia among 30 femalechocolate manufacturing workers. Seventeenworkers developed the MSD within 6 to 51weeks of starting work. Perceived strenuouspostures on the assembly line were found tocontribute to the disorders. Although retentionof subjects was low (55%), the authors foundthat the “drop-outs” did not differ in exposureestimates and symptom reporting from thoseretained in the study. The prospective study ofViikari-Juntura et al. [1994] used self-reportedsymptoms and exposure defined byoccupational status to find a temporalrelationship between the development of severeand persistent severe neck pain and jobsinvolving dynamic work, static posture, andwhole body vibration, as compared to officework.
Consistency in Association forExtreme or Static Postures andNeck/Shoulder MSDs
Of the 31 studies we reviewed reporting resultson the association between specific or staticposture and neck and neck/shoulder MSDs, 27found statistically significant associations. Therewere many different studies reporting ORs ofgreater than 3.0 with CIs above 1, indicatingthat the effects were not explained by chance.Consistent associations were also found inthose studies dealing with specific postures andneck MSDs across many industries, from fishworkers [Ohlsson et al. 1995] to fruit pickers[Sakakibara et al. 1995], to assembly lineworkers [Jonsson et al. 1988], to garmentworkers [Vihma et al. 1982; Andersen andGaardboe 1993a,b].
Coherence of Evidence for ExtremeOr Static Postures
See section above under Coherence ofEvidence for Force.
Exposure-Response Relationship forSpecific or Static Postures
The study by Ohara et al. [1976], mentionedearlier, not only portrayed the multifactorialnature of neck and shoulder MSDs, butdocumented that an increase in specific andstatic postures by cash register operators usingnew registers placed on unsuitable counterheights increased symptoms in neck MSDs.
Several studies have suggested anexposure-response effect between increasedlevel or duration of exposure and an increase innumber of cases of neck MSDs. Burt et al.[1990], in their investigation at a major urbannewspaper, found that an increase in the self-reported percentage of time spent typing atVDT keyboards was associated with amoderate increase in neck symptoms. (Jobanalysis found a significant relationship betweenindependent observation of time spent typingand self-reported time) Keyboard time wasconsidered by the authors to be a surrogate fortime spent with the neck held in static postureswith arms unsupported. Rossignol et al. [1987]found that the prevalence of neck symptomsamong 1,545 clerical workers increased withthe number of hours per day using VDTs.Knave et al. [1985] found that, among VDToperators, total daily working hours and timespent at the VDT screen were significant riskfactors for neck pain. Andersen and Gaardboe[1993a,b] found an exposure-responserelationship between persistent neck pain andyears of being a sewing machine operator,controlling for age.
2-21
Conclusions Regarding Extreme orStatic Postures
Overall, the strength of the association (ORranging from about 1.6 [Vihma et al. 1982] to7 [Veiersted and Westgaard 1994], droppingthe outliers) between specific postures andneck MSDs was similar between studies usingthe most restrictive criteria and carrying out aprospective design and those that usedsymptom-based health outcome or self-reported exposures to static or specificpostures and cross-sectional methods. Weconclude that there is strong evidence forsupport of an association between static orspecific postures and neck and neck/ shoulderMSDs based on strength of association criteria.A positive relationship has been observedbetween exposure to this risk factor and neckor neck/shoulder MSDs in studies wherechance, bias, and confounding can be ruled outwith reasonable confidence.
VIBRATION
No study of neck MSDs met the four criteria toaddress strength of association betweenvibration and neck MSDs and only one of thereviewed studies in the tables mentioned neckMSDs and vibration. Viikari-Juntura et al.[1994] selected study groups for theirlongitudinal study based on different workexposures. Machine operators exposed tostatic work and whole-body vibration werecompared to carpenters exposed to dynamicphysical work and presumably no vibration tosee whether occupational status was related toneck MSDs. Results found that the OR forprogressing from no neck pain to moderate tosevere neck trouble was from 3.9 to 4.2; foroperators compared to carpenters; a significantdifference. No vibration measurements were
performed in this study, and vibration was likelyto be confounded by neck twisting and staticloads.
Conclusions—Vibration and Neck orNeck/Shoulder MSDs
We conclude that there is insufficientevidence to support an association betweenvibration and neck or neck/shoulder MSDsbased on strength-of-association criteria. Toofew studies of neck or neck/shoulder MSDshave examined the relationship betweenexposure to vibration and to draw anyconclusions about their relationship.
NECK OR NECK/SHOULDER MSDsAND THE ROLE OF CONFOUNDERSAs in many MSDs, prevalence of neck andneck/shoulder disorders tends to increase withage. Therefore, it is important that studies takeinto account when examining the strength ofoccupational versus non-occupational factors.Age and gender were the primary potentialconfounders that investigators addressed inmany of the studies on neck and neck/shoulderMSDs (The tables at the end of the chapter listsummaries of each of the articles and includewhich particular covariates or confounderswere considered.) These were either dealt withby logistic regression modeling, as in the caseof age (e.g., Andersen and Gaardboe [1993a];Rossignol et al. [1987]; Tola et al. [1988];Ohlsson et al. [1989]; Baron et al. [1991]),through matching of case subjects and referents(e.g., Vihma et al. [1982]), or through study ofa single gender (e.g., Luopajärvi et al. [1979];
Hünting et al. [1994]), or stratifying by gender[Sakakibara et al. 1995]. Most studiesperformed univariate analysis prior to logisticregression to consider factors which needed tobe introduced into the logistic models as
2-22
confounders or covariates.
Almost all the studies we reviewed accountedfor the confounders of age and gender. Manyof the studies controlled for leisure exercises[Andersen and Gaardboe [1993a,b] smoking(Linton [1990]; Milerad and Ekenwall [1990];Bergqvist et al. [1995a,b]; Viikari-Juntura et al.[1994]), medical conditions [Bernard et al.[1994]; Hales et al. [1994]). Reviewing themethods and results of these studies, theconfounding factors do not account for theconsistent relationship that is found with thework-related factors.
CONCLUSIONS
Interpreting association for individualworkplace factors is difficult, as mostepidemiologic studies of MSDs usedpopulations selected because of multiple factors(such as forceful exertion and repetitive tasks).Unlike laboratory experiments, one cannotisolate exposure factors, nor alter some factorswhile keeping others constant to insureaccuracy in examining, recording, andinterpreting results. However, one can examinethe body of epidemiologic evidence and inferrelationships. There have been over 40epidemiologic studies which have examinedwork factors and their relationship to neck andneck/shoulder MSDs. Many studies identifiedindividuals in heavier industrial occupations andcompared them to workers in light industry oroffice environments. Other studies identified asymptomatic group of workers, or those withsymptoms and physical exam abnormalities,and compared them to asymptomatic workersat the same worksite, or to populationreferents, and looked for differences inexposure. These approaches, although quitedifferent, by and large have chosen to focus onsimilar workplace risk factors. These includerepetition, forceful exertions, and constrainedor static postures, usually found in combination.
There is also reasonable evidence for a causalrelationship between highly repetitive work andneck and neck/shoulder MSDs. Most of theepidemiologic studies reviewed defined“repetitive work” for the neck as workactivities which involve continuous arm or handmovements which affect the neck/shouldermusculature and generate loads to theneck/shoulder area; fewer studies examinedrelationships based on actual repetitive neckmovements. The two studies which measuredrepetitive neck movements by head position(using frequency and duration of movements),and fulfilled the four criteria, found strongassociations with neck/shoulder MSDs. Inthose studies defining repetitive work ascontinuous arm or hand movements affectingthe neck/shoulder, nine studies foundstatistically significant ORs greater than 3.0.Eight studies fulfilled all the criteria except forobjective exposure assessment and measuredrepetition for the hand/wrist, not the neck. Ofthese, three had statistically significant ORsgreater than 3, and five had non-significantORs, all under 2.0.
There is reasonable evidence for forcefulexertion and neck MSD found in theepidemiologic literature. Most of theepidemiologic studies reviewed defined“forceful work” for the neck/shoulder as workactivities which involve forceful arm or handmovements which generate the loads to theneck/shoulder area; no study examined arelationships based on actual forceful neckmovements. Of the 17 studies
addressing force as one of the exposurefactors, five studies found statistically significantassociations but did not derive ORs; twostudies found ORs greater than 3.0, sevenstudies from 1 to 3.0, and 2 studies with ORsless than 1.0.
2-23
There is strong evidence that working groupswith high levels of static contraction, prolongedstatic loads, or extreme working posturesinvolving the neck/shoulder muscles are atincreased risk for neck/shoulder MSDs.Consistently high ORs (12 studies foundstatistically significant ORs over 3.0) for tensionneck syndrome associated with static posturesor static loads have been found.
The epidemiologic data are insufficient todocument relationship of vibration and neckdisorders. The few prospective studies which
have included interventions to decreaseworkplace risk factor exposures, includingdecreasing repetitive work and less extremeworking postures, have shown a decrease inincidence of neck MSDs, and an improvementin symptoms among affected workers. Thesedata provide additional evidence that thesedisorders are related to work factors.
However, cumulative exposure-response datais lacking, although VDT studies usingsurrogate exposure variables suggests arelationship.
Table 2-1. Epidemiologic criteria used to examine studies of neck MSDs associated with repetition
Study (first author andyear)
Risk indicator(OR, PRR, IRor p-value)*,†
Participation rate $$70%
Physicalexaminatio
n
Investigatorblinded to caseand/or exposure
statusBasis for assessing neck
exposure to repetition
Met all four criteria:
Ohlsson 1995 3.6† Yes Yes Yes Observation ormeasurements
Met at least one criterion:
Andersen 1993b 6.8† Yes Yes Yes Job titles or self-reports
Baron 1991 2.0 No Yes Yes Job titles or self-reports
Bergqvist 1995b 6.9† Yes Yes Yes Job titles or self-reports
Hales 1989 1.6 Yes Yes Yes Job titles or self-reports
Kamwendo 1991 1.65† Yes No NR‡ Job titles or self-reports
Kiken 1990 1.3 Yes Yes Yes Job titles or self-reports
Knave 1985 NR† Yes No NR Job titles or self-reports
Kuorinka 1979 4.1† Yes Yes NR Job titles or self-reports
Luopajärvi 1979 1.6 Yes Yes Yes Job titles or self-reports
Onishi 1976 3.8† NR Yes NR Observation ormeasurements
Sakakibara 1987 NR† Yes No NR Job titles or self-reports
Schibye 1995 3.3† Yes No NR Job titles or self-reports
Yu 1996 28.9† Yes No NR Job titles or self-reports
Met none of the criteria:
Liss 1995 1.7† No No No Job titles or self-reports
Ohlsson 1989 1.9 NR No NR Job titles or self-reports
*Some risk indicators are based on a combination of risk factors—not on repetition alone (i.e., repetition plus force, posture, or vibration). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).
†Indicates statistical significance. If combined with NR, a significant association was reported without a numerical value.‡Not reported.
2-24
Table 2-2. Epidemiologic criteria used to examine studies of neck/shoulder MSDs associated with repetition
Study (first author andyear)
Risk indicator(OR, PRR, IRor p-value)*,†
Participationrate $$70%
Physicalexaminatio
n
Investigatorblinded tocase and/orexposure
status
Basis for assessingneck/shoulder exposure
to repetition
Met all four criteria:
Jonsson 1988 NR†,‡ Yes Yes Yes Observation ormeasurements
Ohlsson 1995 4.6† Yes Yes Yes Observation ormeasurements
Met at least one criterion:
Andersen 1993a 4.6† Yes No Yes Job titles or self-reports
Bergqvist 1995a 3.6 Yes No Yes Observation ormeasurements
Blåder 1991 NR† Yes Yes No Job titles or self-reports
Ekberg 1994 15.6† Yes No NR Job titles or self-reports
Ekberg 1995 1.2† Yes No NR Job titles or self-reports
Hünting 1981 9.9† NR Yes NR Observation ormeasurements
Milerad 1990 2.1† Yes No NR Job titles or self-reports
Punnett 1991 1.8 Yes No NR Observation ormeasurements
Rossignol 1987 1.8–4.6† Yes No NR Job titles or self-reports
Vihma 1982 1.6† NR No NR Observation ormeasurements
*Some risk indicators are based on a combination of risk factors—not on repetition alone (i.e., repetition plus force, posture, or vibration). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).
†Indicates statistical significance. If combined with NR, a significant association was reported without a numerical value.‡Not reported.
2-26
Table 2-3. Epidemiologic criteria used to examine studies of neck MSDs associated with force
Study (first author and year)
Risk indicator(OR, PRR, IRor p-value)*,†
Participation rate $$70%
Physicalexaminatio
n
Investigatorblinded to case
and/orexposure status
Basis for assessing neckexposure to force
Met at least one criterion:
Baron 1991 2.0 No Yes Yes Job titles or self-reports
Hales 1989 1.6 Yes Yes Yes Job titles or self-reports
Kiken 1990 1.3 Yes Yes Yes Job titles or self-reports
Kuorinka 1979 4.1† Yes Yes NR‡ Job titles or self-reports
Luopajärvi 1979 1.6 Yes Yes Yes Job titles or self-reports
Veiersted 1994 6.7† No Yes NR Observation or measurements
Viikari-Juntura 1994 3.0† Yes No Yes Job titles or self-reports
Wells 1983 2.57† Yes No NR Job titles or self-reports
Met none of the criteria:
Liss 1995 1.7† No No No Job titles or self-reports
*Some risk indicators are based on a combination of risk factors—not on force alone (i.e., force plus repetition, posture, or vibration). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).
†Indicates statistical significance. ‡Not reported.
2-28
Table 2-4. Epidemiologic criteria used to examine studies of neck/shoulder MSDs associated with force
Study (first author and year)
Riskindicator
(OR, PRR, IRor p-value)*,†
Participation rate $$70%
Physicalexaminatio
n
Investigatorblinded to caseand/or exposure
status
Basis for assessingneck/shoulder exposure
to force
Met at least one criterion:
Åaras 1994 NR†,‡ NR No NR Observation or measurements
Andersen 1993a 3.2 Yes No Yes Job titles or self-reports
Bjelle 1981 NR† NR Yes Yes Observation or measurements
Jonsson 1988 NR† Yes Yes Yes Job titles or self-reports
Punnett 1991 0.9 (females)1.8 (males)
Yes No NR Observation or measurements
*Some risk indicators are based on a combination of risk factors—not on force alone (i.e., force plus repetition, posture, or vibration). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).
†Indicates statistical significance. If combined with NR, a significant association was reported without a numerical value.‡Not reported.
2-30
Table 2-5. Epidemiologic criteria used to examine studies of neck MSDs associated with posture
Study (first author and year)
Riskindicator
(OR, PRR, IRor p-value)*,†
Participationrate $$70%
Physicalexamination
Investigatorblinded to case
and/orexposure
status
Basis for assessing neckexposure to posture
Met at least one criterion:
Bernard 1994 1.4† Yes No Yes Job titles or self-reports
Ferguson 1976 NR‡ Yes No No Observation or measurements
Hales 1994 3.8† Yes Yes Yes Job titles or self-reports
Kamwendo 1991 1.65† Yes No NR Job titles or self-reports
Kukkonen 1983 3.6† NR Yes Yes Job titles or self-reports
Kuorinka 1979 4.1† Yes Yes NR Job titles or self-reports
Linton 1990 3.5† Yes No NR Job titles or self-reports
Onishi 1976 3.8† NR Yes NR Observation or measurements
Sakakibara 1987 NR† Yes No NR Observation or measurements
Sakakibara 1995 1.5 Yes Yes NR Observation or measurements
Veiersted 1994 7.2† No Yes NR Observation or measurements
Viikari-Juntura 1994 3.9–4.2† Yes No§ Yes Job titles or self-reports
Welch 1995 7.5 Yes No No Job titles or self-reports
Wells 1983 2.57† Yes No NR Job titles or self-reports
Yu 1996 784.4† Yes No NR Job titles or self-reports
*Some risk indicators are based on a combination of risk factors—not on posture alone (i.e., posture plus force, repetition, or vibration). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).
†Indicates statistical significance. If combined with NR, a significant association was reported without a numerical value.‡Not reported. §Physical examinations were not analyzed because there were too few cases.
2-32
Table 2-6. Epidemiologic criteria used to examine studies of neck/shoulder MSDs associated with posture
Study (first author and year)
Risk indicator(OR, PRR, IRor p-value)*,†
Participationrate $$70%
Physicalexamination
Investigatorblinded to case
and/orexposure
status
Basis for assessingneck/shoulder exposure
to posture
Met all four criteria:
Jonsson 1988 NR†,‡ Yes Yes Yes Observation or measurements
Kilbom 1986 NR† Yes Yes Yes Observation or measurements
Ohlsson 1995 NR† Yes Yes Yes Observation or measurements
Met at least one criterion:
Åaras 1994 NR† NR No NR Observation or measurements
Bergqvist 1995a 4.4† Yes No Yes Observation or measurements
Bjelle 1981 NR† NR Yes Yes Observation or measurements
Blåder 1991 NR† Yes Yes No Job titles or self-reports
Ekberg 1994 4.8†,3.6†
Yes No NR Job titles or self-reports
Holmström 1992 2.0† Yes No Yes Job titles or self-reports
Hünting 1981 9.9† NR Yes NR Observation or measurements
Milerad 1990 2.6† Yes No NR Job titles or self-reports
Rossignol 1987 1.8,4.0†,4.6†
Yes No NR Job titles or self-reports
Ryan 1988 NR† Yes No Yes Observation or measurements
Tola 1988 1.8† Yes No NR Job titles or self-reports
Vihma 1982 1.6† NR No NR Observation or measurements
Viikari-Juntura 1991a 1.5 Yes Yes§ NR Job titles or self-reports
*Some risk indicators are based on a combination of risk factors—not on posture alone (i.e., posture plus force, repetition, or vibration). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).
†Indicates statistical significance. If combined with NR, a significant association was reported without a numerical value.‡Not reported.
2-34
(Continued)
Table 2–7. Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD Prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referent group
RR, OR,or PRR 95% CI Comments
Andersen andGaardboe1993a
Cross-sectional
701 female sewing machineoperators (SMO), comparedto 781 females from thegeneral population of theregion and internal referentgroup of 89 females fromthe garment industry.
Outcome: Case of chronic painwas defined as continuous painlasting for a month or more afterbeginning work and pain for $30days within the past year.
Exposure: Job categorizationbased on “authors’ experiencesas occupational healthphysicians” and involved crudeassessment of exposure leveland exposure repetitveness. Jobs involving highrepetitiveness (severaltimes/min) and low or high force,and jobs with mediumrepetitiveness (many times/hr)combined with high force wereclassified as high exposed jobs;jobs with medium repetitivenessand low force and jobs withmore variation and high forcewere classified as mediumexposed. Job titles such asteachers, self-employed, trainednurses, and the academicprofessions were “lowexposed.”
26.2% Generalpopulation:9.9%Internalreferent group:6.7%
SMO comparedto: (1) Generalpopulation:OR=3.2(2) Internalreferent group:OR=4.9
Logistic Model:Years as SMO:0 to 7 years:1.98 to 15 years:3.8>15 years: 5.0
Age $ 40 years: 1.5
Children (>0): 1.3
Exercise: 0.9
Socioeconomicstatus: 1.29
Smoking: 1.39
CurrentExposure: 1.3
2.3-4.5
2.0-12.8
1.3-2.9
2.3-6.4
2.9-8.7
1.1-2.2
0.8-2.0
0.6-1.3
0.7-2.3
0.99-1.9
0.9-1.9
Participation rate: 78.2%.
Examiners blinded tocontrol/subject status.
Controlled for age, having children,not doing leisure exercise, smokingsocioeconomic status.
Age-matched exposure groupsand controls.
Logistic regression limited to acombined neck/shoulder casedefinition.
No difference in education, maritalstatus, number of children.
Poor correlation betweendegenerative X-ray neck changesand cervical syndrome.
Most frequent diagnosis amongstudy group was “cervicobrachialfibromyalgia” significant for test oftrend with exposure time in years.
Chronic neck pain and palpatoryfindings: Sensitivity: 0.85;Specificity: 0.93.
2-36
(Continued)
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
Andersen andGaardboe1993b
Cross-sectional
From a historical cohort of424 sewing machineoperators, 120 wererandomly selected and 82exposed workers werecategorized by number ofyears of employment: 0-7years, 8-15 years andgreater than 15 years. These were compared to areferent group of 25auxiliary nurses and homehelpers. A total of 107subjects participated.
Outcome: Measured by healthinterview and exam of the neck,shoulder and arm. Case ofchronic pain was defined ascontinuous pain lasting for amonth or more after beginningwork and pain for at least30 days within the past year. Physical examination: Restrictedmovements in the cervical spineand either palpatory tendernessin cervical segments orirradiating pain or tingling atmaximum movements or positiveforaminal test.
Exposure: Exposurecategorization broken downaccording to currentoccupational status by job title. Classification into exposuregroups based on author’sexperiences as occupationalhealth physicians and involvedcrude assessment of exposurelevel and exposurerepetitiveness. High exposurejobs: Involved highrepetition/high force or highrepetition/low force or mediumrepetition/high force. Mediumexposure jobs involved mediumrepetition/low force and lowrepetition and high force. Lowexposure jobs were lowrepetition/low force.
Referents:OR=1
0 to 7 years:2.3
8 to 15 years:6.8
>15 years:16.7
Age at least 40years: 1.9
Children >0years: 0.5
Exercise: 1.4
Smoking: 1.5
Current highexposure: 1.6
0.5-11
1.6-28.5
4.1-67.5
O.9-4.1
0.1-1.7
0.6-2.96
0.7-3.3
0.7-3.6
Participation rate: 78.2%; logisticregression limited to a combinedneck/shoulder case definition.
Age-matched exposure groupsand controls.
Examiners blinded tocontrol/subject status.
Controlled for age, having children,not doing leisure exercise,smoking, socioeconomic status.
Poor correlation betweendegenerative X-ray neck changesand cervical syndrome.
Most frequent diagnosis amongstudy group was “cervicobrachialfibromyalgia” significant for test oftrend with exposure time in years.
Chronic neck pain vs. palpatoryfindings: Sensitivity: 0.85;Specificity: 0.93.
2-37
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Baron et al.1991
Cross-sectional
124 grocery checkersusing laser scanners (119females, 5 males)compared to 157 grocerynon-checkers (56 females,101 males); excluded 18workers in meat, fish, anddeli departments, workersunder 18 and pregnantworkers.
Outcome: Based on symptomquestionnaire and physicalexam. Case defined as havingpositive symptoms and a positivephysical exam. Symptoms musthave begun after employment atsupermarket of employment andin current job; lasted one weekor occurred once a month duringthe past year; no history ofacute injury to part of body inquestion.
Exposure: Based on jobcategorization. Estimates ofrepetition and average and peakforces of hand and wrist basedon observed and videotapedpostures, weight of scanneditems, and subjectiveassessment of exertion.
Specific neck assessment wasnot done.
16% 5% Odds of neckpain, checkers vs. non-checkers:OR=2 0.6-6.7
Participation rate: 85% checkers;55% non-checkers in field study. Following telephone survey 91%checkers and 85% non-checkers.
Examiners blinded to worker’s joband health status.
Adjusted for duration of work, age,hobbies, systemic disease obesity.
Total repetitions/hr ranged from1,432 to 1,782 for right hand and882 to 1,260 for left hand.
Average forces for cashiers werelow and peak forces medium. Force was not analyzed in themodels.
Multiple awkward postures of allupper extremities recorded but notanalyzed in models.
Statistically significant increase inneck MSD with increase in years“checking.”
2-38
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Bergqvist etal. 1995a
Cross-sectional
Office workers usingVDTs, (n=260), 198females; symptomaticcases compared to non-cases.
Outcome: Neck discomfort— anydiscomfort over the last 12months; intense neckdiscomfort— as above, ifoccurred in last 7 days andinterfered with work.
Outcome: Physiotherapist'sdiagnosis of: (1) tension necksyndrome (TNS): ache/pain inthe neck; feeling of tirednessand stiffness in neck; possibleheadache; pain duringmovements; musculartenderness; (2) cervicaldiagnoses—ache/pain in neckand arm; headache; decreasedmobility due to cervical painduring isometric contraction;often root symptoms such asnumbness or parathesias.
Exposure: Based onobservation— static workposture, nonuse of lower armsupport, hand in non-neutralposition, insufficient leg space attable, repeated movements withrisk of tiredness, specular glarepresent on VDT. Measured:Height difference of VDTkeyboard-elbow, high visualangle to VDT.
Neck: 61.5% Female:63%Male: 57%
TNS: 22%Female:25%Male: 13%
Cervical diagnosis: 23%Female:25%Male: 20%
Asympto-maticworkers
Tension necksyndrome:Females nochildren:OR= 2.0
Females withchildren:OR=6.4
Limited restbreak: OR=7.4
Too highlyplacekeyboard:OR=4.4
CervicalDiagnoses:Age >40OR=2.7
Spectacles:OR=4.0
Static Posture:OR=5.1
Spectral glare:OR=1.9
Stomachreactions:OR=3.9
Tiredness: 1.9
0.7-5.6
1.9-21.5
3.1-17.4
1.1-17.6
1.0-7.2
1.3-12.5
0.6-42.5
0.9-4.2
2.0-7.7
1.0-3.5
Participation rate: 92% of 353office workers.
Adjusted for age and gender.
Factors included in analysis: Age,gender, smoking, children at home,negative affectivity, tiredness-related stress reaction, stomach-related stress reaction, use ofspectacles, peer contacts, restbreaks, work task flexibility,overtime, static work position, non-use of lower arm support, hand innon-neutral posture, repeatedmovements with risk of tiredness,height differenceskeyboard/elbow, high visual angleto VDT, glare on VDT.
Found that “frequent overtime”protective for cervical diagnosesOR=0.48 (0.23, 0.99).
Examiner and workplaceinvestigators blinded to case andexposure status.
There are problems withinterpreting results because ofmultiple comparisons and multiplemodels.
Not all significant findingspresented in paper.
2-39
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Bergqvist etal. 1995b
Cross-sectional
322 office workers; VDTusers compared to non-VDT users.52% interactive,29% data entry, 19% non-VDT users.
Outcome: Neck discomfort—anydiscomfort over the last 12months; intense neck/shoulderdiscomfort—as above, ifoccurred in last 7 days andinterfered with work.
Outcome: Physiotherapist'sdiagnosis of tension necksyndrome (TNS)—ache/pain inthe neck; feeling of tirednessand stiffness in neck; possibleheadache; pain duringmovements; musculartenderness.
Exposure: Based on self-reporting of VDT use. VDTusers categorized into dataentry or interactive VDT users.
Neckdiscomfort:60%
Intenseneckdiscomfort:7.4%
Tensionnecksyndrome: 21%
Current VDTwork:OR=1.4
Intenseneckdiscomfort:OR=0.5
Tensionnecksyndrome:OR=1.0
TNS Diagnosis:<20 hr/weekVDT: 1.2
>20 hr/weekVDT: 0.7
TNS diagnosiswith bifocal orprogressiveglasses at VDTwork and $20hr/week VDTwork duration:OR=6.9
0.8-2.4
0.2-1.8
0.5-1.9
0.4-3.7
0.3-1.5
1.1-42.1
Participation rate: 76%.
Adjusted for age and gender.
Intensive neck discomfortassociated with VDT work over 20hr and having stomach reactionsoften and repetitive movements: OR=3.9 (1.1, 13.8).
Originally 535 workers queried in1981. Of those, 182 had left theworkplace (quit, retired, etc.). Possible bias from “healthy workereffect.”
Covariates considered: Children athome, smoking, negativeaffectivity, stomach-related stressreactions, tiredness-related stressreactions. Organizational factorsconsidered: limited or excessivepeer contacts, limited rest breakopportunity, limited work taskflexibility, frequent overtime.
For cervical diagnoses: Excess ORsuggested for combinedoccurrence of VDT work of>20 hr/week and specular glare onthe VDT screen.
2-40
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Bernard et al.1994
Cross-sectional
Of a total population of3,000 workers in theeditorial, circulationclassified advertising andaccounting departments,1,050 were randomlyselected for study and 973participated. Those fulfillingcase definition compared tothose workers not fulfillingdefinition.
Outcome: Health data andpsychosocial information werecollected using a self-administered questionnaire. Definition: Presence of pain,numbness, tingling, aching,stiffness or burning in the neckoccurring $ once a month or7 days continuously within thepast year, reported asmoderately severe. Thesymptom must have begunduring the current job. Workerswith previous nonoccupationalinjuries to the relevant areawere excluded.
Exposure: Based onobservation of work activityinvolving keyboard work, workpace, posture, during a typicalday of a sample of 40 workerswith and 40 workers withoutsymptoms. Exposure to workorganization and psychosocialfactors based on questionnaireresponses.
26% (case)
Cases withdaily neckpain: 22%
ÕÕ Females:OR=2.1
Number of hrspent ondeadline/week(30 to 39 hr vs. 0 to 10 hr)OR=1.7
Work variance(continuallychanging workload;occasionallyvs. often)OR=1.7
Time spent onthe telephone(4 to 6 hr vs. 0to 2 hr):OR=1.4
Perceived lackof importancefor ergonomicissues bymanagement:OR=1.9
1.4-2.4
1.4-3.0
1.2-2.5
1.0-1.8
1.4-2.4
Participation rate: 93%.
Examiners blinded to case andexposure status.
Analysis controlled forconfounders, age, gender, height,psychosocial factors, medicalconditions.
Psychosocial scales analyzed bysplitting the responses intoquartiles, then comparing the 75%response score to the 25%response score for deriving theORs in each scale.
In sub-analysis of jobs havingcomparable number of males andfemales. Only number of hr spenton deadline/week and perceivedlack of importance for ergonomicissues by management weresignificant.
2-41
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Ferguson 1976
Cross-sectional
418 telephonistsinterviewed
Outcome: Symptoms byquestionnaire. Neck achecategorized on 3-pointdiscomfort scale: (1) verycomfortable, (2) barelycomfortable, and (3)uncomfortable, veryuncomfortable.
Exposure: Personal and socialattributes and attitudes toaspects of the work and theequipment were obtained byquestionnaire. Seven bodydimensions were measured, andstanding posture wascategorized by observationagainst a grid according topredetermined criteria.
Tele-phonists:Uncomfort-able orveryuncomfort-able neckache =26%
Chi sq=11.01(df=2), p<0.005
Participation rate: 95%.
Although author states thefollowing: “Discomfort, aching, andother symptoms are common,important but usually neglectedproblems in telephonists whichcould be ameliorated by ergonomicjob and equipment,” the results ofhis study did not support hisconclusion.
Neither discomfort nor aching waslinked to any of the body posturesobserved.
Height and weight were not relatedto discomfort or aching.
Multiple correlations not helpful inidentifying combinations ofpersonal, equipment, environmentalor other variables predictive ofaching and discomfort.
2-42
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Hales andFine 1989
Cross-sectional
Of 96 female workersemployed in 7 highexposure jobs in poultryprocessing: 89 werecompared to 23 of 25female workers in lowexposure jobs.
Outcome: Period prevalence— symptoms in last 12 months byquestionnaire. Case defined as: Pain, aching, stiffness,numbness, tingling or burning inthe neck and symptoms beganafter employment at the plant;were not due to a previousinjury or trauma to the joint;lasted >8 hr; and occurred 4 ormore times in the past year.
Point prevalence: Determined byphysical exam of the neck usingstandard diagnostic. Tensionneck syndrome: Palpable muscletightness, hardening or pain $ 3(on 8 point scale) on passive orresisted neck flexion or rotation.Cervical root syndrome: Pain $(on 8 point scale) radiating fromneck to one or both arms withnumbness in the hand criteria. Case must also fulfill symptomdefinition.
Exposure: Observation andwalk-throughs; jobs categorizedas high exposure and lowexposure based on estimates offorce and repetition of handmaneuvers.
Periodprevalence: 21%
Pointprevalence:12%
Periodprevalence:13%
Pointprevalence:0%
Outcome: Necksymptoms: RR=1.64
Outcome: Necksymptoms andphysical:ORindeterminatebecause of “0"cell
Estimated ORby adding 1 toeach cell incrude 2 X 2table: 3.69
0.4-3.19
0.4-164
Participation rate: 93%.
Adjustment for age and duration ofemployment.
Examiner blinded to case andexposure status.
Exposure based on repetitive andforceful hand/wrist motions andnot neck exposure assessment.
80% of workers involved in jobrotation program.
No information collected on non-work related risk factors.
2-43
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Hales et al.1994
Cross-sectional
Telecommunication workers(n=518, 416 females, 117males) in 3 offices,employed > 6 months.
"Cases" fulfilling neckwork-related MSD definitioncompared to non-cases.
Outcome: Self-administeredquestionnaire and standardizedphysical exam (PE). Casedefined as: Pain, aching,stiffness, burning, numbness ortingling lasting >1 week or>12 times a year; no previoustraumatic injury to neck;occurring after employment oncurrent job within the last yearand positive PE—moderate toworst pain experienced withtension neck or cervical rootsyndrome.
Exposure: Assessed byquestionnaire and observation;number of keystrokes/day; noexposure questions werespecifically aimed at the neckregion.
Physical workstation andpostural measurements weretaken but not analyzed inmodels.
9% ÕÕ Lack ofdecisionmakingopportunities:OR=4.2
Use ofbifocals:OR=3.8
Lack of aproductivitystandard:OR=3.5
Fear of beingreplaced bycomputers:OR=3.0
Highinformationprocessingdemands:OR=3.0
Job requiring avariety oftasks:OR=2.9
Increasingworkprocedure:OR=2.4
2.1-8.6
1.5-9.4
1.5-8.3
1.5-6.1
1.4-6.2
1.5-5.8
1.1-5.5
Participation rate: 93%.
Physician examiner blinded toworker case status.
Logistic analysis adjusted fordemographics, work practices,work organization, individualfactors; electronic performancemonitoring; DAO keystrokes;Denver DAO keystrokes/day.
ORs for psychosocial variablesrepresent risk at scores onestandard deviation above meanscore compared to risk at scoresone SD below mean.
Because of readjustments andchanges of workstations duringstudy period, measurements ofVDT workstations consideredunreliable and excluded fromanalyses.
Number of hr spent in hobbies andrecreational activities notsignificant.
Although keystrokes/day found notsignificant, data available was forworkers typing an average of 8words/min over 8-hr period.
97% of participants used VDT$6 hr so not enough variance toevaluate hr of typing.
Over 70 variables analyzed inmodels may have multiplecomparison problem.
2-44
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Hunting et al.1994
Cross-sectional
308 of 400 apprentice andjourneymen, electriciansfrom one labor unionparticipated.
Outcome: Three-symptomdefinitions used; most restrictiveincludes neck symptomsoccurring $once/month or lasting>1 week during past year, andno previous traumatic injury tosite.
Exposure: Questionnaire dealingwith lifting activities, workingoverhead, working with handtools.
16%
3% withmedicalvisits,missedwork, orlight duty
ÕÕ ÕÕ1 to 3 yearsworked: OR=1
4 to 5 yearsworked:OR=1.3
6 to 10 yearsworked:OR=1.6
>10 yearsworked:OR=1.3
ÕÕ Participation rate: 75%.
98% of participants were male.
Stratified by most experienced vs. least experienced electrician, byyears worked, by age group,current work as an electrician.
Analysis of specific work factors(repetition, force, extreme posture,vibration, or combinations of riskfactors) not analyzed in this paperwhich dealt with prevalence ofsymptoms among electricians.
2-45
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Kamwendo etal. 1991
Cross-sectional
420 medical secretaries; compared those frequentlyhaving neck pain to thoseless frequently having pain.
Outcome: Questionnaire using 6point scale ranging from “veryoften” to “almost never” andNordic Questionnaire. Definitionof neck MSD: Discomfort, ache,or pain during previous year;whether they had pain in last 7days, whether pain preventedthem from doing daily duties. 10 questions on psychosocialwork environment included.
Exposure: Based onquestionnaire. Low exposurewas regarded as 1 to 4 hr sittingor working with office machines,high exposure was regarded as5 to 8 hr.
63% periodprevalence.
33% pointprevalence.
15% withconstantneck pain.
ÕÕ OR for workwith officemachines 5 hror more/day:1.65
Working >5years: OR=1.6
Sitting 5 ormore hr/day:OR=1.9
1.02-2.67
0.9-2.8
0.86-2.6
Participation rate: 96%.
Neck symptoms associated with a"poorly experienced psychosocialwork environment.”
Age, length of employmentsignificantly related to neck pain.
Questionnaire includedpsychosocial scales, length ofemployment, part-time or full-timework, average hr sitting workingwith machines.
Ability to influence work, a friendlyspirit of cooperation between co-workers, being given too much todo significantly positivelyassociated with neck pain.
2-46
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Kiken et al.1990
Cross-sectional
294 poultry processors. Plant #1 (n=174)Plant #2 (n=120)
Outcome: Period prevalence— based on questionnaire. Case— pain, aching, stiffness, burning,numbness or tingling in the neck,began after employment at theplant; not due to previousaccident or injury outside work;lasted >8 hr and occurred 4 ormore times in the past year.
Point prevalence: Based onsymptom and physical examusing standard diagnosticcriteria. Case must fulfillsymptom definition listed above.
Exposure: Observation andwalkthrough; jobs categorizedas high exposure and low exposure based on observedforce and repetition of handmaneuvers.
Plant #1:(Highexposure)Any symp-toms: 34%
Periodprevalence: 9%
Pointprevalence:4%
Plant #2:(Highexposure)Anysymptoms:42%
Periodprevalence:5%
Pointprevalence:1%
Plant #1: (Lowexposure)Any symp-toms: 16% Periodpreva-lence: 3%
Pointpreva-lence: 3%
Plant #2:(Low expo-sure) Anysymptoms:11%
Periodprevalence:3%
Pointprevalence:0%
OR=
2.2
2.9
1.3
OR=
3.9
1.8
ÕÕ
0.9-5.0
0.4-21.4
0.2-11
1.5-10.2
0.2-15.2
ÕÕ
Participation rate: 98%.
Analysis stratified by gender andage.
Higher exposure jobs (HE) werelocated in the receiving,evisceration, whole bird grading,cut up and deboning departments. Lower exposure jobs (LE) werelocated in the maintenance,sanitation, quality assurance andclerical departments.
Examiners blinded to case andexposure status.
30% of workers in job rotationprogram may influenceassociations.
Annual turnover rate -50% at plant1 and 70% at plant 2; makingsurvivor bias a strong possibility.
2-47
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Knave et al.1985
Cross-sectional
400 VDT operators from4 industries using VDTs >4hr/day; compared to157 office employeeswithout VDT work at thesame industries.
Outcome: Questionnaire—symptom questionnaire based onfrequency and intensity scores:negligible=1, slight=2,pronounced=3.
Exposure: Based on self-assessment “hrs of typing.” Aspecial gaze direction instrumentrecorded time spent looking atVDT screen. Observation wasconducted but not included inanalysis.
Resultsestimatedfromhistogram:
Rt. side ofneck: 5% Lt. side ofneck: 20%
Resultsestimatedfromhistogram:
Rt. side ofneck: 5%
Lt. side ofneck: 0%
ÕÕTyping hrsignificantlyrelated to necksymptoms.
Dose-responserelationshipfound betweenregisteredwork durationand musculo-skeletalcomplaints.
ÕÕ Participation rate: Initially exposed97%; referent 100%; Phase IVexposed 84% referents 84%.
Cases and referents matched onage and gender.
Musculoskeletal complaintsgrouped in analysis; because oflarge number of comparisons,some without a prior hypotheses,reliable conclusions limited top<0.001.
Significant difference betweenfemales and males in reported necksymptoms.
No statistical difference betweencases and referents in discomfortscores, but “tendency towardshigher discomfort scores forshoulder, neck, and back amongthe exposed group.”
No difference in cases andreferents in whether work was“interesting” or they had a “positiveattitude” towards work.
Age, smoking, educational status,and drinking did not correlate withsymptoms.
Females reported more symptomsthan males in both referent andcase groups.
‘Registered’ total work hrassociated with musculoskeletalsymptoms p<0.05.
2-48
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Kukkonen etal. 1983
Cross-sectional/Inter-vention
104 female data entryworkers. 60 data entryoperators (noted as “studygroup”) were grouped with44 data entry operatorswho worked at anotherbank and were comparedwith 57 female workers invarying office tasks.
Outcome: Questionnaire— stiffness and pain in the neckand shoulder region, frequencyof symptoms and localization. Physical exam (PE): A clinicalfunctional examinationperformed by a physiotherapist.
Exposure: Observation ofposture, movements andworking techniques,assessment of characteristicsof desk, chair, equipment,interview with foremen andworkers to get determination ofphysical, mental, and socialenvironment at workplace. Foremen and workers wereinterviewed so that theorganization of work and thephysical, mental, and socialenvironment at the workplacecould be determined.
Data entrygroups:47%
Tensionnecksyndromein studygroup pre-interven-tion: 54%
Tensionnecksyndromein studygroup post-interven-tion: 16%
28%
Tensionnecksyndromein dataentrycomparisongroup pre-interven-tion: 43%
Tensionnecksyndromein dataentrycomparisongroup post-interven-tion: 45%
2.3 1.1-4.6 Participation rate: Not reported.
Examiners blinded to case status.
No adjustment for confounders.
Examiner blinded to case status.
Average duration of employment3.5 years.
Intervention consisted of:Adjustment of desk, chairs, dataprocessing equipment individuallyto suit each worker, who wasinstructed to carry out adjustmentsherself. Document holders wereadded. The study group wasgiven a short course of basictraining on pertinent aspects ofergonomics. Four lessons onrelaxation was given by means ofexercises.
Physiotherapy was given toworkers for whom the doctorprescribed—17 from the studygroup and none from the firstreference group had treatments.
2-49
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Kuorinka andKoskinen1979
Cross-sectional
93 scissor makers, (n=90females, 3 males)compared with 113 femaledepartment store shopassistants fromLuopäjarvi’s 1979 study.
Excluded those withseropositive rheumaticaffections as well ascashiers.
Outcome: Symptoms and physical examination—twotender spots symptoms of neckstiffness and fatigue/ weaknessand/or palpable hardenings +muscle tenderness in neckmovements. Physiotherapistexamined workers, diagnoseswere from predetermined criteria[Waris 1979]. In problem casesorthopedic and physiatric teamshandled cases.
Exposure: Based on jobanalysis from work history ofprevious year from productionand salary forms. Conductedrecord review of hrworked/task, productionstatistics, absences: used onlycases where 80% of hr cross-checked (n=76). Work methodsfor each type of stationanalyzed. Stations classifiedaccording to dominance ofinspection or manipulation ofscissors, and length of cycleusing observation and video-taping. Observations madelooking at hand/wrist force,repetition and hand grasp. Calculated index for wristdeviation.—Work methods for each workstation analyzed: Cycle time.—Total workload duringinvestigation/year recordedindividually as pieces handled.
61% 28% Scissor makersvs. referents:OR=4.1
Short cycletasks vs. long-cycle tasksand tensionnecksyndrome:OR=1.64
2.3-7.5
0.7-3.8
Participation rate: 81%.99% female study group, nosignificant age difference.Used Waris [1979] criteria forexamination which called forblinding of examiners, otherwise itwas not mentioned.No association between tensionneck syndrome and: (1) age, (2)duration of employment, and(3) weight/height2.Total workload for the number ofpieces handled in one yearsignificantly associated withtension neck syndromeAlthough authors state norelationship between short cycledand longer cycled tasks; bothgroups of tasks would beclassified as highly repetitive usingKilbom, Silverstein’s and othercriteria. Lack of variance incomparison groups.Authors noted: “earlier unpublishedquestionnaire pertaining toactivities outside factory — extrawork, hobbies, did not indicatecorrelations with work...”Found that “diseases” seem toaccumulate in same individuals.Physical workload was low.A slight trend towards tensionneck being more common inmanipulation tasks than ininspection but not statistically significant.
2-50
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Linton 1990 Cross-sectional
22,180 employeesundergoing screeningexaminations at theiroccupational health careservice in Sweden. 85% ofthe Swedish workforce iscovered by health careservices.
Cases compared to “non-cases” defined by outcome.Groups selected a prioriwhich would representexposure as well as little orno exposure forpsychosocial variables.
Outcome: Cases defined fromquestionnaire responses asthose persons reporting “yes” tohaving seen a health careprofessional for neck pain in thelast year.
Exposure: Based onquestionnaire responses—questions asked regardingheavy lifting, monotonous orassembly line work, sitting,uncomfortable work postures(bending or twisting), vibration. Psychosocial work environment: Work content, workload, socialsupport.
18% hadseen healthcareprofes-sional forneck pain
31% hadexperi-enced neckpain
ÕÕ Monotonouswork and poorpsychosocialenvironment:OR = 3.6
Lifting and poorpsychosocialenvironment:OR=2.7
Uncomfortableposture and poorpsychosocialenvironment:OR=3.5
2.8-4.6
2.0-3.6
2.7-4.5
Participation rate: Authors hadaccess to all workers’ records;85% of working population hasoccupational health care services.
Analysis stratified for age, gender.
Lifestyle factors asked: Exercise,eating, smoking, alcoholconsumption.
On univariate analysis, heavylifting, monotonous work,uncomfortable posture, andvibration had elevated ORs. Sittingdid not.
On univariate analysis, eatingregularly and smoking had elevatedORs. Alcohol and exercise did not.
Authors caution direct comparisonof ergonomic and psychosocialvariable’s ORs. The scales werenot consistent for the differentfactors measured.
2-51
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Liss et al.1995
Cross-sectional
1,066 of 2,142 dentalhygienists from OntarioCanada Dental HygienistsAssociation compared toreferent group, 154 of 305dental assistants who donot scale teeth.
Outcome: Mailed survey, casedefinitions based on NordicQuestionnaire, percent reportingneck symptoms >7 days in past12 months.
Exposure: Based on mailedsurvey and self-reportedanswers—length of practice,days/week worked,patients/day, patients withheavy calculus, percent of timetrunk in rotated position relativeto lower body, instruments used,hr of typing/week, type ofpractice.
43% 30% 1.7
Had to modifytheir work orwere unable towork at somepoint,(hygienistscompared todentalassistants):OR=2.4
1.1-2.6
1.1-5.4
Participation rate: 50% from bothgroups.
Study population >99% female.
No association with duration ofemployment.
Not controlled for confounders.
Very low response rate,confounders not considered, studyhas methodologic problems whichinfluence interpretation of results.
2-52
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Luopäjarvi etal. 1979
Cross-sectional
Assembly line workers(n=152 females) comparedto shop assistants in adepartment store(n=133 females).
Cashiers excluded fromcomparison group.
Outcome: Tension necksyndrome (TNS): Neck stiffnessand fatigue/weakness and twotender spots and/or palpablehardenings + muscle tendernessin neck movements.
Exposure: Observation, videoanalysis, and interviews used toassess exposure to repetitivearm work, static muscle workaffecting neck/shoulder area.
37% 28% TNS: OR=1.56
Had seen adoctor for necksymptoms:OR=4.38
0.9-2.7
2.1-9.24
Participation rate: 84%.
Workers excluded fromparticipation for previous trauma,arthritis and other pathology.
No difference in mean agesbetween exposed and referents.
Examined only females.
Factory opened only short time sono association between duration ofemployment and MSDs possible.
Social background, hobbies,amount of housework notsignificant.
2-53
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Milerad andEkenvall 1990
Cross-sectional
99 dentists randomlyselected from Stockholmdentist registry whopracticed $ 10 yearscompared to100 pharmacists selectedfrom all pharmacists inStockholm.
Outcome: Based on telephonequestionnaire. Neck symptoms atany time before the interview("lifetime prevalence"). Furtheranalyzed according to Nordicquestionnaire as to durationduring last 12 months and duringlast 7 days, effect on workperformance and leisureactivities, and sick leave.
Exposure: Based onquestionnaire. Exposuresincluded: (1) abduction of armparticularly in sit-down dentistry;(2) work hrs/day; and (3) staticpostures.
54%
Male: 45%
Female:63%
Pharma-cists: 26%
Male: 18%
Female:32%
2.1
2.6
2.0
1.4-3.1
1.2-5.0
1.3-3.1
Participation rate: 99%.
Analysis stratified by gender.
No difference in leisure timeexposure, smoking, systemicdisease, exposure to vibration.
Symptoms increased with age infemale dentists only.
Duration of employment highlycorrelated with age: dentists (r=0.84), pharmacists(r=0.89).
No relation between symptoms andduration of employment.
Equal problems dominant andnondominant sides.
Genders “equally prone to developneck symptoms when subjected toequal work-related musculoskeletalstrain.”
No analysis of exposure factors. Only discussion of “probablereasons” for high risk using workpositions, flexing neck.
2-54
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Ohlsson et al.1995
Cross-sectional
Industrial Workers(n=82 females) exposed torepetitive tasks with shortcycles mostly far <30 sec,usually with a flexed neckand arms elevated andabducted intermittently; 68former workers (meanemployment time 21 years)who had left the factoryduring the seven yearsbefore the study; theseworkers were compared to64 referents with norepetitive exposure at theircurrent jobs.
Outcome: Pain in the last7 days and physical exam (PE)diagnosing tension necksyndrome, cervical syndrome.
Tension neck: Tightness ofmuscles, tender spots in themuscles. Cervical syndrome: Limited neck movement, radiatingpain provoked by testmovements, decreasedsensibility in hands/fingers;muscle weakness of upper limb.
Exposure: Videotaping andobservation. Analysis of postures, flexion of neck (criticalangles 15E and 30E). 74workers videotaped $10 min from back and sides. Averagecounts of two independentreaders for frequencies,duration, and critical angles ofmovement used. Repetitive industrial work tasksdivided into 3 groups: (1) fairlymobile work, (2) assembling orpressing items, and (3) sorting,polishing and packing itemsWeekly working time, workrotation, patterns of breaks,individual performance rate(piece rate). Only exposurereadings from right arm wereused.
Tensionneck: 40%
Cervicalsyndrome:1%
Tensionneck: 13%
Cervicalsyndrome: 0%
Tension necksyndrome(industrialworkers
compared toreferents):
OR=3.6
Õ
1.5-8.8
Õ
Participation rate: Currentworkers: 96%; past workers: 86%; referents: 100%.
Controlled for age.
No exposure information availableto examiners, “not possible tocompletely blind the examiners.”
Questionnaire included individualfactors, work/environment,symptoms, psychosocial scales.
Muscle strength measured by(maximum voluntary capacity) atelevation, abduction, and outwardrotation of both arms measured bydynamometer.
Videotape analysis revealedconsiderable variation in postureeven within groups performingsimilar assembling tasks.
Logistic models replacing repetitivework with videotape variablesfound muscular tension tendencyand neck flexion movementssignificantly associated withneck/shoulder diagnoses.
Inverse relationship betweenduration of industrial work andMSDs, largest OR employed <10years.
Assembly group has high OR (6.7)with regard to neck/shoulder MSDcompared to referents.
Significant association betweentime spent in neck flexion positions< 60E.
2-55
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Ohlsson et al.1989
Cross-sectional
Electrical equipment andautomobile assemblers(n=148), 76 former femaleassembly workers who quitwithin 4 years compared to60 randomly sampledfemale from generalpopulation.
Outcome: Determined by questionnaire—any neck pain,neck pain affecting work ability,and neck pain in the last 7 daysand the last 12 months.
Exposure: Based on jobcategorization andquestionnaire—number of itemscompleted/hr.
Work pace divided into fourclasses: (1) slow: <100items/hr; (2) medium: 100 to 199items/hr; (3) fast: 200 to 700items/hr; (4) very fast: >700 items/hr.
Pain in last12 months:39%
Workinability inlast 12months:13%
Pain in last7 days:21%
Pain in last12 months:32%
Workinability inlast 12months: 7%
Pain in last7 days:17%
1.9
2.8
1.9
0.9-3.7
0.9-8.8
0.7-3.6
Participation rate: Not reported.
For younger females, increase inpain occurred with increasedduration of employment.
OR increased with increasing workpace, except for very high paces,which there was a decrease.
Logistic models checked forinteraction and controlled for age.
Study group consisted of femalesonly.
Significant association betweensymptoms and duration ofemployment much stronger forworkers <35 years old thanworkers >35 years old.
2-56
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Onishi et al.1976
Cross-sectional
The following werecompared to 101 femaleoffice workers:
Film rolling workers: 127(females).
Subjects categorized as:
Group I: Without symptomsof cervico-brachial disorder.
Group II: Subjectivesymptoms in the neck,shoulder, or upper limbs.
Group III: Symptoms andclinical signs.
Outcome: Based on (1) symptoms of neck stiffness,dullness, pain, numbness; (2)pressure (<1.5 kv/cm²)measured by strain transducerat which subject felt pain;(3) physical exam: range ofmotion, tests, nervecompression tenderness.
Exposure: Observation of jobtasks, then job categorization.
Film rollers wind 1 roll of 35 mmfilm every 2.5 to 5 sec over 7.5hr/day.
Loading of trapezius wasexamined in two workers duringwork activities byelectromyography.
Group I:29%
Group II:39%
Group III:23%
Participation rate: Not reported.
Body weight, weight skin foldthickness, muscle strength and gripstrength obtained.
Body height and weightdifferences not statisticallysignificant.
No difference between workerswith tenderness threshold above1.5 kg/cm² and those below withrespect to age, height, weight, skinfold thickness, grip strength, upperarm abduction strength, backmuscle strength.
Authors noted that continuousloading of the trapezius seemscharacteristic to repetitiveoperations where the upper limbsare used.
2-57
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Ryan andBampton 1988
Cross-sectional
Data process operators(n=143). Group withhighest scores (n=41)designated "cases,"compared to lowest scores(n=28).
Outcome: Symptoms (pain,ache, sore, hurts, numb,swollen, etc.) occurring$3 times/week with no physicalexam signs or $ weekly withphysical exam signs of muscletenderness present; diagnosed“myalgia” as diffuse muscle painand tenderness.
Exposure: Ergonomicassessment measuring anglesand distances of each operatorseated at his/her workstation. Wrist extension, ulnar deviation,elbow angle, shoulderabduction, and shoulder flexionwere measured. Alsomeasured: person and furniturefit, eye-copy and eye-keyboardfit, elbow-keyboard heightdifference, popliteal-chair heightdifference, and copy placement.
Shoulder:44%symptomonly
Neck: 43%symptomsonly
Neck/shouldersymptomsoccurring $3 timesweeklywith nosigns orweeklywith signs:44%
ÕÕ Not reported ÕÕ Participation rate: 99%.
Interviewers blinded toquestionnaire responses.
No adjustment for confounders;cases for analysis were thosewith either neck, shoulder, orlower arm scales having highersymptom scores compared tothose with low scores.
Cases had higher visual glareindex, feeling there wasinsufficient time for rest breaks,more boredom, more work stress,and needed to push themselves >3times/week; lower peer cohesion,autonomy, clarity. Higher staffsupport and work pressure.
Significant differences in thosetrained in adjustment of theirchairs.
No differences for height, weight,age, marital and parental status,handedness, time in current job,time spent keying or typing,whether this was their first job,length of training time.
Significant difference in smallermean elbow angle and shoulderflexion of the left arm, and smallereye-copy distance.
2-58
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Sakakibara etal. 1987
Cross-sectional
Orchard workers (n=48,20 males and 20 females).
Compared symptoms aftercompletion of thinning ofpears, bagging of pearsand bagging of apples(covering fruit with paperbags while on the trees).
Internal comparison usingsame study population.
Outcome: Shoulder paindescribed as the presence ofstiffness and pain daily.
Exposure: Observation of jobs. Angles of flexion of the shoulderand extension of the neck onone subject were measuredevery 25 min during a whole daydoing each task. No observationwas made on neck repetition.
Farmers worked approximately 8hr/day for 10.6 to 13.6 dayseach year bagging or thinningpears and bagging apples.
EstimatedfromhistogramsPears:
Rt. side:20%Lt. side:20%
EstimatedfromhistogramsApples:
Rt. side:9%Lt. side: 9%
p<0.05
p<0.01
ÕÕ Participation rate: 77%.
Stratified by gender.
General fatigue, gastricdisturbances, appetite loss andheadache showed no difference infrequency between tasks.
Exposure data based onmeasurement of one worker maynot be generalized to others.
The angle of forward flexion in theshoulder and that of extension inthe neck was statisticalllysignificantly positively correlated(r=0.88, p#0.01). The proportion ofworkers with >90E forwardshoulder flexion was significantlyhigher for thinning out pears andbagging pears than for baggingapples.
The authors presumed that thesymptoms of dizziness and tinnitusmay be associated with thecochlear-vestibular symptoms ofvertebral insufficiency due tocontinuous extension of the head.
Results presented in paper inhistograms.
2-59
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Sakakibara etal. 1995
Cross-sectional
Of 65 female Japanesefarmers. 52 completed thequestionnaire and physicalexam in late June forbagging pears and late Julyfor bagging apples.
Questionnaire: Stiffness andpain in neck region. Symptomsin past 12 months for $one day,or symptoms in past 12 monthsfor $8 days.
Exam: Pain in motion of the neckjoint such as flexion/extension,lateral bending, and rotation.
Exposure: Observation of tasksand measurements ofrepresentative workers (onlytwo workers measured) .
Angle of arm elevation duringbagging was measured in onesubject.
Pearbagging
Neckpain=40%
Neck painin jointmotion:55.8%
Applebagging
Neckpain=25%
Neck painin jointmotion: 36.5%controls
Workersbagging pearswith neck pain vs. applebaggingwith neck pain,p<0.05
Workersbagging pearswith pain injoint motion vs.apple baggingwith pain injoint motion:PRR=1.5
0.99-2.35
Participation rate: 80%.
Examiners not blinded to casestatus due to design of study.
Same population examined twotimes. 2nd exam occurred onemonth after first. These resultsused in analyses for comparison oftwo tasks.
Stiffness and pain during applebagging may have been pain thatwas a residual of pear baggingoperations.
Number of fruit bagged/day wassignificantly more in pear baggingthan in apple bagging.
Exposure measurements onlyobtained on 2 workers andgeneralized to all workers.
2-60
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Schibye et al.1995
Cohort Follow-up of 303 sewingmachine operators at ninefactories representingdifferent technology levelswho completedquestionnaire in 1985.
In April 1991, 241 of 279traced workers respondedto same 1985questionnaire.
Operators still workingwere compared to thosewho moved to otheremployment in 1991.
Outcome: NordicQuestionnaire— discomfort,ache, or pain in the neck duringthe previous year; whether theyhad neck pain in last 7 days, andwhether pain prevented themfrom doing daily duties.
Exposure: Assessed byquestions regarding type ofmachine operated, workorganization, workplace design,units produced/day, paymentsystem, and duration ofemployment as a sewingmachine operator.
Necksymptomsin previousyear foremployeesmaintaininga piece-workgroups of<100units/day: 36%
Necksymptomsin previousyear foremployeesmaintaininga piece-workgroups of100 to 125units/day: 53%
Necksymptomsin previousyear foremployeesmaintaininga piece-workgroups of>125units/day: 61%
Developingneck symptomimprovement in1991 amongoperatorscompared tootheremploymentgroup OR=0.85
Neck symptomimprovement inotheremploymentgroup vs. operator group:12 monthsymptoms:OR=3.3
7 daysymptoms:OR=3.9
0.29-2.4
1.4-7.7
1.3-11.9
Participation rate, 1985: 94%.
Participation rate, 1991: 86%.All participants were female.
77 of 241 workers still operated asewing machine in 1991.82 workers had another job in1991. Among those 35 years orbelow, 77% had left job; amongthose above 35 years, 57% leftjob.20% reported musculoskeletalsymptoms as the reason forleaving job.No significant changes inprevalences among thoseemployed as sewing machineoperators from 1985 to 1991;significant decrease in those whochanged employment.As many as 50% of respondentsreported a change in the responseto positive or negative symptomsfrom 1985 to 1991.Operators always working at thesame machines showedsignificantly higher neck symptomscompared to those working atdifferent machinesAlthough the authors state that theanalysis did not show thedevelopment of neck (or shoulder)symptoms among workers whohad worked as a sewing machineoperator to be significantly relatedto exposure, exposure time, orage, there was a significant drop-out rate of those above 35 years.
2-61
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Veiersted andWestgaard1994
Cohort 30 female chocolate manu-facturing workers. 17 whocontracted trapeziusmyalgia within 6 to51 weeks compared tothose workers without.
Outcome: Trapeziusmyalgia—neck and shoulder painlasting >2 weeks of a degreemaking it difficult to continuework. At least one tender ortrigger point present. Prospective interviews every10 weeks to detect symptoms ofmuscle pain. Daily “pain diaries”kept by subjects.
Exposure: Static muscle tensionduring work was between 1 and2% of maximal voluntary activityof the trapezius musclesrecorded by electromyographicmeasurements of trapeziusmuscle in earlier study. Interviews conductedprospectively every 10 weeksconcerning exposure at workfor 1 year.
56% ÕÕ Perceivedstrenuouspostures:OR=7.2
Physicalenvironment:OR=0.9
Psychosocialfactors:OR=3.3
Perceivedstrenuousprevious work:OR=6.7
2.1-25.3
0.5-1.7
0.8-14.2
1.6-28.5
Participation rate: 55%.Drop-out rate may limit generaliz-ability of results although drop-outsdid not differ in exposure estimatesand complaints.
Excluded subjects with: (1) nosimilar occupation during last 5years; (2) known musculoskeletaldisorder predisposing for myalgia;(3) neck or shoulder pain sufficientto initiate medical visit, (4) ifemployed <26 weeks.
Several anthropometric, non-work-related, general health, personality,psychosocial, and previousemployment variables included ininitial interview and follow-ups.
Subjects on a fixed-wage system.
Work was mainly machine-paced.Nine of 17 with trapezius myalgiahad sick leave after medicalconsultation.
No difference in general healthstatus, anthropometric measures.None of the models showed anyeffect of the “physical environ-ment.” Parameters which in-cluded exposure to draft, vibration(floor or machine), or noise.
Observation time was con-siderably shorter for workers whocontracted neck pain compared tostatus used in analysis. Non-patients had more opportunities toreport a positive answer.
The perceived strenuous postures were not reflected in any of theconventional EMG parameters(static, median or peak loads).
2-62
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Viikari-Junturaet al. 1994
Cohortlongitud-inal;2 quest-ionnaires3 yearsapart
688 machine operators and553 carpenters comparedto 591 office workers. Allmale.
Outcome: Neck trouble,categorized on 5 point scale("not any" to "daily").
Exposure: Based on jobcategory. Machine operators—static work with whole bodyvibration, carpenters—dynamicphysical work, officeworkers—sedentary work. Forinitial evaluation, observation ofwork sites were performed.
12 monthprevalencefor severeneck painfor1984/1987
Machineoperators:28/40%
Carpenters:25/32%
Officeworkers:9/12%
ÕÕ Carpenters vs. office workers:No neck pain tomoderate:OR=1.6
No neck pain tosevere:OR=1.6
Persistentlysevere:OR=3.0
Machineoperators vs. office workers:
No neck pain tomoderate:OR=1.8
No neck pain tosevere:OR=3.9
Persistentlysevere:OR=4.2
1.0-2.5
0.8-3.0
1.4-6.4
1.1-2.8
2.3-6.9
2.0-9.0
Participation rate: 81% machineoperators; 79% carpenters;89% office workers.
Adjusted for occupation, smoking,and physical exercise, age,duration or current occupation.
2% had retired.
In multivariate analysis;“occupation” was only significantpredictor in change from no necktrouble to moderate neck trouble.
Twisting or bending trunk not asignificant predictor of neck pain.
In multivariate analysis: occupation, age, and currentsmoking were significantpredictors in change from no necktrouble to severe neck trouble.
Interaction between age andoccupation not significant.
Job satisfaction not associatedwith neck trouble and otherpredictors.
2-63
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Welch et al.1995
Cross-sectional
39 of 47 sheet metalworkers attending ascreening for occupationallung disease. Casescompared to those withoutsymptoms.
Outcome: Symptom survey;pain, aching, stiffness, burning,numbness or tingling in neck$ once/month, or lasting > oneweek, no history of previoustraumatic injury. Symptomsbegan after working as a sheetmetal worker and prior toretirement.
Exposure: Questionnaire surveyobtaining types of tasksperformed, tools used,frequency of task performance. Hanging duct work dichotomizedinto > and <40% of time worked.
21% Compari-son groupwith nosymptoms
Percent timehanging duct:OR=7.5 0.8-68
Participation rate: 83%.
Smoking cigarettes, averagenumber of years working not foundto be significantly differentbetween symptomatic andasymptomatic; other confounders(age, gender) not mentioned.
Average length of employment intrade: 33 years.
Pilot study.
Hrs/week using hand tools,percent of time in the shop vs. timein the field not significant.
Duration of employment notincluded in article.
2-64
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Wells et al.1983
Cross-sectional
196 male letter carrierscompared to 203 malemeter readers and postalclerks.
104 letter carriers hadweight increased from 25to 35 lbs. in the year prior tothe study.
Outcome: Telephone interviewcase status based on currentpain; frequency, severity,interference with work, etc.;score of 20 required to be acase—more points given to neckand shoulder problems thatinterfered with routine dailyactivities.
Exposure: Based on jobcategory; based on self-reported information on weightcarried, previous work involvinglifting and work-related injuries.
All lettercarriers:12%
Lettercarrierswithincreasedweight:12%
Lettercarrierswith noweightincrease:12%
Postalclerks:5%
Meter readers:7%
All lettercarriers vs. clerks andreaders:OR=2.57
Letter carrierswith increasedweight vs. clerks:OR=2.63
Letter carrierswith no weightincrease vs. clerks:OR=2.87
1.13-6.2
0.9-8.8
0.9-9.8
Participation rate: 99% amongletter carriers, 92% meter readers,97% postal clerks.
No significant difference inschooling and marital status.
Comparison group (gas meterreaders) used because of similar“walking rate” without carryingweight compared to letter carriers. Postal clerks neither walk nor carryweight.
More weight given to scoring neckand shoulder. Outcome influencedresults when ranking of bodyMSDs though would not influencegroup comparisons.
Adjusted for age, number of yearson the job, Quetelet ratio andprevious work experience.
Study limited to males.
Letter carriers with increased bagweight walked on average 5.24 hr;those with no change in bagweight walked 4.83 hr.
Letter bag straps usually carriedon the shoulder.
2-65
Table 2–7 (Continued). Epidemiologic studies evaluating work-related neck musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
Yu and Wong1996
Cross-sectional
151 VDT users from aninternational bank in HongKong; of these 90 weredata entry, dataprocessing, computerprogrammers; 61 infrequentusers of VDTs.
Outcome: Questionnaire surveyused to collect information ondiscomfort or ache during workafter starting the current job.
Exposure: Questionnaire surveyon “undesirable postures”including frequent bending of theback and inclining the neckforwards.
31.4% Frequent usersof VDTs vs. infrequentusers:p=0.0025
Logistic modelfor neck paininclining neckat work:OR=784.4
Fixed keyboardheight:OR=90.1
Frequent VDTuse:OR=28.9
Female gender:OR=1.6
Age (years):OR=1.2
33.2-18,630
7.6-1056
2.8-291.8
0.35-6.8
1.02-1.5
Participation rate: 80%. Agesranged from 18 to 41 years, 74%between 21 to 30 years.
Analysis controlled for “age andgender, and other covariates.”
Queried about personal particulars,job nature and characteristics,working posture, general healthconditions.
Males with significantly longermean VDT working experiencecompared to females (5 vs. 2.7years).
Non-workplace factors notexamined.
2-66
(Continued)
Table 2–8. Epidemiologic studies evaluating work-related neck/shoulder disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
Åaras 1994 Prospective 15 female assemblyworkers makingtelephone exchanges.
27 female VDT users.
25 female data entryoperators.
29 male VDT users.
Outcome: Assembly Workers: musculoskeletal sick leave/man-labor years; pre- and post-intervention.
Data Entry and VDT Users:Survey: Pain intensity for theneck and shoulder regionaccording to Nordicquestionnaire.
Exposure: Load on trapezius asmeasured by EMG. Quantification of the muscle loaddone by ranking the intervalestimate (0.1 s) to produce anamplitude probability distributionfunction. Both total duration andnumber of periods/min. whenmuscle activity was below 1%MVC were calculated.
Intervention: Replacingworkstands with fixed heights toworkplaces easily adjustable forboth sitting and standing. Handtools were counter- balancedand adjustable arm restsintroduced. For VDT operators,tables and chairs adjusted togive more relaxed position of theshoulders, operators given morework surface for keyboard andmouse, and distances betweenoperators and screen/documentsadjusted.
Number ofmusculoskeletaldiagnoses: pre-intervention,1967 to 1974: 52(30.6%)
Number ofmusculoskeletaldiagnoses post-intervention,1975 to 1982: 35(14.3%)
Duration ofsick-leave/man-labor year(days)
Median sickdays pre-intervention:22.9
Median sickdays post-intervention: 1.8
Shoulder painintensity:3.4
2.2
4.4-50.8
0-34.4
2.3-4.4
1.3-3.3
Participation rate: Not reported.
Study designed to evaluate if there isa relationship between trapezius loadand incidence of MSD.
Other intervening variables that mayhave reduced symptoms or sickleave were not discussed.
Mean static trapezius load inassemblers was reduced from 4.3%MVC to 1.4% (post-intervention);mean static trapezius load in VDTusers reduced from 2.7% MVC to1.6% MVC (post-intervention).
The mean intensity and duration ofneck pain showed no significantreduction after intervention in thedata dialogue females.
2-67
(Continued)
Table 2–8 (Continued). Epidemiologic studies evaluating work-related neck/shoulder disordersMSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
AndersenandGaardboe1993a
Cross-sectional
701 female sewing machine operators,compared to781 females from thegeneral population ofthe region and internalreferent group of89 females from thegarment industry.
Outcome: Case of chronic neckpain was defined as continuouspain lasting for a month or moreafter beginning work and pain for$ 30 days within the past year.
Exposure: Categorization brokendown according to currentoccupational status by job title. Classification into exposuregroups based on author’sexperiences as occupationalhealth physicians and involvedcrude assessment of exposurelevel and exposurerepetitiveness. High exposurejobs were those involving highrepetition/high force or highrepetition/low force or mediumrepetition/high force. Mediumexposure jobs were thoseinvolving medium repetition/lowforce and low repetition and highforce. Low exposure jobs werelow repetition/low force.
For the analysis, “length ofemployment as a sewingmachine operator” wasconsidered the variable ofinterest, the rest wereconfounders.
34.2% Generalpopulation:12.9%
Internalreferentgroup: 10.1%
Sewingmachineoperatorscompared to:(1) Generalpopulation:OR=3.5(2) Internalreferent groupOR=4.6
Logistic model Years assewingmachineoperator (0 to 7years):OR=3.17 (8 to 15 years):OR=11.2(>15 years):OR=36.7
Age >40 years: OR= 1.96
Current highexposure (-/+):OR=0.32
Children (>0):OR =0.35
2.6-4.7
2.2-10.2
0.6-16.1
2.4-52.3
7.1-189
0.8-5
0.1-1
0.1-1.9
Participation rate: 78.2%.
Examiners blinded to case status.
Respondents excluded if hadprevious trauma to neck, shoulder, orarms or had inflammatory disease attime of response.
Odds ratios adjusted for age, havingchildren, not doing exercise,socioeconomic status, smoking, andcurrent neck/shoulder exposure.
Age-matched exposure groups andcontrols.
Presented study as “general surveyof health in the garment industry” tominimize information bias.
Exercise (-/+):OR=1.28
Smoking (=/-):OR=2.3
0.5-3.4
0.9-6.1
2-68
Table 2–8 (Continued). Epidemiologic studies evaluating work-related neck/shoulder disordersMSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
AndersenandGaardboe1993b
Cross-sectional
From a historical cohortof 424 sewing machineoperators, 82 wererandomly selected andcategorized by numberof years ofemployment: 0 to7 years, 8 to 15 yearsand greater than 15years. These werecompared to a referentgroup composed of21, 25 and 36operators from eachgroup and 25 of55 auxiliary nurses andhome helpers whoparticipated in thestudy.
Outcome: Measured by healthinterview and exam of the neck,shoulder and arm. Case ofchronic pain was defined ascontinuous pain lasting for amonth or more after beginningwork and pain for $ 30 dayswithin the past year. Physicalexamination: Restrictedmovements in the cervical spineand either palpatory tendernessin cervical segments orirradiating pain or tingling atmaximum movements or positiveforaminal test.
Exposure: Exposure categoriza-tion broken down according tocurrent occupational status byjob title. Classification intoexposure groups based onauthor’s experiences as occupa-tional health physicians andinvolved crude assessment ofexposure level and exposurerepetitiveness. High exposurejobs: Involved high repetition/high force or high repetition/ lowforce or medium repetition/ highforce. Medium exposure jobsinvolved medium repetition/ lowforce and low repetition and highforce. Low exposure jobs werelow repetition/low force.
50.9%
Tension necksyndrome: 40%
CervicalSyndrome: 20%
46.2% Referents:OR=1
0 to 7 years:OR=2.3
8 to 15 years:OR=6.8
>15 years:OR=16.7
Age $ 40years: OR=1.9
Children >0years: OR= 0.5
Exercise:OR=1.4
Smoking:OR=1.5
Current highexposure:OR=1.6
0.5-11
1.6-28.5
4.1-67.5
O.9-4.1
0.1-1.7
0.6-2.96
0.7-3.3
0.7-3.6
Participation rate: 78.2%.
Logistic regression limited to acombined neck/shoulder casedefinition.
Age-matched exposure groups andcontrols.
Examiners blinded to control/subjectstatus.
Controlled for age, having children,not doing leisure exercise, smoking,socioeconomic status.
Poor correlation betweendegenerative X-ray neck changesand cervical syndrome.
Most frequent diagnosis among studygroup was “cervicobrachialfibromyalgia” significant for test oftrend with exposure time in years.
Chronic neck pain vs. palpatoryfindings: Sensitivity: 0.85;Specificity: 0.93.
2-69
Table 2–8 (Continued). Epidemiologic studies evaluating work-related neck/shoulder disordersMSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Bergqvistet al. 1995a
Cross-sectional
260 office workersusing VDTs, (198females); symptomaticcases compared tonon-cases.
Outcome: Neck/shoulderdiscomfort: Any discomfort overthe last 12 months; intense neckdiscomfort: As above, ifoccurred in last 7 days andinterfered with work.
Physiotherapist's diagnosis of(1) Tension neck syndrome: Ache/pain in the neck; feeling oftiredness and stiffness in neck;possible headache; pain duringmovements; musculartenderness; (2) Cervicaldiagnoses: Ache/pain in neckand arm; headache; decreasedmobility due to cervical painduring isometric contraction;often root symptoms such asnumbness or parathesias.
Exposure: Based on observationan ergonomic evaluation usingdata on each individual’s mostcommon work situations: Staticwork posture, nonuse of lowerarm support, hand in non-neutralposition, insufficient leg space attable, repeated movements withrisk of tiredness, specular glarepresent on VDT. Measured: Height difference of VDTkeyboard-elbow, High visualangle to VDT.
Neck/shoulder: 61.5% Female: 63%Male: 57%
Intensiveneck/shoulderdiscomfort:stressfulstomachreactions: OR=5.4
Repeated workmovements:OR=3.6
Too highlyplaced VDT:OR=4.4
1.6-17.6
0.4-29.6
0.9-60.3
Participation rate: 92% of 353 officeworkers, of which 260 were VDTusers.
Adjusted for age and gender.
Examiner and workplaceinvestigators blinded to case andexposure status.
Factors included in analysis: Age,gender, smoking, children at home,negative affectivity, tiredness-relatedstress reaction, stomach-relatedstress reaction, use of spectacles,peer contacts, rest breaks, worktask flexibility, overtime, static workposition, non-use of lower armsupport, hand in non-neutral posture,repeated movements with risk oftiredness, height differenceskeyboard/elbow, high visual angle toVDTs, glare on VDTs.
There are problems with interpretingresults because of multiplecomparisons and multiple models.
Not all significant findings presentedin paper.
2-70
Table 2–8 (Continued). Epidemiologic studies evaluating work-related neck/shoulder disordersMSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Bergqvistet al. 1995b
Cross-sectional
322 office workersfrom 7 Stockholmcompanies; VDT userscompared to non-VDTusers 52% interactive,29% data entry,19% non-VDT users.
Outcome: Neck/shoulderdiscomforts: Any discomfortover the last 12 months; intenseneck/shoulder discomfort: Asabove, if occurred in last 7 daysand interfered with work.
Physiotherapist's diagnosis oftension neck syndrome:Ache/pain in the neck; feeling oftiredness and stiffness in neck;possible headache; pain duringmovements; musculartenderness.
Exposure: Video display terminaluse: Based on self-reporting ofVDT use. VDT userscategorized into data entry orinteractive VDT users.
Ergonomic Factors: Same asBergqvist 1995a.
Neck/shoulderdiscomfort: 60%
Intenseneck/shoulderdiscomfort: 7.4%
Neck/shoulderdiscomfort: Current VDTwork vs. noVDT work:OR=1.4
ForaccumulatedVDT work > 5PY²: OR=1.3
Intenseneck/shoulderdiscomfort: Current VDTwork vs. noVDT work:OR=0.5
ForaccumulatedVDT work >5PY²: OR=0.8
0.8-2.4
0.7-2.5
0.2-1.8
0.3-2.5
Participation rate: 92% questionnaire;91% physiotherapy exam;82% workplace exam.
Examiner and workplaceinvestigators blinded to case andexposure status.
Intensive neck/shoulder discomfortwas associated with VDT work over20 hr and having “stomach reactions”often and repetitive movements. OR=3.9 (1.1-13.8).
Originally 535 workers queried in1981, of those 182 had left theworkplace (quit, retired,etc.)–possible bias from “HealthyWorker Effect.”
Covariates considered: Children athome, smoking, negative affectivity,stomach-related stress reactions,tiredness-related stress reactions;organizational factors consideredlimited or excessive peer contacts,limited rest break opportunity, limitedwork task flexibility, frequentovertime.
For cervical diagnoses: Excess ORsuggested for combined occurrenceof VDT work of >20 hr/wk andspecular glare on the VDT screen.
2-71
Table 2–8 (Continued). Epidemiologic studies evaluating work-related neck/shoulder disordersMSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Bjelle et al.1981
Case-control
13 workers ofindustrial plantconsecutively seen athealth clinic with acute,nontraumaticneck/shoulder pain notdue to causativedisease ormalformation comparedto 26 controls. Matched on age,gender, and place ofwork.
Outcome: Physician diagnosedneck/shoulder pain.
Exposure: Anthropometric andisometric muscle strength weretested with strain gaugeinstruments. Patients asked toperform their maximal efforts. Measurements made for thefollowing contractions: Shoulderelevation at the acromion,abduction and forward flexion ofthe shoulder joints at neutralposition, and semi-pronated.
Grip strength measured byvigorimeter.
Video recording of armmovements at work. Shoulderloads estimated from videos.Consisted of measuring theduration and frequency ofshoulder abduction or forwardflexion of >60E.
Electromyography measurementof shoulder load during assemblywork on 3 patients and 2 healthyvolunteers. Muscular load leveldetermination made by computeranalysis of myoelectricamplitude.
6 with tendinitis Controlswithouttendinitis
Cases hadsignificantlylonger durationand higherfrequency ofabduction orforward flexionthan controls,2.5/min.(p<0.001).
Cases hadsignificantlyhigher shoulderloads thancontrols.
Median numberof sick-leavedayssignificantlydifferentbetween casesand controls(p<001).
Participation rate: Not reported.
Investigators completed the videoanalyses blinded to case status.
Anthropometric data, age nodifference between cases andcontrols.
Isometric strength test: Controlssignificantly stronger in 6 of 14 testsbut probably influenced by paininhibition in cases.
No significant difference in cycle time(9 vs. 12 min).
2-72
Table 2–8 (Continued). Epidemiologic studies evaluating work-related neck/shoulder disordersMSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Blåder et al.1991
Cross-sectional
Of 224 sewingmachine operatorsfrom 4 plants, 199completed a symptomsurvey. Of 155 whoreported shoulder orneck pain in the past12 months, 131 wereexamined.
Outcome: Survey: Shoulder orneck pain in past 12 months.
Exam: Tenderness on palpation,range of motion, pain duringmotion or isometric musclecontraction, active and passiverange of motion was measuredby use of a goniometer. Diagnoses were not made duringthe examinations, but test formswere later analyzed by criteriafrom Waris [1979].
Exposure: From questionnaire: employment duration, hr/wk.
Plants selected byrepresentatives of SwedishLabour Union familiar with worksites with similar loads.
Muscletenderness:Acromioclavicular joint: 15%
Biceps tendon:35%
Decreased ROM:30%
Acromioclavi-cular: 5%
Õ Age
Nationality
Employmentduration
Working >30hr/wk
p <0.05
non-significant
p <0.05
p <0.05
Participation rate: 89% forquestionnaire, 87% for physicalexam.
Only those with symptoms givenphysical exam. Physicians andphysiotherapist not blinded tosymptom status.
High rate of turnover in plant.
Authors state that study involvedcontrol group taking into accountpsychosocial factors, but results notincluded in this article.
Questionnaire included information onbackground, family situation,employment, job conditions, health.
Physical exam occurred 1 to 3months after questionnaire.
In 3 consecutive years 147 sewingmachine operators left this work inthe factories. 48% answered follow-up questionnaire. (17% left becauseof neck problems contributing todecision to leave work.)
2-73
Table 2–8 (Continued). Epidemiologic studies evaluating work-related neck/shoulder disordersMSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Ekberg et al.1994
Case-control
Study population wereaged 18 to 59 years,had to have yearlyincomes of SEK 45,000and not been on sickleave for more than2 months in past 6months, not employedin large rubber industryin area.
“Cases” had consulteda community physicianfor musculoskeletaldisorders of the neck,shoulder, arm, or upperthorax during the studyperiod from semi-ruralcommunity in southernSweden. Cases hadto have been illimmediately prior tophysician visit andhave been on sickleave at most less than4 weeks. No trauma,infectious cause,accident, malignancy,rheumatic disease,abuse, or pregnancy.
Controls wererandomly selected fromSwedish insuranceregistry.
Outcome: Self-administeredquestionnaire; a modified versionof the Nordic questionnaireasking about musculoskeletalsymptoms in the past 6 months.Questionnaire includedbackground factors, age,gender, ethnic background,family situation, smoking habits,and exercise.
Exposure: Assessed byquestionnaire; sevendeterminants were:uncomfortable sitting position,uncomfortable standing position,physically demanding work, lightlifting (less than 6 kg), repetitivemovements demanding precision,work with lifted arms, andmonotonous work position. Rating scales were based onaverage duration of hours perday of each item of exposure.
52 items on psychosocial workconditions reduced to 8 factorsby factor analysis: psychologicalwork climate, quality of workcontent, work pace, demands onattention, work planning, jobsecurity, job constraints, andwork role ambiguity.
Õ Õ
Female gender:OR=15.5
Immigrant:OR=28.3
Current smoker:OR=8.2
RepetitivePrecisionMovements: Low:OR=1Med: OR=3.8High: OR=15.6
Light Lifting:Low: OR=1.0Med + High:OR=49.7
Lifted arms:Low: OR=1.0Med: OR=5.9High: OR=3.7
Work Pace:Low: OR=1Med: OR=7.6Rushed: OR=10.7
ORs for controlswith MSDsymptoms in bothneck and shoulderand other bodyparts:
RepetitivePrecisionMovements:OR=7.5
Light lifting:OR=13.6
Lifted arms:OR=4.8
Uncomfortablesitting positions:OR=3.6
90% CI usedin this paper
3.4-71
3.1-257
2.3-29
0.7-202.2-113
9.0-273
0.9-370.4-30
1.6-36
2.2-52
2.4-23
4.8-39
1.3-18
1.4-9.3
Participation Rate: 73%.
Logistic analysis adjusted for age,gender, smoking, having preschoolchildren.
Age and having preschool childrenwere not significant factors.
Ambiguity of work role, demands onattention and work content alsostatistically significant.
2-74
Table 2–8 (Continued). Epidemiologic studies evaluating work-related neck/shoulder disordersMSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Ekberg et al.1995
Cross-sectional
637 of 900 residentsbetween the ages of18 to 59 years, with anaverage yearly incomeof $ $8000 U.S. dollars.
Outcome: Based on modifiedNordic questionnaire; casedefined as the presence ofsymptoms during the past6 months.
Exposure: 20 questionnaireitems on physical workconditions which were factoranalyzed. Self-reportedperception of physical workenvironment factors considered: Uncomfortable sitting or standingposition; physically demandingwork; light lifting; repetitivemovements demanding precision;work with lifted arms,monotonous work position.
Questionnaire on workorganization, work content andrelations in the work situation.
Symptoms neck:Male: 33%Female: 53%
Shoulder:Male: 35%Female: 40%
Õ Gender: OR=1.3
ImmigrantStatus:OR=1.3
Repetitivemovementsdemandingprecision:OR=1.2
High workpace: OR=1.2
Low workcontent lack ofstimulation andvariation:OR=1.3
Work roleambiguity:OR=1.2
1.1-1.5
1.0-1.6
1.0-1.3
1.0-1.3
1.1-1.5
1.0-1.3
Participation rate: 73%.
Symptom responses in neck andshoulder correlated (r=0.56) andcollapsed into one variable for theanalyses.
Age, smoking, exercise habits, familysituation with preschool children notsignificantly associated withsymptoms.
Social work climate, demands onattention, work planning, job securityand job constraints not significantlyassociated with symptoms.
2-75
Table 2–8 (Continued). Epidemiologic studies evaluating work-related neck/shoulder disordersMSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Holmströmet al. 1992
Cross-sectional
Of 2500 constructionworkers randomlyselected from 4,159active members oftrade union registry ofthe south of Sweden,1,773 (71%)participated. Thisgroup wasrepresented by allconstruction tradesexcept painters,electricians andplasterers. Allparticipants musthave worked in thepast 6 months,including short periodsof sick leave orunemployment.
Outcome: Self-reported historyof musculoskeletal problems wasobtained through a mail survey.
Case of “neck and shoulder pain”defined as: Pain, ache,discomfort from theneck/shoulder are experiencedsometimes often or very oftenduring the past 12 months.
Case of “considerable neck andshoulder pain” defined as neckand/or shoulder trouble with“severe” or “very severe”functional impairment.
Exposure: Data on physicalworkload, psychosocial factorsand individual and employmentrelated factors obtained from mailsurvey.
Hands aboveshoulder<1 hr/day 1 to 4 hr/day>4 hr/day
Hands at waist<1 hr/day /1 to 4hr/day >4 hr/day
Stooping<1 hr/day1 to 4 hr/day >4 hr/day
Kneeling<1 hr/day1 to 4 hr/day>4 hr/day
Sitting<1 hr/day1 to 4 hr/day>4 hr/day
RoofersPlumbersFloorMachines/ Tools.
Õ
1.11.5
2.0
1.01.1
1.2
1.01.4
1.5
1.41.4
1.5
0.61.6
0.8-1.51.2-1.9
1.4- 2.7
0.7-1.30.9-1.3
0.8-1.6
0.8-1.31.1-1.8
1.1-2.1
1.1-1.81.1-1.8
1.1-2.1
0.3-1.00.9-2.7
Participation rate: 71%.
Neck/shoulder pain related toincreasing age, smoking, weightinactivity during free time, heightunder 185 cm.
Controlled for age, physical factors.
Dose-response relationship forworking with hands above shoulderlevel.
Stress index showed a dose-response. Stress questionspertained to rushing, job pressure,and inability to relax.
Psychosocial factors stronglyassociated with neck and/or shouldertrouble and neck and shoulder painwhen age and physical factors keptconstant in logistic models forpsychosocial pre-rate ratio, “high”level compared with “low” level forconsiderable neck pain; the followingpsychosocial scales weresignificant:Qualitative demands: 1.4 (1.0-2.0)Quantitative demands: 3.0 (2.1-4.0)Solitary work: 1.5 (1.2-1.8)Anxiety (health): 3.2 (2.5- 4.0)Psychosomatic: 5.0 (3.6-6.9)Psychological: 4.7 (3.6-6.0)Stress: 3.4 (2.6-4.2)
0.7
1.61.51.31.1
0.4-1.2
Õ Õ Õ Õ
The following were not significant:Discretion, support, under-stimulation, anxiety (work), jobsatisfaction, quality of life.
2-76
Table 2–8 (Continued). Epidemiologic studies evaluating work-related neck/shoulder disordersMSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Hünting et al.1981
Cross-sectional
VDT users: 53 dataentry; 109conversational VDTusers; 78 typists;compared to55 “traditional officeworkers” not usingVDTs or typewriters.
Outcome: Questionnaire: Symptoms of pain, stiffnessfatigue, cramps, numbness,tremor scaled as: Daily,occasionally, seldom, never;
Medical Exam: Included ananamnesis and palpation ofpainful pressure points andtendons and tendon insertionpoints in the shoulders, arms,and hands.
Exposure: (1) Questionnaire,(2) Observation andmeasurements of work-station,and (3) Body posture measuredusing method described byHünting et al. 1980b.
Medical findingsin shoulder andneck:
ConversationalVDT users: 28%
Typewriter:35%
Data Entryterminal VDTusers: 38%
Medicalfindings inshoulder andneck:
Traditionalofficeworkers:11%
Medicalfindings:
Conversationalterminal VDTusers vs. trad.office workers:OR=1.35
Typewriter vs.trad. officeworkers:OR=3.18
Data entryterminal usersvs. trad. Officeworkers:OR=9.9
0.6-3.1
1.3-2.6
3.7-26.9
Participation rate: Not reported.
No adjustment for age and gender.
Blinding of examiners not mentionedin paper.
Medical findings in neck and shouldersignificant in data entry workers forhead inclination greater than 56E vs.<56E. Not significant inconversational terminal workers ortypewriters.
Medical findings in neck and shouldersignificant for typists with headrotation greater than 20E compared to<20E.
The lower the table and keyboardheights, the more frequently pains inthe shoulder, neck, and arms. Nodocument holders used. Authorsconcluded the higher the table, thehigher the documents, the better theposture of the head and trunk.
Increased neck/shoulder findingsoccurred with increased turning ofthe head or head inclination.
Job satisfaction, relationship withcolleagues, superiors, decisionmaking abilities, use of skills notsignificantly different among groups.
2-77
Table 2–8 (Continued). Epidemiologic studies evaluating work-related neck/shoulder disordersMSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Jonssonet al. 1988
Cohort Electronics Workers(n=69 female) out ofinitial 96 workers.
Outcome: Three separatephysical exams at yearlyintervals (one initially) assessingtenderness on palpation, pain orrestriction with active andpassive movements; symptomsin previous 12 months withregard to character, frequency,duration, localization, and relationto work or other physicalactivities. Analyzed if score onany symptom of 2 or greater thanon a 4 point scale; “severe”symptom score = 4.
Carried out at outset of study: MVC of forearm flexors,shoulder strength, handgrip,heart rate using a bicycleergometer and rating ofperceived exertion.
Exposure: Computerized via twovideo recordings (rear and side),real time; obtained frequency andduration of working postures andmovements, neck flexion greaterthan 20E.
Severe neckdisorders:After 1 year:24%
22% at 2ndexam
At 3rd exam, 38subjectsreallocated tovaried tasks hadimproved (16%of these hadseveresymptoms)
26% withunchangedworkingconditionsdeterioratedfurther
Severe neckdisorders:11% initially
Predictors ofchange ofhealth statusfrom 2nd to 3rdexamination:
Palpationtenderness,neck/ shoulderangle: OR=1.6
Shoulderelevated, % ofwork-cycle:OR= 1.04
Satisfactionwith workcolleagues:OR=25
Satisfactionwith worktasks: OR=24.5
Participation rate: 72%.
Predictors of deterioration werepreviously physically heavy jobs,high productivity (after 1 year), andprevious sick leave.
Predictors of improvement werereallocation, physical activity in sparetime, and high productivity (after 2years).
Predictors of remaining healthy werework without elevating the shouldersand satisfaction with work tasks.
Subjects reallocated to new taskscharacterized as more dynamic andvaried: Non-sitting, no inspection ofsmall details on printed circuit boards,standing and walking, occasionallysitting, caretaking work, surveillanceof machinery, assembling of biggerand heavier equipment.
2-78
Table 2–8 (Continued). Epidemiologic studies evaluating work-related neck/shoulder disordersMSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Kilbom et al.1986
Kilbom andPersson1987
Cross-sectional
106 of 138 femaleassemblers in twoelectronicmanufacturingcompanies agreed toparticipate; 10excluded because ofsymptoms in past 12months. 96 underwentmedical, physiological,and ergonomicevaluation.
Outcome: Three separatephysical exams at yearlyintervals (one initially) assessingtenderness on palpation, pain orrestriction with active andpassive movements; symptomsin previous 12 months withregard to character, frequency,duration, localization, and relationto work or other physicalactivities. Analyzed if score onany symptom of 2 or >on a 4point scale; “severe” symptomscore = 4.
Exposure: Carried out at outsetof study: MVC of forearmflexors, shoulder strength,handgrip, heart rate using abicycle ergometer and rating ofperceived exertion. Includedvideo analysis of postures andmovements of the head, shoulderand upper arm includingdurations and frequencies. Recorded work cycle time andnumber of cycles/hr, time at restfor the arm, shoulder and head,rest periods, and average andtotal duration/work cycle and hr. The mean number of neckforward flexions >20E/hr was728 (s.d. 365) in the initial 96workers.
MSD symptomsin the neck/shoulder using a4 point severityscale:
None: 78%
Slight: 8%
Moderate: 7%
Severe: 3%
Õ LogisticRegressionmodel (allvariablessignificant atthe p<0.05level)
Headache
Averagetime/work cyclewith upper arm0-30E abducted
Averagetime/work cyclein neck flexion
Excessivegeneral fatigueat end ofworking day
Participation rate: 77%. The authorsfollowed up on the non-participantsand found no significant differencesfrom participants.
No relation between maximal staticstrength and symptoms.
Examiner blinded to case status.
Questions included spare timephysical activities, hobbies,perceived psychosocial stress atwork, work satisfaction, number ofbreaks, rest pauses.
Clinically diagnoses found werelargely myofascial symptoms.
Headache, sleep problems, dizzinessshowed a weak positive correlation.
Age, years of employment,productivity, muscle strength werenot related to symptoms.
There was large inter-workervariation in working posture andworking techniques.
The more dynamic workingtechnique, the less symptoms in theneck and neck/shoulder symptoms.
Authors note: “a strong positiverelationship to disorders wasobtained with VIRA variablesdescribing neck forward flexion andupper arm elevation.”
See Jonsson et al. 1988 for follow-up.
2-79
Table 2–8 (Continued). Epidemiologic studies evaluating work-related neck/shoulder disordersMSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Linton andKamwendo1989
Cross-sectional
420 of 438 medicalsecretaries and officepersonnel at aSwedish hospital.
Those reportingfrequently having neckand shoulder pain(1 to 3) compared tothose less frequentlyhaving pain (4 to 6)points).
Outcome: 3-point scalecollapsed from 6-point frequencyscale ranging from “almostnever” to “almost always” havingneck or shoulder discomfort; andNordic Musculoskeletal PainQuestionnaire.
Exposure: 10-questionstandardized form on thepsychological work environmentwith 1 to 4 categorical scales. Overall score and indexes onwork content, psychologic workdemand and social support atwork.
Duties included daily use oftypewriter, VDT, plus mailtelephone and appointmentduties.
Shoulder painfrequency
Very often:16.9%
Sometime wk:3.8% Sometimes a wk:4.8%
Sometimes days:13.8%
Sometimes 1day: 28.6%
Never: 32.1%
Õ Thosefrequentlyhaving neckand shoulderpain vs. thoseless frequentlyhaving pain:
Poor WorkContent:OR= 2.5
Lack of SocialSupport:OR=1.6
1.3-4.9
0.9-2.8
Participation rate: 96%.
75% sat >5 hr/day.
43% worked with office machineseach day.
Psychosocial scale scored: 10 to 20as good environment. 20 to 40 aspoor environment.
Authors noted that: (1) Secretariesexposed to high work demandsperiodically, (2) they also felt helplessto change the work environment, andthat (3) internal conflict withindepartments may have affectedresponses.
2-80
Table 2–8 (Continued). Epidemiologic studies evaluating work-related neck/shoulder disordersMSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Maeda 1982 Cross-sectional
119 accountingmachine operatorsaged 17 to 29 years ina post-check office.
Outcome: Based onquestionnaire responses of painand stiffness in the right and leftsides of the neck and shoulderbased on frequency of “almostevery day, occasionally, andnever or seldom” during theprevious several wk. Scoreswere factor analyzed.
Exposure: Anthropometricparameters relevant to the jobtasks were measured on51 operators who showed largeor small factor scores.
p<0.05
Partialcorrelationcoefficientbetween headneck tilt andfactor score1 to 5,controlling forother angles“A and C”, age,and length ofservice 0.25
Participation rate: Not reported.
Examiners blinded to case status: Not reported.
Constrained tilted head posture wasassociated with neck/shoulderstiffness.
2-81
Table 2–8 (Continued). Epidemiologic studies evaluating work-related neck/shoulder disordersMSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Milerad andEkenvall1990
Cross-sectional
99 dentists randomlyselected fromStockholm dentistregistry who practiced$ 10 years comparedto 100 pharmacistsselected from allpharmacists inStockholm.
Outcome: Based on telephonequestionnaire: Neck symptomsat any time before the interview("lifetime prevalence"). Furtheranalyzed according to Nordicquestionnaire as to durationduring last 12 months and duringlast 7 days, effect on workperformance, leisure activities,and sick leave.
Exposure: Questionnaireincluded: (1) abduction of armparticularly in sit-down dentistry,(2) work hr/day, (3) staticpostures.
All dentists:Neck andShoulder: 36%
Neck andShoulder andArm: 16%
17%
3%
2.1
5.4
1.3-3.0
1.6-17.9
Participation rate: 99%.
Analysis stratified by gender.
No difference in leisure time, smoking,systemic disease, exposure tovibration.
Symptoms increased with age infemale dentists only.
Duration of employment highlycorrelated with age (r=0.84, 0.89).
No relation between symptoms andduration of employment.
Equal problems dominant and non-dominant sides.
2-82
Table 2–8 (Continued). Epidemiologic studies evaluating work-related neck/shoulder disordersMSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Ohara et al.1976
Cross-sectional
and pro-spective
For cross-sectionalstudy: 399 cashregister operatorscompared with99 office machineoperators and410 other workers(clerks andsaleswomen). Allfemale.
For prospective study: 56 workers employed<7 months had testingpre- and post-intervention usingquestionnaire andphysical exam.
86 operators, newlyhired afterinterventions, also hadevaluation after10 months of working.
Outcome: Assessed bystandard health inventory andmedical examination (usedclinical classification according tothe committee on cervicobrachialdisorders of the JapanAssociation of Industrial Health,in Table 3 in the paper).
Periodic physical examperformed twice a year from1973. Primary exams performedon 371 operators. 130 (35%)received detailed exams.
Exposure: To repetitivemovements relocatingmerchandise across counter andbagging, involved muscle activityof the fingers, hands, and arms;extreme and sustained postures.
Interventions: (1) a 2-operatorsystem, 1 working the register,one packing articles, changingroles every hr; (2) continuousoperating time <60 min; max.working hr/day 4.5 hr;(3) 15-min resting period everyhr; (4) electronic cash registerswith light touch keyboardsubstituted for half of previouslyused
Cash registeroperators
Interventions didnot result inreduced musclefatigue of theneck, shoulders,and upper backbrought onpresumably bythe continuouslifting of theupper limbs.
Officemachineoperatorsand otherworkers(clerks andsaleswomen)
NR Participation rate: for prospectivestudy = 100%.
Participation rate: for cross-sectionalstudy, unable to calculate from datapresented.
Unknown whether examiners blindedto case status.
Interventions did not reducecomplaints in the shoulder region, butdid improve symptoms in the arms,hands, fingers, low back, and legs. The lack of improvement in theshoulder region was stated to be dueto the use of the same narrow checkstands, unsuitable counter height,and necessity of continuous lifting ofthe upper limbs.
Operators hired after theinterventions and then examined after10 months had less Grade I,II , or III occupational cervicobrachialdisorders in examination than thosehired before intervention.
Only 14.5% with >3 yearsemployment at worksite.
Narrow work space and counterheight not adjusted for height ofworker. mechanical cash registers.
2-83
Table 2–8 (Continued). Epidemiologic studies evaluating work-related neck/shoulder disordersMSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Ohlssonet al. 1995
Cross-sectional
Industrial Workers(n=82 females)exposed to repetitivetasks with short cyclesmostly far <30 sec.,usually with a flexedneck and armselevated and abductedintermittently; 68 formerworkers (meanemployment time 21years) who had leftthe factory during the 7years before thestudy; these workerswere compared to 64referents with norepetitive exposure attheir current jobs(female residents of anearby town currentlyemployed as customerservice, ordering andprice marking insupermarkets, asoffice workers (noconstant computerwork) or as kitchenworkers.
Outcome: Pain in the last 7 daysand PE diagnosing tension necksyndrome, cervical syndrome.
Tension neck: Tightness ofmuscles, tender spots in themuscles. Cervical syndrome:Limited neck movement, radiatingpain provoked by testmovements, decreasedsensibility in hands/fingers;muscle weakness of upper limb.
Muscle strength measured byMVC at elevation, abduction, andoutward rotation of both armsmeasured by dynamometer.
Exposure: Videotaping andobservation. Analysis ofpostures, flexion of neck (criticalangles 15E and 30E). 74workers videotaped $10 min.from back and sides. Averagecounts of two independentreaders for frequencies,duration, and critical angles ofmovement used.
Repetitive industrial work tasksdivided into 3 groups: (1) Fairlymobile work; (2) Assembling orpressing items; and (3) sorting,polishing and packing items.
Industrialworkers: 50%
Referents:16%
Allneck/shoulderclinicaldiagnoses(industrialworkerscompared toreferents):OR=2.7
Logistic Model:Repetitive workvs. none:OR=4.6
Age (57 vs.37): OR=1.9
Musculartensiontendency:(score 4.5 vs.1) : OR=2.3
Stress/worrytendency:OR=1.9
1.2-6.3
1.9-12
1.0-3.5
1.3-4.9
1.1-3.5
Participation rate: Current workers: 96% Past workers: 86%;Referents: 100%.
No exposure information available toexaminers, “not possible tocompletely blind the examiners.”
Questionnaire included individualfactors, work/environment,symptoms, psychosocial scales.
Videotape analysis revealedconsiderable variation in postureeven within groups performing similarassembling tasks.
Logistic models replacing repetitivework with videotape variables foundmuscular tension tendency and neckflexion movements significantlyassociated with neck/shoulderdiagnoses.
Inverse relationship between durationof industrial work and MSDs, largestOR in those employed <10 years.
Assembly group had high OR (6.7)with regard to neck/shoulder MSDcompared to referents.
Significant association between timespent in neck flexion positions <60E.
Weekly working time, workrotation, patterns of breaks,individual performance rate(piece rate).
Only exposure readings fromright arm were used.
2-84
Table 2–8 (Continued). Epidemiologic studies evaluating work-related neck/shoulder disordersMSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Punnett et al.1991
Cross-sectional
254 of 275 (92%)meatcutters andwrappers whoattended health andsafety training classes.
Workers fulfillingoutcome casedefinition (cases) werecompared to non-cases; also comparedto the U.S. industrialpopulation.
Outcome: Based on self-reported symptom survey. Cases were defined if they metthe following: $ 20 episodes inthe previous year or usualduration of $ one wk; reporteddate of pain onset afteremployment in the retail meatindustry; no history of systemicdisease related to soft tissuepain; and, no history of acuteinjury.
Exposure: Based on interviewand authors observations.
Exposure: Repetitive andstrenuous activities (it was notstated whether this was forspecific area or involved neckand all upper extremity areas) for0.5 to 8 hr/day in refrigeratedareas.
Cutters cut an average121 (+ 278) large pieces ofmeat/day filled 701 (+ 830 boats).
Wrappers filled374 (+ 602 boats/day). Wrapped1,299 (+ 1,365 boats andweighed 1,399 boats).
OverallPrevalenceNeck/Shoulder:53%
Õ Male: 1.8Female: 0.9
1.0-3.20.5-1.9
Participation rate: 92%.
Stratified by gender and age.
Neck/shoulder disorders associatedwith external duration of staticpostures (>5 sec.) or lifting $ 5 lbs.while abducting, flexing or extendingthe shoulder.
Neck/shoulder pain did not vary byjob category.
98% of respondents performed liftingtasks at work. “They judged lifting anaverage load/day was 41 (+ 23) lblifted 33 times and carried 9 feet. Heaviest load = 71 (+ 31 lb), lifted11 times and carried 9 feet/lift.” Listing an average load with a 40 to50% standard deviation can bemisleading.
Neck/shoulder cases lifted both the“typical” and “heaviest” loads withgreater frequency than non-cases.
Association was found for extendedduration of and lifting weight inabduction/flexion and extension ofthe shoulder.
2-85
Table 2–8 (Continued). Epidemiologic studies evaluating work-related neck/shoulder disordersMSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Rossignolet al. 1987
Cross-sectional
191 Computer and dataprocessing services,public utilities ofMassachusetts StateDepartment, at 38 worksites selected atrandom fromMassachusettsemployers of >50workers.
28 of the 191 did notuse a computer.
Outcome: Self-administeredquestionnaire case defined as: Neck pain, stiffness, or sorenessoccurring almost always ormissed work due to neck pain,stiffness or soreness.
Exposure: Self-reports ofnumber of hr worked each daywith a keyboard machine with aVDT. Subjects selected afterobservation of worksite.
½ to 3 hr of VDTuse/day (n=31):39%
4 to 6 hr of VDTuse/day (n=28):57%
7 or more hr ofVDT use/day(n=104): 61%
No VDT use(n=28):25%
Up to 3 hr ofVDT usecompared to 0hr of use:OR=1.8
4 to 6 hr of VDTuse comparedto 0 hr of use:OR=4.0
>7 hr of VDTuse comparedto 0 hr of use:OR=4.6
0.5-6.8
1.1-14.8
1.7-13.2
Participation rate: In 6 industrygroups 67 to 100%.
Participation rate: For individualclerical workers; 94 to 99%.
Assessed magnitude of confoundingby age, cigarette smoking, industry,educational VDT training.
Study presented to participants as a“general health” survey (as opposedto an occupationally related survey)to avoid observation bias.
2-86
Table 2–8 (Continued). Epidemiologic studies evaluating work-related neck/shoulder disordersMSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Ryan andBampton1988
Cross-sectional
143 data processoperators; using a 0 to10 point scale, thegroup with symptomscores of 8 or above(n=41) weredesignated "cases,"and were compared togroup with symptomscores of 2 or less(n=28).
Outcome: Based on symptomsoccurring three or more times/wkwith no physical exam signs, or$ weekly symptoms withphysical exam signs of muscletenderness or hardeningpresent.
Cases were selected by havinga combination of symptoms in thelower arm and shoulder/neckarea meeting a summary scoreof eight or more. These caseswere compared to a comparisongroup with a score of 2 or less.
Exposure: Ergonomicassessment measuring anglesand distances of each operatorseated at his/her workstationperformed; Questionnaireresponses to: Time spent incurrent job, time spent altogetherkeying or typing work, training inthe adjustment of their chair,desk, or keyboard.
Shoulder: 44%symptom only
Neck: 43%symptoms only
Neck/shouldersymptomsoccurring $ 3times weeklywith no signs orweekly withsigns: 44%
Comparisongroup hadsymptomscores <2.
More non-cases trained inadjustment ofchairs
Cases withhigher scoresof visualdiscomfort
Cases felt therewas notenough time forrest breakscompared tonon-cases
Cases hadmore boredom,more workstress, andneeded to pushthemselves >3times/wk; lowerpeer cohesion,autonomy,clarity in theauthoritystructure.Higher staffsupport andwork pressure.
p<0.05
p<0.05
p<0.05
p<0.05
Participation rate: 99%.
Interviewers blinded to questionnaireresponses.
Height, weight, sex, age, maritalstatus, parental status evaluated andnot found to be confounders.
Handedness, time spent in currentjob, time spent altogether keying ortyping work, training in adjustment ofkeyboard and desk evaluated in twogroups and no significant differencesfound.
Psychosocial and work environmentscales included pertaining to jobsatisfaction as well as the WorkEnvironment Scale [R. Moos 1974].
Authors diagnosed “myalgia” asdiffuse muscle pain and tenderness.
2-87
Table 2–8 (Continued). Epidemiologic studies evaluating work-related neck/shoulder disordersMSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Tola et al.1988
Cross-sectional
828 Machineoperators; 658carpenters;compared to 657 officeworkers; All male,ages 25 to 49 years.
Outcome: Postal questionnaireon neck or shoulder symptomsfrequency in last year, andinfluence on work methods, dailyduties and activities or leisuretime hobbies. Pain DrawingDiagram used to distinguish bodyareas. For logistic regressionmodel 12 month prevalence ofneck and shoulder symptoms on8 days or more.
Exposure: Exposure based onoccupation: Machine operatorsknown to be exposed to staticloading due to prolonged sittingand low-frequency whole bodyvibration, fast work pace, andupper trunk twisting. Carpentersexposed to dynamic physicalwork with varying postures andloads, static loading ofneck/shoulder-arm, and maleoffice workers, of whom only40% were performing routineoffice tasks.
Daily symptoms:
machineoperators: 11%carpenters: 8%
Change workmethods:
machineoperators: 19%carpenters: 21%
Dailysymptoms:
officeworkers: 2%
Change workmethods:
officeworkers:10%
Machine vs.office:OR=1.7
Carpenter vs.office:OR=1.4
Machine vs.carpenter:OR=1.3
Use of twistedor bentpostures duringworkLittle: OR=1.0Moderate:OR=1.2Rather much:OR=1.6Very much:OR=1.8
Working in adraft:No: OR=1.0Yes: OR=1.1
Job satisfac-tionVery good:OR=1.0Rather good:OR=1.1Moderate orpoor: OR=1.2
Age (years)25 to 29:OR=1.030 to 34:OR=1.235 to 39:OR=1.340 to 44:OR=1.545 to 49:OR=1.6
1.5-2.0
1.1-1.6
1.1-1.4
1.0-1.5
1.4-1.9
1.5-2.2
1.0-1.3
1.0-1.3
1.1-1.4
1.0-1.5
1.1-1.6
1.3-1.8
1.4-1.9
Participation rate: 74% machineoperators, 67% carpenters, 67%office workers.
Adjusted for years in occupation,age. Interaction terms tested for,none found.
Education, general health, and leisuretime activities, car driving included inanalysis.
Study restricted to males aged 25 to49 years.
Education status (“$ some vocationalschool” compared to “no > somecourses”) statistically significant formachine operators’ and carpenters’reporting of symptoms.
2-88
Table 2–8 (Continued). Epidemiologic studies evaluating work-related neck/shoulder disordersMSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Vihma et al.1982
Cross-sectional
40 Sewing machineoperators with shortwork cycles comparedto 20 seamstresses.
Outcome: Neck or shouldercomplaints defined byquestionnaire: Recurrent pain oraching in present work (during orafter work).
Exposure: Observation andinterview; hr continuously sitting,standing time, survey of workpostures, length of work cycle. Sewing machine operator cycletime was 30 to 60 sec. induration. Seamstresses hadlonger cycle.
Sewing machineoperators withneck/shouldercomplaints: 98%
Seam-stresseswith neck/shouldercomplaints:60% PRR = 1.6 1.1-2.3
Participation rate: Not reported.
Random selection of participants.
Cases and referent group matchedfor age and duration of employment.
Sewing machine operators found tohave significantly greater static workcompared to seamstresses.
2-89
Table 2–8 (Continued). Epidemiologic studies evaluating work-related neck/shoulder disordersMSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
Viikari-Juntura et al.1991a
Cohort 154 subjects (72female, 82 male) fromHelsinki, Finland. Subjects were part ofa longitudinal studypopulation that startedin Finland in 1955; andfrom 1961 to 1963. During that time, 1084subjects underwentcross-sectionalexamination. In 1985, aquestionnaire wassent to all subjects;801 (74%) responded. Of the respondents,180 lived in the Helsinkiarea. It was from thisgroup that162 responded. Eightwere excluded due toillnesses. Theproportions of thehighest income levelsin the sampleexceeded the Finnishpopulation.
Outcome: Based onQuestionnaire data: Ache, pain,stiffness, numbness in theirneck/shoulder in last 12 months. Visual analogue scale ofintensity, disability. Severe neckdisability: Pain for >7 days in last12 months and mean disabilityindex $ 15.
Physical exam (P.E.): Two testsfor cervical nerve rootinvolvement, neck compressiontest, shoulder abduction test. Because of small number ofabnormal physical findings, theP.E. was eliminated from analysis
Exposure: Questionnaire: Amount of work with handsoverhead, work in forward bentposition, work in twisted or bentposition.
10% of femaleand 2% of malereported severeradicular neckpain
21% of femaleand 2% of malereported anytype of severeneck/shoulderpain
Õ Female: Severeneck/shouldersymptoms vs.no symptomsAlexithymia(low verbalproductivity)(continuous):OR=1.02
Social confi-dence (mode-rate fears vs.no fears):OR=0.04(much fear vs.no fears):OR=1.4
Type of income(monthlysalary): OR=0.5
Sense ofcoherence(continuous):OR=0.95
Twisted or benttorso(>3 hr/day vs.<1 hr/day:
OR= 0.9>3 hr/day vs.<1hr/day
Sitting in aforwardposture 1-3hr/day vs.<1hr/day:OR=10.7 >3hr/day vs. <1hr/day: OR=1.5
0.97-1.1
0.0-4.5
0.05-42.2
0.05-5.2
0.9-0.99
0.8-10.0
.4-291
0.07,29.6
Participation rate: 90%.Controlled for physical and creativehobbies, no interactions seen.
Because of low numbers, maleswere not included in analysis.
Subjects comprised of mostly highsocioeconomic status who reportedlight physical workloads.
Data collection in 1955 to 1963: Intelligence, alexithymia, socialconfidence, hobbies, motordevelopment, verbal development,level of education of parents, type ofincome of family.
Data collection in 1985: Questionnaire on family relationships,socioeconomic status, work history,characteristics of present work, jobsatisfaction, mental resources.
Data collection in 1986 to 1987:Questionnaire: Physicalcharacteristics of work, amount ofphysical exercise, illnesses, trauma.
Measurements taken in adolescence,such as intelligence, alexithymia,social confidence, hobbies andsocioeconomic status of the familyshowed no consistent associationwith neck/shoulder symptoms inadulthood.
2-90
3-1
CHAPTER 3Shoulder Musculoskeletal Disorders:Evidence for Work-Relatedness
SUMMARYThere are over 20 epidemiologic studies that have examined workplace factors and their relationship toshoulder musculoskeletal disorders (MSDs). These studies generally compared workers in jobs with higherlevels of exposure to workers with lower levels of exposure, following observation or measurement of jobcharacteristics. Using epidemiologic criteria to examine these studies, and taking into account issues ofconfounding, bias, and strengths and limitations of the studies, we conclude the following:
There is evidence for a positive association between highly repetitive work and shoulder MSDs. Theevidence has important limitations. Only three studies specifically address the health outcome of shouldertendinitis and these studies involve combined exposure to repetition with awkward shoulder postures orstatic shoulder loads. The other six studies with significant positive associations dealt primarily withsymptoms. There is insufficient evidence for a positive association between force and shoulder MSDsbased on currently available epidemiologic studies. There is evidence for a relationship between repeatedor sustained shoulder postures with greater than 60 degrees of flexion or abduction and shoulder MSDs.There is evidence for both shoulder tendinitis and nonspecific shoulder pain. The evidence for specificshoulder postures is strongest where there is combined exposure to several physical factors like holding atool while working overhead. The association was positive and consistent in the six studies that useddiagnosed cases of shoulder tendinitis, or a constellation of symptoms and physical findings consistentwith tendinitis, as the health outcome. Only one [Schibye et al. 1995] of the thirteen studies failed to find apositive association with exposure and symptoms or a specific shoulder disorder. This is consistent withthe evidence that is found in the biomechanical, physiological, and psychosocial literature.
There is insufficient evidence for a positive association between vibration and shoulder MSDs based oncurrently available epidemiologic studies.
INTRODUCTION
Shoulder MSDs and their relationship to workrisk factors have been reviewed by severalauthors [Hagberg and Wegman 1987;Kuorinka and Forcier 1995; Sommerich et al.1993; Winkel and Westgaard 1992]. Hagbergand Wegman [1987] attributed a majority ofshoulder problems occurring in a variety ofoccupations to workplace exposure. Kuorinkaand Forcier [1995] looked specifically atshoulder tendinitis and stated that theepidemiologic literature is “most convincing”regarding
work-relatedness, especially showing anincreased risk for overhead and repetitivework.
The focus of this review is to assess evidencefor a relationship between shoulder tendinitisand workplace exposures to the following:awkward postures, forceful exertions, repetitiveexertions, and segmental vibration. Alsoincluded are studies relevant to shoulderdisorders—as defined by a combination ofsymptoms and physical examination findings orby symptoms alone, but not specifically definedas tendinitis—and those studies for which
3-2
the health outcome combined neck andshoulder disorders, but where the exposurewas likely to have been specific to the shoulder.Chapter 2 discusses studies involving neck-shoulder disorders where assessment ofexposure was likely specific to the neck region.
Pertinent information about the 39 reviewedstudies is presented in several ways. Detaileddescriptions of the studies are provided inTable 3-5. The text of this section on shouldersis organized by exposure risk factor. Thediscussion within each risk factor is organizedaccording to criteria presented on Pages 1-1 to1-10 of the Introduction. Conclusions arepresented with respect to the specific MSD ofconcern, shoulder tendinitis.
REPETITION
Definition of Repetition for ShoulderMSDsStudies that addressed the physical factor ofrepetition and its relation to shoulder MSDswere included in this review. Studies usuallydefined repetition, or repetitive work, for theshoulder as work activities that involvedcyclical flexion, extension, abduction, orrotation of the shoulder joint. Repetitivenesswas defined in four different ways in thereviewed studies: (1) the observed frequency ofmovements past pre-defined angles of shoulderflexion or abduction, (2) the number of pieceshandled per time unit, (3) short cycletime/repeated tasks within cycle, and (4) adescriptive characterization of repetitive workor repetitive arm movements. Some of thestudies that examined repetition as a risk factorfor shoulder MSDs had several concurrent orinteracting physical work load factors.Therefore, repetitive work should not be
considered the primary exposure factor,particularly independent of posture. Somestudies indirectly inferred shoulder repetition bycharacterizing hand, wrist, and forearmmovements.
Studies Reporting on the Associationof Repetition and Shoulder MSDsThree of the reviewed studies reported resultson the association between repetition andshoulder tendinitis [English et al. 1995; Ohlssonet al. 1994, 1995]. For all three studies, someor all of the results were for associations with acombined exposure to repetition and awkwardposture. Six additional studies reported resultson the association between repetition and non-specific shoulder disorders [Sakakibara et al.1995], non-specific shoulder symptoms[Andersen and Gaardboe 1993a; Ohlsson et al.1989], combined neck-shoulder disorders[Bjelle et al. 1981; Chiang et al. 1993] orcombined neck-shoulder symptoms [Kilbom etal. 1986; Kilbom and Persson 1987].
Studies Meeting the Four Evaluation Criteria
Four studies met all four of the criteria [Chianget al. 1993; Kilbom et al. 1986; Ohlsson et al.1994, 1995] (Table 3-1, Figure 3-1). Chianget al. [1993] studied workers in the fishprocessing industry in Taiwan. The healthoutcome of “shoulder girdle pain” was definedas self-assessed symptoms of pain in the neck,shoulder or upper arms, and signs of muscletender points or palpable hardenings uponphysical examination. Pain referred from anerve root or other spinal source was includedin the case definition. The force requirements ofthe jobs were estimated by surface
3-3
electromyographs (EMGs) in the forearm flexormuscles. This is not a direct measure ofshoulder muscle activity. There may be norelationship between the level of activity in theforearm and shoulder girdle muscles. Threecategories, based on both force andrepetitiveness, were used as the exposureoutcome: Group I (low force, lowrepetitiveness), Group II (high force or highrepetitiveness), and Group III (high force andhigh repetitiveness). Force was also evaluatedindependently in multivariate analyses.
Kilbom et al. [1986] performed a prospectivestudy in which female employees in theelectronics manufacturing industry wereobserved for a 2-year period. The healthoutcome in the neck, shoulder, or arm regionswas based on symptoms and physical findings.Symptom severity was coded on the basis of itscharacter, frequency, and/or duration. Changesin severity status at follow-up evaluations wereused as the dependent variables in multipleregression analyses. Neck, shoulder, and upperarm posture was determined by VIRA.Although the health outcome combinedsymptoms from different body regions,knowledge of biomechanical theory can beused to identify significant predictors related tothe shoulder symptom severity.
For the two Ohlsson et al. [1994, 1995]studies, the authors reported that the examinerscould not be completely blinded to exposedversus referent status, but that a standardprotocol was followed and observer bias waslikely to have been minimal. As examiners wereblinded to objective exposure measures,analyses testing associations between neck-shoulder disorders and specific postures wouldnot have been biased [Ohlsson et al. 1995].
In the first of the Ohlsson et al. studies, a cross-sectional study, women in the fish industry werecompared to a control population of womenemployed in municipal workplaces in the sametowns [Ohlsson et al. 1994]. Diagnoses ofshoulder disorders (e.g., tendinitis,acromioclavicular syndrome, frozen shoulder)were made on the basis of symptomsdetermined by interview and a physical exam.Exposure evaluation of each work task held bythe fish industry population was evaluated withergonomic workplace analysis (EWA). Tendifferent factors were rated on a scale from 1 to5 and the combined ratings were used as aprofile of the work task. Based on this profile,the authors reported that fish industry work wasfound to be “highly repetitive” and to include“poor work postures.”
Ohlsson et al. [1995] compared a group ofwomen who performed industrial assemblywork to a referent group of women from anearby town who were employed in jobscharacterized as having varied and mobile worktasks. One examiner assessed signs andsymptoms. The examiner was blinded tospecific exposure information, but notcompletely blinded to factory worker versusreferent group status. Shoulder tendinitisincluded supraspinatus, infraspinatus, andbicipital tendinitis. Another health outcomecombined neck and shoulder disorders (tensionneck, cervical syndrome, thoracic outletsyndrome, frozen shoulder, tendinitis,acromioclavicular syndrome). In a descriptiveassessment, it was reported that the work tasksin the study group involved repetitive armmovements with static muscular work of the
3-4
neck and shoulder muscles. The percentage oftime spent in specific upper arm postures wasdetermined from videotaped observation of 74(out of 82) workers. The average result fromtwo independent videotape analyses was used.Posture category demarcations included 0, 30,and 60 degrees for arm elevation, and 30, 60,and 90 degrees for arm abduction.
Studies Not Meeting the Four EvaluationCriteria
Bjelle et al. [1981] compared cases with acute,non-traumatic shoulder-neck pain to age- andsex-matched, paired controls. To determineexposure, each case and control was filmedand a biomechanical analysis was performed todetermine the frequency and duration ofshoulder abduction or forward flexion > than60 degrees.
In the study by English et al. [1995], caseswere determined by medical diagnosis andcontrols were selected from patients evaluatedat specified orthopedic clinics. For statisticalanalyses, all diagnoses were grouped byanatomical site. The diagnoses for shouldercases were rotator cuff injury, rupture of longhead of biceps, shoulder capsulitis, andsymptomatic acromioclavicular arthritis. It isassumed that shoulder tendinitis is included inthis group. Exposure measures weredetermined by a standardized interviewconducted by an interviewer who was“unaware of the case-control status of theindividual wherever this was possible.”
In a study by Sakakibara et al. [1995], thehealth status of a group of women farmworkers was assessed during the performanceof two different tasks, with a1-month interval between the tasks. The health
outcome was defined by self-assessedsymptoms of shoulder stiffness and pain and aphysical examination for muscle tenderness andjoint pain on movement. Whether the examiningphysician was aware of the prior hypothesisregarding differing exposures between the twotasks (bagging pears versus bagging apples)was not stated. Exposure was based on self-report of the number of hours per day spentbagging, the number of pears or apples baggedper day, and the total number of days spentbagging each fruit. One worker was observedfor 3 hours while performing each bagging job,with repeated goniometric measures ofshoulder forward flexion angles done eachminute. While there was no difference in thetotal number of days or number of hours perday spent bagging each fruit, significantly morepears than apples were bagged per day. Theproportion of time spent with the angle ofshoulder forward flexion greater than 90degrees was significantly larger when baggingpears (75%) than when bagging apples (41%).
One study did not meet any of the criteria. In across-sectional study by Ohlsson et al. [1989],the exposed population was factory employeeswho produced and assembled plasticcomponents. Work exposure wascharacterized as “repetitive arm and handmovements in constrained work postures.” Thereferent population was composed of womenrandomly sampled from the general populationin a nearby area. The health outcome wasdetermined by self-reported symptoms ofshoulder pain during the previous seven days.The exposure measure was the self-reportednumber of items completed per hour. The rangewas from less than 100 items completed perhour (slow category) to more than 700 items
3-5
per hour (very fast category). Self-reportingwas believed to be accurate because workerswere paid by the piece.
Strength of Association:Repetition and Shoulder MSDs
Using the data presented in the study byOhlsson et al. [1994], for supraspinatus,infraspinatus, or bicipital tendinitis the oddsratio (OR) for working in the fish industry(repetitive work, poor posture) was calculatedas 3.03 (95% CI 2.5–7.2). For shouldertendinitis alone, the PRR was calculated as 3.5(95% CI 2.0–5.9). For clinical diagnoses of theneck and shoulder, the OR for working in thefish industry versus the referent population was3.2 (95% CI 2.0–5.3).
Using data presented in the study by Ohlsson etal. [1995] for supraspinatus, infraspinatus, orbicipital tendinitis, the OR for being anassembly worker (repetitive arm movementswith static load on shoulders) versus thereferent population was 4.2 (95% CI1.35–13.2). For neck-shoulder disorders, theOR for being an assembly worker versus thereferent group was 5.0 (95% CI 2.2–11.0).
Using multiple logistic regression analysis withage, gender, and force as covariates, Chiang etal. [1993] found that highly repetitive upperextremity movements were associated withshoulder girdle pain (OR 1.6, 95% CI1.1–2.5). When tested in the same model withforce and repetition, the interaction term forforce and repetition was also significant (OR1.4, 95% CI 1.0–2.0). Several factors couldhave resulted in an underestimation of thestrength of association: no requirement thatsymptoms had begun on current job means thatsome symptomatic workers may havetransferred to lower risk jobs. Relative to
shoulder MSDs, the major limitation of thisstudy was that the exposure assessment wasnot specific to movement at the shoulder jointand may therefore have either over- orunderestimated repetition at the shoulder. Insome cases the exposure assessment may havebeen a measure of repetitive upper armmovements, but it may also have been ameasure of repetitive hand and distal upperextremity activity occurring in the context of astatic load on the shoulder muscles.
For the shoulder diagnoses used to form theirgroup of cases, English et al. [1995] found anassociation with repeated shoulder rotation withan elevated arm (OR 2.30, p< 0.05). They alsofound what appeared to be a protective effectassociated with elbow flexion (OR 0.4, 95%CI 0.2–0.8). This effect was greatest at lowamounts of daily cumulative exposure to elbowflexion; the protective effect decreased (RRincreased) as the number of hours of total dailyelbow flexion increased. In a laboratory studyof shoulder muscle activity in relation todifferent combinations of shoulder and elbowjoint postures (a total of 21 different postures),Herberts et al. [1984] found that humeralrotation and elbow flexion had insignificanteffects on shoulder muscle activity. However,the postures tested by that study werestationary, whereas the associations reportedby English et al. [1995] appear to be related torepetitive movements.
For symptoms of shoulder pain within theprevious 7 days, the OR for assembly workersversus the referent group was 3.4 (95% CI1.6–7.1) [Ohlsson et al. 1989]. A significantlyhigher proportion of the farm workers studiedby Sakakibara et al. [1995]
3-6
had signs of shoulder muscle tenderness whilebagging pears than while bagging apples. Therewas no way to analyze the relative contributionto risk of repetitive shoulder exertions(increased number of pears picked per day)and awkward posture (greater portion of eachday spent with extreme forward flexion whenpicking pears).
Consistency of Association
Repetitiveness was defined in four differentways in the reviewed studies: (1) the observedfrequency of movements past pre-definedangles of shoulder flexion or abduction, (2) thenumber of pieces handled per time unit, (3)short cycle time/repeated tasks within cycle,and (4) a descriptive characterization ofrepetitive work or repetitive arm movements.
Repetition Characterized as Frequency ofMovements Past Pre-Defined ShoulderAngles
Bjelle et al. [1981] and Ohlsson et al. [1995]found a significant positive association betweenthe prevalence of neck-shoulder disorders andthe frequency of upper arm movements past 60degrees of flexion or abduction. English et al.[1995] found a significant association betweendiagnosed cases of shoulder disorders andrepeated shoulder rotation with an elevated armposture.
Repetition Characterized as the Number ofPieces Handled per Time Unit
A significant positive association was foundbetween both nonspecific shoulder symptoms[Ohlsson et al. 1989] and nonspecific shoulderdisorders [Sakakibara et al. 1995] and thenumber of pieces handled per hour or per day.
Repetition Characterized as Short Cycle Time
Chiang et al. [1993] found a significantassociation between a very short or repetitivecycle (<30 seconds or >50% spent repeatingsame task) and shoulder girdle pain.
Repetition Characterized Descriptively
Three studies by Ohlsson et al. found asignificantly higher proportion of shoulderMSDs in exposed populations with workcharacterized as involving repetitive arm andhand movements than in referent populations[Ohlsson et al. 1989, 1994, 1995].
Repetition Combined with Static ShoulderLoad
Except for the study by Sakakibara et al.[1995], in which the increased number of pearsbagged per day was associated with anincreased proportion of the work day spentwith extreme shoulder flexion, the studies usingmeasures of piece work or repetitive armmovements as the exposure outcome did notspecify which joints or body regionsparticipated in the repetitive action. Ohlsson etal. [1995] described the assembly workperformed by the exposed population ascombining repetitive arm movements with astatic shoulder load. It is possible that theassociation between piece work, short cycles,or repetitive hand-arm movements andshoulder disorders reported by the otherauthors is related to a sustained, static load onthe shoulder muscles as the upper arm isstabilized in a posture of mild to severe flexionor abduction, while repetitive movements areperformed by the hand-wrist-forearm.
3-7
Temporal RelationshipIn the prospective study by Kilbom et al. 1986;Kilbom and Persson 1987; and Jonsson et al.1988 the number of shoulder elevations perhour was a strong predictor for a change tosevere status at the 1- and 2-year follow-upevaluations. Although the change in statusincluded problems in the neck and arm, as wellas the shoulder, it is reasonable to assume thatrepetitive shoulder elevations would have hadthe greatest effect on disorders of the shoulder.
Several studies with a cross-sectional designused techniques to determine whether thehealth outcome of interest had occurred since,or was present during, exposure tohypothesized risk factor(s) of interest. Casedefinitions which required a positive physicalexamination finding [Chiang et al. 1993;Ohlsson et al. 1994, 1995] or where symptomshad occurred within the recent past [Chiang etal. 1993; Ohlsson et al. 1989, 1994] weredesigned to focus on disorders most likely tohave been caused or aggravated by currentwork exposures.
Exposure-Response Relationship
Chiang et al. [1993] found a significantincreasing trend in the prevalence of shouldergirdle pain from Group I (low force, lowrepetitiveness) to Group III (high force, highrepetitiveness). However, the health outcomewas not specific to shoulder disorders, and theexposure categories combine increasingrepetitiveness—as defined by either less than a30-second cycle time or a repeated task withinthe job cycle—and increasing forearm flexormuscle activity. Ohlsson et al. [1995] found thatneck and shoulder disorders among assemblyworkers were significantly
associated (p<0.05) with both the number ofarm elevation movements from less than togreater than 60 degrees and the number of armabduction movements from less than to greaterthan 60 degrees. Bjelle et al. [1981] found thatthe frequency of shoulder abduction or forwardflexion (past 60 degrees) was significantlygreater (p<0.005) for cases with neck-shoulderdisorders than for controls.
In the study of assembly workers by Ohlsson etal. [1989], the number of pieces completed perhour was categorized as follows: slow: <100,medium: 100–299, fast: 300–699, very fast:>700. In this study, the ORs are shown in afigure, rather than reported in the text.Compared with the slow-paced group, theodds for symptoms of shoulder pain isapproximately seven times that for thoseworkers in the medium-paced group andapproximately nine times that for those in thefast-June 26, 1997 pace group. While adjustingfor age and length of employment, the OR forshoulder pain was significantly higher for themedium- and fast-paced groups than for theslow-paced group (p=0.0006). The OR for thevery fast-paced group compared to the slow-paced group was between 1.0 and 2.0 and wasnot significantly different from the slow-pacedgroup. The authors hypothesized thatsymptomatic workers may have self-selectedout of the very fast paced jobs or that otherunknown factors may have mitigated the effectsof work pace.
When comparing fish industry workers to thereference population, Ohlsson et al. [1994]found that among those workers younger thanage 45, the ORs for disorders of the neck andshoulders were significantly elevated and
3-8
increased with duration of employment [0–5years, OR 3.2 (95% CI 1.5–7.0); >5 years,OR 10 (95% CI 4.5–24)]. In their study ofassembly workers, Ohlsson et al. [1989] founda statistically significant increase in the odds forpain in the shoulder with duration ofemployment (p=0.03) which was dependent onage. The increase with duration of employmenthad a steeper slope for younger (<35 years)assembly workers than for the older subgroup(i.e., among those workers employed for shortdurations, older women had more symptoms,and among those workers employed for longdurations, younger women had moresymptoms). This was thought to be a reflectionof both survivor bias as well as the possibilitythat older new hires may have experienced arelatively more rapid onset of symptomaticproblems than do younger women.
Coherence of EvidenceRepetitive movements of the upper extremityinvolving flexion or abduction of theglenohumeral joint would increase thefrequency of effects such as fatigue and tendoncirculation disruption hypothesized to occur asa result of such postures. These effects couldbe magnified by the addition of a hand-heldload. Repetition may also be solely related tothe development of tendinitis. In a laboratorystudy, Hagberg [1981] induced acute shouldertendinitis in female subjects performingrepetitive shoulder elevations for one hour. Sixfemale students, ages 18–29, all developedshoulder tenderness (two with tendinitis) whenexposed to 15 shoulder flexions (from 0 to 90degrees) per minute for 60 minutes whileholding up to 3.1 kg (6.4 lb) of weight.
Some of the significant associations reportedmay have been related to exposure to repetitivework in the distal upper extremity while theshoulder and upper arm were maintained in astatic posture [Chiang et al. 1993; Ohlsson etal. 1989, 1994, 1995]. Winkel and Westgaard[1992] have pointed out that, “It is not possibleto use the arm/hand without stabilizing therotator cuff girdle and the glenohumeral joint.Therefore, work tasks with a demand ofcontinuous arm movements generate loadpatterns with a static load component.”
The finding that the supra- and infraspinatusmuscles were particularly prone to fatigue whensubjects performed overhead work ledHerberts et al. [1984] to hypothesize that therotator cuff muscles may develop highintramuscular pressures at relatively lowcontraction levels. These high intramuscularpressures could lead to an impairment ofintramuscular circulation, which couldcontribute to the early onset of fatigue.Intramuscular pressure increases with themuscle contraction level, and impairedcirculation has been demonstrated at levels ofcontraction as low as 10–20 percent ofmaximal voluntary contraction (MVC).[Hagberg 1984].
The increased pressure in rotator cuff musclesand increased pressure on the supraspinatustendon may trigger two different events that areboth related to impaired microcirculation. Theimpaired microcirculation in the tendon mayalso result from tension within the tendonproduced by forceful muscle contractions[Rathburn and Macnab 1970]. Aninflammatory infiltrate with increased
3-9
vascularity and edema within the rotator cufftendons, especially the supraspinatus tendonmay be a result of or a contributor to theprocess. If the inflammation process issufficiently intense, then shoulder tendinitis mayoccur. If the process is less intense, and morechronic, then it may contribute to adegenerative process in the tendons of therotator cuff. In the muscles of the rotator cuff,the impaired microcirculation may lead to smallareas of cell death. A reasonable hypothesis isthat repeated or sustained episodes of muscleischemia result in localized cell death andpersistent inflammation.
Neither of these proposed models for shouldermuscle pain or tendinitis suggest that all muscleactivity is potentially harmful. Both muscles andtendons are strengthened by repeated activity ifthere is sufficient recovery time. However, themodels present plausible mechanisms by whichwork tasks with substantial shoulder abductioncould contribute both to shoulder pain andtendinitis.
There is evidence of a relationship betweenshoulder tendinitis and highly repetitive work.However, there are several limitations to theevidence. In the three studies for which thehealth outcome was shoulder tendinitis, theexposure combined repetition with awkwardshoulder posture and/or a static shoulder load[English et al. 1995; Ohlsson et al. 1994,1995]. Five out of the eight studies reviewedused either nonspecific shoulder disorders,nonspecific shoulder symptoms or combinedneck-shoulder disorders as the health outcome.
Despite the limitations of the evidence,significant and positive relationships betweenrepetitiveness, regardless of the measurement
method, and shoulder MSDs or symptomswere found in all studies. Of the eight studies inwhich the effect of repetition was examined,three studies found ORs above 3.0 [Ohlsson etal. 1989, 1994, 1995] and three studies foundORs from 1.0 to 3.0 [Chiang et al. 1993;English et al. 1995; Sakakibara et al. 1995].The remaining studies were prospective studies[Jonsson et al. 1988; Kilbom and Persson1987] or studies that reported risk indicatorsother than OR [Bjelle et al. 1981].
In none of these studies is it likely that age, themost important personal characteristicassociated with shoulder tendinitis and othershoulder disorders, or nonoccupational factorssuch as sports activities, caring for youngchildren, or hobbies explained theseassociations. There is evidence of a relationshipbetween shoulder tendinitis and highly repetitivework.
FORCE
Definition of Force for ShoulderMSDs
Studies that examined force or forceful work orheavy loads to the shoulder, or describedexposure as strenuous work involving theshoulder abduction, flexion, extension, orrotation that could generate loads to theshoulder region were also included. Most of thestudies that examined force or forceful work asa risk factor for shoulder symptoms or tendinitishad several concurrent or interacting physicalwork load factors. However, there is still aneed to summarize present knowledge aboutthe relationships between forceful work andshoulder MSDs. This section summarizes thatknowledge, while acknowledging that otherfactors can modify the response.
3-10
Neck-shoulder disorders are discussed inChapter 2.
Studies Reporting on the Associationof Force and Shoulder TendinitisThere are five studies which reported results onthe association between force and adverseshoulder health outcomes (Table 3–2, Figure3–2). The epidemiologic studies that addressedforceful work and shoulder MSDs tended tocompare working groups by classifying theminto broad categories based on an estimatedamount of resistance or force of exertion and acombination of estimated rate of repetition[Andersen and Gaardboe 1993a; Chiang et al.1993] or in terms of overall load [Herberts etal. 1984; Stenlund et al. 1992; Wells et al.1983].
Studies Meeting the Four Evaluation Criteria
Chiang et al. [1993] studied workers in the fishprocessing industry. (This study was describedin detail in the section on shoulder MSDs andrepetition.) Chiang et al. [1993] did not reportan exposure specific to the shoulder.
Studies Not Meeting the Four EvaluationCriteria
Andersen and Gaardboe [1993a] performed across-sectional study in which a cohort ofsewing machine operators was compared to arandom sample of women in the generalpopulation of the same region. Chronicshoulder pain was defined as a havingexperienced a continuous pain episode lastingmore than 1 month and either daily pain or painlasting more than 30 days in the same locationwithin the previous year (per self-administeredquestionnaire). In order to compare the currentexposure of sewing machine operators andthose in the control group, the authors’
experience and knowledge of the jobs wereused to assign job titles to exposure categoriesbased on crude assessments of force andrepetitiveness. High exposure wascharacterized as a combination of highrepetitiveness (activity repeated several timesper minute) and low or high force, or mediumrepetitiveness (activity repeated many times perhour) and high force. Medium exposure wascharacterized as medium repetitiveness and lowforce, or low repetitiveness (jobs with morevariation) and high force. Those in teaching,academic, self-employed, or nursingprofessions were classified as low exposure.The exposure classification scheme in this studydoes not allow separation of the effects of forcefrom those of repetition. More sewing machineoperators than referents were considered tohave high exposure (41% versus 15%), butmore in the referent population wereconsidered to be in the medium exposure group(44% versus 22%). Because the outcome ofinterest was duration of historical exposure,current exposure was included as anindependent variable in multivariate regressionanalyses.
Herberts et al. [1984] added to the 1981 studyby comparing the prevalence of supraspinatustendinitis between plate-workers and officeclerks. Tendinitis in welders was determined bya combination of self-reported symptoms andpositive physical examination findings. The onlyinformation given regarding plate-work is that itis dynamic in character. It is presumed thatplate-workers handled heavy loads morefrequently than office clerks.
In a cross-sectional study, the prevalence ofosteoarthrosis in the acromioclavicular joint,
3-11
as determined by radiography, was comparedamong three groups of workers in theconstruction industry [Stenlund et al. 1992].The three groups were bricklayers, rockblasters, and construction foremen. Theforemen did not perform manual workcurrently, or in the past, and were consideredthe control population. A standardizedinterview was used to determine exposurefactors, including job title and the sum of loadslifted during all working years (expressed intonnes). Analyses were performed separatelyfor right and left sides.
In a study of letter carriers, Wells et al. [1983]evaluated the effect of a load carried on theshoulder. Letter carriers, who carry a load andwalk, were compared to gas meter readers(who walk without carrying a load) and postalclerks. Utilizing information from telephoneinterviews, points were assigned to symptomcharacteristics such as frequency, length ofepisodes, and interference with work ability.Case definition required a report of recurrentshoulder pain with greater than 20 points. Asubset of letter carriers had experienced anincreased load during the previous year. (ThePostal Service had increased maximum weightcarried from 25 to 35 pounds, but not alllocations had implemented this change.)
Strength of Association—Forceand Shoulder MSDsThe studies are presented in alphabetical orderin Table 3-2. Results of studies where ORs, orother measures of association, were specificallyassociated with a measure of exposure, arepresented in the section on Exposure-ResponseRelationship.
Andersen and Gaardboe [1993a] found that
current work as a sewing machine operatorwas associated with chronic shoulder pain (OR1.72, 95% CI 1.17–2.55). Using multiplelogistic regression analysis with age, gender,and repetitiveness as covariates, Chiang et al.[1993] found that high force exertionsmeasured in the forearm were associated withshoulder girdle pain (OR 1.8, 95% CI1.2–2.5). When tested in the same model withforce and repetition, the interaction term forforce times repetition was also significant (OR1.4, 95% CI 1.0–2.0). Two factors could haveresulted in an underestimation of the strength ofassociation: (1) no requirement that symptomshave started on current job meant that somesymptomatic workers may have transferred tolower risk jobs, and (2) no matching of healthstatus and exposure status by side (left, right, orboth) may have caused non-differentialmisclassification. For supraspinatus tendinitis,Herberts et al. [1984] calculated a prevalencerate ratio (PRR) for plate-workers versus officeclerks of 16.2 (90% CI 10.9–21.5) “under theassumption that missing data had the samecharacteristics as those considered.” Theabsence of specific exposure information was amajor limitation of this study.
The age-adjusted OR associated withosteoarthritis of the acromioclavicular joint was 2.16 (95% CI 1.14–4.09) (right side) and 2.56 (95% CI 1.33–4.93)(left side) for manual construction workersversus foremen [Stenlund et al. 1992]. Becausethere was a lower participation rate amongbricklayers and blasters, self-selection into thestudy because of having symptoms could haveresulted in overestimation of the strength ofassociation. While some of the items handledrequired a bilateral lift (e.g., jackhammer),other loads may have been specific to the rightor left hand. Because the
3-12
exposure measure did not separate load bysides, non-differential misclassification mayhave caused underestimation of the strength ofassociation.
Consistency of Association:Force and Shoulder MSDs
Despite different outcome and exposuremeasures, all of the studies had positiveassociations. Each study used a different casedefinition, ranging from relatively mildsymptoms to radiographic evidence ofosteoarthritis, and a different measure ofexposure. Chiang et al. [1993] used EMGmeasures of forearm flexor muscle activity.Wells et al. [1983] evaluated the effect of adirect load on the shoulder. Stenlund et al.[1992] used an estimate of the cumulative,lifetime load carried. Andersen and Gaardboe[1993a] compared sewing machine operatorsto a referent population. However, positive andsignificant associations were found, regardlessof the measure of health outcome or exposure.
Temporal Relationship: Force andShoulder MSDsAll of the studies of forceful exertions used across-sectional study design. To increase thelikelihood that shoulder symptoms were causedor aggravated by current exposure, Chiang etal. [1993] required that symptoms hadoccurred within the previous 30 days.
Wells et al. [1983] used several analyticalmethods to increase confidence in a relationshipbetween carrying the increased load and havingshoulder disorders. The use of age, the numberof years on the job, and previous heavy workexperience as covariates when performinganalysis of covariance helped ensure that thedifference in the proportion of shoulder
disorders between letter carriers with andwithout the increased load was related tocurrent exposure rather than past peakexposures or cumulative duration. Althoughbaseline symptom status in the group with theincreased load could not be obtained, therewas no significant difference in the prevalenceof shoulder problems between the two groupswhen results were adjusted for the amount ofweight currently carried. Therefore, thedifference in symptom prevalence was likelyrelated to the load increase rather than priordifferences in symptom status. The cross-sectional studies are consistent with exposureoccurring before the onset of the shoulderMSDs.
Exposure-Response RelationshipWhen sewing machine operators werecompared with an external control population,there was a trend of increasing ORs for chronicshoulder pain with increasing duration of workas a sewing machine operator [Andersen andGaardboe 1993a]. The OR for 0–7 years was1.38 (95% CI 0.86–2.39), for 8–15 years itwas 3.86 (95% CI 2.29–6.50), and for >15years it was 10.25 (95% CI 5.85–17.94),while controlling for other factors including ageand current exposure.
Chiang et al. [1993] found a significantincreasing trend in the prevalence of shouldergirdle pain from Group I (low force, lowrepetitiveness) to Group III (high force, highrepetitiveness). However, the health outcome isnot specific for shoulder tendinitis and theexposure categories combine increasing force,as measured in the forearm flexor muscles, andincreasing repetitiveness.
3-13
In the study of bricklayers and blasters, andacromioclavicular osteoarthritis, Stenlund et al.[1992] found that for the left side, ORsincreased with the level of lifetime load lifted.For a lifetime load of 710–24,999 tonnesversus less than 710 tonnes, the left side ORwas 7.29 (95% CI 2.49–21.34), and forgreater than 25,000 tonnes versus less than 710tonnes, the left side OR was 10.34 (95% CI3.10–34.46).
For severe, but not disabling, shoulder pain, theOR for letter carriers versus postal clerks was3.6 (95% CI 1.8–7.8) [Wells et al. 1983]. Forthose letter carriers who had experienced aweightload increase within the previous year,versus postal clerks, the OR was 5.7 (95% CI2.1–17.8). Furthermore, letter carriers who hadexperienced the weightload increase hadsignificantly more shoulder problems than thosewhose bag weight had not been increased. Ifletter carriers tend to keep the mail-bag strapon one shoulder, the fact that the side of theload was not matched with the side of theshoulder problem could have resulted in non-differential misclassification and anunderestimation of the strength of association.However, some of the health effects may havebeen related to activation of contralateralmuscles involved in stabilizing the shouldergirdle [Winkel and Westgaard 1992].
Coherence of EvidenceHigh shoulder muscle force requirements cancause increased muscle contraction activity,which may lead to an increase in both musclefatigue and tendon tension, and may possiblyimpair microcirculation as well.
Force may also be related to a static load onshoulder muscles. Sjøgaard et al. [1988] found
that muscular fatigue will occur at EMG levelsas low as 5% of maximal voluntary contraction(MVC) if sustained for 1 hour. Other studieshave demonstrated that when the period ofmuscle contraction is extended to more than anhour, the endurance limit of force may be aslow as 8% MVC [Jonsson 1988]. Workersperforming repetitive work with the hands andwrists, while maintaining static upper armelevation may experience fatigue even at lowload levels. Jonsson [1988] reported that manyconstrained work situations are characterizedby static load levels near or exceeding 5%MVC, even when characterized by a fairly lowmean muscular load.
Because the five studies reviewed had aconsiderable diversity of exposure assessmentapproaches and health outcomes, there isinsufficient epidemiologic evidence to concludethat forceful exertions are associated withrotator cuff or bicipital tendinitis. The one studythat used shoulder tendinitis as the healthoutcome reported a strong association relatedto job category (OR for plate-workers versusclerks: 16.2 (95% CI 10.9–21.5), but did notdescribe or measure specific exposure riskfactors [Herberts et al. 1984]. One of thereviewed studies did present evidence for anassociation between acromioclavicularosteoarthrosis and cumulative, lifetime load onthe shoulder muscles [Stenlund et al. 1992].Another study reported a significant associationbetween severe shoulder pain and a directshoulder load [Wells et al. 1983].
3-14
POSTURE
Definition of Awkward Posture forShoulder MSDsFor the shoulder, a relaxed, neutral posture isone in which the arm hangs straight down bythe side of the torso. As the arm is flexed,abducted, or extended, the included anglebetween the torso and the upper arm increases.In one study, postures in which the includedangle was equal to or greater than 45 degreesrequired substantial supraspinatus muscleactivity, while deltoid muscle activity underwenta pronounced increase as the angle of shoulderflexion or abduction increased from 45 to 90degrees [Herberts et al. 1984]. As the arm iselevated, the space between the humeral headand the acromion narrows such that mechanicalpressure on the supraspinatus tendon is greatestbetween 60 and 120 degrees of arm elevation[Levitz and Iannotti 1995]. While there is acontinuum of severity from an included angle of30 degrees to a maximally abducted arm,postures with shoulder abduction or flexion past60 degrees are considered awkward.
Studies Reporting on the Associationof Awkward Postures and ShoulderMSDs
Six of the reviewed studies reported results onthe association between awkward postures andshoulder tendinitis [Baron et al. 1991; Bjelle etal. 1979; English et al. 1995; Herberts et al.1981; Ohlsson et al. 1994, 1995] (Table 3-3,Figure 3-3). Seven additional studies reportedresults on the association between awkwardpostures and non-specific shoulder disorders[Sakakibara et al. 1995], non-specific shouldersymptoms [Hoekstra et al. 1994; Milerad andEkenvall 1990; Schibye et al. 1995] combinedneck-shoulder disorders[Bjelle et al. 1981; Jonsson et al. 1988;
Ohlsson et al. 1995] or combined neck-shoulder symptoms [Kilbom and Persson1987].
Studies Meeting the Four Evaluation Criteria
Four studies met all four of the evaluationcriteria.
Using a prospective study design, Jonsson et al.[1988] assessed the health and exposure statusof 69 electronics manufacturing plantemployees at the beginning of the study andafter one and two years. Employees whodropped out before completion of the studywere compared to those who fully participated;there was no significant difference in medicalstatus, working technique, or work history.Employees who had upper extremity disordersresulting in a physician visit or sick leave wereexcluded from the initial study group. Thedependent variables related to health statuswere of two types: a change in symptomseverity and being symptom free. Symptomstatus was assessed by interview and a physicalexamination by a physiotherapist. Thesymptoms severity index compiled data fromthe five body regions combined and was notspecific for the shoulder region. Because theexposure was determined by direct observationfor each individual, and clearly separatedergonomic risk factors by body region, it wasstill possible to evaluate associations likely tospecifically involve the shoulder.
Kilbom and Persson [1987] and Kilbomet al. [1986] performed a study inwhich female employees in the electronics manufacturing industry wereobserved for a 2-year period. The health outcome of fatigue, ache, or pain
3-15
in the neck, shoulder, or arm regions was basedon symptoms information. Symptom severitywas coded on the basis of its character,frequency, and/or duration. Changes in severitystatus at follow-up evaluations were used as thedependent variables in multiple regressionanalyses. Neck, shoulder, and upper armposture was determined by computerizedanalysis (VIRA) of videotapes of individuals.Although the health outcome combinedsymptoms from different body regions,knowledge of biomechanical theory can beused to identify significant predictors related tothe shoulder symptom severity.
Two of the reviewed studies in which tendinitiswas the health outcome are Ohlsson et al.[1994, 1995]. For both studies, the authorsreported that the examiners could not becompletely blinded to exposed versus referentstatus, but that a standard protocol wasfollowed and observer bias was likely to havebeen minimal. Because examiners were blindedto objective exposure measures, analysestesting associations between neck-shoulderdisorders and specific postures would not havebeen biased [Ohlsson et al. 1995].
In a cross-sectional study, women in the fishindustry were compared to a control populationof women employed in municipal workplaces inthe same towns [Ohlsson et al. 1994].Diagnoses of shoulder disorders (e.g.,tendinitis, acromioclavicular syndrome, frozenshoulder) were made on the basis of symptomsdetermined by interview and a physical exam.Exposure evaluation of each work task held bythe fish industry population was evaluated withergonomic workplace analysis (EWA). Ten
different factors were rated on a scale from 1 to5 and the combined ratings were used as aprofile of the work task. Based on this profile,the authors reported that fish industry work wasfound to be “highly repetitive” and include“poor work postures.”
Ohlsson et al. [1995] compared a group ofwomen who performed industrial assemblywork to a referent group of women from anearby town who were employed in jobscharacterized as having varied and mobile worktasks. One examiner assessed signs andsymptoms. The examiner was blinded tospecific exposure information, but notcompletely blinded to factory worker versusreferent group status. Shoulder tendinitisincluded supraspinatus, infraspinatus, andbicipital tendinitis. Another health outcomecombined neck and shoulder disorders (tensionneck, cervical syndrome, thoracic outletsyndrome, frozen shoulder, tendinitis, andacromioclavicular syndrome). In a descriptiveassessment, it was reported that the work tasksin the study group involved repetitive armmovements with static muscular work of theneck and shoulder muscles. The percentage oftime spent in specific upper arm postures wasdetermined from videotaped observations of 74(out of 82) workers. The average result fromtwo independent videotape analyses was used.Posture category demarcations included 0, 30,and 60 degrees for arm elevation, and 30, 60,and 90 degrees for arm abduction.
Studies Not Meeting the Four EvaluationCriteria
Summaries of studies that specifically evaluatedassociations with shoulder tendinitis arepresented next [Baron et al. 1991; Bjelle et al.1979, 1981;
3-16
English et al. 1995; Herberts et al. 1981].Summaries of other studies are presented inalphabetical order.
In the study by Baron et al. [1991], grocerystore workers who performed the job ofchecker were compared to a non-checkergroup that performed a variety of other jobs(e.g., general stocking, working in the producesection, the bakery, salad bar, pharmacy, andcourtesy counter). There was a lowparticipation rate among non-checkers (55%),which could have resulted in an underestimationof the OR for checkers if symptomatic non-checkers were more likely to participate thanthose non-checkers without symptoms. Theauthors evaluated this possibility by performinga sufficient number of telephone interviews withnon-participants to raise the non-checkerparticipation rate for interviews to 85%. TheOR for shoulder symptoms among the fullparticipant population was similar to the OR forthe full participant plus telephone interviewpopulation. The case definition was shouldersymptoms lasting at least one week oroccurring at least once per month during theprevious year that began while the worker wasperforming her current job and positive physicalexamination findings consistent with a shouldertendinitis. Detailed descriptions of the checkerjobs were presented based on both on-site andvideotape analyses of a few representativeworkers per workstation. No videotaping ofnon-checkers was performed. Shoulder flexionand/or abduction ($90 degrees) was observedduring a variety of different tasks performed bythe checkers. The exposure measures used instatistical analyses were: (1) checker versusnon-checker and, (2) for exposure-responseassessment among checkers, the total numberof months and the number of hours per week
working as a checker.
Bjelle et al. [1979] compared cases withpersistent shoulder pain to controls employedas manual workers. After an extensive medicalevaluation, a diagnosis of bicipital and/orsupraspinate tendinitis was made for a majority(12/17) of the cases. Physical workload wascategorized in relation to sitting or standingposture, weight lifting, and carrying. The workheight of the hands was categorized based onposition relative to the acromion height, perindividual. Placement of workers into exposurecategories was determined by the combinedefforts of each study participant and aphysician.
Bjelle et al. [1981] compared cases with acute,non-traumatic shoulder-neck pain to age- andsex-matched, paired controls. An extensivephysical examination was performed andworkers with inflammatory rheumatoid diseaseswere excluded. To determine exposure, eachcase and control was filmed and abiomechanical analysis was performed todetermine the duration and frequency ofshoulder abduction or forward flexion greaterthan 60 degrees.
In a study by English et al. [1995], casesdetermined by medical diagnosis, and controlswere selected from patients evaluated atspecified orthopedic clinics. For statisticalanalyses, all diagnoses were grouped byanatomical site. The diagnoses for shouldercases included rotator cuff injury, rupture of thelong head of the biceps, shoulder capsulitis, andsymptomatic acromioclavicular arthritis. It isassumed that shoulder tendinitis was included inthis group. Exposure measures weredetermined by a standardized interview
3-17
conducted by an interviewer who was,“unaware of the case-control status of theindividual wherever this was possible.”
In a study by Herberts et al. [1981], theprevalence of supraspinatus tendinitis wascompared between welders and officeworkers. Tendinitis cases were based on acombination of symptoms reported on a nurse-administered questionnaire and a positivephysical examination done by a physiotherapist.For welders, an “experienced physiotherapist”rated work-load on the shoulder as low, high,or very high; no description of the classificationscheme was given.
Hoekstra et al. [1994] evaluated governmentoffice workers at two locations. The casedefinition for shoulder symptoms wassymptoms that began after starting current job,lasting greater than one week, or occurring atleast once per month during the past year withan intensity greater than two on a five pointscale, and no preceding acute, non-occupational injury. A self-administeredquestionnaire was used to determine exposureto factors such as “perceived adequacy ofadjustment of video display terminal (VDT).”Walk-through ergonomic evaluations of factorssuch as workstation surface height and furnitureadjustability were used to provide descriptivedifferences between the two office locations.
Milerad and Ekenvall [1990] compared theprevalence of self-reported, non-specificshoulder symptoms between dentists andpharmacists. Dentistry, as a profession, wasdescribed as work “with the arms abducted and unsupported” whereas, pharmacists had“physically light and varied work.”
In a prospective study by Sakakibara et al.[1995], the health status of a group of womenfarm workers was assessed during theperformance of two different tasks, with a 1-month interval between the tasks. The healthoutcome was defined by self-assessedsymptoms of shoulder stiffness and pain and aphysical examination for muscle tenderness andjoint pain on movement. Whether the examiningphysician was aware of the prior hypothesisregarding differing exposures between the twotasks (bagging pears versus bagging apples)was not stated. Exposure was based on self-report of the number of hours per day spentbagging, the number of pears or apples baggedper day, and the total number of days spentbagging each fruit. One worker was observedfor 3 hours while performing each bagging job,with repeated goniometer measures of shoulderforward flexion angles done each minute. Whilethere was no difference in the total number ofdays or number of hours per day spent baggingeach fruit, significantly more pears than appleswere bagged per day. The proportion of timespent with the angle of shoulder forward flexiongreater than 90 degrees was significantly largerwhen bagging pears (75%) than when baggingapples (41%).
Schibye et al. [1995] performed a prospectivestudy of a population of sewing machineoperators in which the change in self-reportedshoulder symptom status was compared withthose sewing machine operators who continuedto work and those operators that moved intoother occupations (e.g., shop assistant, healthcare worker, and fishing industry worker).
3-18
Strength of Association—AwkwardPosture and Shoulder MSDsResults are presented in the section onExposure-Response Relationship (Table 3-3,Figure 3-3) for studies where ORs, or othermeasures of association, were specificallyassociated with a measure of exposure.
Using data presented in the study by Ohlsson etal. [1994], for supraspinatus, infraspinatus, orbicipital tendinitis, the PRR for working in thefish industry (repetitive work, poor posture)versus the referent population was calculated as3.03 (95% CI 2.0–4.6). For shoulder tendinitisalone, the PRR was calculated as 3.5 (95% CI2.0–5.9). In the same study, the authors alsointerviewed a large group of former fishindustry employees and found that a quarter ofthose workers who left employment had doneso because of problems with their neck orupper limbs. This proportion increased with ageand also occurred after a shorter duration ofemployment among the oldest workers. Thisevidence of a survivor bias highlights theimportance of controlling for age. Higher riskswere found for the workers less than 45 yearsold and these risks may be a more accurateassessment of the true risk.
Using data presented in the study by Ohlsson etal. [1995], for supraspinatus, infraspinatus, orbicipital tendinitis, the OR for being anassembly worker (repetitive arm movementswith static load on shoulders) versus thereferent population was 4.2 (95% CI1.35–13.2). For neck-shoulder disorders, theOR for being an assembly worker versus thereferent group was 5.0 (95% CI 2.2–11.0).
For shoulder disorders consistent withtendinitis, Baron et al. [1991] found that the
OR for being a checker versus a non-checkerwas 3.9 (95% CI 1.4–11.0). Because non-checkers also performed work requiringawkward postures, the reported OR mayunderestimate the risk for checkers. Shortstature (# 5'2") was associated with anelevated, but not statistically significant, OR forshoulder disorders (2.1, 95% CI 0.7–6.9).Because work-station height was fixed, it islikely that short stature workers experiencedmore frequent and/or more severe episodes ofshoulder flexion and/or abduction.
The OR for work performed at or aboveacromion height (i.e., hands above theshoulder) versus work performed belowacromion height was 10.6 (95% CI 2.3–54.9)[Bjelle et al. 1979]. In this study, all cases werepatients who had been examined by the samephysician. Placement of cases and controls intoexposure categories was performed by eachsubject in collaboration with a physician who“had personal knowledge of the work involvedin each case.” Whether or not the physicianwho performed the clinical examinations is thesame person as the physician involved inexposure classification is not stated. If this wasthe same person, a potential bias towardsassigning cases to higher exposure categoriescould have resulted in overestimation of thestrength of association. However, two otherfactors could have resulted in anunderestimation of the strength of association.The exposure outcome was based on currentwork load without any stated restriction thatcases’ symptoms had started on their currentjob. If some of the cases, defined as havingproblems non-responsive to therapy lastinglonger than 3 months, had transferred to alower risk job, the strength of association
3-19
may have been underestimated. Location of thedisorder and exposure were not matched byside (left, right, or both) and this would havecaused non-differential misclassification,resulting in some underestimation of the strengthof association.
English et al. [1995] found that the risk ofhaving a medically diagnosed shouldercondition was increased by repeated shoulderrotation with an elevated arm (OR 2.30,p<0.05). Non-differential misclassification dueto a combination of complicated exposuredefinitions using a questionnaire, and the factthat analyses did not relate health outcomes andexposure on a temporal basis, or by left/rightside, may have caused an under-estimate of thestrength of association.
For supraspinatus tendinitis, Herberts et al.[1981] found that the PRR for welders(characterized as using awkward postures toperform overhead work) versus clerks was18.3. However, in determining this PRR, theauthors performed extrapolation based on anassumption that, “the drop-out group does notdeviate from the examined group,” without anydata to support this assumption. To determine amore reliable indicator of risk, unextrapolateddata presented in the study were used tocalculate a crude OR=8.3 (95% CI 0.63–432).The office clerks were older than the welders,so that confounding by age may have caused anunder-estimation of the strength of association.
In a study of teleservice employees, there wasan association between reporting shouldersymptoms and working at one location versusanother location; the OR was 4.0 (95% CI1.2–13.1) [Hoekstra et al. 1994]. Descriptivedifferences between workstation design at the
two locations provided a plausible explanationfor this finding. At the higher risk location, theworkstation surface was too high to serve as akeyboard support, there were nonadjustablechairs, and it was observed that “nonadjustablefurniture universally promoted undesirablepostures (i.e. elevated arms, hunchedshoulders).” Having shoulder symptoms wasalso positively associated with using a non-optimally adjusted desk height (OR 5.1, 95%CI 1.7–15.5) and a non-optimally adjustedVDT screen (OR 3.9, 95% CI 1.4–11.5).Because exposure was self-reported withoutany indication of whether or not studyparticipants had received education regardinggood VDT workstation design, the phrase,“non-optimally adjusted,” may have had variousmeanings to the study participants. This couldhave caused non-differential misclassification ofexposure and an under-estimation of thestrength of association. On the other hand, apossible reporting bias related to selfassessment of both symptoms and exposurecould have resulted in an overestimation of thestrength of the association. A plausibleexplanation for the association betweenshoulder symptoms and these workstationdesign factors is that the non-optimally adjustedworkstation components forced the employeesto abduct the upper arms and/or hunch theshoulders.
For shoulder symptoms without concomitantneck symptoms, Milerad and Ekenvall [1990]found that the OR for being a dentist (workwith both arms abducted) versus being apharmacist was 3.8 (95% CI 1.2– 10.3). Aswith most cross-sectional studies, the survivorbias may have resulted in
3-20
underreporting of the strength of exposure.Conversely, the exposed group may have hadbetter recall of self-reported symptoms with aresultant overestimation of the OR.
In the study of farm workers by Sakakibara etal. [1995], the point prevalence of musculartenderness in the shoulder regions (per physicalexamination) was significantly higher whenperforming pear bagging (48%) than whenperforming apple bagging (29%). Theproportion of time spent with the shoulder inforward flexion greater than 90 degrees wassignificantly larger when bagging pears (75%)than when bagging apples (41%). Whether ornot there was a recovery period between pearand apple bagging is not stated. If there wasinsufficient recovery after pear bagging,persistent muscle tenderness or increasedsusceptibility may have caused underestimationof the difference in shoulderdisorder prevalence between these two work tasks.
With the exception of the study by English et al.[1995], in which the strength of association mayhave been underestimated, for the studies inwhich the health outcome was shouldertendinitis [Baron et al. 1991; Bjelle et al. 1979;Herberts et al. 1981; Ohlsson et al. 1994,1995], the magnitude of association was strong.ORs ranged from 2.0 to 10.6. In none of thesestudies is it likely that nonoccupational factorssuch as sports activities or personalcharacteristics such as age explain theseassociations.
Consistency of AssociationAll but one of the reviewed studies relevant toposture and shoulder disorders found a positiveassociation between shoulder disorders or
shoulder symptoms and awkward shoulderposture. Awkward postures were consistentlydescribed as overhead work, arm elevation,and specific postures relative to degrees ofupper arm flexion or abduction. Thisassociation was found in cross-sectional, case-control, and prospective studies among a greatvariety of types of work performed.
Temporal RelationshipIt is important to determine whether symptomsor MSDs occur as a consequence of work-related exposures. This can be done mostclearly with a prospective study design.
In the study by Jonsson et al. [1988], thepercent of the work cycle spent with theshoulder elevated was negatively associatedwith remaining healthy (symptom free).Because workers with pre-existing shoulderconditions were excluded from studyparticipation, the onset of new symptoms mayhave been associated with the daily and/orcumulative duration of exposure to elevatedshoulder postures. In the study by Kilbom andPersson [1987], three of the work exposurevariables that were strong predictors for achange to severe status at the 1- and/or 2-yearfollow-up evaluations were related to shoulderposture: (1) percent of work cycle time witharm abduction greater than 30 degrees, (2)percent of work cycle time with arm abductiongreater than 60 degrees, and (3) percent ofwork cycle time with arm extension.
A few studies utilized techniques to improve theability to detect possible relationships
3-21
despite a cross-sectional study design. Thecase definition used by Baron et al. [1991]required that symptoms began while the workerwas on the currently held job. Bjelle et al.[1979] filmed and analyzed the job held at thetime the worker/case became symptomatic.The results of the prospective studies aresimilar to the cross-sectional studies. There isno evidence that shoulder disorders predictedthe onset of exposure.
Exposure-Response Relationship
The level of an exposure can be described intwo different ways. It may be related to theamount of exposure over a relatively short timeperiod, such as a day or week, or it may berelated to cumulative or life-time exposure overa number of years. Studies that testedassociations related to daily or weekly variationin exposure are presented first, followed bystudies that evaluated cumulative exposure byusing independent variables, such as duration ofemployment or estimated lifetime exposure.
Four studies have some evidence of exposure-response relationships. Baron et al. [1991]found a significantly larger OR for shoulderdisorders among employees working greaterthan 25 hours/wk as a checker compared tothose working less than 20 hours/wk. Bjelle etal. [1981] found that the duration of hoursworked per day with the shoulder flexed orabducted >60 degrees was significantly higher(p<0.025) for cases with neck-shoulderdisorders than for controls. Ohlsson et al.[1995] found that neck and shoulder disordersamong assembly workers were significantlyassociated (p<0.05) with the percent of timespent with the shoulder abducted or elevated>60 degrees. Although it is more difficult todetect associations with homogenous exposure,
this association was significant despite very littlevariability in exposure to arm abduction greaterthan 60 degrees. While the analysis amongassembly workers was performed withoutcontrolling for age, there is no evidence tosuggest that older workers were more likely tobe on high exposure jobs, and therefore asubstantial bias is unlikely.
When comparing fish industry workers to thereference population, Ohlsson et al. [1994]found that among those workers younger than45 years, the ORs for disorders of the neckand shoulders were significant and increasedwith duration of employment (0–5 years, OR3.2; 95% CI 1.5–7.0) (>5 years, OR 10; 95%CI 4.5–24). Ohlsson et al. [1995] found adecreasing trend when they compared OR afterstratifying the factory workers by employmentduration (<10 years, OR 9.6; 10–19 years, OR4.4 and $20 years: 3.8). Given the cross-sectional study design, this finding could be anartifact caused by the survivor bias (i.e.,workers with disorders left, while symptom-free ‘survivors’ stayed; see Table 3-5). Theassumption of a survivor bias is based on thefinding that 28% of a group of former assemblyworkers reported pain in the musculoskeletalsystem as their reason for leaving employmentat the factory. In the study by Schibye et al.[1995], improvement in shoulder symptomsamong those who were no longer sewingmachine operators appeared greater at follow-up, but was not significant. The fact that manyof those who left sewing jobs moved intoindustries such as health care and fishing, whereawkward postures and high force loads mayoccur, might explain why a large differencebetween sewing machine operators and non-
3-22
sewing machine operators was absent. Thesefour studies provide some support for therelationship between shoulder abduction andshoulder MSDs.
Coherence of EvidenceDiscussions of the probable influence ofworkplace exposure factors in thepathophysiology of localized muscle fatigue,myalgia, and tendinitis have been presented bya number of authors [Bjelle et al. 1981;Hagberg 1984; Herberts and Kadefors 1976;Herberts et al. 1984; Levitz and Iannotti 1995].Posture is important: when the arm is raised orabducted, the muscle activity in supraspinatusand other muscles increases, and thesupraspinatus tendon comes in contact with theundersurface of the acromion. The mechanicalpressure on the tendon from the acromion isgreatest between 60 and 120 degrees of armelevation. [Levitz and Iannotti 1995]. Thedegree of upper arm elevation is also importantin the onset and intensity of localized musclefatigue in the trapezius, deltoid, and rotator cuffmuscles. [Hagberg 1981; Herberts andKadefors 1976; Herberts et al. 1984]. In alaboratory study, EMG signals from thesemuscles were analyzed. The supraspinatusmuscle was found to be highly active at $45degrees of abduction. The deltoid muscleunderwent a pronounced increase in activity asshoulder flexion or abduction increased from 45to 90 degrees [Herberts et al. 1984]. Theearlier sections on Coherence of Evidence alsodiscussed the rate of fatigue and role ofimpaired micro-circulation in shoulder tendinitis.
Overall, there is epidemiologic evidence for arelationship between repeated or sustainedshoulder postures with more than 60 degrees offlexion or abduction and shoulder MSDs. There
is evidence for both shoulder tendinitis andnonspecific shoulder pain. The evidence forincreased risk of MSDs due to specificshoulder postures is strongest when there is acombination of exposures to several physicalfactors such as force and repetitive work. Anexample of this combination would be holding atool while working overhead. The strength ofassociation was positive and consistent in thesix studies that used diagnosed cases ofshoulder tendinitis, or a combination ofsymptoms and physical findings consistent withtendinitis, as the health outcome [Baron et al.1991; Bjelle et al. 1979; English et al. 1995;Herberts et al. 1981; Ohlsson et al. 1994,1995]. Only one [Schibye et al. 1995] of thethirteen studies failed to find a positiveassociation with exposure and symptoms or aspecific shoulder disorder. However, in thisstudy discontinuing employment as a sewingmachine operator was associated with areduction in neck and shoulder symptoms.While most of the studies that consideredspecific shoulder postures as an exposurevariable were cross-sectional, the twoprospective studies found that the percent ofwork cycle spent with the shoulder elevated[Jonsson et al. 1988] or abducted [Kilbom etal. 1986; Kilbom and Persson 1987] predictedchange to more severe neck and shoulderdisorders. While there is insufficient evidence todevelop a quantitative exposure-disorderrelationship, three studies reported a significantassociation with shoulder flexion or abductiongreater than 60 degrees [Bjelle et al. 1981;Kilbom and Persson 1987; Ohlsson et al.1995]. Among the studies for which shouldertendinitis was the health outcome, the largestORs were associated with work aboveacromion height [Bjelle et al. 1979;
3-23
Herberts et al. 1981]. These results areconsistent with the current models for thepathophysiology of shoulder tendinitis andstressful shoulder muscle activities. In none ofthese studies does “age,” an important personalcharacteristic associated with shouldertendinitis, explain the positive results. Most ofthe studies controlled for a variety ofconfounders, such as occupational sportsactivities in their analyses. In summary, there isevidence that repeated or sustained shoulderabduction or flexion is associated with shouldertendinitis, and the evidence is stronger for highlyrepetitive, forceful work.
VIBRATIONThree of the studies evaluated exposure to low-frequency vibration found in industrial settings(Table 3-4, Figure 3-4). Because of the smallnumber of studies, the full outline used for thesections on repetition, force, and posture willnot be repeated here. The study by Stenlund etal. [1992] is summarized in the section onforce. Vibration exposure occurred in one ofthe three job categories: rock blaster. Theexposure outcome, lifetime exposure tovibration expressed in hours, was determinedfrom a weighted summary of the number ofself-reported hours using specific tools.However, because the rock blaster jobcategory was also the only one where workersperformed heavy lifts several times per day, theauthors concluded that, “vibration exposure isindivisible from static load and heavy lifting inthe present data.” When both cumulative liftingexposure and cumulative vibration exposurewere included in the same multivariate model ofan association with acromioclavicularosteoarthrosis, the OR for lifting and right- sideosteoarthrosis remained significant while the weaker ORs for vibration became
non-significant.
In the study by Stenlund et al. [1993], the samepopulation of bricklayers, rock blasters, andforemen described in Stenlund et al. [1992]were evaluated to determine whether signs oftendinitis or muscle attachment inflammation inthe shoulders were related to lifetime workload, years of manual work, lifetime exposureto vibration, or job title. The case definition for“signs of shoulder tendinitis” was pronounced(i.e., grade 3 out of 3) pain upon palpation ofthe muscle attachment or pronounced pain inresponse to isometric contraction of any of therotator cuff muscles or the biceps muscle. Thecase definition of “clinical entity of tendinitis”was “signs of shoulder tendinitis” plus thesubject’s report of shoulder pain during the pastyear. Using multivariate models that includedage and hours spent in arm intensive sportsactivities, a significant association withcumulative vibration exposure was found whenit was tested in isolation from the otherexposure variables. For “clinical entity oftendinitis” the OR for the left side was 1.86(95% CI 1.00–3.44) and the OR for the rightside was 2.49 (95% CI 1.06–5.87). For “signs of shoulder tendinitis” the OR for the left side was 1.66 (95% CI 1.06–2.61)and the OR for the right side was 1.84 (95% CI 1.10–3.07). Whencumulative vibration exposure was testedin the same model with cumulative lifting load,significant associations were not found foreither variable. Several factors could haveresulted in an underestimation of the strength ofassociation: (1) bricklayers or rock blasterswith tendinitis may have been more likely toleave their jobs than foremen, (2) subjects mayhave had difficulty recalling exposurethroughout their
3-24
lifetimes, (3) the inability to separate exposureby left and right sides. These factors may havecaused nondifferential misclassification. Mostimportant is the authors’ observation thatvibration exposure occurred through the usedof hand-held, heavy tools (e.g., jack-hammers)and thus is intertwined with exposure to a staticload on the shoulders (from stabilizing the upperextremity while using the tool) as well as beingassociated with the heavy lifting tasksperformed by rock blasters.
In a cross-sectional study by Burdorf andMonster [1991], riveters and control subjectsin an aircraft company were investigated forvibration exposure and self-reported symptomsof pain or stiffness in the shoulder. Riveterswere exposed to hand-arm vibration fromworking with hand drills, riveting hammers,bucking bars, and grinders. Controls weremanual workers selected from the machineshop, maintenance, and welding departments inthe same factory. In order to focus on the effectof vibration alone, a walk-through survey wasperformed to confirm that there were “nostriking differences in dynamic and static jointloads during normal working activities.”Participation was 76% among riveters and 64%among controls. An analysis of non-respondents revealed that controls with healthcomplaints were more likely to haveparticipated than those without, while riveterswith health complaints were less likely to haveparticipated. The health outcome, determinedby a self-administered questionnaire, wasshoulder pain or stiffness occurring for at least afew hours during the prior year. Only subjectswho reported having no symptoms beforestarting their present work were included inlogistic regression analyses. The vibrationtransmitted by hand-tools was measured and
weighted according to International StandardsOrganization (ISO) standards. Tool vibrationprofiles and time-work studies of riveters andcontrols were used to determine daily vibrationexposure for each group. For riveters, on thebasis of daily tool operating time, the equivalentfrequency-weighted acceleration for a period of4 hours was 2.8 m s -2. For controls, it was 1.0m s -2. Using a multiple logistic regressionmodel that included age, there was a weakassociation between shoulder symptoms andthe number of years riveting (0.05# p<0.10).When the age-adjusted ORs for riveterscompared to controls were plotted by theduration (in years, from 0 to 20) of riveting, theslope for shoulder symptoms was very gradual,with ORs ranging from 1.0 to 2.0. While theresults of the analysis of non-respondentsdescribed above suggest that the strength ofassociation may have been underestimated, thereported associations are weak and it isunlikely that the response bias would haveresulted in a large increase in the magnitude ofassociation.
There is insufficient evidence for an associationbetween shoulder tendinitis and exposure to segmental vibration. In four separate evaluations, stratified by “signs oftendinitis” (positive physical examinationfindings), “clinical entity of tendinitis” (signs plus symptoms), left andright side, Stenlund et al. [1993] found an association between shouldertendinitis and vibration exposure to segmentalvibration; the range of ORswas from (OR for right side 1.66, 95% CI1.06–2.61) (OR for left side 1.84, 95% CI1.10–3.07). However, work with vibrationexposure also placed a large, static load on
3-25
shoulder muscles so that the effects of forcefulshoulder muscle exertions could not beseparated from vibration.
ROLE OF CONFOUNDERSShoulder MSDs are multifactorial in origin andmay be associated with both occupational andnon-occupational factors. The relativecontributions of these covariates may bespecific to particular disorders. For example,the confounders for non-specific shoulder painmay differ from those for shoulder tendinitis.Two of the most important confounders oreffect modifiers for shoulder tendinitis are ageand sport activities. Most of the shoulderstudies considered the effects of age in theiranalysis. Some studies considered sportactivities [Baron et al. 1991; Stenlund et al.1993; Jonsson et al. 1988; Kilbom et al.1986]. Some studies also used multivariatemethods to simultaneously adjust for severalconfounders or effect modifiers. For example,Ohlsson et al. [1995] found that forshoulder/neck diagnoses, repetitive work wasthe strongest predictor 4.6 (95% CI 1.9–12); age, muscle tension, andstress/worry tendency were also significantpredictors. It is unlikely that the majority of thepositive associations between physicalexposures and shoulder MSDs are due to theeffects of non-work confounders.
CONCLUSIONSThere are over 20 epidemiologic studies thathave examined workplace factors and theirrelationship to shoulders (MSDs). Thesestudies generally compared workers in jobswith higher levels of exposure to workers withlower levels of exposure, following observationor measurement of job
characteristics. Using epidemiologic criteria toexamine these studies, and taking into accountissues of confounding, bias, and strengths andlimitations of the studies, we conclude thefollowing:
There is evidence for a positive associationbetween highly repetitive work and shoulderMSDs. The evidence has important limitations.Only three studies specifically addressed thehealth outcome of shoulder tendinitis and thesestudies investigated combined exposure torepetition with awkward shoulder postures orstatic shoulder loads. The other six studies withsignificant positive associations dealt primarilywith symptoms. There is insufficient evidencefor a positive association between force andshoulder MSDs based on currently availableepidemiologic studies. There is epidemiologicevidence for a relationship between repeatedor sustained shoulder postures with greater than60 degrees of flexion or abduction and shoulderMSDs. There is evidence for both shouldertendinitis and nonspecific shoulder pain. Theevidence for specific shoulder postures isstrongest where there is combined exposure toseveral physical factors like holding a tool whileworking overhead. The strength of associationwas positive and consistent in the six studiesthat used diagnosed cases of shoulder tendinitis,or a combination of symptoms and physicalfindings consistent with tendinitis, as the healthoutcome. Only one [Schibye et al. 1995] of thethirteen studies failed to find a positiveassociation with exposure and a specificshoulder disorder or symptoms of a shoulderdisorder.
3-26
This is consistent with the evidence that is foundin the biomechanical, physiological, andpsychosocial literature.
There is insufficient evidence for a positiveassociation between vibration and shoulderMSDs based on currently availableepidemiologic studies.
Table 3-1. Epidemiologic criteria used to examine studies of shoulder MSDs associated with repetition
Study (first author andyear)
Risk indicator(OR, PRR, IR,
or p-value)*,†Participation rate $$70%
Physicalexaminatio
n
Investigatorblinded to case
and/orexposure
status
Basis for assessingshoulder
exposure to repetition
Met all four criteria:
Chiang 1993 1.6† Yes Yes Yes Observation or measurements
Kilbom 1986, 1987 NR†,‡ Yes Yes Yes Observation or measurements
Ohlsson 1994 3.5† Yes Yes Yes Observation or measurements
Ohlsson 1995 5.0† Yes Yes Yes Observation or measurements
Met at least one criterion:
Bjelle 1981 NR† NR Yes Yes Observation or measurements
English 1995 2.3†,§ Yes Yes Yes Job titles or self-reports
Sakakibara 1995 1.7† Yes Yes NR Job titles or self-reports
Met none of the criteria:
Ohlsson 1989 3.4† NR No NR Job titles or self-reports
*Some risk indicators are based on a combination of risk factors—not on repetition alone (i.e., repetition plus force, posture,or vibration). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).
†Indicates statistical significance. If combined with NR, a significant association was reported without a numerical value.‡Not reported. §Repeated shoulder rotation with elevated arm.
3-27
Table 3-2. Epidemiologic criteria used to examine studies of shoulder MSDs associated with force
Study (first author andyear)
Risk indicator(OR, PRR, IR or
p-value)*,†Participation rate $$70%
Physicalexamination
Investigatorblinded to
case and/orexposure
status
Basis for assessingshoulder exposure to
force
Met all four criteria:
Chiang 1993 1.8† Yes Yes Yes Observation or measurements
Met at least one criterion:
Andersen 1993a 1.38–10.25† Yes No Yes Job titles or self-reports
Herberts 1981, 1984 15–18† NR‡ Yes NR Job titles or self-reports
Stenlund 1992 2.2–4.0† Yes Yes Yes Job titles or self-reports
Wells 1983 5.7† Yes No NR Job titles or self-reports
*Some risk indicators are based on a combination of risk factors—not on force alone (i.e., force plus repetition, posture,or vibration). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).
†Indicates statistical significance.‡Not reported.
3-29
Table 3-3. Epidemiologic criteria used to examine studies of shoulder MSDs associated with posture
Study (first author andyear)
Riskindicator
(OR, PRR, IR,or
p-value)*,†
Participation rate $$70%
Physicalexamination
Investigatorblinded to
case and/orexposure
status
Basis for assessingshoulder
exposure to posture
Met all four criteria:
Jonsson 1988 NR†,‡ Yes Yes Yes Observation or measurements
Kilbom 1986, 1987 NR† Yes Yes Yes Observation or measurements
Ohlsson 1994 3.5† Yes Yes Yes Observation or measurements
Ohlsson 1995 5.0† Yes Yes Yes Observation or measurements
Met at least one criterion:
Baron 1991 3.9† No Yes Yes Observation or measurements
Bjelle 1979 10.6† NR Yes No Observation or measurements
Bjelle 1981 NR† NR Yes Yes Observation or measurements
English 1995 2.3†,§ Yes Yes Yes Job titles or self-reports
Herberts 1981 8.3 NR Yes NR Job titles or self-reports
Hoekstra 1994 5.1† Yes No Yes Job titles or self-reports
Milerad 1990 2.4† Yes No NR Job titles or self-reports
Sakakibara 1995 NR† Yes Yes NR Observation or measurements
Schibye 1995 NR Yes No NR Job titles or self-reports
*Some risk indicators are based on a combination of risk factors—not on posture alone (i.e., posture plus force, repetition, or vibration). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).
†Indicates statistical significance. If combined with NR, a significant association was reported without a numerical value.‡Not reported. §Repeated shoulder rotation with elevated arm (p< 0.05 level, most of study used 0.01 level).
3-31
Table 3-4. Epidemiologic criteria used to examine studies of shoulder MSDs associated with vibration
Study (first author andyear)
Riskindicator
(OR, PRR, IR,or p-value)*†
Participation rate $$70%
Physicalexamination
Investigatorblinded to case
and/orexposure
status
Basis for assessingshoulder exposure to
vibration
Met at least one criterion:
Burdorf 1991 1.5 No No NR‡ Observation or measurements
Stenlund 1992 2.2–3.1† Yes Yes Yes Self-reports, weight of tools
Stenlund 1993 1.7–1.8† Yes Yes Yes Job titles or self-reports
*Some risk indicators are based on a combination of risk factors—not on vibration alone (i.e., vibration plus force, posture,or repetition). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).
†Indicates statistical significance.‡Not reported.
3-33
(Continued)
Table 3-5. Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
Andersenand Gaardboe1993a
Cross-sectional
424 female sewing machine operators(SMO), compared to781 females from thegeneral population of theregion and internalreferent group of89 females from thegarment industry.
Outcome: Case of chronicshoulder pain was defined ascontinuous pain lasting for amonth or more after beginningwork and pain for at least30 days within the past year.
Exposure: Categorization brokendown according to currentoccupational status by job title. Classification into exposuregroups based on author’sexperiences as occupationalhealth physicians and involvedcrude assessment of exposurelevel and exposurerepetitiveness. High exposurejobs were those involving highrepetition/high force or highrepetition/low force or mediumrepetition/high force. Mediumexposure jobs were thoseinvolving medium repetition/lowforce and low repetition and highforce. Low exposure jobs werelow repetition/low force.
For the analysis, “length ofemployment as a sewingmachine operator” wasconsidered the variable ofinterest, the rest wereconfounders.
Shoulder pain:Sewingmachineoperators,25.2%
Years ofexposure:0-7=12.3%
8-15=33.7%
>15=57.1%
8.5% 3.21
1.56
4.28
7.27
1.68-7.39
0.76-3.75
2.14-10.0
3.82-16.3
Participation rate: 78.2%.
Examiners blinded to case status.
Respondents excluded if hadprevious trauma to neck, shoulder,or arms or had inflammatory diseaseat time of response.
ORs adjusted for age, havingchildren, not doing exercise,socioeconomic status, smoking, andcurrent neck/shoulder exposure.
Age-matched exposure groups andcontrols.
Presented study as “general surveyof health in the garment industry” tominimize information bias.
3-35
(Continued)
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
AndersenandGaardboe1993b
Cross-sectional
From a historical cohortof 424 sewing machineoperators, 120 wererandomly selected and82 exposed workerswere categorized bynumber of years ofemployment: 0 to7 years, 8 to 15 yearsand greater than 15years. These werecompared to a referentgroup of 25 auxiliarynurses and homehelpers. A total of 107subjects participated.
Outcome: Measured by healthinterview and exam of the neck,shoulder and arm. Case ofchronic pain was defined ascontinuous pain lasting for amonth or more after beginningwork and pain for at least30 days within the past year. Physical examination: Restrictedmovements in the cervical spineand either palpatory tendernessin cervical segments orirradiating pain or tingling atmaximum movements or positiveforaminal test.
Exposure: Exposurecategorization broken downaccording to currentoccupational status by job title. Classification into exposuregroups based on author’sexperiences as occupationalhealth physicians and involvedcrude assessment of exposurelevel and exposurerepetitiveness. High exposurejobs: Involved highrepetition/high force or highrepetition/low force or mediumrepetition/high force. Mediumexposure jobs involved mediumrepetition/low force and lowrepetition and high force. Lowexposure jobs were lowrepetition/low force.
Rotator cuffsyndrome:
Number ofworkers byexposure timein years:0-7: 1;8-15: 6;>15: 11
Controls: 1 Chi sq fortrend=9.51,p<0.01
Participation rate: 78.2%; logisticregression limited to a combinedneck/shoulder case definition.
Age-matched exposure groups andcontrols.
Examiners blinded to control/subjectstatus.
Controlled for age, having children,not doing leisure exercise, smoking, socioeconomic status.
Poor correlation betweendegenerative X-ray neck changesand cervical syndrome.
Most frequent diagnosis amongstudy group was “cervicobrachialfibromyalgia” significant for test oftrend with exposure time in years.
Chronic neck pain vs. palpatoryfindings: Sensitivity: 0.85;Specificity: 0.93.
3-36
(Continued)
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
Baron et al.1991
Cross-sectional
124 Grocery checkersusing laser scanners (119females, 5 males)compared to 157 othergrocery workers (56females, 101 males). Excluded 18 workers inmeat, fish, and delidepartments, workersunder 18, and pregnantworkers.
Outcome: Based on symptomquestionnaire and physical exam. (1) Rotator cuff syndrome—painwith resisted abduction or deltoidpalpation (2) Bicipitaltendinitis—pain on Yergason’smaneuver. Case defined ashaving positive symptoms inshoulder and a positive physicalexam of a particular body part. Symptoms must have begun afteremployment at the supermarketand in the current job; lasted oneweek or occurred once a monthduring the past year; and wherethere was no history of acuteinjury to body part in question.
Exposure: Job category andestimates of repetitive andaverage and peak forces basedon observed and videotapedpostures, weight of scanneditems, and subjective assessmentof exertion.
Checkers:15%
Checkersusingscanners:34%
Checkers5'2" or less inheight: 21%
Othergroceryworkers:7%
Othergroceryworkers5'2" orless inheight:13%
Checkers vs.others:OR=3.9
Checkersusingscanners vs.others:OR=8.6
Checkers<5'2" vs.other groceryworkers<5'2":OR=2.1
1.4-11.0
1.0-72.2
0.7- 6.9
Participation rate: 85% checkers; 55%non-checkers in field study. Following telephone survey 91%checkers and 85% non-checkers.Examiners blinded to worker’s job andhealth-status.
Logistic regression model adjusted forduration of work. No difference ingroups between age, gender, andhobbies so that these were notcontrolled for.Number of hr worked/week as achecker statistically significantlyrelated to shoulder disorders forworkers checking >25-hr/ /week(OR=3.5, p<0.05) (OR estimated from figure).
Total repetitions/hr ranged from 1,432to 1,782 for right hand and 882 to1,260 for left hand.
Average forces were low and peakforces medium.Multiple awkward postures recordedfor upper extremities among cashiers.
No statistical significance associatedbetween duration of employment as achecker and shoulder MSDs.
3-37
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Bergenuddet al. 1988
Cross-sectional
574 of 830 surveyrespondents participated ina health exam.
In 1983, 1,070 residents ofMalmö, Sweden,responded to questions onshoulder pain in a healthsurvey as part of alongitudinal study begun in1,938 of 1,542 residents.
Outcome: Based on symptomsurvey: Occurrence of shoulderpain lasting $24 hr during the lastmonth and physical exam (jointmotion, tenderness on palpationof supraspinatus, biceps,tendons and acromioclavicularjoint).
Exposure: Based on jobclassification; classified as: Lightphysical demands (white collar)=275; Moderate physicaldemands (nurses, lightindustry)=237; Heavy (blue collar,e.g., carpenters, bricklayers)=50.
Prevalenceofoccupationalworkload insubjects withshoulder pain
Heavy work:11%
Moderatework: 49%
Light work:40%
Õ Õ Participation rate: 69%.Unknown whether examiners blindedto case status.Analysis stratified by gender.Only 9% of workers included in studywere in the Heavy Physical DemandsJobs category, compared to 49% inLight category and 42% in moderatecategory. Only 1% of females werein Heavy Physical DemandJobs category.Sick leave due to shoulder pain wasrestricted to males in jobs withmoderate or heavy physical demands(p<0.05) (data not shown in article).At one year follow-up, 61 (77%) of 79subjects with shoulder pain re-examined. 35 had continued shoulderpain.Misclassification of work categories apossibility: Likely no observation of jobtasks performed..No differences in overall physicaldemands of jobs among subjects withshoulder pain compared to thosewithout shoulder pain, but femaleswith signs of supraspi-natus tendinitismore often had jobs with physicaldemands.Authors state that shoulder pain maybe related to intelligence in males inthis study; “more talented” males hadless shoulder joint symptoms. Wequestion author’s conclusions.Females showed significantassociation with shoulder pain anddissatis-faction. No association withrelation to family or friends or level oflife success. Author states bothgroups of females rated their lifesuccess low, and subjects withshoulder pain did not rate level ofsuccess differently.
3-38
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Bernardet al. 1994
Cross-sectional
Of a total population of3,000 workers in theeditorial, circulation,classified advertising, andaccounting departments,1,050 were randomlyselected for study and973 participated;894 responded to theshoulder questions.
Cases fulfilling shoulderdefinition compared to non-cases.
Outcome: Health data andpsychosocial information werecollected using a self-administered questionnaire. Definition: Presence of pain,numbness, tingling, aching,stiffness or burning in theshoulder occurring $once amonth or 7 days continuouslywithin the past year, reported asmoderately severe. The symptommust have begun during thecurrent job. Workers withprevious injuries to the relevantarea were excluded.
Exposure: Based on observationof work activity involvingkeyboard work, work pace,posture, during a typical day of asample of 40 workers withsymptoms and 40 workerswithout symptoms. Exposure towork organization andpsychosocial factors based onquestionnaire responses.
17% (case)
3% (casewith dailypain)
Õ Female:OR=2.2
Perceivedlack ofdecisionmakingparticipation: OR=1.6
Years at the newspaper:OR=1.4
Perceivedincreased jobpressure:OR=1.5
1.5-3.3
1.2-2.1
1.2-1.8
1.0-2.2
Participation rate: 93%.
Examiners blinded to case andexposure status.
For calculation of the ORs of thepsychosocial scales, the responseswere divided into quartiles, then the 75th percentile was compared to 25thpercentile.
Model adjusted for race, age, gender,height, psychosocial factors, medicalconditions.
Age, height, hr typing away fromwork, other medical conditions werenot found to be significant.
In a sub-analysis of jobs withcomparable number of males andfemales, there were no significantfactors related to shoulder MSDs.
3-39
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Bjelle et al.1979
Case-control
17 cases of shouldertendinitis from a populationof male industrial workerswho were patients at anoccupational health center. These 17 were chosenfrom 20 consecutive malepatients from 6 industriesand had been sufferingfrom pain over a period of>3 months in one or bothshoulders.
34 non-cases werematched for age andworkshop.
Outcome: Cases were non-responsive to analgesics, non-steroidal anti-inflammatoryagents, physiotherapy, andoutcome measured by exam. Case defined as shoulder painlasting >3 months with noresolution post-treatment.
Exposure: Defined as work withhands at or above shoulder level. 3 classes work performed: (A)with hands below shoulder oracromion height, (B) at or aboveacromion 3 to 8 times/day (<1/hrplus for duration >1 min) (C) $8times at or above acromion($1/hr. plus duration >1 min). Exposure assessed by interviewand physician observation andknowledge of work.
Electromyographs on 15 cases.
Open muscle biopsies on11 cases.
With work ator aboveshoulders:65%
With workat oraboveshoulders:15% 10.6 2.3-54.9
Participation rate: Not reported.
Matched for age, gender and workshop.
Three of the 20 were diagnosed withinflammatory rheumatoid diseases notpreviously diagnosed, 17 had noinflammatory rheumatic disease.
Mean age (53 years) of casessignificantly older than other workers(37.6 years).
Myopathic signs not found on EMG ormuscle biopsies. Muscle enzymes(creatine phosphokinase and/oraldolase) were elevated in 6 cases.
Present and previous employment, physical workload not differentbetween cases and referents.
Work performed with hands aboveacromion height significantly greaterfor cases than referents.
2-year follow-up showed that only8 cases working in the same or lessheavy types of work, 7 of these hadslight shoulder complaints.
3-40
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Bjelle et al.1981
Case-control
20 workers of industrialplant consecutively seen athealth clinic with acute,nontraumatic shoulder-neckpain.
Of these, 13 were not dueto causative disease ormalformation. These13 were compared to26 controls, matched onage, gender and place ofwork.
Outcome: Physician evaluated allpatients with acute non-traumaticshoulder-neck pains referred tothe outpaient clinic of therheumatology department. Eachpatient had to undergo anextensive clinical examination,including local anaesthesia for thedefinition of pain location. Exploratory puncture of theglenohumeral joint was performedin patients with tenderness overthe joint.
Exposure: Anthropometric andIsometric muscle strength weretested with strain gaugeinstruments. Patients asked toperform their max-mal efforts. Measurements made for thefollowing contractions: shoulderelevation at the acromion,abduction and forward flexion ofthe shoulder joints at neutralposition and semipronated. Gripstrength measured byvigorimeter.
Video recording of armmovements at work. Shoulderloads estimated from videos.Consisted of measuring theduration and frequency ofshoulder abduction or forwardflexion of >60°.EMG measurement of shoulderload during assembly work on 3patients and 2 healthy volunteers. Muscular load level determinationmade by computer analysis ofmyo-electric amplitude.
6 with rightshouldertendinitis:46%
NoControlswithtendinitis:0%
Cases hadsignificantlylongerduration andhigherfrequency ofabduction orforwardflexion thancontrols,p<0.001.
Cases hadsignificantlyhighershoulderloads thancontrols.
Mediannumber ofsick-leavedayssignificantlydifferentbetweencases andcontrols(p<0.01).
Participation rate: Not reported.
Video analyses were done blinded tocase status.
No significant difference betweencases and controls in anthropometry.
Isometric strength test: controlssignificantly stronger in 6 of 14 testsbut probably influenced by paininhibition in cases.
No significant difference in cycle time(9 vs. 12 min) between cases andcontrols.
The supraspinatus muscle showed asignificant change of the mean powerfrequency (p<0.05) towards lowerlevels, indicating a fatiguing processfor four of the five investigatedassemblers during work.
3-41
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Burdorf andMonster1991
Cross-sectional
194 riveters exposed tovibration compared to 194workers in the same plantwith little or no exposure tovibration.
Outcome: Standardized Nordicquestionnaire, pain or stiffness.
Exposure: Employed >12 months,not exposed to hand/armvibration.
Observation, time-work studies,measurements of vibrating tools.
No shoulder measurements.
Occupational history treated asdichotomous variable with “1” forheavy physical work.
31% 20% 1.5 Participation rate: Riveters=76%,controls=64%.
Examiners blinded to exposure orcase status: Not reported.
Confounders controlled for includedheight, weight, and smoking habits.
Age and height significantly differentbetween groups.
Years of riveting work associatedwith pain or stiffness in shoulder(0.05#p#0.10).
Follow-up of nonrespondantsshowed no difference in age or workexperience. Sick leave significantlydifferent.
3-42
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Burt et al.1990
Cross-sectional
836 Newspaper employeesin the Editorial Departmentand selected jobs in theAdvertising, Circulation,Data Processing, andFinance Departments from4 company locations,(460 female and 376 male).
Cases compared to non-cases.
Outcome: Based on symptomquestionnaire. Case defined aspain, aching, stiffness, burning,numbness or tingling in shoulderlasting >1 week or occurring onetime/month in the past year. Symptoms must have begun oncurrent job; no previous accidentor acute injury to the joint, norelated systemic disease.
Exposure: Based onquestionnaire and job sampling. Exposure variables included worktime spent typing on computer;typing speed; keyboard type; hrworked/week; workload; numberof years worked.
Time spenttyping: 50%
TypingSpeed: Slow: 6%Moderate:11%Fast: 15%
42% Õ
Typing Speed:
Moderate: 2.6 Fast: 4.1
Pre-existingArthritis:OR=2.3
Dissatisfiedwith job:OR=2.3
Õ
1.1-5.91.8-9.4
1.2-4.4
1.2-4.3
Participation rate: 81%. (Authorsnote that those out on assignment or illor on vacation counted as non-participants.)
Number of workers in number of non-typing jobs not reported.
Reporters characterized by highperiodic demands (deadlines)although they had high control and jobsatisfaction.
Job analysis found significantcorrelation (r=0.56) between reportedaverage typing time/day and observed8 hr period of typing (p<0.0001).
Length of employment and symptomsin shoulder not significant.
3-43
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Chiang et al.1993
Cross-sectional
207 fish processing workers, 67 males and140 females, divided in3 groups:
(I) Low force, lowrepetition (comparisongroup, n=61);
(II) High force or highrepetition (n=118);
(III) High force and highrepetition (n=28).
Outcome: Shoulder girdle pain asdefined by Anderson (1984) (thepainful condition of the shoulderwith limitation of movement,which may occur in associationwith tension neck or merge withpain in the suprascapular orupper dorsal regions). Symptomsin these regions occurring in last30 days and physical examfindings of $two tender points orpalpable hardenings which mayeither be caused or aggravatedby work conditions.
Exposure: Assessed byobservation and recording oftasks and biomechanicalmovements of three workerseach representing one of 3 studygroups. Highly repetitive jobswith cycle time k=<30 sec or>50% of cycle time performingthe same fundamental cycles. Hand force estimate from EMGrecordings of forearm flexormuscles. Classification ofworkers into 3 groups accordingto the ergonomic risks of theshoulders and upper limbs: GroupI: Low repetition and low force;Group II: Low repetition or lowforce; Group II: High repetitionand high force.
Prevalenceof Physician-observedDisorders:
Group II: 37%(male 31%;female 39%)
Group III:50%(male 50%female 50%)
Prevalence ofPhysician-observedDisorders:
Group I:10%(male 9%female10%)
Repetitivemovement ofthe upper limb(Rep):OR=1.6
Sustainedforcefulmovement ofthe upper limb(force):OR=1.8
Rep timesforce:OR=1.4
Age:OR=1.0
Gender:OR=1.1
1.1-2.5
1.2-2.5
1.0-2.0
0.9-1.1
0.7-1.7
Participation rate: Not quantified;however, authors stated that “all ofthe workers who entered the fishprocessing industry before June 1990and were employed there full-timewere part of the cohort.” Of the232 employees who agreed toparticipate, 207 met study criteria.Examiners blinded to exposure status.(“Workers examined in randomsequence to prevent observer bias.”)Workers with hypertension, diabetes,history of traumatic injuries to upperlimbs, arthritis, collagen diseaseexcluded from study group.Eight plants used in study. Authorsreported “no plant effect".Case definition based on physiciandiagnosis not significantly differentfrom definition based on symptoms inGroups II : 37% vs. 44% or Group III:50% vs. 50%. Group I about 2/3 theprevalence (10% vs. 15%).Dose-response for physicianobserved shoulder girdle pain amongthree exposure groups.Dose-response for physicianobserved shoulder girdle pain bygender in three exposure groups.Logistic model controlled for age andgender.Significant trend found for duration ofemployment and exposure group inworkers <12 months, 12 to 60months, but not in workers employed>60 months.
3-44
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Englishet al. 1995
Case-control
Cases: n=580; 174 malesand 406 females withdiagnosed soft tissueconditions of the upper limbat 2 orthopedic clinics;ages 16 to 65 years.
Controls: 996 controls;558 males and 438 femalesattending the same clinics;diagnosed with conditionsother than diseases of theupper limb, cervical orthoracic spine; ages 16 to65 years.
Outcome: Based on standarddiagnosis for rotator cuff injury;rupture of the long head ofbiceps, shoulder capsulitis,symptomatic acromioclaviculararthritis.
Exposure: Based on self-reported risk factors at work formusculoskeletal disordersconcentrating on detailedcomponents of movements andactivities at work: awkwardpostures, grip types, wristmotions, lifting, shoulderpostures, static postures, handtool use, and job category.
Questionnaire obtainedinformation on repetitivemovements of the upper limb:Shoulder flexion, shoulderrotation with elevated arm,keeping the whole arm raised >1min, shoulder rotation with elbowflexed.
Frequency ofshoulderproblems
Rotator cuff:8.3%
Rupture oflong head ofbiceps: 0.3%
Shouldercapsulitis:3.6%
Symptomaticacromiocla-viculararthritis:0.2%
Õ
Õ
Õ
Õ
Per 5 years ofage: 1.4
For elbowflexion: 0.4
Per hr of totaldaily elbowflexion: 1.1
Repeatedshoulderrotation withelevated arm:RR=2.3
Wrist rotationat low rates:RR=0.18
Wrist rotationwithincreasingrates:RR=2.02/30reps/min.
1.2-1.5,p<0.01
0.2-0.8,p<0.01
0.9-1.2,p<0.01
Notreportedp<0.05
Notreportedp<0.05
Notreportedp<0.05
Participation rate: 96%.
Administered questionnaire blinded tocase status.
Controlled for age, height, gender,weight, whether MSD was due to anaccident, study center.
Total daily exposure to elbow flexiondid not contribute to shoulder injury.
Risks highest for female hairdressers.
“Repetitive” defined as a frequency of>once/min of 14 specific movements.
Sporting activities, hobbies; averagehr of driving/week; whether claim forcompensation made were analyzed inmodels.
Jobs with pinching between thumband forefinger protective againstshoulder disorders. May reflect handmovement and exertion with noshoulder movement or exertion.
Small number of subjects/group limitspower to detect significantdifferences.
3-45
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Flodmarkand Aase1992
Cross-sectional
58 industrial workersmaking ventilation shafts(51 males and 7 females)compared to symptomprevalence in 170 blue-collar workers in Örebro,Sweden.
Compared workers withsymptoms to thoseworkers without symptomsfor risk factor analysis.
Outcome: Questionnaire surveyusing Nordic questionnaire forsymptoms as to duration duringlast 12 months and during last7 days, effect on workperformance and leisureactivities, and sick leave. Type Abehavior assessed by Bortnerquestionnaire.
Exposure: No objectivemeasurements.
Symptoms inpast 12months: 40%
Symptomsin past 12months:23% 2.2 1.4-4.4
Participation rate: 87%.
Aim of the study was to furtherinvestigate relationship between TypeA behavior and musculoskeletalsymptoms.
The Bortner Score for Type Abehavior significantly higher for thosewith shoulder symptoms than thosewithout.
No difference in headache, tiredness,sleeping, irritation, lack ofconcentration or problems with eyes,nose, stomach, skin.
Authors suggest that Type A personsmore likely to ignore symptoms tominimize their potential effect on workcapacity.
3-46
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Hales andFine 1989
Cross-sectional
Of 96 female workersemployed in 7 highexposure jobs in poultryprocessing, 89 werecompared to 23 of25 female workers in lowexposure jobs.
Outcome: By questionnaire:Period Prevalence: Symptoms inlast 12 months. Case defined as:pain, aching, stiffness,numbness, tingling or burning inthe shoulder, and symptomsbegan after employment at theplant; were not due to a previousinjury or trauma to the joint; lasted>8 hr; and, occurred 4 or moretimes in the past year.
Point Prevalence: Determined byphysical exam of the upperextremity using standarddiagnostic criteria case must alsofulfill symptom definition (listedabove).
Exposure: Observation andwalk-through; jobs categorizedas High exposure and Lowexposure based on estimatedhand force and hand repetition,not shoulder exposure.
Anysymptom ofthe shoulder:49% (highexposuregroup)
Periodprevalencefor shouldercase: 19%
Pointprevalencefor shouldercase: 7%
43% (lowexposuregroup)
4%
4%
1.2
3.8
0.9
0.7-2.0
0.6-22.8
0.1-7.3
Participation rate: 91%.
Examiner blinded to case andexposure status.
Analysis adjusted for age andduration of employment.
Although shoulder MSDs surveyed byquestionnaire, exposure assessmentwas based on hand/wrist exposure,so that risk for shoulder may not beaccurate.
High exposure departments: Breasttrim, thigh debone, leg cut/disjoint,tender cut, knuckle cut, breast,knuckle cut, thigh fat trim.
Lower exposure departments: Breast,thigh, or quality control inspectors.
3-47
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Hales et al.1994
Cross-sectional
533 Telecommunicationworkers (416 females and117 males) in 3 offices,employed $6 months.
"Cases" fulfilling shoulderWRMSD definitioncompared to non-cases.
Outcome: Self-administeredquestionnaire and standardphysical examination; casedefined as: pain, aching,stiffness, burning, numbness ortingling >1 week or >12 times ayear; no previous traumatic injuryto the area; occurring afteremployment on current job withinthe last year and positive physicalexam: moderate to worst painexperienced with positivephysical finding of thesymptomatic joint.
Exposure: Work practices andwork organization assessed byquestionnaire and observation;number of keystrokes/day.
Physical workstation and posturalmeasurements obtained but notused in final analyses.
Rotator cufftendinitis:6% (n=513)
Bicipitaltendinitis:less than 1%(n=516)
Overallshoulder: 6%
Fear ofreplacementby computers: 1.5
Number oftimes arisingfrom chair: 1.9
1.1-2.0
1.2-3.2
Participation rate: 93%.
Physician examiner blinded to workercase study.
Logistic analysis adjusted fordemographics, work practices, workorganization, individual factors;electronic performance monitoring;DAO keystrokes; Denver DAOkeystrokes/day.
ORs for psychosocial variablesrepresent risk at scores one standarddeviation above mean scorecompared to risk at scores one SDbelow mean.
Because of readjustments andchanges of workstations during studyperiod, measurements of VDTworkstations considered unreliableand excluded from analyses.
Number of hr spent in hobbies andrecreational activities not significant.
Although keystrokes/day was foundto not be significant, data availablewas for workers typing an averageof 8 words/min over 8-hr period.
97% of participants used VDT$6 hr/day, so not enough variance toevaluate hr of typing.
Over 70 variables analyzed in modelsmay have multiple comparison bias.
3-48
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Herbertset al. 1981
Cross-sectional
131 male shipyard welderswith >5 years of workexperience compared to 57male office clerks. Allworkers participated in theshipyard’s medical programwhich offered medicalexams every 5 years.
Outcome: Positive answers toquestions about repeatedoccurrences of shoulder painduring work; shoulder stiffnessthat affected work andweakness in shoulder thataffected work or weakness ornumbness in arm or hand andparticipation in a follow up exam.
Clinical examination with jointrange of motion, active andpassive and simultaneous painanalysis, rating of gross power inflexion, abduction and rotation,rating of tenderness to palpation.
Exposure: Estimation of workloadwith assessment of theworkplace into 3 groups veryhigh, high or low. Static loadingwhile holding tools; awkwardpostures; shoulder level oroverhead work.
Supraspi-natustendinitis(ST) resultsof 23welderscalled backfor clinicalfollow-upexams:16 weldershadsupraspi-natustendinitis.
ShoulderPain reportsfrom thequestion-naire: 27%
ShoulderPainPrevalence fromquestion-naire:1.8%
Prevalencerate ratio(PRR) ofshoulder painresults fromquestionnaire,welders vs.officeworkers:PRR=15.2
PRR fromestimatedprevalence(“propor-tionation” ofcases)reported inarticle:PRR=18.3
2.1-108(90% CI)
14.7-22.1(90% CI)
Participation rate: Not reported.
Incidence estimated to be 15 to 20% ayear.
Welders with and without tendinitiswere age-matched.
We question the methods used toapproximate the prevalence ofshoulder tendinitis. Authors statedthat they took into account the missingdata in the investigation and assumedthat the drop-out group did not deviatefrom the examined group, so theyused “proportionation” to obtain thenumber of cases of supraspinatustendinitis cases in the welders forcalculations of prevalence rate ratios;number of supraspinatus tendinitiscases increased from 16 to 24.
Number of years active welding, shoulder load, and welding yearsshowed no significant difference. However, a sample size of 11matched pairs may not have enoughpower to detect a difference.
Turnover of shipyard weldersmentioned at 33%.
Shoulder tendinitis was not found tobe associated with increasing age.
3-49
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Herbertset al. 1984
Cross-sectional
131 male shipyard weldersand 188 plate workerscompared to 57 male officeclerks. Welders andplateworkers chosen had>5 years of job experience.
23 symptomatic welders,30 symptomatic plateworkers compared to 18asymptomatic welders and30 plate workers by clinicalexam.
Age-matched pairs: 11 welders;15 plateworkers.
Nurse-administered symptomquestionnaire: Case defined aspain, weakness, stiffness inshoulder excluding effectsoriginating from neck, plus clinicalexam with tenderness, range ofmotion gross power measured bydynamometer.
Exposure: Observation of jobs;workers compared by use of jobtitle; EMG measurements ofmuscles of shoulder region.
Electromyographic analysis of theshoulder muscle load completedon 9 volunteers to study theinfluence of hand tool mass andarm posture.
Question-naire results,shoulder painof the supra-spinatustendinitistype Welders:27%
Plate-workers:32%
Supraspi-natustendinitisresults of 23welderscalled backfor clinicalfollow-upexams:16 weldershad supra-spinatustendinitis
Supraspi-natustendinitisresults of 30plate-workerscalled backfor clinicalfollow-upexams: 15plateworkershad supra-spinatustendinitis
Question-naireresults,shoulderpain of thesupraspi-natustendinitistype:Officeworker:2%
PRR=18.3
PRR=16.2
13.7-22.1 (90% CI)
10.9-21.5
(90% CI)
Participation rate: Not reported.
Not mentioned whether examinersblinded to case or exposure status.
Controls were matched for age andgender.
Plateworkers with shoulder painaveraged 6 years older than welderswith shoulder pain.
EMG analysis using fine monopolarwire electrodes showed that in workwhere the hand was positionedoverhead, the intramuscular pressurein the supraspinatus muscle hadextremely high pressure levelscompared to pressure levels in otherskeletal muscles.
Turnover rate of welders was 30%; may be explanation for lack ofassociation with duration.
Welding seen as static work;plateworking dynamic work.
3-50
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Hoekstraet al.1994
Cross-sectional
108 of 114 teleservice representatives working at2 Governmentadministration centers: Aand B.
Outcome: Self administered questionnaire. Case defined asthe presence of pain, numbness,tingling, aching, stiffness orburning in the shoulder, and noprevious injury; symptoms beganafter starting the job; lasting >1week or occurred once a monthwithin the past year; reported as“moderate” or greater on a 5-pointscale.
Exposure: Observation of workstations, measurement andevaluation of work station;observation of postures.
Center A:13%
Center B:44% Non-optimallyadjusteddesk heightwork Non-optimallyadjustedscreen
Õ
4.0
5.1
3.9
Õ
1.2-13.1
1.7-15.5
1.4-11.5
Participation rate: 95%.
Representatives perceived littlecontrol over actions of others; littleparticipation in decision making; littlefreedom to regulate own activities.
Perception that workload was highand variable.
Analysis controlled for gender andlocation and interactions checked.
Variables considered in logistic modelincluded location, age, seniority, hrspent typing at VDT, hr on the phone,3 chair variables, and perceivedadequacy of: (1) chair adjustment,VDT screen, (2) keyboard adjustment,VDT screen, (3) desk adjustment; jobcontrol, workload variability.
Center B location had nonadjustablework stations and mostlynonadjustable chairs causing elevatedarms, hunched shoulders and otherundesirable postures.
Linear regression also performed onpsychosocial variables in separatemodels for health outcomes of jobdissatisfaction and mental andphysical exhaustion (not for shoulderMSDs).
Did not include non-work-relatedvariables in analyses.
3-51
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Hughes etal. 1997
Cross-sectional
104 male aluminum smelterworkers: 62 carbonsetters, 36 crandoperators, 9 carbon plantworkers. There were 14workers who were notfrom selected jobs andwere excluded.
Outcome: Symptoms occurring inthe shoulder >once per month orlasting longer than 1 week in theprevious year, no acute ortraumatic onset; occurrencesince working at the plant, nosystemic disease. Physicalexamination: Active, passive,and resisted motions, pinch andgrip strength, 128 Hz vibrationsensitivity, two-pointdiscrimination. Psychosocialscales from questionnaire basedon Theorell and Karasek JobStress Questionnaire, and onWork Apgar questionnaire used.
Exposure: For carbon settersand crane operators (non-repetitive jobs) and modified job-surveillance checklist methodwas used. Job task analysisused a formula based on therelative frequency of occurrenceof posture during tasks.
14.9% withpositivesymptomsand physicalexam.
24% hadsymptoms inthe elbow-forearm inthe previousweek.
Õ Model basedon MSDdefined bysymptomsand physicalexamAge: OR=0.93
Good health:OR=0.35
Low decisionlatitude:OR=4.0
Years offorearm twist:OR=46
Model basedon MSDdefined bysymptoms
Age: OR=0.96
Smoker:OR=0.41
Low decisionlatitude:OR=4.5
High Jobdemand:OR=3.0
Yearsforearm twist:92
0.8-1.0
0.1-0.87
0.8-19
3.8-550
0.8-0.98
0.1-1.4
1.3-16
0.7-13
7.3-4
Participation rate: carbonsetters: 65%; crane operators: 56%;carbon plant: 33%.
Examiners blinded to exposure andhealth status: Not reported.
Analysis controlled for age, smokingstatus, sports and/or hobbies.
Psychosocial data collectedindividually; physical factors based onestimates of each job.
Job risk factors entered into the modelfor hand/wrist included (1) thenumber of years of handling >2.7kgs./hand, (2) push/pull, (3) lift/carry,(4) pinching, (5) wristflexion/extension, 60 ulnar deviation,and (7) forearm twisting.
Health interview included informationabout metabolic diseases, acutetraumatic injuries, smoking, hobbies.
Low participation rate limitsinterpretation.
3-52
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Ignatiuset al. 1993
Cross-sectional
1,917 of 3,248 male postalemployees completed aninterviewer-administeredquestionnaire; 1,081 wereletter delivery postmencompared to 836 otherpostal workers.
Outcome: history of symptomsand severity of recurrent jointpain as defined by Wells et al.[1983].
Exposure: work factors related toweight of letter bags, distancewalked each day, use oftransporting tools.
Postmen carry/day an averageload of 45 lbs; walked 4.5 km plus1,300 steps for 3.7 hr/day.
Recurrentjoint pain:55.1%
Severe jointpain: 12.0%
38.4%
6.2%
1.8
2.2
1.5 -2.2
1.5-3.1
Participation rate: 59%
Severe shoulder pain associated withage, work experience, bag weightand walking time.
Bags usually carried on one shoulder.
3-53
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Jonssonet al. 1988
Prospec-tive
Electronics Workers(n=69 females) out of initial96 workers.
(See Kilbom et al. 1986 for initial study.)
Outcome: Three separatephysical exams at yearly intervals(one initially) assessingtenderness on palpation, pain orrestriction with active andpassive movements; symptoms inprevious 12 months with regardto character, frequency, duration,localization, and relation to workor other physical activities. Analyzed if score on anysymptom of $2, on a 4 pointscale; “severe” symptom scoreequals 4.
Exposure: Carried out at outsetof study: Maximum voluntaryisometric contraction (MVC) offorearm flexors, shoulderstrength, handgrip, heart rateusing a bicycle ergometer andrating of perceived exertion. Videotaping performed for theanalysis of working postures andmovements.
Reallocation tasks:Non sitting; no inspection of smalldetails on printed circuit boards;standing and walking,occasionally sitting; caretakerwork; surveillance of machinery;and assembling bigger andheavier equipment.
Severeshoulderdisorders:
22% at 2ndexam
After 1 year;24%
Initially:11% ofsubjectshadshoulderMSDs
20% withunchan-gedworkingconditions
At 3rd examduring 3rdyear of longi-tudinal study: 38 subjectsreallocated tovaried taskshad improved(16% of thesehad severesymptomsinitially)significanceat p<0.05
Those withunchangedworking tasksdeterioratedfurther (26%).
Participation rate: 72% of originalgroup had 3 exams one year apart. 80% had 1st and 3rd year exams.
Questionnaire included spare timephysical activity, hobbies, perceivedpsychological stress at work, worksatisfaction, number of breaks, restpauses.
Most of physiologic and ergonomicevaluations conducted only at outsetof study.Low muscle strength not a risk factorfor subsequent symptoms.Relative time spent with shoulderelevated negatively related to“remaining healthy” after both 1 and 2years.Muscular strength and endurance notrelated to improvement nor remaininghealthy.At 2nd and 3rd examination, therewas a strong negative relationshipbetween “remaining healthy” andsatisfaction with colleagues.
Predictors of remaining healthy werework without elevating the shouldersand satisfaction with work tasks.
No mention of examiner being blindedto case status.Predictors of deterioration werepreviously physically heavy jobs, highproductivity (after 1 year), andprevious sick leave.
Predictors of improvement werereallocation, physical activity in sparetime, and high productivity (after 2years).
3-54
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Kiken et al.1990
Cross-sectional
294 Poultry Processors at2 plants. Plant #1=174Plant #2=120
Outcome: Period prevalencesymptom in last 12 months byquestionnaire. Case: Pain,aching, stiffness, burning,numbness or tingling in theshoulder, began after employmentat the plant; not due to previousaccident or injury outside work;lasted >8 hr and occurred 4 ormore times in the past year.
Point prevalence determined byphysical exam. Rotator cuffdefined as pain $3 on a 0 to 8scale on active and resistedshoulder abduction. Case mustfulfill symptom definition (listedabove).
Exposure: Determined byobservation; level of exposurewas based on exposure torepetitive and forceful handmotions, not shoulder.
Exposure measurementsestimated for the hand and wrist region and NOT theshoulder area.
Plant #1:Anysymptom forshouldercase: 46%
Periodprevalence:13%
Pointprevalencefor shouldercase: 3%
Plant #2:Anysymptom forshouldercase: 50%
Periodprevalence:14%
Pointprevalencefor shouldercase: 3%
28%
3%
0%
30%
5%
0%
1.6
4.0
Indeterminate
1.7
2.8
Indeterminate
0.9-2.9
0.6-29
Õ
0.8 -3.3
0.4-19.6
Õ
Participation rate: 98%.
Examiners blinded to case andexposure status.
Analysis stratified for gender andage.
Higher exposure jobs (HE) werelocated in the receiving, evisceration,whole bird grading, cut up anddeboning departments. Lowerexposure jobs (LE) were located inthe maintenance, sanitation, qualityassurance and clerical departments.
30% of workers involved in a jobrotation program may have influencedassociations made.
Annual turnover rate close to 50% atplant 1 and 70% at plant 2 makingsurvivor bias a strong possibility --leading to underestimation ofassociations.
3-55
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Kilbom et al.1986
Cross-sectional
106 of 138 femaleassemblers in twoelectronic manufacturingcompanies agreed toparticipate; 10 excludedbecause of symptoms inpast 12 months. 96 underwent medical,physiological, andergonomic evaluation.
(See Jonsson et al. 1988,earlier in this table, forfollow-up.)
Outcome: Three separatephysical exams at yearly intervals(one initially) assessingtenderness on palpation, pain orrestriction with active andpassive movements; symptoms inprevious 12 months with regardto character, frequency, duration,localization, and relation to workor other physical activities. Analyzed if score on anysymptom of $2, on a 4 pointscale; “severe” symptom scoreequals 4.
Exposure: Carried out at outsetof study: Maximum voluntaryisometric contraction (MVC) offorearm flexors, shoulderstrength, handgrip, heart rateusing a bicycle ergometer andrating of perceived exertion. Videotaping during therepresentative part of workingday from rear and side. Upperarm studied at rest and in 0 to30E, 30 to 60E, 60 to 90E, inextension and >90E abduction. The shoulder recorded as restingor elevated; also frequency ofchanges in posture betweendifferent angular sectors/hr,duration of postures. Work cycletime and number of cycles/hr,time at rest for arm, shoulder,head.
MSDsymptoms inthe shoulderusing a fourpoint severityscale:
None: 84%
Slight: 5%
Moderate:7%
Severe: 3%
LogisticRegressionmodel (allvariablessignificant atthe p<0.05level).
Shorterstature
Years ofemployment inelectronics.
Fewer totalnumber ofupper armflexions/hr.
Greaterpercentage ofwork cycletime withupper armabducted 0 to30E.
Participation rate: 77%.
See Jonsson et al. 1988 for follow-up.
No relation between maximal staticstrength and symptoms.
Examiner blinded to case status.
Questions included spare timephysical activities, hobbies, perceivedpsychosocial stress at work, worksatisfaction, number of breaks, restpauses.
59% had no symptoms or only slightones. There were no cases ofshoulder tendinitis.
Age showed a weak positivecorrelation.
Years of employment, productivity, muscle strength were not related tosymptoms.
There was large inter-workervariation in working posture andworking techniques.
The authors followed up on the non-participants and found no significantdifferences from participants.
The more dynamic working technique,the less symptoms.
3-56
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Kvarnström1983b
Cross-sectional
and
Case-control
112 cases of prolongedshoulder disordersidentified in a workplace of11,000 employees. Thetotal number of employeeswas approximately halffactory workers and halfoffice workers.
Case more than controlstudy:
Controls chosen at randomfrom factory workers,matched for age andgender.
Outcome: Shoulder casesfulfilled the following: symptomsfrom shoulder was the mainreason for inability to work, offwork longer than 4 weeks,fatigue in one of both shoulders,pain in shoulder brought on bywork and aching at rest werepresent, and Clinical examinationdemonstrated tenderness of theshoulder muscles, especiallymuscularis trapezius, levatorscapulae, and/or infraspinatusand/or tenderness at the tendoninsertions of the rotator cuffmuscles.
Muscle strength in shoulderassessed with regards to fourfunctions
Exposure: (1) Informationobtained through interview:organization of work, physicalwork load, physical environment,psychosocial work environment,social and ethnic conditions,(2) detailed work history. Factors0,1, or 2 given to different typesof work depending on theworkload borne by the shoulder. This factor multiplied by numberof years spent at job, andproducts were added, (3) 2company engineers graded thedegree of monotony andrepetitiveness in each job held bycases and controls.
Die castingmachineoperators(involvedheavy workwith repetitivemovements oftheshoulders):RR=5.4
Plasticworkers:RR=2.2
Spraypainters:RR=3.7
Surfacetreatmentoperators: RR=4.7
Assembly lineworkers:RR=5.2Ergonomicexperts’evaluation:cases hadsignificantly more mono-tonous andrepetitivework thancontrols.
Participation rate: Not reported.
Examiners not blinded to exposure,but selection based on diagnosis ofshoulder MSD.All 112 shoulder disorders occurred inlaborers; none in office workers.RR for Swedish workers: 0.46; RR forimmigrants: 3.1.All cases except one were paid piecerate.“Young persons significantly less illthan middled-aged.”The following questionnaireresponses were significantly differentbetween cases and controls: Grouppiece rate, shift work, heavy work,monotonous, stressful, detrimental tohealth, heavy lifting, and unsuitableworking conditions. 9 cases and 1control cited poor relationship withsupervisor.No difference in environmentalcondition, job content. Cases more likely to be married, haveill spouses, have children at home,work alternating shifts than controls.Work history showed no differencebetween points for cases andcontrols (see exposure column).Muscle strength bilaterally significantlylower in cases in four functions.
3-57
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
McCormacket al. 1990
Cross-sectional
Manufacturing workers:packaging or foldingworkers (41 males, 328females); sewing workers(28 males, 534 females);boarding workers (19males, 277 females)compared to knittingworkers (203 males, 149females); non-officeworkers (204 males, 264females) compared withknitting workers(203 males, 149 females).These groups werecompared to a referentgroup consisting of non-office workers maintainingmachinery, involved intransportation, or workedas cleaners and sweepers. None of the referent groupused rapid repetitivemovements comparable tothe employees in the otherjob categories.21, 25 and 36 operatorsfrom each group and 25 of55 auxiliary nurses andhome helpers (controls)participated in the study.
Outcome: Questionnaire andphysical examination initially bynurse screening; if employeeanswered affirmative to questionregarding symptoms in upperextremity and/or had any positivephysical findings, then hadphysician examination. The term"shoulder condition" used todefine abnormalities of shoulder;consisted of bursitis, bicipitaltendinitis and impingementsyndrome.
Exposure: Based on observationof job activities; only the boardingworkers had activities requiringreaching overhead (frompersonal communication with firstauthor).
Packaging/foldingworkers:2.7%
Sewingworkers:2.5%
Boardingworkers:2.4%
Knittingworkers:1.1%
non-officeworkers:
2.1%
2.1%
2.1%
2.1%
1.3
1.2
1.1
1.3
0.5-3.8
0.5-2.7
0.4-2.9
0.5-3.1
Participation rate: 91%.
Examiners not blinded to exposurestatus (information obtained frompersonal communication).
11 Physician examiners; inter-examiner potential problemacknowledged by authors.
Questionnaire asked types of jobs,length of time on job, production rate,nature and type of upper extremitycomplaint and general health history.
Age, sex, race, job category andyears of employment not statisticallysignificant with "shoulder conditions."
Patients with objective diagnosticshoulder findings: Of 45 casesdiagnosed: 25 graded as “mild”,19 graded as “moderate; 1 graded assevere.
3-58
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Milerad and Ekenvall1990
Cross-sectional
99 Dentists randomlyselected from Stockholmdentist registry whopracticed $10 yearscompared to100 pharmacists selectedfrom all pharmacists inStockholm.
Outcome: Based on telephonequestionnaire: Shouldersymptoms at any time before theinterview "lifetime prevalence." Further analyzed according toNordic questionnaire as toduration during last 12 monthsand during last 7 days, effect onwork performance and leisureactivities, and sick leave.
Exposure: Questionnaireincluded: (1) abduction of arm,particularly in sit-down dentistry,(2) static postures, (3) workhr/day.
Male: 36%Female: 67%
Neck andshoulder:36%
Neck andshoulder andupper arm:16%
15%28%
17%
3%
2.42.4
2.1
5.4
1.0 -5.41.5-3.7
1.3-3.0
1.6-17.9
Participation rate: 99%.
Stratified analysis by gender.
No difference in leisure timeexposure, smoking, systemic disease,exposure to vibration.
Symptoms increased with age infemale dentists only.
Duration of employment highlycorrelated with age (r=0.84, 0.89).
No relation between symptoms andduration of employment.
Equal problems dominant andnondominant sides.
3-59
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Ohara et al.1976
Cross-sectionaland Pro-spective
For cross-sectional study:399 cash registeroperators compared with99 office machineoperators and 410 otherworkers (clerks andsaleswomen). All female.
For prospective study: 56 workers employed <7months had testing pre-and post-intervention usingquestionnaire and physicalexam.
86 operators, newly hiredafter interventions, alsohad evaluation after10 months of working.
Outcome: Assessed by standardhealth inventory and medicalexamination (used clinicalclassification according to thecommittee on cervicobrachialdisorders of the JapanAssociation of Industrial Health, inTable 3 in the paper).
Periodic physical exam performedtwice a year from 1973. Primaryexams performed on 371operators. 130 (35%) receiveddetailed exams.
Exposure: To repetitivemovements relocatingmerchandise across counter andbagging, involved muscle activityof the fingers, hands, and arms;extreme and sustained postures.
Interventions: (1) a 2-operatorsystem, 1 working the register,one packing articles, changingroles every hr; (2) continuousoperating time <60 min; max.working hr/day 4.5 hr;(3) 15- min resting period everyhr; (4) electronic cash registerswith light touch keyboardsubstituted for half of previouslyused mechanical cash registers.
Shoulderstiffness: Cashiers:81%
Shoulderdullnessand pain:
Cashiers: 49%
Shoulderstiffness :
OfficeWorkers:72%
Shoulderdullnessand pain:
Otherworkers:68%
Officeworkers:30%
1.7
2.0
2.2
1.0-2.8
1.4-2.8
1.4-3.5
Participation rate: for prospectivestudy = 100%.
Participation rate: for cross-sectionalstudy, not reported.
Unknown whether examiners blindedto case status.
Interventions did not reducecomplaints in the shoulder region, butdid improve symptoms in the arms,hands, fingers, low back, and legs. The lack of improvement in theshoulder region was stated to be dueto the use of the same narrow checkstands, unsuitable counter height, andnecessity of continuous lifting of theupper limbs.
Operators hired after the interventionsand then examined after 10 monthshad less Grade I, II , or III occupationalcervicobrachial disorders inexamination than those hired beforeintervention.
Only 14.5% with >3 yearsemployment at worksite.
Narrow work space and counterheight not adjusted for height ofworker.
3-60
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Ohlssonet al. 1989
Cross-sectional
Electrical equipment andautomobile assemblers(n=148), former femaleassembly workers whoquit within 4 years (n=76)compared to randomlysampled females fromgeneral population (n=60).
Outcome: Based onquestionnaire: Any shoulderpain, shoulder pain affectingwork ability, and shoulder pain inthe last 7 days.
Exposure: Based on jobcategory.
Shoulderpain inprevious 12months: 55%
Shoulderpain inprevious 7days: 38%
Work inauxiliaryprevious 12months: 21%
45%
18%
10%
2.0
3.4
2.4
1.1-4.0
1.6-7.1
1.0-5.8
Participation rate: Not reported.
Significant association for shouldersymptoms and medium and fast pacecompared to slow pace but not veryfast pace.
Significant association with durationof employment (p=0.03), but muchstronger for workers <35 years thanworkers >35 years.
Significant interaction between ageand employment.
Older females employed for shorterperiods had more symptoms thanyounger ones.
3-61
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Ohlssonet al. 1994
Cross-sectional
Exposed Group: 206 of247 females working in13 fish processing plantsparticipated.
322 females who leftemployment in the fishprocessing industry in the10 years prior to the study.
Comparison group: All 208females employed in thesame towns as theexposed; 71 wereemployed in day nurseries;92 in offices; 42 caretakersof elderly; 3 gardeners.
Outcome: Defined by criteriafrom questionnaire and physicalexamination: standard diagnosisof frozen shoulder,supraspinatus tendinitis,infraspinatus tendinitis, bicipitaltendinitis acromioclavicularsyndrome.
Exposure: Assessed byquestionnaire (length ofemployment; psychosocialfactors, physical factors) and byobservational methods(Ergonomic Workplace Analysis)and NIOSH guidelines for lifting. Analyzed 10 items: work site,general physical activity, lifting,work postures and movements,job content, job restrictiveness,worker communication, difficultyof decision making, repetitivenessof the work, and attentiveness.
74 workers videotaped $10 min.from the back and sides. Average counts of twoindependent readers forfrequencies, duration and criticalangles of movement used.
Frozen shoulder: 2%
Supraspi-natustendinitis:15%
Infraspinatustendinitis:12%
Bicipitaltendinitis:10%
Acromiocla-vicularsyndrome:17%
0.5%
5%
3%
4%
6%
4.1
3.4
4.7
2.4
3.1
PRR ofshoulderdisorders:2.95PRR forsuprapi-natus,infraspinatusand bicipialtendinitis: 3.03
PRR forsuprapinatusandinfraspinatus tendinitisalone: 3.5
0.5-37
1.6-7.2
1.4-15.2
1.1-5.4
1.6-6.0
2.2-4.0
2.0-4.6
2.0-5.9
Participation rate: 83%.No exposure information available toexaminers, however, it was notpossible to completely blind thestudy/referent group status.All activities (trimming of cod, packingfish and herring filleting) were foundto be highly repetitive with poorworking postures and fastmovements by standardized“ergonomic workplace analysis”(EWA) methods; very few pauses inthe work cycle; tasks not varied.Sports activities were highlyassociated with shoulder tendinitis(OR=4, 9) in multiple logisticregression analysis.In the control group, prevalences ofupper limb disorders increased substantially with age. Among theexposed, the prevalence remainedalmost constant with age.Excess prevalence for exposedfemales most pronounced for females<45 years. There was a pronounceddose-response for disorders of theneck or shoulders vs. duration ofexposure in the industry. No suchassociations seen in group >45 years. Authors explained as perhaps due tothe “healthy worker effect,” but, itwould be more accurate to describe itas “survivor bias.”Psychosocial work environment,stress and worry factors, tendenciestowards muscular tension differedsignificantly between exposed andcontrols.
3-62
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Ohlssonet al. 1995
Cross-Sectional
Industrial Workers(n=82 females) exposed torepetitive tasks with shortcycles mostly far <30 sec,usually with a flexed neckand arms elevated andabducted intermittently;68 former workers (meanemployment time 21 years)who had left the factoryduring the 7 years beforethe study; these workerswere compared to 64referents with no repetitiveexposure at their currentjobs (female residents of anearby town currentlyemployed as customerservice, ordering and pricemarking in supermarkets,as office workers (noconstant computer work)or as kitchen workers.
Outcome: Measured by physicalexam and questionnaire.Frozen shoulder: Limited out-ward rotation and abduction.Infraspinatus, supraspinatustendinitis: Local tenderness overtender insertion, pain withresisted abduction.Bicipital tendinitis: Pain withresisted elevation of arm, resistedflexion of elbow.Acromicoclavicular syndrome: Pain with horizontal adductionand/or outward rotation of arm.
Exposure: Videotaping andobservation. Analysis ofelevation of the arm: 0E, 30E, 60E,and for abduction 30E, 60E, 90E.74 workers videotaped $10 min.from back and sides. Averagecounts of two inde-pendentreaders for frequencies, duration,and critical angles of movementused. Repetitive industrial work tasksdivided into 3 groups: (a) fairlymobile work, (b) assembling orpressing items, and © sorting,polishing and packing itemsWeekly working time, workrotation, patterns of breaks,individual performance rate (piecerate).Only exposure readings fromright arm were used. Muscle strength (maximumvoluntary capacity) measured byhand dynamometer at elevation,
50% (n=82)
Employmentduration:<10 years(n=19): 53%
10 to 19years(n=25): 48%
>20 years(n=38): 50%
16%(n=64)
5.0
9.6
4.4
3.8
2.2-11.0
2.8-33.0
1.5-13.0
1.4-10.0
Participation rate: current workers:96%; past workers: 86%;referents: 100%.Questionnaire included individualfactors, work/environment,symptoms. No exposure information available toexaminers, however, it was notpossible to completely blind thestudy/referent group status.Psychosocial scales assessed:control over one’s work, stimulation,psychological climate, work strain,fellowship at work and social networkat work. Age, stress/worrytendency, subjective muscular tensiontendency, social network outside ofwork, psychosomatic symptoms.Age and employment status (repetitivevs. referent) controlled for in logisticmodel.For continuous variables, OR are for75th vs. 25th percentiles.Videotape analysis revealedconsiderable variation in posture evenwithin groups performing similarassembling tasks.Logistic models replacing repetitivework with videotape variables foundmuscular tension tendency and neckflexion movements significantlyassociated with neck/shoulderdiagnoses.Significant association between timespent with upper arm abducted >60°and neck/shoulder diagnoses.
3-63
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Onishi et al.1976
Cross-sectional
Female industrial workers: 42 reservationists;95 fluorescent lampassemblers;109 photographic filmrollers; 46 teachers ofhandicapped children;101 office workers.
Outcome: Based on(1) symptoms of shoulderstiffness, dullness, pain,numbness; (2) pressure (<1.5kv/cm2) measured by straintransducer at which subject feltpain. (3) physical exam: rangeof motion, tests, nervecompression tenderness.
Exposure: Observation of jobtasks, then job categorization.
Reservations; Key 15,000 to20,000 strokes/day or more onbusy days 2 to 3 times/week.
Assemblers inspect lamps onceevery 3.5 to 4.5 sec; all work12 hr/day.
Film rollers wind 1 roll of 35mmfilm every 2.5 to 5 sec over 7.5hr/day.
Prolonged contraction oftrapezius noted in 2 film rollers.
Teachers and nurses daily careof disabled children e.g., lifting.
Office workers: Record keeping,copying, etc.
ShoulderTenderness:
Reserva-tionists: assemblers:70%
Film rollers:84%
Teachers:58%
ShoulderStiffness:
Reservatio-nists(N=45):56.6%
Assemblers(N=94):66.6%
Film Rollers(N=127):59.1%
Teachers(N=52):65.4%
Officeworkers(n=101):48%
34.7%
1.1
6.0
1.6
2.5
3.7
2.7
2.1
0.6-1.9
3.0-12.2
0.7-3.3
1.1-5.6
2.0-7.0
1.5-4.9
0.9-4.6
Participation rate: Not reported.
Unknown whether examiners blindedto case status.
Body height, weight skin foldthickness and muscle strength, gripstrength, obtained.
Body height and weight differencesnot significant.
Significant difference between bodyfat in reservationists and officeworkers.
Significant difference in grip strengthin teachers and nurses comparedwith office workers.
Those with habitual shoulder stiffnesshad lower threshold of localtenderness than those withoutstiffness.
No difference between workers withtenderness threshold above1.5 Kb/cm2 and those below withrespect to age, height, weight, skinfold thickness, grip strength, upperarm abduction strength, back musclestrength.
3-64
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Punnettet al. 1985
Cross-sectional
162 female garmentworkers, 85% wereemployed as sewingmachine operators andsewing and trimming byhand.
Comparison: 76 of 190 fullor part-time workers onday shift in a hospital whoworked as nurses or aids;lab techs or therapists;food service workers.
Employees typing >4 hr/dayexcluded from comparisongroup.
Outcome: Self-administeredquestionnaire about pain andstandardized physical exam.
Cases defined as the presencesof persistent shoulder pain(lasted for most days for onemonth or more within the pastyear); were not associated withprevious injury, and, began afterfirst employment in garmentmanufacturing or hospitalemployment. Key questionsbased on the arthritis supplementquestionnaire of NHANES.
Exposure: Self-administeredquestionnaire; number of years inthe industry, job category,previous work history.
Garmentworkers:19.6%
Hospitalemployees8.8%
ShoulderMSDs inGarmentworkers vs.Hospitalemployees:OR= 2.2
ShoulderMSDs inStraight stitchworkers vs.Hospitalemployees:OR=3.9
ShoulderMSDs in Topstitchworkers vs.HospitalemployeesOR=5.0
1.0-4.9
p#0.05
p#0.05
Participation rate: 97% (garmentworkers), 40% (hospital workers).
Analysis stratified for number ofyears employed, decade of age,native language.
Age and length of employment not apredictor of risk of shoulder MSDs.
Prevalence of pain not associatedwith years of employment in garmentworkers.
Non-English speakers significantlyless likely to report pain (RR 0.6p<0.05).
Native English speakers significantlyolder than non-native Englishspeakers (p<0.03).
Logistic regression model foundgarment work and languagesignificantly related to shoulder pain.
3-65
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Rossignolet al. 1987
Cross-sectional
191 computer and dataprocessing services, publicutilities of MassachusettsState Department, 28 ofwhom did not use akeyboard with a VDT.
Centers selected at randomfrom 38 work sites with>50 employees.
Outcome: Self-administeredquestionnaire case defined as:“Almost always experienced”shoulder pain, stiffness orsoreness or missed work due toshoulder pain, stiffness orsoreness.
Exposure: Self-reported numberof hr/day working on a keyboardwith a VDT. Subjects selectedafter observation of work sites.
0.5 to 3 hr ofVDT use/day(n=31): 35%
4 to 6 hr ofVDT use/day(n=28): 48%
>7 hr of VDTuse/day(n=104):51%
Compari-son group(with nocomputeruse)(n=28):18%
Up to 3 hr ofVDT usecompared to0 hr of use.OR=2.5
4 to 6 hr ofVDT usecompared to0 hr of use:OR=4.0
>7 hr of VDTuse comparedto 0 hr of use: OR=4.8
0.7-10.8
1.0-16.9
1.6-17.2
Participation rate: in six industrygroups 67 to 100%.
Participation rate: for individualclerical workers: 94 to 99%.
“Assessed magnitude of confoundingby age, cigarette smoking, industry,educational VDT training.”
The study was presented as “Generalhealth survey to avoid observationbias.”
3-66
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Sakakibaraet al. 1987
Cross-sectional
48 Orchard workers(20 males and 20 females).
Compared symptoms aftercompletion of thinning ofpears, bagging of pearsand bagging of apples(covering fruit with paperbags while on the trees).
Internal comparison usingsame study population.
Outcome: Shoulder paindescribed as the presence ofstiffness and pain daily.
Exposure: Observation of jobs.Angles of flexion of the shoulderon one subject were measuredevery 25 min. during a whole daydoing each task.
Farmers worked approximately 8hr/day for 10.6 to 13.6 days eachyear bagging or thinning pearsand bagging apples. Medianshoulder flexion was 110E to119E for thinning pears andbagging pears; 30E baggingapples.
Workersthinningpears(estimatedfromhistograms):46%
Workersbaggingpears(estimatedfromhistograms):29%
Workersbaggingapples:21%
Workersthinning pearsvs. workersbaggingapples:OR=2.2
Workersbagging pearsvs. baggingapples:OR=1.4
1.2-4.1
0.7-2.8
Participation rate: 77%.
Stratified by gender.
General fatigue, gastric disturbances,appetite loss and headache showedno difference in frequency betweentasks.
Stiffness and pain in shoulderssignificantly higher from thinning andbagging pears than apples whichauthors attributed to working postureof elevated arms and neck extension.
Exposure data based onmeasurement of one worker may notbe generalized to others.
The proportion of workers with >90Eforward shoulder flexion wassignificantly higher for thinning outpears and bagging pears than forbagging apples.
3-67
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Sakakibaraet al. 1995
Cross-sectional
Of 65 female Japanesefarmers. 52 completed thequestionnaire and physicalexam in late June forbagging pears and late Julyfor bagging apples.
Questionnaire: Stiffness and painin shoulder region. Symptoms inpast 12 months for $one day, orsymptoms in past 12 months for$8 days.
Exam: Muscular tenderness inshoulder region; maximal graspingpower measured bydynamometer and back musclepower by myosphenometer.
Exposure: Observation of tasksand measurements ofrepresentative workers (only twoworkers measured).
Angle of arm elevation duringbagging was measured in onesubject.
Angle of forward flexion ofshoulder for bagging pears was110 to 139o. 75% of angles wereabove 90o. For bagging applesthe angle of forward flexion was0 to 140o; 41% of the angleswere >90o.
Pear bagging
Muscle tenderness:48.1%
Pain in jointmotion:23.1%
Applebagging
Muscletender-ness:28.8%
Pain in jointmotion: 21.2%controls
Workersbagging pearswith muscletenderness vs. applebaggingwith muscletenderness:OR=1.7
Workersbagging pearswith pain injoint motionvs. applebagging withpain in jointmotion:OR=1.1
1.1-2.9
0.53-2.3
Participation rate: 80%.
Examiners not blinded to case statusdue to design of study.
Same population examined two times. 2nd exam occurred one month afterfirst. These results used in analysesfor comparison of two tasks.
Stiffness and pain during applebagging may have been pain that wasa residual of pear bagging operations.
Number of fruit bagged/day wassignificantly more in pear bagging thanin apple bagging.
Exposure measurements onlyobtained on 2 workers andgeneralized to all workers.
3-68
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Schibye etal. 1995
Pro-spective
Follow-up of 303 sewingmachine operators at ninefactories representingdifferent technology levelswho completedquestionnaire in 1985.
In April 1991, 241 of279 traced workersresponded to samequestionnaire.
Outcome: Cases defined by theNordic questionnaire forsymptoms as to duration duringlast 12 months and during last 7days, effect on workperformance and leisureactivities, and sick leave.
Exposure: Assessed byquestions regarding type ofmachine operated, workorganization, workplace design,units produced/day, and paymentsystem, time of employment as asewing machine operator.
Workerswhodelivered orcollectedtheir ownmaterials:18%shouldersymptoms;the rest 33%
Õ Õ Õ Participation Rate in 1985: 94%.Participation Rate in 1991: 86%.All participants were female.
77 of 241 workers still operated asewing machine in 1991.
82 workers had another job in 1991. Among those 35 years or younger,77% had left their jobs; among thoseabove 35 years, 57% had left theirjobs.
20% reported musculoskeletalsymptoms as the reason for leavingjob.
No significant changes in prevalencesamong those employed as sewingmachine operators from 1985 to 1991;significant decrease in those whochanged employment.
3-69
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Stenlundet al. 1992
Cross-sectional
55 of 75 rockblastors, 54 of75 bricklayers randomlyselected from unionrecords and 98 of 110foremen selected fromforemen employed in largeconstruction firms.
Outcome: Based on a grading ofacromioclavicular joints ofshoulders. Grade 0 = normalGrade 1 = minimal changesGrade 2 = moderate changesGrade 3 = severe osteoarthritisGrade 4 = joint destroyed
Exposure: Based on self-reported estimates of loads lifted,hr of exposure to vibration, jobtitle, and years of employment. The weights of tools alsoobtained.
Bricklayers lifted a mean of29,439 tonnes; Rockblasters, amean of 33,210 tonnes; Foremen,a mean of 2,261 tonnes.
BricklayersRt side:59.3% Lt side:40.7%
RockblastersRt side:61.8% Lt side:56.4%
Foremen
36.7%
23.4%
Foremen
36.7%
23.4%
2.2
1.8
2.1
4.0
Years ofmanual work>28 years vs.<10 yearsRt side: 2.9Lt side: 2.5
10 to 28years vs.<10 yearsRt side: 1.1Lt side: 2.3
Load lifted725,000 vs.710 tonnesRt side: 3.2Lt side:10.3
Vibration725,000 hrvs <9001 hrRt side: 2.2Lt side: 3.1
1.0-4.7
0.8-3.9
0.9-4.6
1.8-9.2
1.2-7.41.0-5.9
1.1-4.71.0-5.3
1.1-9.23.1-34.5
1.0-4.61.4-6.9
Participation rate: 80%.
Classification of X-rays achieved withblinding of investigators to age, nameor exposure status.
Study looked at manual work andexposure to vibration and relationshipto osteoarthritis in acromioclavicularjoint using shoulder x-rays.
Logistic regression models adjustedfor age, smoking, dexterity, checkedfor interactions.
Questionnaire included questionsabout smoking, dexterity, ethnicity,citizenship.
Risks were elevated as length ofemployment increased and asexposure to vibration and amountlifted increased.
X-ray grades 2 and 3 for analysis.
Smoking significantly associated withosteoarthritis of right shoulder (OR=2,2.4) but not left side. Significancefound, but is it meaningful?
Left handedness significantlyassociated with osteoarthritis of leftside (OR=2.5).
The age adjusted odds ratio forosteoarthrosis in the rightacromioclavicular joint for brick layersand rock blasters as compared withforemen, was 2.16 on the right side95%CI(1.14-4.09), and was 2.56 95%CI (1.33-4.93).
3-70
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Stenlundet al. 1993
Cross-sectional
55 of 75 rockblasters and54 of 75 bricklayersselected randomly fromunion records, and 98 of110 foremen randomlyselected from foremenemployed in largeconstruction companies.
Outcome: Based onquestionnaire of previous injuriesand diseases of musculoskeletalsystem and previous shoulderpain, and physical exam.
Case defined as “Signs ofshoulder tendinitis” as palpablepain of the muscle attachment orpronounced pain reaction toisometric contraction in any of the4 rotator cuff muscles or bicepsmuscles.
”Clinical entity of tendinitis”defined as pain during the lastyear, pronounced pain reaction topalpation or isometric contraction.
Exposure: Based on self-reported estimates of load lifted,hr of exposure to vibration, jobtitle and years of employment.
Load defined as 0 to 709 tonnes,710 to 25,999 tonnes, >25,999tonnes vibration defined as hr ofexposure: 0 to 8,999, 9000 to255,199, >255,999 hr to each toolmultiplied by factor correspondingto vibration energy. Years ofmanual work: 0 to 9, 10 to 28,>28 years.
BricklayersRt. side: 11.1%; Lt. side: 14.8%
RockblastersRt. side: 32.7%Lt. side:40.0%
Foremen
8.2%
17.1%
8.2%
17.1%
0.4
Õ
1.7
3.3
Clinical EntityLoadRt. side: 1.0Lt. side: 1.6
VibrationRt. side: 1.9Lt. side: 2.5
Manual WorkRt. side: 0.9Lt. side: 2.3
Signs ofTendinitisLoadRt. side: 1.0Lt. side: 1.8
VibrationRt. side: 1.7Lt. side: 1.8
Manual WorkRt side: 1.1Lt side: 1.9
0.2-1.3
Õ
0.7-4
1.2-9.3
0.5-2.20.6-4.1
1.0-3.41.1-5.9
0.5-1.80.9-6.3
0.6-1.80.9-3.4
1.1-2.61.1-3.1
0.7-1.81.0-3.4
Participation rate: 80%.
Examiners blinded to exposure statusor job title.
Unconditional multiple regressionanalysis adjusted for age,handedness, smoking and sportactivities. In all models left and rightsides calculated separately.
Vibration related to shoulder tendinitisalthough confounded by static loadsand lifting.
Interactions tested for.
The study looked at manual work andexposure to vibration and theirrelationship to signs of tendinitis of theshoulder.
Exposure-response found wherecomparison of high vibration exposurecompared to low exposure.
3-71
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Sweeneyet al. 1994
Cross-sectional
105 of 164 sign languageinterpreters for the deaf,who attended aprofessional conference ofsign language interpreters.
Outcome: Symptom questionnaireand physical exam:
Symptom case defined as thepresence of pain, aching,stiffness, burning, numbness ortingling in the shoulder lasting$ one week or once/month withinthe past 12 months; no previousinjury and symptoms occurredafter becoming a sign-languageinterpreter.
Symptom-exam case: Defined asthe presence of symptoms and apositive exam for the shoulder.
Exposure: Based onquestionnaire (years ofemployment as a sign languageinterpreter; numbers of hrs/weekengaged in signing).
Symptomcase: 22%
Symptomcase withmoderate tosevereshoulderdiscomfort:50%
Positivesymptom +positiveexam: 1%
>20 hrsigning,comparedto<10 hr/week
Õ
2.5
Õ
0.8- 8.2
Õ
Participation rate: 64%.
Examiner blinded to exposure status.
Generalizability of results to other signlanguage interpreters is limited.
3-72
Table 3-5 (Continued). Epidemiologic studies evaluating work-related shoulder musculoskeletal disorders
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
Wells et al. 1983
Cross-sectional
Of 199 letter carriers,196 were compared to76 of 79 meter readers and127 of 131 postal clerks.
Outcome: Telephone interviewbased on current pain;frequency, severity, interferencewith work, etc; score of 20required to be a case. Morepoints given to neck and shoulderproblems that interfered withroutine daily activities.
Exposure: Based on jobcategory; based on self-reportedinformation on weight carried, previous work involving lifting andwork-related injuries.
All lettercarriers:18%
Lettercarriers:increasedweight: 23%
Lettercarriers:no weightincrease:13%
Postalclerks:5%
Postalclerks:5%
Postalclerks: 5%
3.6
5.7
3.3
1.8-7.8
2.1-17.8
1.1-11.1
Participation rate: 99% among lettercarriers, 92% meter readers, 97%postal clerks.
Schooling and marital status asked.
Symptoms alone used for MSDdefinition.
Comparison group (gas meterreaders) used because of similar“walking rate” without carrying weightcompared to letter carriers. Postalclerks neither walk nor carry weight.
During analysis, more weight wasgiven to scoring neck and shoulderthan other body regions. Outcomeinfluenced results when ranking ofbody MSDs, though, would notinfluence group comparison.
Adjusted for age, number of years onthe job, quetlet ratio and previouswork experience.
104 letter carriers had bag weightincreased from 25 to 35 lbs in theyear prior to the study.
Letter carriers with increased bagweight walked on average 5.24 hr;those with no change in bag weightwalked 4.83 hr.
Letter bags usually carried on theshoulder.
3-73
4-1
CHAPTER 4Elbow Musculoskeletal Disorders(Epicondylitis): Evidence forWork-Relatedness
SUMMARY Over 20 epidemiologic studies have examined physical workplace factors and their relationship toepicondylitis. The majority of studies involved study populations exposed to some combination of workfactors, but among these studies were also those that assessed specific work factors. Each of the studiesexamined (those with negative, positive, or equivocal findings) contributed to the overall pool of data to makeour decision on the strength of work-relatedness. Using epidemiologic criteria to examine these studies,and taking into account issues of confounding, bias, and strengths and limitations of the studies, weconclude the following:
There is insufficient evidence for support of an association between repetitive work and elbowmusculoskeletal disorders (MSDs) based on currently available epidemiologic data. No studies havingrepetitive work as the dominant exposure factor met the four epidemiologic criteria.
There is evidence for the association with forceful work and epicondylitis. Studies that base exposureassessment on quantitative or semiquantitative data tended to show a stronger relationship for epicondylitisand force. Eight studies fulfilling at least one criteria showed statistically significant relationships.
There is insufficient evidence to draw conclusions about the relationship of postural factors alone andepicondylitis at this time.
There is strong evidence for a relationship between exposure to a combination of risk factors (e.g., forceand repetition, force and posture) and epicondylitis. Based on the epidemiologic studies reviewed above,especially those with some quantitative evaluation of the risk factors, the evidence is clear that an exposureto a combination of exposures, especially at higher exposure levels (as can be seen in, for example,meatpacking or construction work) increases risk for epicondylitis. The one prospective study which had acombination of exposure factors had a particularly high incidence rate (IR=6.7), and illustrated a temporalrelationship between physical exposure factors and epicondylitis.
The strong evidence for a combination of factors is consistent with evidence found in the sports andbiomechanical literature. Studies outside the field of epidemiology also suggest that forceful and repetitivecontraction of the elbow flexors or extensors (which can be caused by flexion and extension of the wrist)increases the risk of epicondylitis.
Epidemiologic surveillance data, both nationally and internationally, have consistently reported that thehighest incidence of epicondylitis occurs in occupations and job tasks which are manually intensive andrequire high work demands in dynamic environments—for example, in mechanics, butchers, constructionworkers, and boilermakers.
Epicondylar tenderness has also been found to be associated with a combination of higher levels of forcefulexertions, repetition, and extreme postures of the elbow. This distinction may not be a true demarcation ofdifferent disease processes, but part of a continuum. Some data indicate that a high
4-2
percentage of individuals with severe elbow pain are not able to do their jobs, and they have a higher rate ofsick leave than individuals with other upper extremity disorders.
INTRODUCTION
Epicondylitis is an uncommon disorder, with theoverall prevalence in the general populationreported to be from 1% to 5% [Allender1974]. There are fewer epidemiologic studiesaddressing workplace risk factors for elbowMSDs than for other MSDs. Most of thesestudies compare the prevalence of epicondylitisin workers in jobs known to have highlyrepetitive, forceful tasks (such as meatprocessing) to workers in less repetitive,forceful work (such as office jobs); the majorityof these studies were not designed to identifyindividual workplace risk factors.
The text of this section on epicondylitis isorganized by work-related exposure factor.The discussion within each factor is organizedaccording to the criteria for evaluating evidencefor work-relatedness in epidemiologic studiesusing the strength of association, theconsistency of association, temporalrelationships, exposure-response relationship,and coherence of evidence. Conclusions arepresented with respect to epicondylitis for eachexposure factor. Summary information relevantto the criteria used to evaluate study quality ispresented in Tables 4-1 to 4-4. A moreextensive summary (Table 4-5) includesinformation on health outcomes, covariates, andexposure measures. All tables are presented atthe end of this chapter. Not all the articlessummarized in the tables are referenced in thisnarrative, but they have been reviewed andevaluated and are included for information.
There are 19 studies referenced in Tables 4-1through 4-4, 18 cross-sectional studies and one
cohort. Those studies using symptom andphysical examination findings to defineepicondylitis used consistent criteria—almost all studies using physical examination fordiagnosis required pain with palpation of theepicondylar area and pain at the elbow withresisted movement of the wrist. However,studies using a definition based on symptomdata alone used various criteria, some based onfrequency and duration of symptoms [Burt etal.1990; Hoekstra et al. 1994; Fishbein et al.1988] others based on elbow symptomspreventing work activities [Ohlsson et al.1989].
REPETITION
Definition of Repetition for ElbowMSDs
For our review, we chose studies thataddressed the physical factor of repetition andits relation to elbow MSDs, especially thosestudies that focused on epicondylitis. Studiesusually defined repetition, or repetitive work,for the elbow as work activities that involved(1) cyclical flexion and extension of the elbowor (2) cyclical pronation, supination, extension,and flexion of the wrist that generates loads tothe elbow/forearm region. Most of the studiesthat examined repetition as a risk factor forepicondylitis had several concurrent orinteracting physical work load factors. Weattempted to select those studies in whichrepetition was either the single risk factor or thedominant risk factor based on our review
of the study and our knowledge of theoccupation. This method eliminated those
4-3
studies in which a combination of high levels ofrepetition and high levels of force exist, or thosestudies which selected their exposure groupsbased on highly repetitive, forceful work.
Studies Reporting on the Associationof Repetition and EpicondylitisSeven studies reported results on theassociation between repetition and adverseelbow health outcomes including epicondylitis.The epidemiologic studies that addressrepetitive work and epicondylitis compareworking groups by classifying them intocategories based on some estimation ofrepetitive work, such as percent of time typing[Burt et al. 1990], number of items per hour[Ohlsson et al. 1989], or number of handmanipulations per hour [Baron et al. 1991].Those studies which may have measuredrepetitive work but have exposure to higherlevels of force will be discussed in the “Force”section.
Studies Meeting the Four EvaluationCriteria
None of the studies (see Table 4-1 and Figure4-1) reviewed for the elbow summary sectionmet all four evaluation criteria outlined in theIntroduction Section.
Studies Meeting at Least One of the Criteria
The studies will be summarized in alphabeticalorder as they appear in Table 4-1.
Andersen and Gaardboe [1993a] used a cross-sectional design to compare sewing machineoperators with a random sample of womenfrom the general population of the same region.Elbow pain, not epicondylitis, was the MSD ofinterest in this study. A case of elbow pain was
based on self-reported symptoms lasting morethan 1 month since starting career, or pain formore than 30 days. Exposure was based on theauthors’ experiences as occupational healthphysicians and involved crude assessment ofexposure level and exposure repetitiveness.Analysis dealt with exposure as “duration ofexposure as a sewing machine operator”.Statistical modeling controlled for age, havingchildren, not doing leisure exercise, smoking,and socioeconomic status. For this study, theexposure classification scheme does not allowseparation of the effects of repetition from thoseof force, although repetition may be a moreobvious exposure.
Baron et al. [1991] explored epicondylitisamong grocery store workers, comparing theprevalence among grocery store cashiers tothat among non-cashiers and identified workrisk factors while controlling for covariates.Detailed ergonomic assessment of grocerychecking and cashiering was completed usingboth on-site observational techniques andvideotaped analyses. The majority of cashierswere categorized as having “medium” levels ofrepetition for the hand (defined in this study asmaking 1250 to 2500 hand movements perhour). Repetitive movements were notrecorded directly for the elbow; however, thenumber of hand movements serve as anapproximation for elbow repetitions. Age,hobbies, second jobs, systemic disease, andheight were considered as covariates in themultivariate analyses. The diagnosis ofepicondylitis required standard physicalexamination techniques of palpation andresisted extension and flexion of the elbow.
Burt et al. [1990] studied 834 employees usingcomputers at a metropolitan newspaper, using a
4-4
self-administered questionnaire for caseascertainment. Exposure assessment was basedon self-reported typing time and observation ofemployees’ job tasks, then categorization byjob title. A separate job analysis using achecklist and observational techniques wascarried out for validating questionnaireexposure data. Workers fulfilling the casedefinition for elbow/forearm pain werecompared to those who did not fulfill the casedefinition. Prevalence of cases was associatedwith percent of time typing and typing speed.Logistic regression controlled for age, gender,metabolic disorders, and job satisfaction.
Automobile assembly line workers werecompared to a randomly selected group fromthe general population in the study by Byströmet al. [1995]. A case of epicondylitis requiredsymptoms and physical examination. “Job title”was used as a surrogate for exposure in theanalysis. No assessment of repetition orrepetitive work was completed specifically forthe elbow.
McCormack et al. [1990] had a randomlyselected population of 2,261 textile workersfrom over 8,000 eligible workers. Workerswere analyzed by job category, afterobservation of jobs. Epicondylitis caseascertainment was by clinical exam. Of the 37cases of epicondylitis identified, 13 werecategorized as mild, 22 were moderate, and 2were severe. Eleven examiners may haveintroduced an interexaminer reliability problem.Age, gender, race, and years of employmentwere analyzed as confounders.
Ohlsson et al. [1989] studied electricalequipment and automobile assemblers, former
assembly workers and compared these twogroups to a random sample from the generalpopulation. A case of elbow pain was based onquestionnaire responses; exposure was basedon job categorization as well as questionnaireresponses. Repetitive exposure was based on aself-reported frequency of task itemscompleted per hour (work pace). Resultsshowed no association with work pace andelbow symptoms, and no association betweenlength of employment and elbow symptoms.
Punnett et al. [1985] compared neck/shoulderMSDs based on symptom reporting alone in162 women garment workers and 76 womenhospital workers such as nurses, laboratorytechnicians, and laundry workers. There was alow participation rate among the hospitalworkers. Eighty-six percent of the garmentworkers were sewing machine operators andfinishers (sewing and trimming by hand). Thesewing machine operators were described asusing highly repetitive, low force wrist andfinger motions, while the finishers had shoulderand elbow motions as well. The exposedgarment workers likely had more repetitivejobs than most of the hospital workers.
Strength of Association—Repetitionand Elbow MSDsNo studies met the four criteria to discussstrength of association.
Strength of Association—Studies NotMeeting the Four Criteria For the other studies not fulfilling all the criteria,the odds ratio (OR) reported in the
Baron et al. [1991] study for epicondylitisoverall was 2.3, but this was not statisticallysignificant.
4-5
Anderson and Gaardboe [1993a] used yearsemployed as a sewing machine operator as asurrogate for exposure and found no significantassociation with epicondylitis. None of the other studies that looked atepicondylitis among working groups carried outindependent exposure assessment of workersor representative workers that focused on theelbow.
Burt et al. [1990] found a statistically significantOR of 2.8 for elbow/forearm symptoms innewspaper employees who reported typing80%–100% of their working day compared tothose typing 0%–20%. (Typing hours has beenused as a surrogate of both repetition andduration of exposure.)
Likewise, Punnett et al. [1985] found asignificant prevalence rate ratio (PRR=2.4) ofpersistent elbow symptoms among garmentworkers performing repetitive, forceful workcompared to hospital workers. Analysis by jobtitle showed that underpressers, whose jobsconsisted of ironing by hand, had a PRR of 6.0.Among stitchers (sewing machine operators),the significant PRR for the task of setting liningswas 7.7. When standardized to the agedistribution of the hospital workers, the rateratio did not change.
McCormack et al. [1990] and Ohlsson et al.[1989] based exposure on job title and foundno association between repetitive work andepicondylitis, with non-significant ORs between0.5 and 2.8.
Temporal Relationship—Repetitionand EpicondylitisThere were no prospective studies which
addressed repetition as a physical factor alone;all the studies were cross-sectional, so atemporal relationship cannot be established.However, some cross-sectional studies allowus to infer causality by use of restrictive casedefinitions. Studies by the National Institute forOccupational Safety and Health (NIOSH)investigators [Burt et al. 1990; Baron et al.1991] excluded from analysis those workerswho reported symptoms experienced prior totheir present job and those with acute injury tothe elbow not related to the job.
Consistency in Association forRepetition and EpicondylitisThe studies were not consistent in showing anassociation between repetitive work andepicondylitis. In terms of strength ofassociation, there were no studies that hadstatistically significant ORs greater than 3.0,four studies had ORs between 1.0 and 3.0, thatwere statistically significant; and two studieshad nonsignificant ORs less than 1.0.
Coherence of Evidence for Repetition
The evidence for epicondylitis in thebiomechanical and sports literature does notaddress repetition alone, but has consistentevidence with a combination of forcefulexertion, awkward or extreme postures, andrepetitive movements. Please refer to thediscussion under Coherence of Evidence forForce.
4-6
Exposure-Response Relationship forRepetitionIn Baron et al.’s [1991] study, there was adose-response relationship for the elbow forthe number of hours per week working as achecker, with ORs up to around 3.0, but notfor the duration of employment (the averagelength of employment was 8 years).
Conclusions Regarding Repetition
There is insufficient evidence for support of anassociation between repetitive work and elbow MSDs based on currently availableepidemiologic data. There were no studies thatmet the four criteria. Of the 7 studies examiningrepetitive work, no studies found ORs above3.0, 5 studies found ORs from 1–3, and 2studies found an OR less than one.
FORCE
Definition of Force for Elbow MSDs
For our review, we included studies thatexamined force or forceful work or heavy loadsto the elbow, or described exposure asstrenuous work involving the forearm extensorsor flexors, which could generate loads to theelbow/forearm region. Most of the studies thatexamined force or forceful work as a risk factorfor epicondylitis had several concurrent orinteracting physical workload factors.
Studies Reporting on the Associationof Force and Epicondylitis
Thirteen studies reported results on theassociation between force and adverse elbowhealth outcomes, including epicondylitis. Theepidemiologic studies that addressed forcefulwork and epicondylitis compared workinggroups by classifying them into broad
categories based on an estimated amount ofresistance or force of exertion and acombination of estimated rate of repetition(e.g., Viikari-Juntura et al. [1991b]; Kurppa etal. [1991]; Chiang et al. [1993]) or in terms ofoverall elbow stress [Dimberg 1987; Ritz1995].
Studies Meeting the Four EvaluationCriteria
Of the studies examining epicondylitis andforceful exertion, three studies [Chiang et al.1993; Luopajärvi et al. 1979; Moore and Garg1994] fulfilled all four criteria. Most of thesestudies used combinations of risk factors in theiranalysis, of which forceful exertion was one.
Chiang et al. [1993] assessed exposure thoughobservational methods, recording of tasks andbiomechanical movements of representativeworkers. With these methods, they categorizedfish processing workers into three exposuregroups according to the ergonomic risks to theshoulders and upper limbs: (1) those with lowforce and low repetition (the comparisongroup), (2) those with high force or highrepetition, and (3) those with both high forceand high repetition. The diagnosis ofepicondylitis included standard physicalexamination techniques of palpation andresisted extension and flexion of the elbow.Examination-defined cases were about one-halfthe number of cases defined by symptom alone.The analysis was stratified by gender, and thosewith metabolic diseases associated with MSDswere excluded. There was no significantdifference in age between the comparisongroups. Multivariate analysis was not carriedout for the elbow in this study.
4-7
Luopajärvi et al. [1979] determined MSDsdifferences between female assembly lineworkers and shop assistants in a departmentstore (cashiers were excluded from thecomparison group). Exposure assessmentinvolved on-site observation, video analysis andinterviews. The assembly work was found to berepetitive, with up to 25,000 cycles perworkday involving hand and finger motions.Specific cycles were not recorded for elbowmotions; however, motions involving the handsand fingers involve tendons and muscles fromthe flexors and extensors that have their originat the elbow. Static muscle loading of theforearm muscles, deviations of the wrist, andlifting were also found. The diagnosis ofepicondylitis included standard physicalexamination techniques of palpation andresisted extension and flexion of the elbow.Subjects with previous trauma, arthritis, andother pathologies associated with MSDs wereexcluded. All participants were female.Covariates considered in the analysis includedage, social background, hobbies, and theamount of housework performed. Duration ofemployment was not an issue because thefactory had only been open a short time.
Moore and Garg [1994] carried out a medicalrecords review using an epicondylitis casedefinition based on symptoms and physicalexamination and a semi-quantitative ergonomicassessment of 32 jobs at a meatpacking plant.The authors used their “Strain Index” tocategorize jobs as “hazardous” or “safe” basedon a number of factors: observation, videoanalysis, and judgements based on force,repetition, posture, and grasp. Force was
estimated as percent of maximal strength bycomparing the reported weight of the pertinentobject with estimated average maximal strengthof the worker for different types of pinches andgrasps, then categorized into five levels.
These values were derived from population-based data stratified according to age, gender,and hand dominance. Repetition was recordedas cycle-time and exertions per minute. Theexposure assessment in this study gave moreweight to the factor of “force” than to repetitionor posture (the force variable could increase toa higher categorization level if the job wasrepetitive, involved jerky motions, or extremepostures). Work histories, demographics, andpre-existing morbidity data were not collectedon each participant. The diagnosis ofepicondylitis extracted from the medicalrecords included standard physical examinationtechniques of palpation and resisted extensionand flexion of the elbow. Analyses were basedon “full-time equivalents” for jobs, not individualworkers. This analysis did not control forpotential confounders; there was a slightpreponderance of morbidity of all MSDsamong females.
Studies Meeting at Least One Criteria
The Andersen and Gaardboe study [1993a],which did not carry out ergonomic assessmentpertaining to the elbow, found a non-significantassociation between repetitive, forceful workand symptoms or physical findings consistentwith epicondylitis. In the Andersen andGaardboe study [1993a], the exposed groupconsisted of sewing machine operators.
Baron et al.’s [1991] measure of force wasbased on estimated assessment of exertion by
4-8
experienced ergonomists through observationof tasks and video analysis, as well as weight ofscanned items. Average forces for the grocerycheckers were categorized as “low” and peakforces “medium” on a three-tiered scale (“low,medium, and high”).
Byström et al.’s [1995] study of automobileassembly workers is reviewed in the Repetitionsection.
Dimberg’s studies [1987] fulfilled three of thecriteria but did not mention if examiners wereblinded to exposure status. In the 1987 study,exposure was assessed by observationalmethods, jobs were categorized according tothe amount of elbow stress in a particular job,but no individual measurements were made.Numerical results from the logistic regressionmodel were not given in the paper, althoughemployee category (blue collar versus whitecollar), gender, and degree of elbow stresswere said not to be significant predictors ofhaving any one of the three types ofepicondylitis. The author classified epicondylitisinto three types: leisure-related, no knowncause, and work-related groups based onhistory. When the author specifically looked at“work-related” epicondylitis (criteria for suchdesignation was not given) with respect toelbow stress, he found a significant trend withincreasing levels of elbow stress.
The exposure assessment approach wasdifferent for the 1989 study by Dimberg et al.In the 1987 study by Dimberg, the exposureclassification scheme was focused principallyon the elbow and identified jobs with heavyelbow-straining work. In the 1989 study, theauthor focused on multiple health outcomes inthe upper extremity and used an exposureclassification scheme that was more broadly
focused on the stress to the hand/wrist, elbow,and shoulder areas.
One study by Kurppa et al. [1991] wasprospective. Here, workers in meat processingwere categorized into strenuous andnonstrenuous jobs based on repetitive andforceful work. The strenuous tasks for themeatcutters consisted of cutting approximately1,200 kg of veal or 3,000 kg of pork per day;the nonstrenuous tasks consisted primarily ofoffice work. Workers had to have a physicianvisit and diagnosis in order to be considered acase—a restrictive definition requiringsignificant enough symptoms to seek outmedical care.
Twenty-five percent of cases were diagnosedby physicians outside the plant, so examinationtechniques may not have been the same asthose for the other 75%. The nonstrenuousgroup was similar to the strenuous group withregards to age, gender, and duration ofemployment, except for the small number ofmale sausage makers and malemeatpackers—these were excluded fromcalculation of individual IRs.
Punnett et al.’s [1985] study of garmentworkers is reviewed in the Repetition section.
Ritz [1995] did not mention the participationrate in their study of welders and pipefitters butfulfilled the other three criteria. Workersstudied were likely to be a representativesample, however, since all male employeeswho were taking their
annual examinations during a three month
4-9
period were enrolled in the study. The multiplelogistic model analysis considered age and avariety of confounding factors. Among thesepublic gas and water work employees, thewelders and pipefitters who installed andrepaired pipes were considered to have highexposure.
Roto and Kivi [1984] based their exposure onjob title alone, but fulfilled the other threecriteria. They compared meatcutters who hadforceful, repetitive work to constructionworkers who had more varied tasks. Theauthors stratified the analysis by age and foundthe majority of cases in the older age groups.They also found that the meatcutters withepicondylitis had been exposed, on theaverage, five years longer than the othermeatcutters. All the meatcutters had more than15 years in their current occupation, which theauthors attributed to support of the work-relatedness of the condition, although increasingage may have been a confounder or effectmodifier.
Viikari-Juntura et al. [1991b] studied subjectsat the same meat processing plant as Kurppa etal. [1991] using 3 cross-sectional examinationscovering a period of 31 months. The sameexposure assessment scheme used in theKurppa et al. [1991] study mentioned abovewas used comparing workers in strenuous andnonstrenuous work. This study compared theprevalence of all cases of epicondylitis; casesdue to injury or known non-occupationalcauses were not excluded. The diagnosis ofepicondylitis included standard physicalexamination techniques of palpation andresisted extension and flexion of the elbow; theauthors stated that palpation pressure increasedon the second of the three cross-sectional
examinations and may have influenced results.The investigators stated the comparison groupwas selected similar to the study group ingender, age, and duration of employment.
In conclusion, for the studies with less than ourfour criteria, four are supportive [Kurppa et al.1991; Ritz 1995; Dimberg 1987; and Roto andKivi 1984], two are non-supportive [Dimberget al. 1989; Byström et al. 1995], and one isnot very informative [Andersen and Gaardboe1993a]. The results from the positive studiesare unlikely to be due to confounding orselection bias. Overall, these studies providelimited support for the association of forcefulrepetitive work and epicondylitis.
Strength of Association—Force andEpicondylitisChiang et al. [1993] did not find an associationbetween hand-intensive work (categorizedbased on forceful exertion and repetition) andepicondylitis when analyzing all workers at sixfish processing plants. However, in examiningthe highest level of exposure (we calculated theodd ratios for men and women separately,which was not done in the article), we found asignificant difference between males in thehighest exposed group (Group III) and males inthe lowest exposed group (Group I) (OR=6.75) and a non-significant OR of 1.44 forwomen. Exposure in Group III was based on acombination of high-force exertion and highrepetition; analysis of working techniques bygender was not performed, so the reason forthe difference in the groups by gender is notknown. The Chiang et al. [1993] studyprovides limited support for the association
between high levels of forceful repetitive elbowwork and epicondylitis.
4-10
Luopajärvi et al. [1979] found a non-significantdifference overall in the prevalence ofepicondylitis and pronator teres syndrome (3versus 11 cases, OR 3.35 [95% confidenceinterval (CI) 0.86–19.1]); for lateralepicondylitis only, an OR of 2.73 (95% CI0.66–15.94). There were five cases of medialepicondylitis in the assembly workers and nonein the shop assistants. The increase in medialepicondylitis (an indeterminate OR because of“zero” cases in the shop assistants) wasattributed to the difficult grasping movementsinvolved in the assembly line work. They foundthat their female assembly workers tended tohave physically light work, but this workrequired highly repetitive movements of thewrists and fingers and static muscle loading ofthe forearm muscles.
Using the Strain Index, Moore and Garg[1994] found a significant relationship betweenhazardous jobs (of which force was a majorcomponent) and upper extremity MSDs (ofwhich epicondylitis was an importantcomponent). The results found a significant ORof 5.5 for a case of epicondylitis to occur in ahazardous job. When approximating theclassification scheme for low and high forceused by Silverstein et al. [1987] and then byKurppa et al. [1991], Viikari-Juntura et al.[1991b], and Chiang et al. [1993], theassociation between forcefulness and theoverall upper extremity morbidity in the studywas again statistically significant (p<0.02).
The overall conclusion from the three studiesthat met our four criteria is that there isevidence for association between force
and epicondylitis based on strength ofassociation.
Strength of Association—Studies Not Meetingthe Four Criteria: Force andElbow MSDs
Baron et al. [1991] found an OR of 2.3 for thecombination of factors, but this was notstatistically significant. The authors mention thatergonomic analysis of the non-checkersshowed that they also performed workrequiring repetitive motions and awkwardpostures; therefore, the comparison probablyresulted in a lower OR than had the referentgroup been truly unexposed to the ergonomicstressors.
Kurppa et al. [1991] found a strong significantrelationship between strenuous jobs andepicondylitis (IR= 6.7), while Viikari-Juntura etal. [1991b] did not (OR=0.88, nonsignificant).These results may have been influenced byallowing “cases” who had recurrence in thesame elbow to be counted as new cases (12out of 57 employees with epicondylitis hadmore than one episode, and were countedtwice). There was a median of 184 daysbetween the episodes. In examining this study,it is important to see if the odds of havingepicondylitis would be elevated if theseworkers with recurrences were only countedonce. We recalculated the OR using only“persons” and not “single episodes ofepicondylitis” in order to obtain a moreconservative estimate. We counted, only once,the employees with recurrence, as well as thefour employees mentioned with simultaneousoccurrence in both elbows and subtracted thesefrom the strenuous job cases. This gave a totalof 44 cases of epicondylitis among thestrenuous group.
Using this estimate, more restrictive than that
4-11
found in the article, gives an OR of 5.5 (2.4,12.7) for epicondylitis among the workers withstrenuous jobs versus those with nonstrenuousjobs. The Kurppa et al. [1991] prospectivestudy also found the IR of epicondylitis innonstrenuous jobs to be similar to Allender's[1974] population background prevalence rate(1%) for epicondylitis.
Ritz [1995] found a significant OR for 10 yearsof high exposure to elbow straining work: 1.7for currently held jobs and 2.2 for formerly heldjobs. The significant OR for moderate exposurein the current job was 1.4 for 10 years ofexposure. This study provides support for theassociation of forceful work with epicondylitis.
We calculated odd ratios from data inDimberg’s [1987] study and found an OR formoderate stress versus none or light elbowstress of 2.9, and for heavy versus none or lightstress of 7.4. Heavy stress in the elbows wasassigned to job titles like blaster, driller, orgrinder. The major limitation of this analysis ofthe work-related cases is that it did notconsider age, a likely confounder. Overall, thisstudy provides support for the associationbetween forceful work and epicondylitis,particularly in older workers.
The 1989 Dimberg et al. study was notsupportive of an association between lateralepicondylitis and forceful repetitive work, butwas positive for “mental stress at work” at theonset of symptoms for lateral epicondylitis(p<0.001). As a result of the specific elbowexposure assessment, we believe that withregards to stressful or
forceful elbow exertions that the 1987 study ismore informative.
The study conducted by Roto and Kivi [1984]found an OR of 6.4 (95% CI 0.99–40.9) usingan exposure assessment based on job titlealone (meatcutters were assumed to have moreforceful jobs than construction workers). Onlyone referent had epicondylitis.
In the paper by Viikari-Juntura et al. [1991b],the cases of epicondylitis not listed as insidiousall involved forceful, repetitive tasks (althoughsome of these tasks were not related to work).Prevalences of “epicondylar pain” and “sickleave due to epicondylar pain” weresignificantly different between the two groups(OR 1.9 and 2.1). There was no significantdifference in the prevalence of epicondylitis(combined work and non-work related)between workers in strenuous versusnonstrenuous jobs (OR=0.88). In 95 womensausage makers, there were four cases withinsidious onset, while among 160 womenreferents there were two cases, one withinsidious onset, the other related to an“exceptional task of cutting cheese.” Theresulting OR was 6.9 (95% CI 0.74–171). Thisstudy also found that rates of “epicondylarpain” and “sick leave due to epicondylar pain”differed significantly between the two groups(OR 1.9 and 2.1, respectively). Rates ofmedically diagnosed cases of epicondylitis werenot statistically different between the twogroups, but the results for epicondylar pain(causing sick leave in the two groups), and thefact that the majority of cases in both groupswere due to events involving strenuous,repetitive tasks, give some support to forceful,repetitive work asa cause.
Byström et al. [1995] noted that the lowfrequency could not be attributed to selected
4-12
subjects being absent, as all persons on leaveparticipated in the investigation. The authorsalso stated that “exposure to repetitiveness andforce in automobile assembly line work may beless than in other investigated work situations.”Because the authors did not give quantitative orqualitative information on the forcefulness orrepetitiveness of jobs included in the studygroup, it is difficult to know whether these jobswere appropriate to use to study epicondylitis.
Temporal Relationship: Force andEpicondylitisSee temporal relationship above in Repetitionand Epicondylitis.
Consistency of Association
The studies that met the four criteria were fairlyconsistent in their strength of associationbetween force and epicondylitis, with mostORs between 2.5 and 7.0. Focusing on thosestudies that compared workers exposed toforce that was documented to be at a high level,to those exposed to a low level, all studies[Chiang et al. 1993; Kurppa et al. 1991;Moore and Garg 1994] were consistent.
Of those 10 studies that examined force but didnot fulfill the four criteria, two studies had asignificant OR greater than 3.0, three studieshad significant ORs between 1.0 and 3.0, onehad a nonsignificant OR between 1.0 and 3.0,and two had an OR less than 1.0. Two hadstatistically significant findings but did not reportORs. Most of these studies examined workersin repetitive, forceful job tasks and did notseparate out
the independent effect of repetition through anyanalytic method.
Viikari-Juntura et al.’s [1991b] study did notexclude workers with elbow symptoms orphysical findings that were due to acute injurynot related to the job, which may account forthe contrasting result. In fact, in that study, fourworkers with acute non-work-relatedepicondylitis in the nonstrenuous group werenoted in the journal article. Anotherconsideration for inconsistency is due togrouping of studies, which may all fulfill goodepidemiologic criteria, may all examine thesame risk factor, but may compare groups thatdo not have similar contrasting levels ofexposure. For example, the Chiang et al.[1993] study found statistically significantresults in men when comparing high force/highrepetition jobs to low force/low repetition jobs.Baron et al. [1991], on the other hand,compared checkers in low force, mediumrepetition jobs to noncheckers in low force, lowrepetition jobs.
Two factors explain the difficulty in determiningthe reasons for the apparent inconsistenciesamong the studies on forceful and repetitivework. First, very few of the exposureassessments were quantitative—this is due toexisting limitations in directly measuringexposure in detail in most field studies. As aresult, there is likely to be frequent non-differential misclassification of exposure.Second, most of the studies completed havebeen cross-sectional, and therefore subject tosurvivor bias.
As an example, Chiang et al. [1993] found thatepicondylitis was significantly associated withincreasing repetitiveness and
forcefulness among fish processors employedless than 12 months. For those working for 12
4-13
to 60 months, a similar trend was found, but areverse trend was found in those workersemployed for over 60 months. The authorsstated that because most of the workers weresemi-skilled, they were likely to leave their jobif they felt frequent muscle pain because of it.They went further to say that the selectionmechanism may explain the lack of significantassociations between the disorders and theduration of employment. There was noindication that the authors pursued thishypothesis by trying to identify former workerswho may have left. Turnover rate was notdiscussed. This example highlights twoimportant factors concerning the cross-sectional studies examining work-relatedepicondylitis: there is some evidence that olderworkers may be at higher risk of epicondylitis[Dimberg 1987; Ritz 1995], and there is also a“survivor” effect, which results in the loss to thestudy of affected workers. These two factorsmake the interpretation of duration of diseaserelationships complex and may affect theestimate of the risk of disease. There were studies that used more accurateexposure assessment or had comparisongroups with marked differences in levels ofexposure to forceful and repetitive work thatwere positive, such as the Kurppa et al. [1991]study of meatcutters, sausage makers, andpackers, Moore and Garg's [1994] study ofpork processors; Dimberg's [1987] study ofblasters, drillers, grinders, and others in anengineering industry; Ritz’s [1995] study ofpipefitters and welders in a public utility; andRoto and Kivi’s [1984] study of meatcutters.There were studies with these characteristicsthat were negative, such as the Viikari-Junturaet al. [1991b] study of meatcutters, sausagemakers, and packers; and the study byDimberg et al. [1989] of blue- and white-collar
workers in the automobile industry. In both ofthese studies, those cases of epicondylitis listedin the comparison groups were due to highlyrepetitive, forceful activities. The lack of asignificant difference in the prevalence of thedisorder between the two groups may bebecause the referent, “low” exposure groupshad a higher incidence of non-work-relatedlateral epicondylitis.
Coherence of Evidence The epidemiologic results of finding the majorityof cases occurring in highly repetitive, forcefulwork [Moore and Garg 1994; Chiang et al.1993; Kurppa et al. 1991; Kopf et al.1988]are consistent with the evidence frombiomechanical and physiologic findings, as wellas from sports medicine literature and oldermedical clinical case series. In cases of lateralepicondylitis occurring in workplaces as well asin sports, the forearm extensors are repetitivelycontracted and produce a force that istransmitted via the muscles to their origin on thelateral epicondyle. These repetitive contractionsproduce chronic overload of the bone-tendonjunction, which in turn leads to changes at thisjunction. The most common hypothesis is thatmicroruptures occur at the attachment of themuscle to bone (usually at the origin of theextensor carpi radialis brevis muscle), whichcauses inflammation. PeÉina et al. [1991] didnot agree with the microrupture theory; theytheorized that overuse leads to avascularizationof the affected muscle origin, which leads tooverstimulation of the free nerve endings andresults in aseptic inflammation. Furtherrepetition of the offending movements causesangiofibroblastic hyperplasia of the origin.Nirschl [1975] stated that the degree ofangiofibroblastic hyperplasia is correlated to theduration and severity of symptoms. On
4-14
histologic analysis of severe cases ofepicondylitis, one can see the characteristicinvasion of fibroblasts and vascular tissue, thetypical picture of angiofibroblastic hyperplasia.
Prior to many of the epidemiologic studies,there were numerous reports in the medicalliterature of clinical case series that suggest arelationship between epicondylitis andrepetitive, forceful work. For example, as earlyas 1936 Cyriax reported that with regard topatients with lateral epicondylitis, “thosepatients who remember no special overexertionwill be found to be working at screwing, lifting,hammering, ironing, etc., or to be violinists,surgeons, masseurs, etc.” Cyriax haddesignated a “Chronic Occupational” variety oftennis elbow, in which he stated that “often nohistory of an injury is obtainable, but thepatient's occupation at once provides the clue.”He cited “work which entails repeatedpronation and supination movements withelbow almost fully extended” to be responsiblefor epicondylitis [Cyriax 1936]. Feldman et al.[1987] reported that occupations with worktasks requiring repeated pronation andinternal/external rotation of the forearm are athigh risk of pronator teres syndrome(compression of the median nerve as it coursesthrough the pronator teres muscle in theforearm). A number of case series havereported similar findings [Hartz et al. 1981;Morris and Peters 1976].
Sinclair [1965] reported 2 case series ofpatients with tennis elbow (lateral epicondylitis),44 patients treated between 1959-1961 and 38patients treated between 1961-1963. In thefirst group of 267, the 130 (48%) whose onsetoccurred spontaneously had occupations thatincluded gripping tools with consequent
forearm extensor muscle contraction andrepetitive supination/ pronation of the forearm.In the second group of 26, the 23 (88%) whohad spontaneous onset worked in jobs withconstant gripping or repetitive movements.
Many case studies of professional athletes havedocumented that forceful, repeated dorsiflexion,pronation, and supination movements with theelbow extended can cause epicondylitis.[Ollivierre et al. 1995; Priest et al. 1977; Kinget al. 1969]. Most cases have occurred inbaseball pitchers and tennis players.Occupations involving movements describedabove have also been found to have increasesin rates of elbow MSDs. This literature has alsoreferred to increased occurrence in occupationsrequiring force, awkward postures, andrepetitive use of the elbow and forearm[Lapidus and Guidotti 1970; Mintz and Fraga1973; Berkeley 1985]. These reports, thoughmainly case series, have lead to further studiesthat examined the links between exposure andepicondylitis.
An example of an early occupational study isone by Mintz and Fraga [1973], who foundthat foundry workers (with an average of 14years of employment) who used tongs requiringtwisting and bending of the elbows/forearms foreight hours per day had decreased elbowflexion and extension and pain on physical examination, as well as severeradiographically documented osteoarthritislocalized to the elbows. In the studies that arereviewed in Tables 4-1
through 4-4, the occupations with the highestrates of epicondylitis, such as drillers, packers,meatcutters, and pipefitters, are consistent withthe force-repetition model of the causation of
4-15
epicondylitis. The development of epicondylitisin these workers is consistent with proposedbiological mechanisms and is plausible.
The lack of elbow MSDs and work factors insome of the studies with occupations likesewing workers [McCormack et al. 1990] orautomobile assembly line workers [Byström etal. 1995], most likely reflects the interplay oftwo factors. The movement of affected workersout of high exposure jobs limits the ability ofcross-sectional studies to accurately determineassociations between work factors andepicondylitis. Our ability to accurately identifyworking conditions with an elevated risk forepicondylitis may require an exposureassessment of each job to a degree that hasbeen beyond the limits of currentepidemiological methods. As a result,misclassification of exposure may be common.Overall, the majority of the epidemiologicstudies are supportive of the hypothesis of anincrease risk of epicondylitis for occupationsthat involve forceful and repetitive work,frequent extension, flexion, supination, andpronation of the hand and the forearm. Thesurveillance data are also supportive of thishypothesis [Roto and Kivi 1984; WashingtonState Department of Labor and Industry 1996].The highest relative risks for epicondylitis inFinland were with mechanics, butchers, foodindustry workers, and packers; the highest industries inWashington State for 1987-1995 [Silverstein etal. In Press] were construction workers, meatdealers, and foundry workers—all occupationswith repetitive, forceful work involving the armsand hands and requiring pronation andsupination.
Evidence of a Dose-Response
Relationship for ForceThe Baron et al. [1991] study is mentionedabove in the Repetition Section as showing adose-response relationship for number of hoursof work per week. Chiang et al. [1993] foundthat among men the prevalence of epicondylitisincreased with increasing force and repetition infish processors. In several studies, onlydichotomous divisions were made, soconclusions concerning an exposure-responserelationship cannot be drawn. However, wecan see significantly contrasting rates of elbowMSDs between high- and low-exposuregroups. Moore and Garg [1994] found a higherrisk in workers with high-strain jobs comparedto those with low-strain jobs. Kurppa et al.[1991] found higher risk in workers withstrenuous jobs compared to those withnonstrenuous jobs, and that female sausagemakers had an increase in epicondylartenderness with increasing duration ofemployment. While Dimberg [1987] found nodifference in epicondylitis between blue- andwhite-collar workers, he found that workerswith elbow pain severe enough to require aphysician consult were significantly more oftenin those jobs identified independently as havinghigh elbow stress. Dimberg also found astatistically significant correlation coefficient forlateral epicondylitis and time spent in thepresent job. Luopajärvi et al. [1979] found ahigher rate of epicondylitis and pronator teressyndromes in a high-exposure group of assembly line packerscompared to the referent group of shopassistants. Overall, these studies provideconsiderable evidence for a
difference in level of risk for epicondylitis whenthere are marked differences in the level ofexposure to forceful and repetitive tasks.
4-16
Ritz [1995] reported a positive dose-responserelationship between duration of exposure togas and waterworks jobs regarded asmoderately and highly stressful to the elbowand epicondylitis. Roto and Kivi [1984]reported that all workers with epicondylitis intheir meat-packing facility worked for morethan 15 years in the strenuous job category andhad been exposed an average of 5 years longerthan non-diseased workers. Kopf et al. [1988]reported that in their study of brick layers, withincreasing levels of job demands (defined aseither heavy physical work, awkward workingpostures, repetitive movements, or restriction instanding position), the OR increased from 1.8to 3.4. These studies, with less clear contrastsin exposure, provide support for the exposure-response relationship between epicondylitis andforceful, repetitive work.
POSTURE
Definition of Postures forElbow MSDsWe chose to include those studies thataddressed posture or examined workers inthose activities or occupations that requirerepeated pronation and supination, flexion/extension of the wrist, either singly or incombination with extension and flexion of theelbow.
Studies Reporting on the Associationof Posture and Epicondylitis
The six studies in Table 4-3 addressed posturevariables. Of these, only the studies by Mooreand Garg [1994] and Luopajärvi et al. [1979]fulfilled all four criteria. The details of thesestudies are discussed in the Repetition andForce sections.
Strength of Association—Posture and Epicondylitis
Studies Meeting the Four EvaluationCriteria
The Moore and Garg [1994] study (alsodiscussed above) recorded wrist posture usinga classification similar to Armstrong et al.[1982] and Stetson et al. [1991]. Pinch graspwas also noted to be present or absent. In thisstudy, posture was not found to be significantlyassociated with “hazardous” jobs. This may bedue to the heavier weighting given the forcerating system than the posture or repetitionscale. For example, if a job required extremeposture, the authors increased the force ratinginstead of the posture rating. If a combination ofextreme posture and high-speed movement wasrequired, then the force rating was raised bytwo levels, but not the posture rating. Data thatwould allow analysis of the incidence ofepicondylitis and the exposure to extremeposture were not presented.
Luopajärvi et al.’s [1979] assessment wasfocused on the extreme work position of thehands but not the elbow; it included extension,flexion and deviation of the wrists. Althoughthere was a non-significant association betweenassembly line work and the presence of eitherepicondylitis or pronator teres syndrome inshop assistants (11 cases versus 3), there were5 cases of medial epicondylitis and 2 cases ofpronator teres syndrome in the assemblyworkers and none in the shop assistants. Thegreater prevalence of medial epicondylitis in
assembly workers was attributed to the difficultgrasping movements involved in the assemblyline work. The authors stated that the overallprevalence may have been “connected with theconstant overstrain of flexors in work.”
4-17
Studies Not Meeting the FourEvaluation Criteria
The Dimberg [1987] study stated that over-exertion of the extensor muscles of the wristdue to gripping and twisting movements prior tothe onset of symptoms was verified in 28 of the40 (70%) of the cases, of which 14 wereconsidered to be caused by work. In the studyby Dimberg et al. [1989], the guidelines forclassification include repeated rotation of theforearms and wrists in Group 1, large andfrequent rotations in extreme positions in Group2, but fail to include work involving frequentrotations in the highest exposed group, Group3. The difference in exposure classificationscheme may explain why there was norelationship between prevalence of epicondylitisand increasing work strain.
Hughes and Silverstein [1997] found a strong,statistically significant association (OR 37)between elbow/forearm disorders and “thenumber of years of forearm twisting” in theirstudy of aluminum workers. However, thisstudy had an overall low participation rate(55%), which limits the interpretation of itsresult.
The other study that may be interpreted asrelated to a posture variable is the one byHoekstra et al. [1994]. This study evaluatedvideo display terminal users at two work sitesdiffering only in whether adjustable officeequipment was present. By self-reportedsymptoms and exposure
observations, the Hoekstra et al. [1994] studyfound that having a “non-optimally adjusted”chair was associated with elbow MSDs. Thisimproper chair adjustment was thought toincrease shoulder and elbow flexion, as well as
wrist deviation, thus producing more symptoms.These conclusions should be considered to behypothesis generating and not definitive.
Temporal RelationshipThere are no prospective studies that addressposture and epicondylitis. The one prospectivestudy concerning epicondylitis did not addressposture.
Consistency in Association
There are too few occupational epidemiologicstudies that address posture and epicondylitis tomeaningfully discuss consistency of association.
Coherence of Evidence
Please refer to the “Repetition Section andCoherence of Evidence” for a discussion of thesports literature, and the combination of factors,including extreme postures that have beendocumented concerning epicondylitis.
Exposure-Response Relationship
There is little evidence on which to base adiscussion exposure response relationship in theepidemiologic studies. Once again, the reader isreferred to the biomechanical sports literature.
EPICONDYLITIS AND THE ROLE OFCONFOUNDERS
The model for epicondylitis clearly implies thatboth occupational and non-occupationalactivities can cause the disorder. Severalstudies [Ritz 1995; Andersen andGaardboe 1993a; Dimberg 1987] directlyaddress the issue of work-related versus non-work-related exposures by assessing both.Two of the most important potentialconfounders or effect modifiers are age andduration of employment. In Dimberg's [1987]
4-18
and Ritz’s [1995] studies, older workers hadhigh rates of epicondylitis. Nevertheless, in bothstudies the increase in the risk for epicondylitisin the high-exposure group does not seemrelated primarily to age, independent ofintensity and duration of exposure.Furthermore, the incidence of elbow MSDsunlike most MSDs, has been found to decreaseafter retirement age, after peaking during the fourthand fifth decades.
Many of the studies controlled for severalpossible confounders in their analyses. Ingeneral, for epicondylitis, psychosocial factorsor gender do not appear to be importantconfounders in occupational studies.
CONCLUSIONSThe epidemiologic studies reviewed in thissection focused principally on the risk ofepicondylitis in workers performing repetitivejob tasks requiring forceful movements. Theseforceful movements included, but were notlimited to, repeated dorsiflexion, flexion,pronation, and supination, sometimes with thearm extended. Clinical case series ofoccupationally-related epicondylitis and studiesof epicondylitis among athletes had suggestedthat repeated forceful dorsiflexion, flexion,pronation, and supination, especially with thearm extended, increased the risk ofepicondylitis. In general, the epidemiologicstudies have
not quantitatively measured the fraction offorceful hand motions most likely to contributeto epicondylitis; rather, they have used as asurrogate qualitative estimation the presence orabsence of these types of hand movements[Viikari-Juntura et al. 1991b]. Although we
recognize this limitation of the epidemiologicstudies, there is value in assessing where we arein regards to the epidemiologic evidence ofcausal inference.
There is epidemiologic evidence for therelationship between forceful work andepicondylitis. Those studies that base theirexposure assessment on quantitative orsemiquantitative data have shown a solidrelationship. We conclude that there isinsufficient evidence for the association ofrepetitive work and epicondylitis. For extremeposture in the workplace, the epidemiologicevidence thus far is also insufficient, and weturn to the sports medicine literature to assist usin evaluating the risk of the single factors ofrepetition and posture. The strongest evidenceby far when examining the relationship betweenwork factors and epicondylitis is thecombination of factors, especially at higherlevels of exposure. This is consistent with theevidence that is found in the biomechanical andsports literature.
Most of the relevant occupational studies werecross-sectional; the current estimates of thelevel of exposure were used to estimate pastand current exposure. Despite the cross-sectional nature of the studies, it is likely, in ouropinion, that the exposures predated the onsetof disorders in most cases.
When we examine all of the studies, a majorityof studies are positive. The association betweenforceful and repetitive work involvingdorsiflexion, flexion, supination, and pronationof the hand is definitely biologically plausible.These motions can cause the contraction of themuscle-tendon units that attach in the area ofthe medial and lateral epicondyles of the elbow.
4-19
The evidence for a qualitative exposure-response relationship overall was considerablefor the combination of exposures, with studiesexamining differences in levels of exposure forthe elbow, and corresponding evidence forgreater risk in the highly exposed group. Incontrast, we found one study with cleardifferences in exposure and no evidence of anincrease in risk [Viikari-Juntura et al. 1991b].
In summary, the combination of the biologicalplausibility, the studies with more quantitativeevaluation of exposure factors finding strongassociations, and the considerable evidence forthe occurrence with combinations of factors athigher levels of exposure provide evidence forthe association between repetitive, forcefulwork and epicondylitis. There are severalimportant qualifications to this conclusion.Forceful and repetitive work is most likely asurrogate for repetitive, forceful hand motions
that cause contractions of the muscles whosetendons insert in the area of the lateral andmedial epicondyles of the elbow. While thestudies do not identify the number or intensity offorceful contractions needed to increase therisk of epicondylitis, the levels are likely to besubstantial. Future studies should focus on thetypes of forceful and repetitive hand motionssuch as forceful dorsiflexion, pronation, andsupination that result in forceful contractions ofthe muscle tendon units that insert in the area ofthe lateral and medial epicondyles. Commonnon-occupational activities, such as sportactivities, which cause epicondylitis should beconsidered. Older workers may be at someincreased risk. Finally, even though theepidemiologic literature shows that manyaffected workers continue to work with definitesymptoms and physical findings of epicondylitis,survivor bias should be addressed.
Table 4-1. Epidemiologic criteria used to examine studies of elbow MSDs associated with repetition
Study (first author andyear)
Risk indicator (OR,PRR, IR or p-
value)*,†
Participationrate $$70%
Physicalexamination
Investigatorblinded to caseand/or exposure
status
Basis for assessing elbowexposure to repetition
Met at least one criterion:
Andersen 1993a 1.7 Yes No Yes Job titles or self-reports
Baron 1991 2.3 No Yes Yes Observation or measurements
Burt 1990 2.8† Yes No Yes Job titles or self-reports
Byström 1995 0.74 Yes Yes No Job titles or self-reports
McCormack 1990 0.5–1.2 Yes Yes NR‡ Job titles or self-reports
Met none of the criteria:
Ohlsson 1989 1.5–2.8 NR No NR Job titles or self-reports
Punnett 1985 2.4† No No NR Job titles or self-reports
*Some risk indicators are based on a combination of risk factors—not on repetition alone (i.e., repetition plus force, posture,or vibration). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).
†Indicates statistical significance.‡Not reported.
4-20
Table 4-2. Epidemiologic criteria used to examine studies of elbow MSDs associated with force
Study (first author andyear)
Risk indicator(OR, PRR, IR or
p-value)*,†Participation
rate $$70%Physical
examination
Investigatorblinded to caseand/or exposure
status
Basis for assessingelbow exposure to force
Met all four criteria:
Chiang 1993 6.75† (males)1.44 (females)
Yes Yes Yes Observation ormeasurements
Luopajärvi 1979 2.7 Yes Yes Yes Observation ormeasurements
Moore 1994 5.5† Yes Yes Yes Observation ormeasurements
Met at least one criterion:
Andersen 1993a 1.7 Yes No Yes Job titles or self-reports
Baron 1991 2.3 No Yes Yes Observation ormeasurements
Byström 1995 0.74 Yes Yes No Job titles or self-reports
Dimberg 1987 NR†,‡ Yes Yes NR Observation ormeasurements
Dimberg 1989 NR Yes Yes NR Observation ormeasurements
Kurppa 1991 6.7† Yes Yes NR Observation ormeasurements
Punnett 1985 2.4† Yes No NR Job titles or self-reports
Ritz 1995 1.4–1.7† NR Yes Yes Observation ormeasurements
Roto 1984 6.4† Yes Yes Yes Job titles or self-reports
Viikari-Juntura 1991b 0.88 Yes Yes NR Observation ormeasurements
*Some risk indicators are based on a combination of risk factors—not on force alone (i.e., force plus repetition, posture, orvibration). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).
†Indicates statistical significance. If combined with NR, a significant association was reported without a numerical value.‡Not reported.
4-22
Table 4-3. Epidemiologic criteria used to examine studies of elbow MSDs associated with posture
Study (first author andyear)
Riskindicator
(OR, PRR, IRor p-
value)*,†
Participationrate $$70%
Physicalexaminationor medicalrecords
Investigatorblinded to
case and/orexposure
status
Basis for assessingelbow exposure to
posture
Met all four criteria:
Luopajärvi 1979 2.7 Yes Yes Yes Observation ormeasurements
Moore 1994 NR‡ Yes Yes Yes Observation ormeasurements
Met at least one criterion:
Dimberg 1987 NR† Yes Yes NR Observation ormeasurements
Dimberg 1989 NR Yes Yes NR Observation ormeasurements
Hoekstra 1994 4.0† Yes No Yes Job titles or self-reports
Hughes 1997 37.0† No Yes NR Observation ormeasurements
*Some risk indicators are based on a combination of risk indicators—not on posture alone (e.g., posture plus repetition, force,or vibration). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).†Indicates statistical significance. If combined with NR, a significant association was reported without a numerical value.‡Not reported.
4-24
Table 4-4. Epidemiologic criteria used to examine studies of elbow MSDs associated with vibration
Study (first author andyear)
Riskindicator
(OR, PRR, IRor
p-value)*,†
Participation rate $$70%
Physicalexaminationor medicalrecords
Investigatorblinded to case
and/orexposure
status
Basis of assessing elbowexposure to vibration
Met at least one criterion:
Bovenzi 1991 4.9† NR‡ Yes Yes Observation ormeasurements
*Some risk indicators are based on a combination of risk indicators—not on vibration alone (e.g., vibration plus repetition,force, or posture). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).
† Indicates statistical significance.‡ Not reported.
4-26
(Continued)
Table 4–5. Epidemiologic studies evaluating elbow musculoskeletal disorders
MSD prevalence
Study Studydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
Andersenand Gaardboe1993a
Cross-sectional
424 female sewingmachine operators,compared to781 females from thegeneral population ofthe region and aninternal referentgroup of 89 femalesfrom the garmentindustry.
Outcome: Questionnaire: continuous pain lasting > 1month since starting career;pain for > 30 days.
Exposure: Job categorizationbased on “authors’experiences” as occupationalhealth physicians andinvolved crude assessmentof exposure level andexposure repetitiveness. Jobs involving highrepetitiveness (severaltimes/min) and low or highforce, and jobs with mediumrepetitiveness (manytimes/hr) combined with highforce were classified as highexposed jobs; jobs withmedium repetitiveness andlow force and jobs with morevariation and high force wereclassified as mediumexposed. Job titles such asteachers, self-employed,trained nurses, and theacademic professions were“low exposed.” Exposurealso measured as years assewing machine operator.
4.5% 2.6% 1.7 0.9-3.3 Participation rate: 78.2%.
Examiners blinded tocontrol/subject status.
Adjusted for age, number ofchildren, exercising, smoking,socioeconomic status.
4-27
(Continued)
Table 4–5 (Continued). Epidemiologic studies evaluating elbow musculoskeletal disorders
MSD prevalence
Study Studydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
Baron et al.1991
Cross-sectional;case-referent
Grocery checkers usinglaser scanners (n=124,119 females, 5 males)compared to othergrocery store workers(n=157, 56 females, 101males); excluded 18workers in meat, fish,and deli departments,workers under 18, andpregnant workers.
Outcome: Self-administeredquestionnaire and physicalexam. Case defined as thepresence of pain, numbness,tingling, aching, stiffness orburning in the elbow regionas previous non-occupationalinjury; symptoms must havebegun after employment atthe supermarket ofemployment and in thecurrent job, and last >1 weekor occurred once a monthwithin the past year.
Physical Exam: Tendernessat the lateral/medialepicondyle and pain withpalpation and resisted motion.
Exposure: Based on jobcategory, estimates ofrepetitiveness, average andpeak forces based onobserved and videotapedpostures, weight of scanneditems, and subjectiveassessment of exertion.
The majority of cashierswere categorized as having“medium” levels of repetitionfor the hand (defined in thisstudy as making 1250 to2500 hand movements/hr).
8% amongcheckers
Õ 2.3 0.5-11 Participation rate: 85%checkers; 55% non-checkers infield study. Following telephonesurvey 91% checkers and 85%non-checkers.
Examiners blinded to worker’sjob and health status.
Age, hobbies, second jobs,systemic disease and heightwere considered as covariatesin the multivariate analyses.
Total repetitions/hr ranged from1,432 to 1,782 for right handand 882 to 1,260 for left hand.
Average forces were low andpeak forces medium.
No statistical significanceassociated between duration ofemployment as a checker andelbow MSDs.
Multiple awkward postures ofall upper extremities recordedbut not analyzed in models.
Statistically significant increasein elbow MSD with increase inhr/week “checking.”
4-28
Table 4–5 (Continued). Epidemiologic studies evaluating elbow musculoskeletal disorders
MSD prevalence
Study Studydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Bovenzi et al.1991
Cross-sectional
Vibration-exposedforestry operators usingchain-saws (n=65) andmaintenance workers(n=31, control group).
Outcome: Epicondylitissyndrome: Pain at theepicondyle either during restor motion, local tenderness atthe lateral or medialepicondyle; pain duringresisted flexion/extension ofthe fingers and wrist with theelbow flexed, palpated localtenderness at thelateral/medial epicondyle.
Exposure: Direct observationof awkward postures,manual forces andrepetitiveness evaluated viachecklist. Vibrationmeasured from two chainsaws.
29.3 6.4% For vibrationexposedgroup>7.5 m/s2:OR=4.9(adjusted)
OR=5.99(unadjusted)
1.27-56
Participation rate: Not reported.
Analysis controlled for age andponderal index.
Controls found to have severalrisk factors for MSDs at work-static arm and hand overload,overhead work, stressfulpostures, non-vibrating handtool use.
Controls actually had a greaterproportion of the time in workcycles shorter than 30 sec thanforestry workers.
4-29
Table 4–5 (Continued). Epidemiologic studies evaluating elbow musculoskeletal disorders
MSD prevalence
Study Studydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Burt et al.1990
Cross-sectional
Newspaper employees(n=836, females=55%). Workers fulfilling casedefinitions compared tothose who did not fulfillcase definition.
Outcome: Self administeredquestionnaire. Case definedas the presence of pain,numbness, tingling, aching,stiffness, or burning in theelbow region as previousnon-occupational injury. Symptoms began afterstarting the job, last > 1 weekor occurred once a monthwithin the past year; reportedas “moderate” (3) or greateron a 5-point scale.
Exposure: Based onobservation of job tasks, thencategorized by job title. Aseparate job analysis using achecklist and observationaltechniques was carried outfor validating questionnaireexposure data.
Male: 11%Female: 14%
Õ 80% to 100%time typingcompared to0% to 19%: OR=2.8
Reporterscompared toothers: OR=2.5
1.4-5.7
1.5-4.0
Participation rate: 81%.
Analysis controlled for age,gender, years on the job.
Psychosocial factors dealingwith job control and jobsatisfaction were addressed inquestionnaire.
Job analysis found significantcorrelation (0.56) betweenreported average typingtime/day and observed 8 hrperiod of typing (p < 0.0001).
Reporters were characterizedby high, periodic demands(deadlines), although they hadhigh control and high jobsatisfaction.
Number of workers in somenon- typing jobs not reported.
Case definition based onsymptoms alone.
4-30
Table 4–5 (Continued). Epidemiologic studies evaluating elbow musculoskeletal disorders
MSD prevalence
Study Studydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Byströmet al. 1995
Cross-sectional
Automobile assemblyline workers (n=199)compared to a randomlyselected group from thegeneral population(n=186). Theautomobile assemblyline workers wererandomly selected froma primary group of700 assembly lineworkers. Theseoriginal 700 workershad been randomlyselected from the2,334 assemblyworkers of a Swedishautomobile factory.
Outcome: Epicondylitis wasdefined as tenderness topalpation of the lateral ormedial epicondyle and pain atthe same epicondyle or in theforearm extensors or flexorson resisted wrist extensionor flexion.
Exposure: No evaluation ofrepetition, force, posture, orvibration occurred in thisstudy to evaluate risk factorsfor epicondylitis. “Assemblyline worker” vs. “Populationreferent” was used. Handgrip strength was evaluated. Forearm muscular load andwrist angle were evaluatedfor a subgroup in thispopulation but were not usedin this analysis [Hägg et al1996].
Tenderlateralepicondyle:4.3%
Epicondy-litis: 0 cases
Tenderlateralepicondyle:12.4%
Epicondy-litis: 1%
PRR fortender lateralepicondyle:0.74 0.04-1.7
Participation rate: 96%. Comparison group is from theMUSIC study (Hagberg andHogstedt, 1991).
Examiners were blinded toquestionnaire responses butnot exposure status.
Analysis stratified by genderand age <40 years. Psychosocial variables andother potential confounders oreffect modifiers wereaddressed by Fransson-Hallet al. [1995].
Pain-pressure threshold (PTT)was evaluated. PTT was notrelated to age. It was higheramong women with shortemployment compared to thosewho had been employed for along time.
No correlation was foundbetween low MCV andsubjective or objective signs.
4-31
Table 4–5 (Continued). Epidemiologic studies evaluating elbow musculoskeletal disorders
MSD prevalence
Study Studydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Chiang et al.1993
Cross-sectional
207 fish processingworkers, 67 males and140 females, dividedin 3 groups: (I) lowforce, low repetition(comparison group,n=61); (II) high forceor high repetition(n=118); (III) highforce and highrepetition (n=28).
Outcome: Prevalence oflateral or medial epicondylitis(local tenderness, pain inresisted extension or flexionof the wrist and fingers,decreased hand grip strengthcompared to the oppositehand).
Exposure: Assessed byobservation and recordingof tasks and biomechanicalmovements of three workers,each representing one of3 study groups. Highlyrepetitive jobs with cycle time<30 sec or >50% ofcycle-time performing thesame fundamental cycles. Hand force from EMGrecordings of forearmflexor muscles. Classification of workers into3 groups according tothe ergonomic risks of theshoulders and upper limbs: Group I: low rep. and lowforce; Group II: high repetitionor high force; Group III: highrepetition and high force.
Group II:15%Male: 10%;Female: 17%
Group III:21%Male: 33%;Female: 18%
Physicianobservedepicondy-litis, allcases:14.5 %
Group I:10%Male: 6%;Female: 14%
Crude ORscalculatedfrom datapresented:Group II vs.Group I,males: OR=1.7
Group II vs.Group I,females:OR=1.2
Group III vs.Group I,males: OR=6.75
Group III vs.Group I,females: OR=1.44
0.3-9.2
0.4-3.4
1.6-32.7
0.3-5.6
Participation rate: Authorsreported: “In order to prventselective bias all employees inthe fatories were observedinitially.”
Workers examined in randomsequence to prevent observerbias, examiners blinded to casestatus.
Analysis stratified by gender. No significant age difference inexposure groups.
Logistic regression notperformed for epicondylitisbecause of lack of significanttrend with increasing exposure.
Workers with hypertension,diabetes, history of traumaticinjuries to upper limbs, arthritis,or collagen diseases excludedfrom study group.
Physician observed cases hadabout ½ the prevalence ofsymptoms of elbow pain (9.8vs. 18.0; 5.3 vs. 19.5; 35.7 vs.17.9).
No dose-response for elbowpain or physician observedepicondylitis.
4-32
Table 4–5 (Continued). Epidemiologic studies evaluating elbow musculoskeletal disorders
MSD prevalence
Study Studydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Dimberg 1987 Cross-sectional
A questionnaire wasdistributed to every fifthperson in the automobilecompany’s personnelfile selected by randomnumbers. Final sampleconsisted of546 workers, 494 malesand 52 females. (25 were excluded dueto military service,pregnancy, or studyaway).
Outcome: Only workersreporting elbow problemswere examined by thephysician. Physical exam:case defined as physicalfindings of lateral elbow painand pain with palpation overlateral epicondyle and painincrease with dorsiflexion ofwrist with resistance.
Exposure: Observation ofthe work site thencategorization of jobs “withrespect to elbow stress” bya Physical Work StressGroup composed of aphysician, physiotherapist,and safety engineer. Table 2in the article lists types ofjobs with respect tosubjects’s elbow stress.
Lateralhumeralepicondylitisamong allsubjects:7.4%
Blue collarworkers: 5.3%
White collarworkers: 11%
Blue collar:under age 40years: 4.6%
Blue collar:over age 40years: 8.9%
White collar:under age 40years: 6.1%
White collar:over age 40years:13.9%
Õ Epicondylitis,blue vs.white collarworkers:0.7Distribution ofepicondylitiscases bytype of workstress:
Leisurerelatedepicondylitis:low workstress: 85%;medium workstress: 15%;high workstress: 0%No-known-cause group:epicondylitis:low workstress: 75%;medium workstress: 25%;high workstress: 0%Work-relatedepicondylitis:low workstress: 14%;medium workstress: 36%;high workstress: 50%
0.3-1.2
Participation rate: 98.9%.Physician blinded to exposurestatus: not reported.Results age stratified.Physician-consulted elbow painsignificantly greater in jobs withincreased elbow stress.Work considered to be thecause in 35%. Authors foundthat work-related group hadwork defined by high stress(categorized by low, moderate,and high) compared to leisure-related epicondylitis andepicondylitis of no-known-cause.Authors reported thatproportion of workers whoconsulted a physician for theirelbow problems wassignificantly greater withincreasing elbow stress (p <0.05).Multiple regression analysesincluded gender, employeecategory, age, and degree ofstress as independentvariables—only age significantlyrelated to prevalence.Overexertion of the extensormuscles of the wrist due togripping and twistingmovements prior to onset wasverified in 28 (70%) of thosewith epicondylitis.Tennis players among“sufferers”: 15% totalpopulation: 12%. All racquetsports: 20% among sufferers,15% among total population.
4-33
Table 4–5 (Continued). Epidemiologic studies evaluating elbow musculoskeletal disorders
MSD prevalence
Study Studydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Dimberg et al.1989
Cross-sectional
2,814 automotiveworkers, both blue-and white-collarworkers: 2,423 males,382 females.
Outcome: Questionnaireresults of elbow trouble(pain, ache, discomfort)preventing normal work inlast 12 months.
Physical exam performed on615 of 641 symptomaticworkers. Epicondylitis: tenderness at thelateral/medial epicondyleand pain with resistance.
Exposure: Observation ofjobs, then classification into 3Physical Work Stress Groupsby physician,physiotherapist, and safetyengineer. Guidelines forclassification with respect tothe strain on the subject’sneck and upper extremitieslisted for light, moderatelyheavy, and heavy workincluded in article.
Blue collar White collar UnivariateResults:p<0.001:higher age;longer time inpresent job;ponderalindex, moresymptoms;more mentalstress at theonset ofsymptoms.
p<0.05:salaried staffvs. others;heavyweight; lessracquetsports, moresymptoms.
p<0.01:vibratinghand tools,moresymptoms;time inpresent job,moresymptoms.
p>0.05:gender; straingroup; fulltime;hrs/week;piece-work;fixed pay;smoking,house-owner.
Participation rate: 96%.Not stated whether examinerblinded to exposure status.
Multivariate analysis performed,although the confounderscontrolled for were not statedby authors, nor were ORspresented. Vibrating tools,ponderal index, and mentalstress at work listed assignificant.
Guidelines for classification ofjobs as listed in the article donot seem to reflect increasingelbow stress. Group 1 includes“repeated rotation of theforearms and wrists occurssporadically”; Group 2 includesless specifically “large andfrequent rotations in extremepositions”; Group 3 does notinclude any reference torepeated rotation or extremeposition of the forearms orwrists. The classification usedseems unlikely to pick upincreased elbow stress thatwould reflect higher strain andrisk of epicondylitis.Increased ponderal indexcorrelated with elbowsymptoms in multivariateanalysis.
Mental stress at work with theonset of symptoms correlatedwith right-sided lateralepicondylitis. Mental stress variables notuniformly collected, so this mayimpact interpretation.
4-34
Table 4–5 (Continued). Epidemiologic studies evaluating elbow musculoskeletal disorders
MSD prevalence
Study Studydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Fishbein et al.1988
Cross-sectional(mailedsurvey)
2212 musiciansperforming on a regularbasis with one or moreof the InternationalConference ofSymphony and OperaMusicians (ICSOM). Total population of themembership was 4,025musicians in 48 ICSOMorchestras. Oneorchestra did notparticipate.
Outcome: Outcome based onself-reported responses fromsurvey. Self-reported elbowpain, with severity definedin terms of the effect ofthe problem on the musician’sperformance.
Exposure: Questionnaireresponses to orchestralinstrument, age they beganplaying, age they joined theorchestra, number of weekseach year spent playingprofessionally.
10% rightelbow: 6 %severe
8% leftelbow: 4%severe
Õ Severemedicalproblem andits affect onperformance,females vs.males:OR=2.04 1.6-2.6
Participation rate: 55%. Lowresponse rate due to the factthat many orchestras were notin season at the time of thesurvey.
Statistical weighting performed;"severe" pain was defined aspain that affects performance.
Health habits, such as extent ofexercise, use of cigarettes,alcohol, beta blockers, andother drugs.
Average age beginning playinginstrument is 10 years. Average age joining aprofessional orchestra is 23years. Average age: malemusicians–43 years, femalemusicians–40 years.
Severe problems were morelikely in ages under 35 thanover 45 years. Authorsspeculated that musicians withsevere problems leave theorchestra.
Low participation rate limitsinterpretation.
4-35
Table 4–5 (Continued). Epidemiologic studies evaluating elbow musculoskeletal disorders
MSD prevalence
Study Studydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Hales et al.1994
Cross-sectional
518 telecommunicationworkers (416 femalesand 117 males). Workers fulfillingoutcome definitioncompared to those notfulfilling outcomedefinition.
Outcome: Pain, aching,stiffness, burning,numbness, or tingling >1week or >12 times a year;occurring after employmenton current job within the lastyear and positive physicalexamination (PE): Moderateto worst pain experiencedwith medial or lateralepicondyle palpation.
Exposure: Assessed byquestionnaire. Questionsaddressed number ofovertime hr, co-worker useof same workstation, taskrotation, hr spent at the(VDT) workstation, hr spenttyping, number and types ofwork breaks, length of timesitting, frequency of arisingfrom a chair, number ofkeystrokes estimated foreach directory assistanceoperator.
7% Õ Fear of beingreplaced bycomputers:OR=2.9
Lack ofdecision-makingopportunities:OR=2.8
Surges inworkload:OR=2.4
Race (non-white)OR=2.4
1.4-6.1
1.4-5.7
1.2-5.0
1.2-5.0
Participation rate: 93%.
ORs for psychosocial representrisk at scores one standarddeviation (SD) above the meancompared to risk at scores oneSD below mean. May be aproblem with non-normaldistribution.
Analysis controlled for age,gender, individual factors, andnumber of keystrokes/day.
Physician examiners blinded tocase and exposure status.
Although keystrokes/day wasnot significant–workers onlytyped average of 8 words/minover 8-hr period.
97% of workers “used” VDTs $6 hr/day–not enough varianceto adequately evaluate hrtyping.
Number of hr on hobbies andrecreation not significant.
Over 70 variables analyzed inmodels–may have multiplecomparison problem.
4-36
Table 4–5 (Continued). Epidemiologic studies evaluating elbow musculoskeletal disorders
MSD prevalence
Study Studydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Hoekstraet al. 1994
Cross-sectional
108 of 114 teleservicerepresentatives workingat 2 governmentadministration centers: A and B.
Outcome: Self administeredquestionnaire. Case definedas the presence of pain,numbness, tingling, aching,stiffness, or burning in theelbow region as previousnon-occupational injury;symptoms began afterstarting the job, last > 1 weekor occurred once a monthwithin the past year; reportedas “moderate” (3) or greateron a 5-point scale.
Exposure: Measurement andevaluation of work station;observation of postures toprovide descriptivedifferences between the twolocations.
Center A
Center B
19%
21%
"Non-optimally"adjustedchair: 4.0
Õ
1.2-13.1
Participation rate: 95%.
Analysis controlled for gender.
Interactions evaluated.
Variables considered in logisticmodel included location, age,seniority, hr spent typing atVDT, hr on the phone, 3 chairvariables: (1) Perceivedadequacy of chair adjustment,VDT screen, (2) Perceivedadequacy of keyboardadjustment, VDT screen,(3) Perceived adequacy of deskadjustment, job control,workload variability.
Linear regression alsoperformed on psychosocialvariables in separate models forjob dissatisfaction andexhaustion.
Center B generally hadnonadjustable chairs and workstations. Authors notedelevated arms, hunchedshoulders and other"undesirable" postures.
Did not include non-work-related variables in analyses.
4-37
Table 4–5 (Continued). Epidemiologic studies evaluating elbow musculoskeletal disorders
MSD prevalence
Study Studydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Hughes andSilverstein1997
Cross-sectional
104 male aluminumsmelter workers:62 carbon setters,36 crane operators,9 carbon plant workers. There were 14 workerswho were not fromselected jobs and wereexcluded.
Outcome: Symptomsoccurring in theelbow/forearm >once/month or lastinglonger than one week inthe previous year, noacute or traumatic onset;occurrence since workingat the plant, no systemicdisease.
Physical examination: Active,passive, andresisted motions, pinchand grip strength, 128Hz vibration sensitivity, two-point discrimination.
Psychosocial scales fromquestionnaire based onTheorell and Karasek JobStress Questionnaire, andon Work ApgarQuestionnaire.
Exposure: For carbonsetters and craneoperators (non-repetitivejobs) a modified job-surveillance checklistmethod was used. Job taskanalysis used a formulabased on the relativefrequency of occurrenceof postures during (a)task(s).
11.6% withpositivesymptomsand physicalexam
24% hadsymptoms intheelbow/forearm in thepreviousweek
Õ Model basedon MSDdefined bysymptomsand physicalexam
Age:OR=0.96
Low decisionlatitude:OR=3.5
Years offorearmtwist: OR=37
Model basedon MSDdefined bysymptoms
Age:OR=0.96
Years ofulnardeviation:OR=0.005
Yearsforearmtwist: OR=4
0.9-1.2
0.6-19
3.0-470
0.9-1.2
0.0-16
0.18- 4
Participation rate: Carbonsetters: 65%; crane operators:56%; carbon plant: 33%.
Examiners blinded to exposureand health status: not stated.
Analysis controlled for age,smoking status, sports, and/orhobbies.
Psychosocial data collectedindividually; physical factorsbased on estimates of each job.
Job risk factors entered into themodel for hand/wrist included:(1) the number of yearshandling > 2.7 kg/hand,(2) push/pull, (3) lift/carry,(4) pinching, (5) wristflexion/extension, (6) ulnardeviation, and (7) forearmtwisting.
Health interview includedinformation about metabolicdiseases, acute traumaticinjuries, smoking, hobbies.
Low participation rate limitsinterpretation.
4-38
Table 4–5 (Continued). Epidemiologic studies evaluating elbow musculoskeletal disorders
MSD prevalence
Study Studydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Kopf et al.1988
Cross-sectional
Bricklayers (n=163)compared to othermanual workers (n=144)employed by stateagencies in Hamburg,Germany.
Outcome: Questionnairebased, self-reportedsymptoms. Self-reportedpain in the elbow.
Exposure: Based on jobcategories, bricklayer vs.other manual laborers. Physical stress of bricklayersdescribed as lifting andcarrying bricks weighing 5 to24 kg up to 100 times/hr withthe left hand and handling thebricklayer’s trowel with theright hand.
Not reported Not reported Painful leftelbow,bricklayersvs. othermanualworkers:OR=2.8
Notreported
Participation rate: bricklayers: 65%, manual workers: 69%.
Controlled for confounders:age, job satisfaction, jobsecurity, vibration, moistness,Scheuerman’s disease.
Karasek’s model of job latitudeand job demands were includedin the questionnaire.
Physically demanding previoustasks, medical disposition forMSD, being a member of a tradeunion included in analysis.
64% attributable risk proportionof elbow pain is explained bybeing a bricklayer.
For increasing levels of jobdemands (heavy physical work,awkward working positions,repetitive movements, andrestriction in standing position),OR increased from 1.8 to 3.4.
4-39
Table 4–5 (Continued). Epidemiologic studies evaluating elbow musculoskeletal disorders
MSD prevalence
Study Studydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Kurppa et al.1991
Cohort; 31monthfollow-up
Sausage makers (107females) compared tononstrenuous jobs (197females).
Meatcutters (102 males)compared tononstrenuous jobs(n=141).
Packers (118 females)compared tononstrenuous jobs (197females).
Outcome: Tenderness topalpation of the epicondyleand epicondylar painprovoked by resistedextension or flexion of thewrist and fingers with theelbow extended. Incidencebased on visits to doctorduring 31 month visit.
Disease considered "new"episode if new sick leavewith same diagnosisoccurred at same anatomicsite within 60 days after endof former sick leave.
Exposure: Data obtainedfrom “previous publishedliterature” and walkthrough.
“Cutting of veal (appx. 1,200kg/day) or pork (appx. 3,000kg/day) (meatcutters);spraying the sausages andhanging them on bars(sausage makers); peelingsausages, inserting them intoslicing machine, setting theslices into packages, settingpackages on a conveyor belt,collecting finished packagesinto bags; room temperature8E to 10E (packers);nonstrenuous tasks includedprimarily office work.”
Sausagemakers(females):11.1cases/100person-years
Meatcutters(males):6.4cases/100person-years
Packers(males):7.0cases/100person-years
Workers inNon-strenuousjobs: 1.1cases /100person-years
Workers innon-strenuousjobs: 0.9cases/100person-years
Workers inNonstrenu-ous jobs: 1.1cases/100person-years
IR of males instrenuousjobs vs.nonstrenuousjobs: 5.7
IR of femalesin strenuousjobs vs.nonstrenuousjobs: 8.1
IR of totalnumber ofcases ofepicondylitisin strenuousjobs vs.nonstrenuousjobs: 6.7 3.3-13.9
Participation rate: 93% ofstrenuous workers retainedduring study; 90% ofnonstrenuous workers.
Examiners blinded to exposureor past episodes: not reported. Diagnoses made by differentphysicians at differentlocations. Plant physiciansagreed to the diagnostic criteriaand made 75% of diagnoses. 25% of physicians were notinvolved in agreement ofdiagnostic criteria. 13% ofepicondylitis diagnosed byconsulting specialists at thenearby medical center, 12%elsewhere, usually at municipalhealth centers.
No adjustment for confounders,but referent group selectedsimilar to strenuous group withregards to age, gender, andduration of employment, exceptfor male sausage makers andmale packers who wereyounger than the rest of thestudy population–these wereexcluded from calculations ofincidence rates.
“New" episode of epicondylitismay be recurrence of samedisease. 12 employeesreafflicted with epicondylitiswith median of 184 daysbetween episodes.
There were 68 diagnoses ofepicondylitis among 57individuals.
4-40
Table 4–5 (Continued). Epidemiologic studies evaluating elbow musculoskeletal disorders
MSD prevalence
Study Studydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Luopajärvi etal. 1979
Cross-sectional
Female assembly lineworkers (n=152)compared to femaleshop assistants in adepartment store(n=133). Cashiersexcluded fromcomparison group.
Outcome: Epicondylitisdiagnosed by interview andphysical exam.
Symptoms include musclepain during effort, localswelling, and local ache atrest. Signs includetenderness at the ateral ormedial epicondyle onpalpation, pain duringresisted extension/flexion ofthe wrist and fingers with theelbow extended. Physiotherapist examinedworkers, diagnoses werefrom pre-determined criteria(Waris 1979). In problemcases orthopedic andphysiatric teams handledcases.
Exposure: Exposure torepetitive work, awkwardhand/arm postures, andstatic work assessed byobservation, video analysisand interviews. Videorecordings showed repetitivemotins of the hands andfingers up to 25,000cycles/day, static muscleloading of the forearmmuscles, and deviations ofthe wrist, lifting.
5.9% 2.3% 2.7 0.66-15.9
Participation rate: 84%. Workers excluded fromparticipation for previoustrauma, arthritis and otherpathologies.
Examiner blinded to casestatus: yes, according to theWaris et al. 1979, epidemiologicscreening procedure, whichwas used in study.
No association between ageand MSDs or length ofemployment and MSDs. Gendernot an issue because studypopulation was all female.
Factory opened only short timeso no association betweenduration of employment andMSDs possible.
Social background, hobbies,amount of housework notsignificant.
4-41
Table 4–5 (Continued). Epidemiologic studies evaluating elbow musculoskeletal disorders
MSD prevalence
Study Studydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
McCormacket al. 1990
Cross-sectional
Randomly selectedpopulation of 2,261textile workers from8,539 eligible workers;4 groups compared with468 non-office workers
Manufacturing workers:
A. Packaging/foldingworkers (41 males,238 females).
B. Sewing workers(28 males, 534 females).
C. Non-office workers(204 males, 264females).
D. Boarding workers(19 males, 277 females).
Outcome: Based onphysician administeredphysical exams. Reproducible tendernesswith direct pressure on thelateral epicondyle. Severitygraded as mild, moderate,and severe.
Exposure: Assessment byobservation of jobs. Exposure to repetitive finger,wrist and elbow motionsassumed from job title; noobjective measurementsperformed.
Boardingworkers:1.0%
Sewingworkers:2.1%
Packaging/foldingworkers:2.2%
Knitting:1.4%
Non-officeworkers:1.9%
Boarding vs.non-office:OR=0.5
Sewing vs.non-office:OR=1.1
Packaging vs.non-office:OR=1.1
Knitting vs.non-office:OR=1.2
0.09-2.1
0.4-2.9
0.4-3.2
0.5-3.4
Participation rate: 91%.
Physician or nurse examinersnot blinded to case or exposurestatus (personalcommunication).
Age, gender, race, and yearsof employment analyzed.
Prevalence higher in workerswith < 3 years of employment.
Questionnaire asked types ofjobs, length of time on job,production rate, nature and typeof upper extremity complaint,and general health history.
11 physician examiners;interexaminer reliability potentialproblem acknowledged byauthors.
Epicondylitis significantlyassociated with years ofemployment, age, race.
Job category not related toepicondylitis, however nomeasurement of force,repetition, posture analysis, etc.
Of 37 cases of epicondylitisidentified: 13 were categorizedas mild, 22 were moderate, and2 were severe.
4-42
Table 4–5 (Continued). Epidemiologic studies evaluating elbow musculoskeletal disorders
MSD prevalence
Study Studydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Moore andGarg 1994
Cross-sectional
Workers employed in32 jobs at a porkprocessing plant(n=230).
Workers in jobsclassified as“hazardous” comparedto those in “safe” jobs.
Outcome: OSHA logsverified by medical recordsdata for 20 months. Epicondylitis: localized elbowpain that increased withtension of muscle-tendon unitand direct palpation. A caserequired that a physicalexamination specific toepicondylitis was performed.
Exposure: Observation andvideo analysis, semi-quantitative methods usingmotion and time methods(MTM), force estimated as %maximal strength (5 levels),wrist posture (3 levels), typeof grasp (2 levels), highspeed work (yes or no),localized mechanicalcompression (yes or no),vibration (yes or no), andcold (yes or no). Observedvideotaped representativeworker in each job. Repetition as cycle-time andexertions/min measures. Jobs classified as"hazardous" or "safe" basedon data, experience ofauthors, and judgements.
Work histories, demographic,pre-existing morbidity datanot collected on eachparticipant.
Workers in“hazardousjobs”: 23%
Workers in“safe jobs”:3%
Odds ofepicondylitisin workers in“hazardousjobs”compared toworkers in“safe jobs”:OR=5.5(based onpersonalcommuni-cation)
1.5-62
Participation rate: Casesidentified from medical records. Jobs analyzed fromobservational methods.Investigators blinded toexposure, case outcomestatus, and personal identifierson medical records. Repetitiveness and “type ofgrasp” were not significantfactors between hazardous-and safe-job categories.No pattern of morbidity accord-ing to date of clinic visits.Strength demands significantlygreater for hazardous jobcategories compared to safe. IR based on full-time equivalentsand not individual workers, mayhave influenced overall results. Workers had a maximum of32 months of exposure atplant–duration of employmentanalysis limited.Duration of exposure notcollected on study sample.Average maximal strengthderived from population-baseddata stratified for age, gender,and hand dominance.Using estimates of Silverstein’sclassification, associationbetween forcefulness, andoverall observed morbidity wasstatistically significant; repetitionwas not. 31 of 32 jobs were inhigh repetitive category–novariance to find difference.
4-43
Table 4–5 (Continued). Epidemiologic studies evaluating elbow musculoskeletal disorders
MSD prevalence
Study Studydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Ohlssonet al. 1989
Cross-sectional
Electrical equipment andautomobile assemblers(n=148), former femaleassembly workers whoquit within 4 years(n=76) compared torandomly sampledfemales from generalpopulation (n=60).
Outcome: Questionnaire: Any elbow pain, elbow painaffecting work ability,and elbow pain in the lastseven days and the last12 months.
Exposure: No exposuremeasurements; based on jobcategorization.
Work pace divided into4 classes: (1) Slow <100 items/hr;(2) Medium 100 to 199items/hr; (3) Fast 200 to 700items/hr; (4) Very Fast >700items/hr.
Elbow pain inlast 12months: 21%
Elbow pain inlast 7 days:14%
Work inabilityin last 12months: 10%
Elbow painin last 12months:17%
Elbow painin last 7days: 11%
Workinability inlast 12months: 3%
1.5
1.9
2.8
0.6-3.4
0.7-5.3
0.8-10.7
Participation rate: Not reported.
Work pace assessed byquestionnaire, the number ofitems completed/hr.
No association between lengthof employment and elbowsymptoms.
No statistical significanceassociated with work pace(data not present).
Logistic models evaluated forinteraction and controlled forage.
Study group consisted offemales only.
4-44
Table 4–5 (Continued). Epidemiologic studies evaluating elbow musculoskeletal disorders
MSD prevalence
Study Studydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Punnett et al.1985
Cross-sectional
162 female garmentworkers, 85% wereemployed as sewingmachine operators andsewing and trimming byhand.
Comparison: 76 of 190full or part-time workerson day shift in a hospitalwho worked as nursesor aids; lab techniciansor therapists; foodservice workers.
Employees typing>4 hr/day excludedfrom comparison group.
Outcome: Self-administeredquestionnaire concerningsymptoms
Cases defined as thepresences of persistentelbow pain, numbness ortingling (lasted for mostdays for one month or morewithin the past year); werenot associated with previousinjury; and, began afterfirst employment in garmentmanufacturing or hospitalemployment. Key questionsbased on the arthritissupplement questionnaire ofNational Health and NutritionExamination Survey(NHANES).
Exposure: Self-administeredquestionnaire; # of years inthe industry, job category,previous work history.
Garmentworkers: 6.5%
Hospitalemployees:2.8%
ElbowSymptoms inGarmentworkers vs.Hospitalemployees:OR= 2.4
Persistentelbow pain infinishers vs.hospitalemployees:OR=5.6
Persistentelbow pain inunderpresservs. hospitalemployees:OR=5.0
1.2-4.2
Participation rate: 97%(garment workers), 40%(hospital workers).
Analysis stratified for numberof years employed, decade ofage, native language.
Health outcome based onsymptoms alone for elbowMSDs.
Age and length of employmentnot a predictor of risk of elbowMSDs.
Prevalence of pain notassociated with years ofemployment in garmentworkers.
Non-English speakerssignificantly less likely to reportpain (RR 0.6 ; p<0.05).
Native English speakerssignificantly older than non-native English speakers(p<0.03).
4-45
Table 4–5 (Continued). Epidemiologic studies evaluating elbow musculoskeletal disorders
MSD prevalence
Study Studydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Ritz 1995 Cross-sectional
290 males from thepublic gas and waterworks of Hamburg,Germany examinedduring routine medicalcheck-up at thecompany occupationalhealth center. Employees, excluded ifon sick leave, came formedical treatment, pre-employment checkups,or to file a worker’scompensation claim.
Outcome: Physiciandiagnosed; required localtenderness to palpation at theepicondyle and pain duringresisted movement of thewrist and fingers (extensionor flexion of the wrist orfingers with an extendedelbow) AND elbow painduring the lifting of a chair. Epicondylitis wascategorized as severe(Grade II and Grade III) if bothfunctional tests were positiveand as moderate (Grade I) ifonly symptom was a severetenderness to palpation or amoderate pain in theresistance test. Clinical signsof epicondylitis > Grade 0 atone or more of the fouranatomical sites wasconsidered sufficient for thediagnosis.
Exposure: All current andformer job titles evaluated bymembers of the teamaccording to possible bio-mechanical strain to theelbow and grouped intocategories of high, moderate,and non work-relatedexposure. Exposurecategorization was based oncompany job descriptions,interviews with employees,and workplace observations.
Exposure duration wasdefined for all subjects as the
41employees:14% hadepicondylitis
11% fulfilledWaris’scriteria forepicondylitis (Waris,1979)
10 years ofhighexposure toelbowstrainingwork forcurrently heldjob: OR=1.7
Highexposure toelbowstrainingwork forformerly heldjob:OR= 2.16
10 years ofhighexposure toelbowstrainingwork forcurrently heldjob usingdiagnosticcriteria forepicondylitis[Waris et al.1979]:OR=1.89
1.0-2.7
1.1-4.3
1.2-3.1
Participation rate: Not reported.
Examiner blinded to exposurestatus.
Logistic regression modelcontrolled for age, age-squared, and an indicator termfor “history of cervical spinesymptoms” (yes, no).
The following variables testedfor confounding: having everplayed tennis, squash, otherracquet sports, rowing,bowling, the duration of havingplayed these sports, injuriesinvolving the elbow joint,ponderal index, handedness,and former surgical treatmentfor epicondylitis.
The variable “time in yearssince retiring from a job withhigh or moderate exposure”was retained in the model forworkers formerly employed inhigh exposure jobs whenduration of exposure wastricotomized.
Mean length of employmentwas not significantly differentbetween cases and non-cases.
Increasing duration of currentexposure increased the risk ofbeing diagnosed withepicondylitis.
4-46
Table 4–5 (Continued). Epidemiologic studies evaluating elbow musculoskeletal disorders
MSD prevalence
Study Studydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
(Continued)
Roto and Kivi1984
Cross-sectional
Meatcutters, (n=90)compared toconstruction workers(n=72) not exposed torepetitive movements.
Outcome: Defined byphysical exam: localtenderness, pain duringresisted extension/flexion ofthe wrist and fingers, anddecreased hand grip powerin comparison to other hand.
Exposure: Based on job title(meatcutter vs. constructionworker).
Meatcutters:8.9%
Construc-tionworkers:1.4%
6.4 0.99-40.9
p= 0.05
Participation rate: 100% formeat cutters, 94% forconstruction workers.
Authors state that examinerswere blinded to occupation ofsubjects because part of largergroup of meat processingworkers examined, but it isunclear whether constructionforemen (referents) wereexamined separately.
Serologic testing for rheumatoidarthritis was done to control forpotential confounding (nonedetected).
7 additional meatcutters hadlocal tenderness in epicondylarregion.
All with epicondylitis had > 15years of employment.
Authors stated that on average,meatcutters with epicondylitishad been exposed five yearslonger than other meatcutters,supporting the association withmeatcutting.
4-47
Table 4–5 (Continued). Epidemiologic studies evaluating elbow musculoskeletal disorders
MSD prevalence
Study Studydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
Viikari-Juntura1991b
Cross-sectional
All permanent workersexposed to repetitiveand manually stressfultasks in a meatpackingplant (102 meatcutters,150 packers, and125 sausage makers)were compared to332 workers innonstrenuous jobs(supervisors,maintenance men,accountants, and officeworkers).
Outcome: Elbow trouble(pain, ache, discomfort)preventing normal work inlast 12 months and physicalexam: tenderness at thelateral/medial epicondyle andpain with resistance.
Exposure: Based onobservation:
Meatcutters: High force/highrepetition.
Sausage makers: Highrepetition/low force with highforce tasks.
Packers: High repetition/lowforce with high force jobs.
Nonstrenuous jobs, mainlyoffice jobs.
“Cutting of veal (appx. 1,200kg/day) or pork (appx. 3,000kg/day) (meatcutters);spraying the sausages andhanging them on bars(sausage makers); peelingsausages, inserting them intoslicing machine, setting theslices into packages, settingpackages on a conveyor belt,collecting finished packagesinto bags; room temperature8E to 10E (packers);nonstrenuous tasks includedprimarily office work.”
Epicondy-litis: 0.8%
Lateral: 0.6%Medial: 0.2%
Epicondy-litis: 0.8%
Lateral:0.6%Medial: 0.3%
The OddsRatio ofepicondylitisin strenuousjobs vs. non-strenuousjobs: 0.88
Elbow Pain(without thephysicalexam): Male: 1.8Female: 1.6
0.27-2.8
1.1-2.81.2-2.3
Participation rate: 94%.
No adjustment for confoundersin analysis. Authors stated thatthe comparison group wasselected similar to the studygroup to sex, age, and durationof employment.
Examiners blinded to case andexposure status.
Male packers and male sausagemakers younger and length ofemployment shorter than othergroups.
Palpation pressure increased on2nd of cross-sectionalexaminations–may haveinfluenced results.
For female sausage makers,elbow pain for preceding 12months increased with age andduration of employment. Nosuch associations in othergroups.
Age and current occupationalcorrelated (r=0.52) for femalesausage makers.
Cases were not excluded dueto direct trauma.
4-48
5-1
CHAPTER 5Hand/Wrist Musculoskeletal Disorders(Carpal Tunnel Syndrome, Hand/WristTendinitis, and Hand-Arm VibrationSyndrome): Evidence for Work-Relatedness
Musculoskeletal disorders (MSDs) of the hand/wrist region have been separated into three componentsfor the purpose of this review: (a) Carpal Tunnel Syndrome (CTS), (b) Hand/Wrist Tendinitis, and (c)Hand-Arm Vibration Syndrome (HAVS). Each of these are described with regard to the evidence forcausality between workplace risk factors and development of MSDs.
5a-1
CHAPTER 5aCarpal Tunnel Syndrome
SUMMARY Over 30 epidemiologic studies have examined physical workplace factors and their relationship to carpaltunnel syndrome (CTS). Several studies fulfill the four epidemiologic criteria that were used in this review,and appropriately address important methodologic issues. The studies generally involved populationsexposed to a combination of work factors, but a few assessed single work factors such as repetitivemotions of the hand. We examined each of these studies, whether the findings were positive, negative, orequivocal, to evaluate the strength of work-relatedness using causal inference.
There is evidence of a positive association between highly repetitive work alone or in combination withother factors and CTS based on currently available epidemiologic data. There is also evidence of a positiveassociation between forceful work and CTS. There is insufficient evidence of an association between CTSand extreme postures. Individual variability in work methods among workers in similar jobs and the influenceof differing anthropometry on posture are among the difficulties noted in measuring postural characteristicsof jobs in field studies. Findings from laboratory-based studies of extreme postural factors support a positiveassociation with CTS. There is evidence of a positive association between work involving hand/wristvibration and CTS.
There is strong evidence of a positive association between exposure to a combination of risk factors (e.g.,force and repetition, force and posture) and CTS. Based on the epidemiologic studies reviewed above,especially those with quantitative evaluation of the risk factors, the evidence is clear that exposure to acombination of the job factors studied (repetition, force, posture, etc.) increases the risk for CTS. This isconsistent with the evidence that is found in the biomechanical, physiological, and psychosocial literature.Epidemiologic surveillance data, both nationally and internationally, have also consistently indicated thatthe highest rates of CTS occur in occupations and job tasks with high work demands for intensive manualexertion–for example, in meatpackers, poultry processors, and automobile assembly workers.
INTRODUCTIONIn 1988, CTS had an estimated populationprevalence of 53 cases per 10,000 currentworkers [Tanaka et al. (in press)]. Twentypercent of these individuals reported absencefrom work because of CTS. In 1994, theBureau of Labor Statistics (BLS) reported thatthe rate of CTS cases that result in “days awayfrom work” was 4.8 cases per 10,000workers. The agency also reported that themedian number of days away from work forCTS was 30, which is even greater than themedian reported for back pain cases [BLS1995]. In 1993, the incidence rate (IR) forCTS workers’ compensation cases was 31.7cases per 10,000 workers; only a minority ofthese cases involved time off of work
[Washington State Department of Labor andIndustry 1996]. These data suggest that about5 to 10 workers per 10,000 workers will misswork each year due to work-related CTS.
In recent years, the literature relatingoccupational factors to the development of CTS has been extensively reviewed by numerous authors [Moore 1992; Stock1991; Gerr et al. 1991; Hagberg et al. 1992;Armstrong et al. 1993; Kuorinka and Forcier 1995; Viikari-Juntura 1995]. Most of these reviews reach a similarconclusion—work factors are one of the important causes of CTS. One review [Moore 1992] found the evidence
5a-2
more equivocal, but stated that theepidemiologic studies revealed a fairlyconsistent pattern of observations regarding thespectrum and relative frequency of CTS[among other musculoskeletal disorders(MSDs)] among jobs believed to be hazardous.The epidemiologic studies which form the basisfor these reviews are outlined in Tables 5a–1 to5a–4 of this chapter.
Thirty studies of occupational CTS are listed onTables 5a–5. Twenty-one are cross-sectionalstudies, six are case-control, and three involvea longitudinal phase; all have been publishedsince 1979. We included one surveillance study[Franklin et al. 1991] because it has beenincluded in many of the earlier reviews. The fewearlier studies of CTS identified were clinicalcase series, or did not identify work place riskfactors and were not included in the tablesrelated to CTS.
OUTCOME AND EXPOSUREMEASURESIn four of 30 studies listed in Tables 5a–1 to5a–4, CTS was assessed based on symptomsalone; in another nine studies, the casedefinition was based on a combination ofsymptoms and physical findings.Electrophysiological tests of nerve functionwere completed in 14 studies. Electrodiagnostictesting (nerve conduction studies) has beenconsidered by some to be a requirement for avalid case definition of CTS, as is similarly usedfor a clinical diagnosis in individuals with CTS.A few studies which have looked at therelationship of occupational factors to CTShave used a health outcome based onelectrodiagnostic testing alone [Nathan et al.1988; Schottland et al. 1991; Radecki 1995.]However, some authors [Nilsson 1995;Werner et al. 1997] have discouraged the use
of labeling workers as having “CTS” or“median nerve mononeuropathy” based onabnormal sensory nerve conduction alone(without symptoms). The reason for this view isillustrated in a recent prospective study byWerner et al. [1997]. On follow-up six toeighteen months after initial evaluation, theyfound that asymptomatic active workers withabnormal sensory median nerve function (byNerve Conduction Studies [NCS]) were nomore likely to develop symptoms consistentwith CTS than those with normal nervefunction. Studies which have used nerveconduction tests for epidemiologic field studieshave employed a variety of evaluation methodsand techniques [Nathan et al. 1988, 1994b;Bernard et al. 1993; Osorio et al. 1994].Normal values for nerve conduction studieshave also varied from laboratory to laboratory.NCS results have been found to vary withelectrode placement, temperature, as well asage, height, finger circumference and wrist ratio[Stetson 1993], suggesting that “normal” valuesmay need to be corrected for those factors.
Several epidemiologic studies have used asurveillance case definition of CTS basedon symptoms in the median nerve distributionand abnormal physical examination findingsusing Phalen’s test and Tinel’s sign, and havenot included NCS. Two recent studies[Bernard et al. 1993; Atterbury et al. 1996]looked at CTS diagnosis based onquestionnaire and physical examination findingsand its association with the “gold standard” ofnerve conduction diagnosed medianmononeuropathy. Both studies foundstatistically significant evidence to support theuse of an epidemiologic CTS case definitionbased on symptoms and physical examination(not requiring NCS) for epidemiologic surveillance studies. Nathan
5a-3
[1992a] also found a strong relationshipbetween symptoms and prolonged sensorymedian nerve conduction. (It is important tonote here that a case definition used forepidemiologic purposes usually differs from oneused for medical diagnosis and therapeuticintervention.)
Researchers have relied on a variety ofmethods to assess exposure to suspectedoccupational risk factors for CTS. Thesemethods include direct measurement,observation, self-reports, and categorization byjob titles. Most investigators agree that use ofobservational or direct measurement methodsincreases the quality (both the precision andaccuracy) of ergonomic exposure assessments,but these methods also tend to be costly andtime consuming. In general, misclassificationerrors tend to dilute the observed associationsbetween disease and physical workload[Viikari-Juntura 1995].
REPETITIONDefinition of Repetition for CTSFor our review, we identified studies thatexamined repetition or repetitive work for thehand and wrist for CTS as cyclical or repetitivework activities that involved either 1) repetitivehand/finger or wrist movements such as handgripping or wrist extension/flexion, ulnar/radialdeviation, and supination or pronation. Most ofthe studies that examined repetition or repetitivework as a risk factor for CTS had severalconcurrent or interacting physical workloadfactors. Therefore, repetitive work should beconsidered in this context, with repetition asonly one exposure factor, accompanied byothers such as force, extreme posture, and, lesscommonly, vibration. Studies Reporting on the Association
of Repetition and CTSNineteen studies reported on the results of theassociation between repetition and CTS. Several studies in Table 5a-1 quantitativelymeasured [Moore 1992; Chiang et al. 1990,1993; Silverstein et al. 1987] or observed[Stetson et al. 1993; Nathan et al. 1988,1992a; Barnhart et al. 1991; Osorio et al.1994] and categorized repetitive hand and wristmovements in terms of: a) the frequency orduration of tasks pertaining to the hand/wrist, b)the ratio of work-time to recovery time, c) thepercentage of the workday spent on repetitiveactivities, or d) the quantity of work performedin a given time. The rest of the studies generallyused job titles or questionnaires to characterizeexposure.
Studies Meeting the Four Evaluation CriteriaFive epidemiologic studies of the hand/wristarea addressing repetitiveness and CTS[Chiang et al. 1990, 1993; Moore and Garg1994; Osorio et al. 1994; Silverstein et al.1987] met the four criteria. Chiang et al. [1990]studied 207 workers from 2 frozen foodprocessing plants. Investigators observed jobtasks and divided them into low or highrepetitiveness categories of wrist movementbased on cycle time, as previously described bySilverstein et al. [1987]. Jobs were alsoclassified according to whether or not workers’hands were exposed to cold work conditions.The resulting exposure groups were:Group 1–Not Cold, Low Repetitiveness(mainly office staff and technicians);Group 2–Cold Exposure or HighRepetitiveness; and Group 3–Cold Exposureand High Repetitiveness. CTS diagnosis wasbased on abnormal clinical examination andnerve conduction studies. Prevalence of CTS
5a-4
was 3% in Group 1, 15% in Group 2, and 37%in Group 3. Statistical modeling that alsoincluded gender, age, length of employment,and cold resulted in an odds ratio (OR) of 1.87(p=0.02) for CTS among those with highlyrepetitive jobs. The OR for CTS among thoseexposed to cold conditions and highrepetitiveness was 3.32 (p=0.03). The authorscautioned that cold exposure may have at leastpartially acted as a proxy for forcefulhand/wrist exertion in this study group.
Chiang et al. [1993] studied 207 workers from8 fish processing factories in Taiwan. Jobs weredivided into 3 groups based on levels ofrepetitiveness and force. The comparison group(low force/low repetitiveness) was comprisedof managers, office staff, and skilled craftsmen(group 1). The fish-processing workers weredivided into high repetitiveness or high force(group 2), and high force and highrepetitiveness (group 3). Repetition of upperlimb movements (not specifically the wrist) wasdefined based on observed cycle time[Silverstein et al. 1987]. CTS was defined onthe basis of symptoms and positive physicalexamination findings, ruling out systemicdiseases and injury. CTS prevalence for theoverall study group was 14.5%. CTSprevalence increased from group 1, to group 2,and to group 3 (8.2%, 15.3%, and 28.6%,respectively), a statistically significant trend (p<0.01).Repetitiveness alone was not a significantpredictor of CTS (OR 1.1). Statistical modelingshowed that women in this study group had ahigher prevalence of CTS than men (OR 2.6,95% confidence interval [CI] 1.3–5.2).Because the proportion of women varied byexposure group (48%, 75%, and 79% fromgroup 1 to 3), further analyses were limited to
females. The OR for repet-itiveness was 1.5(95% CI 0.8–2.8), con-trolling for oralcontraceptive use and force.
Moore and Garg [1994] evaluated 32 jobs in apork processing plant and then reviewed pastOSHA illness and injury logs and plant medicalrecords for CTS cases in these job categories.A CTS case required the recording ofsuggestive symptoms (numbness and tingling)combined with electrodiagnostic confirmation(as reported by the attendingelectromyographers) of a case. Incidence ratios(IRs) were calculated using the full-timeequivalent number of hours worked reportedon the logs. The exact number of workers wasnot reported. Exposure assessment includedvideotape analysis of job tasks forrepetitiveness and awkward postures. Theforce measure was an estimate of the percentmaximum voluntary contraction (%MVC)based on weight of tools, and parts andpopulation strength data adjusted for extremeposture or speed. Jobs were then categorizedas hazardous or safe (for all upper extremityMSDs, not for CTS), based on exposure dataand the judgment of the investigators. Thehazardous jobs had a relative risk (RR) forCTS of 2.8 (95% CI 0.2–36.7) compared tothe safe jobs. Due to the lack of data fromindividual workers, the study was unable tocontrol for common confounders. Potential forsurvivor effect (79% of the workforce was laidoff the year prior to the study), a limited latencyperiod (8–32 months), and the potential forincomplete case ascertainment (underreportingis known to be a problem with OSHA illnessand injury logs) limit confidence in this estimate.This study did not specifically address therelationship between repetitiveness and CTS.No significant association was identified
5a-5
between repetitiveness and the grouped “upperextremity musculoskeletal disorders,” but therewas very little variability in repetitiveness (31 ofthe 32 jobs had a cycle time less than 30seconds).
Osorio et al. [1994] studied 56 supermarketworkers. Exposure to repetitive and forcefulwrist motions was rated as high, moderate, orlow, following observation of job tasks. TheCTS case definition was based on symptomsand nerve conduction studies. CTS-likesymptoms occurred more often (OR 8.3, 95%CI 2.6–26.4) among workers in the highexposure group compared to the low exposedgroup. The odds of meeting the symptom andNCS-based CTS case definition among thehigh exposure group were 6.7 (95% CI0.8–52.9), compared to the low exposuregroup.
Silverstein et al. [1987] studied 652 workers in39 jobs from 7 different plants (electronics,appliance, apparel, and bearing manufacturing;metal casting, and an iron foundry).Investigators divided jobs into high or lowrepetitiveness categories, based on analysis ofvideotaped job tasks of 3 representativeworkers in each job. High repetitiveness wasdefined as cycle time less than 30 seconds or atleast 50% of the work cycle spent performingthe same fundamental movements. Jobs werealso divided into high or low force categoriesbased on EMGs of representative workers’forearm flexor muscles while they performedtheir usual tasks. EMG measurements wereaveraged within each work group tocharacterize the force requirements of the job.High force was defined as a mean adjustedforce >6 kg. Jobs were then classified into 4groups: low force/low repetitiveness, high
force/low repetitiveness, low force/highrepetitiveness, and high force/highrepetitiveness. Fourteen cases (2.1%prevalence) of CTS were diagnosed based onstandardized physical examinations andstructured interviews.
The OR for CTS in highly repetitive jobscompared to low repetitive jobs, irrespective offorce, was 5.5 (p<0.05) in a statistical modelthat also included age, gender, years on the job,and plant. The OR for CTS in jobs withcombined exposures to high force and highrepetition was 15.5 (p<0.05), compared tojobs with low force and low repetition. Age,gender, plant, years on the job, hormonalstatus, prior health history, and recreationalactivities were analyzed and determined not toconfound the associations identified.
Studies Meeting at Least One CriterionFourteen additional studies met at least one ofthe criteria.
Barnhart et al. [1991] studied ski manufacturingworkers categorized as having repetitive ornonrepetitive jobs based on observationalexposure methods for hand/wrist exposure. Theparticipation rate for this study was below70%. Three different case definitions were usedfor CTS based on symptoms, physical examfindings, and NCS using the mean median-ulnardifference in each group. Each case definitionused the NCS results. The authors reported asignificant prevalence ratio (PR) of 2.3 for themean median-ulnar sensory latency nervedifference among those in repetitive jobscompared to those in non-repetitive jobs.However, the difference was found in the ulnarrather than in the median nerve. The mediannerve latencies were not statistically differentbetween the two groups.
5a-6
Baron et al. [1991] studied CTS in 124grocery store checkers and 157 other grocerystore workers who were not checkers. TheCTS case definition required symptoms thatmet pre-determined criteria on a standardizedquestionnaire and physical examinations. TheOR for CTS among checkers was 3.7 (95%CI 0.7–16.7), in a model that included age,hobbies, second jobs, systemic disease, andobesity. Participation rates at the work siteswere higher among the exposed group(checkers: 85% participation, non-checkers:55% participation). After telephone interviewsin which 85% of the non-checkers completedquestionnaires, investigators reported that theproportion of non-checkers meeting the casedefinition did not increase.
Cannon et al. [1981] in a case-control study ofaircraft engine workers did not find a significantassociation with the performance of repetitivemotion tasks (OR 2.1, 95%CI 0.9–5.3), butfound a significant association with self-reported use of vibrating hand tools, history ofgynecologic surgery, and an inverse relationshipwith years on the job. One must assume fromthe article that “repetitive motion tasks” weredefined by job title. The diagnosis of CTS wasbased on medical and workers’ compensationrecords.
In English et al.’s [1995] case-control study ofupper limb disorders diagnosed in orthopedicclinics, the case series included 171 cases ofCTS and 996 controls. Exposure was based onself-reports; repetitiveness was defined as amotion occurring more than once per minute.The logistic regression model of CTS foundsignificant associations with height (negative),weight (positive), presentation at the clinic as aresult of an accident (negative), and two
occupational factors: 1) uninterrupted shoulder rotation with elevatedarm (OR 1.8, 95% CI 1.2–2.8) and 2)protection from repeated finger tapping (OR0.4, 95% CI 0.2–0.7). The authors note thatthe latter observation presented “difficulties ofinterpretation.” Limitations of this study concernthe lack of exposure assessment for repetition,and the questionable reliability for reported limbmovements as an accurate measure ofrepetition.
Feldman et al. [1987] studied electronicworkers at a large manufacturing firm using aquestionnaire survey and biomechanical jobanalysis. Four work areas with 84 workerswere identified as “high risk” with highlyrepetitive and forceful tasks. Workers in thesehigh risk areas had physical examinations andNCS. Sixty-two workers from the high riskarea had repeat NCS one year later.Comparing these high risk workers to theothers, one can calculate ORs for symptoms ofnumbness and tingling [OR 2.26 (p<0.05)] anda positive Phalen’s sign [2.7 (p<0.05)].Longitudinal NCS of workers in the high riskarea showed significant worsening in themedian motor latency and sensory conductionvelocity in the left hand, and motor changesover a year’s period, which the authorsattributed to work exposure. A limitation of thisstudy concerns inadequate exposureinformation about the extent of workerexposure to repetitive and forceful work.
McCormack et al. [1990] studied 1,579 textileproduction workers and compared them to 468other nonoffice workers, a comparison groupthat included machine maintenance workers,transportation workers, cleaners, andsweepers. The textile production workers weredivided into four broad job categories based onsimilarity of upper extremity exertions. No
5a-7
formal exposure assessment was conducted.Health assessment included a questionnaire andscreening physical examination followed by adiagnostic physical examination. CTS wasdiagnosed using predetermined clinical criteria.The severity of cases was also reported asmild, moderate, or severe. The overallprevalence for CTS was 1.1%, with 0.7% inboarding, 1.2% in sewing, 0.9% in knitting,0.5% in packaging/folding, and 1.3% in thecomparison group. None of the differenceswere statistically significant. A statistical modelthat also included age, gender, race, and yearsof employment showed that CTS occurredmore often among women in this study(p<0.05). Interpretation of these data,especially with a low prevalence disorder likeCTS, is difficult since gender varied with job(94% of boarding workers were female,compared to 56% in the comparison group),and the comparison group (machinemaintenance workers, transportation workers,cleaners and sweepers) may have also beenexposed to upper extremity exertions.Interactions among potential confounders werenot addressed, but they are suspected becauseof significant associations between race andthree MSDs.
Morgenstern et al. [1991] mailedquestionnaires to 1,345 union grocery checkersand a general population group. Exposure wasbased on self-reported time working as achecker. Symptoms of CTS were significantlyassociated with age and the use of diuretics,and nonsignificantly associated with averagehours worked per week, and years worked asa checker. A positive CTS outcome was basedon the presence of all four symptoms: pain inthe hands or wrist, nocturnal pain, tingling in thehands or fingers, or numbness. The estimatedattributable fraction of CTS symptoms toworking as a checker was about 60%, using
both a general population comparison groupand a low exposed checker group. Thelimitations of this study are: 1) the use of anoverly sensitive health outcome measure, forexample, 32% of the surveyed populationreported numbness; and 2) the use of self-reported exposure.
Nathan et al. [1988] studied median nerveconduction of 471 randomly selected workersfrom four industries (steel mill, meat/foodpackaging, electronics, and plasticsmanufacturing). Median nerve sensory latencyvalues were adjusted for age for statisticalanalyses. Thirty-nine percent of the studysubjects had impaired sensory nerveconduction, or “slowing” of the median nerve.The five exposure groups were defined asfollows: Group 1 is very low force, lowrepetition (VLF/LR); Group 2 is low force,very high repetition (LF/VHR); Group 3 ismoderate force, moderate repetition (MF/MR);Group 4 is high force/moderate repetition(HF/MR); and Group 5 is very high force/highrepetition (VHF/HR). There was no significantdifference between Group 1 and Group 2, thegroups that had the greatest differences inrepetition. The authors reported a significantlyhigher number of subjects with median nerveslowing in Group 5 (VHF/HR) compared toGroup 1 (VLF/LR), but not in other groups,using a statistical method described as a“pairwise unplanned simultaneous testprocedure” [Sokal and Rohlf 1981]. Theauthors also reported that when individualhands were the basis of calculations rather thansubjects, Group 3 had a significantly higherprevalence of median nerve slowing.Calculations of the data using PRs and chi-squares [Kleinbaum et al. 1982] resulted insignificantly higher prevalences of median nerve
5a-8
slowing in each of Groups 3, 4, and 5(moderate to high repetition, with moderate tovery high force) compared to Group 1(VLR/LF). PRs are 1.9 (95% CI 1.3–2.7), 1.7(95% CI 1.1–2.5), and 2.0 (95% CI 1.1–3.4)for Groups 3, 4, and 5, respectively. Aconservative (Bonferroni) adjustment of thesignificance level to 0.0125 for multiplecomparisons [Kleinbaum et al. 1982] wouldresult in Group 5 no longer being statisticallysignificantly different from Group 1 (p=0.019),but Group 4 (p=0.009), and Group 3(p=0.000) remain statistically significantlyhigher than Group 1 in prevalence of mediannerve slowing.
In 1992, Nathan et al. [1992a] reported on afollow-up evaluation in the same study group.Sixty-seven percent of the original studysubjects were included. Hands (630), ratherthan subjects, were the basis of analysis in thisstudy. Novice workers (those employed lessthan 2 years in 1984) were less likely to returnthan non-novice workers (56% compared to69%, p=.004). Maximum latency differences inmedian nerve sensory conduction weredetermined as in the Nathan et al. [1988] study.The authors state that there was no significantdifference in the prevalence of median nerveslowing between any of the exposurecategories in Nathan et al. [1988] using thesame statistical method described in the Nathanet al. 1988 study. However, calculations usingcommon statistical methods result in thefollowing PRs for slowing: Group 3–1.5 (95%CI 1.0–2.2), Group 4–1.4 (95% CI 0.9–2.1),and Group 5–1.0 (95% CI 0.5–2.2),compared to Group 1. Group 5 had the sameprevalence of slowing (18%) as Group 1 in1989. In 1984 the prevalence of slowing was29% in Group 5, and 15% in Group 1. The
drop in prevalence of median nerve slowing inGroup 5 between 1984 and 1989 might beexplained by the higher drop-out rate amongcases in Group 5 compared to Group 1 (PR2.9, 95% CI 1.3–6.6). This was not addressedby the authors.
Punnett et al. [1985] compared the symptomsand physical findings of CTS in 162 womengarment workers and 76 women hospitalworkers such as nurses, laboratory technicians,and laundry workers. Eighty-six percent of thegarment workers were sewing machineoperators and finishers (sewing and trimming byhand). The sewing machine operators weredescribed as using highly repetitive, low forcewrist and finger motions, whereas finishingwork also involved shoulder and elbowmotions. The exposed garment workersprobably had more repetitive jobs than most ofthe hospital workers. CTS symptoms occurredmore often among the garment workers (OR2.7, 95% CI 1.2–7.6) compared to the hospitalworkers. There was a low participation rate(40%) among the hospital workers.
Schottland et al. [1991] carried out acomparison of NCS findings in poultry workersand job applicants as referents. No exposureassessment was performed, and applicantswere not excluded if they had prioremployment in the plant. Results indicated thatthe right median nerve sensory latency wassignificantly longer in 66 female poultry workerscompared to 41 female job applicants. In thesetwo groups of women there were lesspronounced differences in the left mediansensory latency. The latencies in the 27 malepoultry workers did not differ significantly fromthe 44 male job applicants, although the powercalculations presented in the paper noted
5a-9
limited power to detect differences among maleparticipants. The OR for percentage of femalepoultry workers who exceeded the criteriavalue for the right median sensory latency is2.86 (95% CI 1.1–7.9). The major limitationsof this study are the absence of detailedinformation on exposure and the inclusion offormer poultry workers into the applicantgroup, as well as the inadequate sample size,and the personal characteristics of theseworkers. This study found a significantassociation between highly repetitive, highlyforceful work and abnormal NSC consistentwith CTS. It does not allow analysis ofrepetition alone.
Stetson et al. [1993] used measurements ofsensory nerve conduction velocity of themedian nerve as indicators of nerve impairmentor CTS; clinical examination results were notreported in this article. Three groups werestudied: a reference group of 105 workerswithout occupational exposure to highly forcefulor repetitive hand exertions, 103 industrialworkers with hand/wrist symptoms, and 137asymptomatic industrial workers. Exposure wasassessed with a checklist by trained workers.Factors considered included repetitiveness(Silverstein criteria), force defined by theweight of an object that is carried or held,localized mechanical stress, and posture.Exposure assessments were available on 80%of the industrial workers. Most of the industrialworkers were on repetitive jobs (76%), aminority carried more than ten pounds some ofthe time (32%), and gripped more than sixpounds at least some of the time (44%). Theanalysis controlled for several confoundersincluding age, gender, finger circumference,height, weight, and a square-shaped wrist. Inthe comparison of the asymptomatic to
symptomatic industrial workers, the meanexposure for the symptomatic industrialworkers was nonsignificantly slightly greater forall exposure factors except for repetitiveness.The median sensory amplitudes weresignificantly smaller (p<0.01) and latencies longer (p<0.05 ) forindustrial workers with exposure to high gripforces compared to those without. Meansensory amplitudes were significantly smaller(p<0.05) and motor and sensory latencies weresignificantly longer (p<0.01) in the industrialasymptomatic workers compared to the controlgroup. These findings for the motor latenciesare similar to Feldman et al. [1987]. Since mostof the industrial workers were exposed torepetitive work, it is not clear whether thisstudy population allowed a comparisonbetween repetitive and non-repetitive work.Overall this study suggests that repetitive workcombined with other risk factors is associatedwith slowing of median nerve conduction. The Wieslander et al. [1989] case-controlstudy used self-reported information collectedvia telephone interview about the duration ofexposure (number of years and hours perweek) to several work attributes includingrepetitive work. Definitions for these workattributes were not provided. Three categoriesof duration of exposure were defined for eachattribute (<1 year,1–20 years, and >20 years), but the asymmetryof the categories was not explained. Asignificant OR for reporting repetitivemovements of the wrist comparing CTSpatients to hospital referents (OR 4.6) andgeneral population referents (OR 9.6) wasreported, but only among those employedgreater than 20 years. Those employed from1–20 years compared to the referent
5a-10
population had elevated ORs for repetitivemovements of the wrist (1.5 for CTS patientscompared to hospital referents, and 2.3compared to population referents), but thesewere not significant. Jobs with increasingnumbers of work risk factors gave increasingORs (from 1.7 to 7.1) among CTS cases whencompared to referents; these were statisticallysignificant when there were two or more riskfactors. Given the limited quality of theexposure data and findings (repetition is asignificant risk factor only after 20 years ofexposure), this is only suggestive of arelationship between repetition alone and CTS. Studies Not Meeting Any of the CriteriaLiss et al. [1995] conducted a mail surveyconcerning CTS among 2,124 Ontario dentalhygienists compared to 305 dental assistantswho do not scale teeth. Both groups had a lowresponse rate (50%). The age adjusted ORwas 5.2 (95% CI 0.9–32) for being told by aphysician that you had CTS and 3.7 (95% CI1.1–1.9) using a questionnaire-based definitionof CTS. The major limitations of this study arethe low participation rate, the lack of a detailedexposure assessment for repetitiveness, andself-reported health outcome.
Strength of Association—Repetitionand CTSThree of the five studies that met all four criteriaevaluated the effect of repetitiveness alone onCTS: Chiang et al. [1990], Silverstein et al.[1987], and Chiang et al. [1993].
Chiang et al. [1990] reported an OR of 1.9(p<0.05) for CTS among those with highlyrepetitive jobs. The OR for CTS among thoseexposed to high repetitiveness and cold was3.32 (p<0.05). The additional effect attributed
to cold may be at least partially explained byforceful motions among workers who were alsoexposed to cold. Force was not evaluated inthis study.
Silverstein et al. [1987] reported an OR of 5.5(p<0.05) for repetition as a single predictor ofCTS. Among workers exposed to highrepetition and high force, the OR was 15.5(p<0.05).
Chiang et al. [1993] reported a significant trendof increasing prevalence of CTS with increasingexposure to repetition and/or force (8.2%,15.3%, and 28.6%, p<0.05). Repetition (of thewhole upper limb, not the wrist) alone did notsignificantly predict CTS (OR 1.1).
In summary, three studies that met all fourcriteria reported ORs for CTS associated withrepetition. The statistically significant ORs forCTS attributed to repetition alone ranged from1.9 to 5.5. The statistically significant ORs forCTS attributed to repetition in combination withforce or cold ranged from 3.3 to 15.5. Gender,age, and other potential confounders wereaddressed and are unlikely to account for theassociations reported.
Five other studies observed job tasks, thengrouped them into categories according toestimated levels of repetitiveness combinedwith other risk factors [Feldman et al. 1987;Moore and Garg 1994; Nathan et al. 1988,1992a; and Osorio et al. 1994]. CTS casedefinitions reported here required more thansymptom-defined criteria. Moore and Garg[1994] reviewed medical records; Nathan et al.[1988] and Osorio et al. [1994] performednerve conduction studies.
5a-11
Feldman et al. [1987] reported an OR of 2.7(p<0.05) for a positive Phalen’s test amongworkers in high exposure jobs, compared tolow exposure jobs.
Moore and Garg [1994] reported an OR of2.8 (0.2, 36.7) for CTS among workers in“hazardous” jobs compared to workers in“nonhazardous” jobs.
Nathan et al.’s [1988] data result in PRsfor four groups with varying levels ofrepetitiveness and force from very low (VL) tovery high (VH), compared to a very low force,low repetition group (VLF/LR): LF/VHR versus VLF/LR: 1.0 (95% CI0.5–2.0)MF/MR versus VLF/LR: 1.9 (95% CI1.3–2.7)HF/MR versus VLF/LR: 1.7 (95% CI 1.1–2.5)VHF/HR versus VLF/LR: 2.0 (95% CI1.1–3.4).
Nathan et al. [1992a] data, a 5-year follow-upof the 1988 study, result in PRs for thefollowing groups:LF/VHR versus VLF/LR: 1.0 (95% CI 0.6–1.9) MF/MR versus VLF/LR: 1.5 (95% CI 1.0–2.2)HF/MR versus VLF/LR: 1.4 (95% CI 0.9–2.1)VHF/HR versus VLF/LR: 1.0 (95% CI 0.5–2.2).
Osorio et al. [1994] reported an OR of 6.7(95% CI 0.8–52.9) for CTS among workers inhigh exposure jobs, compared to workers inlow exposure jobs. Using a symptom-basedcase definition, the OR for the same
comparison groups was 8.3 (95% CI 2.6–26.4).
To summarize, three of the five studiesreviewed resulted in statistically significantpositive findings for CTS associated withcombined exposures. Feldman et al. [1987]reported an elevated OR for CTS with highcombined exposure. Nathan et al.’s [1988]data resulted in elevated PRs for CTS amongthe three highest combined exposure groups.Nathan et al.’s [1992a] data resulted in anelevated PR for CTS among one of the highcombined exposure groups. There wasevidence of survivor bias in the highestexposure group.
The following studies used job title or jobcategory to represent exposure torepetitiveness combined with other exposuresand defined CTS based on physicalexamination [Baron et al. 1991, McCormack etal. 1990, Punnett et al. 1985] or nerveconduction studies [Schottland et al. 1991].
Baron et al. [1991] reported an OR of 3.7(95% CI 0.7–16.7) for CTS, defined bysymptoms and physical examination, amonggrocery checkers compared to other groceryworkers.
McCormack et al. [1990] reported thefollowing ORs for CTS among workers in eachof four broad job categories that wereconsidered exposed, compared to acomparison group of maintenance workers andcleaners that was considered to have lowexposure:Boarding versus Low: 0.5 (95% CI 0.1–2.9)Sewing versus Low: 0.9 (95% CI 0.3–2.9)
5a-12
Packaging versus Low: 0.4 (95% CI 0.0–2.4)Knitting versus Low: 0.6 (95% CI 0.1–3.1)
Punnett et al. [1985] reported an OR of 2.7(95% CI 1.2–7.6) for CTS among garmentworkers versus hospital workers.
Schottland et al. [1991] reported an OR of2.86 (95% CI 1.1–7.9) for prolonged rightmedian sensory latency among female poultryworkers, compared to female applicants for thesame jobs. No significant differences wereidentified among males.
In summary, two of the four studies reviewedabove reported significantly elevated ORs forCTS or median sensory nerve conductionslowing.
Wieslander et al. [1989] reported an OR forCTS (surgical cases, confirmed by NCS) of2.7 (95% CI 1.3–5.4) among those with self-reported exposure to repetitive wrist movement>20 years, compared to hospital referents, and4.5 (95% CI 2.0–10.4), compared topopulation referents. Significant OR s for CTSamong those with combined job risk factorsranged from 3.3 to 7.1.
The remaining two studies relied on self-reported symptoms and self-reportedexposures from mail [Morgenstern et al. 1991]or telephone surveys [Liss et al. 1995]. Dataquality and response rates limit interpretation offindings.
In conclusion, among the studies that measuredrepetition alone, there is evidence that repetitionis positively associated with CTS. The majorityof studies provide evidence of a strongerpositive association between repetition
combined with other job risk factors and CTS.
Temporal Relationship: Repetitionand CTS The question of which occurs first, exposure ordisease, can be addressed most directly inprospective studies. However, study limitationssuch as survivor bias can cloud theinterpretation of findings. In our analysis ofNathan et al.’s [1992a] data, 2 of 3 groups thatwere exposed to forceful hand/wrist exertionswere more likely to have median nerve slowingwhen nerve conduction testing was repeated 5years later. The highest exposure group had thesame prevalence of slowing as the lowestexposure group in 1989, whereas they had ahigher prevalence rate in 1984. As discussedabove, this apparent decrease in prevalenceover 5 years can probably be explained by ahigher drop-out rate among cases in the highestexposure group, compared to the lowestexposure group. These interpretations of thedata differ from those of the authors. Furtherstudy is needed to clarify these issues.However, to our knowledge, there is noevidence demonstrating that those with CTSwould be more likely to be hired in jobs thatinvolve high exposure to repetitive hand/wristexertions and combined job risk factors,compared to those without CTS. In fact,employment practices tend to exclude newworkers with CTS from jobs that requirerepetitive and intensive hand/wrist exertion.
Feldman et al. [1987] reported longer medianmotor (but not sensory) latencies amongworkers with combined exposure to hand/wristexertion, compared to nerve conductionfindings in the same group one year earlier.
Cross-sectional studies provide evidence that
5a-13
exposure occurred before CTS, by using casedefinitions that exclude pre-existing cases, andby excluding recently hired workers from thestudy. The studies that provide evidence thatrepetitive and combined job exposures areassociated with CTS followed these practices,therefore the associations identified cannot beexplained by disease occurring beforeexposure.
Consistency in Association forRepetition and CTS One study [English et al. 1995] reported astatistically significant negative associationbetween repetitive work and CTS. The specificexposure was self-reported repeated fingertapping; the investigators stated that they haddifficulty interpreting this finding. All of the otherstatistically significant findings pointed to apositive association between repetitive workand CTS. The non-significant estimates of RRwere also mostly greater than one. Coherence of Evidence for RepetitionOne of the most plausible ways that repetitivehand activities may be associated with CTS isthorough causing a substantial increase in thepressure in the carpal tunnel. This in turn caninitiate a process which results in eitherreversible or irreversible damage to the mediannerve [Rempel 1995]. The increase in pressure,if it is of sufficient duration and intensity, mayreduce the flow of blood in the epineuralvenules. If prolonged, this reduction in flowmay affect flow in the capillary circulation,resulting in greater vascular permeability andendoneural and synovial edema. Because of thestructure of the median nerve and the carpaltunnel, this increase in fluid and resultingincrease in pressure may persist for a longperiod of time. If the edema becomes chronic,
then it may trigger a fibrosis which damages thefunction of the nerve. The interplay betweenacute increases in pressure and chronic changesto the nerve could partially explain why there isnot a stronger correlation between symptoms ofCTS and slowing of the median nerve. Bothsymptoms and slowing of the median nerve arelikely to have both acute and chroniccomponents in many cases of CTS.
The work determinants of pressure in thecarpal tunnel are wrist posture and load on thetendons in the carpal tunnel. For example, thenormal resting pressure in the carpal tunnel withthe wrist in a neutral posture is about 5millimeters of mercury (mmHg), and typing withthe wrist in 45E of extension can result in anacute pressure of 60 mmHg. Substantial loadon the fingertip with the wrist in a neutralposture can increase the pressure to 50 mmHg.A parabolic relationship between wrist postureand pressure in the carpal tunnel has beenfound. In laboratory studies of normal subjects,elevated carpal tunnel pressures quickly returnto normal once the repetitive activity stops;patients with CTS take a long time for thepressure to return to their baseline values. Oneof the supporting observations for this model isthat at surgery for CTS, edema and vascularsclerosis (fibrosis due to ischemia) are common[Rempel 1995].
This model of the etiology of work-related CTSis consistent with two observations from theepidemiological literature. First, it illustrateswhy both work and nonwork factors such asobesity may be important because anything thatincreases pressure in the carpal tunnel maycontribute to CTS. Second, it explains whyrepetitiveness independent of wrist posture andload on the flexor tendons may not be a major
5a-14
risk factor for CTS.
Exposure-Response Relationship forRepetitionEvidence of an exposure-response relationshipis provided by studies that show a correlationbetween the level or duration of exposure andeither the number of cases, the illness severity,or the time to onset of the illness. Silverstein etal. [1987] showed an increasing prevalence ofCTS signs and symptoms among industrialworkers exposed to increasing levels ofrepetition and forceful exertion. Thisrelationship was not seen when repetition alonewas assessed. Similar findings on an exposure-response relationship were reported by Chianget al. [1993], Osorio et al. [1994], Wieslanderet al. [1989], and by Stock [1991] in herreanalysis of the Nathan et al. [1988] data.
Morgenstern et al. [1991] and Baron et al.[1991] reported increased prevalence of CTSwith increasing length of time working as agrocery cashier.
Conclusions Regarding RepetitionBased on the epidemiologic studies notedabove, especially those with quantitativeevaluation of repetitive work, the strength ofassociation for CTS and repetition has beenshown to range from an OR of 2 to 15. Thehigher ORs are found when contrasting highlyrepetitive jobs to low repetitive jobs, and whenrepetition occurred in combination with highlevels of forceful exertion. Those studies withcertain epidemiologic limitations have also beenfairly consistent in showing a relationshipbetween repetition and CTS. The evidencefrom those studies which defined CTS basedon symptoms, physical findings, and NCS islimited, due to the variety of methods used
[Nathan et al. 1988; Stetson et al. 1993;Barnhart et al. 1991].
There is evidence of a positive associationbetween highly repetitive work alone and CTS.There is strong evidence of a positiveassociation between highly repetitive work incombination with other job factors and CTS,based on currently available epidemiologicdata.
FORCE AND CTSDefinition of force for CTSThe studies reviewed in this section determinedhand/wrist force exposure by a variety ofmethods. Some investigators [Armstrong andChaffin 1979; Chiang et al. 1993; Silverstein etal. 1987] measured force by EMGs ofrepresentative workers’ forearm flexor muscleswhile they performed their usual tasks. EMGmeasurements were averaged within each workgroup to characterize the force requirements ofthe job; jobs were then divided into low or highcategories if the average force was above orbelow a cutoff point. Moore and Garg [1994]estimated force as %MVC, based on weight oftools and parts and population strength data,adjusted for extreme posture or speed. Jobswere then predicted to be either hazardous orsafe (for any upper extremity musculoskeletaldisorder), based on exposure data andjudgment. Stetson et al. [1993] estimatedmanipulation forces based on weights of toolsand parts and systematically recordedobservations of one or more workers on eachjob. Jobs were then ranked according to gripforce cutoffs. Nathan et al. [1988, 1992a] andOsorio et al. [1994] estimated relative levels offorce (e.g., low, moderate, high) afterobservation of job tasks. McCormack et al.[1990] grouped jobs into broad job categories
5a-15
based on similarity of observed job tasks; onejob group (boarding) required forcefulhand/wrist exertions. Baron et al. [1991] andPunnett et al. [1985] used job title as asurrogate for exposure to forceful hand/wristexertions.
Much of the epidemiologic data on CTS andforce overlaps with those studies discussed inthe above section on repetition. Repetitivework is frequently performed in combinationwith external forces, and much of theepidemiologic literature has combined thesetwo factors when determining association withCTS.
Studies Reporting on the Associationof Force and CTSEleven studies reported results on theassociation between force and CTS. Theepidemiologic studies that addressed forcefulwork and CTS tended to compare workinggroups by classifying them into broadcategories based on estimates of theforcefulness of hand/wrist exertions incombination with estimated repetitiveness. Inmost studies the exposure classification was anordinal rating (e.g., low, moderate, or high); insome studies job categories or titles were usedas surrogates for exposure to force exertions.
Studies Meeting the Four Evaluation CriteriaFour studies that evaluated the relationshipbetween forceful hand/wrist exertion and CTSmet all four criteria: Chiang et al. [1993],Moore and Garg [1994], Osorio et al. [1994],Silverstein et al. [1987]. Chiang et al. [1993]studied 207 workers from 8 fish-processingfactories in Taiwan. Jobs were divided into 3groups based on levels of force andrepetitiveness. The comparison group (low
force/low repetitiveness) was managers, officestaff, and skilled craftsmen. The fish-processingworkers were divided into high force or highrepetitiveness (group 2), and high force andhigh repetitiveness (group 3). Hand forcerequirements of jobs were estimated byelectromyographs of forearm flexor muscles ofa representative worker from each groupperforming usual job tasks. High force wasdefined as an average hand force of >3 kgrepetition of the upper limb (not specifically thewrist) was defined based on observed cycletime [Silverstein et al. 1987]. CTS was definedon the basis of symptoms and positive physicalexamination findings, ruling out systemicdiseases and injury. CTS prevalence for theoverall study group was 14.5%. CTSprevalence increased from group 1 to group 3(8.2%, 15.3%, and 28.6%), a statisticallysignificant trend p<0.01). Statistical modelingshowed that women in this study group had ahigher prevalence of CTS than men (OR 2.6,95% CI 1.3–5.2). Force also significantlypredicted CTS (OR 1.8, 95% CI 1.1–2.9), butnot repetitiveness. Because the proportion ofwomen varied by exposure group (48%, 75%,and 79% from groups 1 to 3), the possibility ofan interaction between gender and jobexposure exists, but this was not statisticallyexamined. In an analysis limited to females, the2 significant predictors of CTS were oralcontraceptive use (OR 2.0, 95% CI 1.2–5.4),and force (OR 1.6, 95% CI 1.1–3.0). Concernover interpretation of these findings is raisedbecause oral contraceptive use varies with age,and age may vary with job exposures.
These potential interactions were not examined,and women’s ages by job group were notreported.
5a-16
Moore and Garg [1994] evaluated 32 jobs in apork processing plant and then reviewed pastOSHA 200 logs and plant medical records forCTS cases in these job categories. IRs werecalculated using the full-time equivalent (FTE)number of hours worked as reported on thelogs. The exact number of workers was notreported. Exposure assessment includedvideotape analysis of job tasks forrepetitiveness and awkward postures. Theforce measure was an estimate of the %MVC,based on weight of tools and parts andpopulation strength data, adjusted for extremeposture or speed. Jobs were then predicted tobe either hazardous or safe (for all UpperExtremity MSDs), based on exposure data andjudgment. CTS was determined by reviewingOSHA 200 logs and plant medical records.The proportion of CTS in the overall studygroup during the 20 months of caseascertainment was 17.5 per 100 FTEs. If theoccurrence of CTS did not vary over thisperiod, the proportion of CTS in a 12-monthperiod would be 10.5 per 100 FTEs. Thehazardous jobs had a RR for CTS of 2.8 (0.2,36.7) compared to the safe jobs. Potential forsurvivor effect (79% of the workforce was laidoff the year before the study), limited latencyperiod (8-32 months), and the potential forincomplete case ascertainment (underreportingis common on OSHA 200 logs, and logs werenot reviewed for the first 12 months of thestudy) limit confidence in this estimate. One ofthe more hazardous jobs, the Ham Loaders,required extreme wrist, shoulder and elbowposture and was rated 4 on a 5-point scale forforce, yet there was no observed morbidity.Since this job did not start until 1989, theperiod of observation for musculoskeletaldisorders for this job was only 8 months. Other
jobs studied allowed for up to a 32-monthlatency period. The possibility of differentialcase ascertainment between exposed andunexposed jobs exists, both because ofdifferent observation periods, as well as thelikelihood that turnover may have been greaterin the exposed jobs. It is also unclear whetheremployees worked full-time or part-time hours.
Osorio et al. [1994] studied 56 supermarketworkers. Exposure to repetitive and forcefulwrist motions was rated as high, moderate, orlow, following observation of job tasks (97%initial concordance with 2 independentobservers). The CTS case definition was basedon symptoms and nerve conduction studies.CTS-like symptoms occurred more often (OR8.3, 95% CI 2.6–26.4) among workers in thehigh exposure group compared to the lowexposed group. The odds of meeting thesymptom and NCS-based CTS case definitionamong the high exposure group were 6.7 (95%CI 0.8–52.9), compared to the low exposuregroup.
Silverstein et al. [1987] measured force byelectromyographs of representative workers’forearm flexor muscles while they performedtheir usual tasks. EMG measurements wereaveraged within each work group tocharacterize the force requirements of the job;jobs were then divided into high or lowcategories if the mean adjusted force wasabove or below4 kg. Jobs were then classified into 4 groupsthat also accounted for repetitiveness: lowforce/low repetitiveness, high force/lowrepetitiveness, low force/high repetitiveness,and high force/high repetitiveness. Fourteencases (2.1% prevalence) of CTS were
5a-17
diagnosed based on standardized physicalexaminations and structured interviews.
The OR for CTS in high force jobs comparedto low force jobs, irrespective of repetitiveness,was 2.9 (p>0.05). The plant- adjusted OR forCTS in jobs with combined exposures to highforce and high repetition was 14.3 (p<0.05),compared to jobs with low force and lowrepetition. Age, gender, plant, years on the job,hormonal status, prior health history, andrecreational activities were analyzed anddetermined not to confound the associationsidentified. The OR for CTS in jobs withcombined exposure from the multiple logisticanalysis was 15.5 (95% CI 1.7–142.)
Studies Meeting at Least One CriterionBaron et al. [1991] studied CTS in 124grocery store checkers and 157 other grocerystore workers who were not checkers. TheCTS case definition required symptoms thatmet pre-determined criteria on a standardizedquestionnaire. Physical examinations were alsoperformed, but participation rates at the worksites were higher among the exposed group(checkers: 85% participation, non-checkers:55% participation). Telephone interviews tonon-checkers resulted in questionnairecompletion by 85% of the non-checkers.Based on a questionnaire case definition, theOR for CTS among checkers was 3.7 (95%CI 0.7–16.7), in a model that included age,hobbies, second jobs, systemic disease, andobesity.
McCormack et al. [1990] studied 1,579 textileproduction workers compared to 468 othernonoffice workers, a comparison group thatincluded machine maintenance workers,transportation workers, cleaners, and
sweepers. The textile production workers weredivided into four broad job categories based onsimilarity of upper extremity exertions. TheBoarding group required the most physicalexertion. No formal exposure assessment wasconducted. Health assessment included aquestionnaire and screening physicalexamination followed by a diagnostic physicalexamination. CTS was diagnosed usingpredetermined clinical criteria. The severity ofcases was also reported as mild, moderate orsevere. The overall prevalence for CTS was1.1%, with 0.7% in Boarding, 1.2% in Sewing,0.9% in Knitting, 0.5% in Packaging/Folding,and 1.3% in the comparison group. None ofthe differences were statistically significant. Astatistical model that also included age, gender,race, and years of employment showed thatCTS occurred more often among women in thisstudy (p<0.05). Interpretation of these data,especially with a low prevalence disorder likecarpal tunnel syndrome, is difficult since gendervaried with job (e.g., 94% of Boarding workerswere female, compared to 56% in thecomparison group), and the comparison groupmay have also been exposed to upper extremityexertions (machine maintenance workers,transportation workers, cleaners andsweepers). Interactions among potentialconfounders were not addressed, but they aresuspected because of significant associationsbetween race and three musculoskeletaldisorders.
Nathan et al. [1988] studied median nerveconduction of 471 randomly selected workersfrom four industries (steel mill, meat/foodpackaging, electronics, and plasticsmanufacturing). Jobs were grouped into 5relative levels of force (from very light to veryhigh) after observation of job tasks. Jobs were
5a-18
also rated for repetitiveness (5 levels). Thirty-nine percent of the study subjects had impairedsensory conduction, or “slowing” of the mediannerve. The 5 exposure groups were defined asfollows: Group 1 is very low force, lowrepetition (VLF/LR); Group 2 is low force,very high repetition (LF/VHR); Group 3 ismoderate force, moderate repetition (MF/MR);Group 4 is high force/moderate repetition(HF/MR); and Group 5 is very high force/highrepetition (VHF/HR). The most logicalcomparisons to evaluate the effect of forcewould be Groups 3, 4, and 5 (moderate, high,and very high force) compared to Group 1 (lowforce). Group 2 jobs are not a goodcomparison because they are very highlyrepetitive, which may confound thecomparisons. The authors reported asignificantly higher number of subjects withmedian nerve slowing in Group 5 (VHF/HR)compared to Group 1 (VLF/LR), but not inother groups, using an uncommon statisticalmethod (pairwise unplanned simultaneous testprocedure [Sokal and Rohlf 1981]). Theauthors also reported that when individualhands were the basis of calculations rather thansubjects, Group 3 had a significantly higherprevalence of median nerve slowing.Calculations of the more familiar PRs and chi-squares [Kleinbaum et al. 1982], using thepublished data, result in higher prevalences ofmedian nerve slowing in each of Groups 3, 4,and 5, compared to Group 1 (PRs: 1.9, 95%CI 1.3–2.7; 1.7, 95% CI 1.1–2.5; and 2.0,95% CI 1.1–3.4, respectively). A conservativeadjustment (Bonferroni) of the significance levelto 0.0125 for multiple comparisons [Kleinbaumet al. 1982] would result in Group 5 no longerbeing statistically significantly different fromGroup 1 (p=0.019), but Group 4 (p=0.009)and Group 3 (p=0.000) remain statistically
significantly higher than Group 1 in prevalenceof median nerve slowing.
In 1992 Nathan et al. [1992a] reported on afollow-up evaluation in the same study group.Sixty-seven per cent of the original studysubjects were included. Hands (630), ratherthan subjects, were the basis of analysis in thisstudy. Novice workers (those employed lessthan 2 years in 1984) were less likely to returnthan non-novice workers (56% compared to69%, p=0.004). Probable CTS was defined onthe basis of symptoms reported during astructured interview and a positive Phalen’s orTinel’s test. Maximum latency differences inmedian nerve sensory conduction weredetermined as in the 1984 study. The authorsstate that there was no significant difference inthe prevalence of slowing between any of theexposure categories in 1989. However,calculations using common statistical methodsshow significantly higher prevalences of slowingin Group 4 (PR 1.4, 95% CI 0.9–2.1)compared to Group 1. Group 3's prevalence ofslowing was 26% compared to Group 1's18%, but this difference was not statisticallysignificant (p=0.07). Group 5 had the sameprevalence of slowing (18%) as Group 1 in1989; the prevalence of slowing in Group 5was 29% in 1984. The drop in prevalence ofslowing in Group 5 between 1984 and 1989might be explained by the higher drop-out rateamong cases in Group 5 compared to Group 1(PR 2.9, 95% CI 1.3–6.6). This was notaddressed by the authors.
Punnett et al. [1985] compared the symptomsand physical findings of CTS in 162 womengarment workers and 76 women hospitalworkers such as nurses, laboratory technicians,and laundry workers. Eighty-six percent of the
5a-19
garment workers were sewing machineoperators and finishers (sewing and trimming byhand). The sewing machine operators weredescribed as using highly repetitive, low forcewrist and finger motions, whereas finishingwork also involved shoulder and elbowmotions. The exposed garment workers likelyhad more repetitive jobs than most of thehospital workers. CTS symptoms occurredmore often among the garment workers (OR2.7, 95% CI 1.2–7.6) compared to the hospitalworkers. There was a low participation rate(40%) among the hospital workers.
Stetson et al. [1993] conducted nerveconduction studies on 105 administrative andprofessional workers, and 240 automotiveworkers. Hand/wrist forces were estimatedbased on weights of tools and parts andsystematically recorded observations of one ormore workers on each job. Jobs were thenranked according to grip force cutoffs: <6 lb,>6 lb, >10 lb. Median nerve measures differedamong the groups: index finger sensoryamplitudes were lower and distal sensorylatencies were longer among automotiveworkers in jobs requiring grip force >6 lb and>10 lb, compared to those requiring less than 6lb (p<0.05 for all). At the wrist, median sensoryamplitudes were also lower and distal mediansensory latencies were also longer among the>6 lb, and the >10 lb exposure groups (p<0.05for 3 of 4 differences). Age, height, and fingercircumference were included in statisticalmodels. The automotive workers were thendivided into two groups, symptomatic (n=103)and asymptomatic (n=137), based on whetheror not they met standard interview criteria forCTS symptoms. When comparisons weremade to the administrative and professionalworkers, 15 of 16 measures of median and
ulnar nerve function showed lower amplitudesand longer latencies (p<0.05) among theasymptomatic automotive workers; differenceswere greater between the symptomaticautomotive workers and the white collarworkers. The symptomatic automotive workershad lower amplitudes and longer latencies for 5of 6 median sensory measures (p<0.05),compared to the asymptomatic automotiveworkers; there were no significant differences inulnar nerve function between these two groups.Asymptomatic automotive workers had“healthier” median nerves than automotiveworkers with CTS symptoms, but there wereno differences between these 2 groups in ulnarnerve function, suggesting that the casedefinition was specific for CTS.
Of the studies that addressed CTS, almost allexamined occupations and jobs in which forcewas combined with another exposure factor(such as repetition or awkward postures).Chiang et al. [1993] estimated exposure tohand/wrist force independent of repetitivenessand found statistically significant RRs for CTSranging from 1.6 to 1.8. Estimates of RR thatwere not statistically significant ranged from 0.4to 6.7 [McCormack et al. 1990; Osorio et al.1994]. Relative risk estimates for CTS amongworkers exposed to a combination of forcefuland repetitive hand/wrist exertions ranged from1.0 to 15.5 [Nathan et al. 1988, 1992a;Silverstein et al. 1987].
Study limitations may impact the interpretationof findings. One limitation to consider is gendereffect. Of the studies listed above reportingstatistically significant associations betweenforceful hand/wrist exertions and CTS, gendereffect was controlled for in the analyses. Otherpotential limitations such as selection factors
5a-20
impact the interpretation of the studiesreviewed. Survivor bias can be a concern. Ifworkers with CTS are more likely to leave jobsthat require forceful and repetitive hand/wristexertions than jobs without those demands,then the workers in the highest risk jobs may be“survivors” (those who did not get CTS). Ouranalysis of Nathan’s [1992a] data from afollow-up of industrial workers shows thatcases (with median nerve slowing) were morelikely to drop out of the most highly exposedgroup than the unexposed group, which mightexplain why the RR for high exposuredecreased from 2.0 to 1.0 over a 5-yearperiod. Survivor bias results in anunderestimate of the RR.
Refined or exact measures of exposure toforceful hand/wrist exertions are not alwaysused in epidemiologic studies (e.g., sometimesexposure is based on job category and notactual forceful measurements); this can result insome study subjects being assigned to thewrong exposure category. When this occurs,the usual effect is again to underestimate the RRbetween exposure groups.
Stetson et al. [1993] did not report RRestimates for exposure variables, but theyreported that median sensory amplitudes weresignificantly smaller and distal sensory latencieswere significantly longer in groups with forcefulhand exertions (p<0.05). Age, height, andfinger circumference were included in statisticalmodels.
Temporality, Force and CTS
Temporal issues can usually best be addressedusing longitudinal studies. However, study
limitations, such as survivor bias, can cloud thefindings of even prospective studies. In our re-analysis of Nathan et al.’s [1992a] data, 2 of 3groups exposed to forceful hand/wrist exertionswere more likely to have median nerve slowingwhen nerve conduction testing was repeated 5years later. The highest exposure group had thesame prevalence of slowing as the lowestexposure group in 1989, whereas there hadbeen a higher prevalence rate in 1984. Asdiscussed above, this apparent decrease inprevalence over 5 years can likely be explainedby survivor bias. Our interpretations of the datadiffer from those of the author. Further study isneeded to clarify these issues. To ourknowledge, there is no evidence that workerswith pre-existing CTS are more likely to seekor to be employed in jobs with high forcerequirements. We believe that employmentpractices would, if they had any influence, tendto exclude new hires with CTS from jobs withhigh force requirements for the hand/wrist.
Case definitions in most of the cross-sectionalstudies excluded cases that occurred beforeworking on the current job. This limits CTScases studied to those that occurred followingcurrent exposure. Several of the studiesreviewed also required a minimum time periodof working on the job before counting CTScases. This increases the likelihood thatexposure to forceful hand/wrist exertionoccurred for a sufficient length of time todevelop CTS. There is evidence that CTS is also attributableto nonwork causes (hobbies, sports, othermedical conditions, and hormonal status inwomen, etc.). One issue which deals withtemporality is whether those withnonwork-related CTS would be more likely tobe hired into jobs requiring more forceful
5a-21
hand/wrist exertions than those without CTS.Again, it seems unlikely that those withpre-existing CTS would be preferentially hiredinto jobs requiring highly forceful hand/wristexertions.
Consistency of Association for Forceand CTS
Most of the statistically significant estimates ofRR for CTS among workers with exposure toforceful hand/wrist exertions were positive. Nostudies found statistically significant negativeassociations between forceful hand/wristexertions and CTS. One study reported ORsthat were less than one among the groups thatwere described as exposed to repetitive handmovements; chance and study limitationscannot be ruled out as possible explanations forthis finding. The other nonsignificant estimatesof RR were, with one exception, greater thanone.
Statistical significance can be a function ofpower (the ability of a study to detect anassociation when one does exist). In general,larger studies are necessary in order to havesufficient power to detect associations with rarediseases. CTS is a less frequently observeddisorder than tendinitis, for example, and solarger studies are required to detectassociations with confidence.
Coherence of Evidence, Force andCTS
Please refer to the Repetition and CTS Section.
Exposure-Response Relationship,Force and CTS
None of the studies reviewed demonstrated
that increasing levels of force alone resulted inincreased risk for CTS. The only evidence foran increasing risk for CTS that can beattributed to increasing levels of force alone isfrom a comparison across 2 studies that usedthe same methods. Chiang et al. [1993] andSilverstein et al. [1987] used the same methodsto measure hand/wrist force requirements andrepetitiveness of jobs. Chiang et al. [1993]used a lower cutoff point (3 kg compared to 4kg) in Silverstein et al.’s [1987] study forclassifying jobs as “high force”; theseinvestigators used identical definitions ofrepetitiveness. Therefore, a comparison of theRR estimates between the 2 studies providessome information about the level of riskassociated with different levels of force. Chianget al. [1993] reported an OR of 2.6 (95% CI1.0–7.3) for the high force and repetitive(HF/HR) (>3 kg) group (limited to females toavoid confounding) compared to the low forceand repetitive (LF/LR) group; whereasSilverstein et al. [1987] reported an OR of15.5 (95% CI 1.7–142) for the HF/HR group(in a statistical model that included gender, age,years on the job, plant and exposure level)compared to the LF/LR group. Thiscomparison provides limited evidence of anincreased RR for CTS with increasing level ofhand/wrist force.
There is more evidence of a dose-responserelationship for CTS with increasing levels offorce and repetition combined. Chiang et al.[1993] reported a statistically significant trendof increasing prevalence of CTS with increasingexposure level (8.2% [LF/LR], 15.3% [HF orHR], and 28.6% [HF/HR], p<0.01). Silversteinet al. [1987] suggested a multiplicative effectwhen exposure to high force and highrepetitiveness were combined (15.5),compared to high force (1.8) or highrepetitiveness (2.7) alone.
5a-22
Of the remaining nine studies, seven areconsistent with the combined effect of force andrepetition [Stetson et al. 1993; Moore andGarg 1994; Osorio et al. 1994; Armstrong andChaffin 1979; Nathan et al. 1988; Punnett et al.1985; Baron et al. 1991], one is not[McCormack et al. 1990]; and one is equivocal[Nathan et al. 1992a].
In conclusion, there is evidence that forcealone is associated with CTS. There is strongevidence that a combination of forcefulhand/wrist exertion and repetitiveness areassociated with CTS.
POSTURE AND CTSDefinition of Extreme Postures ForCTSWe selected those studies which addressedposture of the hand/wrist area including thoseaddressing pinch grip, ulnar deviation, wristflexion/extension. Posture is a difficult variableto examine in ergonomic epidemiologic studies.It is hypothesized that extreme or awkwardpostures increase the required force necessaryto complete a task. Posture may increase ordecrease forceful effort; its impact on MSDsmay not be accurately reflected in measurementof posture alone. Reasons that the variable“extreme posture” has not been measured oranalyzed in many epidemiologic studies are: 1)because of the extreme variability of posturesused in different jobs as well as the extremevariability of postures between workersperforming the same job tasks,2) because several studies have taken intoaccount the effects of posture when determiningother measured variables such as force[Silverstein et al. 1987; Moore and Garg1994]; and 3) stature often has a major impacton postures assumed by individual workersduring job activities.
Studies Meeting the Four Evaluation Criteria Two studies fulfilled the four criteria for postureand CTS: Moore and Garg [1994], Silversteinet al. [1987]. The overall study designs arementioned above; the following section willcover the posture assessment.
For the exposure assessment of the posturevariables in the Silverstein et al. [1987] study,three representative workers from eachselected job performing the jobs for at leastthree cycles were videotaped using twocameras. The authors then extrapolated theposture data to non-observed workers.
Moore and Garg [1994] used a wristclassification system similar to that used byStetson et al. [1993], classifying the wrist angleestimated from videotape as neutral, non-neutral or extreme if the flexion/extension anglewas 0° to 25°, 25° to 45° and greater than 45°,respectively; or if ulnar deviation was less than10°, 10° to 20°, and greater than 20°,respectively.
Strength of Association: Posture andCTSSilverstein found no significant associationbetween percentages of cycle time observed inextreme wrist postures or pinch grip and CTS.“CTS jobs” had slightly more ulnar deviationand pinching but these differences were notstatistically significant. The authors noted thatamong all the postural variables recorded, thevariability between individuals with similar oridentical jobs was probably the greatest forwrist postural variables. This individual variationwithin jobs was not taken into account in theanalysis, creating a potential formisclassification of individuals by using thevariable “job category” in the analysis. Theeffect of exposure misclassification is usually todecrease differences between exposure groups
5a-23
and decrease the magnitude of association.
Moore and Garg’s [1994] classification of jobsdid not separate the posture variables fromother work factors, and used posture alongwith other variables to classify jobs into“hazardous” and “safe” categories. The RR ofCTS occurring in hazardous jobs was 2.8 butnot statistically significant (p=0.44).
Studies Not Meeting All Four EvaluationCriteriadeKrom et al. [1990] compared certainexposure factors between 28 CTS cases froma community sample and 128 CTS cases froma hospital (a total of 156 CTS cases) to 473community “non-cases” (n=473). The authorsrelied on self-reported information aboutduration of exposure (hours per week) to CTSrisk factors (flexed wrist, extended wrist,extended and flexed wrists combined; pinchgrasp and typing), with respondents recallingexposure from the present to 5 years prior fromthe questionnaire date. Four groups of durationwere used in the analyses (0; 1–7; 8–19,20–40 hours/week). In this study, the selectionprocess of cases was not consistent. Initially, arandom population sample was used, thenhospital outpatients were used to supplementthe number of CTS cases when numbers werefound to be insufficient. This may be a problemwhen estimating the etiologic role of workload,as cases seeking medical care may cause areferral bias. However, the authors stated thatthey came up with the same relationshipbetween flexed and extended wrist using onlyCTS cases from the population-based data.The risk of CTS was found to increase with thereported duration of activities with flexed wrist(RRs from 1.5 to 8.7, with increasing hours) oractivities with extended wrist (RR from 1.4 to5.4 with increasing hours) over the past 5years, but not for working with a flexed orextended wrist in combination, or working with
a pinched grasp. Given the period of recall forself-reported exposure (0–5 years), and noindependent observation or attributes ofexposure, these results must be interpreted withcaution (meaning that within the limitations ofthe data and conclusions, when considered withother studies that have more stringent methods,the RRs seem consistent and supportive and donot offer alternate conclusions).
Armstrong and Chaffin’s [1979] pilot study offemale sewing machine operators withsymptoms and/or signs for CTS compared tocontrols found that pinch force exertion(exposure measurements estimated from EMG,film analysis) was significantly associated (OR2.0). Pinch force was a combination offactors—posture and forceful exertion. Theauthors reported that CTS-diagnosed subjectsused deviated wrist postures more frequentlythan nondiseased, particularly during forcefulexertions. What is unable to be answered dueto the study design, was whether the deviatedpostures were necessitated due to symptomsand signs of CTS, or the deviated posturescaused or exacerbated the symptoms and signs.
Stetson et al. [1993] found that “grippinggreater than 6 pounds” per hand was asignificant risk factor for median distal sensorydysfunction (an indicator of CTS) when thestudy population was divided into exposed andnon-exposed groups. “Gripping greater than 6pounds” is a variable which combines twowork-related variables, posture and forcefulexertion. As seen with other studies referencedabove, the single work-related variable was notfound to be associated with median nervedysfunction, but the combination of variableswas significant. Looking specifically at wristdeviation in the Stetson et al. [1993] study, themidpalm to wrist sensory amplitude was smallerin the group not exposed to wrist deviation
5a-24
(p=0.04) compared to those exposed to wristdeviation (contrary to what was expected).Also, no significant differences were found inthe mean measurements between nonexposedand exposed groups for use of pinch grip.
Tanaka et al. [1995] analysis of theOccupational Health Supplement of the NHISpopulation survey depended on self-reportedCTS, self-reported exposure factors, andoccupation of the respondent for analysis. Self-reported bending and twisting of the hand andwrist (OR 5.9) was found to be the strongestvariable associated with “medically-calledCTS” among recent workers, followed by race,gender, vibration and age (repetition and forcewere not included in the logistic models).Limitations of self-reported health outcome andexposure do not allow the conclusions of thisstudy to stand alone; however, when examinedwith the other studies, it suggests a relationshipbetween posture and CTS.
The two other studies which examined postureand its relationship to CTS did not focus on thehand and wrist. English et al. [1995] found arelationship between self-reported rotation ofthe shoulder and elevated arm and CTS, an ORof 1.8. Liss et al. [1995] found an OR of 3.7for self-reported CTS comparing risk factorsfrom dental hygienists to dental assistants, withself-reported percent of time the trunk was in arotated position relative to the lower body asone of the factors.
Given these limitations of categorizing posture,three studies [Stetson et al. 1993; Loslever andRanaivosoa 1993; Armstrong and Chaffin1979] using different methods to measureposture and estimate force, found that thecombination of significant force and posturewas significantly related to CTS. Marras andShoenmarklin [1993] also found posture to be
significantly associated with CTS whencomparing jobs where grip strength was threetimes greater than in the low risk jobs. In thosestudies which used self-reports for categorizingposture, the associations were also positive.
Temporal RelationshipThere were no longitudinal studies whichexamined the relationship between extremeposture and CTS. Two cross-sectional studiesthat met the evaluation criteria addressed theassociation between posture and CTS.Silverstein et al. [1987] did not find a significantrelationship between CTS and extremeposture, but exposure assessment was limitedto representative workers; inter-individualvariability limited the ability to identify actualrelationships between postures and CTS. In theStetson et al. [1993] study, the authorsmentioned the limitations of interpretation oftheir posture results due to misclassification ofworkers. They extrapolated exposure data tonon-observed workers, so individual variabilityin work methods and differing anthropometryare not accounted for. These limitations allinfluence outcome, and the conclusions must beinterpreted with caution, and considered alongwith biomechanical and laboratory studies.
Coherence of EvidenceFlexed wrist postures may reduce the area ofthe carpal tunnel thus potentially increasing thepressure in the tunnel with a concomitantincrease in the risk of CTS [Skie et al. 1990;Armstrong et al. 1991]. Marras andShoenmarklin [1993] found that the variables ofwrist flexion, extension, angular velocity, andwrist flexion, extension, angular accelerationdiscriminated between jobs with a high versus alow risk of having an upper extremityreportable injury (an OSHA recordabledisorder due to repetitive trauma). The authorssuggested that this result was due to high
5a-25
accelerations requiring high forces in tendons.Szabo and Chidgey [1989] showed thatrepetitive flexion and extension of the wristcreated elevated pressures in the carpal tunnelcompared to normal subjects, and that thesepressures took longer to dissipate than innormal subjects. Observed repetitive passiveflexion and extension appeared to “pump up”the carpal tunnel pressure; active motion of thewrist and fingers also had an effect over andabove that of the passive motions tested.Laboratory studies demonstrate that carpalcanal pressure is increased from less than5mmHg to more than 30 mmHg during wristflexion and extension [Gelberman et al. 1981].
Exposure-Response Relationship,CTS and PostureFew studies address exposure-responserelationship between CTS and extremeposture. deKrom et al. [1990] reported anincreased risk of CTS with workers reportingincreasing weekly hours of exposure to wristflexion or extension (but not a combination offlexion/extension). Laboratory studies alsosupport a dose-response relationship ofincreased carpal tunnel pressure due toincreasing wrist deviation from neutral [Weisset al. 1995] and pinch force [Rempel 1995].
In conclusion, there is insufficient evidence inthe current epidemiologic literature todemonstrate that awkward postures alone areassociated with CTS.
VIBRATION AND CTSDefinition of Vibration for CTSWe selected studies that addressed manualwork involving vibrating power tools and CTSspecifically.
Studies Meeting the Four Evaluation Criteria Two studies examining the association betweenvibration and CTS fulfilled the four criteria
[Chatterjee 1992; Silverstein et al. 1987].Chatterjee et al. [1982] performed independentexposure assessment of the vibrating tools, andfound the rock drillers to be exposed tovibration between the frequencies of 31.5 and62 Hertz.
Silverstein et al. [1987] is discussed above.Silverstein [1987] had no quantitative measuresof vibration, but observed exposure fromvideotapes and found all jobs with vibrationexposure to be highly repetitive and mostlyforceful jobs.
Studies Not Meeting the Evaluation CriteriaThere are seven studies on Table 5a–4 thatmeet at least one of the four criteria.
In addition, there are 2 clinical case studies ofvibration and CTS [Rothfleish and Sherman1978; Lukas 1970] that were not controlled forconfounders and not referenced in Table 5a–4.Rothfleisch and Sherman [1978] found anexcess of power hand tool users among CTSpatients. Lucas [1970] examined workers usingvibrating hand tools including stone cutters,tunnelers, coal miners, forest workers andgrinders (all with a mean of 14 years exposureto vibration) and found CTS in 21%. He foundthat the prevalence of CTS in some groups wasas high as 33% (neither study had a referentgroup.)
Cannon et al. [1981] found that the self-reported use of vibrating tools, in combinationwith reported forceful and repetitive handmotions, was associated with a greaterincidence of CTS than was repetitive motionalone.
Bovenzi’s study in 1994 compared stoneworkers (145 quarry drillers and 425 stonecarvers) exposed to hand-transmitted vibrationto 258 polishers and machine operators who
5a-26
performed manual activity only not exposed tohand-transmitted vibration. CTS was assessedby a physician, and exposure was assessedthrough direct observation to vibrating tools andby interview. Vibration was also measured in asample of tools.
Strength of Association: Vibrationand CTSChatterjee et al. [1982] found a significantdifference between rock drillers with symptomsand signs of CTS and the controls using thefollowing NCS measurements: median motorlatency, median sensory latency, mediansensory amplitude, and median sensoryduration, all at the p<0.05 level. Based onnerve conduction measurements, they alsofound an OR of 10.9 for rock drillers havingabnormal NCS amplitudes in the median andulnar nerves compared to controls. Bovenzi etal. [1991] found an OR of 21.3 for CTS basedon symptoms and physical exam comparingvibration-exposed forestry operators usingchain-saws to maintenance workers performingmanual tasks. Bovenzi’s study in 1994 found anOR of 0.43 for CTS defined by signs andsymptoms, controlling for several confounders.In the Silverstein et al. [1987] study the crudeOR for high force/high repetition jobs withvibration compared to high force/high repetitionwithout vibration was 1.9, but not statisticallysignificant. This suggested that there may havebeen confounding (the OR was not statisticallysignificant) between high force/high repetitionand vibration. Nilsson et al. [1990] found thatplaters operating tools such as grinders andchipping hammers had a CTS prevalence of14% compared to 1.7% among office workers.Nathan et al. [1988] found a PR of 2.0 (95%CI 1.3–3.4) for slowing of nerve conductionvelocity when grinders were compared toadministrative and clerical workers. Cannon etal. [1981] found an OR of 7.0 for CTS with theuse of vibrating hand tools, although there was
a strong potential for confounding by hand orwrist posture and forceful exertion.
Temporal RelationshipThere were no longitudinal studies whichexamined the relationship between vibrationand CTS.
Consistency in Association All studies on Table 5a–4 examining vibrationand CTS found a significantly positiverelationship between CTS and vibrationexposure. Most studies had ORs greater than3.0, so that results were less likely to be due toconfounding.
Coherence of Evidence and VibrationThe mechanism by which vibration contributesto CTS and tendinitis development is not wellunderstood, probably because vibrationexposure is usually accompanied by exposureto forceful and repetitive movements. Musclesexposed to vibration exhibit a tonic vibrationreflex that leads to increasing involuntarymuscle contraction. Vibration has also beenshown to produce short-term tactilityimpairments which can lead to an increase inthe amount of force exerted during manipulativetasks. Vibration can also lead to mechanicalabrasion of tendon sheaths. Neurological andcirculatory disturbances probably occur
independently by unrelated mechanisms.Vibration may directly injure the peripheralnerves, nerve endings, and mechanoreceptors,producing symptoms of numbness, tingling,pain, and loss of sensitivity. It has been found inrats that vibration has caused epineural edemain the sciatic nerve [Lundborg et al. 1987].Vibration may also have direct effects on thedigital arteries. The innermost layer of cells inthe blood vessel walls appears especiallysusceptible to mechanical injury by vibration. Ifdamaged, these vessels may become less
5a-27
sensitive to the actions of certain vasodilatorsthat require an intact endothelium. The NIOSHCriteria Document on exposure to hand-armvibration NIOSH [1989] quoted Taylor [1982]as follows: “ It is not known whether vibrationdirectly injures the peripheral nerves therebycausing numbness and subsequent sensory loss,or whether the para-anaesthesia of the hands issecondary to the vascular constriction of theblood vessels causing ischemia . . . in the nerveorgans.”
Exposure-Response Relationship,CTS and VibrationIn the studies examined, only dichotomouscategorizations were made, so conclusionsconcerning an exposure-response relationshipcannot be drawn. However, we can seesignificantly contrasting rates of CTS betweenhigh and low exposure groups. Wieslander etal. [1989] found that based on exposureinformation obtained from telephone interviews,CTS surgery was significantly associated withvibration exposure. Exposure for 1–20 yearsgave an OR of 2.7, more than 20 years gave anOR of 4.8.
ConclusionIn conclusion, there is evidence supporting
an association between exposure to vibrationand CTS.
CONFOUNDING AND CTSIt is clear that CTS has several non-occupational causes. When examining therelationship of occupational factors to CTS, it isimportant to take into account the effects ofthese individual factors; that is, to control fortheir confounding or modifying effects. Studiesthat fail to control for the influence of individualfactors may either mask or amplify the effectsof work-related factors. Most of the
epidemiologic studies of CTS that addresswork factors also take into account potentialconfounders.
Almost all of the studies reviewed controlled forthe effects of age in their analysis [Chiang et al.1990, 1993; Stetson et al. 1993; Silverstein etal. 1987; Wieslander et al. 1989; Baron et al.1991; Tanaka et al. 1995, In Press;McCormack et al. 1990]. Likewise, moststudies included gender in their analysis, eitherby stratifying [Schottland et al. 1991; Chiang etal. 1993], by selection of single gender studygroups [Morganstern et al. 1991; Punnett et al.1985] or by including the variable in the logisticregression model [Silverstein et al. 1987;Stetson et al. 1991; Baron et al. 1991].Through selection of the study population andexclusion of those with metabolic diseases,most studies were able to eliminate the effectsfrom these conditions. Other studies did controlfor systemic disease [Chiang et al. 1993; Baronet al. 1991]. Anthropometric factors have alsobeen addressed in several studies [Stetson et al.1993; Nathan et al. 1997; 1992b; Werner etal. 1997]. As more is learned aboutconfounding, more variables tend to beaddressed in more recent studies (smoking,caffeine, alcohol, hobbies). In those olderstudies which may not have controlled formultiple confounders, it is unlikely that they arehighly correlated with exposure, especiallythose with ORs above 3.0. When examiningthose studies that have good exposureassessment, widely contrasting levels ofexposure, and that control for multipleconfounders, the evidence supports a positiveassociation between occupational factors andCTS.
CONCLUSIONSThere are over 30 epidemiologic studies whichhave examined workplace factors and their
5a-28
relationship to CTS. These studies generallycompared workers in jobs with higher levels ofexposure to workers with lower levels ofexposure, following observation ormeasurement of job characteristics. Usingepidemiologic criteria to examine these studies,and taking into account issues of confounding,bias, and strengths and limitations of the studies,we conclude the following:
There is evidence for a positive associationbetween highly repetitive work and CTS.Studies that based exposure assessment onquantitative or semiquantitative data tended toshow a stronger relationship for CTS andrepetition. The higher estimates of RR werefound when contrasting highly repetitive jobs tolow repetitive jobs, and when repetition is incombination with high levels of forcefulexertion. There is evidence for a positiveassociation between force and CTS based oncurrently available epidemiologic data. There isinsufficient evidence for a positiveassociation between posture and CTS. There isevidence for a positive association between
jobs with exposure to vibration and CTS.There is strong evidence for a relationshipbetween exposure to a combination of riskfactors (e.g., force and repetition, force andposture) and CTS. Ten studies allowed acomparison of the effect of individual versuscombined work risk factors [Chiang et al.1990, 1993; Moore and Garg 1994; Nathan etal. 1988, 1992a; Silverstein et al. 1987;Schottland et al. 1991; McCormack et al.1990; Stetson et al. 1993; Tanaka et al. [InPress]. Nine of these studies demonstratedhigher estimates of RR when exposure was to acombination of risk factors, compared to theeffect of individual risk factors. Based on theepidemiologic studies reviewed above,especially those with quantitative evaluation ofthe risk factors, the evidence is clear thatexposure to a combination of job factorsstudied (repetition, force, posture, etc.)increases the risk for CTS. This is consistentwith the evidence that is found in thebiomechanical, physiologic, and psychosocialliterature.
Table 5a-1. Epidemiologic criteria used to examine studies of carpal tunnel syndrome (CTS) associated withrepetition
Study (first author andyear)
Risk indicator(OR, PRR, IR or
p-value)*,†Participation rate $$70%
Physicalexamination,and/or nerveconduction
studies
Investigatorblinded to
case and/orexposure
status Basis for assessing
hand exposure to repetition
Met all four criteria:
Chiang 1990 1.87† Yes Yes Yes Observation or measurements
Chiang 1993 1.1 Yes Yes Yes Observation or measurements
Moore 1994 2.8 Yes Yes Yes Observation or measurements
Osorio 1994 6.7 Yes Yes Yes Observation or measurements
Silverstein 1987 5.5† Yes Yes Yes Observation or measurements
Met at least onecriterion:
Barnhart 1991 1.9–4.0† No Yes Yes Observation or measurements
Baron 1991 3.7 No Yes Yes Observation or measurements
Cannon 1981 2.1 NR‡ Yes NR Job titles or self-reports
English 1995 0.4 Yes Yes Yes Job titles or self-reports
Feldman 1987 2.26† Yes No NR Observation or measurements
McCormack 1990 0.5 Yes Yes NR Job titles or self-reports
Morgenstern 1991 1.88 Yes No No Job titles or self-reports
Nathan 1988 1.0 NR Yes NR Observation or measurements
Nathan 1992a 1.0 No Yes NR Observation or measurements
Punnett 1985 2.7† No Yes NR Job titles or self-reports
Schottland 1991 2.86†,1.87
NR Yes NR Job titles or self-reports
Stetson 1993 NR Yes Yes NR Observation or measurements
Weislander 1989 2.7† Yes Yes No Job titles or self-reports
Met none of the criteria:
Liss 1995 5.2 3.7†
No No No Job titles or self-reports
*Some risk indicators are based on a combination of risk factors—not on repetition alone (i.e., repetition plus force, posture,or vibration). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).
†Indicates statistical significance. ‡Not reported.
5a-29
Table 5a-2. Epidemiologic criteria used to examine studies of carpal tunnel syndrome (CTS) associated with force
Study (first author and year)
Risk indicator(OR, PRR, IR,
or p-value)*,†Participation rate $$70%
Physicalexamination,and/or nerveconduction
studies
Investigator blinded tocase and/orexposure
status Basis for assessing
hand exposure to force
Met all four criteria:
Chiang 1993 1.8† Yes Yes Yes Observation or measurements
Moore 1994 2.8 Yes Yes Yes Observation or measurements
Osorio 1994 6.7 Yes Yes Yes Observation or measurements
Silverstein 1987 15.5† Yes Yes Yes Observation or measurements
Met at least one criterion:
Armstrong 1979 2.0† NR‡ No No Observation or measurements
Baron 1991 3.7 No Yes Yes Observation or measurements
McCormack 1990 0.4-0.9 Yes Yes NR Job titles or self-reports
Nathan 1988 1.7-2.0† NR Yes NR Observation or measurements
Nathan 1992a 1.0, 1.4†, 1.6 No Yes NR Observation or measurements
Punnett 1985 2.7† No Yes NR Job titles or self-reports
Stetson 1993 NR† Yes Yes NR Observation or measurements
*Some risk indicators are based on a combination of risk factors—not on force alone (i.e., force plus repetition, posture,or vibration). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).
†Indicates statistical significance. If combined with NR, a significant association was reported without a numerical value.‡Not reported.
5a-31
Table 5a-3. Epidemiologic criteria used to examine studies of carpal tunnel syndrome (CTS) associated withposture
Study (first author andyear)
Risk indicator(OR, PRR, IR,
or p-value)*,†Participato
n rate$$70%
Physicalexamination,and/or nerveconduction
studies
Investigator blinded to
case and/orexposure
status Basis for assessing
hand exposure to posture
Met all four criteria:
Moore 1994 2.8 Yes Yes Yes Observation or measurements
Silverstein 1987 NR‡ Yes Yes Yes Observation or measurements
Met at least one criterion:
Armstrong 1979 2.0† NR No No Observation or measurements
deKrom 1990 5.4† Yes Yes NR Job titles or self-reports
English 1995 1.8† Yes Yes Yes Job titles or self-reports
Stetson 1993 NR† Yes Yes NR Observation or measurements
Tanaka 1995 5.9† Yes No No Job titles or self-reports
Met none of the criteria:
Liss 1995 3.7† No No No Job titles or self-reports
*Some risk indicators are based on a combination of risk factors—not on posture alone (i.e., posture plus repetition, force, or vibration). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).
†Indicates statistical significance. If combined with NR, a significant association was reported without a numerical value.‡Not reported.
5a-33
Table 5a-4. Epidemiologic criteria used to examine studies of carpal tunnel syndrome (CTS) associated withvibration
Study (first author andyear)
Risk indicator(OR, PRR, IR,
or p-value)*,†Participation
rate $$70%
Physicalexamination,and/or nerveconduction
studies
Investigator blinded tocase and/orexposure
status Basis for assessing hand
exposure to vibration
Met all four criteria:
Chatterjee 1992 10.9† Yes Yes Yes Observation or measurements
Silverstein 1987 5.3† Yes Yes Yes Observation or measurements
Met at least one criterion:
Bovenzi 1991 21.3† NR‡ Yes Yes Observation or measurements
Bovenzi 1994 3.4† Yes Yes No Observation or measurements
Cannon 1981 7.0† NR Yes NR Job titles or self-reports
Färkkilä 1988 NR† NR Yes NR Job titles or self-reports
Koskimies 1990 NR† NR Yes No Observation or measurements
Tanaka In Press 1.8† Yes No No Job titles or self-reports
Weislander 1989 3.3† Yes Yes No Job titles or self-reports
*Some risk indicators are based on a combination of risk factors—not on vibration alone (i.e., vibration plus repetition, posture,or force). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).
†Indicates statistical significance. If combined with NR, a significant association was reported without a numerical value.‡Not reported.
5a-35
(Continued)
Table 5a–5. Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
Armstrong and Chaffin1979
Case-control
18 female sewingmachine operators withCTS histories comparedto 18 female sewingmachine operatorswithout CTS histories.
Outcome: CTS defined ashistory of symptoms, surgicaldecompression of the mediannerve, positive Phalen’s test, orthenar atrophy.
Exposure: Hand/wristpostures and estimation offorearm flexor force in variouswrist and hand posturesassessed by film analysis andEMG.
Õ Õ For pinch forceexertion: 2.0
For handforce: 1.05
1.6-2.5
1.0-1.2
Participation rate: Not reported.
All cases of CTS diagnosed prior tostudy in working sewing machineoperators, may cause referral biasin estimating role of workload.
Subjects excluded if history offractures, metabolic or soft tissuedisease.
No association found betweenhand size or shape and CTS.
CTS diagnosed subjects useddeviated wrist more frequently thannon-diseased, particularly duringforceful exertions.
5a-37
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
(Continued)
Barnhartet al. 1991
Cross-sectional
Ski manufacturingworkers: 106 withrepetitive jobs comparedto 67 with non-repetitivejobs.
Outcome: CTS determined by:(1) Case 1: Electro-diagnosisof median-ulnar difference(latency on response time);(2) Case 2: Either Tinel's orPhalen's test and electro-diagnosis; (3) Case 3: Everhaving symptoms of hand pain,tingling, numbness, ornocturnal hand pain and Tinel'sor Phalen's test and electro-diagnosis.
Exposure: Jobs classified asrepetitive and non-repetitive. Repetitive jobs entailedrepeated or sustained flexion,extension, or ulnar deviation ofthe wrist by 45E, radialdeviation by 30E, or pinch grip(determined by observation).
Case 1:34%
Case 2:15.4%
Case 3: 32.5%
19%
3.1%
18.2%
1.9
3.95
1.6
1.0-3.6
1.0-15.8
0.8-3.2
Participation rate: 70% (repetitivejobs), 64% (non-repetitive jobs).
Examiner blinded to subject’s jobstatus but clothing may have biasedobservations.
Controlled for age and gender.
Found for both right and left handof those with repetitive jobs; meandifference between distal sensorylatencies of median and ulnarnerves were primarily due to ashorter mean sensory latency ofthe ulnar nerve.
There was no difference in mediannerve distal sensory latenciesbetween groups.
Hormonal status, systemic diseaseincluded in questionnaire.
Diabetes significantly more frequentin those with CTS than without(p=0.01).
5a-38
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
(Continued)
Baron et al.1991
Cross-sectional
119 female grocerycheckers vs. 56 otherfemale grocery storeemployees (comparisongroup).
Outcome: CTS case definedas having moderate to severesymptoms of pain, stiffness,numbness, tingling. Symptomsbegun after employment in thecurrent job; lasted > one weekor occurred > once a monthduring the past year; no historyof acute injury to part of bodyin question and a positivephysical exam of eitherPhalen's or Tinel's test.
Exposure: Based on jobcategory, estimates ofrepetitive, average, and peakforces based on observed andvideotaped postures, weight ofscanned items, and subjectiveassessment of exertion.
Exposure level in checkers:Average forces: LowPeak force: MediumRepetition: Medium
Exposure level in referents:Average force: MediumPeak force: Medium to lowRepetition: Medium.
11% 4% 3.7 0.7-16.7 Participation rate: 85% checkers;55% non-checkers in field study. Following telephone survey 91%checkers and 85% non-checkers.
Adjusted for duration of work.
Total repetitions/hr ranged from1,432 to 1,782 for right hand and882 to 1,260 for left hand.
Multiple awkward postures of allupper extremities recorded but notanalyzed in models.
Examiners blinded to worker’s joband health status.
Controlled for duration of work,hobbies.
5a-39
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
(Continued)
Bovenziet al. 1991
Cross-sectional
65 vibration-exposedforestry operators usingchain-saws compared toreferents composed of31 maintenance workers(electricians, mechanics,and painters).
Outcome: CTS cases definedas having symptoms of pain,numbness, or tingling in themedian nerve distribution, andphysical exam findings ofTinel's or Phalen's test,diminished sensitivity to touchor pain in 3½ fingers on radialside, weakness in pinching orgripping.
Exposure: Direct observationof awkward postures, manualforces, and repetitivenessevaluated via checklist. Thefocus of the study was tocompare vibration-exposedworkers to controls doingmanual work. Vibrationmeasured from two chain-saws. Vibration exposure foreach worker assessed interms of 4-hr energy-equivalent frequency-weightedacceleration according to ISO5349.
38.4% 3.2% 21.3 (adjusted) p=0.002 Participation rate: Not reported.
Examiners blinded to case status.
Controlled for age and ponderalindex (height and weight variable). Metabolic disease also considered.
Controls also found to have severalrisk factors for MSDs atwork—static arm and handoverload, overhead work, stressfulpostures, non-vibrating hand-tooluse.
Controls had a greater proportion oftime in work cycles shorter than30 sec than forestry workers.
Chain saw operators workedoutdoors and were exposed tolower temperatures thanmaintenance workers.
5a-40
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
(Continued)
Bovenzi andthe ItalianGroup 1994
Cross-sectional
Case group: Stoneworkers employed in9 districts in Northernand Central Italy;145 quarry drillers and425 stone carversexposed to vibration.
Referent group:Polishers and machineoperators (n=258) whoperformed manualactivity but were notexposed to hand-transmitted vibration.
All stone workersemployed in 6 districtsparticipated in the survey(n=578, 69.8%),whereas, in the threeother districts they wereselected on basis ofrandom sampling of thequarries and mills in thegeographic areas(n=250, 30.2%).
Outcome: CTS assessed byphysician assessment. CTSdefined as symptoms,(1) parathesias, numbness, orpain in median nervedistribution; (2) nocturnalexacerbation of symptoms andpositive Tinel's or Phalen's test.
Exposure: Direct observationof vibrating tools assessed byinterview. Vibration measuredin a sample of tools.
8.8% 2.3% 3.4 1.4-8.3 Participation rate: 100%. “All theactive stone workers participated inthe study, so self-selection wasnot a source of bias.”
Physician administeredquestionnaires containing workhistory and examinations, sounlikely to be blinded to casestatus.
Adjusted for age, smoking, alcoholconsumption, and upper limbinjuries.
Leisure activities and systemicdiseases included in questionnaire.
Univariate analysis showed noassociation between systemicdiseases and vibration so were notcriteria for exclusion.
Dose-response for CTS and lifetimevibration exposure not significant.
5a-41
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
(Continued)
Cannon et al.1981
Case-control
Aircraft engine workersat 4 plants: 30 CTScases identified throughworker’s compensationclaims and medicaldepartment recordsduring a 2-year periodcompared to 90 controlsfrom the same plant,16 workers receivingcompensation benefitsfor treatment of CTS, and14 cases who had notreceived compensationbenefits.
Three controls randomlychosen from the sameplant for each CTS case.
Outcome: CTS cases identifiedthrough worker’scompensation claims andmedical department recordsduring a 2-year period.
Exposure: Based on jobcategory, years on the job,identified through recordreview and interviews.Exposure to vibrating tools,repetitive motion.
Buffing, grinding, and handtools were measured with anaccelerometer and found to bein the range of 10 to 60 Hz.
Õ Õ For vibratinghand tool use:7.0
For repetitivemotion tasks: 2.1
History ofgynecologicsurgery:3.7
Years on thejob:0.9
3.0-17
0.9-5.3
1.7-8.1
0.8-1.0
Participation rate: Participation rateunable to be calculated from datapresented. 30 cases identifiedthrough record review of 20,000workers.
Cases and controls on gender.
Controlled for gynecologic surgery,race, diabetic history, years on thejob, use of low-frequency vibratingtools.
Information obtained through self-administered questionnaires andpersonal interviews on cases andcontrols on age, sex, race, weight,occupation, years employed,worker compensation status,history of metabolic disease,hormonal status of females, historyof gynecologic surgery.
Number of years employedsignificantly different among cases(5.5 years) and controls(11.7 years). Range of yearsemployed among cases included0.1 year to 28 years.
5a-42
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
(Continued)
Chatterjeeet al. 1982
Case-control
16 rock drillers comparedwith 15 controls.
Outcome: CTS wasdetermined by symptoms fromquestionnaire and interview bymedical investigator, clinicalexams carried out blindly, andnerve conduction studies. ForTable 5-7, CTS based solely onNCS results; Table 5-9 basedon symptoms and NCS.
Exposure: To vibration carriedout by measurement ofvibration spectra of the rockdrills and observation of jobs. Exposed group were thoseminers who regularly usedrock-drills in the fluorsparmines or other miners usingsimilar rock-drills. Exposurevaried from 18 months to25 years (mean 10 years). The rock drillers were exposedto vibration level in excess ofthe damage level criterionbetween the frequencies of31.5 and 62 Hz.
44% 7% Abnormalamplitudes ofdigital-actionpotentials fromfingerssupplied by themedian andulnar nerves;the OR invibrationexposed vs.controls:OR=10.89 1.02-524
Participation rate: 93%.
Examiners blinded to case status.
Groups standardized for age andgender.
Exclusionary criteria: History ofconstitutional white finger,secondary causes of Raynaud’sphenomenon, > one laceration orfracture in the hands or digits,severe or complicated injuryinvolving nerve or blood vessels orsignificant surgical operation,history of exposure to vibrationfrom tools other than rock drills.
Significant differences foundbetween controls and vibrationgroup for symptoms of numbnessand tingling: median motor latency;median sensory latency; mediansensory amplitude; median sensoryduration. All at the p< 0.05 level.
Skin temperature controlled for inNCVs.
5a-43
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
(Continued)
Chiang et al.1990
Cross-sectional
207 active workers from2 frozen food plantsdivided into 3 groups: (1) low-cold, low-repetition (comparisongroup, mainly office staffand technicians, n=49),(2) low-cold, high-repetition (non-frozenfood packers, n=37),(3) high-cold, high-repetition (frozen foodpackers, n=121).
Outcome: CTS defined assymptoms of numbness, pain,tingling in the fingersinnervated by the mediannerve, onset since work incurrent job, no relationship tosystemic disease or injury andphysical exam of Tinel's test orPhalen's sign. Nerveconduction testing wasperformed on motor andsensory nerves of both upperlimbs. If subject had abnormalresults and symptoms andphysical exam findings, wasconsidered CTS. If nosymptoms, considered assubclinical CTS.
Exposure: Job analysesconducted by industrialhygienist, to cold and repetitionassessed by observation.
Highly repetitive jobs had cycletimes <30 sec. >50% of cycletime cold exposure wasdefined as whether the jobrequired hands to be locallyexposed to cold. The meanskin temperature of their handswas in the range of 26 to28EC, even with wearinggloves.
Group 2: 40.5%clinical plus8.1%sub-clinical
Group 3: 37.2%clinical plus22.3%sub-clinical
Group 1:4% clinicalplus 2%sub-clinical
Group 2 vs.Group 1:OR=8.28
Group 3 vs.Group 1:OR=11.66
LogisticRegressionModel:Cold:OR=1.85(p<0.22)
Repetitiveness:OR=1.87(p<0.018)
Cold xRepetitive-ness:OR=1.77(p<0.03)
1.18-58.3
2.92-46.6
Participation rate: Not specificallymentioned, however, paper statesthat “in order to prevent selectivebias, all of the employees in thefactories were observed initially.”
Examiners blinded to exposurestatus and medical history.
Controlled for age, sex, and lengthof employment. Interaction termstested.
Excluded subjects with diabetes,thyroid function disorders, historyof forearm fracture, unspecifiedpolyneuropathy, rheumatoidarthritis.
Workers in cold groups woregloves and exerted higher forcesthan workers in non-cold groups. Force was not evaluated in thisstudy. Confounding is possibleaccording to authors.
CTS was independent of age andlength of employment. Authorsconsidered this to be due to healthyworker effect.
OR for group 1 vs. group 2 is 8.3(1.2-58.3) when adjusted for sexbut 2.2 (0.2-21.1) when adjustedfor sex, age, and length ofemployment suggesting survivalbias.
5a-44
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
(Continued)
Chiang et al.1993
Cross-sectional
207 fish processingworkers divided in3 groups: (1) low-force,low-repetition(comparison group,n=61); (2) high-force orhigh-repetition (n=118);(3) high-force and high-repetition (n=28).
Outcome: CTS defined ashaving symptoms ofnumbness, pain, or tingling inthe fingers innervated by themedian nerve, onset after jobbegan, and no evidence ofsystemic disease or injury andphysical exam findings ofpositive Tinel's sign or Phalen'stest.
Exposure: Assessed byobservation and recording oftasks and biomechanicalmovements of 3 workers, eachrepresenting 1 of 3 studygroups. Highly repetitive jobswith cycle time <30 sec or>50% of cycle time performingthe same fundamental cycles. Hand force from EMGrecordings of forearm flexormuscles. Classification ofworkers into 3 groupsaccording to the ergonomicrisks of the shoulders andupper limbs: Group 1: low-repetition and low-force; Group2: high-repetition and high-force; Group 3: high-repetitionor high-force.
Group 2 (Male): 6.9%
Group 2(Female):18.0%
Group 3 (Male): 0.0%
Group 3(Female): 36.4%
Group 1(Male):3.1%
Group 1(Female):13.8%
2 vs. 1 (male): OR= 2.2
2 vs. 1(female):OR=1.3
3 vs. 1 (male):Õ
3 vs. 1(female):OR=2.6
Repetition:OR=1.1
Force:OR=1.8
Repetition andforce:OR=1.1
Male vs.female:OR=2.6
0.2-22.0
0.5-3.5
Õ
1.0-7.3
0.7-1.8
1.1-2.9
0.7-1.8
1.3-5.2
Participation rate: Paper stated thatall of the workers who entered thefish-processing industry beforeJune 1990 and were employedthere full-time were part of thecohort.Workers examined in randomsequence to prevent observer bias;examiners blinded to case status.Analysis controlled for age,stratified by gender.Contraceptive use (females):significant (OR=2.0, 95% CI 1.2 to5.4); tubal ligation not significant.Workers with hypertension,diabetes, history of traumaticinjuries to upper limbs, arthritis,collagen diseases excluded fromstudy group.No significant age difference inexposure groups.
Physician-observed cases about½ the prevalence of symptoms ofelbow pain (9.8 vs. 18.0; 15.3 vs.19.5; 35.7 vs. 17.9).Dose-response for symptoms bothin the hand and in the wrist(p<0.03) and physician-observedCTS (p<0.015).Age, gender, repetitiveness,forceful movement of upper limbsand interaction of repetitivenessand forceful movement calculatedin logistic regression.Significant trend for duration ofemployment in <12 months but not12 to 60 months or >60 months.
5a-45
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
(Continued)
deKrom et al.1990
Nestedcasecontrol
28 CTS cases from acommunity sample and128 CTS cases from ahospital (total n=156)compared to communitynon-cases (n=473).
Participants blinded toaim of study—told it wasabout “general health.”
Outcome: Tingling pain andnumbness in mediandistribution, frequency$2/week, awakened at nightand nerve conduction studies.Motor latency < 4.5 months,different median to ulnar DSL <4.0 months, controlled fortemperature.
CTS diagnosed by clinicalhistory and neurophysiologicaltests.
Exposure: Awkwardhand/finger postures and pinchgrasps assessed byquestionnaire: Self-reportedinformation about duration ofexposure (hr/wk) to flexedwrist, extended wrist,extended and flexed wristcombined, pinched grasp. Typing hr categorized as0, 1 to 7, 8 to 19, 20 to40 hr/wk of exposure 0 to 5years ago, responsestruncated at 40 hr/wk.
5.6%prevalencein thegeneralpopulation(28 casesfrom501 subjectcommunitysample)
Õ For work:20 to 40 hr/wkwith flexedwrist: OR=8.7
For work:20 to 40 hr/wkwith extendedwrist: OR= 5.4
3.1-24.1
1.1-27.4
Participation rate: 70% responserate obtained for both hospital andcommunity samples.Controlled for age, weight, slimmingcourses, gender, and checked forinteractions.Cases seeking medical care maycause referral bias in estimatingetiologic role of work-load. However, authors came up withsame relationship between flexedand extended wrist using only CTScases from population-based data.The associations from this studyare based on very small samplesizes. >64% of cases reported 0hr/wk to each of the exposures.In random sample, age, and sexstratified, included twice as manyfemales as males.No significant relationship betweenpinch grasp or typing.Dose-response found for durationof activities with flexed or extendedwrist statistically significant; dose-response relationship for bothpresent but not statisticallysignificant.Typing hr not significant but verysmall numbers (<5 in comparisongroups); may have been unable todetect a difference.Females with hysterectomy withoutoophorectomy significantlyincreased risk, PRR=2.0 (1 to 3.6),compared to females not operatedon; increase may be detection bias.Wrist fractures, thyroid disease,rheumatism, and diabetes notsignificant for CTS.Varicosis significant risk for males12.0 (3.6-40.1).Oral contraceptives not significantlyassociated with CTS.
5a-46
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
(Continued)
English et al.1995
Case-control
Cases: CTS patients(n=171) ages 16 to 65years from orthopedicclinics. Controls:(n=996) 558 males and438 females attendingthe same clinicsdiagnosed withconditions other thandiseases of the upperlimb, cervical, or thoracicspine; ages 16 to 65years.
Outcome: CTS based onagreed criteria diagnosed byorthopedic surgeons usingcommon diagnostic criteria (notspecified).
Exposure: Based on self-reported risk factors at work:questions addressed:awkward postures, grip types,wrist motions, lifting, shoulderpostures, static postures, etc.and job category.
Õ Õ Rotatingshoulder withelevated armand CTS: OR=1.8
Repeatedfinger tappingand CTS: OR=0.4
1.2-2.8
0.2-0.7
Participation rate: 96%.
Due to design of study (casesselected by diagnoses), blinding ofexaminers not an issue.
Adjusted for height, weight, andgender.
Significant negative associationwith height and presentation at theclinic as a result of an accident andCTS.
A significantly positive associationwith height.
Included “frequency of movements”in regression analysis.
5a-47
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
(Continued)
Färkkiläet al. 1988
Cross-sectional
79 chain saw usersrandomly selected from186 forestry workerswith >500 hr ofsawing/year.
Outcome: CTS based on nerveconduction studies, motor andsensory conduction velocity,distal and proximal latencies,Tinel’s and Phalen's tests andsubjective symptoms.
Exposure: Chain saw vibrationnot measured. Duration ofchain saw use determined byinterview.
26% Õ Significantcorrelationbetweennumbness inthe hands(r=0.38,p<0.05) andCTS andmuscle fatigue(r=0.47,p<0.05) andCTS.
Õ Participation rate: 100% ofprofessional forestry workers.
Significant correlation between CTSand HAVs found.
Randomly selected from EMG out of186.
Alcohol consumption did notcorrelate with numbness in thehands or arms (r=0.14, p=NS) orsensory disturbances.
Only motor nerve recordings wereanalyzed for this study.
5a-48
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
(Continued)
Feldmanet al. 1987
Cross-sectionalforsymptomsurvey
Pro-spectivefor nervecon-ductionstudies
586 electronics workersat a manufacturing firmwith 700 employees.
Outcome: Based onquestionnaire survey and insome an abbreviatedneurologic examination thatinvolved tests of handsensation, finger grip, andstrength of thenar muscles. Tinel’s and Phalen's done.“Standard nerve conduction” ofleft and right median nerves.
Exposure: Two subjectsrandomly selected forbiomechanical analyses fromeach of four high-risk areas,determined from questionnaireand walk-through observationsof tasks involving repetitiveflexion, extension, pinching,and deviated wrist postures. Videotaping andelectromyography done.
Highly repetitive job taskdefined as <30 sec cycle or>50% of cycle performing thefundamental cycle.
Wrist posture characterized interms of flexion and extension: >45 flexed, 15 to 45 flexion,neutral, 15 to 45 extension, and>45 extension and deviation. Hand posture characterized by6 types of grip.
No quantitative measures ofvibration were obtained.
Wristtingling andnumbness:18%
Wristtingling andnumbness:8.7%
Numbness andtingling infingers:OR=2.26
High-risk vs.low-risk jobs:p<0.005
1.4-4.46
Participation rate: 84%.Examiners blinded to case andexposure status: Not stated.Analysis not controlled forconfounders.Questionnaire obtained data onpast medical history, exposure toneurotoxins, cigarettes, hobbies,and symptoms.For nerve conduction testing, thetemperature of limbs was monitoredand controlled for.More females were in high-riskareas and jobs than males. There were no workers >60 yearsold in high-risk group. There were34 workers >60 years incomparison groups.Rheumatoid arthritis more prominentin low-risk group (8.2%) than high-risk (2.4%) group.Nerve conduction in high-riskworkers performed year 1 andyear 2. Right sensory amplitudeabnormal (<8µV) in 22% ofworkers at year 1 and 35.5% atyear 2. Left sensory amplitudeabnormal in 16.7% and 29% atyear 2.Most apparent changes (increases)seen in bilateral sensory velocitiesand motor latencies (abnormal>4.5). Right motor latency abnormalin 8% at year 1 and 11% in year 2. Left motor latency abnormal in 2%in year 1 and 23% at year 2.Authors offered parameters forstaging CTS in high-risk subjects (0to 4 stages).
5a-49
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
(Continued)
Franklinet al. 1991
Retro-spectivecohort: from1984 to1988
Workers in WashingtonState (n=1.3 million full-time workers in 1988).
Worker’s compensationdata for WashingtonState, usingcompensable (time loss)and non-compensableclaims for January 1984to December 1988.
Outcome: Assessed usingworkers’ compensation claimsfor CTS using ICD codes 354.0and 354.1. Incident claim wasthe first appearance of a paidbill for claimant with aphysician diagnosis. Algorithmwas developed to identifyunique claimants whichremoved multiple claims.
Exposure: Not measured. Workers in the same industrialclassification assumed toshare similar workplaceexposures.
25.7 claims/1,000 FTEs(oyster andcrabpackers)
23.9 claims/1,000 FTEs(meat andpoultryworkers)
1.74claims/1,000 FTEs(industrywide rate)
14.8 (oysterand crabpackers)
13.8 (meat andpoultryworkers)
11.2- 19.5
11.6- 16.4
Participation rate: This is a recordsreview so it does not apply.
Among claimants, the female-to-male ratio was 1.2:1.
Mean age of claimants was 37.4.
Diagnosis and data entry errorscomprised 25% of CTS surgeryclaims—cases were not coded asCTS.
82% of claims were true cases ofCTS.
5a-50
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
(Continued)
Koskimieset al. 1990
Cross-sectional
217 forestry workerswho used chain saw>500 hr during previous3 years.
Outcome: 125 randomlyselected for EMG of sensoryand motor nerves both hands.
CTS diagnosis based onsymptoms, exclusion of otherconditions, results of Phalen’sand Tinel’s test, and findings insensory and motor nerve EMG.
Exposure: Number of years ofvibration exposure (onlyworkers who had 500 hrduring previous 3 years wereincluded.
Activevibration:5% whitefinger
CTS: 20%
Alcoholconsumptionand CTS casesr=0.15
Vibrationexposure timeand motor NCVin mediannerve of righthand: r=-0.27but not lefthand: r=-0.12
Exposure timewith bothmotor NCV inulnar nerve ofright handr=-0.26 and lefthand r=-0.39.
Distal latenciesin mediannerve andexposure inright handr=0.17; left handr=0.21.
Numbness andsensory NCSof mediannerve; righthand r=0.679; left handr=0.53.
p=NS
p=0.01
p=NS
p=0.05
p<0.001
p=0.05
p=0.05
p<0.001
p<0.01
Participation rate: Not reported.
Examiners may not have beenblinded to exposure status becauseof design of study.
No comparison group becausestudy was part of longitudinal studyof workers followed since 1972.
Most of 25 CTS workers had mildsymptoms at work despite severereduction of sensory NCS ofmedian nerve.
Males with primary Raynaud’sdisease, rheumatoid arthritis,diabetes, or positive urine glucoseslide test results excluded fromstudy.
12 (48%) of those with CTS hadbilateral diagnosis. The authorsstated that the left hand is thedominant working hand in sawing,the right hand acting more to directthe saw during the operation.
5a-51
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
(Continued)
Liss et al.1995
Cross-sectional
1,066 of 2,142 dentalhygienists from OntarioCanada DentalHygienists Associationcompared to referentgroup, 154 of 305 dentalassistants.
Outcome: Mailed survey,2 CTS case definitions:(1) based on positive responseto "told by a physician that youhad CTS", (2) if during last 12months, for >7 daysexperienced numbness andtingling, pain, or burning indistribution of median nerve,night pain or numbness inhands, and no previouswrist/hand injury.
Exposure: Based on mailedsurvey: Length of practice,days/wk worked, patients/day,patients with heavy calculus,percent of time trunk in rotatedposition relative to lower body,instruments used, hr oftyping/wk, type of practice.
Respondertold thatthey hadCTS: 7%
Question-naire basedCTS: 11%
Respondertold thatthey hadCTS: 0.9%
Question-nairebasedCTS: 3.0%
OR=5.2
OR=3.7
0.9-32
1.1-11.9
Participation rate: 50% responserate from both groups.
Study population >99% female.
OR were age adjusted.
Confounders considered includedtyping, hobbies, and takingestrogens.
5a-52
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
(Continued)
Loslever andRanaivosoa1993
Cross-sectional
17 selected jobs withfrequent and repeatedabsences of workersdueto CTS investigated atthe request ofoccupational doctors andmanagers. Biomechanical datarecorded on a number ofworkers from each job,ranging from 1 to4 workers. Involving961 workers.
Outcome: Occupationalphysician from each factoryinvolved in the study completedquestionnaire concerning eachjob and the number of CTScases. The prevalence of CTSwas then calculated from ratioof CTS cases and total numberof employees that worked atthat place.
Exposure: Videotaping ofmovements, use of vibratingtools, and two measurementtechniques used: (1) Flexion-extension measurements: Subjects recorded at severalpoints during the day for15 min. An angle meter used tomeasure flexion-extensionangles of the wrist: Rated highflexion, low flexion, lowextension, and high extensionusing fuzzy cutting functions. Each modality characterized byits arithmetic mean and itsrelative duration. (2) Force:Electromyography used; valuesunder 2 daN considered as lowforces. Calculated time spentover 2 daN, maximal force,number of peak exertions, andthe arithmetic mean of the nvalues during a period.
Meanprevalencerate amongjobs (jobschosen atworkplaceswhere CTShad beenreported):35% (range8 to 66%);prevalenceof CTS inboth hands:20%
High force withhigh flexionand CTS:r=0.62
High force andhigh extensionand CTS:r=0.29
Participation rate: Cases selected.
Occupational doctor suppliedinformation on gender, age, yearson the job, hand orientation, has orhas not contracted CTS.
Subjects spent 60 to 80% of theirtime in extension ranging from 13 to30E.
Vibratory tools more often used intasks with high prevalence of CTS(27%) than in ones with lowprevalence of CTS (13%).
92% of population were female.
Non-standard data analysisapproaches, no statistical testing.
Examiners not blinded.
Authors believe higher rate of CTSin both hands (20%) vs. dominanthand (100%) argue for non-occupational factors being moreimportant.
5a-53
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
(Continued)
Marras andShoenmarklin1993
Cross-sectional
40 volunteers at a highlyrepetitive, hand-intensive industrial jobsin 8 different plants. Halfthe workers wereemployed in jobs that hadOSHA recordablerepetitive traumaincidents, half theworkers were in jobswith no history ofrecordable repetitivetrauma incidents. Twosubjects from 10repetitive, hand-intensive jobs wererandomly chosen toparticipate.
Outcome: CTS wasdetermined from evaluation ofOSHA illness and injury logsand medical records. Theindependent variable wasexposure to jobs in which CTShad occurred previously. Alow-risk job was defined ashaving a zero incidence rate; ahigh-risk job was defined ashaving an incidence rate ofeight or more recordablerepetitive trauma.
Exposure: Included number ofwrist motions/8-hr shift, weightof loads, handgrip types andforces, work heights, andmotion descriptions. Wristmotion monitors measured inthe radial/ulnar,flexion/extension, andpronation/supination planes:wrist angles, angular velocity,angular acceleration.
High-riskjob: 8incidents/200,000 hrexposure
Low-riskjob: 0incidents
Model forpredicting highvs. low job riskbased uponmotioncomponent:
PositionRadial/ulnarROM: OR=1.52Flexion/exten-sion ROM:OR=1.3Pronation/supinationROM:OR=1.2
VelocityRadialulnar vel:OR= 2.4Flexion/extension vel:OR=3.8Pronation/supination vel:OR=1.9
AccelerationRadial/ulnaraccel: OR=2.7Flexion/extensionaccel:OR=6.1Pronation/supinationaccel: OR=2.96
1.1-2.1
1.0-1.7
0.9-1.6
1.3-4.3
1.5-9.6
1.2-3.2
1.5-4.9
1.7-22
1.4-6.4
Participation rate: Not reported.
Examiners blinded: not stated.
Confounders controlled for: Age,gender, handedness, jobsatisfaction.
All the jobs required gloves excepttwo-one “low-risk” and one “high-risk.”
Significant difference betweengroups with regards to age, yearswith the company, and trunk depth.
No significant difference in jobsatisfaction, number of wristmovements, age, weight, stature,hand dimensions.
Turnover rate: High-risk jobs: 33%;low-risk jobs: 0.5%.
Grip forces were three times asgreat in the high-risk jobs than inthe low-risk jobs.
Variance between subjects withinjobs accounted for a substantialpercentage of total variance inwrist motion.
5a-54
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
(Continued)
McCormacket al. 1990
Cross-sectional
Textile workers: 4 broad job categoriesinvolving intensive upper extremity use.Workers randomlychosen: Sewing workers (n=562); boarding workers(n=296); packagingworkers (n=369); andknitting workers (n=352) compared toother non-office workers (n=468).
Outcome: Assessed byquestionnaire and screeningphysical examination initially bynurse. CTS diagnosed onclinical grounds of symptomsand positive Tinel's sign andPhalen's test. Physicianreassessed physical findingsby “standardized methods.”
Exposure: Assessment byobservation of jobs. Exposureto repetitive finger, wrist andelbow motions assumed fromjob title; no objectivemeasurements performed.
Prevalencesof CTS
Boarding:0.7%
Sewing: 1.2%
Packaging:0.5%
Knitting:0.9%
1.3% (non-office)
Boarding vs.non-officeOR=0.5
Sewing vs.non-officeOR=0.9
Packaging vs.non-officeOR=0.4
Knitting vs.non-officeOR=0.6
0.05-2.9
0.3-2.9
0.04-2.4
0.1-3.1
Participation rate: 91%.
Physician or nurse examiners notblinded to case or exposure status(personal communication).
Prevalence higher in workers with<3 years of employment. Race andage not related to outcome. Females found to have significantlymore CTS than males.
Job category not found to besignificant, however nomeasurement of force, repetition,posture analysis, etc.
Questionnaire asked types of jobs,length of time on job, productionrate, nature and type of upperextremity complaint, and generalhealth history.
11 physician examiners;interexaminer reliability potentialproblem acknowledged.
5a-55
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
(Continued)
Moore andGarg 1994
Cross-sectional
32 jobs in which 230workers were employed. This study was more anevaluation of jobs than ofindividuals.
Outcome: CTS identified fromOSHA logs and medicalrecords. A case requiredelectrophysiologic testing,confirmed as abnormal byelectromyographer andpresence of suggestivesymptoms.
Exposure: Observation andvideotape analysis of jobs. Force, wrist posture, grasptype, high-speed work,localized mechanical stress,vibration, cold, and work timeassessed via observation ofvideotape. Jobs classified ashazardous or safe based ondata and judgement.
13.7% 4.9% 2.8 0.2-36.7 Participation rate: Study based onrecords.Investigators blinded to exposure,case outcome status, and personalidentifiers on medical records.Repetitiveness, “type of grasp”were not significant factorsbetween hazardous and safe jobcategories.
No pattern of morbidity according todate of clinic visits.Strength demands significantlyincreased for hazardous jobcategories compared to safe jobcategories.
IR based on full-time equivalentsand not individual workers, mayhave influenced overall results.
Workers had a maximum of 32-months of exposure at plant–soduration of employment analysislimited.Average maximal strength derivedfrom population-based datastratified for age, gender, and handdominance. Using estimates of Silverstein’sclassification, association betweenforcefulness and overall observedmorbidity was statisticallysignificant; repetition was not.No control for confounders.
No information on work history,number of unaffected workers, orexposure duration.
5a-56
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
(Continued)
Morgensternet al. 1991
Cross-sectional
1,058 female grocerycashiers from a singleunion.
Comparison group wasthose who reported nosymptoms.
Cashiers were alsocompared to results froma general populationstudy from Rochester,Minnesota (Stevens et al.1988).
Outcome: Defined CTS as self-reported hand/wrist pain,nocturnal pain, tingling in thehands or fingers, andnumbness.
Exposure: Duration, use oflaser scanner determined fromsurvey (no measurements).
12% 5.4%
For adifference of25 hr/wk: 1.88 0.9-3.8
Participation rate: 82%.
Controlled for age.
Information collected on age, sex,pregnancy status, work history asa checker, specific job-relatedtasks, use of selected drugs,history of wrist injury.
In logistic regression, “Use ofdiuretics” significantly associatedwith CTS, OR=2.66 (1.00-7.04);thought to be related to fluidretention by authors.
Laser scanning found not to besignificant factor.
5a-57
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
(Continued)
Nathan et al.1988
Cross-sectional
471 industrial workersfrom 27 occupations in4 industries. Jobsgrouped into 5 classesbased on resistance andrepetition rate.
Outcome: Case defined asNCS-determined impairedsensory conduction (sensorylatency). Sensory latenciesassessed antidromically foreight consecutive 1-cmsegments of the nerve. Amaximum latency difference of0.4 ms or greater used todefine impaired sensoryconduction. Case definition didnot deal with symptoms.
Exposure: Jobs grouped into27 occupations with similaritiesof characteristics as to type ofgrip, wrist position,handedness pattern,resistance, frequency, andduration of grasp andpresence of vibratory andballistic components. The27 occupations then groupedinto 5 classes. Resistance(Res.) rated from very light tovery heavy; repetition raterated from low to high.
Group I: very light resistanceand low repetitionGroup II: light resistance andvery high repetitionGroup III: moderate resistanceand moderately high repetitionGroup IV: heavy resistanceand moderate repetitionGroup V: very heavyresistance and high repetition.
Prevalenceof abnormalnerveconductionsensorylatency:
Group II: 27%
Group III: 47%
Group IV: 38%
Group V: 61%
Prevalenceofabnormalnerveconductionsensorylatency:
Group I: 28%
Group II vs. I:PR=1.0
Group I vs. III: PR=1.9
Group I vs. IV:PR=1.7
Group I vs. V:PR=2.0
0.5-2.0
1.3-2.7
1.3-2.7
1.1-3.4
Participation rate: Not reported.
Analysis controlled for age andgender.
No description of symptom statusfor defining CTS.
Method of categorization of jobsand occupations not described.
Classification system is based ononly repetition and not resistanceas listed.
Initially excluded cases of CTS instudy population, yet wassupposedly identifying prevalencesof CTS in exposure groups.
For nerve conduction analysis,wrongly assumed that each hand’snerve conduction study results inan individual were independent. The 2 hands in a single individualare not independent of each other.
5a-58
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
(Continued)
Nathan 1992a Long-itudinal
315 workers using bothhands (each handanalyzed separately)from four industries. These represented 67%of original group ofworkers from 1988published studyrandomly selected fromfour industries (67% oforiginal subjects)
Group I: Very lightresistance and lowrepetition
Group II: Lightresistance and very highrepetition
Group III: Moderateresistance andmoderately highrepetition
Group IV: Heavyresistance and moderaterepetition
Group V: Very heavyresistance.
Outcome: Case defined asNCS-determined impairedsensory conduction (sensorylatency). Sensory latenciesassessed antidromically foreight consecutive 1-cmsegments of the nerve. Amaximum latency difference of0.4 ms or greater used todefine impaired sensoryconduction.
Probable CTS: Presence ofany two primary symptoms(numbness, tingling, nocturnalawakening) or one primarysymptom and 2 secondarysymptoms (pain, tightness,clumsiness).
Exposure: For this article,previous exposureclassification was used from1988 Nathan article. Jobs hadbeen grouped into 27occupations with similarities ofcharacteristics as to type ofgrip, wrist position,handedness pattern,resistance, frequency, andduration of grasp andpresence of vibratory andballistic components. The 27occupations then grouped into5 classes. Resistance ratedfrom very light to very heavy;repetition rate rated from low tohigh.
Group II:19%
Group III:26%
Group IV: 24%
Group V:18%
Group 1:18%
Groups II vs.Group I:
PR=1.1
Group III vs.Group I:
PR=1.5
Group IV vs.Group I:
PR=1.4
Group V vsGroup I:
PR=1.0
0.6-1.9
1.0-2.2
0.9-2.1
0.5-2.2
Participation rate: Overall: 67%;Group 3 participation rate was59%.Examiners blinded: Not reported.Analyzed using gender, handdominance, occupational hand use,duration of employment, andindustry.76% of participants employed insame occupational hand-use classas in 1988. A lower percentage ofnovice workers returned (56%)than non-novice workers (69%) forfollow-up study.Analysis of “hands” instead ofindividual would cancel contributionof exposure effect if there wasunilateral slowing.Data in table two for 1984 subjectsis not the same data as presentedin previous article; numbers haveshifted to other groups. Thesignificant difference seenbetween nerve slowing betweenClass 1 and Class 5 in 1988 paperis no longer significantly different.Authors note that “130 handsexperienced a decrease inoccupational use.” No parametersgiven for decrease and assumptionis made that both hands in anindividual had similar decrease inuse. With one-third of cohort missingfrom 1984 study, there is no way todetermine if homogeneity insymptoms prevalence in 1984 and1989 reflects absence ofprogression or drop-out.
5a-59
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
(Continued)
Nathan 1994b Long-itudinal
101 Japanese furniturefactory workers. Therewere 27 managers, 35clerical workers, 21assembly-line or foodservice workers and 18machine operators. TheirNCS results werecompared to 315workers using bothhands (each handanalyzed separately)from four industries.(These represented 67%of original group ofworkers from 1988published study randomly selected fromfour industries (67% oforiginal subjects) and arethe subject of a separatetable entry in thisdocument.
Group I: Very lightresistance and lowrepetition.
Group II: Lightresistance and very highrepetition.
Group III: Moderateresistance andmoderately highrepetition.
Group IV: Heavyresistance and moderaterepetition.
Group V: Very heavyresistance.
Outcome: Case defined asNCS-determined impairedsensory conduction (sensorylatency). Sensory latenciesassessed antidromically foreight consecutive 1 cm.segments of the nerve. Amaximum latency difference of0.4 ms or greater used todefine impaired sensoryconduction.Probable CTS: Presence ofany two primary symptoms(numbness, tingling, nocturnalawakening or one primarysymptom and 2 secondarysymptoms (pain, tightness,clumsiness).
Exposure: Exposure was notaddressed except is assumedto be self-reported byquestionnaire for the Japaneseworkers. The jobs weregrouped into 5 classes. Resistance rated from verylight to very heavy; repetitionrate rated from low to highrepetition.
8 cm.Sensorylatency:0.30
14 cm.Sensorylatency:0.36
ProbableCTS: 2.5%
DefiniteCTS:2.0
8 cm.Sensorylatency:0.31
14 cm.Sensorylatency:0.45
ProbableCTS:2.0%
DefiniteCTS:8.3
Participation rate: For JapaneseWorkers: 100%Americans: Overall: 67%; Group 3participation rate was 59%.
Examiners blinded: Not reported.
Analyzed using gender, handdominance, occupational hand use,duration of employment, andindustry.
Analysis of “hands” instead ofindividual would cancel contributionof exposure effect if there wasunilateral slowing.
Conducted step-wise regressionanalysis for Probable CTS andreported that repetitions andduration of employment wereprotective. Cigarettes and Agewere also retained in the model.
5a-60
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
(Continued)
Osorio et al.1994
Cross-sectional
56 supermarket workers. Comparison wasbetween high and lowexposure groups.
Outcome: CTS assessed viamedical history, physical exam,median nerve conductionstudies, and vibratorythresholds.
A. CTS-like syndrome:Probable diagnosis: (1) Paintingling numbness in mediannerve distribution and(2) symptoms last >1 wk or $12 times in last year, no acutetrauma or systemic disease,onset or exacerbation sinceworking on current job.
B. Median neuropathy:Sensory median nerveconduction velocity 44 m/secor less.
Exposure: Observation of jobsby ergonomist and industrialhygienist. Analysis based oncategorization by job title afterobservation. Jobs divided into3 categories based on thelikelihood of exposure toforceful and repetitive wristmotions (low, moderate, high),years worked at this store,total years worked as checker,total years using laserscanners.
Symptoms: 63% inhigh-exposure;10% inmoderate-exposuregroup
PositiveNCS: 33%in high-exposure;7% inmoderate-exposuregroup
0% forlow-exposuregroup
0% forlow-exposuregroup
8.3(for CTS-symptoms highvs. lowexposuregroups)
6.7 (forabnormal NCS,high vs. lowexposuregroups)
2.6-26.4
0.8-52.9
Participation rate: 81%.
Adjusted for age, gender, alcoholconsumption, and high-risk medicalhistory.
Interview and testing proceduresperformed by personnel blinded tocase status.
Skin surface temperature notcontrolled.
Dose response for presumptive(symptoms of) exposure toforceful, repetitive wrist motion:CTS-prevalence 63% highexposure; 10% medium exposure;0% low exposure.
Dose response for prevalence ofabnormal median nerve velocity: 33% high; 7% medium; 0% low.
Linear regression showedsignificant relationship betweenyears worked and worsening ofnerve conduction (decreasednerve conduction velocity anddecreased nerve conductionamplitude) adjusted forconfounders (above), howeversmall sample size.
5a-61
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
(Continued)
Punnett et al.1985
Cross-sectional
162 female garmentworkers; 85% wereemployed as sewingmachine operators whosewed and trimmed byhand.
Comparison: 76 of 190full- or part-time workerson day shift in a hospitalwho worked as nursesor aids; lab techniciansor therapists, or foodservice workers.
Employees typing >4hr/day excluded fromcomparison group. 162female garment workerscompared to 73 femalehospital workers.
Outcome: CTS assessed bysymptom questionnaire andphysical exam. Cases definedas the presence of persistentpain (lasted for most days forone month or more within thepast year); were notassociated with previousinjury; and, began after firstemployment in garmentmanufacturing or hospitalemployment. Key questionsbased on the arthritissupplement questionnaire ofthe National Health and NutritionExamination Survey (NHANES). Median nerve symptoms (pain,numbness, or tingling) ifpresent at night or early in themorning or met 2 of 3 criteria: (1) accompanied by weaknessin pinching or gripping;(2) alleviated by absence fromwork for >1 wk;(3) aggravated by houseworkor other non-occupationaltasks.
Exposure: Observation of jobtasks. Information on workhistory obtained byquestionnaire. Job title used asa proxy for exposure inanalyses.
18% 6% 2.7 1.2-7.6 Participation rate: 97% (garmentworkers), 40% (hospital workers).
Controlled for age, hormonal status,and native language.
Pain in the wrist and handsignificantly correlated (p<0.01;r=0.41).
Age distribution not significantlydifferent metabolic disease.
Symptoms of CTS showed trend byage (p<0.01).
Prevalence of pain not associatedwith years of employment ingarment workers.
Length of employment not predictorof risk.
Change in hormonal statussignificantly associated with CTSsymptoms but negativelyassociated with employment ingarment shop.
Logistic model found garment workand age significant for symptoms ofCTS.
Neither metabolic disease norchange in hormonal statusstatistically significant risk.
5a-62
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
(Continued)
Schottlandet al. 1991
Cross-sectional
Poultry workers (27 males, 66 females)compared to jobapplicants (44 males,41 females).
Outcome: Defined asprolonged motor or sensorymedian latencies. Nosymptoms or physical examincluded in case definition.
Exposure: Based on currentemployment status at plant. Nomeasurements made. Repetitive tasks (15 to 50complex operations/min notrare), requiring firm grip, withwrists in flexion or extension,with internal deviations.
41%exceeding2.2 ms forsensorylatencyvalue ofmediannerve onNCS (right-hand,females,correctedfor age)
24%exceeding2.2 ms formediannervesensorylatencyvalue onNCS (left-hand,females,correctedfor age)
20%exceeding2.2 ms formediansensorylatencyvalue(right-hand,females,correctedfor age)
15%exceeding2.2 ms formediannervesensorylatencyvalue onNCS (left-hand,females,correctedfor age)
2.86
1.87
1.1-7.9
0.6-9.8
Participation rate: Not reported.
Not mentioned whether examinersblinded to case status or exposure.
Controlled for age and gender.
Referents not excluded if prioremployment at poultry plant;15 referents had previousemployment in poultry plant; thiswould result in poor selection ofcontrols, would tend to bias resultstowards the null.
Right-hand of female applicantswho never worked in a poultryplant had significantly longermedian palmar latency (MPS) onnerve conduction than referents(p<0.04).
Symptoms of CTS not inquired. Right hand of male workers hadlonger MPS on nerve conductionbut not significant (p<0.07).
From Table 5-2 in paper it showsthere is inadequate sample size fordetecting differences in female’sleft-hand and male’s left- and right-hand MPS.
Concluded there is an elevated riskof CTS, roughly equal to risk fromaging for the right hands of femaleworkers, less risk for male bothhands and female left hands.
5a-63
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
(Continued)
Silversteinet al. 1987
Cross-sectional
652 industrial workers in4 groups: (1) low-force,low-repetition (comparison group,n=93 males, 64 females);(2) high-force, low-repetition (n=139 males,56 females); (3) low-force, high-repetition(n=43 males, 100females); (4) high-force,high-repetition (n=83males, 74 females).
Outcome: CTS determined bymedical examination andinterviews.
Symptoms of pain, numbnessor tingling in median nervedistribution.
Nocturnal exacerbation;symptoms >20 times or >1 wkin previous year; no history ofacute trauma; no history ofrheumatoid arthritis; onset ofsymptoms since current job;positive modified Phalen’s test(45 to 60 sec) or Tinel’s sign;rule out cervical root thoracicoutlet, pronator teressyndrome.
Exposure: To (1) forceful,(2) repetitive, and (3) awkwardhand movements assessed byEMG and video analysis ofjobs. Three workers in eachselected job videotaped for (atleast) 3 cycles. High-force job:A mean adjusted force >6 kg(mean adjusted force =[(variance/mean force)+ meanforce]); low-force job: A meanadjusted force <6 kg.
High repetition = work cycles<30 sec or work cyclesconstituting >50% of the workcycle.
1.0 (Group 2)
2.1 (Group 3)
5.6 (Group 4)
0.6 Group 2 vs.Group 1: OR=1.8
Group 3 vs.Group 1: OR=2.7
Group 4 vs.Group 1:OR=15.5
In separatelogistic models:
(1) Repetitive-ness: OR=5.5 (p<0.05)
(2) Force: OR=2.9 (non-significant)
0.2-21
0.3-28
1.7-142
Participation rate: 90% responserate obtained.
Controlled for age, gender, plant,years on the job. No interactionsfound.
Jobs evaluated by investigatorsblinded to worker health status.
Examiner blinded to medical historyand exposure.
Random sample of 12 to 20 activeworkers/job with 1 year’s seniority,stratified by age and gender.
Interview data included prior healthand injuries, chronic diseases,reproductive status of females,recreational activities, prior jobactivities.
No association found with wristposture, type of grasp, or use ofvibrating tool.
Positive associated with age butnot statistically significance.
No differences in health history orrecreational activities.
No association with gender, orindustrial plant.
Negatively associated with yearson the job but not statisticallyassociated.
Repetitiveness found to be strongerrisk factor than force.
No association with hormonalstatus.
5a-64
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
(Continued)
Stetson et al.1993
Cross-sectional
Comparison of 137asymptomatic industrialworkers, 103 industrialworkers with hand/wristsymptoms, and 105control subjectsrandomly selected notexposed to highlyforceful or repetitivehand exertions.
Outcome: Symptomsconsistent with CTS defined asnumbness, tingling, or burninglocalized to median nerveanatomic area, not caused byacute injury, and occurred >20times in previous year. Nerveconduction studies conductedon the dominant hand; mediansensory and motor, ulnarsensory, distal amplitudes andlatencies were measured. Temperature monitored.
Exposure: Observation andworker interviews usingergonomic checklist. One ormore workers on each jobwere evaluated based onrepetitiveness, forcefulness,mechanical stress, pinch grip,and wrist deviation, then dataextrapolated to other workersperforming jobs. A 3-pointordinal scale used to estimateexposure (none, some,frequent or persistent).
Õ Õ Participation rate: 71% seen, 16%refused, others unavailablebecause of layoffs, transfers, orsick leave.
Industrial population randomlyselected.
Controlled for age, height, skintemperature, and dominant indexfinger circumference.
Comparing the means of the nerveconduction measures, the followingwere statistically significantlydifferent between: (1) theasymptomatic hand group and thecontrols: median sensory amplitudeand distal latency, and median toulnar comparison measures; (2) thesymptomatic hand group andcontrols: median sensory distallatency, and median to ulnarcomparison measures.
Median sensory amplitudes weresmaller and distal latencies longer insymptomatic compared toasymptomatic hand group.
Forceful hand and upper extremityexertions were significantlydifferent between exposed andnon-exposed groups. Repetitionnot significantly different, but littlestatistical power to detectdifference.
5a-65
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
(Continued)
Tanaka et al.In Press
Cross-sectionalinterviewsurvey
Data from the Occupational HealthSupplement of 1988National Health InterviewSurvey conducted by theNational Center forHealth Statistics. Households are selectedby multistage probabilitysampling strategy. Oneadult, 18 years or older,was randomly selectedfor interview. 44,233interviews completed.
Outcome: Outcomes includedthose “Recent Workers” whoworked anytime during the past12 months (excluding armedforces). Self-reported carpaltunnel syndrome= “yes” toquestion: During the past12 months, have you had acondition affecting the wristand hand called carpal tunnelsyndrome? Medically calledCTS = a response of “carpaltunnel syndrome” to thequestion: “What did the medicalperson call your handdiscomfort?”
Exposure: By questionnaire:Did the most recent job requireyou to bend or twist yourhands or wrists many times anhr? Did you work with hand-held or hand-operated tools ormachinery.
Prevalenceof self-reportedCTS amongrecentworkers:1.47%
Prevalenceof medicallycalled CTSamongrecentworkers:0.53%
Logistic modelfor medicallycalled CTSamong recentworkers
Bend/twist:OR=5.9
White race:OR=4.2
Female gender:OR=2.4
Vibration:OR=1.85
BMI $25: OR=2.1
Cigarette use:OR=1.6
Age $40: OR=1.3
Annual income$$20,000:OR=1.5
Education>12: OR=1.2
3.4-10.2
1.9-15.6
1.6-3.8
1.2-2.8
1.4-3.1
1-2.5
0.2-1.9
1-2.4
0.8-1.8
Participation rate: 91.5%.
Multiple logistic regression used toexamine age, gender, race,exposure to vibration, andbending/twisting of the hand/wriststo odds of reporting CTS. Interactions were checked for.
Self-reported CTS prevalenceamong recent workers higher inwhites compared to non-whites,highest in white females.
When vibration was not in themodel the bend/twist OR=5.99. When bend/twist is not in themodel, vibration OR=3.00.
Major limitation is CTS is based onself-reports without medicalvalidation.
No temporal relationship could befound between reported CTS andthe reported occupation/industry orexposure to bending/twisting of thehand/wrist.
5a-66
Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposed workers
Referent group
RR, OR, or PRR 95% CI Comments
Weislanderet al. 1989
Case-control
34 male CTS patients,each matched to 2 otherhospital referents(drawn from amongothersurgical cases, onereferent had beenoperated on for gallbladder surgery and theother for varicose veins)and 2 populationreferents (from a generalpopulation register andtelephone directory)(total comparisongroup=143 males).
Outcome: CTS diagnosedclinically by a hand surgeon,confirmed by electro-diagnosticstudies.
Exposure: To vibrating tools,repetitive wrist movements,and loads on the wristassessed via telephoneinterview using a standardizedquestionnaire. The degree ofexposure was evaluated bothwith regard to the total numberof work years and the averagenumber of exposed hr a wk. Repetitive movementsclassified independently byphysician interviewer andoccupational hygienist. Exposure to repetitive wristmovements was considered toexist if they agreed.
Õ Õ Casescompared to allreferents(hospital- andpopulation-based):Vibrating tooluse: OR=3.3
Use of hand-held vibratingtools 1-20years: OR=2.7
Loads on thewrist: OR=1.8
Casescompared topopulationreferentsalone:Vibrating tooluse: OR=6.1
Repetitivewristmovement for>20 years:OR=4.6
Repetitivewristmovement:OR=2.7
Obesity:OR=3.4
1.6-6.8
1.1-6.7
1.0-3.5
2.4-15
1.8-11.9
1.3-5.4
1.2-9.8
Participation rate: 93%.
Referents matched for gender andage (±3 years.), hospital referentsfor year of operation.
Hospital referents and populationreferents statistically differentcomparing: use of vibrating tool,repetitive movements of wrist,workload on wrist, obesity.
Hospital-based population may notreflect industrial workplace.
Interviewers not blinded to casestatus.
Elevated OR for repetitivemovements of the wrist onlystatistically significant for thecategory ‘>20 years.’
Odds ratios (OR) for any of thethree diseases (thyroid disease,diabetes, rheumatoid arthritis)found to be statistically significantamong cases with CTS comparedto 143 referents; OR=2.8 (1.0-7.6).
ORs tended to increase withincreasing number of risk factorspresent. One factor, OR=1.7 (0.6-4.4); two factors, OR=3.3 (1.2-9.1);>two factors, OR=7.1 (2.2-22.7).
Obesity is >10% above referenceweight.
5a-67
5b-1
CHAPTER 5bHand/Wrist Tendinitis
SUMMARY Eight epidemiologic studies have examined physical workplace factors and their relationship to hand/wristtendinitis. Several studies fulfill the four epidemiologic criteria that were used in this review, andappropriately address important methodologic issues. The studies generally involved populations exposedto a combination of work factors; one study assessed single work factors such as repetitive motions of thehand. We examined each of these studies, whether the findings were positive, negative, or equivocal, toevaluate the strength of work-relatedness, using causal inference.
There is evidence of an association between any single factor (repetition, force, and posture) andhand/wrist tendinitis, based on currently available epidemiologic data. There is strong evidence that jobtasks that require a combination of risk factors (e.g., highly repetitious, forceful hand/wrist exertions)increase risk for hand/wrist tendinitis.
INTRODUCTION
Since the hand/wrist area may be affected bymore than one musculoskeletal disorder, onlythose studies that specifically addresshand/wrist tendinitis are considered here.Studies with outcomes described as hand/wristdisorders or symptoms in general, or those inwhich hand/wrist tendinitis was combined withepicondylitis, e.g., were excluded from thissection because it was not possible to evaluateevidence for work-related hand/wrist tendinitisfrom the data. The seven studies referenced inTable 5b-1 provided data specificallyaddressing hand/wrist tendinitis. In each ofthese studies the outcome was determined usingphysical examination criteria, although the casedefinitions varied among studies. Prevalence orincidence rates of hand/wrist tendinitis reportedin these exposed groups ranged from 4% to56%, and in unexposed groups from 0% to14%. Such wide ranges of prevalence ratesprobably reflect the variability in diagnosticcriteria as much as they do the range ofworkplace exposures in these studies. For
example, one study used very strict criteria[Byström et al. 1995]. The case definitionrequired observation of swelling along thetendon at the time of the physical examination.The only cases of tendinitis diagnosed weredeQuervain’s disease; no other cases oftenosynovitis or peritendinitis were diagnosedamong 199 automobile assembly line workers.In contrast, the studies with the highestprevalence rates either did not clearly statewhat diagnostic criteria were used to determinethe case definition, or the case definitionconsidered recurrences of tendinitis new cases.Whether case definitions were inclusive orexclusive would not affect the relative risk (RR)as long as they were applied non-differentiallybetween groups designated as exposed orunexposed.
Although several studies reported odds ratios,published data were reanalyzed and the resultspresented here and in Tables 5b1-3 as prevalence ratios (PRs). Thiswas done because odds ratios mayoverestimate RR when prevalence rates are
5b-2
high, and to make estimates of RR comparableacross studies. In studies that presented oddsratios in the original articles, the recalculation ofdata as PRs resulted in lower estimates of theRR. In the one prospective cohort study[Kurppa et al. 1991] incidence rates and riskratios are presented.
Except for a study reported by Armstrong et al.[1987a], risk estimates were not reportedseparately for single risk factors. Only theArmstrong et al. study used a formalquantitative exposure assessment as the basisfor determining exposure groups. Other studiesgrouped jobs with similar risk factors togetherand compared them to jobs without those riskfactors. Typically, the selection of jobs for theexposed and unexposed groups was based ongeneral knowledge of the jobs, previouslypublished literature, or questionnaire data.Repetition, force, and extreme postures wereconsidered in combination to determine whichworkers were exposed or unexposed. Formalexposure assessment (such as videotapeanalysis for cycle time, repetition, extremepostures, and estimates of force), was usuallyconducted on a sample of jobs and used asrationale in the grouping of jobs into exposedand unexposed categories, rather than to createquantitative measures of risk factors. In somecases (e.g., Luopajärvi et al. [1979]),investigators noted the difficulty in examiningrisk factors separately because of job rotation.For the purpose of this review, we havegrouped study findings according to the riskfactors present in the exposed job categories,based on the information in published articles.In Tables 5b1–3, studies are listed under singlerisk factors if there was evidence that theexposed and unexposed groups differed in thatrisk factor,
though the risk estimates mostly refer tocombined exposures.
REPETITION
Definition of Repetition forHand/Wrist Tendinitis
Armstrong et al. [1987a] analyzed videotapedjob tasks of a sample of workers, then dividedjob tasks according to level of repetitiveness:high repetition (cycle time <30 sec, or $50% ofthe cycle spent performing the samefundamental motions) or low repetition.Kuorinka and Koskinen [1979] created a“workload index” based on the number ofpieces handled per hour multiplied by thenumber of hours worked, for a dose-responseanalysis within the exposed group. Comparisongroups in the other studies were job categories;selection of the groups to be compared wasbased on observations, questionnaire data, orsurveillance data.
Studies Reporting on the Associationof Repetition and Hand/WristTendinitis
Seven studies addressed repetition: Amano etal. [1988]; Armstrong et al. [1987a]; Byströmet al. [1995]; Luopajärvi et al. [1979]; Rotoand Kivi [1984]; Kuorinka and Koskinen[1979]; and McCormack et al. [1990].
Studies Meeting the Four EvaluationCriteria
Two of the seven studies that addressedrepetition met all four of the evaluation criteria:Armstrong et al. [1987a], and Luopajärvi et al.[1979]. Armstrong et al. studied 652 industrialworkers at seven manufacturing plants(electronics, sewing, appliance, bearingfabrication, bearing assembly, and investment
5b-3
casting). Exposure assessment of jobs includedvideotape analysis and electromyography(EMG) of a sample of workers. Data from thisassessment were then used to categorize jobsaccording to level of repetitiveness and force.Health assessment of workers focused ondeQuervain’s disease, trigger finger, tendinitis,and tenosynovitis. The hand/wrist tendinitiscase definition required abnormal physicalexamination findings (increased pain withresisted but not passive motion or tendonlocking with a palpable nodule, or a positiveFinkelstein’s test) in addition to meetingsymptom criteria on standardized interviews.The PR for the high repetition/low force group(n=143) compared to the low repetition/lowforce group (n=157) was 5.5 (95% confidenceinterval [CI] 0.7–46.3). The PR for the highrepetition/high force group (n=157) comparedto the low repetition/low force group (n=157)was 17.0 (95% CI 2.3–126.2). The effect ofage, gender, years on the job, and plant wereanalyzed. A higher prevalence of tendinitis wasnoted among women but was not significantlyassociated with personal factors, whereassignificant differences in posture were observedbetween males and females.
Luopajärvi et al. [1979] compared theprevalence of hand/wrist tendinitis among 152female assembly line packers in a foodproduction factory to 133 female shopassistants in a department store. Exposure torepetitive work, awkward hand/arm postures,and static work was assessed by observationand videotape analysis of factory workers. Noformal exposure assessment was conducted onthe department store workers; their job taskswere described as variable. Cashiers wereexcluded, presumably because their work wasrepetitive. The health assessment consisted of
interviews and physical examinations conductedby a physiotherapist (active and passivemotions, grip-strength testing, observation, andpalpation). Diagnoses of tenosynovitis andperitendinitis were later determined by medicalspecialists using these findings andpredetermined criteria. The PR for tendinitisamong the assembly line packers compared tothe shop assistants was 4.13 (95% CI2.63–6.49). Age, hobbies and houseworkwere addressed and no associations withmusculoskeletal disorders were identified.
Studies Meeting at Least One Criteria
Amano et al. [1988] reported the prevalence ofcervicobrachial disorders, includingtenosynovitis, among 102 assembly lineworkers in an athletic shoe factory and 102age- and gender-matched non-assembly lineworkers (clerks, nurses, telephone operators,cooks, and key punchers). Exposureassessment was based on videotape analysis ofthe tasks of 29 workers on one assembly line.Assembly line workers produced about 3,400shoes a day. All but one task had cycle timesless than 30 seconds. No formal exposureassessment of the comparison group wasreported. Diagnoses were determined byphysical examination, including palpation fortenderness. The PRs for tenosynovitis of theright and left index finger flexors among theshoe factory workers were 3.67 (95% CI1.85–7.27) and 6.17 (95% CI 2.72–13.97)respectively, compared to the non-factoryworkers. Tenosynovitis of the other digits wasnot diagnosed in the comparison group. Shoeassembly workers held shoe lasts longer in theleft hand and had greater frequency ofsymptoms in the left hand. Comparison subjectswere matched to shoe factory workers ongender and age (within five years).
5b-4
Byström et al. [1995] studied forearm and handdisorders among 199 automobile assembly lineworkers and compared them to 186 randomlyselected subjects from the general Swedishpopulation. For both groups, exposure wasassessed using rating scales on nurse-administered questionnaires that addresseddaily duration of hand and finger movements,wrist position, grip, and hand tool use[Fransson-Hall et al. 1995]. Videotape analysisand electromyograms were conducted on asubgroup [Hägg et al. 1996]. A diagnosis oftenosynovitis or peritendinitis required theobservation of swelling and pain during activemovement on physical examination. A diagnosisof deQuervain’s disease required a positiveFinkelstein’s test. No cases of tenosynovitis orperitendinitis, other than deQuervain’s disease,were found in this study, probably because ofstrict clinical criteria used for the case definition.The PR for deQuervain’s disease among theautomobile assembly line workers was 2.49(95% CI 1.00–6.23) compared to the generalpopulation group. Psychosocial variables andother potential confounders or effect modifierswere addressed by Fransson-Hall et al. [1995].A higher prevalence of deQuervain’s diseasewas noted among men than women.
Kuorinka and Koskinen [1979] studiedoccupational rheumatic diseases and upper limbstrain among 93 scissor makers and comparedthem to the same group of department storeassistants (n=143) that Luopajärvi used as acomparison group. Temporary workers andthose with recent trauma were excluded fromthe scissor
makers group. Exposure assessment includedvideotape analysis of scissor maker tasks. Thetime spent in deviated wrist postures per work
cycle was multiplied by the number of pieceshandled per hour and the number of hoursworked to create a workload index. Cycletimes ranged from 2 to 26 seconds; the numberof pieces handled per hour ranged from 150 to605. No formal exposure assessment wasconducted on the shop assistants. Healthassessment involved interview and physicalexamination by a physiotherapist following astandard protocol. Diagnoses of tenosynovitisand peritendinitis were later determined fromthese findings using predetermined criteria(localized tenderness and pain duringmovement, low-grip force, swelling of wristtendons [Waris et al. 1979]). In equivocalcases, orthopedic and physiatric teamsdetermined case status. The PR for muscle-tendon syndrome among the scissor makerswas 1.38 (95% CI 0.76–2.51) compared tothe department store assistants. Whether or notcashiers were excluded from the comparisongroup in this study, as they were in theLuopajärvi et al. [1979] study is unclear. Thestudy group was 99% female. No relationshipwas found between age- or body-mass indexand muscle-tendon syndrome. The number ofsymptoms increased with the number of partshandled per year. Analyses of subgroups ofscissor makers showed non-significantincreased prevalence of muscle-tendonsyndrome in short versus long cycle tasks andin manipulation versus inspection tasks. Theauthors noted a lack of contrast in exposuresbetween the subgroups. A non-significant trendof increasing prevalence of diagnosed muscle-tendon syndrome with increasing number ofpieces handled per year was noted in a nestedcase-controlanalysis (n=36).
McCormack et al. [1990] studied tendinitis andrelated disorders of the upper extremity among
5b-5
1,579 textile production workers compared to468 non-production textile workers, areference group that included machinemaintenance workers, transportation workers,cleaners, and sweepers. The textile productionworkers were reported as being exposed torepetitive finger, wrist and elbow motions basedon knowledge of jobs; no formal exposureassessment was conducted. Health assessmentincluded a questionnaire and screening physicalexamination followed by a diagnostic physicalexamination. The diagnosis of tendinitisrequired positive physical findings suggestive ofinflammation. The textile production workerswere divided into four broad job categories:boarding (n=296), which was noted to requireforceful work as well as the repetitive hand-intensive work of the other categories; sewing(n=562); packaging (n=369); and knitting(n=352). The PR for tendinitis among all textileproduction workers was 1.75 (95% CI0.9–3.39), compared to the reference groupnon-production textile workers. The PRs and95% CIs comparing tendinitis among eachbroad category of textile production workers tothe reference group are as follows:boarding—3.0 (1.4, 6.4); sewing—2.1 (1.0,4.3); packaging—1.5 (0.7, 3.5); andknitting—0.4 (0.1, 1.4). The authors noted thatthe knitting work was more automated than theother textile production job categories. Raceand age were not related to outcome, but theprevalence of tendinitis was higher in workerswith less than three years of employment.Female gender was a significant predictor of
tendinitis (p=0.01), but job category was astronger predictor (p=0.001).
Roto and Kivi [1984] studied the prevalence oftenosynovitis among 92 male meatcutterscompared to 72 male construction foremen. Noformal exposure assessment was conducted.Meatcutters’ work entailed repetitive physicalexertion of upper extremities and shoulders.Construction foremen’s work did not involverepetitive movements of the upper extremities.Health assessment was by questionnaire andphysical examination. Tenosynovitis wasdefined as swelling, local pain, and fingerweakness during movement. The prevalence oftenosynovitis among the meatcutters was 4.5%.The PR for tenosynovitis as defined by physicalexamination could not be calculated becausethere were no cases among the comparisongroup. The PR of tendinitis-like symptomsreported on the questionnaire among themeatcutters was 3.09 (1.43, 6.67) comparedto the construction foremen. Serologic testingfor rheumatoid arthritis was done to control forpotential confounding, none was detected.Authors noted that tenosynovitis occurred inyounger age groups.
Strength of Association—Repetitionand Hand/Wrist TendinitisThe PRs for repetitive work and hand/wristtendinitis in the studies reviewed above rangedfrom 1.4 to 6.2:
5b-6
Repetition and Hand/Wrist Tendinitis
PR and 95% CI Authors Exposed/Unexposed Groups
5.5 (0.7–46.3)
17.0 (2.3–126.2)
Armstrong et al. [1987a]* HI REP & LO FORCE/LOREP & LO FORCEHI REP & HI FORCE/LOREP & LO FORCE
3.7 (1.9–7.3) to 6.2 (2.7–14.0)
Amano et al. [1988] Shoe assemblers/clerks, nurses,operators, cooks, keypunchers
2.5 (1.0–6.23) Byström et al. [1995] Auto assemblers/generalpopulation
1.4 (0.8–2.5) Kuorinka and Koskinen [1979] Scissor makers/departmentstore assistants
1.8 (0.9–3.4) McCormack et al. [1990] Textile production/ maintenanceworkers, etc.
3.1 (1.4–6.7) Roto and Kivi [1984] Meatcutters/constructionforemen
4.1 (2.6–6.5) Luopajärvi et al. [1979]* Food packers/department storeassistants excluding cashiers
*Study met all four criteria.
In evaluating these RR estimates, studylimitations should be considered in addition tostatistical significance. Statistical significanceaddresses the likelihood that the results are notdue to chance alone, whereas study limitationscan bias the RR estimates in either direction. Allof the PRs were greater than one, and four ofthe seven were statistically significant. Therange (1.4–6.2) might reflect the level ofcontrast in repetitiveness between the exposedand comparison groups. For example, inMcCormack et al. [1990], the comparisongroup consisted of machine maintenanceworkers, transportation workers, and
cleaners and sweepers, whose exposure torepetition was not measured. If there weresome exposure to repetitive work in thecomparison group, then this would tend todecrease the RR for hand/wrist tendinitis amongthe textile workers. Another concern with thisstudy is the possibility that the knitting workersmay not have been exposed to very repetitivework due to greater automation in the knittingprocess. The effect of this potentialmisclassification of exposure would also be todecrease the RR.
Note that Kuorinka and Koskinen andLuopajärvi et al. both used the same
comparison group, but the number of subjects
5b-7
in the department store assistant group was 143for Kuorinka and Koskinen, and 133 forLuopajärvi (who excluded cashiers from thecomparison group). If Kuorinka and Koskinendid not exclude cashiers, this might tend todecrease the RR.
The highest RR (6.2) reported for repetitivework was by Amano et al. [1988]. In this studyit is unclear whether the examiner was blindedto whether the subjects were shoe assemblersor in the comparison group of non-assemblyline workers that included clerks, nurses,telephone operators, cooks, and key punchers.Because the occupational groups wereexamined on separate dates blinding seemsunlikely. The lack of a clear case definitionleaves open the possibility of examiner bias,which might lead to an increased RR.Alternatively, if there were a significant numberof key punchers in the comparison group, whomay have been exposed to repetitive work, thatwould tend to decrease the contrast inexposure and might lead to a decrease in theRR.
In summary, the potential for underestimation ofthe RR has been noted in studies where the RRis at the low end of the range, and the potentialfor overestimation of the RR has been noted atthe high end of the range. Considering theseconcerns and statistical significance, the RR forhand/wrist tendinitis attributable torepetitiveness is probably more likely to be inthe middle range of the estimates, based on thestudies reviewed. The statistically significantestimates of RR in this middle group range from2.5 to 4.1.
Temporal Relationship—Repetitionand Hand/Wrist TendinitisAll of the studies reviewed for this section werecross-sectional, so proving that exposure torepetitive work occurred before hand/wristtendinitis is not possible. However, informationin several of the studies suggests the likelihoodthat exposure to repetitive work occurredbefore the diagnosis of tendinitis. For example,recently employed workers were excluded byKuorinka and Koskinen [1979]. In Luopajärviet al.’s [1979] study group, the minimum lengthof employment was3 years. In the McCormack et al. [1990] study,the minimum average length of employment inthe job categories was more than 7 years.Byström et al. [1995] noted that subjects wereselected for clinical examination 5 months aftercompletion of questionnaires on exposure. Rotoand Kivi’s [1984] subjects had all worked inthe food industry for more than one year.Armstrong and Chaffin [1979] required aminimum length of employment of one year.Case definitions generally required thatsymptoms began after starting the current jobor employment at the plant. This also suggeststhat exposure occurred before disease.
Consistency in Association forRepetition and Hand/Wrist Tendinitis
All of the studies reviewed showed positive RRestimates for hand/wrist tendinitis amongoccupational groups exposed to repetitivework, ranging from 1.4 to 6.2. Four of theseven studies resulted in statistically significantPRs. Considering only statistically significantestimates from studies not noted to have seriouslimitations (which might bias the RR), the rangenarrows to 2.5–4.1.
5b-8
Coherence of Evidence for Repetitionand Hand/Wrist TendinitisDeQuervain’s disease and othertenosynovitis of the hand, wrist, and forearmhave been associated for decades withrepetitive and forceful hand activities as one ofthe possible causal factors [Amadio 1995].DeQuervain’s disease is the entrapment of thetendons of the extensor pollicis brevis andabductor pollicis longus. Other similarconditions are trigger thumb and triggering ofthe middle and ring fingers, characterized bypain with motion of the affected tendon.Despite the fact that the tendon and its sheathmay be swollen and tender, the histopathologyshows peritendinous fibrosis withoutinflammation, and fibrocartilaginous metaplasiaof the tendon sheath tissue. The role ofinflammation early in the process is not clear[Hart et al. 1995]. As in carpal tunnelsyndrome or epicondylitis, acute classicalinflammation does not seem a criticalpathophysiological component of the clinicalcondition, at least once it becomes chronic.Despite the observations that too much forcefuland repetitive activity contributes to carpaltunnel syndrome and epicondylitis, the responseof the tendons and the muscles to repetitiveactivity is likely that of a U-shaped curve. Toolittle and too much activity may be harmful, butintermediate levels of activity are probablybeneficial. The studies of tendon and musclephysiology suggest that a certain amount ofactivity maintains the normal state of thesetissues and leads to adaptive changes. Thesetissues have the ability to repair significantamounts of damage from some overuse; thepoorly understood issue is when overuseexceeds the ability of the tissue to repair thedamage or triggers a more harmful type of
damage [Hart et al. 1995]. Marras and
Schoenmarklin [1991] reported that velocityand acceleration significantly predicted upperextremity musculoskeletal disorders (includingtendinitis) among industrial workers performinghand-intensive job tasks.
Dose-Response Relationship ForRepetition and Hand/Wrist TendinitisKuorinka and Koskinen [1979] reported thatwithin the group of scissor makers, increasedprevalence of muscle-tendon syndromeoccurred in short versus long cycle tasks and inmanipulation versus inspection tasks. Theseincreases were not statistically significant. Theauthors noted a lack of contrast in exposuresbetween the subgroups. A non-significant trendof increasing prevalence of diagnosed muscle-tendon syndrome with increasing number ofpieces handled per year was also noted in anested case-control analysis (n=36) in the samestudy.
The Armstrong et al. [1987a] data resulted in aPR of 17.0 (2.3, 126.2) for jobs that werehighly repetitious and required highly forcefulexertions. This suggests a synergistic effectwhen both risk factors are present because theestimate is greater than the sum of the RRestimate for force or repetition alone.
Conclusions on Repetition andHand/Wrist Tendinitis
There is strong evidence for a positiveassociation between highly repetitive work, incombination with other job risk factors, andhand/wrist tendinitis based on currentlyavailable epidemiologic data. All seven of thestudies reviewed reported positive RR
estimates. Four of these estimates werestatistically significant. Potential confounders
5b-9
(factors associated with both exposure andoutcome that may distort interpretation offindings) considered in the studies of hand/wristtendinitis included gender, age, other medicalconditions, and outside activities. There is noevidence that the associations reported herebetween repetitive work and hand/wristtendinitis are distorted by gender, age, or otherfactors.
FORCE
Definition of Force for Hand/WristTendinitisArmstrong et al. [1987a] based high and lowforce categories on electromyographs offorearm flexor muscles of representativeworkers. Comparison groups in the otherstudies were job categories; selection of thegroups to be compared was based onobservations, questionnaire data, orsurveillance data.
Studies Reporting on the Associationof Force and Hand/Wrist Tendinitis
Five studies addressed force: Armstrong et al.[1987a]; Byström et al. [1995]; Kurppa et al.[1991]; McCormack et al. [1990]; and Rotoand Kivi [1984].
Studies Meeting the Four Criteria
One of the studies that addressed force met allfour of the evaluation criteria: Armstrong et al.[1987a]. Armstrong et al. studied 652 industrialworkers at seven manufacturing plants(electronics, sewing, appliance, bearingfabrication, bearing assembly, and investmentmolding). Exposure assessment of jobsincluded videotape analysis and EMG of asample of workers. Data from this assessmentwere then used to categorize jobs
according to level of repetitiveness and force.Health assessment of workers focused ondeQuervain’s disease, trigger finger, tendinitis,and tenosynovitis. The hand/wrist tendinitiscase definition required abnormal physicalexamination findings (increased pain withresisted but not passive motion or tendonlocking with a palpable nodule, or a positiveFinkelstein’s test) in addition to meetingsymptom criteria on standardized interviews.The PR for the high force/low repetition group(n=195) compared to the low force/lowrepetition group (n=157) was 4.8 (95% CI0.6–39.7). The PR for the high repetition/highforce group (n=157) compared to the lowrepetition/low force group (n=157) was 17.0(95% CI 2.3–126.2). The effect of age,gender, years on the job and plant wereanalyzed. A higher prevalence of tendinitis wasnoted among women, but was not significantlyassociated with personal factors, whereassignificant differences in posture were observedbetween males and females.
Studies Meeting at Least One Criteria
Byström et al. [1995] studied forearm and handdisorders among 199 automobile assembly lineworkers and compared them to 186 randomlyselected subjects from the general Swedishpopulation. For both groups, exposure wasassessed using rating scales on nurse-administered questionnaires that addresseddaily duration of hand and finger movements,wrist position, grip, and hand-tool use[Fransson-Hall et al. 1995]. Videotape analysisand electromyograms were conducted on asubgroup [Hägg et al. 1996]. A diagnosis oftenosynovitis or peritendinitis required theobservation of swelling and pain during activemovement on physical examination. A diagnosisof deQuervain’s disease required a positive
5b-10
Finkelstein’s test. No cases of tenosynovitis orperitendinitis, other than deQuervain’s disease,were found in this study, probably because ofstrict clinical criteria used for the case definition.The PR for deQuervain’s disease among theautomobile assembly line workers was 2.49(95% CI 1.00–6.23) compared to the generalpopulation group. Psychosocial variables andother potential confounders or effect modifierswere addressed by Fransson-Hall et al. [1995].A higher prevalence of deQuervain’s diseasewas noted among men than women.
Kurppa et al. [1991] conducted a prospectivecohort study of tenosynovitis or peritendinitis(and epicondylitis) in a meat processing factoryin Finland. Three hundred seventy-sevenmeatcutters, meatpackers, and sausage makerswere compared to 338 office workers,maintenance workers, and supervisors.Exposure assessment was based on previouslypublished literature and knowledge of jobs atthe plant. Job categories were selected basedon whether or not strenuous manual work wasrequired. The cohort was followed for 31months. Health assessment consisted ofphysical examinations by plant physicians whowere on-site daily, using predetermined criteriafor diagnosing tenosynovitis or peritendinitis(swelling or crepitation and tenderness topalpation along the tendon and pain at thetendon sheath, in the peritendinous area, or atthe muscle-tendon junction during activemovement) and deQuervain’s disease (positiveFinkelstein’s test). Incidence density rates (if arecurrence of tendinitis occurred after 60 days,it was considered a new case) for tendinitiswere compared between each of the strenuousjob categories and either the male or femalecomparison group of combined non-strenuousjob categories (office workers, maintenanceworkers and supervisors). The RR for tendinitis
among the meatcutters (100% males)compared to the male comparison group was14.0 (5.7, 34.4); the RR for tendinitis amongthe meatpackers (79% female) compared tothe female comparison group was 38.5 (11.7,56.1); and the risk ratio for tendinitis among thesausage makers (86% female) was 25.6 (19.2,77.5). A limitation of the study is the fact thatthe subjects were not actively evaluated formusculoskeletal disorders. Investigators reliedon workers to seek medical care. This couldresult in a difference in case ascertainmentbetween the exposed and unexposed groupsbecause workers in non-strenuous jobs maynot have sought medical care formusculoskeletal disorders since they might stillbe able to perform their jobs, whereas workerswith MSDs in strenuous jobs might not be ableto perform their jobs, and would be more likelyto seek medical care. If subjects sought medicalcare, investigators were very likely to capturethe information, even if medical care wasprovided outside the plant, plant nursesreceived and reimbursed the bills, and recordedthe diagnosis and sick leave. However, whendiagnoses were made by physicians outside theplant, diagnostic criteria were unknown; thisoccurred in 25% of the cases. Exposed andcomparison groups were similar in age andgender mix, although gender varied with job.
McCormack et al. [1990] studied tendinitis andrelated disorders of the upper extremity among1,579 textile production workers compared to468 referents that included machinemaintenance workers, transportation workers,cleaners, and sweepers. The textile productionworkers
were reported, based on knowledge of the jobsto be exposed to repetitive finger, wrist andelbow motions; no formal exposure assessment
5b-11
was conducted. Health assessment included aquestionnaire and screening physicalexamination followed by a diagnostic physicalexamination. The diagnosis of tendinitisrequired positive physical findings suggestive ofinflammation. The textile production workerswere divided into four broad job categories.Boarding (n=296), was the only category notedto require forceful work. The PR for tendinitisamong the boarding workers was 3.0 (95% CI1.4–6.4), compared to the reference group.Race and age were not related to outcome, butthe prevalence of tendinitis was higher inworkers with less than three years ofemployment. Female gender was a significantpredictor of tendinitis (p=0.01), but jobcategory was a stronger predictor (p=0.001).
Roto and Kivi [1984] studied the prevalence oftenosynovitis among 92 male meatcutterscompared to 72 male construction foremen. Noformal exposure assessment was conducted.Meatcutters’ work entailed repetitive physicalexertion of upper extremities and shoulders.Construction foremen’s work did not involverepetitive movements of the upper extremities.Health assessment was by questionnaire andphysical examination. Tenosynovitis wasdefined as swelling, local pain, and fingerweakness during movement. The prevalence oftenosynovitis among the meatcutters was 4.5%.The PR for tenosynovitis as defined by physicalexamination could not be calculated becausethere were no cases among the comparisongroup. The PR of tendinitis-like symptomsreported on the questionnaire among themeatcutters was 3.09 (1.43, 6.67) comparedto the construction foremen. Serologic testingfor rheumatoid arthritis was done to control forpotential confounding, none was detected.Authors noted that tenosynovitis occurred inyounger age groups.
Strength of Association—Force andHand/Wrist TendinitisEstimates of RR for hand/wrist tendinitis amongthose in jobs requiring forceful exertion rangefrom 2.5 to 38.5:
The very large risk ratios reported by Kurppaet al. [1991] could be biased upward becauseof the difference in case ascertainment betweenthe exposed and unexposed groups.Investigators did not actively evaluate subjectsfor MSDs, but relied on workers to seekmedical care. As the authors noted, workers innon-strenuous jobs may not have soughtmedical care for MSDs since they might still beable to perform their jobs, while workers instrenuous jobs may not have been able toperform their jobs and would be more likely toseek medical care. This potential for differentialcase ascertainment between the exposed andunexposed groups undermines the credibility ofthe magnitude of the risk estimate.
Statistically significant estimates of RR forhand/wrist tendinitis among workers whoperform strenuous tasks from the remainingstudies range from 2.5 to 3.1.
5b-12
Force and Hand/Wrist Tendinitis
PR and 95% CI Authors Exposed/Unexposed Groups
4.8 (0.6–39.7)
17.0 (2.1–26.2)
Armstrong et al. [1987a] HI FORCE & LO REP/LOFORCE & LO REPHI FORCE & HI REP/LO FORCE & LO REP
2.5 (1.0–6.23) Byström et al. [1995] Auto assemblers/generalpopulation
14.0 (5.7–34.4) to38.5 (11.7–56.1)
Kurppa et al. [1991] Meat processors/officeworkers, maintenance workers,supervisors
3.0 (1.4–6.4) McCormack et al. [1990] Textile boarding workers/maintenance workers, etc.
3.1 (1.4–6.7) Roto and Kivi [1984] Meatcutters/constructionforemen
* Study met all four criteria.
Temporal Relationship—Force andHand/Wrist TendinitisThe Kurppa et al. [1991] study determinedexposure status of 83% of the cohort onOctober 2, 1982, and followed their healthstatus until April 30, 1985. The remainingsubjects entered the study when they becamepermanent employees, and were also followeduntil April 30, 1985.
Although the remaining studies that addressedforce were cross-sectional, the followinginformation increases the likelihood thatexposure to forceful work occurred before theoccurrence of tendinitis; Byström et al. [1995]noted that subjects were selected for clinicalexamination5 months after completion of questionnaires onexposure. McCormack et al. [1990] reportedthat the minimum average length of employment
in the job categories studied was more than 7years. Roto and Kivi’s
[1984] subjects had all worked in the foodindustry for more than one year. Armstrong etal. [1987a] required a minimum of 1 year ofemployment to be included in the study.
Consistency of Association—Forceand Hand/Wrist TendinitisAll of the studies reviewed reported positiveRR estimates for hand/wrist tendinitis amongoccupational groups exposed to forcefulexertions, ranging from 1.8 to 38.5. Four of thefive studies reported statistically significantfindings. If only statistically significant estimatesfrom studies in which limitations were not notedare considered, RR estimates for force andhand/wrist tendinitis range from 2.5 to 3.1.
5b-13
Coherence of Evidence—Force andHand/Wrist TendinitisSee Repetition Section.
Evidence of a Dose-ResponseRelationship—Force and Hand/WristTendinitis
Armstrong et al. [1987a] demonstrated a dose-response relationship between jobs requiringforceful exertions and hand/wrist tendinitis. Theestimate of RR for hand/wrist tendinitis amongworkers with jobs that were classified as HIGHFORCE & LOW REPETITION was 4.8 (0.6,39.7), while the estimate for HIGH FORCE &HIGH REPETITION jobs was 17.0 (2.3,126.2), compared to the comparison group ofLOW FORCE & LOW REPETITION jobs.
Conclusions on Force andHand/Wrist Tendinitis
There is strong evidence for an associationbetween work that requires forceful exertions,in combination with other job risk factors, andhand/wrist tendinitis based on currentlyavailable epidemiologic data. All five of thestudies reviewed reported data that resulted inpositive RR estimates. Four of the fiveestimates were statistically significant.Eliminating one estimate of RR from a studywith noted limitations that might bias theestimate upward does not change thisconclusion. Potential confounders such as ageand gender were examined in these studies (seediscussion of potential confounders on page5b-16) and there was no evidence thatreported associations were distorted byconfounders.
POSTURE
Definition of Posture for Hand/Wrist
TendinitisKuorinka and Koskinen [1979] determined thetime spent in deviated wrist postures per workcycle as part of their “workload index” that wasused in a dose-response analysis
within the exposed group. Comparison groupsin the other studies were job categories;selection of the groups to be compared wasbased on observations, questionnaire data, orsurveillance data.
Studies Reporting on the Associationof Posture and Hand/Wrist Tendinitis
Four studies addressed posture: Amano et al.[1988]; Byström et al. [1995]; Luopajärvi et al.[1979]; and Kuorinka and Koskinen [1979].
Studies Meeting the Four Criteria
Luopajärvi et al. [1979] met all four evaluationcriteria. Luopajärvi et al. [1979] compared theprevalence of hand/wrist tendinitis among 152female assembly line packers in a foodproduction factory to 133 female shopassistants in a department store. Exposure torepetitive work, awkward hand/arm postures,and static work was assessed by observationand videotape analysis of factory workers. Noformal exposure assessment was conducted onthe department store workers; their job taskswere described as variable. Cashiers wereexcluded, presumably because their work wasrepetitive. The health assessment consisted ofinterviews and physical examinations conductedby a physiotherapist (active and passivemotions, grip-strength testing, observation, andpalpation); and diagnoses of tenosynovitis andperitendinitis were later determined by medicalspecialists using these findings andpredetermined criteria. The PR for tendinitisamong the assembly line packers compared tothe shop assistants was 4.13 (95% CI
5b-14
2.63–6.49). Age, hobbies, and houseworkwere addressed, and no associations withmusculoskeletal disorders were identified.
Studies Meeting at Least One CriteriaAmano et al. [1988] reported the prevalence ofcervicobrachial disorders, includingtenosynovitis, among 102 assembly lineworkers in an athletic shoe factory and 102age- and gender-matched non-assembly lineworkers (clerks, nurses, telephone operators,cooks, and key punchers). Exposureassessment was based on videotape analysis ofthe tasks of 29 workers on one assembly line.Characteristic basic postures were summarizedby the investigators as: holding a shoe or a tool,extending or bending the arms, and keeping thearms in a certain position. Assembly lineworkers produced about 3,400 shoes a day.All but one task had cycle times less than 30seconds. No formal exposure assessment of thecomparison group was reported. Diagnoseswere determined by physical examination,including palpation for tenderness. The PRs fortenosynovitis of the right and left index fingerflexors among the shoe factory workers were3.67 (95% CI 1.85–7.27) and 6.17 (95% CI2.72–13.97) respectively, compared to thenon-factory workers. Tenosynovitis of the otherdigits was not diagnosed in the comparisongroup. Shoe assembly workers held shoe lastslonger in the left hand and had greaterfrequency of symptoms in the left hand.Comparison subjects were matched to shoefactory workers on gender and age (within fiveyears).
Byström et al. [1995] studied forearm and handdisorders among 199 automobile assembly lineworkers and compared them to 186 randomlyselected subjects from the general Swedishpopulation. For both groups, exposure was
assessed using rating scales on nurse-administered questionnaires that addresseddaily duration of hand and
finger movements, wrist position, grip, andhand-tool use [Fransson-Hall et al. 1995].Videotape analysis and electromyograms wereconducted on a subgroup [Hägg et al. 1996]. Adiagnosis of tenosynovitis or peritendinitisrequired the observation of swelling and painduring active movement on physicalexamination. A diagnosis of deQuervain’sdisease required a positive Finkelstein’s test.No cases of tenosynovitis or peritendinitis,other than deQuervain’s disease, were found inthis study, probably because of strict clinicalcriteria used for the case definition. The PR fordeQuervain’s disease among the automobileassembly line workers was 2.49 (95% CI1.00–6.23) compared to the general populationgroup. Psychosocial variables and otherpotential confounders or effect modifiers wereaddressed by Fransson-Hall et al. [1995]. Ahigher prevalence of deQuervain’s disease wasnoted among men than women.
Kuorinka and Koskinen [1979] studiedoccupational rheumatic diseases and upper limbstrain among 93 scissor makers and comparedthem to the same group of department storeassistants (n=143) that Luopajärvi used as acomparison group. Temporary workers andthose with recent trauma were excluded fromthe scissor makers group. Exposure assessmentincluded videotape analysis of scissor makertasks. The time spent in deviated wrist posturesper work cycle was multiplied by the number ofpieces handled per hour and the number ofhours worked to create a workload index.Cycle times ranged from 2 to 26 seconds; thenumber of pieces handled per hour ranged from150 to 605. No formal exposure assessment
5b-15
was conducted on the shop assistants. Healthassessment involved interview and physicalexamination by a
physiotherapist following a standard protocol.Diagnoses of tenosynovitis and peritendinitiswere later determined from these findings usingpredetermined criteria (localized tendernessand pain during movement, low-grip force,swelling of wrist tendons [Waris et al. 1979]).In equivocal cases, orthopedic and physiatricteams determined case status. The PR formuscle-tendon syndrome among the scissormakers as 1.38 (95% CI 0.76–2.51)compared to the department store assistants.Whether or not cashiers were excluded fromthe comparison group in this study, as theywere in the Luopajärvi et al. [1979] study isunclear. The study group was 99% female. Norelationship was found between age or bodymass index and muscle-tendon syndrome. Thenumber of symptoms increased with the numberof parts handled per year. Analyses ofsubgroups of scissor makers showed non-significant increased prevalence of muscle-tendon syndrome in short versus long cycletasks and in manipulation versus inspectiontasks. The authors noted a lack of contrast inexposures between the subgroups. A non-significant trend of increasing prevalence ofdiagnosed muscle-tendon syndrome withincreasing number of pieces handled per yearwas noted in a nested case-control analysis(n=36). Strength of Association—ExtremePosture and Hand/Wrist TendinitisThe PRs for extreme postures and hand/wristtendinitis ranged from 1.4 to 6.2. All of the PRswere greater than one and three of the fourstudies reported statistically
significant estimates. As noted in the RepetitionSection, the possibility of examiner bias mightexist in the study reported by Amano et al.[1988], potentially biasing the RR estimateupward. The middle of the range of statisticallysignificant estimates for RR for hand/wristtendinitis is 2.5 to 4.1.
Temporal Relationship
Although all of the studies reviewed in thissection were cross-sectional, at least two of thestudies addressed temporality by reporting aminimum length of employment (Luopajärvi etal. [1979]—5 years) or by evaluating exposurebefore health outcomes [Byström et al. 1995],as discussed in the previous sections onRepetition and Force.
Consistency
All of the studies reviewed showed positive RRestimates for hand/wrist tendinitis amongoccupational groups exposed to extremepostures, ranging from 1.4 to 6.2. Three of thefour studies reviewed resulted in statisticallysignificant PRs. Considering only statisticallysignificant estimates from studies not noted tohave design limitations that might bias the RR,narrows the range to 2.5 to 4.1.
Coherence of Evidence
See Repetition Section.
Dose-Response
See Repetition Section.
5b-16
Posture and Hand/Wrist Tendinitis
PR and 95% CI Authors Exposed/Unexposed Groups
4.1 (2.6–6.5) Luopajärvi et al. [1979] Food packers/department storeassistants
3.7 (1.9–7.3) to 6.2 (2.7–14.0)
Amano et al. [1988] Shoe assemblers/clerks, nurses,operators, cooks, keypunchers
2.5 (1.0–6.23) Byström et al. [1995] Auto assemblers/generalpopulation
1.4 (0.8–2.5) Kuorinka and Koskinen [1979] Scissor makers/department.store assistants
There is strong evidence for a positiveassociation between work that requiresextreme postures, in combination with other jobrisk factors, and hand/wrist tendinitis, based oncurrently available epidemiologic data. All ofthe studies reviewed reported data that resulted in positive RR estimates.Three of the four estimates from these studieswere statistically significant. Taking into accountthe effect of potential confounders (SeeRepetition Section) such as gender, age, andstudy limitations does not alter this conclusion.
Potential Confounders
GenderThe association between gender and tendinitisis not uniform. Byström et al. [1995] reported ahigher prevalence of deQuervain’s tendinitis inmen than in women, and proposed theexplanation that men in their study group usedhand tools more often than women. Ulnardeviation and static muscle loading werelikewise more often reported among men.Armstrong et al. [1987a] reported a higherprevalence of
tendinitis among women but found no significantassociations with other medical factors oractivities outside of work. However, significantdifferences in posture were observed betweenmales and females. Differences in postures maybe due to differences in height between menand women whose workstations have uniformdimensions. In McCormack et al.’s [1990]study of textile workers, three of the fourexposed groups were largely female(89%–95%), limiting the ability to separate theeffect of gender from job effect. However, in ananalysis that included gender and job as riskfactors, they reported that gender was asignificant predictor of tendinitis (p=0.01), butnot as significant a predictor as job category(p=0.001). The other studies reviewed did nothave both male and female subjects.
Age
Several investigators noted that tendinitisappears to be more prevalent in younger agegroups. Byström et al. [1995] reported thatmost of the cases of deQuervain’s tendinitisoccurred in the <40-yr age group.
McCormack et al. [1990] reported that age
5b-17
was not a significant predictor of tendinitis, butyears on the job was inverselyassociated—prevalence was higher if less than3 years on the job. Armstrong et al. [1987]noted that “a significant interaction betweensex, age, and years on the job suggested thatthe risk of hand/wrist tendinitis might actuallydecrease with an increased number of years onthe job, but the effect was too small to meritfurther discussion.” Roto and Kivi [1984] notedthat “The few cases of tenosynovitis occurred inyounger workers.” Kuorinka and Koskinen[1979] and Luopajärvi et al. [1979] found nosignificant association between age andtendinitis.
Other Potential Confounders
McCormack et al. [1990] reported that racewas not associated with tendinitis. Armstrong etal. [1987a] found no significant associationswith personal factors—birth control pills,hysterectomy, oophorectomy, recreationalactivities. No subjects with seropositiverheumatic diseases were included in theKuorinka and Koskinen [1979] study. Theyreported that their earlier unpublishedquestionnaire found no correlations betweenillness and extra work, work outside thefactory, work at home, or hobbies. Luopajärviet al. [1979] excluded subjects with previoustrauma, arthritis, and other pathologies.
There is no evidence in the studies reviewedhere that the associations reported betweenwork factors and hand/wrist tendinitis areexplained by gender, age, or other factors.
CONCLUSIONSEight epidemiologic studies have examinedphysical workplace factors and theirrelationship to hand/wrist tendinitis. Severalstudies fulfill the four epidemiologic criteria thatwere used in this review, and appropriatelyaddress important methodologic issues. Thestudies generally involved populations exposedto a combination of work factors; one studyassessed single work factors such as repetitivemotions of the hand. We examined each ofthese studies, whether the findings werepositive, negative, or equivocal, to evaluate thestrength of work-relatedness, using causalinference.
There is evidence of an association betweenany single factor (repetition, force, and posture)and hand/wrist tendinitis, based on currentlyavailable epidemiologic data. There is strongevidence that job tasks that require acombination of risk factors (e.g., highlyrepetitious, forceful hand/wrist exertions)increase risk for hand/wrist tendinitis.
Table 5b-1. Epidemiologic criteria used to examine studies of hand/wrist tendinitis associated with repetition
Study (first author andyear)
Riskindicators
(OR, PRR, IRor p-value)*,†
Participationrate $$70%
Physicalexamination
Investigatorblinded to
case and/orexposure
status
Basis for assessinghand/wrist exposure to
repetition
Met all four criteria:
Armstrong 1987a 5.5, 17.0†
Yes Yes Yes Observation or measurements
Luopajärvi 1979 4.1† Yes Yes Yes Observation or measurements
Met at least one criterion:
Amano 1988 3.7–6.2† NR‡ Yes NR Job titles or self-reports
Byström 1995 2.5† Yes Yes No Job titles or self-reports§
Kuorinka 1979 1.4 Yes Yes NR Observation or measurements
McCormack 1990 1.8 Yes Yes NR Job titles or self-reports
Roto 1984 3.1† Yes Yes Yes Job titles or self-reports
*Some risk indicators are based on a combination of risk factors—not on repetition alone (i.e., repetition plus force, posture,or vibration). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).
†Indicates statistical significance.‡Not reported. §EMG and video analysis of subgroup reported in Hägg et al. [1996].
5b-18
Table 5b-2. Epidemiologic criteria used to examine studies of hand/wrist tendinitis MSDs associated with force
Study (first author andyear)
Riskindicator (OR,PRR, IR or p-
value)*,†
Participationrate $$70%
Physicalexamination
Investigatorblinded to
case and/orexposure
status
Basis for assessinghand/wrist exposure to
force
Met all four criteria:
Armstrong 1987a 17.0†,4.8
Yes Yes Yes Observation ormeasurements
Met at least one criterion:
Byström 1995 2.5† Yes Yes No Job titles or self-reports§
Kurppa 1991 14.0–38.5† Yes Yes NR‡ Observation ormeasurements
McCormack 1990 3.0† Yes Yes NR Job titles or self-reports
Roto 1984 3.1† Yes Yes Yes Job titles or self-reports
*Some risk indicators are based on a combination of risk factors—not on force alone (i.e., force plus repetition, posture,or vibration). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).
†Indicates statistical significance. ‡Not reported. §EMG and video analysis of subgroup reported in Hägg et al. [1996].
5b-20
Table 5b-3. Epidemiologic criteria used to examine studies of hand/wrist tendinitis MSDs associated with posture
Study (first author andyear)
Riskindicator (OR,PRR, IR or p-
value)*,†
Participationrate $$70%
Physicalexamination
Investigatorblinded to case
and/orexposure
status
Basis for assessinghand/wrist exposure to
posture
Met all four criteria:
Luopajärvi 1979 4.1† Yes Yes Yes Observation ormeasurements
Met at least one criterion:
Amano 1988 3.7–6.2† NR‡ Yes NR Job titles or self-reports
Byström 1995 2.5† Yes Yes No Job titles or self-reports§
Kuorinka 1979 1.4 Yes Yes NR Observation ormeasurements
*Some risk indicators are based on a combination of risk factors—not on posture alone (i.e., posture plus force, repetition, or vibration). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).
†Indicates statistical significance. ‡Not reported. §EMG and video analysis of subgroup reported in Hägg et al. [1996].
5b-22
(Continued)
Table 5b–4. Epidemiologic studies evaluating work-related hand/wrist tendinitis
MSD prevalence
StudyStudydesign Study population
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR, or PRR 95% CI Comments
Amanoet al. 1988
Cross-sectional
102 assembly lineworkers in anathletic shoe factorycompared to 102age and gendermatched non-assembly lineworkers (clerks,nurses, telephoneoperators, cooks,and key punchers).
Outcome: Examinationby a physician: palpationfor tenosynovitis andtenderness.
Exposure: One line of29 shoe assemblyworkers was selectedfor job analysis.Videotapes wereevaluatedfor movements of theupper extremities andshoulders and cycleand holding times.
No formal exposureassessment ofcomparison group.
Tenosynovitis, right index fingerflexors: 32.35%
Tenosynovitis, left index fingerflexors: 36.27%
Tenosynovitisright indexfinger flexors:8.82%
Tenosynovitis left indexfinger flexors:5.88%
PRR=3.67
PRR=6.17
1.85-7.27
2.72-13.97
Participation rate: Not reported.
Unclear whether examiner was blindedto job category (occupational groupsexamined on separate dates). No clearcase definition provided. Potential forexaminer bias exists.
Comparison group was matched ingender and age (within 5 years).
Tenosynovitis of other digits was notdiagnosed in the comparison group.
Neurological exam and clinical tests of pinch strength, tapping, pressure, andvibration sensibility were also done. No significant differences betweengroups in finger-pinch strength. Shoeworkers failed the tapping test moreoften, had lower pressure-sensibility in1 of 10 fingers tested, and had lowervibration-sensibility in 2 of 10 fingers. One of 3 neurological maneuvers(Morley’s test) was more often positivein shoe workers. Exposure to tolueneis noted and is a potential confounderfor neurological findings.
Assembly line workers produced about3,400 shoes a day. All but one taskhad cycle times <30 sec.
Assembly workers held shoe lastslonger in the left hand and had greaterfrequency of symptoms in left hand vs. non-assembly workers, who wereassumed to use right hand (dominanthand) more frequently.
5b-24
(Continued)
Table 5b–4 (Continued). Epidemiologic studies evaluating work-related hand/wrist tendinitis
MSD prevalence
StudyStudydesign Study population
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
Armstrong1987a
Cross-sectional
652 industrialworkers divided into4 groups: (1) lowforce, low repetition(comparison group,n=157), (2) highforce, low repetition(n=195), (3) lowforce and highrepetition (n=143),and (4) high forceand high repetition(n=157).
Outcome: Positivefindings on interviewand physical exam wererequired for casedefinition. Tendinitis/teno-synovitis: localized pain orswelling lasting > aweek, and increasedpain with resisted butnot passive motion. Trigger finger: locking inextension or flexion anda palpable nodule atbase of finger.
DeQuervain’s: positiveFinkelstein test withlocalized pain score of>=4 (range 1 to 8).
Exposure: To force andrepetition assessed byEMG and video analysisof jobs performed by a sample of workers.
3.1% (Group 2)
3.5% (Group 3)
10.8% (Group 4)
0.6% PRR=4.8
PRR=5.5
PRR=17.0
0.6-39.7
0.7-46.3
2.3-126.2
Participation rate: 90% of workersoriginally selected for inclusion actuallyparticipated.
The effect of age, gender, years on thejob, and plant were analyzed. Higherprevalence of tendinitis among women,but not significantly associated withpersonal factors. Significantdifferences in posture were observedbetween males and females.
Examiners were blinded to exposurestatus of study participants.
5b-25
Table 5b–4 (Continued). Epidemiologic studies evaluating work-related hand/wrist tendinitis
MSD prevalence
StudyStudydesign Study population
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Byströmet al. 1995
Cross-sectional
199 automobileassembly lineworkers, comparedto 186 generalpopulation.
Outcome: Tenosynovitisor peri-tendinitis werediagnosed based onphysical examinationobservations: swellingand pain at the tendonsheath, peritendinousarea or muscle-tendonjunction during activemovement of the tendon. deQuervain’s tendinitis:Positive Finkelstein’stest.
Exposure: Dailyduration of hand andfinger movements,manual handling, wristposition, grip type, andhand-tool use wererated by workers on6-point scales inquestionnaires[Fransson-Hall et al.1995]. Forearmmuscular-load and wristangle were evaluatedby EMG and videotapeanalysis for a subgroup[Hägg et al. 1996].
8.04%(deQuervain’stendinitis)
3.23% PRR=2.49 1.00-6.23 Participation rate: 96%. Study grouprandomly selected from assemblydivision of a plant. Comparison group isfrom the MUSIC study [Hagberg andHogstedt 1991].
Examiners blinded to exposure status:no, everyone examined by the authorswas in the exposed group.
Results are reported separately formales and females, and for age <40years. Psychosocial variables andother potential confounders or effectmodifiers were addressed byFransson-Hall et al. [1995].
Higher prevalence of deQuervain’stendinitis in males than infemales—possibly related to greateruse of hand tools, ulnar deviation,and/or static muscle loading.
No cases of tenosynovitis orperitendinitis were found in this study,probably because of strict clinicalcriteria (required observation ofswelling).
5b-26
Table 5b–4 (Continued). Epidemiologic studies evaluating work-related hand/wrist tendinitis
MSD prevalence
StudyStudydesign Study population
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
KuorinkaandKoskinen1979
Cross-sectional
93 scissor makerscompared to 143shop assistants.
Phase One: physicalexamination andinterview. Phase Two: workanalysis. 10-monthinterval betweenphases.
Comparison groupwas from anotherstudy that used thesame method[Luopajärvi et al.1979].
Outcome: Tenosynovitisand peritendinitisdiagnosed by interviewand physical exam.Physiotherapistexamined workers,diagnoses were frompredetermined criteria[Waris 1979] (localizedtenderness and painduring movement andlow grip-force andswelling of wristtendons). In problemcases orthopedic andphysiatric teamsdetermined case status.
Exposure: Work history,hr, and production ratesfor the previous yearwere taken fromcompany records. Aworkload index wasbased on videotapeanalysis of scissormaker workstations: time spent in deviatedwrist-posture(>20E)/work cycle;multiplied by numberpieces handled multipliedby hr worked. Noexposure assessmentof shop assistants.
18.3% 13.5% PRR=1.38 0.76-2.51 Participation rate: 81%.
Examiner was not blinded to casestatus, but diagnosis was madeseparately, using predetermined criteria[Waris et al. 1979].
Study group was 99% female. Norelationship found between age orbody mass index and “muscle-tendonsyndrome.”
The number of symptoms increasedwith the number of parts handled/year. Workers were paid by piece rate.
Within the group of scissor makers,non-significant increased prevalencesof muscle-tendon syndrome in shortvs. long cycle tasks and in manipulationvs. inspection tasks was reported. The authors noted a lack of contrast inexposures between the subgroups. Anon-significant trend of increasingprevalence of diagnosed muscle-tendon syndrome with increasingnumber of pieces handled/year wasnoted in a nested case-control analysis(n=36).
5b-27
Table 5b–4 (Continued). Epidemiologic studies evaluating work-related hand/wrist tendinitis
MSD prevalence
StudyStudydesign Study population
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Kurppaet al. 1991
Cohort: 31-monthfollow-up
377 meatcutters,meatpackers andsausage makerscompared to388 office workers,maintenanceworkers, andsupervisors.
Outcome: Defined asphysician-diagnosedtenosynovitis orperitendinitis of the handor forearm. Criteriawere swelling orcrepitation andtenderness to palpationalong the tendon andpain at the tendonsheath, in theperitendinous area, or atthe muscle-tendonjunction during activemovement of the tendon. deQuervain’s tendinitis: positive Finkelstein’stest (if not positive,included in tendinitisgroup). 25% ofdiagnoses made byphysicians outside plant,criteria unknown.
Exposure: Jobcategories selectedbased on whether ornot strenuous manualwork was required. Exposure data obtainedfrom previous publishedliterature and plant walk-throughs.
12.5/100 personyears(meatcutters)
25.3/100 personyears (meat-packers)
16.8/100 personyears (sausagemakers)
0.9/100person years(males)
0.7/100person years(females)
14 (meat-cutters)
38.5 (meat-packers)
25.6(sausagemakers)
5.7-34.4
11.7-56.1
19.2-77.5
Participation rate: >70%. Job transfersand employee termination followed upwith questionnaire. Questionnaireresponse rate over 70%.
Exposed and comparison groups weresimilar in age and gender mix, althoughgender varied with job.
If same diagnosis occurred at samesite in worker after 60 days, it wasconsidered new episode. Therefore,separate episodes may berecurrences, and thus influenceresults. Median interval of 233 daysbetween episodes.
Packers worked in temperatures 8E to10EC; sausage makers worked intemperatures 8E to 20EC.
Examiners were not blinded tooccupation of subjects.
Plant selected because of high numberof reports of musculoskeletaldisorders. All permanent workers inmeat cutting, sausage making andpacking departments were included,after 3 months of work. Case ascertainment: Workers in non-strenuous jobs may not have soughtmedical care for MSDs since they mightstill be able to perform their jobs.
5b-28
Table 5b–4 (Continued). Epidemiologic studies evaluating work-related hand/wrist tendinitis
MSD prevalence
StudyStudydesign Study population
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Luopajärviet al. 1979
Cross-sectional
152 femaleassembly linepackers in a foodproduction factorywere compared to133 female shopassistants in adepartment store. Cashiers wereexcluded fromcomparison group.
Outcome: Tenosynovitisand peritendinitisdiagnosed by interviewand physical exam.Physiotherapistperformed active andpassive motions, gripstrength tests,observation andpalpation. Medicalspecialists used thesefindings later todiagnose disordersusing predeterminedcriteria [Waris 1979].
Exposure: Exposure torepetitive work,awkward hand/armpostures, and staticwork assessed byobservation and videoanalysis of factoryworkers. No formalexposure assessmentof shop assistants.
55.9% 13.5% PRR= 4.13 2.63-6.49 Participation rate: 84%. Workersexcluded from participation forprevious trauma, arthritis and otherpathologies.
Examiner blinded to case status: Notstated in article.
No association between age and MSDsor length of employment and MSDs. Factory opened only short time. Hobbies and housework were notsignificantly associated with outcome.
Unable to examine effect of job-specific risk factors because of jobrotation.
5b-29
Table 5b–4 (Continued). Epidemiologic studies evaluating work-related hand/wrist tendinitis
MSD prevalence
StudyStudydesign Study population
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
McCormacket al. 1990
Cross-sectional
Textile workers: 4broad job categoriesinvolving intensiveupper extremityuse—sewing (n=562), boarding(n=296), packaging(n=369), and knitting(n=352); comparedto other non-officeworkers (n=468),including machinemaintenanceworkers,transportationworkers, andcleaners andsweepers.
Outcome: Assessed byquestionnaire andscreening physicalexam, followed bydiagnostic physicalexamination.
Tendinitis: Positivephysical findingssuggestive ofinflammation.
Severity reported asmild, moderate orsevere.
Exposure: To repetitivefinger, wrist and elbowmotions based onknowledge of jobs; noformal exposureassessment performed.
Boarding: 6.4%
Sewing: 4.4%
Packaging: 3.3%
Knitting: 0.9%
Overall exposedgroup: 3.75%
Other non-office: 2.1%
PRR=3.0
PRR=2.1
PRR=1.5
PRR=0.4
PRR=1.75
1.4-6.4
1.0-4.3
0.7-3.5
0.1-1.4
0.9-3.39
Participation rate: 90.5% for screening;93.6% of those screened went on tocomplete physical examination.
Stratified random sampling withinoccupational groups.
Not mentioned whether examinersblinded to exposure status (jobcategory).
Prevalence higher in workers with<3 years of employment. Race andage not related to outcome. Femalegender was a significant predictor oftendinitis (p=0.01), but job categorywas a stronger predictor (p=0.001).
10/12 physician examiners recordeddiagnoses within 12% of the mean forthe group.
47.9% of workers who had eitherpositive screening physical exams orreported symptoms on questionnairewere diagnosed with tendinitis ortendinitis-related syndromes.
5b-30
Table 5b–4 (Continued). Epidemiologic studies evaluating work-related hand/wrist tendinitis
MSD prevalence
StudyStudydesign Study population
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
Roto andKivi 1984
Cross-sectional
90 meatcutterscompared toreference group of72 constructionforemen who hadnot been exposed torepetitivemovements of theupper extremities intheir work. Allparticipants weremale.
Outcome: Tenosynovitisdefined as swelling,local pain and fingerweakness duringmovement (determinedby questionnaire andphysical exam).
Exposure: Based on jobtitle. Study groups wereselected based ongeneral knowledge ofjob tasks: meatcutters’work entailed physicalexertion of upperextremities andshoulders. Constructionforemen’s work did notinvolve repetitivemovements of the upperextremities. No formalexposure assessment.
4.5%
Symptomprevalence rate:30.0%
0.0%
Symptomprevalencerate: 10.0%
Indetermin-ate
PRR=3.09
Õ
1.43-6.67
Participation rate: 100% formeatcutters, 94% for comparisongroup.
Authors state that examiners wereblinded to occupation of subjectsbecause part of larger group of meatprocessing workers examined, but it isunclear whether construction foremen(referents) were examined separately.
Serologic testing for rheumatoidarthritis was done to control forpotential confounding (none detected).
Relatively strict diagnostic criteria usedto avoid false positive cases. Authorsnote that tenosynovitis occurred inyounger age groups.
Although the only diagnosed cases oftenosynovitis occurred in themeatcutters (none in the referents), theauthors were reluctant to inferassociation with meatcutting becauseof the relatively low prevalence rate(4.5%).
5b-31
5c-1
CHAPTER 5c Hand-Arm Vibration Syndrome
SUMMARYIn general, the studies listed in Table 5c–1 show strong evidence of a positive association between highlevel exposure to hand-arm vibration (HAV) and vascular symptoms of hand-arm vibration syndrome(HAVS). These studies are of workers with high levels of exposures such as forestry workers, stone drillers,stone cutters or carvers, shipyard workers, or platers. These workers were typically exposed to HAVacceleration levels of 5 to 36 m/s². These studies typically were cross sectional studies which examinedthe relationship between workers with high levels of exposures to HAV with a non-exposed control group.There is substantial evidence that as intensity and duration of exposure to vibrating tools increase, the riskof developing HAVS increases. There also is evidence that an increase in symptom severity is associatedwith increased exposure. As intensity and duration of exposure are increased, the time from exposureonset and beginning of symptoms is shortened.
As described above, the relationship between vibration exposure and HAVS was evaluated favorably withregard to other epidemiological causality criteria, including consistency and coherency of availableinformation and evidence describing the temporal sequence of exposure and outcome.
INTRODUCTION
The 20 epidemiologic studies discussed in thisreview were selected according to criteria thatappear in the introduction of this document. Inour review, we evaluated the studies accordingto criteria that enabled us to assess theresearch. These criteria, including adequateparticipation rate, definition of health outcomeby both symptoms and medical exam criteria,blinding of investigators to exposure/outcomestatus, and independent/objective measure ofexposure, also are described in detail in theIntroduction.
In reviewing the studies, we gave greatestqualitative weight to those which fulfilled all fourof the above criteria. Table 5c-1 (all tables arepresented at the end of the chapter)characterizes the 20 reviewed Hand-ArmVibration studies according to the fourevaluation criteria. Full summary descriptions ofall the studies appear at the end of the chapter.
In addition to the four criteria we used toevaluate the studies, we determined whetherstudies demonstrated statistically significantassociations between exposure attributes andhealth outcomes. We also examined whetherthe observed associations were likely to becaused or substantially influenced by majorstudy flaws, including confounding and selectionbias. Some of these limitations are shown in thedescriptions of individual studies (Table 5c–2).
We then reviewed and summarized the studieswith regard to standard criteria used byepidemiologists to evaluate the causalrelationship between a health outcome and anexposure of interest. These criteria includedstrength of association, temporal relationship,consistency of association, coherence ofassociation, and exposure-responserelationships.
In this review, results of each of the studies
5c-2
examined, whether negative, positive, orequivocal, contributed to the pool of data usedto make our decision regarding the strength ofthe causal relationship between HAVS andworkplace risk factors. Greater or lesserconfidence in the findings reflected theevaluation criteria described above.
Definition of HAV for HAVSHand-Arm Vibration is defined as the transferof vibration from a tool to a worker’s hand andarm. The amount of HAV is characterized bythe acceleration level of the tool when graspedby the worker and in use. The vibration istypically measured on the handle of tool whilein use to determine the acceleration levelstransferred to the worker.
EVIDENCE FOR THE WORK-RELATEDNESS OF HAVS
The hazardous effects of occupational exposureto HAV have been discussed in hundreds ofstudies dating to the work of Loriga in 1911.The composite of vibration-induced signs andsymptoms referred to as hand-arm vibrationsyndrome includes episodic numbness; tinglingand blanching of the fingers, with pain inresponse to cold exposure; and reduction ingrip strength and finger dexterity. These signsand symptoms are known to increase inseverity as exposure to vibration increases inintensity and duration.
A review of pertinent epidemiologic studies ofHAVS has been previously presented [NIOSH1989]; therefore, Table 5c–2 includes onlythose studies completed after 1989. Except fora few longitudinal studies of chain sawyers inthe United Kingdom, Finland, and Japan, theliterature comprises largely cross-sectionalstudies carried out within an industry. Cross-
sectional studies are limited in their ability toascertain temporal relationships betweenexposure and outcome. Because results areobtained at only one point in time, the cross-sectional study design also is subject tounderassessment of the health outcome(particularly in groups with longer durations ofemployment and higher participant attrition).
The studies included in this review varied indesign and quality of information. Sixteen werecross-sectional in design, and three wereprospective cohort in design. One study wasboth cross-sectional and prospective, including10 cross-sectional follow-ups over time and acohort group [Koskimies et al. 1992]. Thirteenof the 20 studies reported assessing case statususing physical exams, while other studies usedonly a questionnaire to determine outcomes. Ofthe studies in which the subjects underwent aphysical exam, five performed a coldprovocation test [Bovenzi et al. 1988; Bovenziet al. 1995; Brubaker et al. 1983; Brubaker etal. 1987; McKenna et al. 1993], threeperformed a nail compression test [Mirbod etal. 1992b; Nagata et al. 1993; Saito 1987],one performed a nerve conduction test[Virokannas 1995], one performedsensorineural physician testing [Bovenzi andBetta 1994], one performed a neurologicalexam [Shinev et al. 1992], one performed anAllan test [Nilsson et al. 1989] and one usedphysician judgement based on workers’complaints and history [Koskimies et al. 1992].
Twelve of the 20 studies conducted anexposure assessment of the tools subjects wereusing; an additional study used exposureassessment information the authors hadcollected in a previous investigation. Theremaining studies estimated exposures by self-
5c-3
report or job title.
The one study that met all four criteria and thefour studies which met the three criteria arediscussed in the following section. Detaileddescriptions for all 20 investigations can befound at the end of the chapter.
Comments Related to SpecificStudies of HAVSThe Bovenzi et al. [1995] cross-sectionalinvestigation of forestry workers comparedvibration white finger (VWF) in this group withshipyard worker referents. VWF wasdiagnosed by symptom report and coldprovocation test; vibration exposures wereestimated by questionnaire report on frequencyof chain saw work and types of saws used,along with direct measurement of vibrationproduced by 27 antivibration and 3 non-antivibration saws. Daily exposure to sawvibration was estimated by linking the twoassessments. The prevalence rates for VWFwere 23.4% in forestry workers and 2.6% inshipyard referents [Odds ratio (OR) 11.8, 95%Confidence Interval (CI) 4.5–31.1]. Forworkers using only antivibration saws, the ORwas 6.2 (95% CI 2.3–17.1); for those usingnon-antivibration saws, the OR was 32.3 (95%CI 11.2–93). A dose-response was observedfor VWF and lifetime vibration dose (OR 34.3,95% CI 11.9–99, for the highest category).Although participation rates were not stated forreferents, the participation appeared to be100% for forestry workers. Authors included10 retired workers to lessen the problems withselection out of the workforce. Resultsdemonstrated that antivibration saw use wasassociated with a lower prevalence of VWF.
Koskimies et al. [1992] examined vibrationsyndrome in a group of forestry workersemployed by the National Board of Forestry inFinland. All those employed in one parishparticipated in a series of 10 cross-sectionalstudies from 1972 to 1990. Results also werereported for a cohort of 57 individuals whoremained in the study from 1972 to 1986.HAVS symptoms were assessed byquestionnaire and physical exam criteria.Exposure to chain saw vibration wasdetermined by measurement of front handleacceleration. Cross-sectional analysis resultsshowed a monotonic decrease in prevalence ofVWF from 40% in 1972 to 5% in 1990. In thecohort of 57, VWF increased from 30% in1972 to 35% in 1975. VWF decreasedmonotonically to approximately 6% in 1986.Over the same time period, modifications ofchain saws used by the workers resulted in adecrease in saw vibration acceleration from 14m/s2 to 2 m/s2. The authors attributed the reduction inVWF to saw changes, although exposures andoutcomes were never linked for individualworkers. Strengths of the study includedobservation of similar results from the series ofcross-sectional analyses and full participationon the part of the 57 subjects. Limitationsincluded failure to assess chain saw exposuremeasures at the individual level. The studydemonstrated the potential for symptomimprovement after exposure reduction.
In the Nilsson et al. [1989] cross-sectionalstudy of male pulp mill machine manufacturingemployees, VWF was examined in a group of89 platers and 61 office workers. VWF wasascertained by physical exam and interview.For platers, vibration exposure was assessedby measuring acceleration intensity on a sample
5c-4
of tools and linking results to subjective ratingsof exposure time. Current and past exposureswere estimated for both platers and officeworkers (some office workers had experiencedexposures in the past). Prevalence for platerswith current exposure was 42%, in comparisonto 2.3% for office workers with no exposures(OR 85, 95% CI 15–486). When thoseexposed to vibration (platers plus officeworkers with previous vibration exposure)were compared to unexposed office workers,prevalences were 40.0% and 2.3%respectively (OR 56, 95% CI 12–269). Adose-response was observed for VWF andyears of exposure. The relationships betweenoutcome and exposure, after adjustment forage, were strong. Representativeness of thereferent group of office workers could not bedetermined.
Bovenzi [1994] examined HAVS cross-sectionally in 570 quarry drillers and stonecarvers, along with a referent group of polishersand machine operators who were not exposedto hand-transmitted vibration. HAVS wasassessed by physician interview, andsensorineural symptoms were staged andgraded. Exposure to vibrating tools wasassessed by interview and linked to vibrationmeasurements obtained from assessment of asample of tools. Prevalences of HAVS were30.2% in the exposed and 4.3% in theunexposed groups (OR 9.33, 95% CI4.9–17.8). Symptoms of VWF increased withlifetime vibration dose (OR 10.2, 95% CI4.8–21.6, for the highest category). Studystrengths included detailed exposureassessment and modeling of relationships,100% participation, and a very stable workpopulation. Because of the work populationstability, results were unlikely to be influenced
by participant attrition.
The Bovenzi et al. [1988] cross-sectionalinvestigation examined VWF in vibration-exposed stone drillers and stonecutters/chippers and a reference group ofquarry and mill workers. VWF was assessedby questionnaire and physical exam. Exposurewas assessed by measuring accelerationintensity on a sample of tools and linking it withself-reported exposure time. VWF prevalencerates were 35.5% in exposed and 8.3% inunexposed groups (OR 6.06, 95% CI2.0–19.6; OR 4.26, 95% CI 1.8–10.4). Asignificant association was observed betweenvibration acceleration level and severity ofVWF symptoms (0% and 18.4% in the lowestand highest categories, respectively).
Strength of Association One of the studies examined met all four of theevaluation criteria [Bovenzi et al. 1995]. Fiveinvestigations met three of the criteria [Bovenziet al. 1988, 1994; Kivekäs et al. 1994;Koskimies et al. 1992; and Nilsson et al.1989]. The criterion that was not met (or notreported) by four of the studies was blinding ofthe physician with regard to worker job status.However, most studies used objectivemeasures for determining case status: coldprovocation [Bovenzi et al. 1988, 1995],sensorineural physician grading [Bovenzi andthe Italian Study Group 1994], and the Allantest [Nilsson et al. 1989]. Use of objectivemeasures lessens the likelihood that case statuswas influenced by knowledge of participants’exposures.
In the Bovenzi et al. [1988] cross-sectionalinvestigation, vibration-exposed stone drillers
5c-5
and stone cutters/chippers showed a 6.06-fold(95% CI 2.0–19.6) increase in risk of VWF incomparison to unexposed quarry and millworkers. Similar results were observed inanother study of stone workers conducted byBovenzi in 1994. Quarry drillers and stonecarvers exposed to vibration showed an OR forVWF of 9.33 (95% CI 4.9–17.8) whencompared to a reference group of polishers andmachine operators. A dose-responserelationship was observed for VWF andlifetime vibration dose, with an OR of 10.2(95% CI 4.8–21.6) for the highest exposurecategory. A study of forestry workers [Bovenziet al. 1995] demonstrated an OR of 11.8 (95%CI 4.5–31.1) for VWF when comparingforestry workers with exposure to chain sawvibration to an unexposed group of shipyardworkers. A lower risk of VWF (OR 6.2, 95%CI 2.3–17.1) was observed for those using onlyantivibration saws. A dose-response betweenVWF and vibration exposure also was observedin this investigation, with an OR of 34.3 (95%CI 11.9–99) for the highest exposure category.Nilsson et al. [1989] observed very strongrelationships between VWF and exposure tovibration in machine manufacturing platers. Incomparison to office workers with noexposure, platers had an OR of 85 (95% CI15–486). Kivekäs et al. [1994] found asignificantly increased OR in the cumulativeincidence of HAVs in a 7-year cohort study(OR 6.5, 95% CI 2.4–17.5). Koskimies et al.[1992] examined a dynamic cohort of forestryworkers at 10 intervals from 1972 to 1990during which time saws were being modified inweight, vibration frequency, and vibrationacceleration. Over the 18-year period, amonotonic decrease in VWF was observed inthe 10 cross-sectional examinations, with anoverall eight-fold reduction in prevalence. Asubset of workers followed
from 1972 to 1986 showed a decrease inVWF from 30% to 6%. The reductions wereattributed to modifications in chain saws duringthe same time period.
The remaining, less rigorous, studies showedvarying relationships between HAVS andexposure. The majority of the studiesdemonstrated moderate to strong positiveassociations. Most compared exposed tounexposed groups with little or no detailedanalysis by exposure level. Two investigationsexamined HAVS in exposed groups and foundan increase in risk by years of employment,with ORs of 8.4 and 8.9 (95% CI 2.9–28.9)when comparing the highest and lowestcategories [Mirbod et al. 1992b; Kivekäs et al.1994]. Another study that examined HAVSprevalence in power tool users found noassociation with duration of employment (with aparticipation rate of only 38%) [Musson et al.1989]. For other investigations, exposed andunexposed groups were defined by job titles.ORs for these studies ranged from 3.2 to 40.6(relative risk [RRs] from 3.2 to 16) [Brubakeret al. 1983; Dimberg and Oden 1991; Letz etal. 1992; McKenna et al. 1993; Mirbod et al.1992a; Mirbod et al. 1994; Nagata et al.1993]. Three studies demonstrated varyingHAVS rates for exposed groups, but includedno referents [Shinev et al. 1992; Starck et al.1990; Virokannas and Tolonen 1995].
Two investigations produced conflictingevidence related to the effects of chain sawmodifications on HAVS in forestry workers.The Brubaker et al. [1987] study, observed a28% increase in prevalence of VWF in acohort of tree fellers over a 5-year period andclaimed that saw modifications were ineffective.Saito [1987] found no new HAVS symptom
5c-6
development over 6 years in a cohort of chainsawyers in reducing symptoms.
Comparing construction workers to officeworkers, one study demonstrated an OR of 0.5(95% CI 0.1–11.8) for HAVS. This study metnone of our four criteria [Miyashita et al. 1992].
In general, the studies in Table 5c-1 showstrong evidence of a positive associationbetween exposure to HAV and vascularsymptoms of HAVS.
TemporalityThe temporal relationship between HAVexposure and symptoms of HAVS is wellestablished by studies which have determinedthe latency between exposure and symptomonset. Of 52 studies reviewed by NIOSH in1989, 44 included some information about thelatency period for the development of vascularHAVS symptoms following initial exposure.Latency ranged from 0.7 to 17 years, with amean of 6.3 years. Unfortunately, because mostof these studies were cross-sectional (i.e.,latency was determined retrospectively) andbecause HAVS develop slowly, the possibilityof recall bias is strong [Gemne et al. 1993].However, longitudinal studies provide supportfor the temporal nature of the association.Kivekäs et al. [1994], in a 7-year follow-up ofFinnish lumberjacks, found a cumulativeincidence rate (IR) of 14.7%, compared to acumulative IR of only 2.3% among referents.The cumulative IR of lumberjacks who hadmore than 25 years of exposure at the end ofthe follow-up period was 30.6%. Other studiesof Finnish forestry workers also showed amarked decrease in HAVS prevalencefollowing the introduction of improved chain
saws [Pyykkö and Starak 1986; Koskimies etal. 1992].
ConsistencyThe literature consistently shows that workersexposed to HAV develop HAVS at asubstantially higher rate than workers notexposed to vibration. Although there isconsiderable variation in the occurrence ofHAVS among different groups using similartypes of vibrating tools, the lack of consistencyprobably is explained by methodologicaldifferences between studies (i.e., someresearchers did not account for exposurevariation over time in the summary estimate ofexposure) or by differences in work methods,work processes, and work organization[Gemne et al. 1993]. Important also is thedifference in the intensity and duration ofexposure.
Coherence of Evidence
The mechanisms by which HAV producesneurological, vascular, and musculoskeletaldamage are supported by some experimentalevidence [Armstrong et al. 1987b; Lundborg etal. 1990; Necking et al. 1992]. Neurologicaland circulatory disturbances probably occurindependently and by unrelated mechanisms.Vibration may directly injure the peripheralnerves, nerve endings, and mechanoreceptors,producing symptoms of numbness, tingling,pain, and loss of sensitivity. Vibration also mayhave direct effects on the digital arteries. Theinnermost layer of cells in the blood vessel wallsappears especially susceptible to mechanicalinjury by vibration. If these vessels aredamaged, they may become less sensitive to theactions of
5c-7
certain vasodilators that require an intactendothelium. Experiments involvinglumberjacks exposed to chain saw vibrationsupport this hypothesis [Gemne et al. 1993].There also is evidence that the walls of thedigital blood vessels are thickened in personswith HAVS [Takeuchi et al. 1986]. Duringcold exposure, vessels with these changes willbecome abnormally narrow and may closeentirely [Gemne 1982]. Symptoms of numbnessand tingling which characterize HAVS may besecondary to vascular constriction of the bloodvessels, resulting in ischemia in the nerve-endorgans.
Other evidence concerning the coherence ofinformation regarding the association betweenvibration exposure and HAVS relates tobackground prevalence of similar disorders inthe general population. One estimate placed theprevalence of Raynaud's phenomenon at 4.6%for females and 2.5% for males in the generalpopulation [Iwata and Makimo 1987]. Only 7of the studies examined in this review foundprevalence rates less than 20% among workersexposed to HAV. In the 1989 NIOSH review,only 9 of 52 cross-sectional studies reported aprevalence rate of less than 20% amongworkers exposed to HAV. This providesstrong evidence that individuals working invibration-exposed occupations are at muchhigher risk of these disorders than those in thegeneral population.
Exposure-Response RelationshipExposure-response relationships involvingHAV have been postulated, including: (1) arelationship between the prevalence of HAVSand vibration acceleration (and cumulativeexposure time), (2) a relationship between thedose and symptom severity, and/or (3) a
relationship between the dose and the latencyof symptom onset.
Support for the first relationship is provided bya few longitudinal studies of workers exposedto HAV. In general, all show strong evidencethat decreasing the acceleration level of a hand-held vibrating tool has a positive relationshipwith prevalence of HAVS. In a study of Finnishforestry workers using chain saws, Koskimieset al. [1992] found that the prevalence ofHAVS symptoms declined from a peak of 40%to 5% after the introduction of light-weight,low-vibration chain saws with reducedacceleration from 14 to 2 m/s2. Likewise, astudy of similar workers in Japan found that theprevalence of vascular symptoms among chainsaw operators who began their jobs before theintroduction of various engineering andadministrative controls peaked at 63%.(Vibration acceleration levels for chain sawsused during this period ranged from 111 to 304m/s2.) In contrast, the peak prevalence forchain saw operators who began working afterthe introduction of antivibration chain saws(acceleration level: 10-33 m/s2) and exposureduration limits (2 hrs/day) was only 2%[Futatsuka and Uneno 1985, 1986].
NIOSH authors ranked 23 cross-sectionalstudies that measured HAV acceleration levelsand estimated a prevalence rate for vascularsymptoms [NIOSH 1989]. To test whether alinear relationship existed between the HAVlevel and the prevalence of vascular symptoms,a correlation coefficient was calculated. Thecorrelation analysis found a statisticallysignificant linear relationship between HAVacceleration level and prevalence of vascularsymptoms (R 0.67, p<0.01), indicating thatprevalence of vascular symptoms tendsto increase as the HAV acceleration level
5c-8
increases. However, the absorption of vibrationenergy by the hand is influenced by thevibration intensity, as well as by frequency,transmission direction, grip and feed forces,hand-arm postures, and anthropometric factors[Gemne et al. 1993].
Several studies reviewed for the currentdocument found relationships betweenprevalence of HAVS and duration of vibration-exposed work [Bovenzi 1994; Bovenzi et al.1995; Letz et al. 1992; Nilsson et al. 1989].One cross-sectional study with a very poorresponse rate found no association withduration of exposure [Musson et al. 1989].
Justification for a relationship between dose andHAVS prevalence and symptom severity isprovided by Bovenzi et al. [1988] and Mirbodet al. [1992b]. In a study of stone-cutters usingrock drills and chisel hammers, Bovenzi foundthat HAVS prevalence increased linearly withthe total number of working hours, from about18% for persons with 6,000 hrs of exposure, tomore than 50% among persons with more than26,000 hrs of exposure. Likewise, in a study of447 workers using chain saws, Mirbod et al.[1992b] found that the prevalence of HAVSincreased from 2.5% among workers with lessthan 14 years of exposure to 11.7% amongworkers with 20–24 years exposure, to 20.9%among workers exposed 30 years or more.Both studies found a statistically significantcorrelation between the severity of symptoms(graded according to the Taylor-Pelmear scale)and a dose measure based on total exposuretime.
Support for a relationship between dose and
latency of symptom onset is provided by Britishstudies conducted in the 1970s among variousoccupational groups, including chain sawyers,grinders, chiselers and swagers [Gemne et al.1993]. Exposure to 10-25 m/s2 chainsawvibration correlated with a latency of about 3years. Pedestal grinders using machines withzirconium wheels were exposed to vibrationlevels of 50 m/s2 and demonstrated a meanlatency of 1.8 years, whereas grinders whoused softer wheels with accelerations of 10-20m/s2 had a mean latency of 14 years. Exposureto 70 m/s2 vibration during swaging correlatedwith a mean latency of about 7 months,although some swagers developed symptoms inas few as 6 weeks.
Confounding and HAVSAge and metabolic disease are the primarypotential confounders for HAVS.
It is important that epidemiologic studiesexamine non-occupational factors, and controlfor them. Most of the studies were able toaddress “age” by stratification in their analyses,or through use of multiple logistic regression.[Bovenzi and Betta 1994; Bovenzi et al. 1995;Brubaker et al. 1983, 1987; Kivekäs et al.1994; Letz et al. 1992; McKenna et al. 1993;Mirbod et al. [1994]. Several authorscontrolled for metabolic disease [Bovenzi andBetta 1994; Bovenzi et al. 1995; Letz et al.1992; McKenna et al. 1993]. This is importantbecause of the effects that some disorders haveon peripheral circulation which may havesymptoms similar to HAVS.
Nonoccupational Raynaud’s phenomena - a
5c-9
rare disorder which mimics HAVS has beenknown to occur in individuals with metabolicdisorders, peripheral neuropathy, alcohol-related illness, as well as other conditions.
In reviewing the methods and results of thesestudies, taking into account substantiallyelevated ORs and evidence of dose-responserelationships, it appears that potentialconfounders do not account for the consistentrelationships seen.
Review of the 20 studies, leads us to theconclusion that there is substantial evidence thatas intensity and duration of exposure tovibrating tools increase, the risk of developing
HAVS increases. Most of the studies showed apositive association between high levelexposure to HAV and vascular symptoms ofHAVS. For many of the studies there is astrong association between HAVS andexposure to vibrating tools in the workplace.The temporal relationships and consistencybetween exposure and symptoms of HAVS arewell established in these studies. Themechanisms by which HAV producesneurological, vascular, and musculoskeletaldamage are supported by some experimentalevidence. Many of the studies showed anexposure-response relationship between doseof HAV and the HAVS prevalence andsymptom severity.
Table 5c-1. Epidemiologic criteria used to examine studies of hand/wrist and hand/arm MSDs associated withvibration
Study (first author andyear)
Riskindicator
(OR, PRR, IRor p-
value)*,†Participation
rate $$70%
Physicalexamination
or coldprovocation
Investigatorblinded to
case and/orexposure
status
Basis for assessinghand/wrist or hand/armexposure to vibration
Met all four criteria:
Bovenzi 1995 6.2–32.3† Yes Yes Yes Observation or measurements
Met at least one criterion:
Bovenzi 1988 6.06† NR‡ Yes NR Observation or measurements
Bovenzi 1994 9.33† Yes Yes No Observation or measurements
Brubaker 1983 NR Yes Yes NR Job titles or self-reports
Brubaker 1987 NR No Yes NR Observation or measurements
Dimberg 1991 NR† Yes No NR Job titles or self-reports
Kivekäs 1994 3.4–6.5† Yes Yes Yes Job titles or self-reports
Koskimies 1992 NR Yes Yes NR Observation or measurements
Letz 1992 5.0–40.6† Yes No No Job titles or self-reports—previous study results used
McKenna 1993 24.0† NR Yes No Job titles or self-reports
Mirbod 1992a, 1994 3.77† NR No NR Observation or measurements
Mirbod 1992b NR NR Yes No Observation or measurements
Musson 1989 NR No No NR Observation or measurements
Nagata 1993 7.1† NR Yes No Job titles or self-reports
Nilsson 1989 14–85† Yes Yes NR Observation or measurements
Saito 1987 NR No Yes NR Job titles or self-reports
Shinev 1992 NR NR Yes NR Observation or measurements
Starck 1990 NR NR No No Observation or measurements
Virokannas 1995 NR† NR Yes NR Observation or measurements
Met none of the criteria:
Miyashita 1992 0.5 NR No No Job titles or self-reports
*Some risk indicators are based on a combination of risk factors–not on vibration alone (i.e., vibration plus force, posture,or repetition). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).
†Indicates statistical significance. If combined with NR, a significant association was reported without a numerical value.‡Not reported.
5c-10
(Continued)
Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
Bovenzi etal. 1988
Cross-sectional
Vibration-exposed stonedrillers (n=32) and stonecutters/chippers (n=44);quarry and mill workersnot exposed to vibration(control group, n=60).
Outcome: Assessed byphysical examination andquestionnaire. VWFsymptoms staged using theTaylor-Pelmear scale.
Exposure: Vibrationexposure assessed bymeasuring the accelerationintensity on a sample of tools,together with subjectiveratings of exposure time.
35.5% 8.3% 6.06 2.01-19.6 Participation rate: Participationrate cannot be determined fromdata in the study.
Significant associationbetween vibration accelerationlevel and severity of VWFsymptoms.
Mean latency period tosymptom onset =12.3 yr.
Frequency-weightedacceleration levels ranged from19.7 to 36.4 m/s2 (rock drillsand chipping hammers) andfrom 2.4 to 4.1 m/s2 (grindersand hand cutters).
5c-12
Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Bovenziand theItalianGroup 1994
Cross-sectional
Case group: Stoneworkers employed in ninedistricts in Northern andCentral Italy: 145 quarrydrillers and 425 stonecarvers exposed tovibration. Referent group: polishers and machineoperators (n=258) whoperformed manual activityonly not exposed tohand-transmittedvibration.
Outcome: HAVs assessedby physician-administeredinterview; sensineuralsymptoms staged accordingto Brammer [1992]. Gradedaccording to the Stockholmscale [Gemne 1987].
Exposure: To vibrating toolsassessed by interview. Vibration measured in asample of tools used.
30.2% 4.3% 9.33 4.9-17.8 Participation rate: 100% “Allthe active stone workersparticipated in the study, soself-selection was not asource of bias.”
Physician administered thequestionnaires containing workhistory and examinations, sounlikely to be blinded to casestatus.
Adjusted for age, smoking,alcohol consumption, andupper limb injuries.
Leisure activities, systemicdiseases included inquestionnaire. Univariateanalysis showed noassociation between systemicdiseases and vibration so wasnot criteria for exclusion.
Univariate analysis showed noassociation between systemicdiseases and vibration so wasnot criteria for exclusion.Dose–response for CTS andlifetime vibration exposure notsignificant.
Frequency-weightedacceleration levels = 15 m/s2
(stone drills), 21.8 m/s2 (stonehammers), 2.84 m/s2 (rotarygrinding tools).
Percent of workers affectedwith HAVs increased inproportion to the square root ofthe exposure duration.
5c-13
Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Bovenzi etal. 1995
Cross-sectional
222 active forestryworkers and 10 retiredforestry workers with>400 hr of sawingcompared with 195randomly chosenshipyard workers neverexposed to handvibration. Controlsexcluded forcardiovascular andmetabolic disease.
Outcome: (1) History ofepisodes of cold provokedwell–demarcated blanching inone or more fingers and(2) occurrence afteremployment and exposure tohand vibration and vibrationwhite finger (VWF) attacks inlast 2 years and (3) abnormaldigital arterial response tocold provocation. Clinically,VWF graded using Stockholmscale.Exposure: Vibrationmeasured on front and rearof 27 antivibration (AV) chainsaws used in the forest; forprevious exposureassessment, 3 non-AV chainsaws were measured. Vibration measurementswere made in the field duringcross-cutting operations byskilled workers according toISO 7505.
Forestry workers gavedetailed list of chain sawsused.Workplace questionnairesvalidated by direct interviewswith employers andemployees, employmentrecords, and amount of fuelused by chain saws
Daily exposure to sawvibration assessed in termsof 8-hr energy–equivalentfrequency–weightedacceleration.
All Forestryworkers:23.4%
Workers usingonly AV chainsaws: 13.4%
Workers usingchain sawswithoutvibrationisolationsystems:51.7%
Shipyardworkers:2.6%
(adjustedOR’s)11.8
6.2
32.3
VWFoperators ofnon-AV andAV saws vs.Operators ofantivibrationsaws only:OR=4.0
Lifetimevibrationdosein 9m(m2S-4 hd)<19: OR=4.119-20: OR=4.720-21: OR=9.4>21: OR=34.3
4.5-31.1
2.3-17.1
11.2-93
1.1-16.4
1.3-16.1
3.1-28.4
11.9-99
Participation rate: 95% vibratingtool users, not reported forcontrol.Analysis controlled for age,smoking, drinking habits.
Physicians blinded to casestatus–since cold provocationtest was used, it was not anissue.Smoking, alcohol, metabolic,cardiovascular, neurologic,previous musculoskeletalinjuries, use of medicinesincluded in questionnaire andaccounted for in logisticregression model.
Cold provocation testingperformed on both forestryworkers and controls.
Exposure–responserelationship found betweenVWF and vibration exposure:the expected prevalence ofVWF increased almost linearlyto either the 8-hrenergy–equivalentfrequency–weightedacceleration or the number ofyears of exposure (withequivalent accelerationunchanged).
5c-14
Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Brubaker etal. 1983
Cross-sectional
146 tree fellers in 7camps employed for $1year compared to 142workers not exposed tovibration matched forlocation.
Outcome: VWF symptomsstaged using Taylor-Pelmearscale.
Ischemic water bath testingfor VWF completed on allsubjects.
Exposure was based onquestionnaire data.
Withsymptoms:51%
Stage 3: 22%
Excludingother vibrationexposure andmedicalhistory: 54%
Stage 3: 25%
Withsymptoms:5%
Stage 3: 2%
2%
Stage 3: 1%
Õ Õ Participation rate: 100%.
Smoking, no significantdifferences.
Age was significantly differentbetween cases and controls.
Height and weight notsignificantly different.
Mean latency period betweenwork and symptoms 8.6 years.
Records of duration ofexposure.
5c-15
Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Brubaker etal. 1987
Cohort: 5-yearfollow-upofexposedgroup.
Fellers at Canadianlumber camps (n=71)who hadbeen interviewedand tested in 1979 to1980 then again in1984 to 1985.
Outcome: Defined as HAVssymptoms, assessed byquestionnaire and digitsystolic blood pressure.
VWF symptoms staged usingTaylor-Pelmear scale.
Ischemic water bath testingfor VWF completed on allsubjects.
Exposure: Vibrationmeasurements recorded froma representative sample ofchain saws used in thelogging camp.
Raynaud’ssymptoms:53% (1984 to 1985)
Tingling,numbness:56% (1984 to 1985)
Raynaud’ssymptoms:51% (1979 to1980)
Tinglingnumbness:65% (1979 to1980)
Õ Õ Participation rate: 53%.
Original group (1979 to 1980)included 146 fellers.
16 fellers excluded because ofpotential confounders.
Author concluded antivibrationsaws not effective atpreventing HAVs.
15% of fellers reported newsymptoms of VWF over 5-yearperiod.
28% increase in prevalence ofVWF in workers usingantivibration chain-saws.
Correlation between objectivetest and symptoms poor: 54%reporting symptoms withpositive findings on objectivetests.
5c-16
Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Dimbergand Oden1991
Cross-sectional
2,814 Aircraft engineworkers.
68 Sheet metal workers.26 Polishers/grinders.20 Cleaners.40 Forklift-truck drivers.46 Engine testers.146 Fitters.49 Storemen38 Electric welders.
No control group used.
Outcome: Exposure tovibrating hand-toolsassessed by questionnaire. White fingers as a spasm inblood vessels occurring inone or more fingers inconnection with coolingleading to reversible pallorfollowed by redness.
Exposure: Vibrationassessed by questionnaire:working with vibrating tools,time in present job, leisureactivities.
23%(polishers/grinders)
19% (sheetmetalworkers)
15%(cleaners)
Õ Multivariateanalysisshowedincreasedsymptomswithincreasingage, workwith vibratinghand toolsand weightloss
Õ Participation rate: 96%questionnaire.
Vibrating tool use significantlycorrelated with HAVs symptomprevalence.
Analysis was stratified bygender, age, and employmentcategory.
5c-17
Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Kivekäs etal. 1994
Cohortwith7-yearfollow-up(1978 to1985)
213 lumberjacks and140 referents.
Outcome: HAVs assessedby questionnaire, clinicalexamination, andradiographs.
Exposure: Not measured. Exposure history determinedvia questionnaire.
Prevalence(HAVs)
1978: 16.9%
1985: 24.9%
Cumulativeincidence,HAVs (7years): 14.7%
Prevalence(HAVs):
1978: 5.0%
1985: 5.7%
CumulativeincidenceHAVs (7years): 2.3%
For 1978:OR= 3.4
For 1985:OR= 4.4
OR=6.5
1.7-6.9
2.3-8.1
2.4-17.5
Participation rate: 76% amongexposed workers, 78% amongcontrol.
Follow-up group included 76%of lumberjacks and 78% ofreferents from original group.
Adjusted for age.
X-ray films read by radiologistsblinded to case status
After adjusting for age, nodifference in lumberjacks with<15-years exposure andreferents, but risk increasedwith increasing duration ofexposure. For those exposedRR=8.9 (2.9-28.9).
No X-ray differences inprevalence of detectabletranslucencies or osteoarthriticchanges in wrists or hands.
5c-18
Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Koskimieset al. 1992
Cohort(18-yearfollow-up)
Finnish forest workers(n=118-124).
Outcome: HAVs assessedby questionnaire andphysical examination.
Exposure: Vibrationacceleration of the fronthandle of chain sawsanalyzed.
Prevalence ofHAVs amongforestryworkers in1990: 5%
Prevalenceof HAVsamongforestryworkers in1972: 40%
Õ Õ Participation rate: 100% ofthose who had a yearlyphysical exam.
Decrease in prevalenceattributed to reduction in weightof saws, increase in vibrationfrequency, and reduction invibration acceleration (from 14to 2 m/s2).
5c-19
Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Letz et al.1992
Cross-sectional
Shipyard workers withfull-time vibrationexposure (n=103); part-time vibration exposure(n=115), and no vibrationexposure (n=53,comparison group).
Outcome: HAVs assessedby self-administeredquestionnaire; gradedaccording to the Stockholmscale.
Vibration measurements from51 pneumatic tools made in 3studies. Extreme variabilityprecluded direct comparisonof tools. Number of hours perweek and years using toolsasked.
Vascularsymptomsamong part-time vibration-exposedworkers: 33%
Vascularsymptomsamong full-time vibration-exposedworkers:70.9%;
Sensorineuralsymptomsamong part-time vibration-exposedworkers:50.4%
Sensorineuralsymptomsamong full-time vibration-exposedworkers:83.5%
Vascularsymptoms:5.7%
Sensori-neuralsymptoms:17%
Part-timevibration-exposedworkers vs.controls:OR=8.23
Full-timevibration-exposedworkers vs.controls:OR=40.6
Part-timevibration-exposedworkers vs.controls:OR= 5.0
Full-timevibration-exposedworkers vs.controls:OR=24.7
2.3-35.4
11-177
2.1-12.1
9.5-67
Participation rate: 79%.
Participants randomly selectedwithin departments.
Significant exposure–responserelationship found afteradjustment for smoking, notage or race.
Average latency to symptomonset <5 years.
Alcohol consumption, pastmedical conditions consideredin analysis.
Exposure–responserelationship found regardingself-reported cumulativeexposure to vibratory tools,sensorineural stages, andcorresponding vascularclassifications but no furtherincreases in workers with >17,000 hr of exposure.
Median latency for appearanceof symptoms of white fingerwas 8,400 hr of vibratorytool/use and 8,200 hr fornumbness.
Participants not blinded topurpose of questionnaire mayhave been over-reporting.
5c-20
Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
McKennaet al. 1993
Cross-sectional
46 pairs of riveters andmatched control subjects(machine operators whohad never used vibratingtools).
Outcome: Defined as cold-induced digital vasospasm.
Exposure: To specific toolsassessed via questionnaire.
35% 2% 24 3.1-510 Participation rate: Not reported.
Matched on age and smokinghabits.
Only males studied.
Excluded those with injury toneck, trunk, upper limbs.
44% of riveters had <2.5 yearsof vibration exposure.
Did not of blind examinersbecause they tested the mostsymptomatic finger.
No differences in resting fingersystolic pressure, vibrationperception, or fingertemperature between casesand controls.
17% of riveters reportedsymptoms of VWF.
5c-21
Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Mirbod etal. 1992b
Cross-sectional
Forestry workers(n=447)
No control group used.
Outcome: HAVs assessedby interview and physicalexamination. Symptomsgraded using theStockholm scale.
Frequency-weightedvibration-accelerationmeasurements made on thehands of chainsaw operators duringdifferent job processes.
9.6% overall
20.9% amongworkers with30 or moreyearsexperience
2.5% amongworkers <14years
11.7% 20 to24 years
Õ Õ Õ Participation rate: Not reported.
HAVs symptom severitypositively correlated withexposure duration.
Chain saw vibration levelsranged from 2.7 to 5.1 m/s2. Low prevalence attributed torecent improvements inworking conditions.
5c-22
Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Mirbod etal. 1994;Mirbod etal. 1992a
Cross-sectional
(A) 164 male dentaltechnicians, (B) 54 maleorthopedists, (C) 256male aircraft technicians,(D) 79 male laborers,(E) 27 male grinders,(F) 46 female sewing-machine operators,(G) 23 male tea-harvesting-machineoperators, (H) 272 malechain-saw operators;compared with 1,027males and 1,301 femalesnot exposed to vibration.
Outcome: HAVs assessedby questionnaire, interviews,field visits, or annual healthexaminations.
Exposure: To vibratingtools assessed byquestionnaire andinterviews. Hand-transmitted vibrationmeasured among a sampleof workers usingrepresentative tools in actualwork activities.
(See firstcolumn for jobcategories)
A: 4.8%B: 3.7%C: 2.3%D: 2.5%E: 3.7%F: 4.3%G: 0.0%H: 9.6%
Males: 2.7%Females: 3.4%
H vs.unexposedMales: 3.77
2.1-6.8 Participation restricted toworkers age 30 to 59 years. Subjects stratified by age inanalysis.
Hand-transmitted vibrationlevels in groups A to G rangedfrom 1.1 to 2.5 m/s2. Hand-transmitted vibration levels ingroup H ranged from 2.7 to 5.1m/s2.
5c-23
Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Miyashitaet al. 1992
Cross-sectional
355 Male constructionworkers (machineoperators) comparedwith 44 male officeworkers. (A) 184 power shoveloperators.(B) 127 bulldozeroperators.(C) 44 forklift operators.
Outcome: HAVs assessedby self-administeredquestionnaire.
Exposure: Status assumedfrom job title (no objectivemeasurements performed).
1.1% 2.3% 0.5 0.1-11.8 Participation rate: Not reported.
Participation restricted to maleworkers age 30 to 49.
Vibration due to construction-machinery operation.
5c-24
Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Musson etal. 1989
Cross-sectional
Impact power-tool usersin The Netherlands(n=169).
No control group used.
Outcome: HAVs based onsymptoms, assessed viapostal questionnaire.
Exposure: Vibration intensitymeasured using fiverepresentative tools. Duration of vibrationexposure assessed viaquestionnaire.
17% Õ Õ Õ Participation rate: 38%questionnaire.
Adjusted for age.
Exposure duration not relatedto HAV symptoms.
5c-25
Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Nagata etal. 1993
Cross-sectional
179 chain-saw workersand 205 local inhabitantswho had never usedvibrating tools (controlgroup).
Outcome: HAVs assessedby dermatological tests andphysical examination.
Exposure: Vibration notmeasured directly; exposureduration expressed as yearssince commencement ofoccupation.
>20-yearsexposure:16%
< 20-yearsexposure:2.4%
2.9% 7.1 for >20-yearsvibrationexposure
2.5-19.9 Participation rate: Not reported.
Adjusted for age.
Examiners not blinded toexposure status.
5c-26
Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Nilssonet al.1989
Cross-sectional
Platers (n=89) and officeworkers (n=61) dividedinto 4 groups accordingto current and pastvibration exposure.
Outcome: Assessed byphysical examinationand interview. VWFsymptoms staged usingthe Taylor-Pelmear scale.
Exposure: Vibrationexposure assessed bymeasuring theacceleration intensity ona sample of tools,subjective ratings, andobjective measures ofexposure time.
Platers withcurrentexposure:42%
Platers withcurrent andformerexposure.
Platers andofficeworkers withcurrent orformerexposure.
Officeworkerswith noexposure:2%
Officeworkerswith novibrationexposureand formerexposure.
Officeworkerswith novibrationexperience.
85
14
56
15- 486
5-38
12-269
Participation rate: 79% amongplaters, not reported amongcontrol.
Controlled for age.
Vibration acceleration levels=5.5 m/s2 (grinders), 10.3 m/s2
(hammers), 1.5 m/s2 (diegrinders).
Mean latency to symptom onset= 9.8 years.
Odds ratio increased by 11%for each year of exposure. Nocorrelation between the Taylor-Pelmear stage and years ofexposure.
5c-27
Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Saito 1987 Cohort: 6-yearfollow-upprospect-ive
Chain sawers withoutHAV symptoms in 1978(n=155) followed up in1983.
Outcome: Assessed bysymptoms, skin temperature,vibration threshold, nailcompression, pain sense,and cold provocation.
Exposure: Chain sawoperating time determined byquestionnaire.
0% in 1983 0% in 1978 Õ Õ Participation: Follow-up ofcohort.
Improvements in chain sawdesign, age restrictions, and adecrease in weekly operatingtime credited for preventingHAV.
Recovery rates of skintemperature after 10-minprovocation test significantlybetter in 1982 and 1983compared to 1978.
Vibratory sense thresholds at5th minute after coldprovocation significantly betterin 1980, 1982, and 1983compared with 1978.
Age significance correlated torecovery rates from 1978 to1983.
5c-28
Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Shinev etal. 1992
Cross-sectional
77 male fettlers; 59 malemolders; 85 malepolishers.
No control group used.
Outcome: HAV assessed byneurological examination.
Exposure: Vibrationcharacteristics of chippingand caulking hammers, airtampers, and polishingmachines measured.
22.1%(fettlers)6.8%(molders)25%(polishers)
Õ Õ Õ Participation rate: Not reported.
Percussive vibration hadgreater effect on muscle andbone pathology than constanthigh-frequency vibration.
5c-29
Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Starck etal. 1990
Cross-sectional
Forest workers (n=200),pedestal grinders (n=12),shipyard workers(n=171), stone workers(n=16), and platers (n=5).
No control group used.
Outcome: HAV based onsymptoms, assessed viaquestionnaire.
Exposure: Vibrationmeasurements taken on asample of tools during normaloperation at the workplace.
40% (forestworkers using1st generationchain saw)
16% (forestworkers using2ndgenerationchain saw)
<7% (forestworkers using3rd generationchain saw)
100% (forpedestalgrinders withzirconiumwheels)
5% (shipyardworkers)
75% (stoneworkers usingpneumatichammers)
50% (stoneworkers usingchisel heads)
40% (platers)
Õ Õ Õ Participation rate: Not reported.
No demographic data aboutstudy participants provided.
Poor correlation betweenvibration exposure and HAVwhen tools were highlyimpulsive.
5c-30
Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome
MSD prevalence
StudyStudydesign Study population Outcome and exposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
VirokannasandTolonen1995
Cross-sectional
Railway workers (n=31)and lumberjacks (n=32)exposed to HAV. Nocontrols used. Articleevaluates the vibrationperception threshold(VPT) among exposedworkers and tries todetermine a dose-response relationshipbetween exposure toHAV and the VPTs.
Outcome: “History of attack”of white finger reported bysubjects.
VPT and electroneuro-myography used asindicators of sensory nervedamage (outcome measure).
Exposure: To vibrating toolsassessed by interview. (Nomeasurements performed). Groups asked aboutexposure time with self-estimated annual use ofvibrating tools and vehicles(hr) and number of years ofexposure to vibration. Mean(SD) duration of exposure tovibration was 8,050 (3,500)among railway workers and21,250 (10, 950) hrs amonglumberjacks.
Railwayworkers: 45%VWF
Lumberjacks:38% VWF
Õ Õ Õ Participation rate: Not reported.
Total exposure to HAV hadsignificant correlation with VPTin railway workers (r=0.55-0.47; p=0.017) and lumberjacks(r=0.77-0.59; p=0.003).
Increase in VPT approximately2 times greater in railwayworkers.
7 workers excluded—2railway workers withpolyneuropathy; 4 railwayworkers with CTS;1 lumberjack with CTS. Thesemay have been related tovibration exposure.
Lumberjacks used chain sawsdaily >1,000 hr per year. Railway workers used hand-held tamping machines -500hrs per year.
Found peak value differencesfor hand-held tampingmachines (40 to 60 Hz) andchain saws (120 to 150 Hz).
Nerve-conductionmeasurements adjusted forskin temperature.
5c-31
6-1
CHAPTER 6Low-Back Musculoskeletal Disorders:Evidence for Work-Relatedness
SUMMARYOver 40 recent articles provided evidence regarding the relationship between low-back disorder and the fivephysical workplace factors that were considered in this review. These included (1) heavy physical work, (2)lifting and forceful movements, (3) bending and twisting (awkward postures), (4) whole-body vibration (WBV),and (5) static work postures. Many of the studies addressed multiple work-related factors. All articles thataddressed a particular workplace factor contributed to the information used to draw conclusions about thatrisk factor, regardless of whether results were positive or negative.
The review provided evidence for a positive relationship between back disorder and heavy physical work,although risk estimates were more moderate than for lifting/forceful movements, awkward postures, andWBV. This was perhaps due to subjective and imprecise characterization of exposures. Evidence for dose-response was equivocal for this risk factor.
There is strong evidence that low-back disorders are associated with work-related lifting and forcefulmovements. Of 18 epidemiologic studies that were reviewed, 13 were consistent in demonstrating positiverelationships. Those using subjective measures of exposure showed a range of risk estimates from 1.2 to5.2, and those using more objective assessments had odds ratios (ORs) ranging from 2.2 to 11. Studiesusing objective measures to examine specific lifting activities generally demonstrated risk estimates abovethree and found dose-response relationships between exposures and outcomes. For the most part, higherORs were observed in high-exposure populations (e.g., one high-risk group averaged 226 lifts per hour witha mean load weight of 88 newtons [N]) . Most of the investigations reviewed for this document adjusted forpotential covariates in analyses; nevertheless, some of the relatively high ORs that were observed wereunlikely to be caused by confounding or other effects of lifestyle covariates. Several studies suggested thatboth lifting and awkward postures were important contributors to the risk of low-back disorder. The observedrelationships are consistent with biomechanical and other laboratory evidence regarding the effects of liftingand dynamic motion on back tissues.
The review provided evidence that work-related awkward postures are associated with low-back disorders.Results were consistent in showing positive associations, with several risk estimates above three.Exposure-response relationships were demonstrated. Many of the studies adjusted for potential covariatesand a few examined the simultaneous effects of other work-related physical factors. Again, it appeared thatlifting and awkward postures both contribute to risk of low-back disorder.
There is strong evidence of an association between exposure to WBV and low-back disorder. Of 19studies reviewed for this document, 15 studies were consistent in demonstrating positive associations, withrisk estimates ranging from 1.2 to 5.7 for those using subjective exposure measures, and from 1.4 to 39.5for those using objective assessment methods. Most of the studies that examined relationships in high-exposure groups using detailed quantitative exposure measures found strong positive associations andexposure-response relationships between WBV and low back disorders. These relationships were observedafter adjusting for covariates.
Both experimental and epidemiologic evidence suggest that WBV may act in combination with other work-related factors, such as prolonged sitting, lifting, and awkward postures, to cause
6-2
increased risk of back disorder. It is possible that effects of WBV may depend on the source of exposure(type of vehicle).
With regard to static work postures and low-back disorder, results from the studies that were reviewedprovided insufficient evidence that a relationship exists. Few investigations examined effects of staticwork postures, and exposure characterizations were limited.
INTRODUCTION
Low-back pain (LBP) is common in thegeneral population: lifetime prevalence has beenestimated at nearly 70% for industrializedcountries; sciatic conditions may occur in onequarter of those experiencing back problems[Andersson 1981]. Studies of workers’compensation data have suggested that LBPrepresents a significant portion of morbidity inworking populations: data from a nationalinsurer indicate that back claims account for16% of all workers’ compensation claims and33% of total claims costs [Snook 1982;Webster and Snook 1994b]. Studies havedemonstrated that back disorder rates varysubstantially by industry, occupation, and byjob within given industries or facilities [seeBigos et al. 1986a; Riihimäki et al. 1989a;Schibye et al. 1995; Skovron et al. 1994].
Back disorder is multifactorial in origin and maybe associated with both occupational andnonwork-related factors and characteristics.The latter may include age, gender, cigarettesmoking status, physical fitness level,anthropometric measures, lumbar mobility,strength, medical history, and structuralabnormalities [Garg and Moore 1992].Psychosocial factors, both work- andnonwork-related, have been associated withback disorders. These relationships arediscussed at length in Chapter 7 and AppendixB.
The relationship of the disorder withemployment can be complex: individuals mayexperience impairment or disability at workbecause of back disorders whether the latterwas directly caused by job-related factors ornot. The degree to which ability to work isimpaired is often dependent on the physicaldemands of the job. Furthermore, when anindividual experiences a back disorder at work,it may be a new occurrence or an exacerbationof an existing condition. Again, originally it mayhave been directly caused by work or bynonwork-related factors. Those suffering backpain may modify their work activities in aneffort to prevent or lessen pain. Thus, therelationship between work exposure anddisorder may be direct in some cases, but not inothers.
When discussing causal factors for low-backdisorders, it is important to distinguish amongthe various outcome measures, such as LBP,impairment, and disability. LBP can be definedas chronic or acute pain of the lumbosacral,buttock, or upper leg region. Sciatic pain refersto pain symptoms that radiate from the backregion down one or both legs; lumbago refersto an acute episode of LBP. In many cases ofLBP, specific clinical signs are absent. Low-back impairment is generally regarded as a lossof ability to perform physical activities. Low-back disability is defined as necessitatingrestricted duty or time away from the job.Although it is not clear which outcome measure
6-3
is best suited for determining the causalrelationship between low-back disorder andwork-related risk factors, it is important toconsider severity when evaluating the literature.
In addition to level of severity, outcomes maybe defined in a number of other ways, rangingfrom subjective to objective. Information onsymptoms can be collected by interview orquestionnaire self-report. Back “incidents” or“reports” include conditions reported tomedical authorities or on injury/illness logs;these may be symptoms or signs that anindividual has determined need for medical orother attention. They may be due to acutesymptoms, chronic pain, or injury related to aparticular incident, and may be subjectively orobjectively determined. Whether an incident isreported depends on the individual’s situationand inclinations. Other back disorders can bediagnosed using objective criteria—forexample, various types of lumbar discpathology.
There are many conditions in the low backwhich may cause back pain, including muscularor ligamentous strain, facet joint arthritis, ordisc pressure on the annulus fibrosis, vertebralend-plate, or nerve roots. In most patients, theanatomical cause of LBP, regardless of itsrelationship to work exposures, cannot bedetermined with any degree of clinical certainty.Muscle strain is probably the most commontype of work or nonwork back pain. Whilethere is sometimes a relationship between painand findings on magnetic resonance imaging(MRI) of disc abnormalities (such as aherniated disc and clinical findings of nervecompression), unfortunately, the most commonform of back disorder is “non-specificsymptoms,” which often cannot be diagnosed.
It is important to include subjectively definedhealth outcomes in any consideration of work-related back disorders because they comprisesuch a large subset of the total. It may be toorestrictive to define cases of back disorderusing “objective” medical criteria. Therefore, incontrast to chapters for musculoskeletaldisorders or other anatomic regions, this reviewof literature on the back used slightly differentevaluation criteria. For consideration of backdisorders, use of a subjective health outcomewas not necessarily considered a studylimitation. Furthermore, because backdisorders were rarely defined by medicalexamination criteria, the evaluation criterionrelated to blinding of assessors (to health orexposure status) was also less relevant to adiscussion of this literature.
In this review, epidemiologic studies of allforms of back disorder were included. Theterm “back disorder” is used to encompass allhealth outcomes related to the back. It shouldbe pointed out that, in some studies, disordersof the low back were not distinguished fromtotal back disorders. We assumed that asignificant portion of these related to the lowback, and articles using such a definition wereincluded in our review.
The 42 epidemiologic studies discussed belowwere selected according to criteria that appearin the introduction of this document. Most (30)used a cross-sectional design, followed byprospective cohort (5), case-control (4), andretrospective cohort (2) designs. One studycombined both cross-sectional and cohortanalyses. Full descriptions of the studies appearin Table 6-6. Twenty-four investigationsdefined the health outcome only by report ofsymptoms on questionnaires or in interviews
6-4
(for example, total back pain, LBP, andsciatica); used symptoms plus medicalexamination (back pain, low-back syndrome,sciatica, back insufficiency, lumbago, herniatedlumbar disc, and lumbar disc pathology),2 used sick leaves and medical disabilityretirements, and 6 used injury/illness reports. The last category included outcomes defined as“low-back complaints, injuries causedspecifically by lifting or mechanical energy,” and“acute industrial back injury.” Clearly, the 42studies used outcome definitions thatcorrespond to several regions of the back andinclude disorders that may have been acute orchronic and subjectively or objectivelydetermined.
In the studies included in this review, exposureswere assessed primarily by questionnaire orinterview (n=17), followed by observation ordirect measurement (n=15) and by job title only(n=10). Study groups included generalpopulations (Swedish, Dutch, U.S., Finnish,and English) and occupational groups (nurses,clerical employees, school lunch preparers,baggage handlers, and individuals working inconstruction, agriculture, maritime, petroleum,paper products, transportation, automobile,aircraft, steel, and machine manufacturingindustries).
This review of epidemiologic studies of low-back disorder examined the following potentialrisk factors related to physical aspects of theworkplace: (1) heavy physical work, (2) liftingand forceful movements, (3) bending andtwisting (awkward postures), (4) WBV, and(5) static work postures. Psychosocialworkplace factors were also included in anumber of studies; these relationships arediscussed separately in Chapter 7. Following
are discussions of the evidence for each work-related physical risk factor.
HEAVY PHYSICAL WORKDefinition
Heavy physical work has been defined as workthat has high energy demands or requires somemeasure of physical strength. Somebiomechanical studies interpret heavy work asjobs that impose large compressive forces onthe spine [Marras et al. 1995]. In this review,the definition for heavy physical work includesthese concepts, along with investigators’perceptions of heavy physical workload, whichrange from heavy tiring tasks, manual materialshandling tasks, and heavy, dynamic, or intensework. In several studies, evaluation of this riskfactor was subjective on the part of participantor investigator, and in many cases, “heavyphysical work” appeared to include otherpotential risk factors for back disorder,particularly lifting and awkward postures.
Studies Reporting on the AssociationBetween LBP and Heavy Physical Work
Eighteen studies appeared to address the riskfactor related to heavy physical work, althoughnone of them fulfilled all four evaluation criteria(Table 6-1, Figure 6-1). In fact, most (78%)had acceptable participation rates, but onlythree defined health outcomes using bothsymptoms and medical exam criteria, and onlytwo assessed exposure independent of self-report.
In nearly all of these studies, covariates wereaddressed in at least minimal fashion, such asrestricting the study population as to gender and conducting age-stratified or
6-5
adjusted analyses; in many, multivariateanalyses were carried out. With regard tohealth outcome, while only three used medicalexams, in addition to symptoms or injuryreports, to arrive at case definitions, in manyinstances standard questionnaire instrumentswere used. The major study limitations, overall,were related to relatively poor ascertainment ofexposure status.
Following are descriptions of seven studies thatwere most informative. Detailed descriptionsfor all 18 investigations can be found in Table6-6.
Bergenudd and Nilsson [1988] followed aSwedish population-based cohort established in1938. Back pain (total) presence and severitywere self-assessed by questionnaire, as of1983; exposures (light, moderate, or heavyphysical work) were assessed based onquestionnaires completed by the cohort from1942 onward. Univariate results demonstratedthat those with moderate or heavy physicaldemands in their jobs had more back pain thanthose with light physical demands (OR 1.83,95% Confidence Interval [CI] 1.2-2.7). Whenstratified by gender, the relationship was slightlystronger for females (OR 2.03, 95% CI1.1–3.7) than for males (OR 1.76, 95% CI1.01–3.1). When prevalence was examined byexposure category, rates were 21.4%, 32.8%,and 31.3% for males (no trend was availablefor females, as none worked in the highestexposure category). Analyses were stratified bygender but did not account for other potentialcovariates. The longitudinal design ensured thatexposures preceded health outcomes.Shortcomings included a relatively lowresponse rate (67%), minimal exposureassessment, limited adjustment for covariates inanalyses, and self-reporting of health
symptoms.
Burdorf and Zondervan [1990] carried out across-sectional study comparing 33 maleworkers who operated cranes with age-matched workers from the same Dutch steelplant who did not operate cranes. Symptoms ofLBP and sciatica were assessed byquestionnaire. Exposure was assessed by jobtitle (crane operators were noted to experiencefrequent twisting, bending, stooping, staticsedentary postures, and WBV) and byquestionnaire (exposures to sedentary postures,WBV, heavy physical work, and frequent liftingwere assessed for both current and past jobs).Crane operators were significantly more likelyto experience LBP (OR 3.6, 95% CI1.2–10.6). Among crane operators alone, theOR for heavy work was 4.0 (95% CI0.76–21.2) after controlling for age, height, andweight. It was determined that this heavy workoccurred in past and not in current jobs.Among crane operators alone, the OR forfrequent lifting was 5.2 (95% CI 1.1–25.5).The frequent lifting in crane operators was alsodetermined to be from jobs held in the past.Among workers who were not craneoperators, history of frequent lifting was notassociated with LBP (OR 0.70, 95% CI0.14–3.5). Among crane operators, univariateORs for WBV and prolonged sedentarypostures were 0.66 (95% CI 0.14–3.1) and0.49 (95% CI 0.11–2.2), respectively. Inmultivariate analyses controlled for age, height,weight, and current crane work, most of theassociations with specific work-related factorswere substantially reduced. The highprevalence of LBP in crane operators wasexplained only by current crane work. Nomeasures of dose-response were examined.
6-6
Limitations included a relatively low responserate for crane operators (67%)—with somesuggestion that those with illness may have beenunder-represented (perhaps underestimatingthe OR)—and self-reporting of healthoutcomes and exposures. The investigatorsattempted to clarify the temporal relationbetween exposure and outcome by excludingcases of back pain with onset before thepresent job.
As part of a Finnish population-based healthsurvey, Heliövaara et al. [1991] conducted across-sectional analysis of chronic low-backsyndrome, sciatica, and LBP. Health outcomeswere determined by interview and examination;work-related exposure information wasobtained by a self-administered questionnaire,which included items related to lifting, carryingheavy objects, awkward postures, WBV,repeated movements, and paced work. Thetotal number of factors was designated the“sum index of occupational physical stress.”Mental work stress measures were alsoincluded. A dose-response was observed forsciatica and the physical stress score (with anOR of 1.9, 95% CI 0.8–4.8 for the highestscore) and for low-back syndrome andphysical stress (OR 2.5, 95% CI 1.4–4.7),after adjusting for a number of covariates. Thestudy did not address temporal relationships,and exposure information was derived fromself-reports. Strengths included a high responserate, objective measure of health outcomes, andmultivariate adjustment for covariates.
Johansson and Rubenowitz [1994] examinedlow-back symptoms cross sectionally in 450blue- and white-collar workers employed ineight Swedish metal companies. The exposedgroup included assemblers, truck
drivers, welders, smiths, and operators ofseveral types of machines (lathes, punchpresses, and milling). Outcome information wasobtained by questionnaire. Exposure data werealso obtained by questionnaire and includedinformation on occupational, psychosocial, andphysical workloads, including sitting, carrying,pushing, pulling, lifting, work postures, andrepetitive movements. Questionnaire itemsrelated to carrying, pushing, pulling, and liftingwere combined to produce an index of manualmaterials handling. The prevalence of work-related LBP was significantly higher in blue-collar employees than in white-collar workers(RR 1.8, p<0.05). In both white and blue-collar workers, work-related LBP was notsignificantly associated with either heavy or lightmaterials handling, or bent or twisted workpostures, after adjustment for age and gender.LBP was significantly associated with extremework postures (blue-collar workers only) andmonotonous working movements (white-collarworkers only). In these analyses, relationshipswere presented as partial correlations; thus, acomparison of risk estimates was not possible.Limitations of the study included the cross-sectional design, collection of outcome andexposure data by self-report, and potentialproblems with multiple comparisons, as manyindependent variables were examined inanalyses. Many of the exposed group (blue-collar workers) were engaged in machineoperation tasks with perhaps limitedopportunity for exposure to work with heavyphysical demands. Also, heavy physical workand lifting were combined into a single index.Strengths included consideration of age andgender as covariates and inclusion of bothphysical and psychosocial workplacemeasures.
6-7
Svensson and Andersson [1989] examinedLBP in a population-based cross-sectionalstudy of employed Swedish women.Information on LBP and sciatica was obtainedby questionnaire, as were exposure-relateditems. Physical exposures included lifting,bending, twisting, other work postures, sitting,standing, monotony, and physical activity atwork. Lifetime incidence rates (IRs) varied byoccupation, with ranges from 61%–83% inyounger age groups and 53%–75% in oldergroups. A posteriori, the authors noted that,for these women, the highest lifetime incidenceof LBP was not found in the jobs with thehighest physical demands. The measure for“physical activity at work” was also notsignificantly associated with LBP in univariateanalyses. Bending forward (RR 1.3), lifting (RR1.2), and standing (RR 1.3) were associatedwith lifetime incidence of LBP in univariateanalyses (p<0.05). None of the measures ofphysical workplace factors were associatedwith lifetime incidence of LBP in multivariateanalyses.
A cross-sectional study of LBP in Finnishnurses was conducted [Videman et al. 1984].LBP and sciatica were ascertained byquestionnaire; exposure information was alsoself-reported and included items related to bothphysical loading factors at work and to workhistory. Exposures were reclassified as“heavy,” “intermediate,” and “light,” based onquestionnaire responses. The derivation of thisclassification was not clear, but it may havebeen a combination of responses to questionson lifting, bending, rotation, standing, walking,and sitting. A dose-response was observedbetween prevalence of previous LBP andworkload category in younger women (77%,79%, and
83% for light, intermediate, and heavycategories). The trend was not observed inolder age groups, nor for sciatica in any agegroup. LBP and sciatica rates were slightlyhigher for nurse aides than for qualified nurses,although the differences were not statisticallysignificant. The authors suggested that aideshad higher rates of back pain because ofheavier workload, including patient handlingand lifting. Lack of consistency of LBP ORacross exposure and age groups suggested thata healthy worker effect was operating and thatinjured workers might be leaving the field, aphenomenon that the cross-sectional studydesign could not address.
Videman et al. [1990] carried out a cross-sectional study of 86 males who died in aHelsinki hospital to determine degree of lumbarspinal pathology. Disc degeneration and otherpathologies were assessed in the cadaverspecimens by discography and radiography.Subjects’ symptoms and workexposures—heavy physical work, sedentarywork, driving, and mixed—were determined byinterview of family members. In comparison tothose with mixed work exposures, those withsedentary and heavy work had increased riskof symmetric disc degeneration with ORs of24.6 (95% CI 1.5–409) and 2.8 (95% CI0.3–23.7), respectively). Similar relationshipswere seen for vertebral end-plate defects andfacet joint osteoarthrosis. Risk of vertebralosteophytosis was highest for those in the heavywork category (OR 12.1, 95% CI 1.4–107).For most pathologic changes, sedentary workappeared to have a stronger relationship thanheavy work. Back pain symptoms wereconsistently higher in those with any form ofspinal pathology, although the difference wassignificant only for anular ruptures. Results of
6-8
this study were notable in that anular rupture, aclassic pathologic condition of the disc, was notassociated with exposure. This study wasunusual in design in that it examined acombination of spinal pathological outcomes,symptoms, and workplace factors. However,participation in the study was dependent onobtaining information from family members;participation rates were not stated. While recallbias is often a problem in studies of thedeceased, in this case, it should have beennondifferential, if present.
Strength of AssociationThe most informative studies were generallythose that carried out exposure assessmentswhich ranked physical workload based onquestionnaire report. In a prospective study ofback injury reports, Bigos et al. [1991b] foundno associations with physical job characteristics(although the authors stated that the studypopulation had low overall exposures). Thisstudy described the biomechanical methods thatwere used to directly assess spinal loadsassociated with jobs, but no results related tothese measures were presented. Svensson andAndersson [1989] appear to have examined ameasure for physical activity at work and itsrelationship to LBP in Swedish women. Noassociations were observed. In a population-based study, Bergenudd and Nilsson [1988]observed significantly more back pain in thosewith heavier physical work (OR 1.8 formoderate/heavy versus light work, p<0.01).ORs were slightly higher for females (OR 2.0)than for males (OR 1.8). Leigh and Sheetz[1989] found that back symptoms wereassociated with self-reporting that “job requiresa lot of physical effort” (OR 1.5, 95% CI1.0–2.2). Masset and Malchaire [1994]observed that LBP was not associated with
overall physical workload in a group of Belgiansteelworkers, although LBP was related toheavy shoulder efforts. In a study of blue-andwhite-collar workers, Johansson andRubenowitz [1994] found higher LBP rates inblue-collar workers (RR 1.8, p<0.05).However, in more detailed analyses ofexposure, back pain was not associated withindices for heavy or light materials handlingafter adjustment for age and gender (withpartial correlation coefficients of less than0.10). Burdorf and Zondervan’s 1990 study ofcrane operators demonstrated increased risk ofLBP with exposure to heavy work (OR 4.0,95% CI 0.8–21.2) after controlling for age,height, and weight. Two studies used indices ofphysical stress to create questionnaireresponses related to lifting, carrying heavyobjects, awkward postures, repeatedmovements, and others. Heliövaara et al.[1991] found that both low-back syndromeand sciatica were associated with physicalstress scores, with ORs of 2.5 (p<0.05) and1.9 (not significant) for the highest scores,respectively. A study of Finnish nursesclassified exposures as “heavy,” “intermediate,”and “light” based on questionnaire responsescores [Videman et al. 1984]; prevalence ofLBP was slightly higher in the heavy categorythan in the light (RR 1.1, not significant) foryounger women only. Sciatica was alsoexamined, and no relationships were found.
The other studies that examined heavy physicalwork as a risk factor for back disorderclassified exposure in a simpler manner, eitherby job title alone or by grouping jobs based onprior knowledge of the work or questionnaireresponses. Burdorf et al. [1991] found that
6-9
heavy physical work was associated with backpain in concrete workers in univariate, but notmultivariate models (no risk estimate wasreported). Hildebrandt [1995] found thatindividuals in jobs described as “heavy non-sedentary” were more likely to experienceback pain than those in sedentary jobs (OR1.2, p<0.05). In a cadaver study of lumbar discpathology, Videman et al. [1990] found thatthose with jobs involving heavy physical workhad increased risk of disc pathology incomparison to those with mixed workexposures (e.g., an OR of 2.8, 95% CI0.3–23.7, for symmetric disc degeneration andan OR of 12.1, 95% CI 1.4–107, for vertebralosteophytosis). For most pathologic changes,sedentary work had a stronger relationship thanheavy work.
Finally, several studies examined back disorderrates by job title or occupation alone.Hildebrandt et al. [1996] observed differencesin back symptom rates by unit and task groupin “nonsedentary” steel workers. The referencegroup also had high symptom rates;comparisons between the two groups did notyield significant differences. In multivariateanalyses, Riihimäki et al. [1989b] found nosignificant difference in sciatic pain forcarpenters and office workers (OR 1.0, 95%CI 0.8–1.3). Partridge and Duthie [1968]found that dock workers had slightly higherLBP rates than civil servants (RR 1.2, notsignificant). In a similar study, Åstrand [1987]classified pulp mill jobs as heavy and thereferent group of clerical jobs as light; millworkers were 2.3 times more likely toexperience back pain than clerical staff(p=0.002). Clemmer et al. [1991] found thatfloor hands, roustabouts, and derrickhands hadthe highest rates for low-back strains and
impact injuries, with RRs of 2.2 and 4.3 (nosignificance testing was done) in comparison tocontrol room operators and maintenanceprofessionals, those with the lowest rates. Astudy of hospital employees that matched caseswith controls by department found that those onthe day shift had an OR of 2.2 (p<0.005) incomparison to those working other shifts[Ryden et al. 1989]. In the last two studies, theauthors determined a posteriori that job titles(or shifts) that were observed to have high backdisorder rates were those requiring the heaviestphysical effort.
Although in all 18 of these studies the authorsstated that “heavy physical effort or work” wasat least one of the risk factors of interest, theactual estimates of these exposures varied fromassumptions based on job title to self-reportedscores based on self-reported work activities.In no case were measured physical loads usedas independent variables. Study populationsincluded individuals working in health care,office work, manufacturing, construction, andgeneral populations, all with varying degrees ofphysical work requirements. Some studiescreated physical “stress” indices that includedmore than one risk factor. Since most estimatesof physical load were subjective, they tended toreflect the relative requirements of the jobs andindividuals included in each study. Healthoutcomes also varied.
In summary, the strength of the relationshipbetween back disorder and heavy physicalwork in some of the studies with morequantitatively defined exposures ranged fromnone [Bigos et al. 1991b; Johannsson andRubenowitz, 1994; Masset and Malchaire1994; Svensson and Andersson 1989;Videman et al. 1984] to ORs of 1.9 (not
6-10
significant) for sciatica and 2.5 (p<0.05) forlow-back syndrome [Heliövaara et al. 1991],1.5 (95% CI 1.0–2.2) [Leigh and Sheetz1989], 1.8 (95% CI 1.2–2.7) [Bergenudd andNilsson 1988], and 4.0 (p<0.05) for LBP[Burdorf and Zondervan 1990]. In anotherstudy, which used a scoring system and focusedon a subject group of nurses, the RR was 1.1(not significant) for the high-exposure category[Videman et al. 1984].
Dichotomous estimates of physical workloadyielded ORs of 1.2 [Hildebrandt 1995], 2.8-12.1 [Videman et al. 1990], and no association(results were observed in univariate but notmultivarate analyses, with no risk estimatesreported) [Burdorf et al. 1991]. Exposuresbased on job title alone yielded estimates fromnone [Hildebrandt et al. 1996], nonsignificantORs of 1.0 and 1.2 [Partridge and Duthie1968; Riihimäki et al. 1989b], to significantORs of 2.2–4.3 [Åstrand 1987; Clemmer et al.1991; Ryden et al. 1989]. Half of the studieshad positive point estimates for this risk factorbut were low to moderate in magnitude. In fivestudies that found no association between backdisorder and heavy physical work, no detailswere given. Two of the highest significant ORswere based on exposed groups in the oil andsteel industries [Burdorf and Zondervan 1990;Clemmer et al. 1991]. For these, true exposureto heavy physical work was probably morelikely than for some of the other studypopulations. For many of the investigations,exposure estimates were subjectively assessed.In many cases, study groups had potentially lowexposures or exposure to heavy physical workin combination with other risk factors.
Temporal RelationshipFourteen of the 18 reviewed studies had across-sectional design that could not directly address this issue. Three mentioned potentialproblems related to this study design. Åstrand[1987] suggested that exposuremisclassification occurred in her study of papermill workers (some individuals were transferredto clerical jobs—the unexposed group—afterexperiencing a back injury in the mill). In theVideman et al. 1984 study of nurses, lack ofconsistency of LBP OR by age and exposuregroup suggested that injured workers wereleaving the field. A study of cadavers carriedout by Videman et al. [1990] seemed to havepotential for problems with temporalrelationships, as exposure information for pastperiods depended on recall of studyparticipants’ activities by family members.
Two cross-sectional studies attempted to clarifytemporal relationships by excluding fromanalysis the cases with disorder onset prior tocurrent job [Burdorf et al. 1991; Burdorf andZondervan 1990]. Both showed resultssuggesting a positive relationship betweenexposure and back disorders. Three studieshad cohort designs in which temporalrelationships between outcome and exposurecould be determined [Bergenudd and Nilsson1988; Bigos et al. 1991b; Clemmer et al.1991]: in one, no association was observed, inanother, a modest increase in risk was seen. Inthe third, exposure (assessed a posteriori byjob title) was significantly associated with backinjuries. A case-control study conducted usinghospital personnel records appeared free fromrecall bias and showed a significant associationbetween low-back injury and working the dayshift (assessed a posteriori as having theheaviest workload) [Ryden et al. 1989].
6-11
Although the majority of studies were limited bytheir cross-sectional designs, results weresimilar for these and other studies with designsthat could assess temporal relationships.
For most studies, the data are compatible witha temporal relationship in which exposurepreceded disorder.
Consistency in AssociationHalf of the 18 studies examined demonstratedno significant association between exposureand outcome. All of those which showedsignificant associations (n=9) were positive indirection, (one OR of 1.2, two ORs between1.5 and 2, and six ORs between 2.2 and 12.1).
Study groups included males working inindustrial environments, office workers, healthcare employees—female, for the mostpart—and population-based groups thatincluded both genders and many occupations.That some consistency in results was notedamong these diverse groups, particularly afteradjustment for covariates, suggests that theobserved associations have validity and can begeneralized across working populations.
Coherence of Evidence
Information derived from a large number oflaboratory and field studies using a wide varietyof approaches provides a plausible explanationfor associations between LBP and physicallydemanding jobs [Waters et al. 1993]. Researchconducted in the 1950s demonstrated that discdegeneration occurs earlier in life amongworkers who perform heavy physical workthan among those who perform lighter work.Similar findings are reported in more recentinvestigations [Videman et al. 1990]. Thestresses induced at the low back during manual
materials handling are due to a combination ofthe weight lifted, and the person’s method ofhandling the load. The internal reaction forcesneeded to equilibrate the body segment weightsand external forces such as weight of the loadbeing lifted are supplied by muscle contraction,ligaments, and body joints. Injury to thesupporting tissues can occur when the forcesfrom the load, body position, and movementsof the trunk create compressive, shear, orrotational forces that exceed the capacities ofthe discs and supporting tissues needed tocounteract the load moments. Rowe [1985]hypothesized that disc and facet degenerationand ligament strain are responsible for thepotentially high rates of LBP disability in thosewhose jobs demand heavy physical activity.
The Videman et al. [1990] cross-sectionalstudy of cadavers addressed two aspects of thecausal chain linking exposure to heavy physicalwork and back disorder. First, the studydemonstrated an association betweensubjective health outcome measures and moreobjective measures: back pain symptoms(assessed from family members) wereconsistently higher in those with signs of spinalpathology. Second, the study demonstrated anassociation between objective measures ofdisorder and heavy work exposures: individualswhose jobs included heavy work exposuresshowed increased risk of symmetric discdegeneration, vertebral osteophytosis, and facetjoint osteoarthrosis. Significant relationshipswere also found for back pain and disability.We agree with the conclusion of Videman et al.[1990] that states that “back injury and
6-12
sedentary or heavy (but not mixed) workcontributed to the development of pathologicfindings in the spine. The severity of back painwas related to the heaviness of work. Work-related factors may be responsible for thedevelopment of pathologic changes and forincreased episodes of LBP and disability.”
Another important contribution to thecoherence of evidence is that the Bureau ofLabor Statistics Annual Survey of Injuries andIllnesses has demonstrated significant elevationsin overexertion injuries and disorders inindustries which are associated with heavywork, such as nursing and personal care and airtransportation. Some broad population surveyssuch as the National Health Interview Survey(NHIS) from 1988 and the 1990 OntarioHealth Survey (OHS) found increased backpain or long-term back problems with exposureto factors such as lifting, pulling, and physicalpushing [Guo et al. 1995; Liira et al. 1996]. Inthe NHIS, the two occupations with the highestsignificant rates of work-related LBP weremale construction laborers (with a prevalenceratio [PR] of 2.1) and female nursing aides,orderlies, and attendants (PR 2.8) [Guo et al.1995]. In the OHS, the number of simultaneousphysical exposures was directly related to riskincrease after adjustment for covariates. Forthe highest exposure index level, the adjustedOR was 3.18 (95% CI 1.72–5.8), whichoccurred in 3% of the population [Liira et al.1996]. It is important to point out that trulyheavy work probably occurs in only a tinyproportion of all jobs in most industries and inonly a minority of many high-risk industries,which is why misclassification of exposures islikely in population-based studies.
Exposure-Response Relationships
Only a few studies examined exposure insufficient detail to assess exposure-responserelationships with low-back disorders. Resultswere mixed. Heliövaara et al. [1991] observedan exposure-response between sciatica andphysical stress score; the Videman et al. [1984]results demonstrated a dose-response betweenLBP prevalence and workload categories inyounger nurses, but not in older groups, or forsciatica in any age group. In Åstrand’s 1987“high exposure group” (pulp mill workers),duration of employment was associated withback pain. Bergenudd and Nilsson [1988] andJohansson and Rubenowitz [1994] observedno exposure-response relationships betweenback disorders and their exposure measures.On the whole, evidence of exposure-responseis equivocal, based on the paucity ofinformation available.
Conclusions: Heavy Physical WorkThe reviewed epidemiologic investigationsprovided evidence that low-back disorders areassociated with heavy physical work. Despitethe fact that studies defined disorders andassessed exposures in many ways, all studieswhich demonstrated significant associationsbetween exposure and outcome were positivein direction and showed low to moderateincreased risk. Exposures were assessedsubjectively, for the most part; and in somecases, classification schemes were crude. Thisstudy limitation may have led tomisclassification of exposure status to the extentthat it caused a dampening effect on riskestimates, where nondifferentialmisclassification caused bias toward a null valuefor the measure of association. This mayaccount for the moderate ORs that were
6-13
observed. A few studies were able to examinedose-response relationships between outcomesand exposure; these results were equivocal.Most studies utilized cross-sectional studydesigns; however, five of six studies which usedspecific methodologies to address temporalityshowed positive associations between exposureand outcome. Many studies addressed potentialeffects of covariates by restriction in selectionof study participants, stratification, ormultivariate adjustment in statistical analyses.
In many studies, “heavy physical work”exposure appeared to include other work-related physical factors (particularly lifting andawkward postures).
LIFTING AND FORCEFULMOVEMENTS
DefinitionLifting is defined as moving or bringingsomething from a lower level to a higher one.The concept encompasses stresses resultingfrom work done in transferring objects fromone plane to another as well as the effects ofvarying techniques of patient handling andtransfer. Forceful movements includemovement of objects in other ways, such aspulling, pushing, or other efforts. Severalstudies included in this review used indices ofphysical workload that combined lifting/forcefulmovements with other work-related risk factors(particularly heavy physical work and awkwardpostures). Some studies had definitions forlifting which include criteria for number of liftsper day or average amount of weight lifted.
Studies Reporting on the Association
Between LBP and Lifting andForceful Movements
Eighteen studies examined relationshipsbetween back disorders and lifting or forcefulmovements. Only one, Punnett et al. 1991case-control study of back pain in autoworkers, fulfilled the four evaluation criteria(Table 6-2, Figure 6-2). The majority (66%)had adequate participation rates; four definedoutcomes using both symptoms and medicalexam criteria. Blinding of investigators withregard to case/exposure status was notmentioned in most, but it could be confirmed intwo papers and inferred (by study methodology) in two others. Seven studies used an exposureassessment that included observation or directmeasurement; an additional nine obtainedexposure information by self-report onquestionnaire or interview. Only two relied onjob title alone to characterize exposure.
Thirteen investigations were cross-sectional indesign; three were case-control, and two wereprospective. Eleven defined the health outcomeby symptom report on interview orquestionnaire.
Descriptions of seven studies which providedthe most information regarding the relationshipbetween low-back disorder and lifting andforceful movements follow. Detaileddescriptions for all 18 investigations can befound in Table 6-6. The Punnett et al. [1991] case-control studyexamined the relationship between back painand occupational exposures in auto assemblyworkers. Back pain cases (n=95) were
6-14
determined by symptoms at interview andmedical examination; controls included thosefree of back pain. For all participants (orproxies in the same jobs), jobs werevideotaped and work cycles were reviewedusing a posture analysis system. Exposuresincluded time spent in various awkwardpostures. Peak biomechanical forces wereestimated for up to nine postures where a loadweighing at least 10 lb was held in the hands. Inmultivariate analyses that adjusted for a numberof covariates (age, gender, length ofemployment, recreational activities, and medicalhistory), time in non-neutral postures (mild orsevere flexion and bending) was stronglyassociated with back disorder (OR 8.09, 95%CI 1.4–44). Lifting was also associated withback disorder (OR 2.16, 95% CI 1.0–4.7).When the subset with physical medical findingswas examined, associations were morepronounced. Although few study subjects wereunexposed to all of the postures studied, astrong increase in risk was observed with bothintensity and duration of exposure. It was notpossible to determine the relative contributionsof different awkward postures because all werehighly correlated. Only participants’ currentjobs (for referents), or job when symptomsstarted (for cases) were analyzed; the studydesign thus assumed a short-term relationshipbetween exposure and outcome (althoughlength of time in job was also included in themodels). The authors attempted to ensure thatexposure preceded disease by identifying timeof onset and measuring exposures in the jobheld just prior. The strong associations, afteradjustment for covariates, are notable.
Burdorf et al. [1991] examined back painsymptoms in a cross-sectional study of maleconcrete fabrication workers and a referent
group of maintenance workers. Back painsymptoms were assessed by questionnaire.Exposures were measured using the OvakoWorking Posture Analysis System, whichassessed postures for the back and lower limbsalong with lifting load. Information onexposures in previous jobs was also collected.Concrete workers experienced significantlymore back symptoms than referents (OR 2.8,95% CI 1.3–6.0). Univariate results showedassociations between back pain and bothposture index and WBV in current job(correlations were presented). Lifting was notfound to be associated with back pain (andexposure was found not to vary significantlyacross the six job categories examined in thestudy). In multivariate analyses adjusting forage, both posture index and WBV weresignificantly associated with back pain, withORs of 1.23 (p=0.04) (for an ordinal scale of6) and 3.1 (p=0.01) (dichotomous),respectively. These two measures were highlycorrelated and analyzed separately. Strengthsof the study include use of a standard symptomquestionnaire, high participation rates, anobjective measure of exposure, and an attemptto clarify the temporal relation betweenexposure and outcome by excluding cases ofback pain with onset before the present job.
Chaffin and Park [1973] carried out aprospective study of back complaints in 411employees of four electronics manufacturingplants. The outcome included visits to the plantmedical department because of backcomplaints over a one-year period. Exposurewas assessed by evaluating 103 jobs with arange of manual lifting for lifting strength rating(LSR) and load weights. The LSR is a ratio ofthe maximum weight lifted on the job to thelifting strength, in the same load position, for alarge/strong man. Results
6-15
showed a strong increase in back complaintincidence with LSR for both males and females(with an approximate five-fold increase in riskcomparing males in the highest and lowestLSR). A similar increase was observed forfemales, although there were no women in thehighest exposure category. No dose-responsewas observed by frequency of lifts (a relativelyhigh risk of back complaints was observed forthe lowest exposure category). Covariates(age, weight, and stature) were examined andfound not to contribute to back complaints. Theprospective study design helped increase thelikelihood that exposure preceded disorder.Study limitations include lack of information onparticipation rates and an outcome consisting ofincident reports. Time of true onset was notascertained, and it is possible that symptomonset preceded or coincided with exposureassessment despite the longitudinal studydesign. The detailed exposure assessmentaddressed only lifting as a risk factor; presenceof other risk factors related to back disorderswas not identified.
A case-control study of prolapsed lumbar discwas carried out using a hospital population-based design [Kelsey et al. 1984]. Cases(n=232) included individuals diagnosed withprolapsed lumbar disc; an equal number ofcontrols matched on sex, age, and medicalservice were selected. Exposure was assessedusing a detailed occupational history that wasnot described but presumably was obtained byinterview. An association with work-relatedlifting without twisting the body was observedat the highest lifting level (25 lb or more)(OR 3.8, 95% CI 0.7–20.1). Twisting withoutlifting was associated with disc prolapse (OR3.0, 95% CI 0.9–10.2); a combination of bothrisk factors had an OR of 3.1 (95% CI
1.3–7.5). The highest risk was observed forsimultaneous lifting and twisting with straightknees (OR 6.1, 95% CI 1.3–27.9). Despitethe fact that exposures were self-reported,these associations were notably strong. Thepotential existed for differential recall bias forcases and controls because study subjects wereinterviewed about work-related factors aftercase status was established. Interviewers maynot have been blinded to case/control status.
In Liles et al. [1984] prospective study of 453individuals working in jobs with manual materialhandling requirements, incidence of backinjuries was examined with regard to lifting. Thestudy group included those who lifted frequently(at least 25 lifts per day of not less than 4.53kg, with exposure of at least two hours perday). The outcome included reported orrecorded lifting injuries to the back. Liftingexposures were assessed until job change (upto a two-year period) using the Job SeverityIndex (JSI). The JSI is a measure of thephysical stress level associated with lifting jobsand is a function of the ratio of job demands tothe lifting capacities of the person performingthe job. Information on weight, frequency oflifting, and task geometry is collected throughcomprehensive task analysis. When the studygroup (working in 101 jobs from 28 plants)was classified into 10 equal categoriesaccording to JSI, a dose-response relationshipwith injury was observed (RR 4.5, 95% CI1.02–19.9 for total injuries, comparingcategory 10 to category 1). Study limitationsincluded no statement relating to response rateor participant selection, no adjustment forconfounders, and no statistical testing. Theoutcome definition specified that the back injurybe lifting-
6-16
related, which increased the likelihood that theoutcome would be related to the exposuremeasured. The prospective designassured thatmeasured exposures preceded injury onset.Other strengths included objective assessmentof exposure.
Using an unusual cross-sectional study design,Marras et al. [1993, 1995] examined therelationship between low-back disorders andspinal loading during occupational lifting. A totalof 403 jobs from 48 diverse manufacturingcompanies were assessed for risk of low-backdisorder using plant medical department injuryreports. Jobs were ranked into three categoriesaccording to risk, then assessed for position,velocity, and acceleration of the lumbar spineduring lifting motions in manual materialshandling using electrogoniometric techniques.Those in high-risk jobs averaged 226 lifts perhour, with an average load weight of 88.4 N. Acombination of five factors distinguishedbetween high- and low-risk jobs: liftingfrequency, load moment, trunk lateral velocity,trunk twisting velocity, and trunk sagittal angle.The highest combination of exposure measuresproduced an OR of 10.7 (95% CI 4.9–23.6 incomparison to the lowest combined measures).In univariate analyses, the most powerful singlevariable was maximum moment (a combinationof both weight of the object and distance fromthe body), which yielded a significant OR of 3.3between low- and high-risk groups [Marras etal. 1995]. The study design was unusual in thatthe unit of analysis appeared to be the jobrather than the individual. Neither participationrates nor total number of participants wasstated. No information appeared regarding theproportions of individuals within jobs who wererecruited
for measurement of lifting motions. However,the unit of analysis was job, and each wascharacterized by measurement of at least onestudy subject. Effects of covariates were notaddressed (multivariate analyses appeared toinclude only biomechanical variables). Thestudy results emphasized the multifactorialetiology of back disorders, includingcontributions of lifting frequency, loads, andtrunk motions and postures. The study designdid not allow for examination of temporalrelationships.
Walsh et al. [1989] examined the relationshipbetween self-reported LBP and work-relatedfactors in a population-based cross-sectionalstudy of 436 English residents. LBP wasascertained by interview, as was lifetimeoccupational history (including exposures tostanding, walking, sitting, driving, lifting, andusing vibrating machinery). Exposures wereascertained either as of the birthday prior toonset of symptoms or by lifetime occupationalhistory prior to onset of symptoms. Using themost recent job (as of the birthday prior tosymptoms), driving was associated withsymptoms in males (RR 1.7, 95% CI 1.0–2.9),as was lifting or moving weights of 25 kg ormore (RR 2.0, 95% CI 1.3–3.1), when allexposures were considered in multivariateanalyses. For women, lifting (RR 2.0, 95% CI1.1–3.7) was associated with symptoms. Whenlifetime exposures were considered, liftingremained significantly associated for males (RR1.5, 95% CI 1.0–2.4). Both sitting (RR 1.7,95% CI 1.1–2.6) and use of vibratingmachinery (RR 5.7, 95% CI 1.1–29.3, basedon one case) were associated with symptoms infemales. The multivariate analyses stratified onsex and adjusted for age and simultaneouswork exposures. While information on
6-17
symptoms and exposures was obtainedcrosssectionally, the authors attempted toconstruct a retrospective cohort design bygathering data on lifetime work exposures andback symptoms. While in the design lifetimeexposures were cumulated only prior todisorder onset, it would not be expected thatparticipants could recall these relationshipsaccurately. Temporal relationships wereunclear.
Strength of AssociationThe most informative studies included those thatemployed independent measures of exposure toassess lifting demands, as they provided thebest contrast among levels of exposure andwere subject to the least misclassification. Acase-control study by Punnett et al. [1991]found an OR of 2.16 (95% CI 1.0–4.7) for therelationship between back pain (ascertained bysymptoms and medical exam) and lifting, afteradjusting for covariates (including awkwardpostures). In their 1973 investigation, Chaffinand Park found a strong increase in incidenceof medical visits related to back problems withincreased LSR (with an approximate five-foldincrease in risk comparing males in the highestand lowest categories); they did not find asimilar dose-response relationship forfrequency of lifts. Marras et al. [1993, 1995]examined the relationship between low-backinjury reports and spinal loading during lifting,and found an OR of 10.7 (95% CI 4.9–23.6)for simultaneous exposures to lifting frequency,load weight, two trunk velocities, and trunksagittal angle. Both lifting and posturescontributed to the high ORs. In Magora’s[1972, 1973] studies of LBP and occupationalphysical efforts, the highest LBP rate wasobserved in those who lifted rarely. When LBPwas ranked by level of sudden maximal effort,
the highest rate was seen for those who did itoften, with a dose-response for three categories(10.9, 11.3, and 18.0, respectively, with a RRof 1.65 [95% CI 1.3–2.1]) when comparinglowest to highest). Liles et al. [1984] found asignificant association between incidence ofback injuries related to lifting and liftingexposures as assessed by JSI: the RR was 4.5(95% CI 1.02–19.9) comparing the highest andlowest exposure categories. Burdorf et al.[1991] found no association between back painsymptoms and lifting load (the latter did notvary across the six job categories examined inthe study). Huang et al. [1988] conducteddetailed ergonomic evaluations of two schoollunch preparation centers with differing rates ofmusculoskeletal (including back) disorders. Thecenter with higher disorder rates had greaterlifting and other work-related demands.Unfortunately, the study was ecologic in designand did not link exposures and outcomes tocalculate risk estimates for the study groups,although several areas for ergonomicintervention were identified.
Other studies assessed exposures by self-report on interview or questionnaire. Johanssonand Rubenowitz [1994] examined low-backsymptoms by index of manual materialshandling (which included lifting and other riskfactors). In neither white- nor blue-collarworkers was LBP significantly associated withthe index. In Kelsey’s 1975 case-control studyof herniated lumbar discs, cases and controlshad similar histories of occupational lifting (RR0.94, p=0.10). In a second case-control studyof prolapsed lumbar disc, Kelsey et al. [1984]found that an association with work-relatedlifting without twisting was observed only at the
6-18
highest lifting level (OR 3.8, 95%CI 0.7–20.1). A combination of both riskfactors at moderate levels yielded an OR of 3.1(95% CI 1.3–7.5). The highest risk was seenfor simultaneous lifting and twisting with straightknees (OR 6.1, 95%CI 1.3–27.9). Svensson and Andersson [1989]found a significant association between lifetimeincidence of LBP and lifting in univariateanalyses (RR 1.2, p<0.05), but not inmultivariate analyses. Holmström et al. [1992]found an association between one-yearprevalence of LBP and an index of manualmaterials handling (OR 1.27, 95% CI 1.2–1.4),after adjusting for age. No association wasobserved in multivariate analyses. Toroptsovaet al. [1995] found that LBP and lifting wererelated in univariate analyses (OR 1.4, p<0.05);no multivariate analyses were conducted. In theWalsh et al. [1989] examination of LBP andwork-related factors, LBP was associated withlifting (in jobs just prior to injury) (RR 2.0, 95%CI 1.1–3.7), when age, sex, and all exposureswere considered in multivariate analyses. Whenlifetime exposures were considered, liftingremained significantly associated for males (RR1.5, 95% CI 1.0–2.4). In Burdorf andZondervan’s 1990 study, an OR of 5.2 (95%CI 1.1–25.5) was observed for LBP andfrequent lifting among crane operators. Norelationship was seen for the referent group ofnoncrane operators from the same plant (OR0.70, 95% CI 0.14–3.5).
In a study that determined exposure status onthe basis of job title, Videman et al. [1984]found slightly higher rates (not significant) ofLBP in nursing aides than in qualified nurses.The authors stated that aides had higherworkloads related to patient handling andlifting. Knibbe and Friele [1996] found that
LBP rates were higher for registered nursesthan for nursing aides, whom they stated hadmore lifting responsibilities (OR 1.2, p=0.04).After adjusting for hours worked, however,aides had the higher rate (RR 1.3, no statisticaltesting done). Undeutsch et al. [1982]examined back pain in baggage handlers, agroup characterized by frequent bending, lifting,and carrying of loads. Although no exposureswere estimated for this group, symptoms weresignificantly associated with length ofemployment after adjusting for age (p=0.035).
In the studies using more quantitative exposureassessments, strengths of association for therelationships between low-back disorder andlifting included estimates including a negativerelationship [Magora 1972], no association[Burdorf et al. 1991], and several positiveassociations with ORs in the 2.2–10.0 range.One study found a positive relationshipbetween sudden maximal efforts and LBP (OR1.7) [Magora 1973]. Punnett et al. [1991]found a point estimate of 2.16 after adjustingfor other covariates; Chaffin and Park [1973]found a strong relationship (OR 5) for LSR (butnot lifting frequency); Marras et al. [1993,1995] found that the highest risk of injury wasrelated to lifting in combination with posture-related risk factors (OR 10.7). Liles et al.[1984] observed an OR of 4.5 for back injuriesand the highest JSI. The investigation of schoollunch preparers did not calculate risk estimates[Huang et al. 1988].
Studies that used subjective measures ofexposure found point estimates including none[Johansson and Rubenowitz 1994; Kelsey1975a,b; Videman et al. 1984] to a range
6-19
including 1.3, 1.4, 2.0, 3.8, and 5.2 [Burdorfand Zondervan 1990; Holmström et al. 1992;Kelsey et al. 1984; Knibbe and Freile 1996;Toroptsova et al. 1995; Undeutsch et al. 1982;Walsh et al. 1989]. Although the Kelsey et al.[1984] exposure estimates were based on self-report, they showed important relationshipsbetween lifting and posture in multivariateanalyses. While the OR for lifting alone was 3.8(for the highest lifting level), the OR rose to 6.1when postures related to twisting and bentknees were included in the model.
In summary, the articles reviewed provideevidence of a strong positive associationbetween low-back disorder and lifting. Resultsfrom these and other studies emphasized theimportance of awkward postures in the risk oflow-back disorder.
Temporal RelationshipTwo prospective studies assessed exposuresprior to identification of back disorders. Bothdemonstrated positive associations betweenexposure and back disorder. Thirteen of the 18studies were cross-sectional analyses. In two ofthese, investigators excluded cases of LBP withonset prior to the current job to increase thelikelihood that exposure preceded disorder. Athird cross-sectional study truncated self-reported exposures on the birthday precedingdisorder onset. One case-control studytruncated exposures prior to disorder onset. Ofthe four cross-sectional and case-controlstudies which attempted to address temporality,three found positive relationships between liftingand back disorder.
Consistency in AssociationAlthough the 18 studies used varying designs,
outcomes, and exposure assessment methods,they were fairly consistent in demonstrating arelationship between lifting and low-backdisorder when objective measures of exposurewere used to evaluate populations with highexposures. Results were less consistent whensubjective exposure measures were utilized.
A NIOSH review of earlier publications relatedto patient lifting demonstrated results consistentwith this review [Jensen 1990]. Acomprehensive literature search evaluated allstudies published between 1967 and 1987 thatcontained original research on nursingpersonnel and back problems. Of 90 studies,six were identified which distinguished betweentwo or more groups of nurses with differingfrequencies of patient handling and reported onback problems for each group. A weightedanalysis of results from the six reportsdemonstrated an overall increase in backproblems of 3.7 in those in the higher liftingfrequency category.
Coherence of EvidenceLifting and manual materials handling have beenstudied as risk factors for low back disorder fordecades. Studies of workers’ compensationclaims have shown that manual materialhandling tasks, including lifting, are associatedwith back pain in 25%-70% of injuries [Cust etal. 1972; Horal 1969; Snook and Ciriello1991]. Data from the 1994 Bureau of LaborStatistics annual Survey of OccupationalInjuries and Illnesses demonstrated that theindustry with the highest rate of time-lossinjuries due to overexertion was nursing andpersonal care facilities (where employees are
6-20
required to engage in frequent patient handlingand lifting).
During lifting, three types of stress aretransmitted through the spinal tissues of the lowback: compressive force, shear force, andtorsional force [Waters et al. 1993]. It has beensuggested that disc compression is believed tobe responsible for vertebral end-plate fracture,disc herniation, and resulting nerve rootirritation [Chaffin and Andersson 1984]. Inearly biomechanical assessments, modelsshowed that large moments are created in thetrunk area during manual lifting. Staticevaluations of the trunk demonstrated that liftingresults in large compressive forces on the spine.
More recently, biomechanical investigationshave focused on spine loading and disctolerances associated with asymmetric loadingof the trunk. In laboratory experiments,dynamic trunk motion components of liftinghave been associated with greater spineloading. Increased trunk motion during liftingactivities has been associated with increasedtrunk muscle activity and intra-abdominalmeasures, among other changes [Marras et al.1995]. Some laboratory studies have shownthat lateral shear forces make trunk motionsmore vulnerable to injury than in a compressiveloading situation. There is also in vitroevidence that the viscoelastic properties of thespine may cause increased strain duringincreased speed of motion [Marras et al.1995].
Current models for lifting-relatedmusculoskeletal injury stress that biomechanicalconsiderations comprise only part of theassessment of risk [Waters et al.
1993]. Other criteria include physiologicmeasures of metabolic stress and muscle fatigueand psychophysical considerations (theworker’s perception of his/her lifting capacity, acombination of perceived biomechanical andphysiologic attributes of the job). All threecriteria are important in assessing risk acrossthe full spectrum of job and individual workervariability.
Exposure-Response RelationshipsEight studies examined exposure-responserelationships in some form. Of these, four founddose-response relationships between low-backdisorder and objective measures of lifting[Chaffin and Park 1973; Liles et al. 1984;Marras et al. 1995; Punnett et al. 1991];another found a dose-response betweendisorder and sudden maximal efforts [Magora1973]. A study of baggage handlers found anassociation between back disorder and lengthof employment [Undeutsch et al. 1982]. Twostudies found no dose-response relationship(using a posture analysis assessment and amanual materials handling index) [Burdorf et al.1991; Johansson and Rubenowitz 1994].
The majority of studies which examinedexposure-response relationships, and inparticular those that utilized quantitativeexposure measures, demonstrated these trends.
Conclusions: Lifting and ForcefulMovements
There is strong evidence that low-backdisorders are associated with work-relatedlifting and forceful movements. The five studiesreviewed for this chapter which showed noassociation between lifting and back disorder used subjective measures of
6-21
exposure, poorly described exposureassessment methodology, or showed littledifferentiation of exposure within the studygroup. The remaining 13 studies wereconsistent in demonstrating positiverelationships, where those using subjectivemeasures of exposure showed a range of riskestimates from 1.2 to 5.2, and those using moreobjective assessments had ORs ranging from2.2 to 11. Studies using objective measures toexamine specific lifting activities generallydemonstrated risk estimates above three andfound dose-response relationships betweenexposures and outcomes. For the most part,higher ORs were observed in high-exposurepopulations (e.g., one high-risk groupaveraged 226 lifts per hour with a mean loadweight of 88 N. Evidence from other studiesand reviews has also suggested that groups withhigh- frequency exposure to lifting of heavyloads, such as nursing staff, are at high risk ofback disorder.
Most of the investigations reviewed for thisdocument adjusted for potential covariates inanalyses: two-thirds of the studies showingpositive associations examined effects of ageand gender. Nevertheless, some of therelatively high ORs that were observed wereunlikely to be caused by confounding or othereffects of lifestyle covariates. Several studiessuggested that both lifting and awkwardpostures were important contributors to the riskof low-back disorder. The observedrelationships are consistent with biomechanicaland other laboratory evidence regarding theeffects of lifting and dynamic motion on backtissues.
BENDING AND TWISTING(AWKWARD POSTURES)
DefinitionBending is defined as flexion of the trunk,usually in the forward or lateral direction.Twisting refers to trunk rotation or torsion.Awkward postures include non-neutral trunkpostures (related to bending and twisting) inextreme positions or at extreme angles. Severalstudies focus on substantial changes from non-neutral postures. Risk is likely related to speedor changes and degree or deviation from non-neutral position. For the purposes of thisreview, awkward postures also includedkneeling, squatting, and stooping. In most of thestudies included in this review, awkwardpostures were measured concurrently withother work-related risk factors for backdisorder.
Studies Reporting on the AssociationBetween LBP and Awkward PosturesTwelve studies examined the relationshipbetween low back disorder and bending,twisting, and awkward postures (Table 6-3,Figure 6-3). Most (nine) also examined theeffects of occupational lifting. See the previousdiscussion of lifting and forceful movements.Nine studies were cross-sectional in design,two case-control, and one prospective.
Participation rates were adequate for 83% ofthe investigations (Table 6-3). Four studiesassessed postures using objective measures (however, in the study by Magora [1972],details on their observation methods were notreported; the rest estimated exposures frominterview or questionnaire responses). Healthoutcomes included low-back and sciatic painsymptoms, lumbar-disc prolapse, and back
6-22
injury reports. In four investigations, outcomeswere defined using both symptoms and medicalexamination criteria. Only one investigation, thePunnett et al. [1991] case-control study ofback pain in auto workers, fulfilled the fourevaluation criteria (Table 6-3, Figure 6-3).
Several other studies, while not meeting all ofthe four criteria, are particularly notablebecause they used objective measures ofexposure assessment [Burdorf et al. 1991;Marras et al. 1993, 1995] or met more thanone of the criteria [Holmström et al. 1992;Kelsey et al. 1984]. As discussed earlier, thephysical examination criterion may be lessimportant in low-back disorders because of thepaucity of specific physical findings in mostcases of low-back disorders.
Descriptions of five studies which offered themost information regarding the effects ofbending, twisting, and awkward posturesfollow. Please note that there is some overlapwith studies that examined lifting effects.Detailed descriptions of the 12 studies appearin Table 6-6.
The Punnett et al. [1991] case-control studyexamined the relationship between back painand occupational exposures in auto assemblyworkers. Back pain cases (n=95) weredetermined by symptoms at interview andmedical examination; controls included thosefree of back pain. For all participants or proxiesin the same jobs, jobs were videotaped andwork cycles were reviewed using a postureanalysis system. Exposures included time spentin various awkward postures. Peakbiomechanical forces were estimated for up tonine postures where a load weighing at least 10lb was held in the hands. In multivariate
analyses that adjusted
for a number of covariates (age, gender, lengthof employment, recreational activity andmedical history), time in non-neutral posturesmild or severe flexion and bending werestrongly associated with back disorder (OR8.0, 95% CI 1.4–44). In the same model, liftingwas also associated (OR 2.16, 95% CI1.0–4.7). When the subset with physicalmedical findings was examined, associationswere more pronounced. Although few studysubjects were unexposed to all of the posturesstudied, a strong increase in risk was observedwith both intensity and duration of exposure. Itwas not possible to determine the relativecontributions of different awkward posturesbecause all were highly correlated. Onlyparticipants’ current jobs (for referents) or jobswhen symptoms started (for cases) wereanalyzed; the study design thus assumed ashort-term relationship between exposure andoutcome. Although length of time in job wasalso included in the models, the authorsattempted to ensure that exposure precededdisease by identifying time of onset andmeasuring exposures in the job held just prior.The strong associations, after adjustment forcovariates, are notable.
Burdorf et al. [1991] examined back painsymptoms in a cross-sectional study of maleconcrete fabrication workers and a referentgroup of maintenance workers. Back painsymptoms were assessed by questionnaire.Exposures were measured using the OvakoWorking Posture Analysis System, whichassessed postures for the back and lowerlimbs, along with lifting load. Information onexposures in previous jobs was also collected.
6-23
Concrete workers experienced significantlymore back symptoms than referents (OR 2.8,95% CI 1.3–6.0).
Univariate results showed associations betweenback pain and both posture index and WBV incurrent job. Correlations were presentedshowing lifting was not found to be associatedwith back pain or to vary significantly acrossthe six job categories examined in the study. Inmultivariate analyses adjusting for age, bothposture index and WBV were significantlyassociated with back pain, with ORs of 1.23(p=0.04) (for an ordinal scale of 6) and 3.1(p=0.001) (dichotomous), respectively. Thosein the highest posture index category were steelbenders, who spent an average of 47% of theirtime in bent back postures (compared to 12%for the lowest exposed group). The postureindex and WBV measures were highlycorrelated and analyzed separately. Strengthsof the study included use of a standardizedsymptom questionnaire, high participation ratesand objective measure of exposure, and anattempt to clarify the temporal relation betweenexposure and outcome by excluding cases ofback pain with onset before the present job.
Using an unusual cross-sectional study design,Marras et al. [1993, 1995] examined therelationship between low-back disorders andspinal loading during occupational lifting. A totalof 403 jobs from 48 diverse manufacturingcompanies were assessed for risk of low-backdisorder using plant medical department injuryreports. Jobs were ranked into three categoriesaccording to risk then assessed for position,velocity, and acceleration of the lumbar spineduring lifting motions in manual materialshandling using electrogoniometric techniques. Acombination of five factors distinguished
between high- and low-risk jobs: liftingfrequency, load moment, trunk lateral velocity,trunk twisting velocity, and trunk sagittal angle.The highest combination of exposure measuresproduced an OR of 10.7 (95% CI 4.9–23.6)(in comparison to the lowest combinedmeasures). The study design was unusual in thatthe unit of analysis appeared to be job ratherthan individual. Neither participation rate nortotal number of participants was stated. Noinformation appeared regarding the proportionsof individuals within jobs who were recruitedfor measurement of lifting motions. However,the unit of analysis was job, and each wascharacterized by measurement of at least onestudy subject. Effects of other covariates werenot addressed (multivariate models appeared toinclude only biomechanical variables). Thestudy results emphasize the multifactorialetiology of back disorders, includingcontributions of lifting frequency, loads, andtrunk motions and postures. The study designdid not allow for examination of temporalrelationships.
A case-control study of prolapsed lumbar discwas carried out using a hospital population-based design [Kelsey et al. 1984]. Cases(n=232) included individuals diagnosed withprolapsed lumbar disc; an equal number ofcontrols matched on sex, age, and medicalservice were selected. Exposure was assessedusing a detailed occupational history (notdescribed, but presumably obtained byinterview). An association with work-relatedlifting, without twisting the body, was observedat the highest lifting level (OR 3.8, 95% CI0.7–20.1). Twisting without lifting wasassociated with disc prolapse (OR 3.0, 95%CI 0.9–10.2); a combination of both riskfactors had an OR of 3.1 (95% CI 1.3–7.5).
6-24
The highest risk was observed for simultaneouslifting and twisting with straight knees (OR 6.1,95% CI 1.3–27.9). Despite the fact thatexposures were self-reported, theseassociations were notably strong. The potentialexisted for differential recall bias for cases andcontrols, because study subjects wereinterviewed about work-related factors aftercase status was established. Interviewers maynot have been blinded to case/control status.
Holmström et al. [1992] examined therelationship between LBP and work taskactivities in a cross-sectional study of maleconstruction workers. One-year prevalence ofLBP was ascertained by questionnaire. Asample of workers was clinically examined.Exposure relative to lifting, handling, and workpostures was obtained by self-report. Afteradjustment for age, the index for manualmaterial handling, which included lifting, wasassociated with LBP with a RR of 1.27 (95%CI 1.2–1.4). Stooping and kneeling posturesshowed a dose-response relationship withLBP, particularly severe LBP (with ORs 1.3,1.8, and 2.6 in comparison to those with nostooping; ORs 2.4, 2.6, and 3.5 in comparisonsto those with no kneeling, respectively). Noassociation was observed with sitting. Inmultiple regression analyses, LBP wasassociated with stooping (p<0.001) andkneeling (p<0.01). While the authors attemptedto adjust for some covariates (age, gender, andpsychosocial factors) in analyses, they did notappear to examine simultaneous effects ofphysical work-related factors in a single model.The cross-sectional design could not ascertainthe temporal relationships between exposureand disorder.
Strength of AssociationThe more informative studies included the Punnett et al’s [1991] case-controlinvestigation, which fulfilled the four evaluationcriteria, plus several others that usedindependent exposure assessments. In thePunnett et al. study, multivariate analyses thatadjusted for covariates demonstrated that timein non-neutral postures was strongly associatedwith back disorders (OR 8.09, 95% CI1.4–44). In the same model, the OR for liftingwas 2.2. Burdorf et al. [1991] foundassociations between posture index and backsymptoms in both univariate and multivariateanalyses: in multivariate analyses adjusting forage, the OR for posture index was 1.23(p=0.04), for an ordinal scale of six levels.Posture index was highly correlated with WBV.However, the Kelsey et al’s [1984] case-control study of prolapsed lumbar discs foundthat twisting without lifting had an OR of 3.0(95% CI 0.9–10.2); in combination, the twohad an OR of 3.1 (95% CI 1.3–7.5). Thehighest risk was observed for a combination oflifting, twisting, and straight knees (OR 6.1,95% CI 1.3–27.9). In the Marras et al. [1993,1995] cross-sectional study, back injuries wereassociated with spinal loading during lifting,which included simultaneous exposures to liftingfrequency, load weight, trunk lateral velocity,trunk twisting velocity, and trunk sagittal angle.An OR of 10.7 (95% CI 4.9–23.6) wasobserved for the highest combination ofexposure measures. Univariate ORs were 1.73(95% CI 1.38–2.15) for trunk lateral velocity,1.66 (95% CI 1.34–2.05) for trunk twistingvelocity, and 1.60 (95% CI 1.31–193) formaximum sagittal flexion when comparing thehigh-and low-risk groups [Marras et al. 1993].
6-25
The other studies showed a range of pointestimates. In univariate analyses, Magora[1972, 1973] found that for bending, thehighest rate of LBP was observed for therarely/never category. For twisting andreaching, the highest LBP rate was in thesometimes category. Johansson andRubenowitz [1994] found no associationsbetween low-back symptoms and bent ortwisted work postures in blue- and white-collarworkers. After adjustment for age and gender,however, extreme work postures weresignificantly associated with the outcome inblue-collar workers. Relationships werepresented as partial correlations, thuspreventing calculation of risk estimates.Riihimäki et al. [1994] observed thatoccupational exposure to twisted and bentpostures were associated with incidence ofsciatic pain in univariate but not multivariateanalyses. No risk estimates were provided. InSvensson and Andersson’s 1989 study of LBPin Swedish women, bending forward wasassociated with lifetime incidence in univariate(RR 1.3, p<0.05) but not multivariate analyses.The Masset and Malchaire [1994] univariateanalyses demonstrated that trunk torsions wereassociated with LBP in steel workers (OR1.55, p<0.05); no associations were shown inmultivariate analyses. Toroptsova et al. [1995]demonstrated that LBP in the past year wasassociated with bending (OR 1.7, p<0.01) inunivariate analyses (multivariate analyses werenot conducted). Riihimäki et al. [1989a]observed a dose-response for sciatic pain andself-reported twisted or bent postures; the ORfor the highest exposure category was 1.5[95% CI 1.2–1.9]. Holmström et al. [1992]observed that stooping and kneeling postureswere associated with LBP, particularly severe
disorder, with ORs of 2.6 and 3.5 (p<0.05),respectively.
In summary, three of the four studies usingmore quantitative exposure assessmentsshowed elevated risk estimates for therelationship between low-back disorder andbending, twisting, or awkward postures, withORs ranging from 1.23 (for a scaled variable)to 8.09; the highest risk estimate, an OR of10.7, was based on combined exposure tolifting and posture risk factors. Most of thesewere based on multivariate analyses thatadjusted for covariates (usually age andgender). The remaining studies demonstraterisk estimates ranging from no association (inone study), 1.3–1.7 in univariate but notmultivariate analyses, to a high of 3.5 in anotherstudy. Studies utilized a number of definitionsfor awkward postures, as noted.
Temporal RelationshipOne prospective study assessed exposuresprior to identification of back disorders. Resultsdemonstrated positive associations in univariatebut not multivariate analyses. [Riihimäki et al.1994]. Nine of 12 studies were cross-sectionalin design. In one of these, investigatorsexcluded cases of LBP with onset prior to thecurrent job to increase the likelihood thatexposure preceded disorder. [Burdorf et al.1991]. No association between exposure andback disorder was observed. One case-controlstudy examined only exposures experienced inthe job just prior to disorder onset [Punnett etal. 1991]. A strong association betweenexposure to awkward postures and back painwas observed.
6-26
Consistency in AssociationAlthough the 12 studies used varying designs,outcomes, and exposure assessment methods,the studies using quantitative exposuremeasures were fairly consistent indemonstrating a moderate relationship betweenawkward postures and low-back disorder.
Coherence of Evidence
Nine of the 12 studies which examined postureeffects also studied effects of lifting. Therefore,a discussion of coherence of evidence for theformer relationship is similar to that found in thesection on lifting and forceful movements.Forward flexion can generate compressiveforces on the structures of the low back similarto lifting a heavy object. Similarly, rapid twistingcan generate shear or rotational forces on thelow back [Marras et al. 1995].
Exposure-Response Relationships
Six studies examined dose-responserelationships between posture and low-backdisorder. In one, no dose-response relationshipwas found between LBP and estimates forbending and twisting/reaching. In the other fivestudies, relationships were demonstratedbetween back injury and spinal loading score,LBP and posture index, sciatic pain andawkward postures, LBP and stooping, andlow-back symptoms and kneeling.
Conclusions: Awkward Postures
The investigations that were reviewed providedevidence that low-back disorders areassociated with work-related awkwardpostures. Results were consistent in showingincreased risk of back disorder with exposure,despite the fact that studies defined disordersand assessed exposures in many ways. Several
studies found risk estimates above three anddose-response relationships between exposuresand outcomes. Many of the studies adjusted forpotential covariates in their analyses, and a fewexamined the simultaneous effects of otherwork-related risk factors in analyses. Severalstudies suggested that both lifting and awkwardpostures were important contributors to risk oflow back disorder.
WHOLE BODY VIBRATION (WBV)
DefinitionWBV refers to mechanical energy oscillationswhich are transferred to the body as a whole(in contrast to specific body regions), usuallythrough a supporting system such as a seat orplatform. Typical exposures include drivingautomobiles and trucks, and operating industrialvehicles.
Studies Reporting on the AssociationBetween LBP and Whole BodyVibration
Nineteen investigations addressed WBV as arisk factor for back disorder. Fifteen studydesigns were cross-sectional, two were cohort,one was case-control, and one had both cross-sectional and cohort components.
None of the 19 studies fulfilled all of the fourevaluation criteria (Table 6-4, Figure 6-4).Participation rates were over 70% for 13investigations. Seven used independentmeasures of exposure for estimation of WBV;in 10 studies, exposure information wasobtained by questionnaire or interview. In twostudies, exposure to WBV was based on jobtitle alone. Health outcomes included symptomreport of LBP, sciatica, or
6-27
lumbago, sick leaves or disability retirementsrelated to back disorders, and medicallyconfirmed herniated lumbar disc.
Five of the nine studies which met two or moreof the evaluation criteria used similarmethodologies and offered the most informationregarding the association between WBV andback disorder. Detailed descriptions for all 19investigations can be found in Table 6-6.
Bovenzi and Betta [1994] examined therelationship between WBV and back disorderin a cross-sectional study of male tractordrivers. The unexposed group included malerevenue inspectors and administration workerswith no vibration exposure. Outcomes includedvarious types of back symptoms reported byquestionnaire. Vibration measures wereobtained from a representative sample oftractors and linked to individual information onnumber of hours driven yearly (obtained byquestionnaire). Self-reported exposures topostural loads were also obtained. Incomparison to referents, tractor driversdemonstrated an OR of 3.22 (95% CI2.1–5.2) for lifetime LBP. For LBP in the pastyear, the OR was 2.39 (95% CI 1.6–3.7). ForLBP in the past year, ORs ranged from 2.31 to3.04 by exposure levels for total vibration dose,equivalent vibration magnitude, and duration ofexposure, after adjustment for covariates. Inmultivariate analyses, chronic LBP showed adose-response relationship with total vibrationdose (OR 2.00, 95% CI 1.2–3.4, for thehighest category), equivalent vibrationmagnitude (OR 1.78, 95% CI 1.04–3.0, forthe highest category), and duration of exposure(OR 2.13, 95% CI 1.2–3.8, for the highestcategory). Exposure-response relationshipswere observed for postural load categories,
with ORs of 4.56 (95% CI 2.6–8.0) for LBP inthe past year and 2.30 (95% CI 1.2–4.5) forchronic LBP (for the highest exposurecategories). Multivariate analyses adjusted forage, body mass index, education, sportsactivity, car driving, marital status, mentalstress, climatic conditions, back trauma andpostural load (or vibration dose, dependingupon the exposure examined).
Bovenzi and Zadini [1992] used a similarcross-sectional study design to examine lowback symptoms in male bus drivers. Referentsincluded maintenance employees who workedfor the same company. Back pain symptomswere assessed by questionnaire. WBV wasmeasured for a sample of buses used over therelevant time period. Cumulative vibrationexposures were calculated using thisinformation, along with questionnaire itemsrelated to work duration, hours, and previousexposures. In comparison to referents, busdrivers demonstrated an OR of 2.80 (95% CI1.6–5.0) for lifetime LBP; the OR for LBP inthe past year was 2.57 (95% CI 1.5–4.4). Inmultivariate analyses, the ORs for LBP in theprevious year were 1.67, 3.46, and 2.63 forthree total vibration dose categories. Similartrends were observed for other measures ofvibration (equivalent vibration magnitude andtotal duration of exposure), and after exclusionof those with exposure in previous jobs.Statistically significantly increasing trends wereobserved for nearly all types of back symptomsby exposure level (to all three measures ofvibration) after adjustment for covariates.Multivariate analyses adjusted for age,awkward postures, duration of exposure, bodymass index, mental workload, education,smoking, sports activities, and previousexposures.
6-28
Three studies of WBV effects were conductedby the same group of Dutch investigators. Thefirst examined back pain and WBV exposurescross sectionally in male helicopter pilots[Bongers et al. 1990]. A referent group ofnonflying Air Force officers (withcharacteristics similar to pilots) was alsoincluded. Information on back symptoms wasobtained by questionnaire. Vibration measureswere assessed in two helicopters of each typeused by the study group. Individual exposureswere calculated by matching this withquestionnaire items related to hours of flyingtime and types of helicopters flown. Informationon exposure to bent/twisted postures was alsoobtained by questionnaire. In comparison tocontrols, ORs for pilots were elevated for anumber of back symptoms: 9.0 (95% CI4.9–16.4) for LBP and 3.3 (95% CI 1.3–8.5)for sciatica. All of the above were adjusted forage, height, weight, climate, bent and twistedpostures, and feeling tense at work. Inmultivariate analyses, ORs for LBP were 13.8,7.5, 6.0, and 13.4 for four categories for totalflight time (in comparison to controls). ORs forLBP by total vibration dose were 12.0, 5.6,6.6, and 39.5. By hours of flight time per day,ORs were 5.6, 10.3, and 14.4 for LBP.Although there was some concern that pilotswith back pain may have dropped out ofemployment, risk estimates were high(particularly in analyses by exposure level).Transient back pain appeared to increase withdaily exposure time, while chronic back painappeared more associated with total flight timeand total vibration dose.
In a second study by the same group, WBVexposures were examined in male tractordrivers and a referent group of inspectors andmaintenance technicians [Boshuizen et al.
1990a,b]. Two investigations were conductedusing the same population: a 1986 cross-sectional study of a cohort identified in 1975,and a cohort analysis of sick leaves anddisability retirements due to back disorderthrough the same time period. For the cross-sectional analyses, information on backsymptoms was obtained by questionnaire.Vibration was measured for a sample ofvehicles and linked with questionnaireinformation related to types of vehicles driven,hours, and previous employment. Informationregarding exposure to awkward postures wasalso collected. Results from the cohort analysisshowed an incidence density ratio of 1.47(95% CI 1.04–2.1) for a comparison of sickleaves due to back disorders in exposed andreferent groups. An increase in sick leaves fordisc disorders by vibration dose was observed,with an OR of 7.2 (95% CI 0.92–179) for thehighest category. Cross-sectional study resultsdemonstrated increases in LBP symptomprevalence by vibration dose category.Multivariate ORs increased by vibration dose(an OR of 2.8, 95% CI 1.6–5.0, for the highestcategory) and years of exposure (an OR of 3.6,95% CI 1.2–11, for the highest category) afteradjustment for duration of exposure, age,height, smoking, awkward postures, and mentalworkload.
Boshuizen et al. [1992] also conducted across-sectional study of back pain in fork-lifttruck and freight container tractor driversexposed to WBV. Referents included otheremployees working for the same shippingcompany, but with no vibration exposure. Backpain symptoms were assessed by questionnaire.Exposures were estimated by measurement ofvibration in a sample of vehicles, combined withquestionnaire responses. Cumulative exposures
6-29
were calculated, truncating at time of symptomonset. Prevalence of back pain was higher inthe exposed group than in referents: the RR forback pain was 1.4 (p<0.05); RRs for LBP andlumbago were 1.4 (p<0.05) and 2.4 (p<0.05),respectively, after adjusting for age. Differencesin LBP were observed only in younger agegroups after multivariate adjustment for mentalstress, years of lifting, awkward postures,height, smoking, and hours of sitting. There wasno association between total vibration dose andback pain (OR 0.99, 95% CI 0.85–1.2) orlumbago (OR 1.14, 95% CI 0.91–1.4). Onlyvibration in the 5 years immediately precedingsymptom onset was significantly associated withback pain (OR 2.4, 95% CI 1.3–4.2) andlumbago (OR 3.1, 95% CI 1.2–7.9). Itappeared that a healthy worker selection effectwas operating, as differences in back pain wereobserved only for those in younger age groups.
Evaluation of the Causal RelationshipBetween Back Disorder and WholeBody Vibration
Strength of AssociationRecent studies that included quantitativeexposure assessments provided the mostinformation regarding the relationship betweenWBV and back disorder [Bongers et al. 1988;Boshuizen et al.1990a, b; Bovenzi and Betta1994; Bovenzi and Zadini 1992]. (Two otherrecent studies also described quantitativeexposure assessments, but no results relating tothese were presented [Burdorf et al. 1993;Magnusson et al. 1996]). In all five, ORs werecalculated by levels of vibration exposure,expressed in several ways (usually includingmagnitude and duration of exposure). In thefive studies, overall ORs comparing back painin exposed and referent groups ranged from 1.4
[Boshuizen et al. 1992] to 9.5 [Bongers et al.1990]. Analyses conducted by exposure leveldemonstrated stronger relationships. In Bovenziand Betta’s 1994 study of tractor drivers, ORsfor lifetime LBP were 3.79 for total vibrationdose, 3.42 for equivalent vibration magnitude,and 4.51 for duration of exposure (for thehighest exposure levels). For LBP in theprevious year, ORs were 2.36, 2.29, and 2.74for the highest levels of the same threeexposure measures. In Bovenzi and Zadini’s1992 study of urban bus drivers, the highestORs for LBP were observed for intermediaterather than the highest exposure categories: 3.46 for total vibration dose, 3.77 forequivalent vibration magnitude, and 3.08 fortotal duration of WBV exposure. The Bongerset al. [1990] investigation of back pain inhelicopter pilots demonstrated that the highestORs for LBP were found in the highestcategories for total flight time (OR 13.4, 95%CI 5.7–32), total vibration dose (OR 39.5,95% CI 10.8–156) and hours of flight time perday (OR 14.4, 95% CI 5.4–38.4). A study oftractor drivers demonstrated LBP ORs of 2.8(95% CI 1.6–5.0) for the highest total vibrationdose and 3.6 (95% CI 1.2–11) for the highestexposure duration category [Boshuizen et al.1990a]. In the same population, the OR for allsick leaves due to back disorder was 1.47,comparing exposed (95% CI 1.04–2.1) andreferent groups [Boshuizen et al. 1990b]. Forsick leaves related to intervertebral discdisorders, the highest OR was observed for thehighest exposure category (OR 7.2, 95% CI0.92–179). The Boshuizen et al. [1992] study offorklift truck and freight container tractordrivers showed no association between backpain and total vibration dose (OR 0.99, 95% CI0.85–1.2) but did show an association forvibration in the preceding five years (OR 2.4,
6-30
95% CI 1.3–4.2). In this study the increase inLBP prevalence in the exposed group was onlysignificant for those in younger age groups (anOR of 5.6 for those age 25-34) in multivariateanalyses. In all five of these cross-sectionalstudies, ORs were calculated by vibrationexposure category after adjusting for a numberof covariates, as mentioned in the detailed studydescriptions, above.
Other studies assessed both exposure and low-back disorder by interview or questionnaire.Burdorf and Zondervan [1990] observed noassociation between WBV exposure and LBPin crane operators in univariate analyses (OR0.66, 95% CI 0.14–3.1); no associations wereobserved in multivariate analyses. Toroptsovaet al. [1995] also found no association betweenLBP and vibration in their study (no definitionfor vibration was provided, but WBV wassuggested). In the Riihimäki et al. 1994prospective study, sciatic pain was associatedwith vibration in univariate but not multivariatemodels (no risk estimates were provided).While the definition for “vibration” was notclear, the authors suggested it could beinterpreted as low-level WBV. The Masset andMalchaire [1994] cross-sectional study foundthat LBP was associated with vehicle driving(OR 1.2, p<0.001) in univariate analyses.Similar results were observed in multivariateanalyses (OR 1.2, p<.005). Riihimäki et al.[1989a] observed an OR of 1.3 (95% CI1.1–1.7) for longshoremen and earthmovers incomparison to a referent group with novibration exposure. In the same study, noassociation was seen for annual car driving (OR1.1, 95% CI 0.9–1.4). Walsh et al.[1989] found that driving (on job held prior tosymptoms) was significantly associated withlow-back symptoms in males (RR 1.7, 95% CI
1.0–2.9) after adjusting for age and other jobexposures in multivariate analyses. Burdorf etal. [1991] found that WBV was significantlyassociated with back pain (OR 3.1, p=0.001)in multivariate analyses that adjusted for age.The Kelsey [1975a] case-control study found asignificant association between herniatedlumbar disc and time driving (OR 2.75,p=0.02), and more specifically, working as atruck driver (OR 4.7, p<0.02). Burdorf et al.[1993] investigation demonstrated an OR of3.29 (95% CI 1.5–7.1) for crane operatorsand 2.51 (95% CI 1.5–5.4) for vibration-exposed straddle-carrier drivers after adjustingfor a number of covariates. In a study of Danishsalespeople, annual driving distance wasassociated with low-back symptoms [Skov etal. 1996]. A dose-response relationship wasobserved in multivariate analyses, with an ORof 2.79 (95% CI 1.5–5.1) for the highestcategory.
Four studies assessed exposures primarily byjob title. Magnusson et al. [1996] observed anOR of 1.79 (95% CI 1.2–2.8) for bus andtruck drivers in comparison to an unexposedreferent group. In a study of crane operators,the exposed group demonstrated ORs of 2.00(95% CI 1.1–3.7) for all intervertebral discdisorders and 2.95 (95% CI 1.2–7.3) for discdegeneration after adjustment for age and shift[Bongers et al. 1988]. An examination of riskestimates of disc degeneration by years ofexposure showed the highest OR (5.73) in thehighest exposure category. In the Johanning[1991] study of subway train operators, an ORof 3.9 (95% CI 1.7–8.6) was observed forsciatica. While not a primary focus ofthe Magora [1972, 1973] studies of LBP ineight selected occupations, it was observed thatbus drivers had back pain rates similar to those
6-31
of the comparison group of bankers (RR 1.19,95% CI 0.8–1.7).
Thus, four out of five studies using quantitativeexposure assessments demonstrated positiveassociations between back disorder outcomesand vibration exposures, with ORs ranging from1.4 to 39.5. The fifth cross-sectional studyfound no overall association between exposureand back disorder but found associations inselected subgroups (which suggested that thestudy population was biased, as noted above).In all of these studies, risk estimates byexposure category were calculated afteradjustment for many covariates.
In the remaining studies, risk estimates varied,including no association (n=3), ORs of 1.2, 1.7,and 2.8 for driving, an OR of 1.8 for truck orbus driving, an OR of 4.7 for truck driving, anOR of 1.3 for machine operation, ORs of 2.0,2.95 and 5.73 for crane operation, an OR of3.1 for WBV, and an OR of 3.9 for subwaytrain operation.
In summary, the evidence from theseinvestigations suggests a positive associationbetween WBV and back disorder.Relationships were particularly strong for high-exposure groups where exposures wereassessed using observational or measurementapproaches.
Temporal RelationshipThree studies had prospective designs in whichtemporal relationships between outcome andexposure could be determined [Bongers et al.1988; Boshuizen et al. 1990b; Riihimäki et al.1994]. In two of these, clear positiverelationships between back disorder andexposure were demonstrated [Bongers et al.
1988; Boshuizen et al. 1990b]. Twelve studieshad a cross-sectional design that could notdirectly address temporality. However, threeattempted to clarify relationships by excludingfrom analysis the cases with disorder onsetprior to current job [Burdorf et al. 1991, 1993;Burdorf and Zondervan 1990]. A fourth cross-sectional study truncated self-reportedexposures on the birthday preceding disorderonset [Walsh et al. 1989]. In these fourinvestigations, positive relationships betweenback disorder and WBV were also observed.
Consistency in AssociationResults with regard to the relationship betweenlow back disorder and WBV were mostconsistent in the studies using observational ormeasurement approaches to exposureassessment. The strength of association wasmore variable in studies using job titles orquestionnaires to assess exposures. Thevariability in the associations does not appear tobe related to confounding exposures, sincemost studies adjusted for age, gender and atleast several other confounders. Studies usingmore quantitative exposure measures werefairly consistent in showing the higher riskestimates.
In addition to the epidemiologic investigationsthat were reviewed for this document, manymore were conducted in the 1960s though the1980s. Others have summarized this evidencein earlier reviews. Hulshof and Veldhuijzen vanZanten [1987] concluded that, although studiesvaried in methodologies and quality, mostshowed a strong tendency toward a positiveassociation between WBV exposure and LBP.Seidel and Heide [1986] stated that theliterature they reviewed indicated an increasedrisk of spine disorders after intense long-term
6-32
exposure to WBV. Bongers and Boshuizen[1990] conducted a meta-analysis of studiespublished through 1990 that examined therelationship between WBV and several backdisorders. The overall OR for WBV exposureand degenerative changes of the spine was 1.5;the summary OR for LBP was also 1.5. Theseconclusions are consistent with the positiveassociations observed in the evidence reviewedabove (although the studies published in the1990s have tended to report larger ORs).
Other evidence for the relationship is providedby surveillance data. The U.S. population-based National Health Interview Survey,carried out in 1988, found that malesemployed as truck drivers and tractorequipment operators had a RR of 2.0 for backpain in comparison to all male workers [Guo etal. 1995].
Coherence of EvidenceLaboratory studies have shown that exposureto WBV causes spine changes that may berelated to back pain. These include fatigue ofthe paraspinal muscles and ligaments, lumbardisc flattening, disc fiber strain, intradiscalpressure increases, disc herniation, andmicrofractures in vertebral end-plates [Wilderand Pope 1996]. Studies of acute effects haveshown that the vertebral end-plate is thestructure that is most sensitive to high WBVexposure, followed by the intervertebral disc[Wikström et al. 1994]. Experimentalinvestigations have demonstrated that highexposures to vibration cause injuries such asdegeneration and fracturing of the vertebralend-plate. With regard to intervertebral discs,several studies have suggested that vibrationcauses creep, an increase in intradiscal pressureresulting from compressive loading. Pressure
peaks may cause ruptures in the superficialstructure of the disc and changes in thenutritional balance that lead to degeneration.Thus, prolonged vibration exposure may causespine pathology through mechanical damageand/or changes in tissue metabolism.
In addition to pathology of the vertebrae andintervertebral discs, vibration exposure hasbeen shown to cause changes inelectromyographic (EMG) activity in muscles ofthe lower back [Wikström et al. 1994]. Forexample, EMG experiments have demonstratedthat lower back muscle exhaustion increasesduring WBV exposure in truck driving.Decreased stability of the lower back mayresult from slower muscle response, perhapsincreasing the risk of injuring other structures.
Laboratory investigations have shown thatother work-related factors, including prolongedsitting, lifting, and awkward postures, may actin combination with WBV to cause backdisorder [Dupuis 1994; Wikström et al. 1994;Wilder and Pope 1996].
Exposure-Response RelationshipsFive of six studies which carried outquantitative exposure assessment demonstratedexposure-response relationships betweenWBV and back disorder.
6-33
Bovenzi and Betta [1994] observed a dose-response between chronic LBP and totalvibration dose, equivalent vibration magnitude,and duration of exposure. Bovenzi and Zadini[1992] found statistically significantly increasingtrends for nearly all types of back symptoms byexposure level, after adjustment for covariates.Bongers et al. [1990] demonstrated increasedORs for sciatic pain and transient back painwith increasing hours of daily flight time. Intheir cohort of tractor drivers, Boshuizen et al.[1990b] observed an increase in risk of sickleaves for disc disorder by total vibration doselevel.
In other studies, Bongers et al. [1988] found anincrease in risk of disc degeneration by years ofexposure to crane operation; Skov et al.[1996] found an increase in low-backsymptoms with annual driving distance.Johanning [1991] found no association betweenyears of employment as a subway trainoperator and back pain symptoms.
The majority of studies which examined backdisorders by exposure level demonstrateddose-response relationships.
Conclusions: Whole Body VibrationThere is strong evidence of a positiveassociation between exposure to WBV andback disorder. Of the 19 studies reviewed forthis chapter, four demonstrated no associationbetween WBV and back pain. Possibleexplanations for these results included use ofsubjective exposure assessments that perhapsresulted in misclassification of exposure statusand, in one cross-sectional study, operation ofa healthy worker selection effect (where thosewith higher exposures dropped out of the studygroup). The remaining 15 studies were
consistent in demonstrating positiveassociations, with risk estimates ranging from1.2 to 5.7 for those using subjective exposuremeasures, and from 1.4 to 39.5 for those usingobjective assessment methods. Most of thestudies that examined relationships in high-exposure groups using detailed quantitativeexposure measures found strong positiveassociations and exposure-responserelationships between WBV and back pain.These relationships were observed afteradjusting for age and gender, along with severalother covariates (which, depending on thestudy, may have included smoking status,anthropometric measures, recreational activity,and physical and psychosocial work-relatedfactors). This evidence is supported by resultsobserved in many earlier epidemiologicinvestigations that have been summarized inother reviews.
Laboratory studies have demonstrated WBVeffects on the vertebrae, intervertebral discs,and supporting musculature. Both experimentaland epidemiologic evidence suggests that WBVmay act in combination with other work-relatedfactors such as prolonged sitting, lifting, andawkward postures to cause increased risk ofback disorder.
It is possible that effects of WBV may dependon the source of exposure. For example, in thestudies reviewed for this document, ORs wereparticularly high for helicopter pilots. It was notpossible to determine differences for othertypes of vehicles (automobiles, trucks, andagricultural, construction, and industrialvehicles).
6-34
STATIC WORK POSTURES
DefinitionStatic work postures include isometric positionswhere very little movement occurs, along withcramped or inactive postures that cause staticloading on the muscles. In the studies reviewed,these included prolonged standing or sitting andsedentary work. In many cases, the exposurewas defined subjectively and/or in combinationwith other work-related risk factors.
Studies Reporting on the AssociationBetween LBP and Static WorkPostures
Ten studies examined relationships betweenlow back disorder and static work postures,which may have included prolonged sitting,standing, or sedentary work. For none wasstatic work posture the primary occupational exposure of interest. Instead, it was often oneof many variables examined in larger studies ofseveral or many work-related risk factors. Nineof the studies were cross-sectional in design;one was a case-control study.
None of the investigations fulfilled the fourresearch evaluation criteria (Table 6-5, Figure6-5). Participation rates were acceptable for60%. For four, case definitions included bothsymptoms and medical examination criteria.Health outcomes included symptom report ofback pain, sciatica, or lumbago, back pain asascertained by symptoms and medical exam,herniated lumbar disc, and lumbar discpathology. One study claimed to assess job-related exposures by observation; the nineothers obtained information on static workpostures by self-report on interview orquestionnaire.
Below are descriptions of four of the moreinformative studies. Detailed descriptions for all10 investigations are found in Table 6-6).
Burdorf and Zondervan [1990] carried out across-sectional study comparing 33 male craneoperators with noncrane operators from thesame Dutch steel plant, matched on age.Symptoms of LBP and sciatica were assessedby questionnaire. Activities in current and pastjobs were assessed by questionnaire;exposures were rated according to level ofheavy work, frequency of lifting, WBV, andprolonged sedentary posture. Crane operatorswere significantly more likely to experienceLBP (OR 3.6, 95% CI 1.2–10.6). Amongcrane operators alone, the OR for heavy workwas 4.0 (95% CI 0.76–21.2) after controllingfor age, height, and weight. It was determinedthat this heavy work occurred in the past andnot in current jobs. Among crane operatorsalone, the OR for frequent lifting was 5.2 (95%CI 1.1–25.5). The frequent lifting in craneoperators was also determined to be from jobsheld in the past. Among noncrane operators,history of frequent lifting exposure was notassociated with LBP (OR 0.70, 95% CI0.14–3.5). Among crane operators, univariateORs for WBV and prolonged sedentarypostures were 0.66 (95% CI 0.14–3.1) and0.49 (95% CI 0.11–2.2), respectively. Inmultivariate analyses controlled for age, height,weight, and current crane work, associationswith specific work-related factors weresubstantially reduced; the high prevalence ofLBP in crane operators was explained only bycurrent crane work. No measures of dose-response were examined. Limitations includeda low response rate for crane operators (67%),with some suggestion that those with illness mayhave been underrepresented (perhaps
6-35
underestimating the OR), and self-report ofhealth outcomes and exposures. Theinvestigators excluded cases of LBP with onsetbefore the present job to increase the likelihoodthat exposure preceded disease.
Kelsey [1975b] carried out a hospitalpopulation-based case-control study ofherniated lumbar discs and their relationship toa number of workplace factors, including timespent sitting, chair type, lifting, pulling, pushing,and driving. Cases were defined by symptoms,medical evaluation, and radiology; exposureswere ascertained by interview (over lifetime jobhistory). Cases (n=223) and controls (n=494unmatched controls) had similar histories ofjob-related lifting (RR 0.94, p=0.10). Findingsindicated that sedentary work (sitting more thanhalf the time at work) was associated with discherniation, but only for the age group 35 yearsand older (RR 2.4, p=0.01). (The RR for thoseless than 35 was 0.81). Disc herniation wasalso associated with time spent driving (RR2.75, p=0.02) and, more specifically, withworking as a truck driver (RR 4.7, p<0.02),suggesting a relationship with WBV. The studydesign had several potential limitations,including possible unrepresentativeness of thestudy population (because the group washospital-based). As exposure information wasobtained retrospectively, cases may have over-reported exposures thought to be associatedwith back problems. Strengths include a well-defined outcome and consistent results incomparisons to the two control groups.
Svensson and Andersson [1989] examinedLBP in a population-based cross-sectional
study of employed Swedish women.Information on LBP and sciatica was obtained
by questionnaire, as were exposure-relateditems. Physical exposures included lifting,bending, twisting, other work postures, sitting,standing, monotony, and physical activity atwork. Lifetime IRs varied by occupation, withranges from 61%–83% in younger age groupsand 53%–75% in older groups. After the studywas completed, the authors noted that for thesewomen, the highest lifetime incidence of LBPwas not found in jobs with the highest physicaldemands. The measure for “physical activity atwork” was also not significantly associated withLBP in univariate analyses. Bending forward(RR 1.3), lifting (RR 1.2), and standing (RR1.3) were associated with lifetime incidence ofLBP in univariate analyses (p<0.05). Sittingwas not (OR 0.84, p=0.10). None of themeasures of physical workplace factors wereassociated with lifetime incidence of LBP inmultivariate analyses.
Videman et al. [1990] studied 86 males whodied in a Helsinki hospital to determine thedegree of lumbar spinal pathology. Discdegeneration and other pathologies weredetermined in the cadaver specimens bydiscography and radiography. Subjects’symptoms and work exposures (heavy physicalwork, sedentary work, driving, and mixed)were determined by interview of familymembers. In comparison to those with mixedwork exposures, those with sedentary (OR24.6, 95% CI 1.5–409) and heavy work (OR2.8, 95% CI 0.3–23.7) had increased risk ofsymmetric disc degeneration. Similarrelationships were seen for end-plate defectsand facet joint osteoarthrosis. For mostpathologic changes,
6-36
sedentary work appeared to have a strongerrelationship than heavy work. Back painsymptoms were consistently higher in thosewith any form of spinal pathology, although thedifference was significant only for anularruptures. This study was unusual in design inthat it examined a combination of spinalpathological outcomes, symptoms, andworkplace factors. However, participation inthe study was dependent on obtaininginformation from family members; participationrates were not stated. While recall bias is oftena problem in studies of the deceased, in thiscase it should have been nondifferential, ifpresent.
Strength of AssociationThe ten studies were approximately equal interms of information they provided relating tostatic work postures. Burdorf and Zondervan[1990] observed an OR of 0.49 (95% CI0.11–2.2) for the univariate relationshipbetween prolonged sedentary postures andLBP in crane operators. Holmström et al.[1992] found no association between LBP andsitting (in univariate or multivariate analyses). Inthe Magora [1972, 1973] cross-sectionalinvestigation, the highest LBP rates wereobserved for those in the “rarely” category forvariables related to sedentary postures, sitting,and standing. No dose responses wereobserved. In the Toroptsova et al. [1995] studyof machine manufacturing workers, sitting,standing, and static work postures were notassociated with LBP history in univariateanalyses. No details were provided. Inmultivariate analyses, Masset and Malchaire[1994] found a nonsignificant associationbetween LBP and seated posture (OR 1.5,p=0.09) in multivariate analyses. Svensson andAndersson’s 1989 study of Swedish women
found that standing was associated with lifetimeincidence of LBP in univariate analyses (OR1.3, p<0.05), but not in multivariate models.Sitting was not associated in univariate analyses(OR 0.84, p=0.10). Walsh et al. [1989] foundthat low-back symptoms were associated withlifetime occupational exposure to sitting infemales only (RR 1.7, 95% CI 1.1–2.6) inmultivariate analyses that considered otherwork exposures. Kelsey’s 1975b case-controlstudy demonstrated that sedentary work (sittingmore than half the time at work) was associatedwith lumbar disc herniations, but only for those35 and older (RR 2.4, p=0.01); the RR for thoseless than 35 was 0.81. In a study of salespeople ,a dose-response was observed for sedentarywork and low back symptoms. An OR of 2.45(95% CI 1.2–4.9) was seen for the highestcategory after adjustment for covariates [Skovet al. 1996]. The Videman et al’s [1990] studyof cadavers found that those with histories ofeither sedentary or heavy work exposure hadincreased risk of symmetric disc degeneration(OR 24.6, 95% CI 1.5–409 and OR of 2.8,95% CI 0.3–23.7, respectively). Similar resultswere seen for other disc pathologies. For mostpathologic changes, sedentary work appearedto have a stronger relationship than heavywork.
In summary, most (n=6) risk estimates forvariables related to static work postures,including standing and sitting, were notsignificantly different from one. Others foundsmall to moderate significant increases in risk:ORs of 1.3 for standing, 1.7 for sitting (femalesonly), and 2.4 and 2.5 for sedentary work. TheVideman et al. [1990] cadaver study found highrisks of disc pathology in those with a history ofsedentary work. Study quality was similaracross the range of point estimates observed.
6-37
Therefore, an estimate of the strength ofassociation is difficult to determine. Themagnitude cannot be estimated based on theavailable data.
Temporal RelationshipEight of 10 studies were cross-sectional indesign. Two of these attempted to useadditional methodologies to increase thelikelihood that exposure preceded disorder byexcluding cases with onset prior to current joband truncating exposures prior to disorderonset. One found a positive relationshipbetween prolonged sitting and LBP symptoms.
Consistency in Association
The studies showed poor consistency inestimation of the relationship between low-back disorder and static work postures,perhaps due to considerable differences indefinition of exposure.
Coherence of Evidence
As mentioned elsewhere, LBP has beenassociated with mechanical forces causing anincreased load on the lumbar spine [Waters etal. 1993]. Increased loading on the spinecauses increased intervertebral disc pressures,which in turn, may be responsible for herniationand back pain. In laboratory experiments, discpressure has been found to be substantiallygreater in unsupported sitting than in standingpositions [Chaffin and Andersson 1984].
Studies reviewed for this document suggestedrelationships between back disorder andnonwork activities seemed to be consistent withthe hypothesis that static
work postures might be associated with back
disorder. Kelsey [1975a] observed that, inaddition to sedentary work, amount of timespent sitting on weekends was associated withherniated discs. The finding that sedentarywork was associated with herniated discs onlyin older age groups suggested that duration ofexposure may be important and that a thresholdmay exist. Toroptsova et al. [1995] observedthat back pain was lower in those who engagedin sports activity, perhaps suggesting thatgreater muscle strength prevents back pain.
Several authors offered explanations for thelack of associations they observed. It waspointed out that perception of “sedentary” issubjective and that many jobs that investigators(or subjects) considered to include prolongedstatic postures may actually have allowedconsiderable movement throughout the day(such as office workers). Other “sedentary”groups (such as industrial sewing machineoperators) may be forced by work schedules tomaintain static postures for long periods. It isimportant to have a true range of exposure ifdifferences in associated disorders are to bedetected.
Exposure-Response RelationshipsThree studies addressed dose-responserelationships, two of which did not demonstrateany trends. Magora [1972, 1973] found thehighest risk of LBP in the lowest exposurecategories for sedentary postures, sitting, andstanding. Videman et al. [1990] found a highrate of lumbar disc pathology in those withhistories of sedentary and heavy work, withrelationships stronger for sedentary work. Adose-response for LBP symptoms andsedentary work was observed by Skov et al.[1996].
6-38
Conclusions: Static Work PosturesTen studies examined the relationship betweenlow-back disorder and static work postures. Inmost cases, this exposure was not of primaryinterest but was one of many potentialworkplace risk factors that were included inanalyses. Static work posture was defined inseveral ways, including sedentary work andwork-related sitting and standing. Exposureinformation was ascertained by interview fornine of 10 studies. The strength of associationcould not be easily estimated because a largeproportion of point estimates did not differstatistically significantly from unity. As a whole,the results from these studies provideinadequate evidence that a relationship existsbetween static work postures and low-backdisorder.
ROLE OF CONFOUNDERS
As mentioned above, back disorder ismultifactorial in origin and may be associatedwith both occupational and nonwork-relatedfactors and characteristics. The latter mayinclude demographics, leisure time activities,history of back disorder, and structuralcharacteristics of the back [Garg and Moore
1992]. The relative contributions of thesecovariates may be specific to particularanatomic areas and disorders. For example, arecent study of identical twins demonstratedthat occupational and leisure time physicalloading contributed more to disc degenerationof the upper than the lower lumbar region[Battié et al. 1995]. For both anatomic areas,age and twin effects (genetic influences andearly shared environment) were the strongestidentifiable predictors for this particular healthoutcome.
Psychosocial factors, both work- andnonwork-related, have been associated withback disorders. These relationships arediscussed at length in Chapter 7 and AppendixB.
In the studies reviewed for this document,gender and age effects were addressed in most(86% and 74%, respectively). Approximately40% addressed work-related psychosocialfactors. In addition to these, many studiesaddressed other potential confounders in theiranalyses.
Table 6-1. Epidemiologic criteria used to examine studies of low back MSDs associated with heavy physical work
Study (first author andyear)
Risk indicator(OR, PRR, IR
or p-value)*,†Participation
rate $$70%Physical
examination
Investigatorblinded to case
and/orexposure
status
Basis for assessing backexposure to heavy physical
work
Met at least one criterion:
Åstrand 1987 2.3† Yes Yes No Job titles or self-reports
Bigos 1991b No association No No NR† Observation or measurements
Burdorf 1991 No riskestimate§
Yes No No Observation or measurements
Clemmer 1991 2.2†, 4.3† Yes No NR Job titles or self-reports
Heliövaara 1991 1.9,2.5†
Yes Yes No Job titles or self-reports
Hildebrandt 1995 1.2† Yes No No Job titles or self-reports
Hildebrandt 1996 No association Yes No No Job titles or self-reports
Johansson 1994 No association Yes No NR Job titles or self-reports
Leigh 1989 1.5† Yes No NR Job titles or self-reports
Masset 1994 No association Yes No NR Job titles or self-reports
Partridge 1968 1.2 Yes Yes No Job titles or self-reports
Riihimäki 1989b 1.0 Yes No NR Job titles or self-reports
Ryden 1989 2.2† Yes No NR Job titles or self-reports
Svensson 1989 No association Yes No NR Job titles or self-reports
Videman 1984 1.1 Yes No NR Job titles or self-reports
Videman 1990 2.8,12.1†
NR Yes NR Job titles or self-reports
Met none of the criteria:
Bergenudd 1988 1.8† No No NR Job titles or self-reports
Burdorf 1990 4.0 No No NR Job titles or self-reports
*Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR). †Indicates statistical significance. ‡Not reported. §Significant associations found in univariate but not multivariate results.
6-39
Table 6-2. Epidemiologic criteria used to examine studies of low back MSDs associated with lifting and forcefulmovements
Study (first author andyear)
Risk indicator(OR, PRR, IR
or p-value)*,†Participation
rate $$70%Physical
examination
Investigatorblinded to case
and/orexposure
status
Basis for assessing backexposure to lifting andforceful movements
Met all four criteria:
Punnett 1991 2.2† Yes Yes Yes Observation ormeasurements
Met at least one criterion:
Burdorf 1991 No association Yes No No Observation ormeasurements
Chaffin 1973 Approx. 5† NR No NR Observation ormeasurements
Holmström 1992 1.3§ Yes Yes Yes Job titles or self-reports
Huang 1988 No risk estimate Yes No NR Observation ormeasurements
Johansson 1994 No association Yes No NR Job titles or self-reports
Kelsey 1975b 0.94 Yes Yes NR Job titles or self-reports
Kelsey 1984 3.8 Yes Yes NR Job titles or self-reports
Knibbe 1996 1.3 Yes No No Job titles or self-reports
Liles 1984 4.5† NR No No Observation ormeasurements
Magora 1972 No association, 1.7†
NR No NR Observation ormeasurements
Marras 1995 10.7† NR No NR Observation ormeasurements
Svensson 1989 1.2§ Yes No NR Job titles or self-reports
Toroptsova 1995 1.4† Yes Yes NR Job titles or self-reports
Undeutsch 1982 No risk estimate NR Yes NR Job titles or self-reports
Videman 1984 No association Yes No NR Job titles or self-reports
Walsh 1989 1.5†,2.0†
Yes No NR Job titles or self-reports
Met none of the criteria:
Burdorf 1990 0.70,5.2†
No No NR‡ Job titles or self-reports
*Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR). †Indicates statistical significance. ‡Not reported. §Significant associations found in univariate but not multivariate results.
6-41
Table 6-3. Epidemiologic criteria used to examine studies of low back MSDs associated with bending, twisting, orawkward postures
Study (first author and year)
Risk indicator(OR, PRR, IR
or p-value)*,†Participation
rate $$70%Physical
examination
Investigatorblinded to case
and/orexposure
status
Basis for assessing backexposure to bending,twisting, or awkward
postures
Met back criteria:
Punnett 1991 8.09† Yes Yes Yes Observation or measurements
Met at least one criterion:
Burdorf 1991 1.2† Yes No No Observation or measurements
Holmström 1992 2.6†,3.5†
Yes Yes Yes Job titles or self-reports
Johansson 1994 NR†,‡ Yes No NR Job titles or self-reports
Kelsey 1984 3 Yes Yes NR Job titles or self-reports
Magora 1972, 1973 No association NR No NR Observation or measurements
Marras 1993, 1995 10.7† NR No NR Observation or measurements
Masset 1994 No association§ Yes No NR Job titles or self-reports
Riihimäki 1989b 1.5† Yes No NR Job titles or self-reports
Riihimäki 1994 No association§ Yes No NR Job titles or self-reports
Svensson 1989 No association§ Yes No NR Job titles or self-reports
Toroptsova 1995 1.7† Yes Yes NR Job titles or self-reports
*Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR). †Indicates statistical significance. If reported with NR, a significant association was reported without a numerical value. ‡Not reported. §Significant associations found in univariate but not multivariate results.
6-43
Table 6-4. Epidemiologic criteria used to examine studies of low back MSDs associated with whole-bodyvibration
Study (first author andyear)
Riskindicator (OR,
PRR, IRor p-value)*,†
Participationrate $$70%
Physicalexamination
Investigatorblinded to case
and/orexposure
status
Basis for assessing backexposure to lifting and whole-body vibration
Met at least one criterion:
Bongers 1988 2.0†–5.7 Yes Yes NR‡ Job titles or self-reports
Bongers 1990 3.3–39.5† Yes No NR Observation or measurements
Boshuizen 1990a, 1990b 1.5–3.6† Yes No NR Observation or measurements
Boshuizen 1992 0.99 Yes No NR Observation or measurements
Bovenzi 1992 2.6† Yes No NR Observation or measurements
Bovenzi 1994 2.4–4.6† Yes No NR Observation or measurements
Burdorf 1991 3.1† Yes No No Job titles or self-reports
Burdorf 1993 2.5–3.3† Yes No NR Observation or measurements
Kelsey 1975b 2.8†,4.7†
Yes Yes NR Job titles or self-reports
Magnusson 1996 1.8† NR No NR Observation or measurements
Magora 1972 1.2 NR No NR Observation or measurements
Masset 1994 1.2† Yes No NR Job titles or self-reports
Riihimäki 1989a 1.3† Yes No NR Job titles or self-reports
Riihimäki 1994 No association Yes No NR Job titles or self-reports
Toroptsova 1995 No association Yes Yes NR Job titles or self-reports
Walsh 1989 1.7† Yes No NR Job titles or self-reports
Met none of the criteria:
Burdorf 1990 0.66 No No NR Job titles or self-reports
Johanning 1991 3.9† No No NR Job titles or self-reports
Skov 1996 2.8† No No NR Job titles or self-reports
*Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR). †Indicates statistical significance. ‡Not reported.
6-45
Table 6-5. Epidemiologic criteria used to examine studies of low back MSDs associated with static workpostures
Study (first author and year)
Riskindicator
(OR, PRR, IRor p-value)*,
†
Participationrate $$70%
Physicalexamination
Investigatorblinded to
case and/orexposure
status
Basis for assessing backexposure to static work
postures
Met at least one criterion:
Holmström 1992 Noassociation
Yes Yes Yes Job titles or self-reports
Kelsey 1975b 0.81,2.4†
Yes Yes NR Job titles or self-reports
Magora 1972, 1973 Noassociation
NR No NR Observation ormeasurements
Masset 1994 1.5 Yes No NR Job titles or self-reports
Svensson 1989 1.3§ Yes No NR Job titles or self-reports
Toroptsova 1995 Noassociation
Yes Yes NR Job titles or self-reports
Videman 1990 24.6† NR Yes NR Job titles or self-reports
Walsh 1989 1.7†
(females)Yes No NR Job titles or self-reports
Met none of the criteria:
Burdorf 1990 0.49 No No NR Job titles or self-reports
Skov 1996 2.45† No No NR Job titles or self-reports
*Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR). †Indicates statistical significance. ‡Not reported. §Significant associations found in univariate but not multivariate results.
6-47
(Continued)
Table 6-6. Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
Åstrand 1987
Åstrand andIsacsson 1988
Cross-sectional,1987
Retro-spective22 yearsfollow up,1988
391 male employeesin a Swedish pulpand paper industrylocated at one of 4sites: Mill 1, Mill 2, Mill3, and Head Office.
Outcome: Medical,psychological and socialindicators. Questionnaireson social and psychologicalfactors; medicalexamination of thoracic andlumbar spine.
Exposure: Based on thetype of work performed ateach job site. All mill workjobs were judged asheavy; all office/clerk jobswere judged as light. Someworker movement betweenoffice/clerk jobs and millwork, based on healthstatus.
29.4 % of manualworkers reportedback pain inresponse to: “Doyou often haveback pain?”
12.9% ofclerksreported backpain inresponse tosamequestion.
Duration ofemploy-ment:1.2
Neuro-ticism: 2.8
p=0.002
1.0-1.5
1.4-5.4
Participation rate: 82.5%.
The proportion of backs evaluated asabnormal by physical examinationwas 16%, similar to U.S. datacollected in 1971. 66% of group withback abnormalities reported back pain.
Psychosocial work factors did notshow any significant association withback pain.
The working conditions of back painsufferers were changed because oftheir reduced working capacity,which tends to offset differences inprevalence of back pain betweengroups doing heavy work and controlpopulations.
Results support Magora’s findings thatheavy work over time is associatedwith increased back pain.
Back pain was associated withoccupation, low education, duration ofemployment, and neuroticism.
In follow-up study, a “healthy workereffect” was documented.
6-49
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Bergenuddand Nilsson1988
Longitudinal 323 males and 252females; allparticipants inMalmo, Sweden,Longitudinal Studysince 1938.
Outcome: Back pain nottracked by exam.“Attended” for exam but BPbased only on selfassessment andquestionnaire, 1983.
Exposure: Exposures andoccupations tracked byquestionnaires since 1942. Work classified into3 categories of heavinessbased on 10 years work.
(1) Light physical work:white collar.
(2) Moderate: Nurses,shop assistants, bakers,and light industry.
(3) Heavy: Carpenters,bricklayers, and heavyindustry.
Point prevalence:LBPmales: 28%females: 30%
5% prevalenceof sciatica
In heavy ormoderate work(LBP):males: 32.4%females: 38.9%
LBP inunexposedmales: 21.4%females:23.9%
All: 1.83Females:2.03Males:1.76
1.2-2.7
1.1-3.7
1.01-3.1
Participation rate: 67% in questionnaire and health survey from830 individuals living in Malmo.
Not controlled for confounders.
Exposures rated from job title.
Weak support for occupationalfactors in causation. Some supportfor workload causing symptoms.
Moderate or heavy physical demandshad more back pain; then lightphysical demand group (p<0.01)statistically significant only in females.
Those with back pain had feweryears of education and were lesssatisfied with their workingconditions. There was no differencein the relationship between family,relatives, or friends.
6-50
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Bigos et al.1986a
Retro-spectivecohortmorbidity(15-monthfollow-up)
Aircraftmanufactureremployees in 33 jobclassifications (n=31,200).
Outcome: Report of lowback injury.
Exposure: 33 jobclassifications.
Highest LB injuryrates in mechanics Rate=38.2
Lowest LBinjury rates inelectronictechniciansand toolgrinders Rate=NS
Highest tolowestcompari-son is inrange of 5to 7 (exactnumbersnotreported)
Participation rate: 100% (includes allrecords).
Exact rates by job titles not reported.
Authors state that differences by jobtitle are difficult to interpret becauseof overlapping confidence intervals.
6-51
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Bigos et al.1991b
Prospective 3,020 aircraftassembly workers;1,613 involved inwork perception andpsychosocial portionof study.
Outcome: A case wasdefined as a subjectreporting an acute industrialback injury.
Subjects answered seriesof questionnaires: Ondemographic andpsychosocial factors, acardiovascularquestionnaire, and a take-home questionnaire onpsychosocial and individualfactors (see comments).
Subjects had physicalexamination to assessphysical attributes: Liftingstrength, aerobic capacity,and flexibility.
Exposure: Based onquestionnaire data of workand home activities. Also“All jobs employing >19workers analyzed forheavy and tiring tasks interms of maximal loads.”
Also analyzed “perceivedphysical exertion” aspotential risk factor.
8% to 9% ofworkers reportedan acute industrialback injury.
N/A Lack ofenjoymentof job tasks:OR=1.7
MMPI: tendtowardssomaticcomplaint ordenial ofemotionaldistress:OR=1.37
Prior backpain:OR=1.7
1.3-2.2
1.1-1.7
1.2-2.5
Participation rate: 43% of the originalnumber of workers solicited 54% ofparticipants returned questionnairewith Minnesota Multiphasic PersonalityInventory (MMPI); 75% participated insome part of the study. Ofvolunteers, respondents and non-respondents were similar.
Employees’ work exposure not aswell documented as psychosocialfactors.
Take home questionnaire had 566question Minnesota MultiphasicPersonality Inventory (MMPI), familyfunction questionnaire (APGAR),Health locus of control (HLOC).
Other information included medicalhistory, previous back discomfort orproblem, and previous back injuryclaims in prior 10 years.
Study did not investigate actualpresence of back symptoms orspecific disorders; subjects followedfor three years and became a case ifthey: (1) reported to medicaldepartment, (2) filed an incident orreport, (3) filed an industrial insuranceclaim.
Authors state that results may notapply as strongly to cases of severesymptoms or in work involving heavyjob requirements (study performed ina manufacturing industry where “jobtasks do not tend to be extremelystressful” for the back.
6-52
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Bongers et al.1988
Retro-spectivecohort(January,1975-December1984)
Dutch, male, steelworkers (n=1,405)
Outcome: Disability pensionfor back-related disorder.
Exposure: Job title andduration of employment. Measurements of vibrationin cranes but not used inthis study.
Crane operators(n=743)
Floor workersin samedepartments(n=662)
IncidenceDensityRatios
All backdisorders:1.32
Interverte-bral discdisorders:2.00
Degenera-tion ofinterverte-bral disc:2.95
COXregression: IDR fordisplace-ment ofdisc: 2.46
IDR fordegenera-tion ofinteverte-bral disc:3.28
0.84-2.1
1.1-3.7
1.2-7.3
1.2-12.5
Participation rate: $70%.
Adjusted for nationality, shiftwork,age, and calendar time.
ORs likely are underestimatedbecause of slight vibration exposureof the control group and potentialhealth-based selection of the exposedgroup before start of the follow-upperiod.
The combination of exposure to W.V.,unfavorable postures, and adverseclimatic conditions is the probablecause of the back disorders.
6-53
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Bongers et al.1990
Cross-sectional
Dutch, male,helicopter aircrewand non-flying airforce officers
Outcome: Back symptoms,by questionnaire.
Exposure: Hr of flight time,types of helicopters flown,and time spent in bent ortwisted postures wereobtained by questionnaire. Vibration measurementswere taken in twohelicopters of each typeused in the study. Cumulative exposureswere obtained bycombining questionnaireand measurement data.
Dutch helicopterpilots and aircrewobservers (n=163)
Back pain, 68%;LBP, 55%;Lumbago, 13%;Sciatica, 12%;Pattern alternating,41%
Non-flying airforce officers(297)
17%11%9%6%
6%
8.09.02.63.3
9.5
4.5-14.34.9-16.41.1-6.01.3-8.5
4.8-18.9
Participation rate: $70%.
Adjusted for age, height, weight,climate, bending forward, twistedpostures, and feeling tense at work.
Prevalence of transient back pain, inparticular, was higher for exposedthan referent group.
Prevalence of transient back painincreased with daily exposure time.
Chronic back pain increased with totalflight time and total vibration dose.
Postures of pilots were constraineddue to cockpit conditions.
Selection bias possible in that pilotswith back trouble could have droppedout of employment.
6-54
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Boshuizenet al.1990a,b
Cross-sectionalfollow-up ofa cohortidentified in1975. Also,includesentire cohortinexaminationof sick leaveand disabilityfollow-ups.
Employees of twoDutch companiesperforming landreclamation andinspection of roads,dikes, and buildingsites. Severalworkers operatevehicles. The cross-sectional studyincluded 577workers, and thecohort study 689.
Outcome: Back painsymptoms were obtainedby questionnaire in thecross-sectional study, andback-related sick leave anddisability retirementinformation was collectedin the cohort study.
Exposure: Vehicle vibrationinformation was combinedwith questionnaire dataregarding vehicle typesdriven, awkward posturesmaintained, hr of work, andprevious jobs held.
Sick leave for allback disorders
LBP prevalence: byvibration dose, 4categories
By vibration, 3categories
By years ofexposure 3categories
Sick leave byvibration dose, 4categories
Dose of 5 years, allback disorders
1.47
RR: 19.1,29.4, 28.03,8.1
1.80, 1.78,2.8
2.44, 2.50,3.60
1.0, 0.97,1.51, 1.45
1.13COXregress.adj. for age
1.04-2.1Participation rate: 79%.
ORs corrected for duration ofexposure, age, height, smoking,awkward postures, and mentalworkload.
Association greater with duration ofexposure than magnitude.
6-55
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Boshuizenet al. 1992
Cross-sectional
Male employees ofsix Dutch shippingcompanies (n=452).
Outcome: Back painsymptoms by questionnaire
Exposure: Measurementof vibration in sample ofvehicles combined withquestionnaire responsesto calculate cumulativedose (before symptomonset.
Fork-lift truck andfreight tractordrivers (n=242).
Prevalence (agestandardized:Back pain, 48%LBP, 41%Lumbago, 19%
Cox regression:Back pain and totaldose:
Lumbago and totaldose:
Vibration exposurein last 5 years andback pain:and lumbago:
Age andprevalence of LBP(multivariate OR): 25-34 35-44 45-54
Employees ofthe samecompanieswithoutvibrationexposure(n=210)
34%30%8%
0.99
1.14
2.43.1
5.61.960.68
p=<0.05p=<0.05p=<0.05
0.85-1.2
0.91-1.4
1.3-4.21.2-7.9
Õ Õ Õ
Participation rate: $70%.
Adjusted for age, mental stress,years lifting > 10 kg and twistingspine, height, smoking, lookingbackwards, and hr sitting.
Authors suggested that a healthy-worker effect was operating in thatolder drivers were subject to health-based selection.
Psychosocial factors were notaddressed, except for “mental stressfrom work”.
6-56
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Bovenzi andZadini 1992
Cross-sectional mailsurvey
Male bus employeesworking in Trieste
Outcome: Back-painsymptoms fromquestionnaire (rev. Nordic).
Exposure: WBV measured.Cumulative exposuresestimated frommeasurements plusquestionnaire results (duration of work, previousexposures, etc.).
234 bus drivers
Univariate results:lifetime prevalenceof LB symptoms,83.8%;LBP, 36.3%;
Previous 12months:LB symptoms,82.9%LBP, 39.7%;
Dose-response fortotal vibration andlifetime LBP;Dose-response for12-mo. LBP.
125maintenanceworkersworking forsame buscompany
66.4%15.2%
65.6%20.0%
3.122.80
2.992.57
4.05
3.25
1.8-5.31.6-5.0
1.8-5.11.5-4.4
1.8-9.3
1.5-7.0
Participation rate: $70%.
Adjusted for age, awkward posture,duration of exposure, BMI, mentalload, education, smoking, sportactivities, previous jobs at risk forback pain and duration of employment.
Does not address sedentary nature ofwork (states sitting is poorlycorrelated with LBP unless incombination with WBV).
Psychosocial: adjusted for “mentalload” (no risk estimate provided).
Results were similar after excludingthose with WBV exposure in previousjobs from analyses.
6-57
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Bovenzi andBetta 1994
Cross-sectional
Tractor drivers,aged 25-65, workingin Italy (n=1155) andmale revenueofficers engaged ininspection andadministrative work(n=220).
Outcome: Surveyquestionnaire (modifiedNordic)
Exposure: Vibration levelswere measured for arepresentative samples oftractors. Information onawkward postures gainedfrom questionnaire. Numberof hr operating yearlyestimated from tractormaintenance records.Cumulative exposuresestimated by combining theinformation.
Tractor drivers
Univariate:Back Pain: 86.1%LBP Lifetime:81.3%
12-month LBP,71.7%Dose-response(highestcategories)Lifetime LBP andtot. vib. dose;Chronic LBP andtot. vib. dose;
Lifetime prevalenceLBP and duration ofexposure:5-15 years16-25 years>25 years
Lifetime prevalenceLBP and totalvibration dose(years m2/s4)<1515-30>30
Revenueofficers
57.3%
42.3%
36.8%
1.83
3.22
2.39
5.49
2.63
3.083.034.51
2.793.443.79
1.1-3.0
2.1-5.2
1.6-3.7
3.6-8.5
1.7-4.10
1.88-5.071.80-5.122.43-8.34
1.70-4.582.05-5.772.20-6.53
Participation rate: 91.2% for exposedand 92.2% for unexposed.
Multivariate analyses adjusted forage, BMI, education, sport activity, cardriving, marital status, mental stress,climatic conditions, back trauma, andpostural load.
Relationships reported betweenvibration exposure and back pain,with clearest dose-responses forchronic LBP outcome.
Independent effects observed forpostural load and vibration.
Results were similar after excludingthose with WBV exposure in previousjobs from analyses.
6-58
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Burdorf andZondervan1990
Cross-sectional
33 male craneoperators and 30male non-craneoperator controlsubjects matchedfor age. Employedfor $ one year.
Outcome: Back painassessed by questionnaire(Nordic). Pain in lowerback in the last 12 months.
Exposure: Defined by jobtitle and questionnaireitems: heavy physicalwork, lifting, WBV, andsedentary postures(current and past).
61% of crane operators had back pain
Risk Factors:
Heavy work
Frequent lifting
Whole bodyvibration
27% ofcontrols hadback pain
3.6
4.02
5.21
0.66
1.2-10.6
0.76-21.2
1.10-25.5
0.14-3.1
Participation rate: 67% of craneoperators and 100% of controls.
Control workers carried out moremoderate or heavy work, lifting,walking, and standing than craneoperator in past.
Physical demands are not significantin multivariate analyses.
Controlled for age, height, and weight.
Crane operators with long workabsences over-represented amongnon-responders.
Results indicate that the current job ofcrane operator is associated withreports of onset of back pain.
6-59
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Burdorf et al.1991
Cross-sectionalprevalencestudy
114 concreteworkers comparedto 52 maintenanceengineers (controls). All male.
Outcome: Back painsymptoms assessed byquestionnaire. Back paindefined as pain whichcontinued for $ a few hrduring the past 12 months.
Exposure: Assessed bytask analysis and OVAKOworking posture analysissystem (OWAS)observation method. Eleven postures ofimportance for occupationalstrain on the back wereused.
For each job, two or threeworkers were chosen atrandom.
Index for postural loadconstructed using ordinalscale for rating the averageproportion of poor backpostures. Six jobs wereranked by index.
59% of concreteworkers had backpain
31% of controlshad backpain
2.80 ageadjustedandcontrolledfor backpain fromprevious job
Model 1PosturalindexOR=1.23
Model 2Whole bodyvibrationOR=3.1
1.31-6.01
p=0.04
p=0.001
Participation rate: 95% concreteworkers; 91% maintenance males.
Workload related to prevalence ofback pain.
Postural load, bending and twisting,as well as whole body vibrationcausal factors.
Questionnaire included previousemployment history, risk factors inpresent and previous jobs.
Univariate analysis controlled forconfounders using Mantel-Haenselchisquare. Age, height, and weightnot significant factors.
Age controlled for in logisticregression.
30% with back pain had symptoms>30 days.
Concrete workers spent significantlymore time in bent and/or twistedpostures.
Postural index and whole bodyvibration significantly correlated (0.48,p<0.001). Therefore, authorsdesigned two separate logisticregression models.
Prolonged standing or sitting not foundto be risk factors.
6-60
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Burdorf et al.1993
Cross-sectional
Crane operators,saddle-carrierdrivers and officeworkers aged 25-60, working in alarge transportcompany (n=275).
Outcome: Back painsymptoms, byquestionnaire.
Exposure: Posturesassessed with OWAS,WBV measured in sampleof each group, and pastwork exposures estimatedby questionnaire.
Crane operators(n=94) and saddle-carrier drivers(n=95)
Multivariateanalyses:
Crane operatorsStraddle-carrierdrivers
Officeworkers(n=86)
3.29
2.51
1.52-7.12
1.2-5.4
Participation rate: $70%.
Adjusted for age and confounders(history of heavy work, exposure toWBV (y/n), history of work requiringprolonged sitting, cold and drafts,working under severe pressure, jobsatisfaction, height, weight, durationof total employment wereconsidered).
Risk estimates were not presented byexposure categories, despitequantitative assessment.
Risk estimates reflect simultaneousexposure to WBV, static postures,and awkward postures.
Only persons with no complaints oflow back pain before starting theircurrent jobs were included inanalyses.
6-61
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Chaffin andPark 1973
Prospectivewith approx.1 yearfollow-up
5 plants in largeelectronicscompany. n=411individuals (279males and 132females).
Outcome: Visit medicaldepartment because of lowback complaint.
Exposure: 103 jobsevaluated for LiftingStrength Rating (LSR) andlifting frequency.
Overall back rate,annual 7.2/100FTEs (25 total backinjuries)
Participation rate: Not reported.
Age, weight, stature not associatedwith low back injuries.
A strong positive trend is indicated inthe incidence rate data as the LSRincreases.
6-62
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Clemmer et al.1991
Retro-spectivecohort
Offshore drillingworkers.
14,518,845 worker-hr over 1979 to 1985(7,259 FTEs), 4,765total injuries.
Outcome: Back-injurycases reported onstandard forms withmention of “rheumatogicalcrux” for which the agentof injury was mechanicalenergy excluding otherbody sites.
Exposure: Based on jobtitle.
543 cases of lowback injuries.
7.5/100
Roustabouts,floorhands, andderrick workers,low-back strainsrate: 6.92
Control roomandmaintenance3.18
RR=2.2 Participation rate: Not reported.
Workers performing the heaviestphysical labor had highest number ofinjuries and highest rates.
Controlling for “job,” age significantlyassociated with back strain inworkers performing heaviest length ofemployment work not associated withback pain.
Job was best predictor of lost time.
Back injuries largely from falls. 75% ofback strains precipitated by pushing,pulling, or lifting.
6-63
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Deyo andBass 1989
Cross-sectional
From the NHANES-IInational survey of27,801 individuals,10,404 files of adultsage 25 or older whohad a physicalexamination werereviewed and 1,134who met the casedefinition wereselected for thisstudy. The meanage of the subjectswas 48.3 years andhalf (51.7) werefemales.
Outcome: Low-back painwithin the past year with$ one episode of near dailypain for $ two weeks.
Exposure: Smoking andobesity, personalcharacteristics.
Prevalence of LBPin current smokers:10.7%.
Ever smoked vs.LBP: 10.9%
50 pack years vs.LBP: 14.1%
BMI vs LBP, Highest quintile:14.8%
LOG REGRESSION:ObesitySmokingChronic coughActivityEducationAgeWorking
Prevalence ofLBP currentnon-smokers:10.2%
9.6%
9.6%
Lowestquintile: 8.5%
1.13
1.47
1.70
Odds ratioeachincrement
1.12 1.05 1.36 1.22 0.84 1.01 0.8
Notsignificant
Significant
Significant
Significant
p<0.0006p<0.0006p<0.0006p<0.0006p<0.0006p<0.0006NS
Participation rate: Not reported.
Lifestyle factors, including smokingand obesity, are risk factors for low-back pain.
The attributable risk for smoking was1.3 cases/100 persons.
Smoking risk increases steadily withcumulative exposure and with degreeof maximal daily exposure.
A stronger association existsbetween back pain and smoking inyounger subjects than among those>age 45.
There is a steady increase in backpain prevalence with increasingobesity, but this elevates moststrikingly in the highest 20% of bodymass index (levels over 29.0kg/sq m).
The association between obesity andLBP could be confounded by otherunmeasured lifestyle differencesbetween the obese and non-obese sothat obesity is just a marker for a truecausal factor or factors.
6-64
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Heliövaaraet al. 1991
Cross-sectional
2,727 males and2,946 females (30 to46 years) withhistory, symptoms,or findings indicatingmusculoskeletaldisease.
Outcome: LBP interviewand tests at medical mobileclinic with uniform criteria.
Low-back syndrome: Symptoms during thepreceding month and majorpathologic finding onphysical exam (fingertip-floor distance >25 cm atflexion, rotation restrictedto 25 degrees or less,objective signs of scoliosisof 20 degrees or more,Lumbar Lordosis,Ladegue’s test positive at60 degrees or less, orsevere abnormality.
Sciatica: Symptomsradiating down leg andfindings of Lumbar nerveroot compression.
Exposure: Based on self-administered questionnaire;index for occupationalphysical stress andoccupational mental stress.
Prior traumaticinjury increasedrisk of LBP and,sciaticaand, low back syndrome
Work load indexand, sciatica and, low back syndrome
Stress indexand,sciaticaand, low back syndrome
No priorinjury
2.5
2.6
2.4
3.1
2.4
2.0
1.9-3.3
2.1-3.1
1.0-5.7
1.7-5.7
1.7-3.5
1.5-2.6
Participation rate: 93% in screening.
Physical and mental stress loadsrelated to both sciatica and LBP.
Controlled for age and gender.
Body mass index, alcoholconsumption, work-related driving,parity, and height were notassociated with LBP.
Diabetes had a significantlydecreased prevalence of LBP(OR=0.4 CI 0.3-0.8).
There was no statistical difference inLBP between sexes; sciaticasignificantly more prevalent amongmales.
No association between smoking andsciatica.
Significant association betweensmoking and LBP in both older andyounger males, but only olderfemales.
Significant association between LBPand osteoarthritis, mental disorders,and respiratory disease.
6-65
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Hildebrandt1995
Cross-sectional
From the Dutchpopulation; a sampleof 8,748 workersfrom three surveyson successiveyears.
Outcome: Back pain casesdefined by symptomquestionnaire ("yes" to"back pain quite often") andresponses to interviewer.
Exposure: Based on jobtitle classification of workdemands; four categoricalexposure variables: tradebranch, trade class,professional branch, andprofessional class.
29.6% (2,327) ofheavy workersreported back pain“quite often.”
Rates of LBP:
Construction: 35%;
Truckers: 31%;
Plumbers: 31%.
23.9% ofsedentaryworkersreported backpain “quiteoften.”
p<0.05
OR=1.2
Õ
1.33-1.55
Participation rate: “Populationsampled was representative of Dutchpopulation.” Unable to calculate.
Workers performing non-sedentarywork at highest risk.
Rates increase with age for males, toage 54, and for females to age 64.
Controlled for age and gender bystratification.
Professions with high prevalence ofback pain on average werecharacterized by physicallydemanding work with dynamiccomponents.
Data originally collected for screeningof health and medical consumption,therefore less specific exposurevariables—only job titles. However,there may be less potential forinformation bias because respondentsdid not then focus exclusively on backpain and work-relatedness.
Conclusion: In non-sedentary work,both males and females have higherprevalence rates than those whowork in sedentary jobs.
6-66
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Hildebrandtet al. 1996
Cross-sectional
436 male workers infive maintenancedepartments of asteel company,compared to 396non-sedentaryworkers alsoexposed to heavyworkloads.
Outcome: Low back paincases defined by symptomquestionnaire (“yes” to lowback pain in last12 months).
Exposure: Assessed byquestionnaire. Workersplaced into one of 18groups based tasksperformed “often” or“predominantly.” Tasksassigned a score on fourindices: (1) physicalworkload, (2) psychosocialworkload, (3) poor climate,and (4) vibration.
Prevalence: 1-year; LBP: 53%
Referencegroup hadhigh physicalexposures.
Õ Õ Participation rate: Varied from 60% to80% in different departments.
Reference group characterized byhigh levels of exposure to adverseworking conditions.
Poor selection of referents.
Prevalence rates adjusted for agedifferences between groups.
Task groups with high prevalencerates of low back symptoms alsoassociated with high exposures tounfavorable working conditions.
Rates work groups (within units)according to self-reported exposuresbut does not cross-tab these withLBP.
6-67
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Holmströmet al. 1992
Cross-sectional
1,773 randomlysampledconstructionworkers (male).
Outcome: (1) LBP historyfrom postal questionnaire. Back pain defined as pain,ache, or discomfort inlower back, includinggluteal regions with orwithout radiating pain intoleg/s experiencedsometime, often, or veryoften during past year,(2) $ for 1 to 7 days, (3)with any degree offunctional impairment.
A sample of workers hadclinical exam: Active spinalmobility test, springing test,straight leg raising,interspinal and paraspinalpalpation from T11 to S1,combined extension andlateral flexion whilestanding and passivelumbar flexion andextension while lying onone's side.
Exposure: Based onquestionnaire datareporting of task activity.
1-year prevalencerate LBP 54%;1-year prevalencefor severe LBP 7%.
Lifting freq: >1/5min
Stooping: >4 hr
Kneeling: > 4 hr
Stress: high
Anxiety: high
<1/5
seldom
seldom
1.12
1.29
1.24
1.6
1.3
p<0.001
1.1-1.5
1.1-1.4
1.4-1.8
1.1-1.4
Participation rate: 76%.
Examined medical records fornonrespondents; same as forrespondents.
Information included individual andemployee-related factors, disorders inlocomotor system, physical workload,and psychosocial factors.
Examiners blinded to case andexposure status.
Multiple logistic regression modelsused; separate models for individual,manual materials handling, andworking postures.
In univariate analysis, no relationshipwith daily traveling time, leisureactivity, or height and weight.
Construction tasks such asbricklaying or carpentry did not affectLBP.
Stress index reflected a high achieverperson.
Longer duration of stooping andkneeling was associated with LBP inall age groups (dose-response).
Only severe LBP related to smoking.
6-68
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Huang et al.1988
Cross-sectional
Subjects consistedof all 24 female full-time workers fromschool lunch centerA and 20 female full-time workers fromcenter B.
All 42 workerscompleted asymptom, health andwork historyquestionnaire and20 from each centeralso participated in aphysicalexamination. Sixworkers from centerB declined toparticipate forpersonal reasonsunrelated to thepurpose of thestudy.
Outcome: Symptomsrelating to upper limbs,trunk and lower limbsduring the previous monthwere solicited from aquestionnaire, while clinicalfindings of pain duringmovements, muscletenderness, signs of CTS,signs of epicondylitis, andsigns of tenosynovitiswere documented in aphysical examination.
Exposure: Ergonomic riskfactors included handlingheavy objects, holdingconstrained postures, toomuch stooping, repetitiveuse of arms and hands,and poor equipment layout. NLE used to evaluatemanual lifting tasks.
Consistentlyconstrainedpostures:17 workers(70.8%)
Poor equipmentlayout: 18 workers(75%)
Consult physician:17 workers(70.8%)
Muscle tenderness:5.1 +/- 5.6
Signs oftenosynovitis:6 workers(30%)
Upper back pain:
3 workers(15%)
3 workers(15%)
5 workers(25%)
0.8 +/-2.3
1 workers(5.0%)
N/A
p<0.05
p<0.01
p<0.01
p<0.01
p<0.05
significant
Participation rate: All 42 workerscompleted a symptom, health, andwork history questionnaire and20 from each center also participatedin a physical examination. Sixworkers from center B declined toparticipate for personal reasonsunrelated to the purpose of the study.
Center A had a significantly higherprevalence of musculoskeletalcomplaints, more clinical findings, andgreater medical treatment experiencethan those in center B.
The ratio of the actual lifting load tothe Action Limit was also larger incenter A than in center B.
No significant difference was foundbetween the centers for low backpain.
Study design was ecologic. Healthoutcomes and exposures wereexamined separately for two centers. Information was not combined forindividual participants.
6-69
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Johanning1991;Johanninget al. 1991
Cross-sectional mailsurvey
Employees of theNew York Citytransit system(n=584)
Outcome: Back-painsymptoms in past year, byquestionnaire survey.
Exposure: Job title. Although, WBV measureswere taken for theexposed group, noanalyses were presented.
Subway trainoperators (n=492)
Any back pain,41%
Sciatic pain
Subwaycontrol toweroperators(n=92)
25% PRR=1.11
3.9
1.04-1.19
1.7-8.6
Participation rate: Not reported.
Controlled for age, gender, job title,employment duration.
Study groups are stable workingpopulations with low turnover rates.
Exposed and unexposed groups aresimilar with regard to demographicsand job histories.
Workers with a history of backproblems or previous WBV exposurewere excluded from the study.
Duration of employment notassociated with risk.
Exposure data was not associatedwith outcome data in these articles.
Vibration measures showed highlateral and vertical acceleration levels.
6-70
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
JohanssonandRubenowitz1994
Cross-sectional
Subjects were 241blue-collar (39%females) and 209white-collar (35%females) workersfrom eight diversifiedmetal industrycompanies inSweden.
The participation ratewas approximately90%. Eighty-sevenpercent of the blue-collar and 95% ofthe white-collarworkers had>2 years experiencein their current jobs.
Outcome: Low-backsymptoms during thepast 12 months as self-reported on the NordicMusculoskeletalQuestionnaire (NMQ),which was supplementedwith an additionalquestion regarding thework-relatedness of thesymptoms.
Exposures: Individual andemployee-related variablesrelated to the psychosocialwork environment and thephysical workload (sitting,manual materials handling,lifting).
Prevalence of low-back symptoms=0.43 (CI 0.37-0.50) for blue-collarworkers, whichreduced to p=0.32(CI 0.26-0.39)when solely work-related symptomswere considered.
Prevalence ofLB symptoms=0.42 (CI 0.35-0.49) amongwt. collarworkers,whichreduced top=0.18(CI 0.11-0.24)when solelywork-relatedsymptomswereconsidered.
PRR=1.76 1.25-2.47 Participation rate: The participationrate was approximately 90%. Eighty-seven percent of the blue-collar and95% of the white-collar workers had>2 years experience in their currentjobs.
Among blue-collar workers 12 of 15correlation tests regarding workloadfactors and work-related symptomswere not significant.
Among blue-collar workers 10 of 15partial correlation tests (adjusted forthe effects of age and sex) regardingpsychosocial job factors and work-related musculoskeletal symptomswere significant.
Among blue-collar workers 7 of 15partial correlation tests regardingpsychosocial job factors andmusculoskeletal symptoms, accordingto the NMQ, were significant.
Among white-collar workers none ofthe relationships between the fivepsychosocial factors and low-backsymptoms were significant, whetheror not work-related.
Calculations of associations based onthe NMQ, without an effort todetermine the work-relatedness ofsymptoms, could have a powerfuleffect-masking result.
6-71
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Kelsey 1975b Case-control Cases wereobtained from apopulation in the agerange 20 to 64 yearsresiding in the NewHaven SMSA whohad lumbar X-raystaken during theperiod June 1971through May 1973 atthe three hospitals inthe area and at theoffice of two of theprivate radiologistsin New Haven. Atotal of 217 pairs (89females and 128males) was obtainedfor the comparisonof cases andmatched controls. For the analysis ofcases andunmatched controls,there were223 cases (91female and 132males) and494 controls(225 females and269 males).
Outcome: Herniated lumbarintervertebraldiscs were the outcomesof interest in this study.Three levels of herniateddisc were classified:Surgical cases, probablecases, and possible cases.
Exposure: Occupation,years of employment,amount of time worked,amount of time spent sitting,type of chair, lifting,pushing, pulling, carrying,lifting frequency, andweight of objects liftedwere the exposures ofinterest.
Sitting >half thetime: <35 years>35 years
Time driving:>half vs. herniation
Occupation:Truck driver vs.herniation
Lifting vs.herniation
EqualFewer
Fewer
Fewer
Equal
RR=0.81RR=2.40
RR=2.75
RR=4.67
RR=0.94
p=0.01
p=0.02
p=0.02
p=0.10
Participation rate: 79% cases; 77% controls.
Results were similar for two controlgroups (less strong for unmatchedcontrols).
Study design subject to nondifferentialrecall problems (with regard tocase/control status).
The association between sedentaryoccupations, especially those whichinvolve driving, and herniated lumbardiscs exists in both sexes and incomparisons between cases andboth control groups.
The strength of this association inthose aged 35 and older and the lackof association in those who are underthat age suggest that a certain amountof time in sedentary occupations isnecessary for an effect to be seen.
This study gave no evidence of anincreased risk for herniated lumbardiscs among males who did lifting ontheir jobs, and little indication of thisamong the females. Chance couldexplain the slight tendency towardsignificance in the female subjects.
6-72
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Kelsey et al.1984
Case-control Persons in the agerange of 20 to 64years who hadlumbar X-ray films ormyelograms takenduring 1979 to 1981,in one of threehospitals, oneneurosurgicalprivate practice, ortwo orthopaedicprivate practices inthe New Haven andHartford, CT areas.
232 matched case-control pairs.
Outcome: Statusdetermined on the basis ofan interview, diagnostictests performed byinterviewers, and datarecorded in medicalrecords. Cases classifiedas “surgical” cases,“probable” cases, and“possible” cases. Controlgroup composed ofpersons without knownprolapsed disc admitted tothe same medical servicesfor conditions not related tothe spine. Cases andcontrols all with recent(within 1 year) diseaseonset.
Exposure: Exposure toactivities performed on thecurrent job assessed byinterview andquestionnaire.
N/A N/A Lifting: >11.3 kg>25/day: OR=3.5
Lifting: > 11.3 kg >5/day andtwisting thebody halfthe time:OR=3.1
Lifting: >11.3 kgwhiletwistingbody withthe kneesalmoststraight:OR=6.1
Carrying: >11.3 kg 5 to 25/day: OR=2.1
Carrying: >11.3 kg >25per/day: OR=2.7
1.5-8.5
1.3-7.5
1.3-27.9
1.0-4.3
1.2-5.8
Participation rate: 72% cases;79% controls.
All case categories combined in case-control analyses (same resultsobserved for all categories).
Controls matched with cases on sex,age and hospital service.
Frequent twisting alone did not affectthe risk of prolapsed disk, whiletwisting with lifting had a detrimentaleffect.
Study design subject to nondifferentialrecall problems (with regard tocase/control status).
6-73
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Knibbe andFriele 1996
Cross-sectional(studyintended toprovidebaseline dataforlongitudinalstudy).
355 femalesemployed ascommunity nurses orcommunity nurseauxiliaries by thehome careorganization of thecity of Rotterdam.
Outcome: Questionnaire,developed from Nordicquestionnaire formusculoskeletal disorders,mailed to nurses.
Exposure: Questionnaireasked (1) if nurses coulddescribe any work tasksthey considered physicallydemanding, and(2) whether the onset ofback pain was related to aspecific work situation. Also job title: Communitynurses vs. Auxiliaries.
Lifetime LBPprevalence: 87%
1-year LBPprevalence: 66.8%
Auxiliaries:61.2
1-week LBPprevalence:20.6%
Prevalence of sickleave due to backpain in previous 3months: 9.7%
N/A Õ
Back pain inlast 7 days,communitynurses vs.communitynurseauxiliary:OR=0.84
Backpain inprevious 12months;communitynurses vs.communitynurseauxiliary:OR=1.54
Õ
0.49-1.45
0.97-2.47
Participation rate: 94%. Males andpregnant females excluded fromsample.
89.9% of nurses described situationsthey considered physicallydemanding. 82.1% of tasks describedinvolved patient transfers. Static loadon the back was mentioned in 23.2%of descriptions.
Prevalence appeared to decreasewith age. Cross-sectional studydesign prevented investigators fromdetermining whether observation wasdue to selection effect or due toexperience.
Rates for community nurses andauxiliaries do not reflect significantdifferences in hrs worked/week (30.7vs. 26.2). Adjusted for hrs workedOR is 1.3 (auxiliaries higher).
Authors state that auxiliaries areresponsible for more lifting activities.
6-74
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Leigh andSheetz 1989
Cross-sectional
959 working malesand 455 workingfemales in the UnitedStates employed >20hr/week.
(U.S. Department ofLabor QES Surveyrespondents.)
Outcome: LBP based onnational survey of workingconditions. Question: “Isthe trouble with back orspine in past year?”
Exposure: Defined by jobtitle and questionnaire onwork conditions, includingworkload.
1-year LBP pastprevalence:19.4% males20.7% female
Occupations: Farmers Clerical Operator Service
Job demands:High
Smoker
ManagersandProfessional
ManagersManagersManagersManagers
Low
Non smoker
5.171.382.392.67
1.68
1.48
1.57-17.00.85-2.251.09-5.251.26-5.69
1.05-2.90
1.00-2.19
Participation rate: Not reported. (Probably to national survey).
Workers in jobs requiring “lots ofphysical effort and lots of repetitivework report more back pain.
Exposure information based on self report and job title.
Health outcome did not distinguishbetween upper and lower back pain.
Gender, race, obesity, height, andrepetitious work are not significantlyassociated with back pain.
6-75
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Liles andDeivanayagan1984
Prospective 28 companies, 63jobs in study 1, 38 instudy 2. Selectedjobs with frequentlifting requirements;manual handlingrequirements.
Study 1: 220 males;24 females.
Study 2: 165 males;44 females.
Outcome: Lifting injury toback, as recorded orreported.
Exposure: Jobs rated byJob Severity Index for lifting(observation, use ofrecords for calculation). Each individual followeduntil job change (up to 2years).
Total of 529 FTEs dividedequally into 10 SI levels.
Total injuries:
Injury rate for thehighest job severityindex category:17.1 injuries/100FTES
Disability injury ratefor the highest jobseverity indexcategory: 11.4 losttime injuries/100FTES
Severe injury ratefor highest jobseverity indexcategory: 120.8days lost/numberof lost time injuries
Total injuries:
Injury rate forthe lowest jobseverity indexcategory: 3.8 injuries/100 FTES
Disability injuryrate for thelowest jobseverity indexcategory 3.0lost timeinjuries/100FTES
Severe injuryrate for thelowest jobseverity indexcategory 3.0dayslost/number oflost timeinjuries
RR=4.5
RR=3.0
RR=40
Participation rate: Not reported (allvolunteers).
Dose response for lifting injuries byJSI.
No adjustment for confounders.
Outcome defined as lifting injuries. Not distinct from exposure.
6-76
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Magnussonet al. 1996
Cross-sectional
Bus drivers, truckdrivers, andsedentary workersrecruited in the stateof Vermont andGothenburg,Sweden
Outcome: Back painsymptoms, byquestionnaire.
Exposure: Ergonomicexposures, byquestionnaire and vibrationlevel measurementsaccording to ISOstandards. Long-termvibration exposurecalculated as product ofdaily exposure and yearsdriving.
Bus drivers(n=111) and truckdrivers (n=117)
Driving
Freq. lifting
Heavy lifting
Long-term vibrationexposure
Vibration and freq.lifting
Vibration andheavy lifting
Sedentaryworkers(n=137)
1.79
1.55
1.86
2.0
2.1
2.06
1.16-2.75
1.01-2.39
1.2-2.8
0.98-4.1
0.8-5.7
1.3-3.3
Participation rate: Not reported.
ORs do not appear to be frommultivariate analyses including othercovariates, except as stated.
Quantitative exposure measures arenot used in analyses that arepresented.
6-77
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Magora 1972 Cross-sectional
A previous article(1970) described theprocess forselecting 3,316individuals from 8occupations forinclusion into thisstudy.
Outcome: The outcomevariable, low-back pain,was defined in a previousarticle [1970]. Symptomsby self-report.
Exposure: The physicalactivities studied in thisinvestigation were sitting,standing, weight lifting, andweight lifting technique.
The exposed groupconsisted ofworkers from 8occupations. Theselection processwas described inan earlier article bythe same author[1970].
Sitting > 4 hr day:Often:Sometimes:Rarely:
StandingVariable:< 4 hr daily
The controlsconsisted of2887individualsfrom 8occupations. The selectionprocess wasdescribed inan earlierarticle by thesame author[1970].
0.950.093.20
2.38
NR
0.8-1.140.05-0.142.69-3.8
1.99-2.85
Participation rate: Not reported.
The use of two hands to lift a load,and especially holding the load awayfrom the body, are related to a higherincidence of LBP.
The lifting risk factors are magnifiedwhen completing unaccustomedtasks.
Rarely sitting reported to beassociated with LBP.
Standing less than 4 hr daily reportedto be associated with LBP.
Variable sitting and standing reportedto be protective.
6-78
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Magora 1973 Cross-sectional
A previous article(1970) described theprocess forselecting 3,316individuals from 8occupations forinclusion into thisstudy byobservation andinterview.
Outcome: The outcomevariable, low-back pain,was defined in a previousarticle (1970).
Exposure: The physicalactivities studied in thisinvestigation were bending,rotation, reaching, suddenmaximal efforts, and thenumber and type of workbreaks, by observation,and interview.
The exposed groupconsisted ofworkers from 8occupations. Theselection processwas described inan earlier article bythe same author(1970).
Among those withLBP:
Bending:Often: 14.5%Sometimes:3.4%Rarely: 23.2%
Spinerotation:Often: 12.1%Sometimes: 22.0%Rarely:10.3%
Suddenmaximal efforts:Often: 18.0%Sometimes: 11.3%Rarely: 10.9%
The controlsconsisted ofindividualsfrom 9occupations. The selectionprocess wasdescribed inan earlierarticle by thesame author(1970).
Amongcontrols:
Bending:Often: 85.5%Sometimes:96.6%Rarely: 76.8%
Spine rotation:Often: 87.9%Sometimes:78%Rarely: 89.7%
Suddenmaximalefforts:Often: 82%Sometimes:88.7%Rarely: 89%
Suddenmaximalphysicaleffortswere foundto berelated to ahighincidence ofLBP.
Suddenmaximalefforts andLBP: 1.65
Notreported
1.3-2.1
Participation rate: Not reported.
It appears that sudden maximalefforts, especially if unexpected, playan important role in the causation ofLBP.
Many of the physical causativefactors, such as bending or rotation,found by other investigators to berelated to a high incidence of LBP areactually sudden maximal effortsincidentally carried out at that momentin a certain position of the spine.
While most bending, twisting, andreaching motions required by eachoccupation are knowingly carried out,sudden maximal physical efforts arecharacterized by theirunexpectedness. This may actuallytrigger LBP through sudden strain ofsoft tissues, possibly caught in acondition or posture < optimal for thiskind of effort.
6-79
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Marras et al.1993
Marras et al.1995
Cross-sectional
403 industrial jobsfrom 48manufacturingcompanies: e.g.,automobileassembly, foodprocessing, lumberand wood,construction, metaland paperproduction, printing,and rubberproduction. No dataprovided on thenumber of workersin study.
Outcome: Existing medicaland injury records in eachindustry were examined foreach job to determine ifworkers on those jobs hadreported work-related low-back disorders. The resultyielded an outcomemeasure of “LBD risk,”which was a normalizedrate of work-related LBD.
Exposure: A triaxialelectrogoniometer wasworn by workers to recordposition, velocity andacceleration of the lumbarspine while workers liftedin either “high” or “low” riskjobs. Workplace andindividual characteristicswere recorded. High riskexposed was >12% injuryrate, yielding 111 high riskjobs, while 124 jobs werelow risk, serving as thecontrol group.
Maximum loadmoment: 73.65 Nm
Sagittal meanvelocity:11.74 E/sec
Maximum weight:104 N 23.3 lb
23.64 Nm
6.55 E/sec
Maximumweight:37 N 8.3 lb
5.17
3.33
3.17
3.19-8.38
2.17-5.11
2.19-4.58
Participation rate: Numbers andproportions of those sampled by jobgroup. No information on number ofindividual participants.
Study provides linkage betweenepidemiologic measures of injury (i.e.,“probabilities of high-risk LBD groupmembership”) and selectbiomechanical and task factors forrepetitive lifting jobs.
Study illustrates multi-factored natureof injury risk, but it does not indicatethe risk of LBD.
Quality and accuracy of injury andmedical records are unknown. Inaccuracies or underreporting wouldaffect the accuracy of the model.
Exposure assessors may not havebeen blinded to risk status of jobsthey were evaluating.
6-80
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Masset andMalchaire1994
Cross-sectional
Steel workers(n=618).
All male and allunder 40 years ofage.
Outcome: Interview-basedchecklist and questionnaire: Back pain defined for threeperiods: (1) during lifetime,(2) past 12 months, and (3)past 7 days by thequestion, “Did you haveany problems in the lowerback?”
Exposure: Interview-basedexposure assessmentusing checklist: posturesand movements of thetrunk, efforts, physical andpsychosocial environment(monotony, responsibility),vehicular driving andexposure to whole bodyvibration.
Lifetime LBPprevalence for allworkers:66%
1-year LBP prevalence for allworkers:50%
1-week LBPprevalence: 25%
Prevalence ofsciatica was low:2-3%
N/A Õ
Vehicledriving:1.15
Heavyefforts oftheshoulder:1.62
Seatedposture:1.46
<0.005
<0.01
0.09
Participation rate: 90%.
Low back fatigue accounted for 25%LBP cases.
No objective measure of workload.
Stratified by age and exposure risklevel.
Ergonomic redesign prior to study,reduced ergonomic hazards.
Physical workload, posture,movements of the trunk, repetition,negative perception of workingenvironment, exposure to WBV, notassociated with back pain.
Information obtained includeddemographics, height, weight, medicalhistory, personality, and social status(smoking, sports, satisfaction withfamily and occupation, abnormalfatigue, temper, headache,depressive tendency, present andpast working environment.
All long-lasting sick workers excludedfrom study; may cause survivor bias.
Back “fatigue” separated from “backpain.”
This cross-sectional study was firstpart of a prospective study.
Heavy efforts with shoulders werestrongly correlated with LBP.
6-81
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Partridge andDuthie 1968
Cross-sectional
206 male civilservants (clericalworkers), age 15to 64 years, and 171male dock workers,age 25 to 64 years.
Outcome: Low-back pain(including lumbar discdisease, pelvic girdle pain,and leg pain).
Participants attended aninterview at which time amedical and socialquestionnaire wasadministered and a medicalexamination wasperformed.
Complaints classified into 8categories.
Exposure: Based on jobtitle (civil servant ordocker).
Dockers: currentrheumaticsymptoms: 43.2%
Low-back pain, 61dockers(Standardized Ratio(SR) by age 106.1)
Civil servants: currentrheumaticsymptoms:34.5%
Low-backpain, 33 civilservants (SR90.4)
RR=1.27 0.98-1.64 Participation rate: 95.7% for dockersand 91.0% for civil servants.
Analyses corrected for age.
Overall complaint rates did not differbetween occupations, despitedifferences in physical effortrequirements. Older civil servantscomplained of more neck/shoulderpain than dockers of a similar age. Difference attributed to static workingpostures involving the neck andshoulder.
Among civil servants, only 5 weeks(16.1%) of sickness absence inprevious year due to back pain. Among dockers, 75 weeks (68%) ofwork lost attributed to lumbar discdisease and backache. Authorsconclude that there is a positivecorrelation between the heaviness ofwork and time lost due to backcomplaints, even if the complaint ratein different occupations does not varysignificantly.
Medical examiners probably notblinded to exposure status.
6-82
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Punnett et al.1991
Case-referent(retro-spective)
219 automotiveassembly workers.
95 cases comparedto 124 referentswithout back pain.
Outcome: Back paincases: (interview andexam) defined as workerswho filed new reports ofback disorders at plantduring a 10-month period. Back pain in interviewdefined as history of $ 3episodes or $ one episodelasting $ one week withinthe year preceding the dateof the interview.
Physical exam consistedof active, passive, andresisted motionsconcentrating 11 rangesof motion of the back.
Referents: No report ofback disorders.
Exposure: Based on videoanalysis of job posturesand bio-mechanical data
84% (185) 20 workersunexposed
Non-neutralpostures:4.9 Mild flexion:5.7
Severeflexion: 5.9
Time in non-neutralposture: 8.09
Lift 44.5N:2.16
Age(years):0.96
Back injury:2.37
1.4-17.4
1.6-20.4
1.6-21.4
1.5-44.0
1.0-4.7
0.9-1.0
1.3-4.3
Participation rate: 84%.
Healthy worker effect.
Of the 124 referents, only 20 workerswere unexposed to all awkwardpostures.
Back disorders were found to beassociated non-neutral trunkpostures.
69% of subjects in job <5 years.
Questionnaire involved demographics,work history, medical history, andnon-occupational activities.
Analyses controlled for gender, age,length of employment, recreationalactivity, medical history, and maximumweight lifted in study job.
Exposure variable for non-neutralposture: The sum of the durationspent in non-neutral postures as acontinuous variable.
A strong trend found for increasinglength of exposure and risk of backdisorders to both mild and severetrunk flexion.
Only current job analyzed: Assumesshort-term relationship betweenoutcome and exposure (however,also included duration of employmentvariables).
6-83
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Riihimäki et al.1989a
Cross-sectional mailsurvey
Longshoremen,earth movingequipment operators(WBV), carpenters(heavy physicalwork), and officeworkers (sedentarywork) (n=2,223)
Outcome: Back painsymptoms, byquestionnaire.
Exposure: Job title andquestionnaire responsesregarding work history,physical work factors, andwork stress.
Longshoremen(n=542), earthmovers (n=311),and carpenters(n=696)
Sciatic pain andmachine operators
Sciatic pain andcarpenters
Sciatica andtwisted or bentpostures
Sciatica and annualdriving
Officeworkers(n=674)
1.3
1.0
1.5
1.1
1.1-1.7
0.8-1.3
1.2-1.9
0.9-1.4
Participation rate: $70%.
Longshoremen and earthmoverscombined in analysis (machineoperators).
After adjustment for age, duration ofemployment was not associated withsymptoms in any group.
Of the three back symptoms, sciatica,lumbago, and LBP, sciaticadiscriminated the best amongoccupational groups.
All three exposed groups wereexposed to $ one work-related riskfactor for back disorder.
6-84
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Riihimäki et al.1989b
Cross-sectional
216 concreteworkers comparedto 201 housepainters (all male),age-matched. Restricted toworkers with 5years workexperience and toworkers <55 years.
Outcome: Radiographicallydetectable degenerativechanges in lumbar region.
Exposure: Based on jobtitle (article refers toWickström [1985]evaluation of concretereinforcement workers).
Grade 2 to 3disc problem:
27.8% concreteworkers
Back problems:55%
Sciatic:53%
Grade 2 to 3disc problem:
15.4% house painters
Backproblems:45%
Sciatic:39%
N/A
Occupa-tioneffect ofconcretework:OR=1.8
Age:OR=6.5
Spondy-lophytes
Occupa-tioneffect ofconcretework:OR=1.6
Age:OR=14.9
p=0.001
1.2-2.5
1.7-26
1.2-2.3
2.3-95
Participation rate: 84% concreteworkers and 86% house painters.
Examiners (radiologists) blinded tocase or exposure status.
Age, self-reported back accidents,body mass index, height, and smokingcontrolled for in analysis.
Height, weight, smoking no effect ondegenerative X-ray changes.
Negative bias for occupational factordue to healthy worker effect.
Positive bias due to recall foridentifying accidents as risk factors.
Individual exposure data not availablefor workers.
Radiographically detectabledegenerative changes associatedwith sciatic pain (1.0, 1.4, 1.9) forthree grades of degeneration (not forLBP or lumbage).
No hypotheses regarding specific riskfactors. Exposure assessed by jobtitle only.
6-85
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Riihimäki et al.1994
Pietri-Talebet al. 1995
Prospective(3-years)
Machine (heavyequipment)operators (688),carpenters (533),and office workers(591). All males.
Outcome: Based on 2Postal questionnaires;LBP=Low-back symptomsin preceding 7 days, 12months, and lifetime. Sciatic pain = pain radiatingto leg/s.
Exposure: Based onspecific occupation: Machine operators wereexposed to static loads,low-level, whole bodyvibration. Carpentersexposed to dynamicphysical work. Officeworkers were sedentaryworkers.
Questionnaire askedamount of twisted or bentpostures, pace of work,monotonous work,problems with co-workersor superiors, draft, cold,vibration.
22% machineoperators
24% carpenters
Physical exercise >once a week
Smokers and ex-smokers
History of lowerback pain:
Mild LBP;Severe LBP
14% office workers
Maximumphysicalexercise oncea week.
Non-smokers
None
1.4
1.5
1.26
1.29
2.74.5
0.99-1.87
1.1-2.1
1.0-1.6(p<0.06)
0.98-1.7p<0.06)
1.7-4.22.7-7.6
(p<0.001)
Participation rate: For follow-up: 81%machine operators, 79% carpenters,and 89% office workers.
Questionnaire included age, level ofeducation, annual car driving, weeklyphysical exercise, occupationalexposure, and history of other backproblems.
Questionnaires administered in 1984and 1987.
Separate logistic regression modelscreated for specific occupation.
History of other types of low backpain predicted sciatica in all groups.
Monotonous work, problems with co-workers or supervisors, and high-paced work were not associated withsciatica three-year cumulative IncidentRate.
Article examines only sciatic pain.
6-86
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Ryden et al.1989
Case-control Cases consisted of84 employees withback injuries and168 controls(matched triplets).Mean age was 34and 83.3% werefemale.
Cases: Employeeswith injuries fromjob-related activitiesthat occurred duringthe working day,not based onindividual lost timefrom the job orworkers’compensation. Theincidence rate at thework site during thestudy period was29/1,000 in 1983,29/1,000 in 1984 and33/1,000 in 1985.
Controls selectedfrom the samepopulation by age,sex, anddepartment. Foreach case, twocontrols wereselected from a listof all employees,stratified bydepartment. Matching for agewas done within a5-year span.
Outcome: Reported work-related low-back injurieswhile employed at the siteof the study during the timeperiod of 1983 through1985.
Exposures: History ofprevious back injury atwork, work shift, heavywork, lifting, bending,slipping, self-reported low-back pain or “slipped disc,”and individual risk factors.
Low-backpain: OR=2.27
Previousback injury:OR=2.13
Workingday shift:OR=2.23
Low backpain:OR=2.27
Self-reportslip disc:OR=6.20
1.07-4.24
1.28-3.89
1.25-4.12
2.64-14.57
Participation rate: Not reported.
Disadvantages of the design include:a lack of detailed information thatcould have helped to focus onselected risk factors. For example,knowledge of pack-years rather thanonly number of cigarettes smoked/daywould have been valuable, ifavailable, as would more specificinformation on body build, includingpercent body fat and fitness level,rather than using height/weight andself-reported exercise level.
Advantages of the design includedeconomy, time savings, flexibility, andthe analysis of a large group of riskfactors simultaneously.
Immediate reporting of injuries,including the nature of the injury andpertinent data regarding where andhow the injuries occurred, is essentialto efforts both to reduce injuries andto rehabilitate those who are injured.
Cases and controls were (over)matched on occupation risk factors. Could not examine these effects.
Those working day shift felt to havegreater physical demands.
6-87
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Schibye et al.1995
Longitudinal Follow-up of 303sewing machineoperators at ninefactoriesrepresentingdifferent technologylevels whocompletedquestionnaire in1985.
In April 1991, 241 of279 traced workersresponded to samequestionnaire.
Outcome: Based on NordicQuestionnaire: pain in thelast 12 months in the lowback (last 7 days).
Exposure: Assessed byquestions regarding:(1) type of machineoperated, (2) workorganization, (3) workplacedesign, (4) unitsproduced/day, (5) paymentsystem, and (6) time ofemployment as a sewingmachine operator.
Prevalences of LBPin Sewing jobs:
12-month: LBP:1985=38%1991=47%
Prevalences1-week: LBP:1985=23%1991=25%
Participation rate: 1985: 94%;1991: 86%. All participants werefemales.
77 of 241 workers still operated asewing machine in 1991.
82 workers had another job in 1991among those 35 years or below, 77%had left job; among those above 35years 57% left job.
20% reported musculoskeletalsymptoms as the only reason forleaving job. Healthy worker effect. Another 13% said symptoms werepart of the reason.
No significant changes in prevalencesamong those employed as sewingmachine operators from 1985 to 1991;significant decrease in those whochanged employment.
As many as 50% of respondentsreported a change in the response topositive or negative symptoms from1985 to 1991.
This was due to a decrease in the riskfactors: e.g., decreased in output andhrs worked/week.
Article examines only neck/shoulderarea in detail (no exposure analysesfor back outcome).
6-88
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Skov et al.1996
Cross-sectional
1,306 Danishsalespersons
Outcome: Musculoskeletalsymptoms, byquestionnaire.
Exposure: Self-reporteddriving distance, time insedentary work, lifting ofheavy loads, psychosocialjob characteristics.
Danishsalespersons(n=1,306)
Annual drivingdistance
Sedentary work (%of worktime)
No unexposedgroup included
Annualdrivingdistance,highestcategory: OR=2.79
Sedentarywork (% ofworktime)highestcategory:OR=2.45
1.5-5.1
1.2-4.9
Participation rate: Not reported.
Covariates considered in multivariateanalyses included age, sex, height,weight, smoking, work-relatedpsychosocial variables, lifting, leisuretime sports activities.
No unexposed group was included.
6-89
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Skovron et al.1994
Cross-sectional
4,000 random-stratified sampledadults in Belgium; abicultural country,uniform health caresystem; 48% male.
Population-basedtelephone survey.
Outcome: Based on backpain symptom reportingfrom structured interviews. Back pain defined byquestion “Have you everhad back pain?” Casesrestricted to those subjectscurrently working.
Exposure: Based oninterview data: occupationand working status, “Areyou satisfied with work”question..
Point prevalenceLBP: 33%
Lifetime prevalence: 59%
Among workersoccupation:
Workdissatisfaction:
Female gender:Increasing age:
NS
2.4
2.16 2.0
p=0.02
p=0.001p=0.001
Participation rate: 86%.
Information included age, gender,social class, habitat, language,working status, occupation, worksatisfaction, lifestyle factors, andfamily history.
Logistic regression models controlledfor age, and gender; interactiontested.
First episode of back pain notassociated with work satisfaction.
Language influence reporting of firsttime occurrence and history of backpain but not severity of impairment asexpressed as daily back pain.
Uniform health care assured equalaccess and reporting.
Results suggest that worksatisfaction is not a cause of LBP, butit intervenes in the expression of LBP.
6-90
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Svensson andAndersson1989
Cross-sectional
Random sample of1,760 38 to 64-year-old females fromGoteborg, Sweden. At the time of theinvestigation, 14females could not belocated.
Approximately 80%of the final sample of1,746 femalesparticipated in thestudy.
Outcome: Low-back pain(LBP) was defined as allconditions of pain, ache,stiffness, or fatiguelocalized to the lower back. All episodes of LBP wereincluded in the study, asdetermined byquestionnaire.
Exposure: Variablesincluded working hr,working hr/week, amountof overtime, lifting,frequency of forwardbending and twisting, workposture, possibility tochange work posture, needto concentrate, monotony,satisfaction with worktasks, possibility to takerest breaks, worried andtense after work, fatiguedat the end of the work day,and education.
Exposed and unexposedwere determined byquestionnaire responses.
UnivariateanalysisfoundsignificantcorrelationsbetweenLBP and 5exposuresin ages 50-64 years: Morebending,lifting, standing, higherdegree ofworry,andexhaustion at the endof the workday.
p<0.05p<0.01p<0.01
p<0.01
p<0.0001
Participation rate: Approximately 80%of the final sample of 1,746 femalesparticipated in the study.
The analysis of correlations betweenthe occurrence of LBP and thedifferent variables describing workhistory, work environment, and stresswas restricted to wage-earningfemales only (sick-listed included).
No significant differences existedbetween the two age groupsconcerning the incidence andprevalence rates of LBP. However,several parameters indicated that theLBP in the older age group was moresevere.
Several of the correlations in theunivariate analysis, when tested inthe covariate analysis, were found tobe dependent on other confoundingfactors.
The findings in the present studystress the importance ofpsychological factors in relation tolow-back pain. These factors areprobably not only related to theindividual’s personality but also to thetype of work and the environment atthe workplace.
Medical examiners discussedquestionnaires with participants—notblinded.
6-91
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Toroptsovaet al. 1995
Cross-sectional
701 random-stratified sampledemployees of aRussian machinebuilding plant 47%male.
Outcome: LBP history fromstructured interviews. Back pain defined as painlasting in area below 12thrib and above gluteal folds. All persons with LBPcomplaints examined byrheumatologist.
Exposure: Based oninterview data: Work,sports, and personalfactors. 10 industrialfactors examined: Lifting,standing, sitting, walking,vibration, static work,postures, repetitive work,and bending.
Frequent trunkflexion
Frequent lifting required in job
No trunkflexion
Occasionallifting (2 or less/day)
1.66
1.43
p<0.01
p<0.05
Participation rate: 88%.
Analysis did not control forconfounders.
Information included personal data,family status, education, profession,anthropometric data, smoking, sportactivity, and professional factors.
Lifetime prevalence: 48%. Prevalencehigher among older workers andsmokers >10/day.
Back pain decreased in group>55 years. The year of retirement forfemales.
No association with sitting or standingpostures, walking, vibration, staticwork postures, and repetitive work.
6-92
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Undeutschet al. 1982
Cross-sectional
366 male cargotransport workers ata large airport.(Baggage handlers).
Outcome: Standardizedinterview administered to allworkers to detectsubjective previous andpresent back symptoms. Clinical orthopaedicexamination administered to134 workers to detectobjective findings.
Exposure: Data on workexperience in the presentoccupation was collected. No other exposure datacollected.
Prevalence ofprevious backcomplaints: 56%
Prevalence ofpresent backsymptoms: 66%
Prevalence ofobjective backfindings atexamination: 70%
N/A N/A N/A Participation rate: Not reported (46%of target population included).
Current back symptoms positivelycorrelated with height, age, and lengthof experience in transport work.
Among workers with presentsymptoms, symptoms occurred mostfrequently during lifting of loads (75%)and while in bended body positions(61%). Changing body position (71%)and absence of work for one or moredays were relieving factors for backsymptoms.
Comparison of interview and clinicalexam results show interview to be asuitable screening method for clinicalback pain (sensitivity=86%,specificity=31%).
Significant association betweenlength of transport work and backsymptoms (p=0.035) adjusted for age.
No heterogeneity with regard toexposure.
6-93
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Videman et al.1984
Cross-sectional
562 nurses and 318nursing aides inFinland, all of themfemales.
Outcome: Based on resultsfrom a pre-testedquestionnaire and fromhealth information obtainedfrom the local PensionRegisters that were usedto identify nurses who hadbeen pensioned due to illhealth during a 4-yearperiod immediatelypreceding the mailing of thequestionnaire.
Exposure: Based on self-assessments from dataobtained using a mailedquestionnaire that includednine questions on physicalloading factors at work andseven questions on workhistory and occupation.
Jobs were reclassified asheavy, intermediate, andlight based on results ofquestionnaire items dealingwith workload.
85% of aides had $one “life-time”episode of LBP andtheir pointprevalence was50% for LBP.
Sciatica: 43% life-time prevalence.
Aides had twicethe lifting, bendingand rotation.
79% ofnurses hadexperienced$ one “life-time” episodeof LBP; pointprevalencewas 41% forLBP
Sciatica: 38%life-timeprevalence
$ one “life-time”episode ofLBP: 1.1 1.01-1.14
Participation rate: 88% nurses; 85%nurses aides.
Workers with back pain wereemployed in heavy jobs on average 1year longer than those with noprevious LBP.
Musculoskeletal disorders as a causeof disability increased with age; the30-years risk for 25-years old aideswas 3.4 times greater than for thenurses; similar results for sciaticawith a risk of 4.5 times greater for theaides than nurses.
The prevalence of LBP and sciaticsymptoms in both nurses and in aidesare high and similar to the resultsfound in Britain.
Physical workload related to patienthandling was mainly responsible forthe differences in LBP and sciaticarates between the aides and nurses. The finding was most evident underthe age of 30 years.
Non work-related factors, such aschildbirth, also contributed to theadverse back conditions.
Study lacks a good unexposedpopulation since both nurses andaides were exposed to varyingdegrees of risk factors for LBP andsciatica.
Workers with LBP were in heavierjobs for longer time than those withoutLBP.
6-94
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
(Continued)
Videman et al.1990
Cross-sectional
From a Finnishworkforce of 86males who hadworked in fourdistinct occupationalgroups: Sedentary,Mixed, Driving, andHeavy. Criteria forinclusion: Deceasedbelow the age of 64who had beenemployed beforedeath and thesubjects’ family ableto provide workinginformation.
Exclusion criteriawere long illnessesor a diseased state,such as cancer orinfectious disease.
Outcome: Objectiveradiologically anddiscography-basedpathologic criteria from thecadaver spines of thestudy population. Degree ofdegeneration was outcomemeasure, i.e., annularruptures. Information onsymptoms was obtainedfrom family members.
Exposure: Type of work,based on work historyreports from family;classification of workbased on heaviness,driving, and sedentary jobs.Classification based onphysically heaviestoccupation held for $ 5years.
54% of heavyworkers had LBPoften, and 36% hadsciatica
50% of drivers hadLBP often, and29% of them hadsciatica
Heavy physicalload vs. not:OR=2.8
Sedentary vs. not:OR=24.6(symmetric discdegeneration)
10% ofsedentaryworkers hadLBP often, and19% hadsciatica
29% of mixedgroup had LBPoften, and10% hadsciatica
Heavy vs.Mixed: 2.7
Driving vs.Mixed: 2.3
Sciatica:NS
1.1-6.2
0.8-6.2
Participation rate: Not reported.
Strength: First study linking pathologicdata with history of occupation andphysical loading factors.
Weakness: Do not know the temporalpattern in development of thepathologic changes.
Possible selection bias due to potentialdifferential rates between workgroups in leaving jobs because ofdegenerative diseases.
Two important findings: Sedentary orheavy work contribute to thedevelopment of pathologic findings inspine. Severity of back pain wasrelated to the heaviness of work, i.e.,work factors responsible fordevelopment of pathologic changesand for the production of pain.
Back pain more common withphysically more loading occupations;p<0.001. Similar but weaker trendbetween loading and sciatica; p=0.03.
General: p<0.01 between groups forback pain; and p<0.07 for sciatica.
Relationships were observedbetween report of symptoms and discpathology; also, exposures and discpathology.
6-95
Table 6-6 (Continued). Epidemiologic studies evaluating back musculoskeletal disorders
MSD prevalence
StudyStudydesign
Studypopulation
Outcome andexposure
Exposedworkers
Referentgroup
RR, OR,or PRR 95% CI Comments
Walsh et al.1989
Cross-sectional
A postalquestionnaire wassent to a randomsample of 267 malesand 268 females inthe age range of 20to 70 who lived inWhitchurch,England.
Four hundred, thirty-six questionnaireswere returned,giving an overallresponse rate of81%.
Outcome: Self-reportedlow-back pain, byinterview.
Exposure: Standing orwalking for > 2 hr; sittingfor > 2 hr; driving a car orvan for > 4 hr; driving atruck, tractor or digger;lifting or moving weights of25kg or more by hand; orusing hand held vibratingmachinery were theexposures of interest.
Lifetime occupationalhistory obtained byinterview.
Lifetime incidenceof LBP was 63%.
Recent Occup.Activity: Males Driving>4hr/d Lifting 25kgFemales Lifting 25kg
Lifetime Occup.Activity:Males Lifting 25kgFemales Sit >2hr/d Vib. machine
Risk of unremittingLBP:Males Lifting 25kgFemales Lifting 25kg
RR=1.7 RR=2.0
RR=2.0
RR=1.5
RR=1.7 RR=5.7
RR=5.3
RR=2.9
1.0-2.9 1.3-3.1
1.1-3.7
1.0-2.4
1.1-2.6 1.1-29.3
1.3-20.9
0.8-10.2
Participation rate: 436 questionnaireswere returned, giving an overallresponse rate of 81%.
The association with use of vibratingmachinery among females (repetitiverisk=5.7) was based on only oneexposed case.Cases of low-back pain wereascertained solely on the basis ofreported symptoms.
Successive birth cohorts reported thedevelopment of low-back pain at anygiven age with increasing frequency.
Driving a car for >4 hr a day wasassociated with low-back pain inmales but not with low-back pain infemales.Authors believe the data give strongsupport for a role of regular heavylifting in the etiology of low-back painand add weight to the evidenceimplicating occupational driving as arisk factor. At the same time,however, they suggest that suchactivities account for only a smallproportion of the total burden of low-back pain in the general population.Author’s estimates of the fraction ofdisease attributable to heavy liftingand car driving are 14 and 4%,respectively, leaving a substantialproportion of cases unexplained.
Authors attempted to recreate aretrospective cohort design; askedparticipants to remember dates andjobs and LBP. Questionable recall fortemporal relationships.
6-96
7-1
CHAPTER 7 Work-Related Musculoskeletal Disordersand Psychosocial Factors
SUMMARYWhile the etiologic mechanisms are poorly understood, there is increasing evidence that psychosocialfactors related to the job and work environment play a role in the development of work-relatedmusculoskeletal disorders (MSDs) of the upper extremity and back. Though the findings of the studiesreviewed are not entirely consistent, they suggest that perceptions of intensified workload, monotonouswork, limited job control, low job clarity, and low social support are associated with various work-relatedmusculoskeletal disorders.
As some of these factors are seemingly unrelated to physical demands, and a number of studies havefound associations even after adjusting for physical demands, the effects of these factors on MSDs may be,in part or entirely, independent of physical factors. It is also evident that these associations are not limitedto particular types of jobs (e.g., video display terminal work [VDT]) or work environments (e.g., offices) but,rather, seem to be found in a variety of work situations. This seems to suggest that psychosocial factorsmay represent generalized risk factors for work-related MSDs. These factors, while statistically significantin some studies, generally have only modest strength.
At present, two of the difficulties in determining the relative importance of the physical and psychosocialfactors are: (1) psychosocial factors are usually measured at the individual level, while physical factors aremore often measured at the group (e.g., job or task) level and often by methods with limited precision oraccuracy and (2) “objective measures" of aspects of the psychosocial work environment are difficult todevelop and are rarely used, while objective methods to measure the physical environment are more readilyavailable. Until we can measure most workplace and individual variables with more comparable techniques,it will be hard to determine precisely their relative importance.
INTRODUCTION
There is considerable confusion regarding thecontribution of psychosocial factors tomusculoskeletal illness and injury. Because ofthis, it is examined in this separate section of thereport. Unlike the more finite (and generallymore familiar) range of physical factors (e.g.,force, repetition, and posture), the concept ofpsychosocial factors includes a vast array ofconditions. Indeed, the term “psychosocial” iscommonly used in the occupational health arenaas a catchall termto describe a very large number of factors
that fall within three separate domains:(1) factors associated with the job and workenvironment, (2) factors associated with theextra-work environment, and(3) characteristics of the individual worker.Interactions among factors within each of thesedomains constitute what is referred to as a“stress process,” the results of which arethought to impact upon both health status andjob performance [Bongers and deWinter 1992;ILO 1986; Sauter and Swanson 1996; WHO1989].
7-2
Included in the domain of job and workenvironment are a host of conditions,sometimes referred to as “work organizationfactors,” which include various aspects of jobcontent (e.g., workload, repetitiveness, jobcontrol, mental demands, job clarity, etc.);organizational characteristics (e.g., tall versusflat organizational structures, communicationsissues); interpersonal relationships at work(e.g., supervisor-employee relationships, socialsupport); temporal aspects of the work andtask (e.g., cycle time and shift work); financialand economic aspects (e.g., pay, benefit, andequity issues); community aspects (e.g.,occupational prestige and status). These workand job environment factors are often thoughtof as demands, or “risk factors,” that may posea threat to health [Hurrell and Murphy 1992].Extra-work environment parameters typicallyinclude factors associated with demands arisingfrom roles outside of work, such asresponsibilities associated with a parent,spouse, or children. Finally, individual workerfactors are generally of three types [Payne1988] corresponding to: genetic factors (e.g.,gender and intelligence); acquired aspects (e.g.,social class, culture, educational status); anddispositional factors (e.g., personality traits, andcharacteristics and attitudes such as life and jobsatisfaction).
PSYCHOSOCIAL PATHWAYSThe purpose of this discussion is to summarizeresearch evidence linking work-relatedpsychosocial factors, as described above, toMSDs of the neck, shoulder, elbow,hand/wrist, and back. It should be recognizedat the outset, however, that the linkagesbetween work-related psychosocial factors andhealth outcomes of all varieties are oftencomplex and influenced by a multitude of
conditions. In particular, both personal andsituational characteristics may lead todifferences in the way individuals exposed tothe same job and work environment perceiveand/or react to the situation [Hurrell andMurphy 1992]. Recent theoretical models ofthe relationship between psychosocial factorsand MSDs [Bongers et al. 1993; Sauter andSwanson 1996] clearly reflect the complexityand multifactorial nature of the problem.
In general, four plausible types of explanationshave been suggested to account forassociations between work-relatedpsychosocial factors and MSDs [Bergqvist1984; Bongers et al. 1993; Bernard et al.1993; Sauter and Swanson 1996; Sauter et al.1983; Ursin et al. 1988]. First, psychosocialdemands may produce increased muscletension and exacerbate task-relatedbiomechanical strain. Second, psychosocialdemands may affect awareness and reporting ofmusculoskeletal symptoms, and/or perceptionsof their cause. Within this second explanationmay fall the “perverse incentive” view, in whichsocieties may provide workers with systems(such as workers' compensation) that may leadto overreporting of MSD symptoms [Frank etal. 1995]. Third, initial episodes of pain basedon a physical insult may trigger a chronicnervous system dysfunction, physiological aswell as psychological, which perpetuates achronic pain process. Finally, in some worksituations, changes in psychosocial demandsmay be associated with changes in physicaldemands and biomechanical stresses, and thusassociations between psychosocial demandsand MSDs occur through either a causal oreffect-modifying relationship.
7-3
The research evidence reviewed in thefollowing discussion is organized into twoseparate sections. The first section includesstudies of disorders of the neck, shoulder,elbow, hand and wrist which are discussedunder the rubric of “upper extremity disorders.”This convention was adopted because many ofthe studies utilize measures which combinesymptoms associated with several upperextremity body areas (e.g., neck and shoulder),and it is therefore not possible in reviewingthese studies to isolate the effects of thepsychosocial variables under consideration onmore specific areas. The second sectionexamines studies of back disorders.Associations reported in this review arestatistically significant in nearly all cases (at thep<0.05 level and frequently also at the p<0.01level). Where possible, odds ratios (ORs) arealso reported.
The studies examined in this review aresummarized in Tables 7-1 and 7-2. Ininterpreting the studies reviewed, it is necessaryto be aware that, in general, researchers havenot used standardized methods for assessingpsychosocial factors in relationship to MSDs.Thus, individual psychosocial factors assessedby investigators vary from study to study.Moreover, even when work-relatedpsychosocial factors (e.g., workload , jobcontrol, social support, job satisfaction, etc.)included by various investigators are the sameor similar, they may be measured by differentmethods and different kinds of scales which canvary in psychometric quality. Thesemethodological limitations complicate theprocess of drawing definitive conclusionsregarding the literature as a whole and whencomparing results between studies, one musttake these differences into account.
UPPER-EXTREMITY DISORDERS(NECK, SHOULDER, ELBOW, HANDAND WRIST)
Individual and Extra-WorkEnvironment FactorsA variety of psychosocial factors associatedwith both the individual worker and extra-workenvironment have been linked to upperextremity MSDs [Sauter and Swanson 1996;Bongers and deWinter 1992; Bongers et al.1993]. These factors have included suchconditions as depression and anxiety [Helliwellet al. 1992], symptoms of psychologicaldistress [Leino 1989], and home problems[Karasek et al. 1987]. The connection betweenfactors of this nature and the job and workenvironment, however, is unclear. Whileaffective problems (such as anxiety anddepression) and symptoms of distress maycertainly be a consequence of the worksituation, they may also be causally related tonon-work circumstances only. Likewise, whileextra-work environment conditions (e.g.,“home problems") may be exacerbated by thework situation (e.g., shift work) their “work-relatedness” remains unclear. Because of theuncertainty regarding the work-relatedness ofthese individual and extra-work environmentfactors (and because discussions can be foundin other sources), only the individualpsychosocial factor, job dissatisfaction, isexamined here.
Job Dissatisfaction
A number of studies suggest associationsbetween low levels of satisfaction with workand upper extremity musculoskeletal symptomsand disorders. Tola et al. [1988], for example,in a study of 1,174 machine operators, 1,054carpenters, and 1,013 office workers, found an
7-4
association (OR 1.2) between jobdissatisfaction and neck and shoulder physicalfindings or symptoms, after adjusting forconfounders. Likewise, Hopkins [1990]reported a positive association between jobdissatisfaction and musculoskeletal symptoms.However, low job satisfaction was not found topredict neck and shoulder problems one yearlater in a study of 154 Finnish workers [Viikari-Juntura et al. 1991a]. Likewise, in a study of273 nursing aids employed in a geriatrichospital [Dehlin and Berg 1977] job satisfactionwas found to be unrelated to reports of everhaving cervical pain.
Job and Work Environment Factors
Intensified Workload
One of the factors most consistently associatedwith upper extremity MSDs has been theperception of an intensified workload, asmeasured by indices of perceived timepressure, workload, work pressure, andworkload variability. Pot et al. [1987], forexample, in a cross-sectional study of 222VDT operators, found high levels of perceivedtime pressure associated with the reporting ofupper extremity musculoskeletal complaints.Kompier [1988] found perceived time pressureto be associated with upper extremitycomplaints (in the preceding 12 months) amongsome 158 male bus drivers. Likewise, Takalaet al. [1991], in a longitudinal study of 351female bank cashiers, reported a positiveassociation between perceived time pressureand symptoms of the neck and shoulder afteradjusting for postural load. Theorell et al.[1991], however, in a sample of some 206workers from six occupations, found thatperceived time pressure was not significantlycorrelated with neck or shoulder symptoms.
Positive associations with upper extremitydisorders have also been found in studies usingmeasures of perceived work pressure andworkload. High levels of perceived workload,for example, were found to be positivelyassociated with musculoskeletal symptoms inthe Pot et al. [1987] and Theorell et al. [1991]studies (which adjusted for physical demandssuch as lifting and awkward postures) reportedabove. Kvarnström and Halden [1983], in acase control study of 112 cases and 112 age-and sex-matched controls from an engineeringfirm, found sick leave due to fatigue or shouldermuscle soreness to be positively associatedwith high perceived workload. Karasek et al.[1987], in a study of 8,700 full-time membersof the Swedish white collar labor unionfederation, found perceived workload to bepositively associated with musculoskeletalaches as measured by a combination of severalquestions (OR 1.1 for males, 1.2 for females).Likewise, Sauter et al. [1983], in a study of248 VDT users, found perceived workload anddemands for attention to be associated withneck, back, and shoulder discomfort afteradjusting for a wide variety of variablesdenoting physical demands. Bernard et al.[1993], in a study of 1,050 newspaperemployees, found perceived increasedworkload demands (increased time workingunder deadline and increased job pressure) tobe positively associated with neck, shoulder,and hand-wrist symptoms. Similarly, Hales etal. [1994], in a study of 553telecommunications workers, found increasedwork pressure to be associated with neck (OR1.2) and upper extremity(OR 1.1) disorders, as defined by physicalexamination and questionnaire. Ryan andBampton [1988], using a total sample of 143data processors, compared 41 individuals
7-5
reporting a number of neck symptoms to 28reporting very few neck symptoms (middlegroup left out) and found a positive associationbetween symptom reports and reports ofhaving to push themselves (OR 3.9). Ekberget al. [1994] compared 109 workers whoconsulted a physician for new musculoskeletalneck and shoulder disorders with 637 controlsand found a positive association (OR 3.5) withrushed work pace. Houtman et al. [1994], in arepresentative sample of 5,865 workers in theNetherlands, found reported high work paceassociated with muscle or joint symptoms (OR1.3) after adjusting for physical stressors andmodifying personal characteristics. However,Dehlin and Berg [1977] in the study describedabove, found no relationship between reportsof high perceived physical and psychologicaldemands and reports of ever having pain in thecervical region. Finally, Houtman et al. [1994],in a representative sample of 5,865 workers inthe Netherlands, found reported high workpace associated with muscle or joint symptoms(OR 1.29) after adjusting for physical stressorsand modifying personal characteristics. Variability in workload (surges in workload)has also been linked to upper extremitydisorders. The studies by Hales et al. [1994] of553 telecommunication workers and Hoekstraet al. [1994] of some 108 teleservicerepresentatives, found perceived workloadvariability to be associated with elbow (OR1.2) and neck (OR 1.2) disorders, but not withshoulder or hand disorders.
Monotonous Work
Monotonous work has been positively linked tothe prevalence of upper extremity symptoms invarious studies. In a study of 143 dataprocessors, Ryan and Bamptom [1988] found
that self-reports of “being bored most of thetime” were highly (OR 7.7) associated withneck symptoms. Likewise, Linton [1990], in astudy of approximately 22,200 Swedishworkers undergoing a screening examination bythe occupational health care service, found thatmonotonous work was positively associatedwith neck/shoulder pain (OR 2.3) during thepreceding year. Ekberg et al. [1994], in thestudy described above, found an associationbetween “low quality work” (lacking stimulationand variation) and neck and shoulder problems(OR 2.6). Similarly, Kvarnström and Halden[1983] in the case control study describedabove, found monotonous work to beassociated with sick leave due to fatigue ortenderness in the shoulder muscles. Finally,Hopkins [1990] in a study of around 280clerical workers found high levels of boredomto be associated with musculoskeletalsymptoms (in any part of the body) duringwork hours.
Job Control
Numerous studies have reported positiveassociations between limited job control orautonomy at work and upper extremityproblems. These include neck symptoms [Ryanand Bamptom 1988, OR 3.9; Hales et al.1994, OR 1.6], neck/back/shoulder symptoms[Sauter et al. 1983; Theorell et al. 1991],musculoskeletal aches [Karasek et al. 1987],and muscle/joint symptoms [Hopkins 1990;Houtman et al. 1994]. The study by Pot et al.[1987], however, failed to support thisrelationship.
Job Clarity
A number of studies, including those of Ryanand Bamptom [1988], Karasek et al. [1987],
7-6
and Ekberg et al. [1994], have shown positiveassociations between reports of role ambiguity(uncertainty about job expectations) and upperextremity disorders (particularly neckdisorders). Similarly, uncertainty regarding jobfuture was found to be predictive of neck andshoulder discomfort [Sauter et al. 1983] andelbow, neck, and hand/wrist symptoms [Haleset al. 1994].
Social Support
Limited social support from supervisors andcoworkers has been found to be positivelyassociated with a variety of upper extremitysymptoms. The studies by Pot et al. [1987],Kompier [1988], Hopkins [1990], Sauter et al.[1983], and Hales et al. [1994], all support apositive association. Linton [1990] reported apositive association between neck symptomsand limited support from supervisors. Ryan andBampton [1988] reported an effect of limitedsupport from coworkers (OR 6.7), but notsupervisors, on neck symptoms, whileKvarnström and Hagberg [1983] reported aneffect of limited support from supervisors butnot coworkers on sick leave due to shouldermuscle symptoms. Dehlin and Berg [1977],however, found no effect of social support onneck/shoulder symptoms, while Theorell et al.[1991] found no effect of social support atwork on neck and shoulder symptoms orsymptoms of the other joints (with or withoutadjustment for physical load). Likewise,Karasek et al. [1987] found no significantassociation between musculoskeletal aches andsocial support at work.
Summary and Conclusions for Upper
ExtremitiesOverall, the epidemiologic studies of upperextremity disorders suggest that certainpsychosocial factors (including intensifiedworkload, monotonous work, and low levels ofsocial support) have a positive association withthese disorders. Lack of control over the joband job dissatisfaction also appear to bepositively associated with upper extremityMSDs, although the data are not as supportive. The evidence for the relationship betweenpsychosocial factors and upper extremitydisorders appears to be stronger forneck/shoulder disorders or musculoskeletalsymptoms in general than for hand/wristdisorders. This stronger association forneck/shoulder disorders may be due to thefollowing reasons: the large number of studiesperformed in the Nordic countries which havefocused more on the neck/shoulder MSDhealth outcome than a hand/wrist outcome;many of the neck/shoulder studies includednumerous psychosocial variables in theirmodels, whereas studies of hand/wrist MSDshave not, as a rule, included as extensivepsychosocial variable testing (therefore thevariables are absent from the risk factormodels); and the fact that most of the studieswith extensive psychosocial scales were inoffice settings, where physical factors may beless important than psychosocial factors in theirrelationship with MSDs. This finding can becontrasted with studies in heavy industrialsettings, where higher exposure to physicalfactors may have
7-7
played a greater role than psychosocial factorsin the development of MSDs. Also,pathophysiologic processes resulting fromadverse psychosocial and work organizationfactors may exert a greater effect on theneck/shoulder musculature to produceincreased muscle tension and strain than on thehand/wrist region.
BACK DISORDERS
Individual and Extra-WorkEnvironment FactorsAs with upper extremity disorders, a host ofpsychosocial factors associated with theindividual worker (e.g., personality andpsychological status) and extra-workenvironment (e.g., living alone) have beenlinked to back pain and disability [Bongers etal. 1993]. As the “work-relatedness” of thesefactors is unclear and because they have beenexamined by others (e.g., Bongers [1993]),with the exception of job dissatisfactiondiscussed above, they will not be extensivelyreviewed in this report. In general, these studiesshow clear associations between measures ofpsychological distress or dysfunction and self-reported back pain. However, the temporalrelationship between psychological factors andmusculoskeletal symptoms/ disorders remainsunclear. One possibility is that psychologicaldistress is simply a consequence of chronic lowback pain, with no etiologic role in thedevelopment of the disorder. Alternatively, it ispossible that psychological factors may havesome etiologic role in the transition from anemployee with a history of back pain to thestatus of an unemployed patient with chronicback pain, due to fear of re-injury, or otherfactors which would make it impossible toperform the job [Feyer et al. 1992].
While there are a number of prospectivestudies of low back pain and individual physicalfactors, there appear to be only a fewprospective studies that incorporate individualand extra-work environment psychosocialfactors. Bigos et al. [1991b] defined, in a 4-year study of 3,020 hourly wage earners at anaircraft manufacturing plant, an outcome asreporting a back pain complaint to the companymedical department, filing a back-relatedincident report, or filing an industrial insuranceclaim. The psychosocial assessment includedpersonality traits, as measured by theMinnesota Multiphasic Personality Inventory(MMPI), and limited information on familysupport, health locus of control, and worksocial support. One question about enjoymentof tasks in the job was also included. Of the 37variables used to evaluate the role of socialsupport, health locus of control, and personalitytraits, three were found to be significant in amultivariate analysis. They were Scale 3 of theMMPI [tendencies towards somatic complaintsor denial of emotional distress (relative risk[RR]=1.4), dissatisfaction with work (RR=1.7),and prior back pain (RR=1.7)]. Althoughsignificant, these variables explained only asmall fraction of the back pain reports in thispopulation. The number of back pain reportswas three times higher in the group with thehighest scores on these three variablescompared with the group with the lowestscores, although only 9% of the work forcewas in the highest risk group. Because thisstudy focused on the reporting of back paincomplaint and not the actual development ofback pain, it would be a mistake to generalizethe results to workers developing back pain.This study suggests
7-8
that individual premorbid personality traits onlyexplain a small fraction of work-related lowerback problems.
Job Dissatisfaction
Job dissatisfaction has been associated withback disorders in both longitudinal and cross-sectional investigations. Bergenudd and Nilsson[1988], studying some 575 residents of Malmofor over 19 years, found job dissatisfaction tobe associated with self-reported back pain. Asdescribed above, Bigos et al. [1991b] found apositive association between job dissatisfactionand workers filing compensation claims forback injury. Here, subjects who stated that they“hardly ever” enjoyed their job tasks were 2.5times more likely to report a back injury thanthose who “almost always” enjoyed their jobtasks. However, as Frank et al. [1995] pointout, some reviewers have argued that theairplane manufacturing jobs with the highestlevels of dissatisfaction were also the mostphysically demanding. Frank et al. [1995] alsonoted that, unfortunately, the extent of theinteraction is difficult to assess because of thelimited measurement of workplacebiomechanical exposures in the Bigos et al.studies [1986a,b; 1991a,b]. Whilepsychosocial and psychological factors wereassessed at the individual level, workplacebiomechanical factors were assessed only atthe group level. Biering-Sorensen et al. [1989],in a one-year follow-up mail survey study ofsome 928 inhabitants of Denmark (whichadjusted for confounders such as previous backpain), also found no association of back painwith job dissatisfaction. Because informationwas limited to the use of mailed surveyquestionnaires, no workplace biomechanicalfactors were measured in this study either.
The cross-sectional study by Dehlin and Berg[1977] of nursing aids described earlier foundan association between dissatisfaction and self-reported back symptoms. However, this studydid not adjust for confounders. Likewise,Magora [1973] in a mailed survey study ofIsraeli workers in 8 occupational categoriesfound job satisfaction to be associated withreports of sick leave due to low back pain. Thisstudy also did not adjust for potentialconfounders. Svensson and Anderson [1989],in a cross-sectional study of 1,746 Swedishresidents, found an association after adjustment.However, in a cross-sectional study by Åstrand[1987] of 391 male Swedish paper companyworkers (clerks and manual workers), noassociation was found between dissatisfactionand back disorders, as assessed by symptomsand physical examination after confounderadjustment.
Job and Work Environment Factors
Intensified Workload
A number of studies have reported associationsbetween perceptions of intensified workload, asmeasured by reports of time pressure and highwork pace, and self-reports of back pain.Heliövaaraet al. [1991] in a study of approximately 5,600Finns, found a composite measure (containingitems on perceived time pressure at work,monotony, and fear of mistakes) to beassociated (OR 2.0) with back disorders(defined by interview and physical examination)after adjusting for potential confounders,including physical load and previous back pain.Lundberg et al. [1989] found perceived timepressure to be associated with perceived backload among 20 workers on a Swedishassembly line. In a similar vein, Houtman et al.
7-9
[1994], in the study of 5,865 Dutch workersacross all occupations reported above, foundan association (OR 1.21) between reportinghigh work pace and self-reported back pain(but not chronic back pain problems, defined asback pain for more than three months or atleast three times in the study period) (OR 1.2). Magora [1973], in the study of Israeliworkers described above, found high levels ofconcentration to be associated with reports ofsick leave due to low back pain (OR 2.9).However, Åstrand [1987], found noassociation between “hustling” and “nervewracking work” and back pain in male papercompany workers.
Monotony Several studies described above [Heliövaara etal. 1991; Houtman et al. 1994] have reportedassociations between perceived monotony andreports of back complaints. Svensson andAnderson [1983], in a study of 940 maleresidents of Goteborg, Sweden, between theages of 40 and 47, similarly found monotonouswork (rated “absolutely” or “unacceptably”boring) to be associated with back complaints.This relationship remained after adjusting forseveral physical factors. However, Svenssonand Anderson [1989] found no relationshipbetween monotony and back pain complaintsamong Swedish women in a multivariateanalysis which included measures of job andtask satisfaction. Similarly, in the Houtman et al.[1994] study, controlling for a combination ofphysical stressors (dangerous work, heavyphysical load, noise at work, dirty work, andbad smell at work) reduced the magnitude ofthe relationship (for back complaints, the ORdecreased from 3.90 to 3.46.) The authorssuggest that this may be because
monotonous work is often work which is alsoeither short-cycled or involves a high static(postural) load.
Job Control
In the study of teleservice operators citedabove, Hoekstra et al. [1994], after controllingfor a number of individual and work-relatedfactors, found perceived job control at work tobe inversely associated with back disorders(OR 0.6), that is, the less perceived job controlat work, the higher the odds of back disorders.Likewise, as noted above, Sauter et al. [1983]found that low job control was related to neck,back, and shoulder discomfort.
Social Support
Bigos et al. [1991b] found a significantunivariate relationship between limited socialsupport at work and back trouble. However,this association was found to be nonsignificantby the investigators when included in amultivariate analysis.
Summary and Conclusions forBack Disorders
In general, the studies reviewed suggest anassociation between back disorders andperceptions of intensified workload asmeasured by indices of both perceived timepressure and workload. Despite theconsiderable differences in the types ofmethods used to assess both the independentand dependent variables, four of the five studiesthat explicitly included measures of intensifiedworkload found significant associations. It isalso noteworthy that all four of these studiesattempted to control or adjust for potentialcovariates. Five of the seven studies that assessjob dissatisfaction
7-10
also found positive associations with backdisorders. While this evidence is clearlysuggestive, Biering-Sorensen et al. [1989]found no association in a large-scaleone-year follow-up study; while Åstrand[1987] likewise found no evidence of anassociation among 391 paper workers. Limitedsupport for an association between backdisorders and low job control is also evident,while the evidence for a relationship betweenmonotonous work and back disorders is mixed.Only one study examined the relationshipbetween social support and back disorders andfound only weak evidence for an association.
Overall ConclusionsWhile the etiologic mechanisms are poorlyunderstood, there is increasing evidence thatpsychosocial factors related to the job andwork environment play a role in thedevelopment of work-related MSDs of theupper extremity and back. Though the findingsof the studies reviewed are not entirelyconsistent, they suggest that perceptions ofintensified workload, monotonous work, limitedjob control, low job clarity, and low socialsupport are associated with various work-related MSDs. As some of these factors areseemingly unrelated to physical demands, and anumber of studies have found associations evenafter adjusting for physical demands, the effects
of these factors on MSDs may be, in part orentirely, independent of physical factors. It isalso evident that these associations are notlimited to particular types of jobs (e.g., VDTwork) or work environments (e.g., offices) but,rather, seem to be found in a variety of worksituations. This observation seems to suggestthat psychosocial factors may representgeneralized risk factors for work-relatedMSDs. These factors, while statisticallysignificant in some studies, generally have onlymodest strength.
At present, two of the difficulties in determiningthe relative importance of the physical andpsychosocial factors are the following: (1)psychosocial factors are usually measured atthe individual level, while physical factors aremore often measured at the group (e.g., job ortask) level and often by methods with limitedprecision or accuracy, and (2) “objectivemeasures” of aspects of the psychosocial workenvironment are difficult to develop and arerarely used, while objective methods tomeasure the physical environment are morereadily available. Until we can measure mostworkplace and individual variables with morecomparable techniques, it will be hard todetermine precisely their relative importance inthe causation of MSDs.
See footnotes at end of table. (Continued)
Table 7–1. Summary of studies examining psychosocial factors and upper extremity disorders (neck, shoulder, elbow, hand, and wrist)
Methods Associations with UE outcomes
Study
Workergroup
(particip.rate) Design
Psychosocialfactor
assessment
MSDoutcome
assessment
Covariateadjust-ments
Job/taskdissat.
Int.wkld.
Mono.work
Lowjob
control
Low job
clarity
Lowsocialsupp.
Bernard etal. 1993
1,050newspaperworkers(93%)
Cross-sectional
Self-reportquestionnairewith job stressscales
MSD casedefinition basedonquestionnaire
+ +
Dehlin andBerg 1977
233 nursingaides (85%)
Cross-sectional
Self-reportquestionnaire—7 scales
Interviews—pain/achesymptoms
o o o
Ekberg et al.1994
109workers vs.637 controls
Cross-sectional(case-control)
Self-report—modified Nordicquestionnaire
MD consults forMSD disorders
+ +
Hales et al.1994
553telecom-municationsworkers
Cross-sectional
Self-reportquestionnairewith job stressscales
Disordersbased onsymptomquestionnaireand MD exam
Controlledfor extrajob factors
+ + +
Hoekstra etal. 1994
108teleserviceworkers(95%)
Cross-sectional
Self-report jobstressquestionnaire
MSD casedefinition basedon self-reportquestionnaire
+
Hopkins1990
291keyboardoperatorsand otherclericalgroups
Cross-sectional
Self-reportquestionnaire—items from habitsof livingquestionnaire
Questionnairesymptoms
+ + + +
7-11
Table 7–1(Continued). Summary of studies examining psychosocial factorsand upper extremity disorders (neck, shoulder, elbow, hand, and wrist)
Methods Associations with UE outcomes
Study
Workergroup
(particip.rate) Design
Psychosocialfactor
assessment
MSDoutcome
assessment
Covariateadjust-ments
Job/taskdissat.
Int.wkld.
Mono.work
Lowjob
control
Low job
clarity
Lowsocialsupp.
See footnotes at end of table. (Continued)
Houtman etal. 1994
5,865workers—generalpopulation
Cross-sectional
Self-report work-livingquestionnaire
Symptomsquestionnaire
Physicalstressors—personalcharacter-istics
+ +
Karasek etal. 1987
8,700 whitecollar laborunionmembers(87%)
Cross-sectional(randomsample)
Self-reportquestionnaire
Questionnaire—musculoskeletalaches
+ + + +
Kompier1988
158 malebus drivers(73%)
Cross-sectional
Self-reportquestionnaire
Self reportquestionnaire—complaints andsick leave
+ +
Kvarnstromand Halden1983
224fabricationworkers
Cross-sectional(case-control)
Structuredinterviewquestionnaire
Disorders frommedical and sickabsencerecords
+ + +/o
Linton 1990 22,200workers—generalpopulation
Cross-sectional
Self-report workenvironmentquestionnaireand habits oflivingquestionnaire
Pain + +
Pot et al.1987
222 VDToperators
Cross-sectional
Structuredinterviewquestionnaire
Complaints—structuredinterview
+/+ o +
7-12
Table 7–1(Continued). Summary of studies examining psychosocial factorsand upper extremity disorders (neck, shoulder, elbow, hand, and wrist)
Methods Associations with UE outcomes
Study
Workergroup
(particip.rate) Design
Psychosocialfactor
assessment
MSDoutcome
assessment
Covariateadjust-ments
Job/taskdissat.
Int.wkld.
Mono.work
Lowjob
control
Low job
clarity
Lowsocialsupp.
Ryan andBampton1988
143 dataprocessors
Cross-sectional(high vs.lowsymptoms)
Self-reportquestionnaire—items from workenvironmentscale
Symptomsbased on MDinterview andexam
+ + + + +/o
Sauter et al.1983
248 VDTusers and85 non-users (90%)
Cross-sectional
Self-reportquestionnaire—workenvironmentscale items
Questionnaire—discomfortscale
Physicalworkdemands(adj.)
+ + + +
Takala et al.1991
351 bankcashiers
Longi-tudinal
Self-reportquestionnaire
Questionnaire—musclesymptoms
Posturalload (adj.)
+
Theorell etal. 1991
207workers in 6occupations
Cross-sectional
Self-report questionnaire
Questionnaire—muscle tensionsymptoms
Physicalload (adj.)
+/o + o
Tola et al.1988
1,174machinists;1,034carpenters;1,013 officeworkers(67% to76%)
Cross-sectional
Mailedquestionnaire—workercharacteristics
Symptoms inlast 12 months;questionnaireand interview
o
+ = Significant association found. o = No significant association found.+/+ = Two different measures of factor (e.g., time pressure and workload) found significant.+/o = Mixed results (on factor significantly associated; second factor not significantly associated).
7-13
See footnotes at end of table. (Continued)
Table 7–2. Summary of studies examining psychosocial factors and back disorders
Methods Associations with back disorders
Study
Worker group(participation
rate) Design
Psychosocialfactor
assessment
MSDoutcome
assessment
Covariateadjust-ments
Jobdissat.
Int.wkld.
Mono.work
Lowjob
control
Lowsocialsupp.
Åstrand1987
391 workers inpaper-pulpindustry
Cross-sectional
Questionnaire—questions onwork conditions
Interview and MDexam—back painabnormalities
o o
Bergenuddand Nilsson1988
575 55-year-oldcity residents(96%)
Longi-tudinal
Interview andmailedquestionnaire
Interview reportsof back pain
+
Biering-Sorenson etal. 1989
928 persons—generalpopulation(82%)
Longi-tudinal
Mailquestionnaire
Questionnaire—back pain in last12 months
o
Bigos et al.1991b
3,020 maleaircraft plantemployees(54% with alldata)
Longi-tudinal
Questionnaire—PersonalityInventory (MMPI),other questions
Back problems—medical reports,insurance claims
Control forprior backproblems
+ o
Dehlin andBerg 1977
233 nursingaides (85%)
Cross-sectional
Questionnaire—7 scales,52 items
Interview—reported pain/achesymptoms
+
Heliövaraaet al. 1987
5,600workers—generalpopulation(92%)
Cross-sectional
Questionnaire—scale assessingcombined hurriedwork,monotonouswork, tight workschedules
MD exam andinterview—backdisorders
Physicalload, priorbackproblems
Combined + +
7-127-14
Table 7–2 (Continued). Summary of studies examining psychosocial factor and back disorders
Methods Associations with back disorders
Study
Worker group(participation
rate) Design
Psychosocialfactor
assessment
MSDoutcome
assessment
Covariateadjust-ments
Jobdissat.
Int.wkld.
Mono.work
Lowjob
control
Lowsocialsupp.
See footnotes at end of table. (Continued)
Hoekstra etal. 1994
108 teleserviceworkers (95%)
Cross-sectional
Job stressquestionnaire
MSD casedefinition based onquestionnaire data
Individualworkfactors
+
Houtman etal. 1994
5,865workers—generalpopulation
Cross-sectional
Questionnaire—work livingquestionnairesurvey
Questionnairesymptoms
Physicalstressors;personalcharacter-istics
+ +
Lundberg etal. 1989
20 maleassembly lineworkers
Cross-sectional
Ratings of timepressure during2-hr work period
Back load ratingsduring 2-hr workperiod
+
Magora1973
3,316 workersin 8occupations
Cross-sectional(low painvs.controls)
Questionnaire—ratings of jobaspects andsatisfaction
Questionnaire—reports of low-back pain and sickleave due to low-back pain
Analysesstratified byoccupation
+ +
Sauter et al.1983
248 VDT users;85 non-users(90%)
Cross-sectional
Questionnaire—workenvironmentscale survey
Questionnaire—reports ofdiscomfort
Physicalworkdemands
+
SvenssonandAnderson1983
940 males—generalpopulation
Cross-sectional
Questionnaire—perceptions ofstress, boredom
Interview report ofback pain
Physicalworkdemands—life and jobsatisfaction
+
7-137-15
Table 7–2 (Continued). Summary of studies examining psychosocial factor and back disorders
Methods Associations with back disorders
Study
Worker group(participation
rate) Design
Psychosocialfactor
assessment
MSDoutcome
assessment
Covariateadjust-ments
Jobdissat.
Int.wkld.
Mono.work
Lowjob
control
Lowsocialsupp.
SvenssonandAnderson1989
1,746 femalesages 38–64—generalpopulation
Cross-sectional
Questionnaire—items on job andtask satisfaction
Interview—reports of backpain
Physicalworkload
+ o
+ = Significant association found.o = No significant association found.
7-147-16
R-1
REFERENCES
Åaras A [1994]. Relationship between trape-zius load and the incidence of musculoskele-talillness in the neck and shoulder. Int J IndErgonomics 14(4):341–348.
Abenhaim L, Suissa S [1988]. Economic scopeof occupationally-induced back pain. Institutede recherche en sante et en securite du travaildu Quebec. Quebec, Canada: IRSST,Research Summary No. 66.
AFL-CIO [1997]. Stop the pain. Washing-ton,DC: AFL-CIO.
Alexander and Alexander [1996]. 1996 U.S.risk management survey. New York, NY:Alexander and Alexander, Inc.
Allender E [1974]. Prevalence, incidence, andremission rates of some common rheumaticdiseases or syndromes. Scand J Rheumatol3:145–153.
Alterman T, Shekells RB, Vernon SW, BurauKD [1994]. Decision latitude, psy-chologicdemand, job strain and coronary heart diseasein the Western Electric study. Am J Epidemiol139(6):620–627.
Amadio PC [1995]. De Quervain’s diseaseand tenosynovitis. In: Gordon SL, Blair SJ,Fine LJ, eds. Repetitive motions disorders ofthe upper extremity. Rosemont, IL: AmericanAcademy of Orthopaedic Surgeons, pp.435–448.
Amano M, Gensyo U, Nakajima H, Yatsuki K[1988]. Characteristics of work actions of shoe
manufacturing assembly line workers and across-sectional factor-control study onoccupational cervicobrachial disorders. Jpn JInd Health 30:3–12.
Andersen JH, Gaardboe O [1993a]. Muscu-loskeletal disorders of the neck and upper limbamong sewing machine operators: a clinicalinvestigation. Am J Ind Med 24(6): 689–700.
Andersen JH, Gaardboe O [1993b]. Preva-lence of persistent neck and upper limb pain ina historical cohort of sewing machineoperators. Am J Ind Med 24:677–687.
Andersson GBJ [1981]. Epidemiologic aspectsof low back pain in industry. Spine 6:53–60.
Andersson GBJ [1996]. The epidemiology ofspinal disorders. In: Frymoyer JW, ed. Theadult spine: principles and practice. 2nd ed.New York, NY: Raven Press Ltd.
Andersson GBJ, Pope MH, Frymoyer JW,Snook S [1991]. Epidemiology and cost. In:Pope M, ed. Occupational low back pain.St. Louis, MO: Mosby Year Book.
Andersson JAD [1984]. Shoulder pain andtension neck and their relation to work. Scand JWork Environ Health 10(6): 435–442.
Armstrong RB, Warren GL, Warren JA[1991]. Mechanisms of exercise-inducedmuscle fibre injury. J Sports Med 12(3):184–207.
Armstrong TJ, Chaffin DB [1979]. Carpaltunnel syndrome and selected personal
R-2
attributes. J Occup Med 21(7):481–486.
Armstrong TJ, Foulke JA, Joseph BS,Goldstein SA [1982]. Investigation ofcumulative trauma disorders in a poultryprocessing plant. Am Ind Hyg Assoc J43(2):103–116.
Armstrong TJ, Fine LJ, Goldstein SA, LifshitzYR, Silverstein BA [1987a]. Ergonomicconsiderations in hand and wrist tendinitis. JHand Surg 12A(5):830–837.
Armstrong TJ, Fine LJ, Radwin RG, SilversteinBS [1987b]. Ergonomics and the effects ofvibration in hand-intensive work. Scand JWork Environ Health 13:286–289.
Armstrong TJ, Punnett L, Ketner P [1989].Subjective worker assessments of hand toolsused in automobile assembly. Am Ind HygAssoc J 50(12):639–645.
Armstrong TJ, Buckle P, Fine LJ, Hagberg M,Jonsson B, Kilbom Å [1993]. A conceptualmodel for work-related neck and upper-limbmusculoskeletal disorders. Scand J WorkEnviron Health 19(2):73–84.
Aro S, Leino P [1985]. Overweight andmusculoskeletal morbidity: a ten-year follow-up. Int J Obes 9:267–275.
Asbury FD [1995]. Occupational repetitivestrain injuries and gender in Ontario1986–1991. J Occup Environ Med 37(4):479–485.
Åstrand NE [1987]. Medical, psychological,and social factors associated with backabnormalities and self-reported back pain: a
cross-sectional study of male employees in aSwedish pulp and paper industry. Br J Ind Med44(5):327–336.
Åstrand NE, Isacsson SO [1988]. Back pain,back abnormalities, and competing medical,psychological, and social factors as predictorsof sick leave, early retirement, unemployment,labour turnover and mortality: a 22-yearfollow-up of male employees in a Swedish pulpand paper company. Br J Ind Med45(6):387–395.
Atterbury MR, Limke JC, Lemasters GK,Li Y, Forrester C, Stinson R, Applegate H[1996]. Nested case-control study of handand wrist work-related musculoskeletaldisorders in carpenters. Am J Ind Med30:695–701.
Barnhart S, Demers PA, Miller M, LongstrethWT Jr., Rosenstock L [1991]. Carpal tunnelsyndrome among ski manufacturing workers.Scand J Work Environ Health 17(1):46–52.
Baron S, Milliron M, Habes D, Fidler A[1991]. Hazard evaluation and technicalassistance report: Shoprite Supermarkets, NewJersey—New York. Cincinnati, OH: U.S.Department of Health and Human Services,Public Health Service, Centers for DiseaseControl, National Institute for OccupationalSafety and Health, NIOSH Report No. HHE88–344–2092.
Battié MC, Bigos SJ, Fisher LD, Hansson TH,Jones ME, Wortley MD [1989]. Isometriclifting strength as a predictor of industrial backpain. Spine 14(8):851–856.
Battié MC, Bigos SJ, Fisher LD, Spengler
R-3
DM, HanssonTH, Nachemson AL, et al.[1990]. The role of spinal flexibility in backpain complaints within industry: a prospectivestudy. Spine 15(8):768–793.
Battié MC, Videman T, Gibbons LE,Fisher L, Manninen H, Gill K [1995].Determinants of lumbar disc degeneration:a study relating lifetime exposures and magneticresonance imaging findings in identical twins.Spine 20:2601–2612.
Behrens V, Seligman P, Cameron L, MathiasCGT, Fine L [1994]. The preva-lence of backpain, hand discomfort, and dermatitis in theU.S. working population. Am J Public Health84(11):1780–1785.
Bennett GE [1946]. Shoulder and elbowlesions distinctive of baseball players. Ann Surg126:107–110.
Berg M, Sanden Å, Torell G, Järvholm B[1988]. Persistence of musculoskeletal symp-toms: a longitudinal study. Ergonomics31(9):1281–1285.
Bergenudd H, Nilsson B [1988]. Back pain inmiddle age. Occupational workload andpsychologic factors: an epidemiologic survey.Spine 13(1):58–60.
Bergenudd H, Lindgärde, Nilsson B, PeterssonC [1988]. Shoulder pain in middle age: a studyof prevalence and relation to occupationalwork load and psychosocial factors. ClinOrthop Res 23:234–238.
Bergqvist U [1984]. Video display terminalsand health. Scand J Work Environ Health10(2):68–77.
Bergqvist U [1989]. Possible health effects ofworking with VDUs (editorial). Br J Ind Med46:217–221.
Bergqvist U, Wolgast E, Nilsson B, Voss M[1995a]. Musculoskeletal disorders amongvisual display terminal workers: individual,ergonomic, and work organizational factors.Ergonomics 38(4):763–776.
Bergqvist U, Wolgast E, Nilsson B, Voss M[1995b]. The influence of VDT work onmusculoskeletal disorders. Ergonomics38(4):754–762.
Bergqvist-Ullman M, Larsson N [1977]. Acutelow back pain in industry. Acta Orthop Scand170(Suppl):1–117.
Berkeley M, Bennett J, Woods W [1985].Elbow problems: injuries to the throwing arm.Zarins B, Andrews J, Carson W, eds.Phildelphia, PA: W.B. Saunders PublishingCompany, pp. 235–249.
Bernard B, Sauter S, Fine LJ [1993]. Hazardevaluation and technical assistance report: LosAngeles Times, Los Angeles, CA. Cincinnati,OH: U.S. Department of Health and HumanServices, Public Health Service, Centers forDisease Control and Prevention, NationalInstitute for Occupational Safety and Health,NIOSH Report No. HHE 90–013–2277.
Bernard B, Sauter S, Fine LJ, Petersen M,Hales T [1994]. Job task and psychosocial riskfactors for work-related musculoskeletaldisorders among newspaper employees. ScandJ Work Environ Health 20(6):417– 426.
Biering-Sørensen F [1983]. A prospective
R-4
study of low-back pain in a general population. I. Occurrence, recurrence, and aetilogy. ScandJ Rehabil Med 15:81–88.
Biering-Sørensen F [1984]. Physicalmeasurements as risk indicators for low backtrouble over a one-year period. Spine9(2):106–119.
Biering-Sørensen F, Thomsen CE, Hilden J[1989]. Risk indicators for low back trouble.Scand J Rehabil Med 21:151–157.
Bigos SJ, Spengler DM, Martin NA, Zeh J,Fisher L, Nachemson A, et al. [1986a]. Backinjuries in industry: a retrospective study. II.Injury factors. Spine 11:246–251.
Bigos SJ, Spengler DM, Martin NA, Zeh J,Fisher L, Nachemson A [1986b]. Back injuriesin industry: a retrospective study. III.Employee-related factors. Spine 11:252–256.
Bigos SJ, Battié MC, Fisher LD [1991a].Methodology for evaluating predictive factorsfor the report of back injury. Spine16(6):669–670.
Bigos SJ, Battié MC, Spengler DM,Fisher LD, Fordyce WE, Hansson TH, et al.[1991b]. A prospective study of work per-ceptions and psychosocial factors affecting thereport of back injury. Spine 16(1):1–6.
Bigos S, Bowyer O, Braen G, et al. [1994].Acute low back problems in adults. Clinicalpractice guideline, quick reference guide No.14. Rockville, MD: U.S. Department of Healthand Human Services, Public Health Service,Agency for Health Care Policy and Research,AHCPR Pub. No. 95–6043.
Bjelle A, Hagberg M, Michaelsson G [1979].Clinical and ergonomic factors in prolongedshoulder pain among industrial workers. ScandJ Work Environ Health 5(3):205–210.
Bjelle A, Hagberg M, Michaelson G [1981].Occupational and individual factors in acuteshoulder-neck disorders among industrialworker. Br J Ind Med 38:356–363.
Blåder S, Barck-Holst U, Danielsson S, FerhmE, Kalpamaa M, Leijon M, et al. [1991]. Neckand shoulder complaints among sewing-machine operators: a study concerningfrequency, symptomatology and dysfunction.Appl Ergonomics 22(4):251– 257.
Bleecker ML, Bohlman M, Moreland R,Tipton A [1985]. Carpal tunnel syndrome: roleof carpal canal size. Neurol 35(11):1599–1604.
BLS [1995]. Workplace injuries and ill-nessesin 1994. Washington, DC: U.S. Department ofLabor, Bureau of Labor Statistics, USDL95–508.
Bongers PM, Boshuizen HC [1990]. Backdisorders and whole-body vibration at work[Dissertation]. Amsterdam, The Nether-lands:University of Amsterdam.
Bongers PM, de Winter CR [1992]. Psy-chosocial factors and musculoskeletal disease:a report of the literature. The Netherlands:TNO Institute of Preventive Health Care,Report No. 92–082.
Bongers PM, Boshuizen HC, Hulshof CTJ,Koemeester AP [1988]. Back disorders incrane operators exposed to whole-body
R-5
vibration. Int Arch Occup Environ Health60:129–137.
Bongers PM, Hulshof CTJ, Dijkstra L,Boshuizen HC [1990]. Back pain and exposureto whole-body vibration in helicopter pilots.Ergonomics 33:1007– 1026.
Bongers PM, de Winter CR, Kompier MAJ,Hildebrandt VH [1993]. Psychosocial factorsat work and musculoskeletaldisease. Scand J Work Environ Health19(5):297–312.
Boshuizen HC, Bongers PM, Hulshof CTJ[1990a]. Self-reported back pain in tractordrivers exposed to whole-body vibration. IntArch Occup Environ Health 62:109–115.
Boshuizen HC, Hulshof CTJ, Bongers PM[1990b]. Long-term sick leave and disabilitypensioning due to back disorders of tractordrivers exposed to whole-body vibration. IntArch Occup Environ Health 62:117–122.
Boshuizen HC, Bongers PM, Hulshof CTJ[1992]. Self-reported back pain in fork-lifttruck and freight-container tractor driversexposed to whole-body vibration. Spine17:59–65.
Boshuizen HC, Verbeek JHAM, Broersen JPJ,Weel ANH [1993]. Do smokers get moreback pain? Spine 18(1):35–40.
Bovenzi M [1990]. Medical aspects of thehand-arm vibration syndrome. Int J IndErgonomics 6(1):61–73.
Bovenzi M, Italian study group on physicalhazards in the stone industry [1994]. Hand-arm
vibration syndrome and dose-response relationfor vibration-induced white finger among quarrydrillers and stonecarvers. Occup Environ Med51(9):603–611.
Bovenzi M, Zadini A [1992]. Self-reported lowback symptoms in urban bus drivers exposedto whole-body vibration. Spine17(9):1048–1059.
Bovenzi M, Betta A [1994]. Low-backdisorders in agricultural tractor drivers exposedto whole-body vibration and postural stress.Appl Ergonomics 25:231–241.
Bovenzi M, Franzinelli A, Strambi F [1988].Prevalence of vibration-induced white fingerand assessment of vibration exposure amongtravertine workers in Italy. Int Arch OccupEnviron Health 61:25–34.
Bovenzi M, Zadini A, Franzinelli A, Borgogni F[1991]. Occupational mus-culoskeletaldisorders in the neck andupper limbs of forestry workers exposed tohand-arm vibration. Ergonomics 34(5):547–562.
Bovenzi M, Franzinelli A, Mancini R, CannavaMG, Maiorano M, Ceccarelli F [1995]. Dose-response relation for vascular disordersinduced by vibration in the fingers of forestryworkers. Occup Environ Med 52:722–730.
Boyce RW, Jones GR, Hiatt AR [1991].Physical fitness capacity and absenteeism ofpolice officers. J Occup Med 33(11):1137–1143.
Brammer AJ, Taylor W, eds. [1981]. Vibrationeffects on the hand and arm in industry. New
R-6
York, NY: John Wiley and Sons.
Brattberg G, Thorslund M, Wikman A [1989].The prevalence of pain in a general population:the results of a postal survey in a county ofSweden. Pain 37:215–222.Brinckmann P [1988]. Stress and strain ofhuman lumbar discs. Clin Biomechanics3(4):232–235.
Broberg E [1984]. Ergonomic injuries at work:ISA-information system on occupa-tionalinjuries. Swedish National Board ofOccupational Safety and Health, Report No.1984:3E.
Bross JD [1966]. Spurious effects from anextraneous variable. J Chron Dis 19:736–747
Brubaker R, Mackenzie C, Bates D [1983]. Vibration white finger disease among treefellers in British Columbia. J Occup Med25(5):403–408.
Brubaker RL, Mackenzie CJG, Hertzman C,Hutton SG, Slakov J [1987]. Longitudinalstudy of vibration-induced white finger amongcoastal fallers in British Columbia. Scand JWork Environ Health 13(4):305– 308.
Buckwalter JA, Woo SL-Y, Goldberg VM,Hadley EC, Booth F, Oegema TR, et al.[1993]. Current concepts review: soft-tissueaging and musculoskeletal function. J BoneJoint Surg [Am] 75A(10):1533–1548.
Burdorf A [1992]. Exposure assessment of riskfactors for disorders of the back inoccupational epidemiology. Scand J WorkEnviron Health 18(1):1–9.
Burdorf A, Zondervan H [1990]. An epi-demiological study of low-back pain in craneoperators. Ergonomics 33(8):981–987.
Burdorf A, Monster A [1991]. Exposure tovibration and self-reported health complaints ofriveters in the aircraft industry. Ann Occup Hyg35(3):287–298.
Burdorf A, Govaert G, Elders L [1991].Postural load and back pain of workers in themanufacturing of prefabricated concreteelements. Ergonomics 34(7):909–918.
Burdorf A, Naaktgeboren B, deGroot HC[1993]. Occupational risk factors for low backpain among sedentary workers.J Occup Med 35:1213–1220.
Burry HC, Gravis V [1988]. Compensatedback injury in New Zealand. N Z Med J101(852):542–544.
Burt S, Hornung R, Fine L [1990]. Hazardevaluation and technical assistance report:Newsday, Inc., Melville, NY. Cincinnati, OH:U.S. Department of Health and HumanServices, Public Health Service, Centers forDisease Control, National Institute forOccupational Safety and Health, NIOSHReport No. HHE 89–250–2046.
Byström S, Hall C, Welander T, Kilbom Å[1995]. Clinical disorders and pressure-painthreshold of the forearm and hand amongautomobile assembly line workers. J Hand Surg[Br] 20B(6):782–790.
Cady LD Jr., Bischoff DP, O'Connell ER,Thomas PC, Allan JH [1979]. Strength andfitness and subsequent back injuries in fire-
R-7
fighters. J Occup Med 21(4):269–272.
Cady LD Jr., Thomas PC, Karwasky RJ[1985]. Program for increasing health andphysical fitness of firefighters. J Occup Med27(2):110–114.
Cannon LJ, Bernacki EJ, Walter SD [1981].Personal and occupational factors associatedwith carpal tunnel syndrome. J Occup Med23(4):255–258.
CDC (Centers for Disease Control) [1989].Occupational disease surveillance: carpal tunnelsyndrome. MMWR 38(28):485–489.
Chaffin DB [1973]. Human strength capabilityand low back pain. Unpublished paperpresented at the American Industrial HealthConference, Denver, CO, April 16–19, 1973.
Chaffin DB [1979]. Manual materials handlingthe cause of overexertion injury and illness inindustry. J Environ Pathol Toxicol 2(5):67–73.
Chaffin DB, Park KS [1973]. A longitudinalstudy of low-back pain as associated withoccupational weight lifting factors. Am Ind HygAssoc J 34:513–525.
Chaffin DB, Andersson GBJ [1984]. Occu-pational biomechanics. New York, NY: JohnWiley and Sons.
Chaffin DB, Herrin GD, Keyserling WM,Foulke JA [1977]. Preemployment strengthtesting in selecting workers for materialshandling jobs. Cincinnati, OH: U.S.Department of Health, Education, and Welfare,Health Services and Mental HealthAdministration, National Institute for
Occupational Safety and Health, DHEW(NIOSH) Publication No. 77–163. Chatterjee D [1992]. Workplace upper limbdisorders: a prospective study with inter-vention. J Occup Med 42(3):129–136.
Chatterjee DS, Barwick DD, Petrie A [1982].Exploratory electromyography in the study ofvibration-induced white finger in rock drillers.Br J Ind Med 39:89–97.
Chiang H, Chen S, Yu H, Ko Y [1990]. Theoccurrence of carpal tunnel syndrome in frozenfood factory employees. Kao Hsiung J MedSci 6:73–80.
Chiang H, Ko Y, Chen S, Yu H, Wu T, ChangP [1993]. Prevalence of shoulder and upper-limb disorders among workers in the fish-processing industry. Scand J Work EnvironHealth 19(2):126–131.
Christensen H, Pedersen MB, Sjøgaard G[1995]. A national cross-sectional study in theDanish wood and furniture industry on workingpostures and manual materials handling.Ergonomics 38(4):793–805.
Clemmer DI, Mohr DL, Mercer DJ [1991].Low-back injuries in a heavy industry: I.Worker and workplace factors. Spine16(7):824–830.
Cohen S, Pyrrell DAJ, Smith AP [1991].Psychological stress and susceptibility to thecommon cold. New Engl J Med 325(9):606–612.
Cornfield J [1956]. A statistical problem arisingfrom retrospective studies. Pro-ceedings of the
R-8
third Berkely Symposium, pp. 135–148.
Cornfield J, Haenszel W, Hammond EC,Lilienfeld AM, Shimkin MB, Wynder EL[1959]. Smoking and lung cancer: recentevidence and a discussion of some questions. JNatl Cancer Inst 22:173–203.
Cust G, Pearson JCG, Mair A [1972]. Theprevalence of low back pain in nurses. Int NursRev 19(2):169–179.
CWCI [1993]. Report on CTDs. SanFrancisco, CA: California Workers’Compensation Institute.
Cyriax JH [1936]. The pathology and treatmentof tennis elbow. J Bone Joint Surg Am18(4):921–940.
Damkot DK, Pope MH, Lord J, Frymoyer JW[1984]. The relationship between work history,work environment and low-back pain in men.Spine 9(4):395–399.
Dammeskiold-Samsøe B, Christiansen E, LundB, Andersen RB [1982]. Regional muscletension and pain (“fibrositis”). Scand J RehabilMed 15:17–20.
Dehlin O, Berg S [1977]. Back symptoms andpsychological perception of work: a studyamong nursing aides in a geriatric hospital.Scand J Rehabil Med 9:61–65.
Dehlin O, Hedenrud B, Horal J [1976]. Backsymptoms in nursing aides in a geriatrichospital. Scand J Rehabil Med 8(2):47.
Dehlin O, Berg S, Hedenrud B, Anderson G,Grimby G [1978]. Muscle training, psycho-
logical perception of work and low backsymptoms in nursing aides. Scand J RehabilMed 10(4):201–209.
Dehlin O, Berg S, Andersson GBJ, Grimby G[1981]. Effect of physical training andergonomic counseling on psychologicalperception of work and on the subjectiveassessment of low-back insufficiency. Scand JRehabil Med 13:1–9.
deKrom MCT, Kester ADM, Knipschild PG,Spaans F [1990]. Risk factors for carpal tunnelsyndrome. Am J Epidemiol132(6):1102–1110.
Deyo RA, Bass JE [1989]. Lifestyle and lowback pain: the influence of smoking and obesity.Spine 14(5):501–506.
Dieck GS, Kelsey JL [1985]. An epidemio-logic study of the carpal tunnel syndrome in anadult female population. Prev Med14(1):63–69.
Dimberg L [1987]. The prevalence andcausation of tennis elbow (lateral humeralepicondylitis) in a population of workers in anengineering industry. Ergonomics30(3):573–580.
Dimberg L, Oden A [1991]. White fingersymptoms: a cross-sectional study. Aviat SpaceEnviron Med 62:879–883
Dimberg L, Olafsson A, Stefansson E, AagaardH, Oden A, Andersson GBJ, et al. [1989]. Thecorrelation between work environment and theoccurrence of cervicobrachial symptoms. JOccup Med 31(5): 447–453.
R-9
Dixon SJ [1973]. Progress and problems inback pain research. Rheumatol Rehabil 12:165.
Dupuis H [1994]. Medical and occupationalpreconditions for vibration-induced spinaldisorders: occupational disease No. 2110 inGermany. Int Arch Occup Environ Health66:303–308.
Earman WA, Andersson GB, Leavitt F,McNeill TW, Durudogan H, Reagan J [1996].Factors influencing the cost of chronic lowback injuries: an analysis of data fromindependent medical examinations.J Occup Rehabil 6(1):5–16.
Ekberg K, Björkqvist B, Malm P, Bjerre-KielyB, Karlsson M, Axelson O [1994]. Case-control study of risk factors for disease in theneck and shoulder area. Occup Environ Med51(4):262–266.
Ekberg K, Karlsson M, Axelson O [1995].Cross-sectional study of risk factors for symp-toms in the neck and shoulder area.Ergonomics 38(5):971–980.
Eklund J, Odenrick P, Zettergren S, JohanssonH [1994]. Head posture measure-ments amongwork vehicle drivers and implications for workand workplace design. Ergonomics37(4):623–639.
English CJ, Maclaren WM, Court-Brown C,Hughes SPF, Porter RW, Wallace WA[1995]. Relations between upper limb softtissue disorders and repetitive movements atwork. Am J Ind Med 27(1):75–90.
Falck B, Aarnio P [1983]. Left-sided carpal
tunnel syndrome in butchers. Scand J WorkEnviron Health 9(3):291–297.
Färkkilä M, Aatola S, Starck J, Korhonen O,Pyykkö I [1986]. Hand-grip force in lumber-jacks: two-year follow-up. Int Arch OccupEnviron Health 58:203–208.
Färkkilä M, Pykkö I, Jäntti V, Aatola S,Starck J, Korhonen O [1988]. Forestryworkers exposed to vibration: a neurologicalstudy. Br J Ind Med 45:188–192.
Feldman RG, Travers PH, Chirico-Post J,Keyserling WM [1987]. Risk assessment inelectronic assembly workers: carpal tunnelsyndrome. J Hand Surg [Am] 12A(5):849–855.
Ferguson D [1976]. Posture, aching and bodybuild in telephonists. J Hum Ergol 5:183–196.
Feyer A, Williamson A, Mandryk J, de Silva I,Healy S [1992]. Role of psychosocial riskfactors in work-related low back pain. Scand JWork Environ Health 18(6):368–375.
Finkelstein MM [1995]. Back pain andparenthood. Occup Environ Med 52(1):51–53.
Fishbein M, Middlestadt S, Ottati V,Straus S, Ellis A [1988]. Medical problemsamong ICSOM musicians: overview of anational survey. Med Prob Perform Art1:136–139.
Flodmark BT, Aase G [1992]. Musculo-skel-etal symptoms and type A behaviour in bluecollar workers. Br J Ind Med 49(10):683–687.
R-10
Frank JW, Pulcins IR, Kerr MS, Shannon HS,Stansfield SA [1995]. Occupational backpain—an unhelpful polemic. Scand J WorkEnviron Health 58:203–208.
Franklin GM, Haug J, Heyer N, CheckowayH, Peck N [1991]. Occupational carpal tunnelsyndrome in Washington State, 1984–1988.Am J Public Health 81(6): 741–746.
Fransson-Hall C, Byström S, Kilbom Å[1995]. Self-reported physical exposure andmusculoskeletal symptoms of the forearm-handamong automobile assembly-line workers. JOccup Environ Med 37(9): 1136–1144.
Frymoyer JW, Pope MH, Costanza MC,Rosen JC, Goggin JE, Wilder DG [1980].Epidemiologic studies of low-back pain. Spine5(5):419–423.
Frymoyer JW, Pope MH, Clements JH[1983]. Risk factors in low back pain.J Bone Joint Surg [Am] 65A:213.
Frymoyer JW, Cats-Baril WL [1991]. Anoverview of the incidence and costs of lowback pain. Orthop Clin North Am 22:262–271.
Futatsuka M, Uneno T [1985]. Vibrationexposure and vibration induced white fingerdue to chain saw operation. J Occup Med27:257–264.
Futatsuka M, Uneno T [1986]. A follow-upstudy of vibration-induced white finger due tochain saw operation. Scand J Work EnvironHealth 12(4):304–306.
Garg A, Moore SJ [1992]. Epidemiology of
low-back pain in industry. Occup Med: Stateof the Art Rev 7(4):593–608.
Gelberman RH, Herginroeder PT, HargensAR, Lundborg GN, Akeson WH [1981]. Thecarpal tunnel syndrome: a study of carpal canalpressures. J Bone Joint Surg 63A(3): 380–383.
Gemne G [1982]. Pathophysiology andmultifactorial etiology of acquired vaso-spasticdisease (Raynaud Syndrome) in vibrationexposed workers. Scand J Work EnvironHealth 8:243–249.
Gemne G, Lundström R, Hansson J [1993].Disorders induced by work with hand-heldvibrating tools: a review of current knowledgefor criteria documentation. Arbete och Hälsa6:1–83.
Gerr F, Letz R [1992]. Risk factors for carpaltunnel syndrome in industry: blaming the victim?[Letter to the editor.] J Occup Med34(11):1117–1119.
Gerr F, Letz R, Landrigan PJ [1991]. Upper-extremity musculoskeletal disorders ofoccupational origin. Ann Rev Public Health12:543–566.
Graham NM, Douglas RM, Ryan P [1986].Stress and acute respiratory infection. Am JEpidemiol 124(3):389–401.
Grandjean E, Hunting W, Nishiyama K [1984].Preferred VDT workstation settings, bodyposture and physical impairments. ApplErgonomics 15(2):99–104.
Guo HR, Tanaka S, Cameron LL, SeligmanPJ, Behrens VJ, Ger J, et al. [1995]. Back pain
R-11
among workers in the United States: nationalestimates and workers at high risk. Am J IndMed 28(5):591–602.
Hadler NM [1993]. Occupational musculo-skeletal disorders. New York, NY: RavenPress.
Hadler N [1997]. Repetitive upper-extremitymotions in the workplace are not hazardous. JHand Surg [Am] 22A(1):19–29.
Hagberg M [1981]. Work load and fatigue inrepetitive arm elevations. Ergonomics24:543–555.
Hagberg M [1984]. Occupational musculo-skeletal stress and disorders of the neck andshoulder: a review of possible pathophysio-logy. Int Arch Occup Environ Health53:269–278.
Hagberg M, Kvarnström S [1984]. Muscularendurance and electromyographic fatigue inmyofascial shoulder pain. Arch Phys MedRehabil 65:522–525.
Hagberg M, Wegman DH [1987]. Preva-lencerates and odds ratios of shoulder-neck diseasesin different occupational groups. Br J Ind Med44(9):602–610.
Hagberg M, Morgenstern H, Kelsh M [1992].Impact of occupations and job tasks on theprevalence of carpal tunnel syndrome. Scand JWork Environ Health 18(6):337– 345.
Hagberg M, Silverstein B, Wells R,Smith M, Hendrick H, Carayon P [1995].Work-related musculoskeletal disorders(WMSDs): a reference book for prevention.
London, England: Taylor and Francis.
Hägg G, Suurküla J, Kilbom Å [1990].Predictors for work-related shoulder/neckdisorders: a longitudinal study of femaleassembly workers. Arbete och Hälsa 10:1–78.
Hägg GM, Öster J, Byström S [1996].Forearm muscular load and wrist angle amongautomobile assembly line workers in relation tosymptoms. Appl Ergonomics 28(1):41–47.
Hales TR, Fine L [1989]. Hazard evaluationand technical assistance report: Cargill PoultryDivision, Buena Vista, CA. Cincinnati, OH:U.S. Department of Health and HumanServices, Public Health Service, Centers forDisease Control, National Institute forOccupational Safety and Health, NIOSHReport No. HHE 89–251–1997.
Hales TR, Sauter S [1992]. Hazard evalua-tionand technical assistance report: U.S. WestCommunications, Phoenix, AZ; Minneapolis,MN; Denver, CO. Cincinnati, OH: U.S.Department of Health and Human Services,Public Health Service, Centers for DiseaseControl and Prevention, National Institute forOccupational Safety and Health, NIOSHReport No. HHE 89–299–2230.
Hales TR, Habes D, Fine L, Hornung R,Boiano J [1989]. Hazard evaluation and tech-nical assistance report: John Morrell and Co.,Sioux Falls, SD. Cincinnati, OH: U.S.Department of Health and Human Services,Public Health Service, Centers for DiseaseControl, National Institute for OccupationalSafety and Health, NIOSH Report No. HHE88–180–1958.
R-12
Hales TR, Sauter SL, Peterson MR, Fine LJ,Putz-Anderson V, Schleifer LR, et al. [1994].Musculoskeletal disorders among visual displayterminal users in a telecom-municationscompany. Ergonomics 37(10): 1603–1621.
Harms-Ringdahl K, Ekholm J [1986]. Intensityand character of pain and muscular activitylevels elicited by maintained extreme flexionposition of the lower-cervical-upper thoracicspine. Scand J Rehabil Med 18:117–126.
Hart DA, Frank CB, Bray RC [1995].Inflammatory processes in repetitive motionand overuse syndromes: potential role ofneurogenic mechanisms in tendons andligaments. In: Gordon SL, Blair SJ, Fine, LJ,eds. Repetitive motions disorders of the upperextremity. Rosemont, IL: American Academyof Orthopaedic Surgeons, pp. 247–262.
Hartz CR, Linscheid RL, Gramse RR, DaubeJR [1981]. The pronator teres syndrome:compressive neuropathy of the median nerve. JBone Joint Surg 63(6): 885–890.
Heliövaara M [1987]. Occupation and risk ofherniated lumbar intervertebral disc or sciaticaleading to hospitalization. J Chronic Dis40(3):259–264.
Heliövaara M, Knekt P, Aromaa A [1987].Incidence and risk factors of herniated lumbarintervertebral disc or sciatica leading tohospitalization. J Chronic Dis 40:251– 258.
Heliövaara M, Mäkelä M, Knekt P, ImpivaaraO, Aromaa A [1991]. Determi-nants of sciaticaand low back pain. Spine 16(6):608–614.
Helliwell PS, Mumford DB, Smeathers JE,
Wright V [1992]. Work-related upper limbdisorders: the relationship between pain,cumulative load, disability, and psychologicalfactors. Ann Rheum Dis 51(12): 1325–1329.
Herberts P, Kadefors R [1976]. A study ofpainful shoulders in welders. Acta OrthopScand 47:381–387.
Herberts P, Kadefors R, Andersson G,Petersen I [1981]. Shoulder pain in industry: anepidemiological study on welders. Acta OrthopScand 52:299–306.
Herberts P, Kadefors R, Högfors C, SigholmG [1984]. Shoulder pain and heavy manuallabor. Clin Orthop 191:166–178.
Herrin GD, Jaraiedi M, Anderson CK [1986].Prediction of overexertion injuries usingbiomechanical and psychophysical models. AmInd Hyg Assoc J 47(6):322– 330.
Heyer N, Checkoway H, Daniell, et al. [1990].Self-reported musculoskeletal symptomsamong office video display terminal operators.In: Sakurai H, Okazaki I, Omae I, eds.Occupational epidemiology. Amsterdam, TheNetherlands: Elsevier Science Publishers, B.V.,pp. 255–258.
Higgs P, Young VL, Seaton M, Edwards D,Feely C [1992]. Upper extremity impairment inworkers performing repetitive tasks. PlastReconstr Surg 90(4):614–620.
Hildebrandt VH [1987]. A review of epi-demiological research on risk factors of lowback pain. In: Buckle P, ed. Musculoskeletaldisorders at work. Proceedings of a con-ference held at the University of Surrey,Guilford, April, 1987. London, England: Taylorand Francis, pp. 9–16.
R-13
Hildebrandt VH [1995]. Back pain in theworking population: prevalence rates in Dutchtrades and professions. Ergonomics38(6):1283–1298.
Hildebrandt VH, Bongers PM, Dul J, van DijkFJH, Kemper HCG [1996]. Identifica-tion ofhigh-risk groups among maintenance workersin a steel company with respect tomusculoskeletal symptoms and workload. Ergonomics 39(2):232–242.
Hill AB [1965]. The environment and disease:association or causation. Proc Royal Soc Med58:295–300.
Hill AB [1966]. Principles of medical statistics.8th ed. London, England: Lancet.
Hill AB [1971]. Principles of medical statistics.9th ed. New York, NY: Oxford UniversityPress.
Hoekstra EJ, Hurrell JJ, Swanson NG [1994].Hazard evaluation and technical assistancereport: Social Security Admin-istrationTeleservice Centers, Boston, MA; FortLauderdale, FL. Cincinnati, OH: U.S.Department of Health and Human Services,Public Health Service, Centers for DiseaseControl and Prevention, National Institute forOccupational Safety and Health, NIOSHReport No. 92–0382–2450.
Holmström E [1992]. Musculoskeletaldisorders in construction workers. Lund,Sweden: Lund University, Department ofPhysical Therapy, pp. 1–175.
Holmström E, Moritz U [1991]. Low backpain correspondence between questionnaire
interview and clinical examination. Scand JRehabil Med 23:119–125.
Holmström EB, Lindell J, Moritz U [1992].Low back and neck/shoulder pain inconstruction workers: occupational work-loadand psychosocial risk factors. Spine17(6):663–671.
Holmström E, Lindell J, Moritz U [1993].Healthy lower backs in the constructionindustry in Sweden. Work and Stress7(3):259–271.
Hopkins A [1990]. Stress, the quality of work,and repetition strain injury in Australia. Workand Stress 4(2):129–138.
Horal J [1969]. The clinical appearance of lowback disorders in the city of Gothen-burg,Sweden. Acta Orthop Scand118(Suppl):7–37.
Houtman ILD, Bongers PM, Smulders PGW,Kompier MAJ [1994]. Psychosocial stressorsat work and musculoskeletal problems. Scand JWork Environ Health 20(2):139–145.
Hrubec Z, Nashold BS [1975]. Epidemio-logyof lumbar disc lesions in the military in WorldWar II. Am J Epidemiol 102(5):366– 376.
Huang J, Ono Y, Shibata E, Takeucki Y,Hisanaga N [1988]. Occupational musculo-skeletal disorders in lunch centre workers.Ergonomics 31(1):65–75.
Hughes RE, Silverstein BA, Evanoff BA[1997]. Risk factors for work-relatedmusculoskeletal disorders in an aluminumsmelter. Am J Ind Med 32:66–75.
R-14
Hulshof C, Veldhuijzen van Zanten B [1987].Whole-body vibration and low-back pain: areview of epidemiologic studies. Int ArchOccup Environ Health 59:205–220.
Hunting KL, Welch LS, Cuccherini BA, SeigerLA [1994]. Musculoskeletal symptoms amongelectricians. Am J Ind Med 25(2):149–163.
Hünting W, Läubli TH, Grandjean E [1981].Postural and visual loads at VDT workplaces.I. Constrained postures. Ergonomics24(12):917–931.
Hurrell JJ, Murphy LR [1992]. Psycho-logicaljob stress. In: Rom WN, ed. Environmental andoccupational medicine. 2nd ed. New York,NY: Little, Brown and Company, pp.675–684.
Hurrell JJ Jr., Murphy LR, Sauter SL, CooperCL [1988]. Occupational stress: issues anddevelopments. New York, NY: Taylor andFrancis.
Ignatius Y, Yee T, Yan L [1993]. Selfreportedmusculoskeletal problems amongst typists andpossible risk factors. J Hum Ergol 22:83–93.
ILO [1986]. Psychosocial factors at work:recognition and control. Geneva, Switzer-land:International Labour Office.
Iwata H, Makimo S [1987]. Prevalence ofRaynaud’s phenomenon in individuals not usingvibrating tools. Sangyo Igaku 29: 500–503.
Jensen RC [1987]. Disabling back injuriesamong nursing personnel: research needs andjustification. Res Nurs Health 10(1): 29–38.
Jensen RC [1988]. Epidemiology of work-related back pain. Top Acute Care TraumaRehabil 2(3):1–15.
Jensen RC [1990]. Back injuries among nursingpersonnel related to exposure. Appl OccupEnviron Hyg 5:38–45.
Johanning E [1991]. Back disorders and healthproblems among subway train operatorsexposed to whole-body vibration. Scand JWork Environ Health 17(6):414– 419.
Johanning E, Wilder DG, Landrigan PJ, PopeMH [1991]. Whole-body vibration exposure insubway cars and review of adverse healtheffects. J Occup Med 33(5):605–612.
Johansson JA [1994]. Work-related and non-work-related musculoskeletal symptoms. ApplErgonomics 25(4):248–251.
Johansson JA, Rubenowitz S [1994]. Riskindicators in the psychosocial and physicalwork environment for work-related neck,shoulder and low back symptoms: a studyamong blue and white collar workers in eightcompanies. Scand J Rehabil Med 26:131–142.
Johnson JV, Stewart W, Hall EM,Fredlund P, Theorell T [1996]. Long-termpsychosocial work environment andcardiovascular mortality among Swedish men.Am J Public Health 86(3):324–331.
Jonsson B [1988]. The static load componentin muscle work. Eur J Appl Physiol57:305–310.
Jonsson BG, Persson J, Kilbom Å [1988].Disorders of the cervicobrachial region among
R-15
female workers in the electronics industry: atwo-year follow-up. Int J Ind Ergo 3(1):1–12.
Kaji H, Honma H, Usui M, Yasuno Y, Saito K[1993]. Hypothenar hammer syndrome inworkers occupationally exposed to vibratingtools. J Hand Surg [Br] 18B(6):761–766.
Kamwendo K, Linton, SJ, Moritz U [1991].Neck and shoulder disorders in medicalsecretaries. Part I. Pain prevalence and riskfactors. Scand J Rehabil Med 23(3):127–33.
Karasek RA, Baker D, Marxer F, Ahlbom A,Theorell T [1981]. Job decision latitude, jobdemands, and cardiovascular disease: aprospective study of Swedish men. Am J PublicHealth 71(7):694–705.
Karasek RA, Gardell B, Lindell J [1987].Work and non-work correlates of illness andbehaviour in male and female Swedish whitecollar workers. J Occup Behav 8(3):187– 207.
Karasek RA, Theorell T, Schwartz JF, SchnallPL, Pieper CF, Michela JL [1988]. Jobcharacteristics in relation to the preva-lence ofmyocardial infarction in the U.S. HealthExamination Survey (HES) and the Health andNutrition Examination Survey (HANES). Am JPublic Health 78(8):910– 918.
Katz JN, Punnett L, Simmons BP, Fossel AH,Mooney N, Keller RB [1996]. Workerscompensation recipients with carpal tunnelsyndrome: the validity of self-reported healthmeasures. Am J Public Health 86(1):52–56.
Kelley JD, Lombardo SJ, Pink M, Perry G,Giangarra CE [1994]. Electromyographic andcinematographic analysis of elbow function in
tennis players with lateral epicondylitis. Am JSports Med 22(3): 359–363.
Kellgren JH, Lawrence JS [1958]. Osteo-arthrosis and disc degeneration in an urbanpopulation. Ann Rheum Dis 17(4):338–397.
Kelsey CA, Mettler FA [1990]. Flexibleprotective gloves: the Emperor's new clothes?Radiology 174(1):275–276.
Kelsey JL [1975a]. An epidemiological studyof acute herniated lumbar inter-vertebral disc.Rheumatol Rehabil 14:144.
Kelsey JL [1975b]. An epidemiological studyof the relationship between occupations andacute herniated lumbar intervertebral discs. IntJ Epidemiol 4(3):197–205.
Kelsey JL, Hardy RJ [1975]. Driving of motorvehicles as a risk factor for acute herniatedlumbar intervertebral disc. Am J Epidemiol102(1):63–73.
Kelsey JL, White AA [1980]. Epidemiologyand impact on low back pain. Spine 5(2):133–142.
Kelsey JL, Golden AL [1988]. Occupationaland workplace factors associated with lowback pain. Occup Med: State of the Art Rev3(1):7–16.
Kelsey JL, Githens PB, White AA, HolfordTR, Walter SD, O’Connor T, et al. [1984]. Anepidemiologic study of lifting and twisting on thejob and risk for acute pro-lapsed lumbarintervertebral disc. J Orthop Res 2(1):61–66.
Kelsey JL, Golden AL, Mundt DJ [1990].
R-16
Low back pain/prolapsed lumbar inter-vertebral disc. Epidemiol Rheum Dis16(3):699–716.
Kennedy JC, Hawkins R, Krissoff WB [1978].Orthopaedic manifestations of swimming. Am JSports Med 6:309–322.
Keyserling WM, Herrin GD, Chaffin DB[1980]. Isometric strength testing as a means ofcontrolling medical incidents on stren-uousjobs. J Occup Med 22(5):332–336.
Kiken S, Stringer W, Fine LJ [1990]. Hazardevaluation and technical assistance report:Perdue Farms, Lewiston, NC; Roberson-ville,NC. Cincinnati, OH: U.S. Department ofHealth and Human Services, Public HealthService, Centers for Disease Control, NationalInstitute for Occupational Safety and Health,NIOSH Report No. HHE 89–307–2009.
Kilbom Å [1994]. Repetitive work of the upperextremity. Int J Ind Ergonomics 14(1/2):51–86.
Kilbom Å, Persson J [1987]. Work techniqueand its consequences for musculo-skeletaldisorders. Ergonomics 30(2): 273–279.
Kilbom Å, Horst D, Kemfert K, Richter A[1986]. Observation methods for reduction ofload and strain on the human body—a review.Abetarskyddsstyrelsen Publikation Service171(84):92.
Kim SH, Chung MK [1995]. Effects ofposture, weight and frequency on trunk muscular activity and fatigue during repetitivelifting tasks. Ergonomics 38(5):853–863.
King JW, Brelsford HJ, Tullos HS [1969].Analysis of the pitching arm of the pro-fessionalbaseball pitcher. Clin Orthop 67:116–123.
Kivekäs J, Riihimäki H, Husman K, HänninenK, Härkönen H, Kuusela T, et al. [1994].Seven-year follow-up of white-finger symptoms and radiographic wrist findingsin lumberjacks and referents. Scand J WorkEnviron Health 20(2):101–106.
Kivi P [1984]. Rheumatic disorders of theupper limbs associated with repetitiveoccupational tasks in Finland, 1975–1979.Scand J Rheumatol 13:101–107.
Klein BP, Jensen RC, Sanderson LM [1984].Assessment of workers’ compen-sation claimsfor back strains/sprains.J Occup Med 26(6):443–448.
Kleinbaum DG, Kupper LL, Morgenstern H[1982]. Epidemiologic research: principles andquantitative methods. London, England:Lifetime Learning Publications.
Knave BG, Wibom RI, Voss M, HedströmLD, Bergqvist UO [1985]. Work with videodisplay terminals among office employees. I.Subjective symptoms and discomfort. Scand JWork Environ Health 11(6):457–466.
Knibbe JJ, Friele RD [1996]. Prevalence ofback pain and characteristics of the physicalworkload of community nurses. Ergonomics39(2):186–198.
Kompier MAJ [1988]. Arbeid en gezondheidvan stadsbus-chauffeurs. Delft Eburon(Proefschrift Rijksuniversitiet Groningen).
Kopf T, Von Feder T, Karmaus W [1988].Risks for musculoskeletal disorders of the lowback, the shoulders, the elbows, and the wristsin bricklayers. In: Hogstedt C, Reuterwall C,
R-17
eds. Progress in occupational epidemiology.Amsterdam: Elsevier Science Publishers B.V.,pp. 219–222.
Koskimies K, Färkkilä M, Pyykkö I, Jäntti V,Aatola S, Starck J, et al. [1990]. Carpal tunnelsyndrome in vibration disease. Br J Ind Med47(6):411–416.
Koskimies K, Pyykkö I, Starck J, Inaba R[1992]. Vibration syndrome among Finnishforest workers between 1972 and 1990. IntArch Occup Environ Health 64:251–256.
Kukkonen R, Luopajärvi T, Riihimäki V[1983]. Prevention of fatigue amongst dataentry operators. In: Kvalseth TO, ed.Ergonomics of workstation design. London,England: Buttersworth, pp. 28–34.
Kumar S [1994]. The back compressive forcesduring maximal push-pull activities in the sagittalplane. J Hum Ergol 23(2):133– 150.
Kuorinka I, Koskinen P [1979]. Occupa-tionalrheumatic diseases and upper limb strain inmanual jobs in a light mechanical industry.Scand J Work Environ Health 5(Suppl3):39–47.
Kuorinka I, Forcier L [1995]. Work-relatedmusculoskeletal disorders (WMSDs):a reference book for prevention. London,England: Taylor & Francis, p. 1.
Kurppa K, Viikari-Juntura E, Kuosma E,Huuskonen M, Kivi P [1991]. Incidence oftenosynovitis or peritendinitis and epicondy-litisin a meat-processing factory. Scand J WorkEnviron Health 17(1):32–37.
Kvarnström S [1983a]. Incidence ofmusculoskeletal disorders in a mechanicalengineering plant, with emphasis on occupat-ional shoulder injuries. Abetarskyddssty-relsenPublikation Service 171(84):79.
Kvarnström S [1983b]. Occurrence ofmusculoskeletal disorders in a manufac-turingindustry with special attention to occupationalshoulder disorders. Scand J Rehabil Med(Suppl 8):1–114.
Kvarnström S, Halden M [1983]. Occupa-tional cervicobrachial disorders in anengineering company. Scand J Rehabil Med8:1–114.
Lapidus PW, Guidotti FP [1970]. Lateral andmedical epicondylitis of the humerus. Ind MedSurg 39(4):30–32; 171–173.
Larsson SE, Bengtsson A, Bodegard L,Henriksson KG, Larsson J [1988]. Musclechanges in work-related chronic myalgia. ActaOrthop Scand 59(5):552–556.
Larsson SE, Bodegard L, Henriksson KG,Öberg PA [1990]. Chronic trapezius myalgia:morphology and blood flow studied in 17patients. Acta Orthop Scand 61(5):394–398.
Lawrence JS [1955]. Rheumatism in coalminers. Part III: Occupational factors. Br J IndMed 12(3):249–261.
Leboeuf-Yde C, Klougart N, Lauritzen T[1996]. How common is low back pain in theNordic population? Spine 21(13):1518– 1526.
Leigh JP, Sheetz RM [1989]. Prevalence of
R-18
back pain among full-time United Statesworkers. Br J Ind Med 46:651–657.
Leigh JP, Markowitz S, Fahs M, et al. [1996].Costs of occupational injuries and illnesses in1992. NIOSH cooperative agreement withERC, Inc., contract no. U60/CCU902886.
Leino P [1989]. Symptoms of stress predictmusculoskeletal disorders. J Epidemiol Com-munity Health 43(3):293–300.
Leino P, Lyyra A [1990]. The effect of mentalstress and social support on the development ofmusculoskeletal morbidity in the engineeringindustry. In: Sakurai H, Okazaki L, Omae I,eds. Occupational epidemiology. Amsterdam,The Nether-lands: Elsevier Science PublishersB.V., pp. 267–272.
Leino P, Aro S, Hasan J [1987]. Trunk musclefunction and low back disorders: a ten-yearfollow-up study. J Chronic Dis 40(4):289–296.
Leino P, Hasan J, Karppi SL [1988].Occupational class, physical workload, andmusculoskeletal morbidity in the engineer-ingindustry. Br J Ind Med 45(10):672–681.
Letz R, Cherniack MG, Gerr F, Hershman D,Pace P [1992]. A cross-sectional epide-miological survey of shipyard workers exposedto hand-arm vibration. Br J Ind Med49(1):53–62.
Levitz CL, Iannotti JP [1995]. Overuse injuriesof the shoulder. In: Gordon SL, Blair SJ, FineLJ, eds. Repetitive motions disorders of theupper extremity. Rosemont, IL: AmericanAcademy of Orthopaedic Surgeon.
Liira JP, Shannon HS, Chambers LW, HainesTA [1996]. Long-term back problems andphysical work exposures in the 1990 OntarioHealth Survey. Am J Public Health86(3):382–387.
Liles DH, Deivanayagam S, Ayoub MM,Mahajan P [1984]. A job severity index for theevaluation and control of lifting injury. HumFactors 26(6):683–693.
Lindman R, Hagberg M, Ängqvist KA,Söderlund K, Hultman E, Thornell L [1991].Changes in muscle morphology in chronictrapezius myalgia. Scand J Work EnvironHealth 17(5):347–355.
Linton SJ [1990]. Risk factors for neck andback pain in a working population in Sweden.Work and Stress 4(1):41–49.
Linton SJ, Kamwendo K [1989]. Risk factorsin the psychosocial work environ-ment for neckand shoulder pain in secre-taries. J Occup Med31(7):609–613.
Liss GM, Jesin E, Kusiak RA, White P [1995].Musculoskeletal problems among Ontariodental hygienists. Am J Ind Med28(4):521–540.
Loslever P, Ranaivosoa A [1993]. Biome-chanical and epidemiological investigation ofcarpal tunnel syndrome at workplaces with highrisk factors. Ergonomics 36(5): 537–555.
Louis, Harris & Associates [1996]. Pain andabsenteeism in the workplace. New York, NY:Louis, Harris & Associates.
Lukaš E [1970]. Lesion of the peripheral
R-19
nervous system due to vibration. Work EnvironHealth 7(1):67–79.
Lundberg U, Granqvist M, Hansson T,Magnusson M, Wallin L [1989]. Psycho-logical and physiological stress responsesduring repetitive work at an assembly line.Work and Stress 3(2):143–153.
Lundborg G, Dahlin LB, Danielsen N, HanssonHA, Necking LE, Pyykkö I [1987]. Intraneuraledema following exposure to vibration. Scand JWork Environ Health 13(4):326–329.
Lundborg G, Dahlin LB, Hansson HA, KanjeM, Necking LR [1990]. Vibration exposureand peripheral nerve fiber damage. J HandSurg [Am] 15A(2):346–351.
Luopajärvi T, Kuorinka I, Virolainen M,Holmberg M [1979]. Prevalence of teno-synovitis and other injuries of the upperextremities in repetitive work. Scand J WorkEnviron Health 5(Suppl 3):48–55.
Maeda K, Hirayama H, Takamatsu M [1977].Occupational cervicobrachial disorders inworkwomen in assembly lines of a cigarettefactory. Jpn J Ind Health 19:8–21.
Maeda K, Horiguchi S, Hosokawa M [1982].History of the studies on occupa-tionalcervicobrachial disorders in Japan andremaining problems. J Human Ergol 11:17–29.
Magnusson M, Hanson T [1994]. The effect ofseat back inclination on spine height changes.Appl Ergonomics 25(5):294–298.
Magnusson ML, Pope MH, Wilder DG,Areskoug B [1996]. Are occupational drivers
at an increased risk for developingmusculoskeletal disorders? Spine 6:710–717.
Magora A [1970]. Investigation of the relationbetween low back pain and occupation. IndMed 39:31–37.
Magora A [1972]. Investigation of the relationbetween low back pain and occupation. III.Physical requirements: sitting, standing, andweight lifting. Ind Med 41(12):5–9.
Magora A [1973]. Investigation of the relationbetween low back pain and occupation. IV.Physical requirements: bending, rotation,reaching, and sudden maximal effort. Scand JRehabil Med 5:191–196.
Magora A, Schwartz A [1978]. Relationbetween the low back pain syndrome andx-ray findings. I. Degenerative osteoarthritis.Scand J Rehabil Med 10:135–145.
Maizlish N, Rudolph L, Dervin K,Sankaranarayan M [1995]. Surveillance andprevention of work-related carpal tunnelsyndrome: an application of the Sentinel EventsNotification System for Occupational Risks.Am J Ind Med 27(5):715–729.
Mäkelä M, Heliövaara M, Sievers K,Impivaara O, Knekt P, Aromaa A [1991].Prevalence, determinants, and consequences ofchronic neck pain in Finland. Am JEpidemiol 134(11):1356–1367.
MaKinnon SE, Novak CB [1997]. Repeti-tivestrain in the workplace. J Hand Surg [Am]22A(1):2–18.
Marcus M, Gerr F [1996]. Upper extremity
R-20
musculoskeletal symptoms among female officeworkers: associations with video displayterminal use and occupational psychosocialstressors. Am J Ind Med 29(2):161–170.
Marley RJ, Fernandez JE [1995]. Psycho-physical frequency and sustained exertion atvarying wrist postures for a drilling task.Ergonomics 38(2):303–325.
Marras WS, Schoenmarklin RW [1991].Quantification of wrist motion in highlyrepetitive, hand-intensive industrial jobs.Washington, DC: U.S. Department of Healthand Human Services, Public Health Service,Centers for Disease Control, National Institutefor Occupational Safety and Health.
Marras W, Schoenmarklin RW [1993]. Wristmotions in industry. Ergonomics36(4):341–351.
Marras WS, Lavender SA, Leurgans SE,Rajulu SL, Allread WG, Fathallah FA, et al.[1993]. The role of dynamic three-dimen-sionaltrunk motion in occupationally-related low back disorders: the effects of work-place factors, trunk position, and trunk motioncharacteristics on risk of injury. Spine18(5):617–628.
Marras WS, Lavender SA, Leurgans SE,Fathallah FA, Ferguson SA, Allread WG, et al.[1995]. Biomechanical risk factors foroccupationally-related low back disorders.Ergonomics 38(2):377–410.
Martin DK, Dain SJ [1988]. Posturalmodifications of VDU operators wearingbifocal spectacles. Appl Ergonomics19(4):293–300.
Masset D, Malchaire J [1994]. Low back pain:epidemiologic aspects and work-related factors in the steel industry. Spine19(2):143–146.
Matheson LN, Brophy RG, Vaughan KD,Nunez C, Saccoman KA [1995]. Workers’compensation managed care: preliminaryfindings. J Occup Rehabil 5(1):27–36.
Mathiowetz V, Kashman N, Volland G,Weber K, Dowe M, Rogers S [1985]. Gripand pinch strength: normative data for adults.Arch Phys Med Rehabil 66(2):69–72.
Matthews KA, Cottington EM, Talbott E,Kuller LH, Siegel JM [1987]. Stressful workconditions and diastolic blood pressure amongblue collar factory workers. Am J Epidemiol126(2):280–290.
Mayer TG, Gatchel RJ, Kishino N, Keeley J,Capra P, Mayer H, et al. [1985]. Objectiveassessment of spinal function followingindustrial injury: a prospective study with com-parison group and one-year follow-up. Spine10(6):482–493.
McCormack RR Jr., Inman RD, Wells A,Berntsen C, Imbus HR [1990]. Prevalence oftendinitis and related disorders of the upperextremity in a manufacturing workforce. JRheumatol 17:958–964.
McKenna K, McGrann S, Blann A, Allen J[1993]. An investigation into the acute vasculareffects of riveting. Br J Ind Med 50:160–166.
McNeil T, Warwick D, Andersson G, SchultzA [1980]. Trunk strengths in attempted flexion,extension, and lateral bending in healthy
R-21
subjects and patients with low back disorders.Spine 5(6):529–538.
Merriam WP, Burwell RG, Mulholland RC,Pearson JCG, Webb JK [1980]. A studyrevealing a tall pelvis in subjects with low backpain. J Bone Joint Surg [Br] 65B:153–156.
Milerad E, Ekenvall L [1990]. Symptoms ofthe neck and upper extremities in dentists.Scand J Work Environ Health 16(1): 129–134.
Mintz G, Fraga A [1973]. Severe osteo-arthritis of the elbow in foundry workers. ArchEnviron Health 27:78–80.
Mirbod SM, Inaba R, Iwata H [1992a]. Astudy on the vibration-dose limit for Japaneseworkers exposed to hand-arm vibration. IndHealth 30:1–22.
Mirbod SM, Yoshida H, Nagata C, Inaba R,Komura Y, Iwata H [1992b]. Hand-armvibration syndrome and its prevalence in thepresent status of private forestry enterprises inJapan. Int Arch Occup Environ Health64:93–99.
Mirbod SM, Yoshida H, Komura Y,Fujita S, Nagata C, Miyashita K, et al. [1994].Prevalence of Raynaud’s phenome-non indifferent groups of workers operating hand-held vibrating tools. Int Arch Occup EnvironHealth 66:13–22.
Miyashita K, Morioka I, Iwata H, Takeda S[1992]. Symptoms of construction workersexposed to whole-body vibration and localvibration. Int Arch Occup Environ Health64:347–351.
Moon SD, Sauter SL [1996]. Beyondbiomechanics: psychosocial aspects ofmusculoskeletal disorders in office work.London, England: Taylor and Francis.
Moore JS [1992]. Carpal tunnel syndrome.Occup Med: State of the Art Rev 7(4):741–763.
Moore JS, Garg A [1991]. Determination ofthe operational characteristics of ergonomicexposure assessments for prediction ofdisorders of the upper extremities and back. In:Proceedings of the 11th Congress of theInternational Ergonomics Association. London,England: Taylor & Francis, pp. 144–146.
Moore JS, Garg A [1994]. A comparison ofdifferent approaches for ergonomic jobevaluation for predicting risk of upper extremitydisorders. IEA 94. Occup Health Saf 2.
Morgenstern H, Kelsh M, Kraus J, MargolisW [1991]. A cross-sectional study ofhand/wrist symptoms in female grocery check-ers. Am J Ind Med 20(2):209–218.
Morris HH, Peters BH [1976]. Pronatorsyndrome: clinical and electrophysiologicalfeatures in seven cases. J Neurol NeurosurgPsychiatry 39:461–464.
Mostardi RA, Noe DA, Kovacik MW,Porterfield JA [1992]. Isokinetic lifting strengthand occupational injury: a prospective study.Spine 17(2):189–193.
Musson Y, Burdorf A, van Drimmelen D[1989]. Exposure to shock and vibration andsymptoms in workers using impact power tools.Ann Occup Hyg 33(1):85–96.
R-22
Nachemson A, Lindh M [1969]. Measure-ment of abdominal and back muscle strengthwith and without low back pain. Scand JRehabil Med 1:60–65.
Nachemson A, Elfstrom G [1970]. Intravitaldynamic pressure measurements in lumbardiscs. Scand J Rehabil Med 1(Suppl):1–40.
Nagata C, Yoshida H, Mirbod S, Komura Y,Fujita S, Inaba R, et al. [1993]. Cutaneoussigns (Raynaud’s phenomenon, sclerodacty-lia,and edema of the hands) and hand-armvibration exposure. Int Arch Occup EnvironHealth 64:587–591.
Nathan PA, Meadows KD, Doyle LS [1988].Occupation as a risk factor for impairedsensory conduction of the median nerve at thecarpal tunnel. J Hand Surg [Br] 13B(2):167–170.
Nathan PA, Keniston RC, Myers LD,Meadows KD [1992a]. Longitudinal study ofmedian nerve sensory conduction in industry:relationship to age, gender, hand dominance,occupational hand use, and clinical diagnosis. JHand Surg [Am] 17A(5):850–857.
Nathan PA, Keniston RC, Myers LD,Meadows KD [1992b]. Obesity as a riskfactor for slowing of sensory conduction of themedian nerve in industry: a cross-sectional andlongitudinal study involving 429 workers. JOccup Med 34(4):379–383.
Nathan PA, Keniston RC, Meadows KD,Lockwood RS [1993]. Validation ofoccupational hand use categories. J OccupMed 35(10):1034–1042.
Nathan PA, Keniston RC, Meadows KD,Lockwood RS [1994a]. The relationshipbetween body mass index and the diagnosis ofcarpal tunnel syndrome [letter to the editor].Muscle Nerve, December 1994,pp. 1491–1492.
Nathan PA, Takigawa K, Keniston RC,Meadows KD, Lockwood RS [1994b].Slowing of sensory conduction of the mediannerve and carpal tunnel syndrome in Japaneseand American industrial workers. J Hand Surg[Am] 19B(1):30–34.
Necking LE, Dahlin LB, Fridin J,Lundborg G, Lundström R, Thornell LE[1992]. Vibration-induced muscle injury: anexperimental model and preliminary findings. JHand Surg [Br] 17B:270–274.
Nicholas JA [1990]. Clinical observations onsports-induced soft-tissue injuries in sports-induced inflammation. In: Leadbetter WB,Buckwalter JA, Gordon SL, eds. Rosemont,IL: American Academy of OrthopedicSurgeons, p. 143.
Nilsson T, Burström L, Hagberg M [1989].Risk assessment of vibration exposure andwhite fingers among platers. Int Arch OccupEnviron Health 61(7):473–481.
Nilsson T, Hagberg M, Burström L [1990].Prevalence and odds ratio of numbness andcarpal tunnel syndrome in different exposurecategories of platers. In: Okada A, DupuisWTH, eds. Hand-arm vibration. Kanazawa,Japan: Kyoei Press Co., pp. 235–239.
Nilsson T, Hagberg M, Burström L, Kihlberg S[1994]. Impaired nerve conduction in the
R-23
carpal tunnel of platers and truck assemblersexposed to hand-arm vibration. Scand J WorkEnviron Health 20:189–199.
Nilsson T, Hagberg M, Burström L, LundströmR [1995]. A five-year follow-up study of nerveconduction across the carpal tunnel amongworkers at a heavy engineer-ing productionplant. In: International Conference on thePrevention of Musculo-skeletal Disorders(PREMUS). Montreal, Canada: InternationalCommittee on Occupational Safety and Health,pp.81–83.
NIOSH [1989]. NIOSH criteria for arecommended standard: occupational exposureto hand-arm vibration. Cincinnati, OH: U.S.Department of Health and Human Services,Public Health Service, Centers for DiseaseControl, National Institute for OccupationalSafety and Health, DHHS (NIOSH)Publication No. 89–106.
NIOSH [1991]. Epidemiological basis formanual lifting guidelines. In: Scientific supportdocumentation for the revised 1991 NIOSHlifting equation: technical contract reports.Springfield, VA: National Technical InformationService (NTIS), NTIS No. PB–91–226274.
NIOSH [1996]. National occupationalresearch agenda. Cincinnati, OH: U.S.Department of Health and Human Services,Public Health Service, Centers for DiseaseControl and Prevention, National Institute forOccupational Safety and Health, DHHS(NIOSH) Publication No. 96–115.
Nirschl RP [1973]. Tennis elbow. Orthop ClinNorth Am 4(3):787–800.
Nirschl RP [1975]. The etiology and treatmentof tennis elbow. J Sports Med 2(6):308–319.
Nirschl R [1993]. Muscle and tendon trauma:tennis elbow. In: Morrey B, ed. The elbow andits disorders. 2nd ed. Philadel-phia, PA: W.B.Saunders Company, pp. 552–573.
Nordgren B, Schek R, Linrotn K [1980].Evaluation and prediction of back pain duringmilitary field service. Scand J Rehabil Med12(1):1–8.
Ohara H, Nakagiri S, Itani T, Wake K,Aoyama H [1976]. Occupational healthhazards resulting from elevated work ratesituations. J Hum Ergol 5(2):173–182.
Ohlsson K, Attewell R, Skerfving S [1989].Self-reported symptoms in the neck and upperlimbs of female assembly workers. Scand JWork Environ Health 15(1):75–80.
Ohlsson K, Hansson GA, Balogh I, StrömbergU, Pålsson B, Nordander C, et al. [1994].Disorders of the neck and upper limbs inwomen in the fish processing industry. OccupEnviron Med 51:826–832.
Ohlsson K, Attewell R, Paisson B,Karlsson B, Balogh I, Johnsson B, et al.[1995]. Repetitive industrial work and neckand upper limb disorders in females. Am J IndMed 27(5):731–747.
Olafsdottir H, Rafnsson V [1995]. New tech-niques increases the prevalences ofmusculoskeletal symptoms from upper limbsamong women in fish fillet plants. In: SecondInternational Scientific Conference onPrevention of Work-Related Musculoskeletal
R-24
Disorders. Montreal, Canada, pp. 248–249.
Ollivierre CO, Nirschl RP, Pettrone FA[1995]. Resection and repair for medical tenniselbow: a prospective analysis. Am J SportsMed 23(2):214–221.
Onishi N, Namura H, Sakai K, Yamamoto T,Hirayama K, Itani T [1976]. Shoulder muscletenderness and physical features of femaleindustrial workers. J Hum Ergol 5(2):87–102.
Osorio AM, Ames RG, Jones J, Castorina J,Rempel D, Estrin W, et al. [1994]. Carpaltunnel syndrome among grocery store workers.Am J Ind Med 25(2):229–245.
Owen B, Damron C [1984]. Personalcharacteristics and back injury among hospitalnursing personnel. Res Nurs Health 7:305–313.
Parker KG, Imbus HR [1992]. Cumulativetrauma disorders. Current issues andergonomic solutions: a system approach.Chelsea, MI: Lewis Publishers.
Partridge REH, Duthie JJR [1968]. Rheu-matism in dockers and civil servants: acomparison of heavy manual and sedentaryworkers. Ann Rheum Dis 27:559–568.
Payne R [1988]. Individual differences in thestudy of occupational stress. In: Cooper CL,Payne R, eds. Causes, coping, andconsequences of stress at work. Chichester,England: John Wiley & Sons, pp. 209–232.
Pecina M, Krmpotic-Nemanic J, Markiewitz A[1991]. Tunnel syndromes. Boston, MA: CRCPress.
Pietri-Taleb F, Riihimaki H, Viikari-Juntura E,Lindström K, Moneta GB [1995]. The role ofpsychological distress and personal-ity in theincidence of sciatic pain among working men.Am J Public Health 85:541– 545.
Pope MH, Rosen JC, Wilder DG, FrymoyerJW [1980]. The relation between biome-chanical and psychological factors in patientswith low back pain. Spine 5(2): 173–178.
Pope MH, Frymoyer JW, Andersson GBJ, etal. [1984]. Occupational low back pain. NewYork, NY: Praeger.
Pope MH, Andersson GBJ, Frymoyer JW, etal. [1991]. Occupational low back pain:assessment, treatment, and prevention. St.Louis, MO: Mosby-Year Book, pp. 105–108.
Porter RW [1987]. Does hard work preventdisc protrusion? Clin Biomechanics 2(4):196–198.
Pot F, Padmos P, Brouwers A [1987].Determinants of the VDU operator’s well-being. In: Knave B, Wideback PG, eds. Workwith display units 86. Selected papers from theInternational Scientific Conference on Workwith Display Units, Stockholm, Sweden, May12–15, 1986. Amsterdam: Elsevier SciencePublishers B.V., pp. 16–25.
Priest JD, Braden V, Gerberich SG [1980].The elbow and tennis, part 1: an analysis ofplayers with and without pain. Physician SportsMed 8:81–91.
Priest JD, Hones HH, Tichenor CJ, Nagel DA[1977]. Arm and elbow changes in experttennis players. Minn Med 60:399– 404.
R-25
Punnett L, Robins JM, Wegman DH,Keyserling WM [1985]. Soft-tissue disordersin the upper limbs of female assembly workers:impact of length of employment, work pace,and selection. Scand J Work Environ Health11(6): 417–425.
Punnett L, Fine LJ, Keyserling WM, HerrinGD, Chaffin DB [1991]. Back disorders andnonneutral trunk postures of automobileassembly workers. Scand J Work EnvironHealth 17(5):337–346.
Pyykkö I, Starak J [1986]. Pathophysiologicand hygienic aspects of hand-arm vibration.Scand J Work Environ Health 12(4):237– 241.
Queinnec Y, Daniellou F, eds. [1991].Shoulder symptoms and headache in lightsedentary work. In: Designing for everyone.Proceedings of the 11th Congress of theInternational Ergonomics Association, Paris,France, July 15–20, 1991. London, England:Taylor and Francis, pp. 129–131.
Radecki P [1995]. Variability in the medianand ulnar nerve latencies: implications fordiagnosing entrapment. J Occup Med 37:1293–1299.
Radwin RG, VanBergeijk E, Armstrong TJ[1989]. Muscle response to pneumatic handtool torque reaction forces. Ergonomics32(6):655–673.
Ranney D, Wells R, Moore A [1995]. Upperlimb musculoskeletal disorders in highlyrepetitive industries: precise anatomical physicalfindings. Ergonomics 38(7):1408– 1423.
Rathburn JB Macnab I [1970]. The micro-
vascular pattern of the rotator cuff. J Bone JointSurg [Br] 52B(3):540–553.
Rempel D [1995]. Musculoskeletal loading andcarpal tunnel pressure. In: Gordon SL, Blair SJ,Fine LJ, eds. Repetitive motions disorders ofthe upper extremity. Rosemont IL: AmericanAcademy of Orthopaedic Surgeons, pp.123–133.
Rempel D, Harrison R, Barnhart S [1992].Work-related cumulative trauma disorders ofthe upper extremity. JAMA 267(6): 838–841.
Rempel D, Dennerlein J, Mote CD, ArmstrongT [1994a]. A method of mea-suring fingertiploading during keyboard use. J Biomechanics27(8):1101–1104.
Rempel D, Manojlovic R, Levinsohn DG,Bloom T, Gordon L [1994b]. The effect ofwearing a flexible wrist splint on carpal tunnelpressure during repetitive hand activity. J HandSurg [Am] 19A(1):106–110.
Riihimäki H [1991]. Low-back pain, its originand risk indicators. Scand J Work EnvironHealth 17(2):81–90.
Riihimäki H [1995]. Hands up or back towork—future challenges in epidemiologicresearch on musculoskeletal diseases. Scand JWork Environ Health 21(6):401–403.
Riihimäki H, Tola S, Videman T, Hänninen K[1989a]. Low-back pain and occupation: across-sectional questionnaire study of men inmachine operating, dynamic physical work, andsedentary work. Spine 14:204–209.
R-26
Riihimäki H, Wickström G, Hänninen K,Luopajärvi T [1989b]. Predictors of sciaticpain among concrete reinforcement workersand house painters: a five-year follow-up.Scand J Work Environ Health 15(6):415– 423.
Riihimäki H, Wickström G, Hänninen K,Mattson T, Waris P, Zitting AG [1989c].Radiographically detectable lumbardegenerative changes as risk indicators of backpain. Scand J Work Environ Health15:280–285. Riihimäki H, Viikari-Juntura E, Moneta G,Kuha J, Videman T, Tola S [1994]. Incidenceof sciatic pain among men in machine operating,dynamic physical work and sedentary work.Spine 19(2):138–142.
Ringel SP, Treihaft M, Carry M, Fisher R,Jacobs P [1990]. Suprascapular neuropathy inpitchers. Am J Sports Med 18(1):80–86.
Ritz BR [1995]. Humeral epicondylitis amonggas- and waterworks employees. Scand JWork Environ Health 21:478–486.
Rodgers SH, The Ergonomics Group, Healthand Environment Laboratories, EastmanKodak Co. [1986]. Ergonomic design forpeople at work. Vol. II: The design of jobs,including work patterns, hours of work, manualmaterials handling tasks, methods to evaluatejob demands, and the physiological basis ofwork. New York, NY: Van Nostrand ReinholdCo., Inc.
Rose L, Ericson M, Glimskar B, Nordgren B,Ortengren R [1992]. Ergo-index: a model todetermine pause needs after fatigue and painreactions during work. In: Kumar S, ed.
Advances in industrial ergonomics and safety,IV, Proceedings of the Annual InternationalIndustrial Ergonomics and Safety Conference,Denver, CO, June 10–14, 1992. London,England: Taylor and Francis, pp. 303–310.
Rossignol AM, Morse EP, Summers VM,Pagnotto LD [1987]. Video display terminaluse and reported health symptoms amongMassachusetts clerical workers. J Occup Med29(2):112–118.
Rothfleisch SD, Sherman S [1978]. Carpaltunnel syndrome: biomechanical aspects ofoccupational occurrence and implicationsregarding surgical management. Orthop Rev7(6):107–109. Rothman KJ, ed. [ 1986]. Modern epidemio-logy. Boston, MA: Little, Brown, and Com-pany.
Roto P, Kivi P [1984]. Prevalence of epicon-dylitis and tenosynovitis among meatcutters.Scand J Work Environ Health 10(3):203– 205.
Rowe ML [1965]. Disc surgery and chroniclow back pain. J Occup Med 7(5):196–202.
Rowe ML [1985]. Backache at work. Fair-port, NY: Perington Press.
Ruberman W [1992]. Psychosocial influenceson mortality of patients with coronary heartdisease. JAMA 267(4): 559–560.
Ruberman W, Weinblatt E, Goldberg JD,Chaudhary BS [1984]. Psychosocialinfluences on mortality after myocardialinfarction. N Engl J Med 311(9):552–559.
R-27
Ryan GA, Bampton M [1988]. Comparison ofdata process operators with and without upperlimb symptoms. Community Health Stud12(1):63–68.
Ryan GA, Hage B, Bampton M [1987].Postural factors, work organization andmusculoskeletal disorders. In: Buckle P, ed.Musculoskeletal disorders at work.Proceedings of a conference held at theUniversity of Surrey, Guilford, April, 1987.London, England: Taylor and Francis,pp. 251–253.
Ryden LA, Molgaard CA, Bobbitt S,Conway J [1989]. Occupational low-backinjury in a hospital employee population: anepidemiologic analysis of multiple risk factors ofa high-risk occupational group. Spine14:315–320.
Sairanen E, Brüshaber L, Kaskinen M [1981].Felling work, low back pain and osteoarthritis.Scand J Work Environ Health 7(1):18–30.
Saito K [1987]. Prevention of the hand-armvibration syndrome. Scand J Work EnvironHealth 13:301–304.
Sakakibara H, Masaru M, Kondo T, YamadaS [1987]. Relation between overhead workand complaints of pear and apple orchardworkers. Ergonomics 30(5):805–815.
Sakakibara H, Miyao M, Kondo T, Yamada S[1995]. Overhead work and shoulder-neckpain in orchard farmers harvesting pears andapples. Ergonomics 38(4):700–706.
Sauter SL [1984]. Predictors of strain in VDTusers and traditional office workers. In:
Grandjean E, ed. Ergonomics and health inmodern offices. London, England: Taylor andFrancis, pp. 129–135.
Sauter SL, Swanson NG [1996]. Psycho-logical aspects of musculoskeletal disorders inoffice work. In: Moon S, Sauter S, eds.Psychosocial factors and musculoskeletaldisorders. London, England: Taylor andFrancis.
Sauter SL, Gottlieb MS, Jones KC, DodsonVN, Rohrer KM [1983]. Job and healthimplications of VDT use: initial results of theWisconsin-NIOSH study. Commun of theACM 26(4):284–294. Schibye B, Skov T, Ekner D, Christiansen J,Sjøgaard G [1995]. Musculoskeletal symptomsamong sewing machine operators. Scand JWork Environ Health 21:427–434.
Schierhout GH, Meyers JE, Bridger RS[1995]. Work-related musculoskeletaldisorders and ergonomic stressors in the SouthAfrican workforce. Occup Environ Med52(1):46–50.
Schlesselman J [1978]. Assessing the effects ofconfounding variables. Am J Epidemiol108:3–8.
Schlesselman J [1982]. Monographs inepidemiology and biostatistics. Case-controlstudies: design, conduct, analysis. New York,NY: Oxford University Press.
Schnall PL, Pieper C, Schwartz JE, KarasekRA, Schlussel Y, Devereux RB, et al. [1990].The relationship between job strain, workplacediastolic blood pressure, and left ventricular
R-28
mass: results of a case-control study. JAMA263(14):1929–1935.
Schnall PL, Schwartz JE, Landsbergis PA,Warren K, Pickering TG [1992]. Therelationship between job strain, alcohol, andambulatory blood pressure. Hypertension19:488–494.
Schnall PL, Landsbergis PA, Baker D [1994].Job strain and cardiovascular disease. Ann RevPublic Health 15:381–411.
Schottland JR, Kirschberg GJ, Fillingim R,Davis VP, Hogg F [1991]. Median nervelatencies in poultry processing workers: anapproach to resolving the role of industrial"cumulative trauma" in the development ofcarpal tunnel syndrome. J Occup Med33(5):627–631.
Scott V, Gijsbers K [1981]. Pain perception incompetitive swimmers. Br Med J 283: 91–93.
Seidel H, Heide R [1986]. Long-term effects ofwhole-body vibration: a critical survey of theliterature. Int Arch Occup Environ Health58:1–26.
Shinev V, Komleva L, Zhuravlev A, DruzhininV [1992]. Study of the physical characteristicsof percussive vibration of hand-held machinesand its effect on the body. Noise and VibrationBulletin, pp. 138–140.
Silverstein BA [1985]. The prevalence ofupper extremity cumulative trauma disorders inindustry [Dissertation]. Ann Arbor, MI: TheUniversity of Michigan.
Silverstein BA, Fine LJ, Armstrong TJ [1986].
Hand wrist cumulative trauma disorders inindustry. Br J Ind Med 43(11):779–784.
Silverstein BA, Fine LJ, Armstrong TJ [1987].Occupational factors and the carpal tunnelsyndrome. Am J Ind Med 11(3):343– 358.
Silverstein B, Grossman E, Kalat J, Nelson N [in press]. Upper limb and low backmusculoskeletal disorders: State and nationalestimates based on workers' compensationaccepted claims. Proceedings for managingergonomics in the 90's. Alexandria, VA: Centerfor Office Technology and the AmericanAutomobile Manufacturer's Association.
Sinclair A [1964]. Tennis elbow in industry. BrJ Ind Med 22:144–148.
Sjøgaard G [1988]. Intramuscular changesduring long-term contraction. In: Corlett N,Wilson J, Manenica I, eds. The ergonomics ofworking postures: models, methods and cases.Proceedings of the First InternationalOccupational Ergonomics Symposium, Zadar,Yugoslavia, April 18–20, 1985, London,England: Taylor and Francis, pp. 136–143.
Sjøgaard G, Savard G, Juel C [1988]. Muscleblood flow during isometric activity and itsrelation to muscle fatigue. Eur J Appl Physiol57:327–335.
Skie M, Zeiss J, Ebraheim NA, Jackson WT[1990]. Carpal tunnel changes and mediannerve compression during wrist flexion andextension seen by magnetic resonance imaging.J Hand Surg [Am] 15A(6):939.
Skov T, Borg V, Orhede E [1996]. Psycho-social and physical risk factors for musculo-
R-29
skeletal disorders of the neck, shoulders, andlower back in salespeople. Occup EnvironMed 53:351–356.
Skovron ML, Mulvihill MN, Sterling RC,Nordin M, Tougas G, Gallagher M, et al.[1987]. Work organization and low back painin nursing personnel. Ergonomics30(2):359–366.
Skovron ML, Szpalski M, Nordin M,Melot C, Cukier D [1994]. Socioculturalfactors and back pain: a population-basedstudy in Belgian adults. Spine 19(2):129– 137.
Slocum D [1960]. Overuse syndromes of thelower leg and foot in athletes. AAOSInstructional Course Lectures, pp. 359–367.
Smith MJ, Stammerjohn LW, Cohen BGF,Lalich NR [1977]. Job stress in video displayoperations. In: Grandjean E, Vigliani E, eds.Ergonomic aspects of video display terminals.London, England: Taylor and Francis, pp.201–210.
Snook SH [1978]. The design of manualhandling tasks. Ergonomics 21(12):963– 985.
Snook SH [1982]. Low back pain in industry.In: White AA, Gordon SL, eds. AmericanAcademy of Orthopaedic Surgeons Sym-posium on Idiopathic Low Back Pain. St.Louis, MO: C.O. Mosby Company,pp. 23–38.
Snook SH [1987]. Approaches to preplace-ment testing and selection of workers.Ergonomics 30(2):241–247.
Snook SH, Webster BS [1987]. The cost of
disability. Clin Orthop 221:77–84.
Snook SH, Ciriello VM [1991]. The design ofmanual handling tasks: revised tables ofmaximum acceptable weights and forces.Ergonomics 34(9):1197–1213.
Snook SH, Campanelli RA, Hart JW [1978].A study of three preventive approaches to lowback injury. J Occup Med 20(7):478– 487.
Sokal RR, Rohlf FJ [1981]. Biometry: theprinciples and practice of statistics in biologicalresearch. 2nd ed. San Francisco, CA: WHFreeman and Co.
Sommerich CM, McGlothin JD, Marras WS[1993]. Occupational risk factors associatedwith soft tissue disorders of the shoulder: areview of recent investigations in the literature.Ergonomics 36(6):697–717.
Spengler DM, Bigos S, Martin NA, Zeh J,Fisher L, Nachemson A [1986]. Back injuriesin industry: a retrospective study. I. Overviewand cost analysis. Spine 11: 241–245.
Starck J, Jussi P, Ilmari P [1990]. Physicalcharacteristics of vibration in relation tovibration-induced white finger. Am Ind HygAssoc J 51(4):179–184.
Stenlund B [1993]. Shoulder tendinitis andosteoarthritis of the acromioclavicular joint andtheir relation to sports. Br J Sports Med27:125–128.
Stenlund B, Goldie I Hagberg M, Hogstedt C,Marions O [1992]. Radiographic osteo-arthrosis in the acromioclavicular joint resultingfrom manual work or exposure to vibration. Br
R-30
J Ind Med 49:588–593.
Stenlund B, Goldie I, Hagberg M, Hogstedt C[1993]. Shoulder tendinitis and its relation toheavy manual work and exposure to vibration.Scand J Work Environ Health 19: 43–49.
Stetson DS, Keyserling WM, Silverstein BA,Leonard JA [1991]. Observational analysis ofthe hand and wrist: a pilot study. Appl OccupEnviron Hyg 6(11):927–937.
Stetson DS, Silverstein BA, Keyserling WM,Wolfe RA, Albers JW [1993]. Median sensorydistal amplitude and latency: comparisonsbetween nonexposed managerial/professionalemployees, and industrial workers. Am J IndMed 24:175–189.
Stevens JC, Sun MD, Beard CM, O’FallonWM, Kurland LT [1988]. Carpal tunnelsyndrome in Rochester, Minnesota, 1961 to1980. Neurology 38:134–138.
Stevens PH, Chase DO, Brownlie AW [1966].Industrial design of a narrow aisle sit-down lifttruck. Hum Factors 8:317–325.
Stock SR [1991]. Workplace ergonomicfactors and the development of musculo-skeletal disorders of the neck and upper limbs:a meta-analysis. Am J Ind Med 19(1):87–107.
Stubbs DA [1986]. Back pain and itsrelationship to manual handling. In: Morrison D,Hartley L, Kemp D, eds. Trends in theergonomics of work. Proceed-ings of the 23rdAnnual Conference of the Ergonomics Societyof Australia, pp. 118–128.
Susser M [1991]. What is a cause and how dowe know one?: a grammar for pragmaticepidemiology. Am J Epidemiol 133(7):635–
648.
Svensson H [1982]. Low back pain in 40- to47-year-old men: II. Socioeconomic factorsand previous sickness absence. Scand J Re-habil Med 14:55–60.
Svensson H, Andersson GBJ [1983]. Low-back pain in 40- to 47-year old men: workhistory and work environment factors. Spine8:272–276.
Svensson H, Andersson GBJ [1989]. Therelationship of low-back pain, work history andwork environment, and stress: a retrospectivecross-sectional study of 38- to 64-year oldwomen. Spine 14(5):517–522.
Sweeney MH, Petersen M, O’Neill V [1994].Hazard evaluation and technical assistancereport: Registry of Interpreters for the Deaf,Ohio Chapter. Cincinnati, OH: U.S.Department of Health and Human Services,Public Health Service, Centers for DiseaseControl and Prevention, National Institute forOccupational Safety and Health, NIOSHReport No. HHE 92–0268–2477.
Szabo RM, Chidgey LK [1989]. Stress carpaltunnel pressures in patients with carpal tunnelsyndrome and normal patients. J Hand Surgery[Am] 14A(4):624–627.
Takala E, Viikari-Juntura E [1991]. Muscleforce endurance and neck-shoulder symp-tomsof sedentary workers: an experimental study onbank cashiers with and without symptoms.Amsterdam, The Netherlands: Elsevier SciencePublishers. B.V., pp. 123–132.
Takala EP, Viikari-Juntara E, Moneta G,
R-31
Saarenmaa K, Kaivanto K [1991]. Predic-torsfor the natural course of neck–shouldersymptoms and headache in light sedentarywork. In: Queinnec Y, Daniellou F, eds.Designing for everyone. Proceedings of the11th Congress of the International Ergono-micsAssociation, Paris, France, July 15–20, 1991.London, England: Taylor and Francis, pp.129–131.
Takeuchi T, Futatsuka M, Imanishi H, YamadaS [1986]. Pathological changes observed in thefinger biopsy of patients with vibration-inducedwhite finger. Scand J Work Environ Health12:280–283.
Tanaka S, Wild DK, Seligman PJ, HalperinWE, Behrens VJ, Putz-Anderson V [1995].Prevalence of work-related carpal tunnelsyndrome among U.S. workers: analysis of theoccupational health supplement data of 1988National Health Interview Survey. Am J IndMed 27(4):451–470.
Tanaka S, Wild DK, Cameron L, Freund E [inpress]. Association of occupational andnon-occupational risk factors with theprevalence of self-reported carpal tunnelsyndrome in a national survey of the workingpopulation. Am J Ind Med.
Tanii K, Kogi K, Sadoyama T [1972].Spontaneous alteration of the working arm instatic overhead work. J Hum Ergol 1:143–155.
Tauber J [1970]. An unorthodox look atbackaches. J Occup Med 12(4):128–130.
Taylor W [1982]. Vibration white finger in theworkplace. J Soc Occup Med 32:159–166.
Theorell T, Harms-Ringdahl K, Ahlberg-Hultén G, Westin B [1991]. Psychosocial job
factors and symptoms from the locomotorsystem: a multicausal analysis. Scand J RehabilMed 23(3):165–173.
Theorell T, Ahlberg-Hulten G, Jodko M, SigalaF, de la Torre B [1993]. Influence of job strainand emotion on blood pressure levels in femalehospital personnel during work hours. Scand JWork Environ Health 19(5):313–318.
Tola S, Riihimäki H, Videman T, Viikari-Juntura E, Hänninen K [1988]. Neck andshoulder symptoms among men in machineoperating, dynamic physical work andsedentary work. Scand J Work Environ Health14(5):299–305.
Toomingas A, Hagberg M, Jorulf L, Nilsson T,Burström L, Kihlberg S [1991]. Outcome ofthe abduction external rotation test amongmanual and office workers. Am J Ind Med19(2):215–227.
Toomingas A, Theorell T, Michélsen H, et al.[1992]. Associations between preceivedpsychosocial job factors and prevalence ofmusculoskeletal disorders in the neck andshoulder regions. In: Hagberg M, Kilbom Å,eds. International Scientific Conference onPrevention of Work-Related Musculo-skeletalDisorders PREMUS, Sweden, May 12–14,1992. Arbete och Hälsa 17:289.
Toroptsova NV, Benevolenskaya LI, KaryakinAN, Sergeev IL, Erdesz S [1995].Cross-sectional study of low back pain amongworkers at an industrial enterprise in Russia.Spine 20(3):328–332.
Torrell G, Sanden A, Järvholm B [1988].Musculoskeletal disorders in shipyard workers.
R-32
J Soc Occup Med 38(4):109–112.
Troup JDG [1978]. Driver’s back pain and itsprevention—a review of the postural, vibratory,and muscular factors, together with the problemof transmitted road shock. Appl Ergonomics9(4):207–214.
Troup JDG, Martin JW, Lloyd DC [1981].Back pain in industry: a prospective survey.Spine 6(1):61–69.
Troup JDG, Foreman TK, Baxter CE, BrownD [1987]. Musculoskeletal disorders at work,tests of manual working capacity and theprediction of low back pain. In: Buckle P, ed.Musculoskeletal disorders at work. London,England: Taylor and Francis, pp. 165–170.
Uhl JE, Wilkinson WE, Wilkinson CS [1987].Aching backs? A glimpse into the hazards ofnursing. AAOHN J 35(1):13–17.
Ulin SS, Armstrong TJ, Snook SH, KeyserlingWM [1993]. Perceived exertion anddiscomfort associated with driving screws atvarious work locations and at different workfrequencies. Ergonomics 36(7):833–846.
Undeutsch K, Gärtner KH, Luopajärvi T,Küpper R, Karvonen MJ, Löwenthal I, et al.[1982]. Back complaints and findings intransport workers performing physically heavywork. Scand J Work Environ Health 8(Suppl1):92–96.
Ursin H, Endresen IM, Ursin G [1988].Psychological factors and self-reports of musclepain. Eur J Appl Physiol 57(3):282–290.
Veiersted KG, Westgaard RH [1992]. Work-
related risk factors for trapezius myalgia. In:Hagberg M, Kolbom Å, eds. InternationalScientific Conference on Prevention of Work-Related Musculoskeletal Disorders PREMUS,Sweden, May 12–14, 1992. Arbete och Hälsa17:307–309.
Veiersted KG, Westgaard RH [1994].Subjectively assessed occupational andindividual parameters as risk factors fortrapezius myalgia. Int J Ind Ergo13(3):235–245.
Veiersted KB, Westgaard RH, Andersen P[1993]. Electromyographic evaluation ofmuscular work pattern as a predictor oftrapezius myalgia. Scand J Work EnvironHealth 19:284–290.
Vessey MP, Villard-Mackintosh L, Yeates D[1990]. Epidemiology of carpal tunnelsyndrome in women of childbearing age.Findings in a large cohort study. Int J Epidemiol 19(3):655–659.
Videman T, Nurminen T, Tola S, Kuorinka I,Vanharanta H, Troup JDG [1984]. Low-backpain in nurses and some loading factors ofwork. Spine 9(4):400–404.
Videman T, Rauhala H, Asp S, Lindstrom K,Cedercreutz G, Kamppi M, et al. [1989]. Patient-handling skill, back injuries, and backpain: an intervention study in nursing. Spine14(2):148–156.
Videman T, Nurminen M, Troup JDG [1990].Lumbar spine pathology in cadaveric material inrelation to history of back pain, occupation, andphysical loading. Spine 15(8):728–740.
Vihma T, Nurminen M, Mutanen P [1982].Sewing machine operators’ work and
R-33
musculoskeletal complaints. Ergonomics25(4):295–298.
Viikari-Juntura E [1995]. The role of physicalstressors in the development of hand/wrist, andelbow disorders. In: Gordon SL, Blair SJ,Armstrong, et al., eds. Pathophysiology andclinical factors in upper extremity repetitivemotion syndromes. Bethesda, MD: AmericanAcademy of Orthopedic Surgeons.
Viikari-Juntura EJ, Vuori J, Silverstein B,Kalimo R, Kuosma E, Videman T [1991a]. Alife-long prospective study on the role ofpsychosocial factors in neck-shoulder and lowback pain. Spine 16:1056–1061.
Viikari-Juntura E, Kurppa K, Kuosma E,Huuskonen M, Kuorinka I, Ketola R, et al.[1991b]. Prevalence of epicondylitis and elbowpain in the meat-processing industry. Scand JWork Environ Health 17(1):38–45.
Viikari-Juntura E, Riihimäki H, Tola S,Videman T, Mutanen P [1994]. Neck troublein machine operating, dynamic physical workand sedentary work: a prospective study onoccupational and individual risk factors. J ClinEpidemiol 47(12):1411– 1422.
Virokannas H [1995]. Dose-response relationbetween exposure to two types of hand-armvibration and sensorineural per-ception ofvibration. Occup Environ Med 52:332–336.
Virokannas H, Tolonen U [1995]. Responsesof workers exposed to vibration in autono-micnervous function tests. Int Arch Occup EnvironHealth 67(3):201–205.
Waersted M, Bjorklund R, Westgaard RH
[1986]. Generation of muscle tension related toa demand of continuing attention. In: Knave B,Wideback PG, eds. Work with display units.Amsterdam, The Netherlands: Elsevier SciencePublishers, B.V. North-Holland, pp. 288–293.
Walsh K, Varnes N, Osmond C, Styles R,Coggin D [1989]. Occupational causes of lowback pain. Scand J Work Environ Health15(1):54–59.
Waris P, Kuorinka I, Kurppa K, Luopajärvi T,Virolainen M, Pesonen K, et al. [1979].Epidemiologic screening of occupational neckand upper limb disorders: methods and criteria.Scand J Work Environ Health 5(Suppl3):25–38.
Washington State Department of Labor andIndustries [1996]. Work-related musculo-skeletal disorders. Washington State summary1992–1994. Olympia, WA: Washington StateDepartment of Labor and Industries,Consultation and Compliance ServicesDivision.
Waters TR, Putz-Anderson V, Garg A, Fine LJ[1993]. Revised NIOSH equation for thedesign and evaluation of manual lifting tasks.Ergonomics 36:749–776.
Webster BS, Snook SH [1994a]. The cost ofcompensable upper extremity cumulativetrauma disorders. J Occup Med 36(7):713–727.Webster BS, Snook SH [1994b]. The cost of1989 workers’ compensation low back painclaims. Spine 19(10):1111–1116.
Weiss ND, Gordon L, Bloom T, So Y, RempelDM [1995]. Position of the wrist associatedwith the lowest carpal-tunnel pressure:implications for splint design.
R-34
J Bone Joint Surg 77A (11):1695–1699.
Welch LS, Hunting KL, Kellogg J [1995].Work-related musculoskeletal symptomsamong sheet metal workers. Am J Ind Med27(6):783–791.
Wells JA, Zipp JF, Schuette PT, McEleney J[1983]. Musculoskeletal disorders amongletter carriers. J Occup Med 25(11):814– 820.
Werner RA, Franzblau A, Albers JW, BucheleH, Armstrong TJ [1997]. Use of screeningnerve conduction studies for predicting futurecarpal tunnel syndrome. Occup Environ Med54:96–100.
Werner RA, Franzblau A, Johnston E [1994a].Quantitative vibrometry and electro-physiological assessment in screening for carpaltunnel syndrome among industrial workers: acomparison. Arch Phys MedRehabil 75:1228–1232.
Werner S, Albers JW, Franzblau A, ArmstrongTJ [1994b]. The relationship between bodymass index and the diagnosis of carpal tunnelsyndrome. Muscle Nerve December:1492.
Westerling D, Jonsson BG [1980]. Pain fromthe neck-shoulder region and sick leave. ScandJ Soc Med 8(3):131–136.
Westgaard R, Aaras A [1985]. The effect ofimproved workplace design on the develop-ment of work-related musculoskeletaldisorders. Appl Ergonomics 16(2):91–97.
Westgaard R, Bjorklund R [1987]. Genera-tion of muscle tension additional to postural
muscle load. Ergonomics 30(7):911–923.
White AA, Gordon SL [1982]. Synopsis:workshop on idiopathic low back pain. Spine7(2):141–149.
WHO [1985]. Identification and control ofwork-related diseases. Geneva, Switzerland:World Health Organization. WHO TechnicalReport Series 714.
WHO [1989]. Work with visual displayterminals: psychosocial aspects and health. JOccup Med 31(12):957–968.
Wickström BO, Kjellberg A, Landström U[1994]. Health effects of long-term occupa-tional exposure to whole-body vibration: areview. Int J Ind Ergonomics 14:273–292.
Wieslander G, Norbäck D, Göthe CJ, Juhlin L [1989]. Carpal tunnel syndrome (CTS)and exposure to vibration, repetitive wristmovements, and heavy manual work:a case-referent study. Br J Ind Med 46(1):43–47.
Wiktorin C, Karlqvist L, Winkel J [1993].Validity of self-reported exposures to workpostures and manual materials handling. ScandJ Work Environ Health 19:208–214.
Wilder DG, Pope MH [1996]. Epidemio-logical and aetiological aspects of low backpain in vibration environments—an update. ClinBiomechanics 11:61–73.
Wilson RN, Wilson S [1957]. Tenosynovi-tis inindustry. Practitioner 178:612–615.Winkel J, Westgaard R [1992]. Occupationaland individual risk factors for shoulder-neck
R-35
complaints. Part II: the scientific basis (literaturereview) for the guide. Int J Ind Ergonomics10:85–104.
Winkel J, Westgaard R [1992]. Occupationaland individual risk factors for shoulder-neckcomplaints. Part II. The scientific basis(literature review) for the guide. Int J IndErgonomics 10:85–104.
Winn FJ, Habes DJ [1990]. Carpal tunnel areaas risk factor for carpal tunnel syndrome.Muscle Nerve 13:254–258.
Wisseman C, Badger D [1976]. Hazardevaluation and technical assistance report:
Eastman Kodak, Windsor, Colorado.Cincinnati, OH: U.S. Department of Health,Education, and Welfare, Public Health Service,Center for Disease Control, National Institutefor Occupational Safety and Health, DHEW(NIOSH) Report No. TA 76–0131.
Yu ITS, Wong TW [1996]. Musculoskeletalproblems among VDU workers in a HongKong bank. Occup Med 46(4):275–280.
Zwerling C, Ryan J, Schootman M [1993]. Acase-control study of risk factors for industriallow back injury: the utility of preplacementscreening in defining high-risk groups. Spine18(9):242–247.
A-1
APPENDIX A Epidemiologic Review
Various investigators have used different occupational epidemiologic methods to identify the patterns ofwork-related MSD occurrence in different working groups, as well as the factors that influence thesedisease patterns. The following section briefly summarizes these study designs and then addresses themost common biases (such as misclassification or selection) that can affect the results of these studies.
TYPES OF EPIDEMIOLOGIC STUDY DESIGNS REVIEWED
The NIOSH reviewers have first addressed studies that use a prospective approach. Prospectivecohort studies, identify groups of subjects (exposed and nonexposed) and observe them over a periodof time to compare the number of new work-related MSD cases in the two groups. All subjects areinitially disease-free. The rate (or risk) of new cases (the incidence) is calculated for both groups, andthe ratio of these two incidences (the relative risk or rate ratio, RR) can be used to assess theassociation of the exposure with the occurrence of the MSD. A RR greater than 1.0 implies that theincidence of cases was higher in the exposed group than in the nonexposed group and that anassociation has been observed between the exposure and the disease. A confidence interval (CI) isderived, which is an estimated range of values within which the true RR is likely to fall. The CI reflectsthe precision of the effect observed in the study. Ordinarily, if the CI includes 1.0, the associationbetween the exposure and the MSD could be due to chance alone and the elevated odds ratio (OR) isnot considered statistically significant.
The cohort study ensures that the exposure to work-related factors occurs before the observation ofthe MSD, thereby allowing a causal interpretation of the observed association. Cohort studies are oftendone prospectively; they follow a group of current workers forward in time. The length of time requiredfor a prospective study depends on the problem studied. With adverse health conditions that occur as aresult of long-term exposure to some factor in the workplace, many years may be needed. Extendedtime periods make prospective studies costly. Arguing causation is more difficult with extended timeperiods because other events may affect outcome. Prospective studies that require long periods of timeare especially vulnerable to problems associated with worker follow-up, particularly worker attrition(workers discontinue participation in the study) and worker migration (diseased workers move to otheremployment before investigators ascertain their disease).
A-2
The second type of epidemiologic study evaluated for this document is the case-control study, whichis retrospective and examines differences in exposures among workers with (cases) and without(controls) MSDs. In such studies, cases should be all incident (new) cases in a given population over adefined period or a representative sample of the cases. Controls should be a representative sample ofnon-cases from the same population. The ratio of the odds of exposed cases to the odds of exposedcontrols is called the OR. An OR above 1.0 indicates an association between the exposure and thework-related MSD, and a 95% CI indicates the probable range of the true OR. Case control studiesare useful for evaluating rarely occurring conditions or small numbers of cases. One limitation of casecontrol studies is the difficulty of obtaining accurate information about past exposures. In occupationalstudies of MSDs, a further limitation of case-control studies is the difficulty of identifying cases who arerepresentative of all cases that occurred in a defined period (many of these workers will have left theworkforce). Another problem with case-control studies is the selection of an inappropriate controlgroup.
Third, the reviewers considered cross-sectional studies. Cross-sectional studies provide a “snapshotin time” of a disease process; that is, they measure both health outcomes and exposures at a single pointin time. These studies usually identify occupations with differing levels of exposure and compare theprevalences of MSDs in each group. Cross-sectional studies are most useful for identifying risk factorsof a relatively frequent disease with a long duration that is often undiagnosed or unreported [Kleinbaumet al. 1982]. Typically, cross-sectional studies do not provide the evidence of the correct temporalrelationship between exposure and disease inherent in prospective studies, but they nevertheless can bevaluable. Some cross-sectional studies discussed here had inclusion criteria such as working at aspecific job for a defined period of time before onset of symptoms. This condition adds a dimension oftemporality to the studies. A common problem with cross-sectional studies that use surveys is obtainingsufficiently large response rates; many people who are asked to participate decline because they arebusy, not interested, etc. The conclusions are therefore based on a subset of workers who agree toparticipate, and these workers may not be representative of or similar to the entire population ofworkers. Furthermore, cross-sectional studies are often confined to current workers who may not berepresentative of true prevalence rates if workers with disease have left the workforce. (The problem ofrepresentativeness is not confined to cross-sectional studies and may occur in the other study designsmentioned whenever subjects are selected, decline, or drop out.) Either ORs or prevalence ratios(PRs) (proportion of diseased in exposed divided by the proportion of diseased in unexposed) may beused to report results in cross-sectional studies.
The last type of observational study used is the case-series study, in which certain characteristics of agroup (or series) of cases (or patients) are described. The simplest design is a set of case reports forwhich the author describes some interesting or intriguing observations that occurred in a small numberof patients. Cases included in case series have usually been drawn from a single patient population,whose makeup may have influenced the observations noted because of selection bias. Case-seriesstudies frequently lead to a generation of hypotheses that are subsequently investigated in a cross-sectional, case-control, or prospective study. Because case-series do not involve comparison groups
A-3
(who do not have the condition or exposure to the risk factors being studied), some investigators wouldnot consider them epidemiologic studies because they are generally not planned studies and do notinvolve any research hypotheses.
BIASES AND OTHER ISSUES IN EPIDEMIOLOGIC STUDIESIn interpreting the validity of epidemiologic studies to provide evidence for work-relatedness of MSDs,several assumptions and sources of bias must be considered when analyzing the findings from suchstudies.
1. Selection bias (internal validity). In occupational health studies, at least two types of selection biasmay occur: (a) a selection of “healthy workers” in the work population studied, and (b) an exclusionof “sick” workers who leave the active workforce. Both of these biases tend to cause anunderestimate of the true relationship between a workplace risk factor and an observed healtheffect because the workers who are in better health tend to be those in the workforce and availablefor study.
A basic assumption underlying the analysis of these studies is that the selected cases of work-related MSDs in the specific studies are representative of all workers at that worksite with work-related MSDs. In a single study, representativeness generally increases with increasing populationsize and participation rate. A parallel assumption is that the nondiseased groups are representativeof the entire nondiseased population. The fact that some cases leave the workforce causes thedisease prevalence among currently employed workers to be underestimated. However, if casesare missing from the current workforce in equal proportion for both nonexposed and exposedworkers, the underestimate of prevalence will not affect the internal validity of the study.
2. Generalizability (external validity). Some studies are based on a single population, occupation, orrestricted data base (individual insurance companies, specific industrial settings) and, therefore, thesample may not be representative of the general population. Another assumption is that MSD casesin one study are comparable to cases in another study. This assumption needs particular scrutiny inwork-related MSD studies because no standardized case definitions may exist for the particularillnesses.
3. Misclassification bias. Misclassification bias may be introduced during selection of cases anddetermination of their exposure. Erroneous diagnoses may result in work-related MSD casesmisclassified as noncases, and similarly, noncases may be misclassified as cases. The calculated RRor OR would usually underestimate the true association because of a dilutional effect if bothexposed and nonexposed cases are equally misclassified. Similarly, misclassification can occurwhen determining the exposure factor of interest. Again, such misclassification will create a biastowards finding no association if equal misclassification is assumed for cases and noncases.
A-4
4. Confounding and effect modification. Other factors may explain the supposed relationship betweenwork and disease. Confounding is a situation in which the relationship (in this case with MSDs)appears stronger or weaker than it truly is as a result of something (the confounder) beingassociated with both the outcome and the apparent causal factor. In other words, the risk estimateis distorted because symptoms of exposed and nonexposed workers differ because of some otherfactors that cause disease. For example, diabetes might result in abnormal nerve conduction testing,a sign of CTS. If a higher proportion of exposed workers than nonexposed workers were diabetic,diabetes would act as a positive confounder, causing an apparent exposure-disease association.
An effect modifier is a factor that alters the effect of exposure on disease. For example, it ispossible that repetitive motion causes tendinitis only in older workers; in this case, age would be aneffect modifier. Although effect modification is not a bias per se, if an investigator has failed toanalyze old and young workers separately, the investigator might have missed a true work/diseaseassociation.
5. Sample size, precision, and CIs. The CI around an estimated measure of effect (such as a RR) is anestimated range of values in which the true effect is likely to fall. It reflects the precision of the effectobserved in the study. Large studies generally have smaller CIs and can estimate effects moreprecisely. In studies that are “statistically significant” the CI excludes the null value for no effect (forexample, a RR of 1.0). Small studies are generally less precise, lead to wider CIs, and less likely tobe “statistically significant” even if the exposed have a greater prevalence of disease than thenonexposed.
B-1
APPENDIX B Individual Factors Associated with Work-
Related Musculoskeletal Disorders (MSDs)
Although the purpose of this document is to examine the weight of evidence for the contribution ofwork factors to MSDs, the multifactorial nature of MSDs requires a discussion of individual factors thathave been studied to determine their association with the incidence and prevalence of work-relatedMSDs. These factors include age [Guo et al. 1995; Biering-Sorensen 1983; English et al. 1995;Ohlsson et al. 1994]; gender [Hales et al. 1994; Johansson 1994; Chiang et al. 1993; Armstrong et al.1987a]; anthropometry [Werner et al. 1994b; Nathan et al. 1993, Heliövaara 1987]; and cigarettesmoking [Finkelstein 1995; Owen and Damron 1984; Svensson and Andersson 1983; Kelsey et al.1990; Hildebrandt 1987], among others. Nonoccupational physical activities, such as nonoccupationalVDT use, hobbies, second jobs, and household activities that might increase risk for MSDs aredescribed in the detailed tables for those studies in which they were analyzed as risk factors.
A worker's ability to respond to external work factors may be modified by his/her own capacity, suchas tissue resistance to deformation when exposed to high force demands. The level, duration, andfrequency of the loads imposed on tissues, as well as adequacy of recovery time, are criticalcomponents in whether increased tolerance (a training or conditioning effect) occurs, or whetherreduced capacity occurs which can lead to MSDs. The capacity to perform work varies with genderand age, among workers, and for any worker over time. The relationship of these factors and theresulting risk of injury to the worker is complex and not fully understood.
Certain epidemiologic studies have used statistical methods to take into account the effects of theseindividual factors (e.g., gender, age, body mass index), that is, to control for their confounding ormodifying effects when looking at the strength of work-related factors. Studies that fail to control for theinfluence of individual factors may either mask or amplify the effects of work-related factors. Thecomments column of the detailed tables notes whether studies have adjusted for potential confounders.
A number of factors can influence a person's response to risk factors for MSDs in the workplace andelsewhere. Among these are the following:
AGE
B-2
The prevalence of MSDs increases as people enter their working years. By the age of 35, most peoplehave had their first episode of back pain [Guo et al. 1995; Chaffin 1979]. Once in their working years(ages 25 to 65), however, the prevalence is relatively consistent [Guo et al. 1995; Biering-Sorensen1983]. Musculoskeletal impairments are among the most prevalent and symptomatic health problems ofmiddle and old age [Buckwalter et al. 1993]. Nonetheless, age groups with the highest rates ofcompensable back pain and strains are the 20–24 age group for men, and 30–34 age group forwomen. In addition to decreases in musculoskeletal function due to the development of age-relateddegenerative disorders, loss of tissue strength with age may increase the probability or severity of softtissue damage from a given insult.
Another problem is that advancing age and increasing number of years on the job are usually highlycorrelated. Age is a true confounder with years of employment, so that these factors must be adjustedfor when determining relationship to work. Many of the epidemiologic studies that looked atpopulations with a wide age variance have controlled for age by statistical methods. Several studiesfound age to be an important factor associated with MSDs [Guo et al. 1995; Biering-Sorensen 1983;English et al. 1995; Ohlsson et al. 1994; Riihimäki et al. 1989a; Toomingas et al. 1991] others have not[Herberts et al. 1981; Punnett et al. 1985]. Although older workers have been found to have lessstrength than younger workers, Mathiowetz et al. [1985] demonstrated that hand strength did notdecline with aging; average hand pinch and grip scores remained relatively stable in their population witha range of 29 to 59 years. Torell et al. [1988] found no correlation between age and the prevalence ofMSDs in a population of shipyard workers. They found a strong relationship between workload(categorized as low, medium, or heavy) and symptoms or diagnosis of MSDs.
Other studies have also reported a lack of increased risk associated with aging. For example, Wilsonand Wilson [1957] reported that the age and gender distribution of 88 patients with tenosynovitis froman ironworks closely corresponded to that of the general population of that plant. Similarly, Wissemanand Badger [1976] reported that the median age of workers with chronic hand and wrist injuries in theirstudy was 23 years, while the median age of the unaffected workers was 24 years. Riihimäki et al.[1989a] found a significant relationship between sciatica and age in machine operators, carpenters, andsedentary workers. Age was also a strong risk factor for neck and shoulder symptoms in carpenters,machine operators and sedentary workers [Riihimäki et al. 1989a]. Some authors may have incorrectlyattributed age as the sole cause of their findings in their analysis, when data presented suggested arelationship with work [Schottland et al. 1991].
An explanation for the lack of an observed relationship between an increased risk for MSDs and agingmay be “survivor bias” (this is different from the “healthy worker effect”). If workers who have healthproblems leave their jobs, or change jobs to one with less exposure, the remaining population includesonly those workers whose health has not been adversely affected by their jobs. As an example, in astudy of female plastics assembly workers, Ohlsson et al. [1989] reported that the degree of increase inthe odds of neck and shoulder pain with the duration of employment depended on the age of theworker. For the younger subjects, the odds increased significantly as the duration of employment
B-3
increased (p=0.01), but for the older ones no statistical change was found with length of employment.The older women who had been employed for shorter periods of time had more reported symptomsthan the younger ones, while older workers with longer employment times reported fewer symptomsthan younger workers. Ohlsson et al. [1989] interviewed 76 former assembly workers and found that26% reported pain as the cause of leaving work. This finding supports the likely role of a survivor biasin this study, the effect of which is to underestimate the true risk of developing MSDS, in this case in theolder workers.
GENDER Some studies have found a higher prevalence of some MSDs in women [Bernard et al. 1994; Hales etal. 1994; Johansson 1994; Chiang et al. 1993]. A male to female ratio of 1:3 was described for carpaltunnel syndrome (CTS) in a population study in which occupation was not evaluated [Stevens et al.1988]. However, in the Silverstein [1985] study of CTS among industrial workers, no genderdifference could be seen after controlling for work exposure. Franklin et al. [1991] found no genderdifference in workers compensation claims for CTS. Burt et al. [1990] found no gender difference inreporting of neck or upper extremity MSD symptoms among newspaper employees using video displayterminals (VDTs). Nathan et al. [1988, 1992a] found no gender differences for CTS. In contrast,Hagberg and Wegman [1987] reported that neck and shoulder muscular pain is more common amongfemales than males, both in the general population and among industrial workers. Whether the genderdifference seen with some MSDs in some studies is due to physiological differences or differences inexposure is unclear. One laboratory study, Lindman et al. [1991], found that women have more type Imuscle fibers in the trapezius muscle than men, and have hypothesized that myofascial pain originates inthese Type I muscle fibers. Ulin et al. [1993] noted that significant gender differences in work posturewere related to stature and concluded that the lack of workplace accommodation to the range ofworkers' height and reach may, in part, account for the apparent gender differences. The reporting biasmay exist because women may be more likely to report pain and seek medical treatment than men[Armstrong et al. 1993; Hales et al. 1994]. The fact that more women are employed in hand-intensivejobs and industries may account for the greater number of reported work-related MSDs amongwomen. Byström et al. [1995] reported that men were more likely to have deQuervain’s disease thanwomen; they attributed this to more frequent use of hand tools. Some studies have reported thatworkplace risk factors account for increased prevalence of MSDs among women more than personalfactors (e.g., Armstrong et al. [1987a], McCormack et al. [1990]). In a recent evaluation of Ontarioworkers compensation claims for “RSI,” Asbury [1995] reported a RR for female to male claimsranging from 1.3 to 1.6 across industries. Within 5 different broad occupational categories, femaleswere approximately 2–5 times as likely to have a lost-time RSI claim. No information on genderdifferences in hand intensive jobs was reported. May researchers have noted that men and women tendto be employed in different jobs.
In order to separate the effect of work risk factors from potential effects that might be attributable tobiological differences, researchers must study jobs that men and women perform relatively equally.
B-4
SMOKING Several papers have presented evidence that a positive smoking history is associated with low backpain, sciatica, or intervertebral herniated disc [Finkelstein 1995; Owen and Damron 1984; Frymoyer etal. 1983; Svensson and Anderson 1983; Kelsey et al. 1984]; whereas in others, the relationship wasnegative [Kelsey et al. 1990; Riihimäki et al. 1989b; Frymoyer 1993; Hildebrandt 1987]. Boshuizen etal. [1993] found a relationship between smoking and back pain only in those occupations that requiredphysical exertion. In their study, smoking was more clearly related to pain in the extremities than to painin the neck or the back. Deyo and Bass [1989] observed that the prevalence of back pain increasedwith the number of pack-years of cigarette smoking and with the heaviest smoking level. Heliövaara etal. [1991] only observed a relationship in men and women older than 50 years. Two studies did not finda relationship between sciatica and smoking among concrete reinforcement workers and house painters[Heliövaara et al. 1991; Riihimäki et al. 1989b].
In the Viikari-Juntura et al. [1994] prospective study of machine operators, carpenters, and officeworkers, current smoking (OR 1.9 1.0–3.5), was among the predictors for change from “no necktrouble” to “severe neck trouble.” In a study of Finnish adults ages 30–64, [Mäkelä et al. 1991], neckpain was found to be significantly associated with current smoking (OR 1.3, 95% CI 1–1.61) when thelogistic model was adjusted for age and gender. However, when the model included mental andphysical stress at work, obesity, and parity, then smoking (OR 1.25, 95% CI 0.99–1.57) was nolonger statistically significant [Mäkelä et al. 1991]. With univariate analysis, Holmström [1992] found aPRR of 1.2 (95% CI 1.1–1.3) for neck-shoulder trouble in “current” smokers versus “never” smokers.But using multiple logistic regression, when age, individual and employment factors were in the model,only “never smoked” contributed significantly to neck-shoulder trouble. Toomingas et al. [1991] foundno associations between multiple health outcomes (including tension neck, rotator cuff tendinitis, CTSor problems in the neck/scapula or shoulder/upper arm) and nicotine habits among platers, assemblersand white collar workers. In a case/referent study, Wieslander et al. [1989] found that smoking or usingsnuff was not related to CTS among men operated on for CTS .
Several explanations for the relationship have been postulated. One hypothesis is that back pain iscaused by coughing from smoking. Coughing increases the abdominal pressure and intradiscal pressureand puts strain on the spine. A few studies have observed this relationship [Deyo and Bass 1989;Frymoyer et al. 1980; Troup et al. 1987]. The other mechanisms proposed include nicotine-induceddiminished blood flow to vulnerable tissues [Frymoyer et al. 1983], and smoking-induced diminishedmineral content of bone causing microfractures[Svensson and Andersson 1983]. Similar associations with diminished blood flow to vulnerable tissueshave been found between smoking and Raynaud's disease.
PHYSICAL ACTIVITY
The relationship of physical activity and MSDs is more complicated than just “cause and effect.”Physical activity may cause injury. However, the lack of physical activity may increase susceptibility toinjury, and after injury, the threshold for further injury is reduced. In construction workers, more
B-5
frequent leisure time was related to healthy lower backs [Holmström et al. 1993] and severe low backpain was related to less leisure time activity [Holmström et al. 1992]. On the other hand, some standardtreatment regimes have found that musculoskeletal symptoms are often relieved by physical activity.Having good physical condition may not protect workers from risk of MSDs. NIOSH [1991] statedthat persons with high aerobic capacity may be fit for jobs that require high oxygen uptake, but will notnecessarily be fit for jobs that require high static and dynamic strengths and vice versa.
When physical fitness is examined as a risk factor for MSDs, results are mixed. For example, someearly case series reported an increased risk of MSDs associated with playing professional sports[Bennet 1946; Nirschl 1993], or with physical fitness and exercise [Kelsey 1975b; Dehlin et al. 1978,1981] while other studies indicate a protective effect and reduced risk [Cady et al. 1979; Mayer et al.1985; Åstrand et al. 1987; Biering-Sorensen 1984]. Boyce et al. [1991] reported that only 7% ofabsenteeism could be explained by age, sex, and physical fitness among 514 police officers 35 years orolder. Cady et al. [1979, 1985], on the other hand, found that physical capacity was related tomusculoskeletal fitness. Cady defined fitness for most physical activities as combinations of strength,endurance, flexibility, musculoskeletal timing and coordination. Cady et al. [1979] evaluated male firefighters and concluded that physical fitness and conditioning had significant preventive effects on backinjuries (least fit 7.1% injured, moderately fit 3.2% injured and most fit 0.8% injured). However, themost fit group had the most severe back injuries. Low cardiovascular fitness level was a risk factor fordisabling back pain in a prospective longitudinal study among aerospace manufacturing workers byBattie et al. [1989]. Good endurance of back muscles was found to be associated with low occurrenceof low back pain [Biering-Sorensen 1984].
Few occupational epidemiologic studies have looked at non-work-related physical activity in the upper extremities. Most NIOSH studies [Hales and Fine 1989; Kiken et al. 1990; Burtet al. 1990; Baron et al. 1991; Hales et al. 1994; Bernard et al. 1994] have excluded MSDsdue to sports injury or other nonwork-related activity or injury and have not included these factors inanalyses. However, many of the risk factors that are important in occupational studies occur in sports activities—forceful, repetitive movements with awkward postures. A combination of high exposure to load lifting and high exposure to sports activities that engage the arm was a risk factor for shoulder tendinitis, as well as osteoarthritis of the acromioclavicularjoint [Stenlund et al. 1993]. Kennedy et al. [1978] found that 15% of competitive swimmers withrepetitive overhead arm movements had significant shoulder disability primarily due to impingementfrom executing butterfly and freestyle strokes. Epicondylitis in professional athletes has been welldocumented, and many of the biomechanical and physiological studies of epicondylitis have been conducted
in professional tennis players and baseball pitchers [King et al. 1969; Nirschl 1993]. One prospectivestudy of healthy baseball players has found slowing of the suprascapular nerve function as the seasonprogresses [Ringel et al. 1990]. Scott and Gijsbers [1981] found an association between athletic
B-6
performance and pain tolerance, and suggested that physically fit persons may have a higher thresholdfor injury.
In summary, although physical fitness and activity is generally accepted as a way of reducing work-related MSDs, the present epidemiologic literature does not give such a clear indication. The sportsmedicine literature, however, does give a better indication that sports involving activities of a forceful,repetitive nature (such as tennis and baseball pitching) are related to MSDs. It is important to note thatprofessional sports activities usually provide players (i.e., workers) with more substantial breaks forrecovery and shorter durations for intense tasks as compared with more traditional work settings inwhich workers are required to perform repetitive, forceful work for 8 hours per day, 5 days per week.
STRENGTH
Some epidemiologic support exists for the relationship between back injury and a mismatch of physicalstrength and job tasks. Chaffin and Park [1973] found a sharp increase in back injury rates in subjectsperforming jobs requiring strength that was greater or equal to their isometric strength-test values. Therisk was three times greater in the weaker subjects. In a second longitudinal study, Chaffin et al. [1977]evaluated the risk of back injuries and strength and found the risk to be three times greater in theweaker subjects. Keyserling et al. [1980] strength-tested subjects, biomechanically analyzed jobs, andassigned subjects to either stressed or non-stressed jobs. Following medical records for a year, theyfound that job matching based on strength criteria appeared to be beneficial. In another prospectivestudy, Troup et al. [1981] found that reduced strength of back flexor muscles was a consistentpredictor of recurrent or persistent back pain, but this association was not found for first timeoccurrence of back pain.
Other studies have not found the same relationship with physical strength. Two prospective studies oflow back pain reports (or claims) of large populations of blue collar workers [Battie et al. 1989; Leino1987] failed to demonstrate that stronger (defined by isometric lifting strength) workers are at lowerrisk for low back pain claims or episodes. One study followed workers for ten years after strengthtesting and the other followed workers for a few years. Neither of these studies included precisemeasurement of exposure level for each worker, so the authors could not estimate the degree ofmismatch between workers' strength and tasks demands. Battie et al. [1990] compared workers withback pain with other workers on the same job (by isometric strength testing) and did not find thatworkers with back pain were weaker. In two studies of nurses [Videman et al. 1989; Mostardi et al.1992] lifting strength was not a reliable predictor of back pain.
When examined together, these studies reveal the following: The studies that found a significantrelationship between strength/job task and back pain used more thorough job assessment or analysisand have focused on manual lifting jobs. However, these studies only followed workers for a period ofone year, and whether this same relationship would hold over a much longer working period remainsunclear. Studies that did not find a relationship, although they followed workers for a longer period oftime, did not include precise measurements of exposure level for each worker, so they could not assess
B-7
the strength capabilities that were important in the individual jobs. Therefore, they could not estimate thedegree of mismatch between workers' strength and task demands.
ANTHROPOMETRY Weight, height, body mass index (BMI) (a ratio of weight to height squared), and obesity have all beenidentified in studies as potential risk factors for certain MSDs, especially CTS and lumbar discherniation.
Few studies examining anthropometric risk factors in relationship to CTS have been occupationalepidemiologic studies; most have used hospital-based populations who may differ substantially fromworking populations. Nathan et al. [1989, 1992, 1994] have published several papers on the basis of asingle industrial population and have reported an association between CTS and obesity; however, themethods employed in their studies have been questioned in a number of subsequent publications [Gerrand Letz 1992; Stock 1991; Werner et al. 1994b]. Several investigators have reported that theirindustrial study subjects with CTS were shorter and heavier than the general population [Cannon et al.1981; Dieck and Kelsey 1985; Falk and Aarnio 1983; Nathan et al. 1992; Werner et al. 1994b;Wieslander et al. 1989]. In the Werner et al. [1994b] study of a clinical population requiringelectrodiagnostic evaluation of the right upper extremity, patients classified as obese (BMI>29) were2.5 times more likely than slender patients (BMI<20) to be diagnosed with CTS. Werner et al. [1994b]developed a multiple linear regression CTS model (with the difference between median and ulnarsensory latencies as the dependent variable) that demonstrated that BMI was the most influentialvariable, but still only accounted for 5% of the variance in the model. In Nathan's [1994a] logisticmodel, body mass index accounted for 8.6% of the total risk; however, this analysis used both handsfrom each study subject as separate observations, although they are not independent of each other.Falck and Aarnio [1983] found no difference in BMI among 17 butchers with (53%) and without(47%) CTS. Vessey et al. [1990] found that the risk for CTS among obese women was double for thatof slender women. The relationship of CTS and BMI has been suggested to relate to increased fattytissue within the carpal canal or to increased hydrostatic pressure throughout the carpal canal in obesepersons compared with slender persons [Werner 1994b].
Carpal tunnel canal size and wrist size has been suggested as a risk factor for CTS, however, somestudies have linked both small and large canal areas to CTS [Bleecker et al. 1985; Winn and Habes1990].
For back MSDs, Hrubec and Nashold [1975] found that height and weight were predictive ofherniated disc disease among World War II U.S. army recruits compared with age-matched controls.Some studies have reported that people with back pain, are, on the average, taller than those without it[Rowe 1965; Tauber 1970; Merriam et al. 1980; Biering-Sorensen 1983]. Heliövaara et al. [1987], ina Finnish population study, found that height was a significant predictor of herniated lumber disc in bothsexes, but a moderately increased BMI was predictive only in men. Severe obesity (exceeding 30kg/m2) involved less risk than moderate obesity. Kelsey [1975a] and Kelsey et al. [1984] failed to
B-8
reveal any such relationships between height or BMI among patients with herniated lumber discs andcontrol subjects. Magora and Schwartz [1978] found an association between obesity and radiologicaldisc degeneration, but Kellgren and Lawrence [1958] did not. A study of Finnish white collar and bluecollar workers found no association between overweight (relative weight (>120%) and lumbosacraldisorders either cross-sectionally or in a 10-year follow-up [Aro and Leino 1985].
Schierhout et al. [1995] found that short stature was significantly associated with pain in the neck andshoulder among workers in 11 factories, but not in the back, forearm, hand and wrist. Height was not afactor for neck, shoulder or hand and wrist MSDs among newspaper employees [Bernard et al. 1994].Kvarnström [1983a] found no relationship between neck/shoulder MSDs and body height in a Swedishengineering company with over 11,000 workers.
Anthropometric data are conflicting, but in general indicate that there is no strong correlation betweenstature, body weight, body build and low back pain. Obesity seems to play a small but significant role inthe occurrence of CTS.
C-1
APPENDIX C Summary Tables
Appendix C contains summary tables of articles reviewed in this document. These tables provide aconcise overview of the studies reviewed relative to the evaluation criteria, risk factors addressed, andother issues.
See footnotes at end of table. (Continued)
Appendix C Table C-1. Summary table for epidemiologic studies evaluating work-related neck musculoskeletal disorders
Componentsof study Andersen 1993a Andersen 1993b Baron 1991 Bergqvist 1995a Bergqvist 1995b Bernard 1994 Ferguson 1976 Hales 1989
Study type CS CS CS CS CS CS CS CS
Participationrate $$70%
Y Y N Y Y Y Y Y
Outcome S S and PE S and PE S and PE S and PE S S S and PE
Exposure Job titlecategorization
Categorization byjob duration
Observation,video analysis,measurement ofitems,(assessment wasfor hand/wrist, notneck)
Questionnaire,observation
Questionnaire,observation
Observation,questionnaire
Measurements,observation,questionnaire
Observation, videotaping, jobcategorization,(assessment wasfor hand/wrist, notneck)
Covariatesconsidered
Age, havingchildren, notexercising,smoking, SES,marital status
Age, havingchildren, notexercising,smoking, SES
Age, gender,duration of workenvironment
Age, gender Adjustments madefor confounders
Age, gender,height,psychosocialfactors
Height, weight Age, duration ofemployment
Investigatorsblinded
Y Y Y Y Y Y NR Y
Repetition Combined Combined Combined Repeated workmovements: 3.6(0.4-29.6)
Combined Time spent typing:NS
Õ Combined
Force Combined Combined Combined Õ Õ Õ Õ Combined
Extremeposture
Combined Õ Combined Too highly placedkeyboard: 4.4(1.1-17.0)
Õ Time spent ontelephone: 1.4(1.0-1.8)
NR, sig. Õ
Vibration Õ Õ Õ Õ Õ Õ Õ Õ
C-2
Appendix C Table C-1. Summary table for epidemiologic studies evaluating work-related neck musculoskeletal disorders
Componentsof study Andersen 1993a Andersen 1993b Baron 1991 Bergqvist 1995a Bergqvist 1995b Bernard 1994 Ferguson 1976 Hales 1989
See footnotes at end of table. (Continued)
Risk factors(combined)
Sewing operatorsvs. referents: 4.9(2.0-12.8)
Current highexposure:1.6 (0.7-3.6)8 to 15 years: 6.8 (1.6-28.5)
Checkers vs.noncheckers: 2.0(0.6-6.7)
Õ VDT work >20 hrand eye glasses atVDT: 6.9 (1.1-42)
Õ High exposure vs.Low exposurejobs(estimated crudeOR): 3.7 (0.4-164) Outcome, necksymptoms:RR=1.64 (0.4-3.9)
Duration ofemployment
0 to 7 years: 1.9(1.3-2.9)8 to 15 years: 3.8(2.3-6.4)>15 years: 5.0(2.9-8.7)
0 to 7 years: 2.3(0.5-11)8 to 15 years: 6.8(1.6-28.5)>15 years: 16.7(4.1-67.5)
NS Õ Õ NS Õ Adjusted for inanalysis
Physicalworkload
Õ Õ Õ Õ Õ Õ Õ Õ
Psychosocialfactors
Õ Õ Job satisfaction:NS
Limited breakopportunity: 7.4(3.1-17.4)
Deadline hr: 1.7work variance: 1.7managementissues: 1.9
Õ Õ
Individual/other factorsconsidered
Age at least 40years: 1.5(1.1-2.2); havingchildren: 1.3(0.8-2.0); SES:1.29 (0.7-2.3);smoking: 1.39(0.99-1.9)
Age $ 40 years:1.9 (0.9-4.1);having children:0.5 (0.1-1.7);exercise: 1.4(0.6-2.9);smoking: 1.5(0.7-3.3)
Age, gender,hobbies controlledfor in analysis
Females withchildren: 6.4;smoking, stressreaction,stomach-relatedstress, use ofspectacles, peercontacts, restbreaks, worktask flexibility,overtime, staticwork position,nonuse of lowerarm support,hand innon-neutralposture, highvisual angle toVDT, glare onVDT
Smoking, stressreaction,stomach-relatedstress, use ofspectacles, peercontacts, restbreaks, work taskflexibility, overtime,static workposition, nonuse oflower arm support,hand innon-neutralposture, highvisual angle toVDT, glare on VDT
Age, gender,height,psychosocialfactors; VDT useoutside of work
Õ Age
Dose/response
Years worked:Sig.
Õ Õ Õ Õ Õ Õ Õ
C-3
See footnotes at end of table. (Continued)
Appendix C Table C-1. Summary table for epidemiologic studies evaluating work-related neck musculoskeletal disorders
Componentsof study Hales 1994 Hunting 1994 Kamwendo 1991 Kiken 1990 Knave 1985 Kukkonen 1983 Kuorinka 1979 Linton 1990
Study type CS CS CS CS CS Prospective,intervention
CS CS
Participationrate $$70%
Y Y Y Y Y NR Y Y
Outcome S and PE S S S and PE S S and PE S and PE S
Exposure Observation,questionnaire
Questionnaire Questionnaire Observation,(assessment wasfor hand/wrist,not neck)
Observation, gazedirectioninstrument, job titleor self-report
Observation,interview
Observation, jobanalysis, videotaping(assessment wasfor hand/wrist,not neck)
Questionnaire
Covariatesconsidered
demographics,work practices,age, gender,hobbies
Years worked,age, current workas electrician,gender
Age, length ofemployment,psychosocialwork environment
Age, gender Age, gender,smoking,educationalstatus, drinking
Gender,prospectivedesign
Age, duration ofemployment, BMI,metabolic disease,hobbies, “extrawork”
Age, gender,exercise, eatingregularly, smoking,alcoholconsumption,psychosocialvariables
Investigatorsblinded
Y NR NR Y NR Y NR NR
Repetition Õ Õ Combined Combined Combined Combined Scissor makersvs. Referents: 4.1(2.3-7.5)
Short cycle tasksvs. long cycletasks: 1.64 (0.7-3.8)
Õ
Force Õ Õ Õ Combined Õ Õ Combined ÕExtremeposture
Use of bifocals:3.8 (1.5-9.4)
Õ Combined Combined Combined Combined Combined Uncomfortableposture and poorpsychosocialenvironment: 3.5(2.7-4.5)
Vibration Õ Õ Õ Õ Õ Õ Õ Univariateanalysis showedelevated OR forvibration
C-4
Appendix C Table C-1. Summary table for epidemiologic studies evaluating work-related neck musculoskeletal disorders
Componentsof study Hales 1994 Hunting 1994 Kamwendo 1991 Kiken 1990 Knave 1985 Kukkonen 1983 Kuorinka 1979 Linton 1990
See footnotes at end of table. (Continued)
Risk factors(combined)
Õ Õ Work with officemachines >5hr/day: 1.65(1.02-2.67)
High exposure vs.low exposurejobs: 1.3 (0.2-11)
Typing hr: Sig. Interventiongroup: PRR=3.6(2.2-5.9) Nointervention 1.0
Scissor-makersvs. departmentstore shopassistants:OR=4.1 (2.3-7.5)
Õ
Duration ofemployment
NS 1 to 3 years: 14 to 5 years: 1.36 to 10 years: 1.6>10 years: 1.3
Length ofemployment: Sig.
Õ Õ Õ Controlled for Õ
Physicalworkload
Õ Õ Being given toomuch to do: Sig.
Õ Õ Õ Õ Õ
Psychosocialfactors
Decision making:4.2; productivitystandard: 3.5; fear ofreplacement bycomputer: 3.0; higher informationprocessingdemands: 3.0; jobtask variety: 2.9;work pressure:2.4
Ability to influencework, cooperativespirit betweenco-workers: sig.
Õ Interest in work,positive attitude
Õ Monotonous workSS, work content,work load, socialsupport
Individual/other factorsconsidered
Electronicperformancemonitoring,keystrokes,hobbies,recreationalactivities: NS
Age group,current work aselectrician: NS
Sitting 5 or morehr/day: 1.6(0.9-2.8); age:Sig.
Õ Õ Õ Extra work,hobbies, outsideactivities: NS
Exercise, eating,smoking, alcoholconsumption
Dose/response
Õ Õ Õ Õ Betweenregistered workduration andmusculoskeletalcomplaints
Õ Õ Õ
C-5
See footnotes at end of table. (Continued)
Appendix C Table C-1. Summary table for epidemiologic studies evaluating work-related neck musculoskeletal disorders
Componentsof study Liss 1995 Luopajärvi 1979 Milerad 1990 Ohlsson 1989 Ohlsson 1995 Onishi 1976 Ryan 1988 Sakakibara 1987
Study type CS CS CS CS CS CS CS CS
Participationrate $$70%
N Y Y NR Y NR Y Y
Outcome S S and PE S S S and PE S and PE S and PE S
Exposure Questionnaire Observation,video analysis,interviews
Questionnaire Questionnaire Videotaping,observation,analysis ofposture, flexion ofneck,questionnaire
Observation, thenjob categorization
Observationmeasurements atwork stations
Observation jobanalysis and neckanglemeasurements
Covariatesconsidered
N Age, gender,socialbackground,hobbies, amountof housework
Gender, age,leisure-timeexposure,systemic disease
Age, gender,duration ofemployment
Age , gender,psychosocialscales
Õ Age, height, lengthof training time
Õ
Investigatorsblinded
N Y NR NR Blinded toexposureinformation but“Not possible tocompletely blindthe examiners.”
NR Y NR
Repetition Combined Combined Combined Combined Combined Combined Õ Combined
Force Combined Combined Õ Õ Industrial workersexposed torepetitive tasksvs. referents: 3.6(1.5-8.80)
Combined Õ Õ
Extremeposture
Combined Combined Combined Combined Õ Combined Significantdifference in meanelbow angle andshoulder flexion ofleft arm
Combined
Vibration Õ Õ NS for exposureto vibration
Õ Õ Õ Õ Õ
C-6
Appendix C Table C-1. Summary table for epidemiologic studies evaluating work-related neck musculoskeletal disorders
Componentsof study Liss 1995 Luopajärvi 1979 Milerad 1990 Ohlsson 1989 Ohlsson 1995 Onishi 1976 Ryan 1988 Sakakibara 1987
See footnotes at end of table. (Continued)
Risk Factors(Combined)
Dental hygienistsvs. dentalassistants: 1.7(1.1-2.6)
Assemblyworkers vs. shopassistants: 1.6(0.9-2.7)
Dentists comparedto pharmacists:2.1 (1.4-3.1)
Assemblers vs.referents pain inlast 12 months:1.9 (0.9-3.7)
Õ Film rollingworkers: 3.8
Lamp assemblers:3.8 (2.1-6.6)Teachers andnurses: 1.5(0.7-3.2)
Õ Pear work vs.apple work rightside: p<0.05
Pear work vs.Apple work at leftside: p<0.01
Duration ofemployment
NS Õ NS Employees<35 years: Sig.
Õ Õ NS Õ
Physicalworkload
Õ Õ Õ Õ Õ Õ Õ Õ
Psychosocialfactors
Õ Õ Õ Increased OR formedium and fastpaced workcompared to slowpaced but ORlower for veryfast paced work
Õ Insufficient rest,break time, moreboredom, morestress, lower peercohesion, lowerantonomy, lowerjob clarity, higherstaff support,higher workpressure
Õ
Individual/other factorsconsidered
Gender (99%females in studygroup); had tomodify work orunable to work atsome point: 2.4 (1.1-5.4)
Õ Leisure timeexposure,smoking systemicdisease
Õ Õ Age, height,marital andparental status,handedness,length of trainingtime
Õ
Dose/response
Õ Õ Õ Õ Õ Õ Õ Õ
C-7
See footnotes at end of table. (Continued)
Appendix C Table C-1. Summary table for epidemiologic studies evaluating work-related neck musculoskeletal disorders
Componentsof study Sakakibara 1995 Schibye 1995 Veiersted 1994 Viikari-Juntuna
1994Welch 1995 Wells 1983 Yu 1996
Study type CS Cohort Cohort Cohort CS CS CS
Participationrate $$70%
Y Y N (55%) Y Y (83%) Y Y
Outcome S and PE S S and PE/ pain diaries S S S S
Exposure Observation,measurements
Questionnaire EMG, interviewsevery 10 weeks
Questionnaire,observation
Questionnaire Questionnaire,interview
Questionnaire
Covariatesconsidered
Õ Subjects served astheir own controls
Metabolic or otherdiseases, gender
All male, smoking,age, physicalexercise, occupation,duration of work, cardriving
Smoking, years ofemployment
Age, gender, numberof years on job,previous workexperience,education, maritalstatus, quetelet ratio
Age, gender, “othercovariates”
Investigatorsblinded
NR NR NR Y N NR NR
Repetition Õ Combined Õ Õ Combined Õ Frequent VDT use:28.9 (2.8-291.8)
Force Õ Combined Strenuous previouswork: 6.7 (1.6-28.5)
Combined Õ Combined Õ
Extremeposture
Combined Combined Strenuous postures:7.2 (2.1-25.3)
No neck pain tosevere, machineoperators vs. officeworkers: 3.9(2.3-6.9)Persistently severe:4.2 (2.0-9.0)
Percent of timehanging duct: 7.5(0.8-68)
Combined Inclining neck atwork: 784.4(33.2-18,630)
Vibration Õ Õ Vibration (floor ormachine)
Combined (machineoperators)
Õ Õ Õ
C-8
Appendix C Table C-1. Summary table for epidemiologic studies evaluating work-related neck musculoskeletal disorders
Componentsof study Sakakibara 1995 Schibye 1995 Veiersted 1994 Viikari-Juntuna
1994Welch 1995 Wells 1983 Yu 1996
Risk factors(combined)
Pear vs. Applebagging: 1.5(0.99-2.35)
Other employmentgroup vs. garmentworkers: 3.3(1.4-7.7)
Physicalenvironment: 0.9(0.5-1.7)
Occupation Sig. fromno neck trouble tomoderate necktrouble; occupationSig. from no neck tosevere neck troubleCarpenters vs.Office workerspersistently severe:3.0 (1.4-6.4)
Õ All letter carriers vs.Clerks and readers:2.57 (1.13-6.2)
Frequent videodisplay terminal use:28.9 (2.8-291.8)
Duration ofemployment
Õ NS Õ Õ Õ Controlled for inanalysis
Õ
Physicalworkload
Õ Õ Õ Õ Õ
Psychosocialfactors`
Õ Õ Psychosocialfactors: 3.3(0.8-14.2)
Job satisfaction: NS Õ Õ Õ
Individual/other factorsconsidered
Õ Age Anthropometrics,general health,previous employmentvariables, draft,noise, personality
Current smoking andage Sig. in model of “no neck trouble tosevere neck trouble”
Õ Education, maritalstatus, quetelet ratio
General health
Dose/response
Õ Õ Õ Õ Õ Õ ÕÕ Not studied.BMI Body mass index.CS Cross-sectional.EMGElectromyography.hrs Hours.MSDMusculoskeletal disordersMVCMaximum voluntary contraction.N No.NR Not reported.NS Not statistically significant.OR Odds ratio.PE Physical examination.PRR Prevalence rate ratio.S Symptoms.SES Socioeconomic status.Sig. Statistically significant.VDTVideo display terminal.vs. Versus.Y Considered (yes).
C-9
See footnotes at end of table. (Continued)
Appendix C Table C-2. Summary table for evaluating work-related neck/shoulder disordersComponents
of study Åaras 1994 Andersen 1993a Andersen 1993b Bergqvist 1995a Bergqvist 1995b Bjelle 1981 Blåder 1991 Ekberg 1994
Study type Prospective CS CS CS CS Case Control CS Case Control
Participationrate $$70%
NR Y Y Y Y NR Y Y
Outcome S and Records S S and PE S S and PE S and PE S and PE S
Exposure Observation andEMG
Job titlecategorization
Categorization byjob duration
Observation,measurements
Job title andquestionnaire
Observation,videotapeanalysis
Questionnaire Questionnaire
Covariatesconsidered
Õ Age, havingchildren,education, maritalstatus, smoking,not exercising
Age, havingchildren,education, maritalstatus, smoking,not exercising
Age, gender,smoking, restbreaks, stress
Age, gender,smoking
Age,anthropometricdata
Age, nationality,employment time,working hr/week
Age, gender,smoking, havingpreschool children
Investigatorsblinded
NR Y Y Y Y Y; Videotapeanalysis blinded tocase status
N NR
Repetition Õ Combined Combined For intensiveneck/shoulderdiscomfort: 3.6(0.4-29.6)
<20 hr/week VDTuse: 1.2 (0.4-3.7)>20 hr/week VDTuse: 0.7 (0.3-1.5)
No sig differencein cycle time
Combined Precise repetitivemovementsHigh: 15.6(2.2-113.0)
Force Static trapeziusload dropped from4.1 to 1.4%NR, Sig.
Combined Combined Õ Õ Cases hadsignificantlyhigher shoulderloads thancontrols
Õ Õ
Extremeposture
Interventionconsisted ofequipment andtool adjustment tocreate relaxedposition ofshoulders andneck: NR, Sig.
Õ Õ For tension necksyndrome: toohighly placedVDT: 4.4(1.1-17.6)
Õ Cases with longerduration andhigher frequencyof abduction orforward flexionthan referents:NR, Sig.
Combined Work with liftedarms 4.8 (1.3-18);uncomfortablesitting posture: 3.6(1.4-9.3)
Vibration Õ Õ Õ Õ Õ Õ Õ Õ
C-10
Appendix C Table C-2. Summary table for evaluating work-related neck/shoulder disordersComponents
of study Åaras 1994 Andersen 1993a Andersen 1993b Bergqvist 1995a Bergqvist 1995b Bjelle 1981 Blåder 1991 Ekberg 1994
See footnotes at end of table. (Continued)
Risk factors(combined)
Õ Sewing machineoperators vs.referents:4.6 (2.2-10.2)
Current highexposure (yes vs.no): 1.6 (0.7-3.6)
Õ VDT work >20 hrand stressfulstomachreactions: 3.9(1.1-13.8)VDT work $ 20 hrand bifocals orprogressiveglasses: 6.9(1.1-42.1)
Õ Working >30 hrperweek: p<0.05
Õ
Duration ofemployment
Õ Years as sewingmachineoperators 0 to 7years: 3.2(0.6-16.1) 8 to 15 years:11.2 (2.4-52) >15 years: 36.7(7.1-189)
Years as sewingmachineoperators0 to 7 years: 2.3(0.5-11)8 to 15 years: 6.8(1.6-28.5)>15 years: 16.7(4.1-67.5)
Õ Õ Õ Working >30hr/week andtension necksyndrome: p<0.05
Õ
Physicalworkload
Õ Õ Õ Õ Õ Õ Õ Õ
Psychosocialfactors
Õ Õ Õ For cervicaldiagnoses:Stressful stomachreactions: 5.4(1.6-17.6)
Combined Õ Smallerrandomized studygroup interviewedby sociologist andpsychologist forpsychosocialhistory
High work pace:3.5 (1.3-9.4);Low workcontent: 2.6(0.7-9.4);Work roleambiguity: 16.5(6.0-46);Demands onattention: 3.8(1.4-11)
Individual/other factorsconsidered
Median sick daysdecreased from22.9 to 1.8
Age >40 yrs: 1.96(0.8-5);exercise:1.28 (0.5-3.4); smoking:2.3 (0.9-6.1); children: 0.35(0.1-1.9)
Age $ 40 years:1.9 (0.9-4.1);children: 0.5(0.1-1.7);exercise: 1.4(0.6-2.96);smoking: 1.5(0.7-3.3)
Children at home,negative,affectivity, peercontacts,overtime, worktask flexibility,visual angle toVDT
Children at home,negative,affectivity, peercontacts,overtime, worktask flexibility,visual angle toVDT
Age-isometrictesting
Cervicalsyndromecorrelated withage
Female: 11.4(4.7-28);immigrant status:4.9 (1.8-14);current smoker:8.2 (2.3-29)
Dose/response
Õ Duration ofemployment assewing machineoperator
Duration ofemployment
Õ Õ Õ Õ Repetitiveprecisionmovements, workpace
C-11
See footnotes at end of table. (Continued)
Appendix C Table C-2. Summary table for evaluating work-related neck/shoulder disordersComponents
of study Ekberg 1995 Holmström 1992 Hünting 1981 Jonsson 1988Kilbom 1986,
1987 Linton 1989 Maeda 1982 Milerad 1990
Study type CS CS CS Cohort CS CS CS CS
Participationrate $$70%
Y Y NR Y Y Y NR Y
Outcome S S S and PE S and PE S and PE S S S
Exposure Questionnaire Questionnaire Observation,questionnaire
Observation,video taping, jobanalysis, MVC offorearm
Observation, videotaping, jobanalysis, MVC offorearm
Questionnairedealing withpsychosocialissues
Observation,measurement
Questionnaire
Covariatesconsidered
Age, smoking,exercise habits,family situationswith preschoolchildren, immigrantstatus, gender
Age, physicalfactors,psychosocialstress scales
Psychosocialfactors
Used prospectivecohort designwith same studysample
Age, spare timephysical activities,hobbies,psychosocialstress, musclestrength
Õ Gender, leisuretime, smoking,systemic disease
Investigatorsblinded
NR Y NR Y Y NR NR NR
Repetition Repetitivemovementsdemandingprecision: 1.2(1.0-1.3)
Õ Combined Combined Combined Õ Õ Combined
Force Õ Õ Õ Combined Combined Õ Õ Õ
Extremeposture
Hand aboveshoulder: <1hr/day: 1.1(0.8-1.5) 1 to 4 hr/day: 1.5(1.2-1.9)>4 hr/day: 2.0(1.4-2.7)
Combined/headinclination >56ESig. forneck/shoulderMSDs
Combined Combined Õ Constrained tiltedhead posture:p<0.05
Combined
Vibration Õ Õ Õ Õ Õ Õ Õ NS
C-12
Appendix C Table C-2. Summary table for evaluating work-related neck/shoulder disordersComponents
of study Ekberg 1995 Holmström 1992 Hünting 1981 Jonsson 1988Kilbom 1986,
1987 Linton 1989 Maeda 1982 Milerad 1990
See footnotes at end of table. (Continued)
Risk factors(combined)
Õ Roofers: 1.6Plumbers: 1.5Floor workers: 1.3
Data entryworkers vs.non-keyboard-using officeworkers: 9.9(3.7-26.9)
At third year, 38workersreallocated hadimproved, 26%with unchangedconditionsdeterioratedfurther: NR, Sig.
Average time/workcycle in neckflexion sig, Upperarm abducted0-30E: NR, Sig.
Õ Õ Dentists vs.pharmacists:2.1 (1.3-3.0);males: 2.6(1.2-5.0); females2.0 (1.3-3.1)
Duration ofemployment
Õ Õ Õ Õ NS Õ Õ NS
Physicalworkload
Õ Õ Õ Õ Õ Õ Õ Õ
Psychosocialfactors
Õ Qualitativedemands: 1.4 (1,2) Quantitativedemands: 3.0(2.1-4)Solitary work: 1.5 (1.2-1.8) Anxiety: 3.2 (2.5-4)
Job satisfaction;relationship withsupervisors,colleagues;decision making,use of skills all NS
Job satisfaction,productivity
Productivity, worksatisfaction,perceived stress:NS
Poor work content:2.5 (1.3-4.9)Lack of socialsupport: 1.6(0.9-2.8)Work demandsocial support atwork
Õ Õ
Individual/other factorsconsidered
Immigrant status:1.3 (1.1-1.5)Social workclimate, workplanning, jobsecurity, jobconstraints
Psychosomatic:5.0 (3.6-6.9)Psychological: 4.7(3.6-6)Stress: 3.4(2.6-4.2)Discretion,support, understimulation,anxiety, jobsatisfaction,quality of life
Medical findings inneck and shouldersignificant fortypists with headrotation>20E compared to< 20E
Õ Age, musclestrength, restpauses: NS
Õ Age Leisure time,smoking NS
Dose/response
Õ Stress index andneck-shoulderMSDs
Õ Õ Õ Õ Õ Õ
C-13
See footnotes at end of table. (continued)
Appendix C Table C-2. Summary table for evaluating work-related neck/shoulder disordersComponents
of study Ohara 1976 Ohlsson 1995 Punnett 1991 Rossignol 1987 Ryan 1988 Tola 1988 Vihma 1982Viikari-Juntura
1991a
Study type CS and Cohort CS CS CS CS CS CS Cohort
Participationrate $$70%
CS study: NR;
Cohort: Y
Y Y N to Y (6industries)
Y Y overall:67% carpenters67% officeworkers
NR Y
Outcome S and PE S and PE S S S S S S and PE
Exposure Observation Observation,video, analysis,muscle strengthtesting
Observation,questionnaire
Questionnaire Observation,workstationmeasurement,questionnaire
Occupation title Observation,interview
Questionnaire
Covariatesconsidered
Used prospectivecohort designwith same studysample
Age, gender,psychosocialscales
Age, gender Age, cigarettesmoking, industry,education, VDTtraining
Height, weight,gender, age,marital status,parental status
Years inoccupation, age,leisure timeactivities, cardriving, generalhealth
Age, duration ofemployment
Physical hobbies,creative hobbies
Investigatorsblinded
NR Y to exposureinformation,no for physical
NR NR Y NR NR NR
Repetition Combined Repetitive work:4.6 (1.9-12)
Combined Combined Õ Õ Combined Õ
Force Õ Õ Combined Õ Õ Õ Õ Õ
Extremeposture
Combined Significant timespent in neckflexion <60°: NR
Associated withextended durationof and liftingweight inabduction/flexionand extension ofthe shoulder
Combined More non-casestrained inadjustment offurniture thancases: NR, Sig.
Use of twisted orbent posturesduring work: Little(referent): 1.0Moderate: 1.2(1.0-1.5)Rather much: 1.6(1.4-1.9)Very much: 1.8(1.5-2.2)
Combined
Sewing machineoperator withsignificantlygreater staticwork compared toseamstresses
Sitting in aforward posture1-3 hr/day: 10.7(0.4-291);>3 hr/day: 1.5(0.7-29.5)
Vibration Õ Õ Õ Õ Õ Õ Õ Õ
C-14
Appendix C Table C-2. Summary table for evaluating work-related neck/shoulder disordersComponents
of study Ohara 1976 Ohlsson 1995 Punnett 1991 Rossignol 1987 Ryan 1988 Tola 1988 Vihma 1982Viikari-Juntura
1991a
Risk factors(combined)
Operators hiredpost-interventionhad less reportsof MSDs
Industrial workersvs. referents: 2.7(1.2-6.3)
Male: 1.8 (1.0-3.2)Female: 0.9(0.5-1.9)
½ to 3 hr of VDTuse: 1.8 (0.5-6.8)4 to 6 hr of VDTuse: 4.0(1.1-14.8) 7 $ hrof VDT use: 4.6(1.7-13.2)
Õ Machine operatorsvs. officeworkers: 1.7(1.5-2.0)Carpenters vs.office workers:1.4 (1.1-1.6)
Sewing machineoperators vs.seamstresses:1.6 (1.1-2.3)
Õ
Duration ofemployment
Õ Õ Õ Õ Õ Õ Õ
Physicalworkload
Õ Õ Õ Õ Õ Õ Cases hadsignificantlyhigher shoulderloads
Õ
Psychosocialfactors
Õ Stress/worrytendency: 1.9(1.1-3.5)
Õ Õ Adequate restbreaks, boredom,work stress jobpressure,autonomy, peercohesion, roleambiguity, staffsupport
Job satisfaction,poor vs. verygood: 1.2 (1.1-1.4)
Õ Social confidence,much fear vs.none: 1.4(0.05-42.2);Sense ofcoherence: 0.95(0.9-0.99)
Individual/other factorsconsidered
Õ Muscle tensiontendency: 2.3(1.3-4.9)
Õ Smoking, industry,education
Õ Working in a draft:1.1 (1.0-1.3)
Õ Alexithymia1.02 (0.97-1.1)
Dose/response
Õ Õ Õ Hours of VDT use Õ Use of twisted orbent posture
Õ Õ
Õ Not studiedCI Confidence intervalCS Cross-sectionalEMG Electromyographyhr HoursMed. MediumMSDSMusculoskeletal disordersMVC Maximum voluntary contractionN NoNR Not reportedNS Not statistically significantOR Odds ratioPE Physical examination
S SymptomsSig. Statistically significantVDT Video display terminalvs. VersusY Considered (yes)
C-15
See footnotes at end of table. (Continued)
Appendix C Table C-3. Summary table for evaluating work-related shoulder musculoskeletal disordersComponents
of study Andersen 1993a Andersen 1993b Baron 1991 Bergenudd 1988 Bernard 1994 Bjelle 1979 Bjelle 1981 Burdorf 1991
Study type CS CS CS CS CS Case control Case control CS
Participationrate $$70%
Y Y N N Y NR NR Y for riveters;N for referents
Outcome S S and PE S and PE S and PE S S and PE PE S
Exposure Job title,categorization byjob duration
Job title,categorization byjob duration
Observation andvideotapeanalysis, weightof scanned items,job category
Questionnaire, jobclassification(light, moderate,heavy physicaldemands)
Questionnaire andobservation
Observation,measurement,
EMG on 15 cases,open musclebiopsies on 11cases
Measurement,videotapeanalysis,observation, EMGon 3 subjects and2 healthyvolunteers
Observation,measurement ofvibration
Covariatesconsidered
Age, havingchildren, notexercising,duration ofemployment, socioeconomicstatus, smokingstatus, currentneck/shoulderexposure
None for theshoulder analysis
Age, gender,hobbies, durationof work, secondjob, metabolicdisease, durationof employment
Gender Age, race,gender, height,medicalconditions,psychosocialfactors, typing hraway from work
Age, gender, andworkshop
Age, gender, andplace of work
Height, weight,smoking status
Investigatorsblinded
Y Y Y NR N N Y NR
Repetition forshoulder
Combined Combined Combined Õ R no surrogate forhand used: number of hrtyping
Combined Combined Õ
Force Combined Combined Combined Õ Õ Combined Cases had Sig.higher shoulderloads thancontrols
Õ
Extremeposture
Combined Combined Combined Õ Õ Combined Combined Õ
C-16
Appendix C Table C-3. Summary table for evaluating work-related shoulder musculoskeletal disordersComponents
of study Andersen 1993a Andersen 1993b Baron 1991 Bergenudd 1988 Bernard 1994 Bjelle 1979 Bjelle 1981 Burdorf 1991
See footnotes at end of table. (Continued)
Vibration Õ Õ Õ Õ Õ Õ Õ 1.5 (noconfidence limits)
Risk factors(combined)
Increasing yearsof experience:1.38-10.25 (Sig.)
Chi sq test fortrend usingexposure time inyears for rotatorcuff syndrome:9.51; p<0.01
Checkers vs.others 3.9(1.4-11.0)Checkers usingscanners vs.others 8.6(1.0-72.2)
Õ Õ Work at or aboveshoulders, cases(65%) vs.referents (15%):10.6 (2.3-54.9)
Cases had Sig.longer durationand higherfrequency ofabduction orforward flexionthan controls,p<0.001
Õ
Duration ofemployment
See under“Physicalworkload”
See under “Riskfactors combined”
Number of hr perweek as achecker Sig.
Õ Years atnewspaper: 1.4(1.2-1.8)
Õ Õ Years of riveting:0.05# p<0.10
Physicalworkload
0 to 7 years: 1.56(0.76-3.75)8 to 15 years:4.28 (2.14-10.0)>15 years: 7.27(3.82-16.3)
Õ Õ Prevalence ofoccupationalworkload insubjects withshoulder pain:Heavy, 11%;Moderate, 49%;Light, 40%
Õ Õ Õ Õ
Psychosocialfactors
Õ Õ Õ Females showedSig. associationwith shoulder painanddissatisfaction
Lack of decisionmakingparticipation: 1.6(1.2-2.1)job pressure: 1.5(1.0-2.2)
Õ Õ Õ
Individual/other factorsconsidered
Age-matchedcontrols
Age-matchedcontrols
Age, gender,metabolic disease
Gender Gender, race,height
Age, gender Age, gender;median number ofsick-leave daysSig. differentbetween casesand controls,p=0.01
Age
Dose/response
Y with years ofemployment
Y with years ofexposure
Õ Õ Õ Õ Õ
C-17
See footnotes at end of table. (Continued)
Appendix C Table C-3. Summary table for evaluating work-related shoulder musculoskeletal disordersComponents
of study Burt 1990 Chiang 1993 English 1995 Flodmark 1992 Hales 1989 Hales 1994 Herberts 1981 Herberts 1984
Study type CS CS Case control CS CS CS CS CS
Participationrate $$70%
Y Y Y Y Y Y NR NR
Outcome S S and PE S and PE S S and PE S and PE S and PE S and PE
Exposure Observation,questionnaire, jobsampling
Observation andrecording ofrepresentativejobs, hand Festimation
Self-reports Õ Observationwalk-through, jobcategorization
High vs. lowexposure(hand/wristexposure)
Observation andquestionnaire
Analyses by jobtitle
Analyses by jobtitle
Covariatesconsidered
Age, gender,psychosocialfactors, metabolicdisease durationof employment
Age, gender,metabolicdiseases
Age, height,gender, weight,injury, studycenter, hobbies,sporting activities,average hr ofdriving,compensationclaim made
Age, headache,tiredness, medicalproblems,sleeping problemsor lack ofconcentration,sleep
Age and durationof employment
Age, race,gender, workpractices, workorganizationfactors, individualfactors, electronicperformancemonitoring,recreational activities, hobbies
Age, job duration Controls matchedfor age andgender
Investigatorsblinded
Õ Y Y Õ Y Y NR NR
Repetition forshoulder
Typing speed fastcompared toslow: 4.1(1.8-9.4)
Repetitivemovement ofupper limb: 1.6(1.1-2.5)
Combined Õ Combined No Combined Combined
Force Õ Sustained forcefulmovement ofupper limb: 1.8(1.2-2.5)
Õ Õ Combined Õ Welders vs. officeworkers: 15-18
Welders vs. officeworkers: 15-18
Extremeposture
Õ Õ Combined Õ Combined Number of timesarising from chair:1.9 (1.2-15.5)
Combined Combined
C-18
Appendix C Table C-3. Summary table for evaluating work-related shoulder musculoskeletal disordersComponents
of study Burt 1990 Chiang 1993 English 1995 Flodmark 1992 Hales 1989 Hales 1994 Herberts 1981 Herberts 1984
See footnotes at end of table. (Continued)
Vibration Õ Õ Õ Õ Õ Õ Õ Õ
Risk factors(combined)
Õ Repetitionmultiplied byforce: 1.4(1.0-2.0)
Repeatedshoulder rotationwith elevated arm:2.3, p<0.05
Õ Any symptom ofshoulder: 49% vs.43%;1.2 (0.7-2.0)
Periodprevalence: 19%vs. 4%; 3.8(0.6-22.8)
Point prevalence:7% vs. 4%;0.9(0.1-7.3)
Õ Welders vs. officeworkers: shouldersymptoms: 15.2(2.1-108)
ShoulderTendinitis: 8.3(NS)
ST results of 23welders calledback for clinicalfollow-up exams:16 had ST; 18.3(13.7-22.1)(90% CI)
ST results of 30plate-workerscalled back forclinical follow-upexams: 15plate-workers hadST: 16.2(10.9-21.5)(90% CI)
Duration ofemployment
NS Õ Õ Õ Õ Õ Õ Õ
Physicalworkload
Õ Õ Õ Õ Õ Õ NS Õ
Psychosocialfactors
Jobdissatisfaction:2.3 (1.2-4.3)
Õ Õ Type A Behavior:p<0.001
Õ Fear ofreplacement bycomputers: 1.5(1.1-2.0)
Õ Õ
Individual/other factorsconsidered
Pre-existingarthritis: 2.3(1.2-4.4)
Plant effect age:1.0 (0.9-1.1)Gender: 1.1(0.7-1.7)
Per 5 years ofage: 1.4 (1.2-1.5)
Õ Õ Typing outside ofwork
Õ Õ
Dose/response
Õ Dose responsefound forshoulderdiagnosis asexposure statusincreased fromGroup 1 toGroup 3
Õ Õ Õ Õ Õ Õ
C-19
See footnotes at end of table. (Continued)
Appendix C Table C-3. Summary table for evaluating work-related shoulder musculoskeletal disordersComponent
of study Hoekstra 1994 Hughes 1997 Ignatius 1993 Jonsson 1988 Kiken 1990Kilbom 1986,
1987 Kvarnström1983
McCormack1990
Study type CS CS CS Prospective CS CS CS and Casecontrol
CS
Participationrate $$70%
Y N N Y Y Y NR Y
Outcome S S and PE S S and PE S and PE S and PE S and PE S and PE
Exposure Analyses basedon questionnaire,self-reports
Observation andjob analysis
Observation,questionnaire,weight of mailbags
Observation,measurement ofexertion,videotaping
Observation(exposure basedon repetitive andforceful handmotions, notshoulder)
Observation,measurement,videotaping,observation
Observation,interview,questionnaire
Observation
Covariatesconsidered
Age, seniority,gender
Controlled for age,smoking status,sports, hobbies
Age, duration ofemployment, bagweight, walkingtime
Age, hobbies,spare time,physical action,psychosocialfactors, breaks,rest pauses
Age and gender Age, years ofemployment,productivity,muscle strength
Õ Age, gender,race, jobcategory, durationof employment,general healthhistory
Investigatorsblinded
Y NR NR Y Y Y N N
Repetition forshoulder
Õ Õ Combined Combined Combined Fewer totalnumber of upperarm flexions/hr.(p<0.05)
Combined Combined
Force Õ Õ Combined Õ Combined Õ Combined Õ
Extremeposture
Non-optimallyadjusted deskheight work: 5.1(1.7-15.5)
Years of forearmtwist: 46.0(3.8-550)
Combined Relative timespent withshoulder elevatednegatively relatedto ‘remaininghealthy ‘ afterboth 1 and 2years: Sig.
Combined Greaterpercentage ofwork cycle timewith upper armabducted 0-30°(p<0.05)
Combined Combined
Vibration Õ Õ Õ Õ Õ Õ Õ Õ
C-20
Appendix C Table C-3. Summary table for evaluating work-related shoulder musculoskeletal disordersComponent
of study Hoekstra 1994 Hughes 1997 Ignatius 1993 Jonsson 1988 Kiken 1990Kilbom 1986,
1987 Kvarnström1983
McCormack1990
See footnotes at end of table. (Continued)
Risk factors(combined)
Center Bcompared toCenter A: 4.0(1.2-13.1)
Õ Letter deliverypostal workerscompared to otherpostal workersRecurrent: 1.8(1.5-2.2)
Severe joint pain:2.2 (1.5-3.1)
38 subjects whowere reallocatedto more variedtasks improved
Plant #1Any symptom forshoulder: 46% vs.28%; 1.6 (0.9-2.9)
Period prevalence:13% vs. 3%; 4.0(0.6-29)
Plant #2Any symptom forshoulder: 50% vs.30%; 1.7 (0.8-3.3)
Period prevalence:14%vs. 5%; 2.8(0.4-19.6)
Õ Die castingmachineoperators: 5.4;plastic workers:2.2; spraypainters: 3.7;surface treatmentoperators: 4.7; assembly lineworkers: 5.2
Boarding workersvs. knittingworkers: 2.1(0.6-7.3)
Duration ofemployment
Õ Õ Õ Õ Õ Years ofemployment inelectronics:p<0.05
Õ NS
Physicalworkload
Õ Õ Õ Low musclestrength no apredictor forshoulder MSD
Õ Õ Õ Õ
Psychosocialfactors
Jobdissatisfaction,exhaustion (notfor shoulder)
Low decisionlatitude: 4.0(0.8-19)
Õ Strong negativerelationshipbetweenremaining healthand satisfactionwith colleagues
Õ Õ 9 cases and 1control reportedpoor relationshipwith supervisor. Sig. differences ingroup piece rate,shift work, heavywork, monotonouswork, stressfulwork,
Õ
Individual/other factorsconsidered
Location Age: 0.93(0.8-1.0); goodhealth: 0.35(0.1-0.87)
Age, workexperience, bagweight, walkingtime
Predictors ofdeterioration,previouslyphysically heavyjob, highproductivity, andsick leave
Õ Shorter stature:p<0.05,productivity: NS,muscle strength:NS
Sig. differences inheavy lifting andunsuitableworkingconditions
Õ
Dose/response
Õ Õ Õ Õ Õ Õ Õ Õ
C-21
See footnotes at end of table. (Continued)
Appendix C Table C-3. Summary table for evaluating work-related shoulder musculoskeletal disordersComponents
of study Milerad 1990 Ohara 1976 Ohlsson 1989 Ohlsson 1994 Ohlsson 1995 Onishi 1976 Punnett 1985 Rossignol 1987
Study type CS CS andProspective
CS CS CS CS CS CS
Participationrate $$70%
Y NR (CS), Y (Prospective)
NR Y Y NR Y Y: clericalworkers N: industry groups
Outcome S S and PE S S and PE S and PE S, PE, andmeasurement
S and PE S
Exposure Questionnaire Observation Job categorization Observation,questionnaire,video analysis
Observation,video analysis,measurement
Observation Observation andquestionnaire
Observation andquestionnaire
Covariatesconsidered
Age, gender,leisure timeexposure,smoking, systemicdisease, durationof employment
Õ Age, gender(females only)
Sports activities,age, gender(females only)psychosocialfactors
Age, employmentstatus
Body height,weight, gripstrength
Age, number ofyears employed,native language
Age, cigarettesmoking, industry,VDT educationaltraining
Investigatorsblinded
NR NR NR Y Yes, to exposureinformation
NR NR Õ
Repetition forshoulder
Combined Combined Combined Combined Combined Combined Combined 4-6 hrs. VDT use:4.0 (1.0-16.9)>7 hrs. VDT use:4.8 (1.6-17.2)
Force Combined Combined Combined Combined Combined Combined Combined Õ
Extremeposture
Combined Combined Combined Combined Combined Combined Combined Õ
Vibration NS Õ Õ Õ Õ Õ Õ Õ
C-22
Appendix C Table C-3. Summary table for evaluating work-related shoulder musculoskeletal disordersComponents
of study Milerad 1990 Ohara 1976 Ohlsson 1989 Ohlsson 1994 Ohlsson 1995 Onishi 1976 Punnett 1985 Rossignol 1987
See footnotes at end of table. (Continued)
Risk factors(combined)
Dentists vs.pharmacists:males: 2.4(1.0-5.4),females: 2.4(1.5-3.7)
Shoulderstiffness:cashiers (81% vs.office workers(72%), 1.7(1.0-2.8)Shoulder dullnessand pain:cashiers (49%)vs. other workers(68%), 2.0(1.4-2.8); vs.office workers(30%), 2.2(1.4-3.5)
Assemblers vs.referents shoulderpain last 7 days:3.4 (1.6-7.1)
Supraspinatus,infraspinatus, orbicipital tendinitisworking in the fishindustry: OR=3.03(2.5-7.2)
Shoulder tendinitisalone: PRR=3.5(2.0-5.9)
Assembly workcompared toreferent 5.0(2.2-11.0)
Shouldertenderness:assemblers vs.ref.: 1.1 (0.6-1.9);film rollers vs.ref.: 6.0(3.0-12.2);teachers vs. ref.:1.6 (0.7-3.3)Shoulderstiffness:reservationistsvs. ref: 2.5(1.1-5.6);assemblers vs.ref.: 3.7 (2.0-7.0);film rollers vs.ref.: 2.7 (1.5-4.9);teachers vs. ref.:2.1 (0.9-4.6)
Garment workersvs. hospitalemployees 2.2(1.0-4.9)
Õ
Duration ofemployment
NS Õ Sig. with durationof employment(p=0.03) foryounger workersbut not olderworkers
For age <45years, duration ofemploymentshowed dose-response withshoulder MSDs
<10 years: 9.6(2.8-33.0)10-19 years: 4.4(1.5-13.0) >20 years: 3.8(1.4-10.0)
Õ NS Õ
Physicalworkload
Õ Õ Õ Õ Õ Õ Õ Õ
Psychosocialfactors
Õ Õ Increasing workpace
Stress, worryfactors,tendenciestowards muscletension Sig.
Control,stimulation,psychosocialclimate, workstrain, socialsupport,psychosomaticsymptoms
Õ Õ Õ
Individual/other factorsconsidered
Õ Sports activities:4-9
Employmentstatus
Body height andweight: NS
Õ
Dose/response
Õ Õ Reported painincreased withincreasing workpace except forvery high paces
For age <45years, duration ofemployment andshoulder MSDs
Õ Õ Õ As VDT useincreased,shouldersymptomsincreased
C-23
See footnotes at end of table. (Continued)
Appendix C Table C-3. Summary table for evaluating work-related shoulder musculoskeletal disordersComponents
of study Sakakibara 1987 Sakakibara 1995 Schibye 1995 Stenlund 1992 Stenlund 1993 Sweeney 1994 Wells 1983
Study type CS CS Cohort CS CS CS CS
Participationrate $$70%
Y Y Y (But there was asignificant dropout ofwork as a sewingmachine operator inthose >35 years
Y Y N Y
Outcome S S and PE S S and PE S and PE S and PE S
Exposure Observation andmeasurement ofpostures
Observation and measurement ofrepresentativeworkers or job titles
Questionnaire Questionnaire,self-reports, weightof toolsjob title, duration ofemployment
Questionnaire andself-reports
Questionnaire Questionnaire, jobcategorization
Covariatesconsidered
Gender, age Õ Cohort study:followed sameworkers over time
Age, smoking,dexterity, ethnicity
Age, handedness,smoking, sportsactivities, duration ofemployment
Õ Age, number ofyears on job,quetelet ratio,previous workexperience,education
Investigatorsblinded
Õ NR NR Y Y Yes NR
Repetition forshoulder
Õ Combined Combined Õ Õ Combined Õ
Force Õ Õ Combined Combined Manual work:right side: 1.1(0.7-1.8) left side: 1.9(1.0-3.4)
Õ Combined
Extremeposture
Thinning out, baggingpears hadsignificantly moreforward shoulderflexion than baggingapples
Combined Combined Õ Õ Combined Combined
Vibration Õ Õ Õ Right side: 2.2(1.0-4.6)Left side: 3.1(1.4-6.9)
Right side 1.7(1.1-2.6) left side 1.8 (1.1-3.1)
Õ Õ
C-24
Appendix C Table C-3. Summary table for evaluating work-related shoulder musculoskeletal disordersComponents
of study Sakakibara 1987 Sakakibara 1995 Schibye 1995 Stenlund 1992 Stenlund 1993 Sweeney 1994 Wells 1983
Risk factors(combined)
Õ Pear baggerscompared to applebaggers: 1.7(1.1-2.9)Posture: NR, Sig.
Development ofshoulder symptomsnot related to workexposure butsignificant dropout ofworkers >35 years
Rockblasters vs.Foremen: 4.0(1.8-9.2)Bricklayerscompared toforemen:right side: 2.2(1.0-4.7)
Rock blasterscompared toforemen:right side: 1.7(0.7-4.0)left side: 3.3(1.2-9.3)
>20 hrs./ weeksigning: 2.5 (0.8-8.2)
Letter carriers withincreased shoulderload vs. postalclerks: 5.7 (2.1-17.8)
Physicalworkload
Õ Õ Õ Right side: 1.0(0.6-1.8)left side: 1.8(0.9-3.4)
Õ Õ
Psychosocialfactors
Õ Õ Õ Õ Õ Õ
Individual/other factorsconsidered
Õ Õ Õ Rock blasterscompared toforemen:Right side: 2.1(0.9-4.6)Left side: 4.0(1.8-9.2)
Õ Õ
Duration ofemployment
Õ Õ Õ Right side: 2.9(1.2-7.4)Left side: 2.5(1.0-5.9)
Õ NS
Dose/response
Õ Õ None for increasingpiece work inprevious years
As length ofemployment andexposure to vibrationand amount liftedincreased,osteoarthritis ofshoulder increased
High vibrationcompared to lowvibration
Õ Õ
Õ Not studied.EMGElectromyography.F Force.MSDMusculoskeletal disorders.N Considered (no).NR Not reported.NS Not statistically significant.R Repetition.
Ref. Referents.S Symptoms.Sig. Significant.ST Supraspinatus tendinitis.PE Physical examination.VDT Video display terminals.Y Considered (yes).
C-25
See footnotes at end of table. (Continued)
Appendix C Table C-4. Summary table for evaluating elbow musculoskeletal disordersComponents
of study Andersen 1993a Baron 1991 Bovenzi 1991 Burt 1990 Byström 1995 Chiang 1993 Dimberg 1987 Dimberg 1989
Study type CS CS CS CS CS CS CS CS
Participationrate $$70%
Y N NR Y Y Y Y Y
Outcome S S and PE S and PE S S and PE S and PE S and PE S and PE
Exposure Job categorizationby job duration
Observationvideotape,questionnaire
Observation,checklist, vibrationmeasured
Questionnaire Observation,videotapeanalysis, EMG offorearm muscleload collected,however, job titleused for analysis
Observationvideotapeanalysis, EMG
Observation jobanalysiscategorization
Observation, jobanalysis,categorization
Covariatesconsidered
Age, number ofchildren, smoking,socioeconomicstatus
Age, gender,hobbies, secondjobs, height,systemic disease
Age, ponderalindex
Age gender,years on job,psychosocialfactors
Gender, age >40years, psycho-social variablesand potentialconfoundersaddressed byFransson-Hall etal. 1995
Age, gender,metabolic disease
Gender, age,employeecategory, degreeof stress, tennisplaying
Ponderal index,gender, age, timein present job,height, weight,smoking, houseownership,racquet sports
Investigatorsblinded
Y Y Y Y Y toquestionnaireresponses, No to exposurestatus
Y NR NR
Repetition Combined Combined Õ 80% of timereported typingvs. 0-19% of time:2.8 (1.4-5.7)
Combined Combined Õ Õ
Force Combined Combined Õ Combined Combined Combined Combined Combined
Extremeposture
Combined Combined Õ Combined Combined Combined Combined Combined
C-26C-26
Appendix C Table C-4. Summary table for evaluating elbow musculoskeletal disordersComponents
of study Andersen 1993a Baron 1991 Bovenzi 1991 Burt 1990 Byström 1995 Chiang 1993 Dimberg 1987 Dimberg 1989
See footnotes at end of table. (Continued)
Vibration Õ Õ Vibration-exposedforestry workersvs. referents: 4.9(1.27-56.0)
Õ Õ Õ Õ p<0.01
Risk factors(combined)
Sewing machineoperators vs.general population1.7 (0.9-3.3)
Checkers vs.Noncheckers:2.3 (0.5-11.0)
Õ Reporterscompared toothers: 2.5(1.5-4.0)
Assembly lineworkers vs.population referents: 0.74(0.04-1.7)
Group III vs. GroupI (females): 1.44(0.3-5.6)High force/highrepetition vs. lowforce/lowrepetition: (males)6.75 (1.6-32.7)
Force and posture:NR, Sig.
Force andposture: NR, NS
Physicalworkload
Õ Õ Õ Õ Õ Õ Õ Õ
Psychosocialfactors
Õ Job satisfaction:NS
Õ Job control andsatisfaction: NS
Addressed byFransson-Hall etal. 1995
Õ Õ Mental stress atthe onset ofsymptoms:p<0.001
Individual/other factorsconsidered
Õ Õ Õ Sick leave morecommon amongstrenuous jobsthannonstrenuous jobs
Õ Õ “Work” the causein 35% of elbowproblems, mostwhite collar
Ponderal indexassociated withelbow symptoms
Duration ofemployment
Õ NS Õ Õ Õ Õ Õ Õ
Dose/response
Õ Õ Õ Y for time spenttyping
Õ Y for males withincreasingforce/repetition
Õ Õ
C-27C-27
See footnotes at end of table. (Continued)
Appendix C Table C-4. Summary table for evaluating elbow musculoskeletal disordersComponents
of study Fishbein 1988 Hales 1994 Hoekstra 1994 Hughes 1997 Kopf 1988 Kurppa 1991 Luopajärvi 1979 McCormack1990
Study type CS CS CS CS CS Cohort CS CS
Participationrate $$70%
N Y Y N N Y Y Y
Outcome S S and PE S S and PE S S and PE S and PE S and PE
Exposure Questionnaire Observation andQuestionnaire
Observation andQuestionnaire
Observation,checklist, formaljob analysis
Questionnaire, jobcategories
Observation,measurements,categorized by jobtitles
Observation,interviews,videotape analysis
Observation, jobcategories basedon manualexposure
Confoundersconsidered
Age, genderstratification,smoking status,alcohol, betablockers, otherdrugs
Age, gender,metabolicdisorder, hobbies,recreation
Age, gender,location, seniority
Age, smokingstatus, sports,hobbies, metabolicdiseases, acutetraumatic injuries,smoking
Age, jobsatisfaction, jobsecurity,moistness,vibration,Scheuerman’sDisease
Workers used astheir owncontrols; age,gender, durationof employment(with exceptions)
Age, gender,socialbackground,hobbies, amountof housework,length ofemployment
Gender, age,race, jobcategory, yearsof employment
Investigatorsblinded
NR Y Y NR NR NR Y NR
Repetition Combined Number of key-strokes per day:NS
Õ Õ Combined Combined Combined Combined
Force Õ Õ Õ Number of yearshandling >2.5kg/hand: NS
Combined Combined Combined Combined
Extremeposture
Combined Õ Non optimally adjusted chair: 4.0(1.2-13.1)
Wrist flexion/extension: NS;years of ulnardeviation: NS;years of forearmtwisting: 37(3.0-470.0)
Combined Combined Combined Õ
Vibration Õ Õ Õ Õ Õ Õ Õ Õ
C-28C-28
Appendix C Table C-4. Summary table for evaluating elbow musculoskeletal disordersComponents
of study Fishbein 1988 Hales 1994 Hoekstra 1994 Hughes 1997 Kopf 1988 Kurppa 1991 Luopajärvi 1979 McCormack1990
See footnotes at end of table. (Continued)
Risk factors(combined)
Female musicianscompared tomales: 2.04(1.6-2.6)
Õ Õ Õ Bricklayerscompared tomanual workers:2.8; Increasing jobdemands ORincreased from1.8 to 3.4
Workers instrenuous vs.nonstrenuousjobs: 6.7(3.3-13.9)
Assemblyworkers vs. shopassistants: for epicondylitis:2.7 (0.66-15.9)
Boarding vs. Non-office workers:0.5 (0.09-2.1)Knitting vs. Non-office workers:1.2 (0.5-3.4)
Physicalworkload
Õ Õ Õ Push/pull; liftcarry: NS
Sig Õ Õ Õ
Psychosocialfactors
Õ Fear ofreplacement bycomputers: 2.9(1.4-6.1); decisionmaking: 2.8(1.4-5.7); surge inworkload: 2.4 (1.2-5.0)
Jobdissatisfaction;exhaustion
Low decisionlatitude:3.5 (0.6-19.0)
Õ Õ Õ Õ
Individual/other factorsconsidered
Õ Race (non-white):2.4 (1.2-5.0)
Õ Age: 0.96(0.9, 1.2)
Õ Õ Õ Age, race Sig
Duration ofemployment
Õ Õ Õ Õ Õ Õ Õ Y, Sig, with <6months and>13 years
Dose/response
Õ Õ Õ Õ Yes, increasinglevels of jobdemands
Õ Õ No
C-29C-29
See footnotes at end of table. (Continued)
Appendix C Table C-4. Summary table for evaluating elbow musculoskeletal disordersComponents
of study Moore 1994 Ohlsson 1989 Punnett 1985 Ritz 1995 Roto 1984 Viikari-Juntura 1991b
Study type CS CS CS CS CS CS
Participationrate $$70%
Y NR Y for casesN for referents
NR Y Y
Outcome PE records S S S and PE S and PE S and PE
Exposure Observation, videotapeanalysis, job strain index
Questionnaire, jobcategorization
Questionnaire, jobcategory
Observation and recordreview and employeeinterviews
Job categorization Observation, jobanalysis; weights ofitems
Confoundersconsidered
Age, gender, duration ofemployment
Age, gender, duration ofemployment
Age, number of yearsemployed, nativelanguage
Age, age-squared, and“history of cervical spinesymptoms”. Having everplayed tennis, squash,other racquet sports,rowing, bowling,
Gender, other worktasks
Age, gender, duration ofemployment, leaving thecompany, changing thetask, being on sick leave
Investigatorsblinded
Y NR NR Y Y NR
Repetition Õ Combined Combined Õ Combined Combined
Force 5.5 (1.5-62) Õ Combined 10 years of highexposure to elbowstraining work: 1.7(1.0-2.7)
Combined Combined
Extremeposture
NR: was not found to besig. associated with“hazardous” jobs.
Combined Combined Õ Combined Õ
Vibration Õ Õ - Õ Õ Õ
Risk factors(combined)
Õ Non significant pain inlast year assembly vs.referents: 1.5 (0.6-3.4)
Work inability in last yearassembly vs. Referents:2.8 (0.8-10.7)
Garment workers vs.hospital employees: 2.4(1.2-4.2)
Õ Meatcutters vs.construction workers:6.4 (0.99-40.9), p=0.05
Strenuous vs.nonstrenuous: NS;difference: 0.88(0.27-2.8)
C-30C-30
Appendix C Table C-4. Summary table for evaluating elbow musculoskeletal disordersComponents
of study Moore 1994 Ohlsson 1989 Punnett 1985 Ritz 1995 Roto 1984 Viikari-Juntura 1991b
Physicalworkload
Õ Õ Õ Õ Õ Õ
Psychosocialfactors
Õ Õ Õ Õ Õ Õ
Individual/other factorsconsidered
Õ Not associated withwork pace
Age; Non-Englishspeakers sig. less likelyto report symptoms
Õ Õ Õ
Duration ofemployment
Õ No association Õ Increased duration ofcurrent exposureincreased risk ofepicondylitis
All with epicondylitis had>15 years of employment
Õ
Dose/response
Õ Õ Õ Õ Õ Õ
Õ Not studied.CS Cross-sectional.EMGElectromyography.F force.Hrs Hours.MSDMusculoskeletal disorders.N no.NR Not reported.NS Not statistically significant.PE Physical examination.R Repetition.Sig. Statistically significant.S Symptoms.Y Considered (yes).
C-31C-31
See footnotes at end of table. (Continued)
Appendix C Table C-5a. Summary table for evaluating work-related carpal tunnel syndrome (CTS)
Componentsof study Armstrong 1979 Barnhart 1991 Baron 1991 Bovenzi 1991 Bovenzi 1994 Cannon 1981 Chatterjee 1982 Chiang 1990
Study type CS CS CS CS CS Case control Case control CS
Participationrate $$70%
NR N N NR Y NR Y Y
Outcome S or surgery or PEfindings
PE and NCS S and PE S and PE S and PE Industry medicalrecords
S and PE and NCS S and PE and NCS
Exposure Observation,video, EMG
Observation Observation,videotapeanalysis, jobcategory
Observation,measurement
Observation,vibration,measurement
Medical records,job category
Observation,Measurement
Observation
Covariatesconsidered
Gender, metabolicor soft tissuedisease
Age, gender Age, gender,hobbies, pastemployment,years on job
Age, gender,weight
Age, smoking,alcohol, upper limbinjuries
Age, gender,race, weight,occupation, yearsemployed,workerscompensationstatus, history ofmetabolic disease,hormonal status,gynecologicsurgery
Age, gender Age, gender,length ofemployment,history ofmetabolic disease
Investigatorsblinded
N Y, but clothingmay have biasedobservation
Y Y N NR Y Y
Repetition Õ Repetitive skimanufacturing vs.others NCS: 1.9(1.0-3.6) PE+NCS:4.0 (1.0-15.8)S+PE+NCS: 1.6(0.8-3.2)
Combined Õ Õ 2.1 (0.7-5.3) Õ 1.87 (p<0.018)
C-32
Appendix C Table C-5a. Summary table for evaluating work-related carpal tunnel syndrome (CTS)
Componentsof study Armstrong 1979 Barnhart 1991 Baron 1991 Bovenzi 1991 Bovenzi 1994 Cannon 1981 Chatterjee 1982 Chiang 1990
See footnotes at end of table. (Continued)
Force Pinch F: 2.0(1.6-2.5)Hand F: 1.05(1.0-1.2)
Õ Combined Õ Õ Õ Õ Õ
Extremeposture
Pinch forceexertion: 2.0(1.6-2.5)
Õ Õ Õ Õ Õ Õ Õ
Vibration Õ Õ Õ 23.1 (noconfidence limits)p=0.002
Quarry drillers andstone carvers vs.polishers andmachineoperators: 3.4(1.4-8.3)
7.0 (3.0-170.0) 10.89(1.02-524.0)
Õ
Risk factors(combined)
Õ Õ Grocery checkersvs. other groceryworkers: 3.7(0.7-16.7)
Chain sawoperators vs.maintenanceworkers: 18.8(2.7-795)
Õ Õ Õ High cold/ highrepetition: 11.66(2.92-46.6)
Duration ofemployment
Õ Õ Y, Sig. Õ Õ 0.09 (0.8-10) Õ NS
Physicalworkload
Õ Õ Õ Õ Õ Õ Õ Õ
Psychosocialfactors
Õ Õ Õ Õ Õ Õ Õ Õ
Individual/other factorsconsidered
Õ Õ Õ Õ Õ Õ Õ Õ
Dose/response
Õ Õ Y, Sig. Õ Y, NS Õ Õ Õ
C-33
See footnotes at end of table. (Continued)
Appendix C Table C-5a. Summary table for evaluating work-related carpal tunnel syndrome (CTS)
Componentsof study Chiang 1993 deKrom 1990 English 1995 Färkkilä 1988 Feldman 1987 Franklin 1991 Koskimies 1990 Liss 1995
Study type CS CS Case control CS CS for symptomsand cohort forNCS
Retrospectivecohort
CS CS
Participationrate $$70%
Y Y Y NR Y Y NR No
Outcome S and PE S and PE and NCS S and PE S and PE and NCS S and in some PEand NCS
Records reviewof workers’compensationcases
S and PE and NCS Mailed survey
Exposure Observation,measurement,EMG
Questionnaire Questionnaire Interview Observation,biomechanicalanalysis,videotaping
Job title andindustry
Records ofvibration exposure
Mailed survey
Covariatesconsidered
Age, gender,metabolic disease,hormonal status
Age, gender,weight, slimmingcourses
Gender, height,weight
Alcohol Gender, pastmedical history,cigarette smoking,hobbies
(No analysesperformed to takethese intoaccount)
None NR Gender, age
Investigatorblinded
Y NR, participantsblinded
Y NR NR Y NR N
Repetition Repetitive fishprocessing vs.other: 1.1(0.7-1.8)
Õ CTS patients vs.other patients: 0.4(0.2-0.7)
Õ Combined Combined Õ Combined
Force Repetitive fishprocessing vs.other: 1.8(1.1-2.9)
Õ Õ Õ Combined Combined Õ Õ
Extremeposture
Õ Reported 20 to 40hrs./week Flexedwrist: 8.7(3.1-24.1)Extended 5.4(1.1-27.4)
CTS patients vs.other patients: 1.8(1.2-2.8)
Õ Õ Combined Õ Combined
C-34
Appendix C Table C-5a. Summary table for evaluating work-related carpal tunnel syndrome (CTS)
Componentsof study Chiang 1993 deKrom 1990 English 1995 Färkkilä 1988 Feldman 1987 Franklin 1991 Koskimies 1990 Liss 1995
See footnotes at end of table. (Continued)
Vibration Õ Õ Õ Vibration:p< 0.05
Õ Õ Vibrationexposure time andNCS Sig. Righthand: r=-0.27;p=0.01Left hand r=-0.12p=NS
Õ
Risk factors(combined)
Repetitive andforceful fishprocessing vs.others: 1.1(0.7-1.8)Female poultryworkers hi R/hi Fvs. low R F: 2.6(1.0-7.3)
Õ Õ Õ Year 2 vs. Year 1,numbness andtingling in fingers:2.26 (1.14-4.46)
Oyster and crabpackers vs.industry-widerates: 14.8(11.2-19.5)
Õ CTS symptoms,dental hygienistsvs. dentalassistants: 3.7(1.1-11.9)Responder toldthat they had CTS:5.2 (0.9-32.0)
Duration ofemployment
Y,<12 months; Nofor 12 to 60months and >60months
Õ Õ Õ Õ Õ Exposure time Sig. Õ
Physicalworkload
Y Õ Õ Õ Õ Õ Õ Õ
Psychosocialfactors
Õ Õ Õ Õ Õ Õ Õ Õ
Individual/other factorsconsidered
Õ Õ Õ Õ Õ Õ Õ Õ
Dose/response
Y, Sig. Y, Sig. Õ Õ Õ Õ Õ Õ
C-35
See footnotes at end of table. (Continued)
Appendix C Table C-5a. Summary table for evaluating work-related carpal tunnel syndrome (CTS)
Componentsof study Loslever 1993 Marras 1991 McCormack
1990
Morgenstern1991 Moore 1994 Nathan 1988 Nathan 1992a Nathan 1992b
Study type CS CS CS CS Retrospectivecohort
CS Cohort Longitudinal
Participationrate $$70%
Jobs selected dueto CTSoccurrence
NR Y Y Y NR N Y=JapaneseN=Overall
Outcome S Records andmedical records
S and PE S PE and NCS fromrecords
NCS S and NCS S and NCS
Exposure Observation;measurements,videotaping
Observation;measurements
Observation, jobtitle
Survey Observation,videotape,measurement
Observation Observation Questionnaire
Covariatesconsidered
Gender, age,years on the job,hand orientation
Age, gender,handedness, jobsatisfaction
Age, gender,race, jobcategory, years ofemployment
Age, gender,pregnancy status,work history jobtasks, use ofselected drugs,history of wristinjury
None Age, gender Age, gender, handdominance,duration ofemployment andindustry
Gender, handdominance,occupational handuse, duration ofemployment,industry, leisureexercise, heavylifting, keyboarduse, coffee, tea,alcohol
Investigatorblinded
N NR NR N Y NR NR NR
Repetition Õ Number of wristmovements: NS
Combined 1.88 (0.9-3.8) Combined Group II vs. Group1:1.0 (0.05-2.0)
Combined Found to be“protective”
Force Combined Grip forces threetimes as great inhigh-risk jobs
Combined Õ Combined Combined Combined
Extremeposture
Combined Radial/ulnar ROM:1.52 (1.1-2.1);Flexion/extensionROM: 1.3(1.0-1.7);Pronation/supination ROM: 1.2(0.9-1.6)
Õ Õ Combined Õ Õ Õ
C-36
Appendix C Table C-5a. Summary table for evaluating work-related carpal tunnel syndrome (CTS)
Componentsof study Loslever 1993 Marras 1991 McCormack
1990
Morgenstern1991 Moore 1994 Nathan 1988 Nathan 1992a Nathan 1992b
See footnotes at end of table. (Continued)
Vibration Õ Õ Õ Õ Õ Õ Õ Õ
Risk factors(combined)
High force withhigh flexion:r=0.62; high forceand highextension: r=0.29
Flexion/extensionvelocity: 3.8(1.5-9.6)Flexion/extensionacceleration: 6.1(1.7-22)
Boarding vs.non-office: 0.5(0.05-2.9)
Packing vs. Non-office 0.4(0.04-2.4)Sewing vs. Non-office 0.9(0.3-2.9)
Õ Meat processorsin hazardous vs.safe jobs: 2.8(0.2-36.7)
Group I vs. GroupIII: 1.7 (1.3-2.3)Group I vs. GroupV: 2.2 (1.3-3.3)
Group V vs.Group I: 1.0(0.5-2.2)Group IV vs.Group I: 1.4(0.9-2.1)Group III vs. GroupI: 1.5 (1.0-2.2)
Americans withsignificantlygreaterprevalence of CTScompared toJapanese
Duration ofemployment
Õ Sig. Prevalence higherin workers with<3 yearsemployment
>34 hrs./week:1.9 (1.1-3.1)>9 years: 1.7(1.0-3.2)
Õ Õ Õ Duration ofemployment foundto be protective
Physicalworkload
Õ Õ Õ Õ Õ Õ Õ Õ
Psychosocialfactors
Õ Job satisfaction:NS
Õ Õ Õ Õ Õ Õ
Individual/other factorsconsidered
Õ trunk depth: Sig. Õ Õ Õ Õ Age, handdominance sig.
Mean age, bodymass index andleisure exerciseSig., cigarettes Sig.
Dose/response
Õ Õ Õ Õ Õ Y, Sig. Õ Õ
C-37
See footnotes at end of table. (Continued)
Appendix C Table C-5a. Summary table for evaluating work-related carpal tunnel syndrome (CTS)
Componentsof study Osorio 1994 Punnett 1985 Schottland 1991 Silverstein 1987 Stetson 1993 Tanaka (In Press) Weislander 1989
Study type CS CS CS CS CS CS Case control
Participationrate $$70%
Y Y for cases; N forcomparison group
NR Y Y Y Y
Outcome S and PE, NCS S and PE NCS S and PE S and PE and NCS S S and PE and NCS
Exposure Job title, observation Observation,questionnaire
Job title Observation,videotape analysis, EMG
Observation,questionnaire, jobanalysis
Questionnaire Telephone interview
Covariatesconsidered
Age, gender, alcohol,medical history
Age, gender,hormonal status,native language,history of metabolicdisease
Age, gender Age, gender, plant,years on job
Age, height, skintemperature,dominant index fingercircumference
Age, gender, race,cigarettes, income,education, BMI
Age, gender, year ofoperation
Investigatorblinded
Y NR NR Y NR No No
Repetition Combined Combined Combined Repetition: 5.5 p<0.05 NS Õ 2.7 (1.3-5.4)
Force Combined Combined Combined Combined Y, Sig. combined Õ Õ
Extremeposture
Õ Õ Combined Ulnar deviation andpinching, elevatedbut NS
Combined (pinchgrip)
Bending/twisting ofthe wrist: 5.9(3.4-10.2)
Õ
Vibration Õ Õ Õ 5.3(no confidence limits)
Õ Vibration: 1.85(1.2-2.8)
Vibrating tool use 3.3(1.6-6.8)
Risk factors(combined)
NCS: 6.7 (0.8-52.9)Super-marketworkers, high vs.low exposuresymptoms: 8.3(2.6-26.4)
Force, repetition,posture: 2.7 (1.2-7.6)
Workers vs.applicants:females, right hand:2.86 (1.1-7.9);males, right hand:1.87 (0.6-9.8)
High force/highrepetition vs. lowforce/low repetition:15.5 (1.7-142.0)
Y, Sig. mediansensory amplitudesSig. smaller (p <0.01) and latencieslonger (p<0.05) withexposure to highpinch grip forces
Õ Õ
C-38
Appendix C Table C-5a. Summary table for evaluating work-related carpal tunnel syndrome (CTS)
Componentsof study Osorio 1994 Punnett 1985 Schottland 1991 Silverstein 1987 Stetson 1993 Tanaka (In Press) Weislander 1989
See footnotes at end of table. (Continued)
Duration ofemployment
Y NS Õ 0.9p>0.09
Õ Õ Õ
Physicalworkload
Y Õ Õ Õ Õ Õ Loads on wrist 1.8(1.0-3.5)
Psychosocialfactors
Õ Õ Õ Õ Õ Õ Õ
Individual/other factorsconsidered
Õ Õ Õ Õ Õ Female gender: 2.4(1.6-3.8); BMI $25:2.1 (1.4-3.1); whiterace: 4.2 (1.9-15.6)Cigarettes: 1.6(1-2.5); annualincome $$20,000: 1.5(1-2.4)
Õ
Dose/response
Y, Sig. Õ Õ Y, Sig. Õ Õ Õ
Õ Not studiedBMI Body Mass IndexCS Cross-sectionalCTSCarpal tunnel syndromeEMGElectromyographyF Forcehrs HoursNCSNerve conduction studiesNR Not reportedNS Not statistically significantPE Physical examinationR RepetitionSig. Statistically significantS SymptomsY Considered (yes)
C-39
See footnotes at end of table (Continued)
Appendix C Table C-5b. Summary table for evaluating work-related hand/wrist tendinitisComponents
of study Amano 1988 Armstrong1987a
Byström 1995 Kuorinka 1979 Kurppa 1991 Luopajärvi 1979 McCormack1990
Roto 1984
Study type CS CS CS CS Cohort CS CS CS
Participationrate $$70%
NR Y Y Y Y Y Y Y
Outcome S and PE S and PE S and PE S and PE S and PE S and PE S and PE S and PE
Exposure Job titles or self-reports
Observation, measurements,video analysis,EMG
Questionnaire,observation,measurements,videotapeanalysis, EMG
Records,observation,measurements, videotapeanalysis
Observation,measurements,video analysis.Reader referredto methods foundin previouspublications
Observation,measurements,video analysis
Observation, jobcategory
Job title
Covariatesconsidered
Age, gender Age, gender,years on job, andindustrial plant
Age, gender,psychosocialfactors(addressed byFransson-Hallet al. 1995)
Age, gender,body mass index,“muscle-tendon”syndrome
Age, gender Gender (onlyfemales in studygroups), age,hobbies,housework,medical conditions
Race, age, gender Rheumatoidarthritis
Investigators blinded
NR Y No NR NRNo=occupation ofsubjects
Y NR Y=occupationmeat processingNo=constructionforemen(referent)
Repetition Combined Combined Combined Combined Combined Combined Combined Combined
Force Combined Combined Combined Combined Combined Combined Combined Combined
Extremeposture
Combined Significantdifferencesbetween malesand females
Combined Combined Combined Combined Combined Õ
Vibration Õ Õ Õ Õ Õ Õ Õ Õ
C-40
Appendix C Table C-5b. Summary table for evaluating work-related hand/wrist tendinitisComponents
of study Amano 1988 Armstrong1987a
Byström 1995 Kuorinka 1979 Kurppa 1991 Luopajärvi 1979 McCormack1990
Roto 1984
Risk factors(combined)
Right index fingerflexor: 3.67(1.85-7.27)Left index fingerflexor: 6.17(2.72-13.97)
Comparisonbetween lowR/low F and highR/high F: 4.8 (0.6-39.7)5.5 (0.7-46.3)17.0 (2.3-126.2)
De Quervain’stendinitis among among autoassemblyworkers vs.generalpopulation: 2.5(1.00-6.23)
Scissor makersvs. shopassistants: 1.38(0.76-2.51)
Meat cuttercompared tooffice workers:risk ratio: 14.0(5.7-34.4);Meat packerscompared tooffice workers:risk ratio: 38.5(11.7-56.1);sausage makerscompared tooffice workers:risk ratio: 25.6(19.2-77.5)
Assembly lineworkers vs. shopassistants: 4.13(2.63-6.49)
Textile workerscompared to non-office workers:3.0 (1.4-6.4)Overall groupexposed: 1.75(0.9-3.39)
Meat cutters vs.constructionworkers: 3.09(1.43-6.67)
Physicalworkload
Õ Õ Õ Õ Õ Õ Õ Õ
Psychosocialfactors
Õ Analyzed byFransson-Hallet al. 1995
Õ Õ Õ Õ
Individual/other factorsconsidered
Õ Õ Õ Pieces handledover the years: anonsignificanttrend with increasing numberof pieces handled
Õ NS for age,hobbies, orhousework
Female gendersignificant fortendinitis atp=0.01;job categorysignificant atp=0.001
Rheumatoidarthritis found notto be aconfounder
Duration ofemployment
Õ Õ Õ Õ Õ No association Õ Õ
Dose/response
Õ With increasingcombination of Rand F
Õ Õ Õ Õ Õ Õ
Õ Not studied.CS Cross-sectionalEMG Electromyography.F Force.HAVSHand-arm vibration syndromeNR Not reported.
NS Not statistically significant.PE Physical examination.R Repetition.S Symptoms.Y Considered (yes).
C-41
See footnotes at end of table (Continued)
Appendix C Table 5c. Summary table for evaluating hand-arm vibration syndrome
Componentsof study Bovenzi 1988 Bovenzi 1994 Bovenzi 1995
Brubaker1983
Brubaker1987
Dimberg1991 Kivekäs 1994
Koskimies1992 Letz 1992
McKenna1993
Study type CS CS CS CS Cohort CS Cohort Cohort CS CS
Participationrate $$70%
NR Y Y Y N Y Y Y Y NR
Outcome S and PE; coldprovocation
S and PE S and PE;coldprovocation
S and PE;coldprovocation
S and PE;coldprovocation
S S and PE S and PE S S andPE;coldprovocation
Exposure Observation;measurements of thetool
Observation,interview,measurements of thetool
Questionnaire,observation,measurements of thetool
Question-naire data
Observation;measurements ofthe tool
Questionnaire
Questionnaire
Measurement of thetools
Questionnaire,measurements of thetool usedfrompreviousstudies
Questionnaire
Covariatesconsidered
Õ Age,smoking,alcoholconsumption, upperlimbinjuries;leisureactivities,systemicdiseases
Age,smoking,drinkinghabits,cardiovascular,neurologic,previousmusculoskeletal injuries,use ofmedicines
Smoking,age,height,weight
Age,gender,psychosocialscales
Õ Age Õ Age, race,smoking,alcohol,medicalconditions
Age,smoking,onlymalesstudied,thosewithinjury tothe neck,upperlimbsexcluded.
Investigators blinded
NR N Y NR NR NR Y NR No N
Repetition Õ Õ Õ Õ Õ Õ Õ Õ Õ Õ
Force Õ Õ Õ Õ Õ Õ Õ Õ Õ Õ
Extremeposture
Õ Õ Õ Õ Õ Õ Õ Õ Õ
C-42
Appendix C Table 5c. Summary table for evaluating hand-arm vibration syndrome
Componentsof study Bovenzi 1988 Bovenzi 1994 Bovenzi 1995
Brubaker1983
Brubaker1987
Dimberg1991 Kivekäs 1994
Koskimies1992 Letz 1992
McKenna1993
See footnotes at end of table (Continued)
Vibration Stonedrillers andcutters vs.quarry andmillworkers:6.06(2.0-19.6)
Stoneworkersvs.polishersandmachineoperators:9.33(4.9-17.8)
Forestryworkers and2.6% in ship-yardreferents:OR = 11.8(4.5-31.1)For workersonly usingantivibrationsaws: OR =6.2(2.3-17.1)For thoseusing non-antivibrationsaws: OR =32.3 (11.2-93)
NR 15% offellersreportednewsymptoms of VWFfrom 1979to 1985;28%increaseinprevalence of VWFin workersusingantivibration chain-saws
Vibratingtool usesig.Correlatedwith HAVSsymptomprevalance
Lumberjackes vs.referents:for 1978:3.4,(1.7-6.9)CumulativeincidenceHAVs(7-years)14.7% vs.2.3%: 6.5(2.4-17.5)
Decreaseinprevalencein forestworkersfrom 1972to 1990,attributed toreduction inweight ofsaws,increase invibrationfrequency,reduction inacceleration
Full-timevibrationworkers vs.referents:5.0(2.1-12.1)Full-timevibrationworkers vs.Controls:40.6(11-177)
Rivetersvs.referents:24 (3.1-510)
Risk factors(combined)
Õ Õ Õ Õ Õ Õ Õ Õ Õ Õ
Physicalworkload
Õ Õ Õ Õ Õ Õ Õ Õ Õ Õ
Psychosocialfactors
Õ Õ Õ Õ Õ Õ Õ Õ Õ Õ
Individual/other factorsconsidered
Õ See“Covariatesconsidered” above
See“Covariatesconsidered”above
Agesignificantly differentbetweencases andcontrols,height andweightwere not.
Õ Vibratingtool usesignificantlycorrelatedwith HAVSsymptomsprevalence
Õ Õ SmokingSig.
Õ
Duration ofemployment
Õ Õ Õ Õ Õ Õ Nodifferece inlumberjacks with <15years ofexposure,but thenincreasedwithduration ofexposure
Õ Õ Õ
Dose/response
Õ Õ Y, betweenincreasingvibrationexposureand“vibrationwhite finger”
Õ Õ IncreasedHAVS withduration ofexposure
Õ Sig. forreportedexposure tovibratorytools inworkerswith <17,000hours ofexposure
Õ
C-43
See footnotes at end of table (Continued)
Appendix C Table 5c. Summary table for evaluating hand-arm vibration syndrome
Componentsof study
Mirbod1992a, 1994
Mirbod1992b
Miyashita1992 Musson 1989 Nagata 1993 Nilsson 1989 Saito 1987 Shinev 1992 Starck 1990
Virokannas1995
Study type CS CS CS CS CS CS Cohort CS CS CS
Participationrate $$70%
NR NR NR N NR Y forplaters;NR for officeworkers
N NR NR NR
Outcome S S and PE
S S S and PE S and PE S andPE
S and PE S S and PE
Exposure Questionnaire;interviews, measurements of theworkersand thetools
Questionnaire;measurements of theworkersand thetools
Job Title Postalquestionnaire,measurement ofrepresentative tools
Based onyears ofexposuresinceemployment
Questionnaire,measurement of tool,exposuretime
Questionnaire
Measurement of tool
Measurement oftools
Interview
Covariatesconsidered
Age Õ Õ Age, height,weight,smoking,timepressure,workingposture
Age Age Follow-up ofcohort
Age,cigarettesmoking,industry,educationVDTtraining
N Age,duration ofemployment
Investigators blinded
NR N N NR N NR NR NR N NR
Repetition Õ Õ Õ Õ Õ Õ Õ Õ Õ Õ
Force Õ Õ Õ Õ Õ Õ Õ Õ Õ Õ
Extremeposture
Õ Õ Õ Õ Õ Õ Õ Õ Õ Õ
Vibration Male chainsawoperatorsvs.referents:3.77(2.1-6.8)
Symptomseveritypositivelycorrelatedwithexposureduration
MaleConstructionworkerscomparedto maleofficeworkers:0.5(0.1-11.8)
Exposureduration notrelated toHAVSsymptoms
For >20yearsvibrationexposure:7.1(2.5-19.9)
Officeworkerswith novibrationexposure toformerexposure:14 (5-38)Officeworkerswith noexposure:85 (15-486)
NR Percussive vibrationhad agreatereffect onmuscleand bonepathologythanconstanthigh-frequencyvibration
Highprevalence of HAVSamongworkersusingvibratingtools
NR
C-44
Appendix C Table 5c. Summary table for evaluating hand-arm vibration syndrome
Componentsof study
Mirbod1992a, 1994
Mirbod1992b
Miyashita1992 Musson 1989 Nagata 1993 Nilsson 1989 Saito 1987 Shinev 1992 Starck 1990
Virokannas1995
Risk factors(combined)
Õ Õ Õ Õ Õ Õ Õ Õ Õ Õ
Physicalworkload
Õ Õ Õ Õ Õ Õ Õ Õ Õ Õ
Psychosocialfactors
Õ Õ Õ Õ Õ Õ Õ Õ Õ Õ
Individual/other factorsconsidered
Õ Õ Õ Õ Õ Õ Age Sig.Correlated torecoveryratesfrom1978 to1983
Õ Poorcorrelationbetweenvibrationexposureand HAVSwhentools werehighlyimpulsive
Õ
Duration ofemployment
Õ Õ Õ Õ Õ Õ Õ Õ Õ Õ
Dose/response
Õ HAVSsymptomseveritypositivelycorrelatedwithexposureduration
Õ Õ Õ OR increased by11% for eachyear ofexposure
Õ Õ Õ Õ
Õ Not studied.CS Cross-sectional.CTSCarpal tunnel syndrome.EMGElectromyography.F Force.Hrs Hours.NCSNerve conduction studies.NR Not reported.NS Not statistically significant.OR Odds ratio.PE Physical examination.R Repetition.S Symptoms.Sig Statistically significant.VPT Vibration perception threshold.Y considered (yes).
C-45
See footnotes at end of table. (Continued)
Appendix C Table C-6. Summary table for evaluating back musculoskeletal disordersComponents
of study Åstrand 1987, 1988 Bergenudd 1988 Bigos 1991b Bongers 1988 Bongers 1990Boshuizen 1990a,
1990b
Study type 1987: CS; 1988: Cohort
Cohort Cohort Retrospective cohort CS CS Cohort
Participationrate $$ 70%
Y N N Y Y Y
Outcome S and PE S S Physical exam fromdisability records
S CS: SCohort: records
Exposure Questionnaire Questionnaire Questionnaire; For jobswith >19 workers: jobanalysis
Job title and records;vibration measurementsobtained but not used
Questionnaire; vibrationmeasurements
Questionnaire; vibrationmeasurements
Covariatesconsidered
Education level,psychosocial factors(including neuroticism)
Years of education,psychosocial factors
Medical history, previousepisodes of back pain,“individual” factors,psychosocial factors(from MMPI)
Nationality, shift-work,age, and calendar time
Age, height, weight,climate, bending forward,twisted postures andfeeling tense at work
Duration of exposure,age, height, smoking,awkward postures, andmental workload
Investigatorsblinded
N NR NR NR NR NR
Heavyphysical work
Combined Workers in moderate andheavy physical demandwork groups vs. lightphysical demand group:1.8 (1.2-2.7)
No association Õ Õ Õ
Lifting andforcefulmovements
Combined Õ Õ Õ Õ Õ
C-46
Appendix C Table C-6. Summary table for evaluating back musculoskeletal disordersComponents
of study Åstrand 1987, 1988 Bergenudd 1988 Bigos 1991b Bongers 1988 Bongers 1990Boshuizen 1990a,
1990b
See footnotes at end of table. (Continued)
Awkwardpostures
Õ Õ Õ Õ Õ Õ
Whole bodyvibration
Õ Õ Õ All back disorders: 1.32(0.84-2.1);Intervertebral discdisorders: 2.00 (1.1-3.7);Disc degeneration byyears of exposure: 5.7(for highest exposurecategory)
LBP in exposed vs.referents: 9.0 (4.9-16.4),Sciatica: 3.3 (1.3-8.5);LBP by total vibrationdose: ORs=12.0, 5.6,6.6, 39.5LBP by hours of flighttime per day: 5.6, 10.3,14.4;
LBP by vibration dosecategory: ORs=19.1,29.4, 28.0, 38.1;By vibration dose:ORs=1.80, 1.78, 2.8;years of exposure: 3.6(1.2-11)
Static workpostures
Õ Õ Õ Õ Õ Õ
Risk factors(combined)
Mill workers vs. clericalworkers: 2.3 p=0.002
Õ Õ Õ Õ Õ
Psychosocialfactors
Neuroticism and backpain: 2.8 (1.4-5.4)
Those with back painless satisfied withworking conditions; nodifference in socialsupport
MMPI: tend towardssomatic complaint ordenial of emotionaldistress and reportinginjury: 1.37 (1.1-1.7)
Õ Õ Õ
Individual/other factorsconsidered
Õ Õ Does not enjoy job tasksand reporting injury: 1.7(1.3-2.2)
Õ Õ Õ
Duration ofemployment
Duration of employmentand back pain: 1.2(1.0-1.5)
Õ Prior back pain andreporting injury: 1.7(1.2-2.5)
Õ Õ Õ
Dose/response
Õ Õ Õ Õ Õ Õ
C-47
See footnotes at end of table. (Continued)
Appendix C Table C-6. Summary table for evaluating back musculoskeletal disordersComponents
of study Boshuizen 1992 Bovenzi 1992 Bovenzi 1994 Burdorf 1990 Burdorf 1991 Burdorf 1993
Study type CS CS mail survey CS CS CS CS
Participationrate $$70%
Y Y Y N Y Y
Outcome S S S S S S
Exposure Questionnaire; vibrationmeasurements
Questionnaire,measurement of WBV
Questionnaire,measurement of vibrationlevels
Questionnaire,job title, and expertknowledge
Questionnaire, taskanalysis and OWAS
Questionnaire,measurements of WBV,Postures assessed withOWAS
Covariatesconsidered
Mental stress, yearslifting >10 kg and twistingspine, height, smoking,looking backwards,hours sitting
Age, awkward posture,duration of exposure,BMI, mental load,education, smoking,sport activities andprevious jobs at risk forback pain
Age, BMI, education,sport activity, car driving,marital status, mentalstress, climaticconditions, back trauma,and postural load (ortotal vibration dose)
Age, height, and weight Age, height, and weight Age, history of heavywork, exposure to WBV,work requiring prolongedsitting, cold, drafts,working under severepressure, jobsatisfaction, height,weight, duration of totalemployment
Investigatorsblinded
NR NR NR NR N NR
Heavyphysical work
Õ Õ Õ Heavy work: 4.02(0.76-21.2)
Heavy physical work sigin univariate but notmultivariate model
Õ
Lifting andforcefulmovements
Õ Õ Õ Frequent lifting: 5.21(1.10-25.5)
No association Õ
Awkwardpostures
Õ Õ Õ Õ Postural Index and LBP:1.23 p=0.04
Õ
Whole bodyvibration
Total vibration dose andback pain: 0.99(0.85-1.2); In youngerworkers: vibration inpast 5 years andlumbago, 3.1 (1.2-7.9)
Low back:Previous 12 monthsprevalence of LBP, busdrivers vs. controls: 2.57(1.5-4.4)Multivariate:LBP symptoms inprevious. 12 months: andtotal vibration dose:OR’s= 1.67, 3.46, 2.63
LBP in the past year:OR=2.39 (1.6-3.7)Postural load category:OR=4.56 (2.6-8.0) (forthe highest exposurecategory)
WBV: 0.66 (0.14-3.1) WBV and LBP, 3.1 p=0.001
Combined
C-48
Appendix C Table C-6. Summary table for evaluating back musculoskeletal disordersComponents
of study Boshuizen 1992 Bovenzi 1992 Bovenzi 1994 Burdorf 1990 Burdorf 1991 Burdorf 1993
See footnotes at end of table. (Continued)
Static workpostures
Õ Õ Õ For univariate analysis:sedentary postures incrance operators: 0.49(0.11-2.2)
Posture index based ontime spent in a workingposture with the back ina bent and/or twistedposition: 1.23 p=0.04
Õ
Risk factors(combined)
Õ Õ Õ Job title: 3.6 (1.2-10.6) Õ Crane operators vs.office workers: 3.29(1.52-7.12)Straddle-carrier driversvs. office workers: 2.5 (1.2-5.4)
Psychosocialfactors
Õ Õ Õ Õ Õ Õ
Individual/other factorsconsidered
Õ Õ Õ Õ Postural load, bending,and twisting are causalfactors.
Standing and sitting arenot found to be riskfactors.
Õ
Duration ofemployment
Õ Õ Õ Õ Õ Õ
Dose/response
Õ Univariate analysis, totalvibration dose:lifetime LBP symptoms:4.05 (1.8-9.3);12 months LBPsymptoms: 3.25(1.5-7.0).
Dose/response ofcombined effects to totalvibration dose andpostural load, highestcombination ofcategories: 4.58.
Õ Õ Õ
C-49
See footnotes at end of table. (Continued)
Appendix C Table C-6. Summary table for evaluating back musculoskeletal disordersComponents
of study Chaffin 1973 Clemmer 1991 Deyo 1989 Heliövaara 1991 Hildebrandt 1995 Hildebrandt 1996
Study type Cohort CS CS CS CS CS
Participationrate $$70%
NR Y NHANES-ll data Y Y Y, but varied from 60%to 80% by department
Outcome S Injury report Data base(LBP)
S and PE S S
Exposure Observation andmeasurement
Job title Data base(smoking, obesity,personal characteristics)
Questionnaire Questionnaire Questionnaire
Covariatesconsidered
Age, weight, stature,number of prior backepisodes, isometric liftingstrengths
Age, job, length ofemployment
Age, gender, smoking, obesity, exercise level,employment status
Age and gender Age and gender Age
Investigatorsblinded
NR NR N N N N
Heavyphysical work
Õ Roustabouts vs. controlroom operator: 4.3 (noconfidence limits)
Õ CombinedORs=1.9, 2.5
Heavy physical workvs. sedentary work: 1.2,p<0.05
Nonsedentary steelworkers vs. referents:No association
Lifting andforcefulmovements
Approx. 5 Õ Õ Õ Õ Õ
Awkwardpostures
Õ Õ Õ Õ Õ Õ
Whole bodyvibration
Õ Õ Õ Õ Õ Õ
Static workpostures
Õ Õ Õ Õ Õ Õ
C-50
Appendix C Table C-6. Summary table for evaluating back musculoskeletal disordersComponents
of study Chaffin 1973 Clemmer 1991 Deyo 1989 Heliövaara 1991 Hildebrandt 1995 Hildebrandt 1996
See footnotes at end of table. (Continued)
Risk factors(combined)
Lifting of loads inpositions which create aLifting Strength Rating $was consideredpotentially hazardous tosome people
Job was best predictorof lost time.
Õ LBP and physical stress:2.5 (1.4-4.7)
Õ NS, Reference group hadhigh exposure toadverse workingconditions
Psychosocialfactors
Õ Õ Ever smoked vs. LBP:1.13, Sig. 50 pack yearsvs. LBP: 1.47, Sig.Body mass index vs.LBP: 1.70, Sig.
Stress load index: 2.4(1.7-3.5)
Õ Õ
Individual/other factorsconsidered
Age, weight, and staturedid not correlate withincreased incidence ofLBP
75% of back strainsprecipitated by pushing,pulling, or lifting.
Õ Body mass index, alcohol, work-related driving,parity, height notassociated with LBP. Smoking sig in both olderand younger males, butonly older females.Prior traumatic injuryincreased risk of LBP:2.5 (1.9-3.3); andsciatica: 2.6 (2.1-3.1)
Rates of LBP:construction: 35%;truckers: 31%;plumbers: 31%
Õ
Duration ofemployment
Õ Õ Smoking risk increasessteadily with cumulativeexposure and withdegree of maximal dailyexposure.
There is a steadyincrease in LBP withincreasing obesity.
Õ Õ Õ
Dose-response
Õ Õ Õ Õ Õ Õ
C-51
See footnotes at end of table. (Continued)
Appendix C Table C-6. Summary table for evaluating back musculoskeletaldisordersComponents
of study Holmström 1992 Huang 1988 Johanning 1991 Johansson 1994 Kelsey 1975b Kelsey 1984 Knibbe 1996
Study type CS CS CS mail survey CS Case control Case control CS
Participationrate $$70%
Y Y N Y Y Y Y
Outcome S; (A sample had PEfor purposes ofvalidation)
S S S Medical records: Sand PE required
S and PE S
Exposure Postal questionnaire Ergonomicassessment includingNLE
Job title, measured WBV inexposed group butresults not presented
Questionnaire Questionnaire Interview andquestionnaire
Questionnaire
Covariatesconsidered
Daily traveling time,leisure activity, heightand weight
Age, height, length ofemployment,olecranon height,weight
Age, gender, jobtitle, employmentduration
Age and gender. Nonwork-related S couldhave an effectmasking result, if notidentified.
Age, gender Age, gender, medicalservice
Age
Investigatorsblinded
Y NR NR NR NR NR N
Heavyphysical work
Õ Õ Õ Blue collar workersvs. white collarworkers: noassociation
Õ Õ Õ
Lifting andforcefulmovements
One year prevalenceof BP and manualmaterials handling:1.3 (1.2-1.4);Lifting frequency: >1per 5 min vs.<1 per 5min: 1.12, p<0.001
The workers in thecenter with higherrates had greaterlifting compared tothe referent center:no risk estimate
Õ No association Lifting vs. herniation:0.94, p=0.10
Lifting >25 lb or more,without twisting thebody: 3.8 (0.7-20.1)
Registered nurses vsnursing aides:Unadjusted OR=1.2,p=0.04; afteradjusting for hrworked, aides hadhigher rate: 1.3
Awkwardpostures
Stooping andkneeling with severeLBP compared to nostooping: 2.6; incomparison to nokneeling: 3.5
More awkwardpostures found incenter A than B,p=0.05.
Õ Extreme workpostures sigassociated withoutcome in blue collarworkers
Combined Twisting withoutlifting: 3.0 (0.9-10.2)
Õ
Whole bodyvibration
Õ Õ WBV and sciaticapain: 3.9 (1.7-8.6)
Õ Combined Õ Õ
C-52
Appendix C Table C-6. Summary table for evaluating back musculoskeletaldisordersComponents
of study Holmström 1992 Huang 1988 Johanning 1991 Johansson 1994 Kelsey 1975b Kelsey 1984 Knibbe 1996
See footnotes at end of table. (Continued)
Static workpostures
No association Õ Õ Õ Sedentary work anddisc herniation forworkers 35 yearsand older: 2.4,p=0.01; for those <35 years, 0.81
Õ Õ
Risk factors(combined)
Õ Õ Õ Õ Time sitting, >35years old: 2.4p=0.01; More thanhalf time driving vs.herniation: 2.75,p=0.02;Truck driver vs.herniation: 4.67,Chi-sq.=5.88, p=0.02
Lifting >25 lb >5 timesper day, and twistingthe body half thetime: 3.1 (1.3-7.5);
Simultaneous liftingand twisting withstraight knees: 6.1(1.3-27.9)
Physically demandingwork vs. lifetime LBP,prevalence: 87%; 1-year LBP,prevalence: 67%; 1-week LBP,prevalence: 21%;Prevalence of sickleave due to backpain in previous 3months: 9.7%
Psychosocialfactors
High stress and LBP:1.6 (1.4-1.8);high anxiety: 1.3(1.1-1.4).
Õ Blue collar workerswere less satisfiedwith “influence onand control of work,supervisor climate,stimulus from workitself, and relationswith fellow workers
In blue-collarworkers, 10 of 15 psychosocial jobfactors sig; inwhite-collar workers,none of the fivepsychosocial factorssig
Õ Õ Õ
Individual/other factorsconsidered
Severe LBP relatedto smoking;construction taskssuch as brick laying,carpentry, etc. didnot affect LBP.
Õ Gastrointestinalproblems: subwaytrain operators vs.referents: 1.6(1.1-2.5)
Õ Õ Carrying >11.3 kg,5-25 per day: 2.1(1.0-4.3)
Carrying >11.3 kg ,>25/day: 2.7(1.2-5.8)
Õ
Duration ofemployment
Õ Õ Õ Õ Õ Õ Õ
Dose/response
Õ Õ Õ Õ Õ Õ Õ
C-53
See footnotes at end of table. (Continued)
Appendix C Table C-6. Summary table for evaluating back musculoskeletaldisordersComponents
of study Leigh 1989 Liles 1984 Magnusson 1996 Magora 1972, 1973 Marras 1993, 1995 Masset 1994 Partridge 1968
Study type CS Cohort CS CS CS CS CS
Participationrate $$70%
Y NR NR NR NR Y Y
Outcome S Records S S Records review S S and PE
Exposure Questionnaire(job title)
Observation, use ofrecords
Questionnaire,vibrationmeasurements
Observation,interview,questionnaire
Observation,measurements
Interview,self-reports
Questionnaire, job title
Covariatesconsidered
Gender, race,obesity, height, andrepetitious work
Õ Õ Õ Õ Gender (males only),age (all participantsyounger than 40).General healthstatus, social,demographic,psychologic factors
Age
Investigatorsblinded
NR N NR NR NR NR N
Heavyphysical work
Self reporting: “Jobrequires a lot ofphysical effort”: 1.5(1.0-2.2)
Õ Õ Õ Õ No association Combined
Lifting andforcefulmovements
Õ Injury rate for highestjob severity indexcategory vs lowest :4.5
Heavy lifting: 1.86(1.2-2.8)Frequent lifting: 1.55(1.01-2.39)
1973: Suddenmaximal efforts andLBP: 1.65 (1.3-2.1)
Combined Heavy efforts of theshoulder, 1.62,p<0.01
Õ
Awkwardpostures
Õ Õ Õ No association:highest rate of backpain found in the“rarely/never bend”category
Õ Univariate analysisshowed trunktorsions associatedwith LBP in steelworkers; noassociation seen inmultivariate
Õ
Whole bodyvibration
Õ Õ Bus and truck driverscompared toreferents: 1.8(1.2-2.8)
Bus driverscompared tobankers: 1.2(0.8-1.7)
Õ Vehicle driving: 1.2(p<0.001)
Õ
C-54
Appendix C Table C-6. Summary table for evaluating back musculoskeletaldisordersComponents
of study Leigh 1989 Liles 1984 Magnusson 1996 Magora 1972, 1973 Marras 1993, 1995 Masset 1994 Partridge 1968
See footnotes at end of table. (Continued)
Static workpostures
Õ Õ Õ No association Õ Seated posture: 1.5,p<0.09
Õ
Risk factors(combined)
High vs. low physicaldemands: 1.68(1.05-2.90)
Õ Driving: 1.79(1.16-2.75)Vibration plusfrequent lifting: 2.1(0.8-5.7)Vibration plus heavylifting: 2.06 (1.3-3.3)
Sudden maximalphysical efforts; prolonged sitting orstanding, inability tosit during the workingday, and poor liftingtechnique related toLBP
Max. load moment,max. lateral velocity,ave. twistingvelocity, liftingfrequency, and max.sagital trunk angle related to high-riskLBP groups:10.7(4.9-23.6)
Õ Rheumatic S:dockers vs. civilservants: 1.2(0.98-1.64);LBP: dockers vs. civilservants: NS
Psychosocialfactors
Õ Õ Õ Õ Õ Negative perceptionof the workenvironment: NS.
Õ
Individual/other factorsconsidered
Smoker vs.nonsmoker and LBP:1.48 (1.0-2.19)
Õ Õ Õ Maximum loadmoment: 73.65 Nmvs. 23.64 Nm: 5.17,(3.19-8.38);Sagittal meanvelocity: 11.74degrees/sec. vs.6.55 degrees/sec: 3.33(2.17-5.11);Max. weight: 104 Nvs. 37 N: 3.17(2.19-4.58)
Physical work load(no objectivemeasurement) andrepetition were NS. Final logistic modelincluded “whole setof variables fromgeneral health status,social, demographic,and psychologiccharacteristics.”
Õ
Duration ofemployment
Õ Õ Õ Õ Õ Õ Õ
Dose/response
Õ Õ Õ Õ Õ Õ Õ
C-55
See footnotes at end of table. (Continued)
Appendix C Table C-6. Summary table for evaluating back musculoskeletal disordersComponents
of study Punnett 1991 Riihimäki 1989a Riihimäki 1989bRiihimäki 1994;
Pietri-Taleb 1995 Ryden 1989 Schibye 1995 Skov 1996
Study type Case referent(retrospective)
CS mail survey CS Prospective Case control Cohort CS
Participationrate $$70%
Y Y Y Y Y Y N
Outcome S and PE S X-ray confirmed S Records S S
Exposure Observation andmeasurements,Videotape analysis
Job title andquestionnaire
Questionnaire andjob title
Postal questionnaire Work injury reportsand self-reports
Questionnaire Questionnaire,self-reports
Covariatesconsidered
Gender, age, lengthof employment,recreational activity,medical history, andmaximum weightlifted in study job
Age, previous backaccidents, awkwardpostures at work,and annual cardriving
Age, self-reportedback accidents, bodymass index, height,and smoking
Age, gender (onlymales were studied,previous history ofback accidents,mental distress,general state ofhealth, smoking,lifestyle factors,education
Age Subjects served astheir own controls
Age, gender, height,weight, smoking,work-relatedpsychosocialvariables, lifting,leisure time sportsactivities
Investigatorsblinded
Y NR Y NR NR NR NR
Heavyphysical work
Õ Combined Õ Õ Combined Õ Õ
Lifting andforcefulmovements
Lift 44.5 N: 2.16 (1.0-4.7)
Õ Õ Õ Õ Õ Õ
Awkwardpostures
Time in non-neutralpostures, mild orsevere bending: 8.09(1.4-44)
Sciatica and twistedor bent postures: 1.5(1.2-1.9)
Õ Association foundbetween twisted andbent postures withsciatica in univariate,but not multivariateanalysis
Õ Õ Õ
C-56
Appendix C Table C-6. Summary table for evaluating back musculoskeletal disordersComponents
of study Punnett 1991 Riihimäki 1989a Riihimäki 1989bRiihimäki 1994;
Pietri-Taleb 1995 Ryden 1989 Schibye 1995 Skov 1996
See footnotes at end of table. (Continued)
Whole bodyvibration
Õ Longshoremen andearthmoverscompared toreferents: 1.3(1.1-1.7)
Õ No association Õ Õ In Danishsalespeople, theannual drivingdistance for highestcategory: 2.8(1.5-5.1)
Static workpostures
Õ Õ Õ Õ Õ Õ Sedentary work(% of worktime):2.45 (1.2-4.9)
Risk factors(combined)
Time in non-neutralposture: 8.09(1.5-44.0)
Sciatic pain andmachine operators:1.3 (1.1-1.7)Sciatic pain andcarpenters: 1.0(0.8-1.3)
Concrete vs. paintingwork and disc spacenarrowing: 1.8(1.2-2.5);Spondylophytes: 1.6(1.2-2.3)
Machine operatorsvs. office workers:1.4 (0.99-1.87);carpenters vs. officeworkers: 1.5(1.1-2.1)
Job title or shiftsrequiring heaviestphysical efforts: 2.2(1.28-3.89)
No sig differences inback pain in garmentworkers versusother employmentgroup upon follow-up
Annual drivingdistance: 2.79(1.5-5.1)
Psychosocialfactors
Õ Õ Õ Monotonous work,problems withco-workers orsupervisors, andhigh paced workwere NS.
Õ Õ Õ
Individual /other factorsconsidered
Age: 0.96 (0.09-1.0)back injury: 2.37(1.3-4.3)
Õ Age and disc spacenarrowing: 6.5(1.7-26.0)
Spondylophytes:14.9 (2.3-95.0)
Physical exercise >1time per week vs. 1time per week: 1.26(1.0-1.6) Smokers vs.non-smokers: 1.29(0.98-1.7)Severe back painand later sciatica: 4.5(2.7-7.6)
Previous back injury:2.13 (1.07-4.24);Working day shift:2.23 (1.28-3.89);Self-reported LBP:1.25 (1.25-4.12);Self-reported slippeddisc: 6.20(2.64-14.57)
Of 82 workers withanother job in 1991,20% reported MSDsa s the reason forchange.
Õ
Duration ofemployment
Analysis controlledfor length ofemployment.
Õ Õ Õ Õ Sig Õ
Dose/response
A strong trend foundfor increasing lengthof exposure and riskof back disorders toboth mild and severetrunk flexion.
Dose/response isobserved for twistedor bent postures(see above)
Õ Õ Õ Õ Dose/response isobserved for annualdriving andsedentary work (seeabove)
C-57
See footnotes at end of table. (Continued)
Appendix C Table C-6. Summary table for evaluating back musculoskeletal disordersComponents
of study Skovron 1994 Svensson 1989 Toroptsova 1995 Undeutsch 1982 Videman 1984 Videman 1990 Walsh 1989
Study type CS CS(retrospective)
CS CS CS CS and lab study CS
Participationrate $$70%
Y Y Y NR Y NR Y
Outcome S S S; then S and PE S and PE (Clinicalorthopaedic examgiven to 134 of the366 subjects)
S X-ray confirmed S
Exposure Interview Questionnaire Interview Interview andquestionnaire
Postal questionnaire Questionnaire,Reports from familymembers
Postalquestionnaire
Covariatesconsidered
Age and gender Age, gender (onlyfemales studied),level of education,psychosocialfactors, workbreaks, demand onconcentration
Analysis did notcontrol forconfounders
Age, height, weight,nationality, years ofexperience intransport work
Age, gender (onlyfemales studied),menstruation,pregnancy, exercise
Age, gender (onlymale cadavers used)physical exercise,heaviness ofoccupation
Age, year of onsetof symptoms,gender
Investigatorsblinded
NR NR NR NR NR NR NR
Heavyphysicalwork
Õ No association Õ Õ Sig. difference inheavy occupationalworkload categoryamong ages 20-29year olds but notother age groups: 1.1
Heavy vs. mixedwork: 2.8 (0.3-23.7)
Heaviest workcategory: 12.1(1.4-107)
Õ
Lifting andforcefulmovements
Õ Lifetime incidence ofLBP and Lifting: 1.2, p<0.01 found inunivariate analysisbut not in multivariateanalysis
Frequent lifting andLBP: 1.43, p<0.05
Combined No association - nosig differencebetween qualifiednurses and nursingaides
Õ Lifting in jobs justprior to injury: 2.0(1.1-3.7)
Awkwardpostures
Õ LBP and bendingforward: 1.3, p<0.05in univariate; not sigin multivariateanalysis
Trunk flexion andLBP: 1.7 p<0.01
Õ Õ Õ Õ
C-58
Appendix C Table C-6. Summary table for evaluating back musculoskeletal disordersComponents
of study Skovron 1994 Svensson 1989 Toroptsova 1995 Undeutsch 1982 Videman 1984 Videman 1990 Walsh 1989
Whole bodyvibration
Õ Õ No association Õ Combined Õ Driving on job heldprior to symptomsin males: 1.7(1.0-2.9)
Static workpostures
Õ “Standing”associated with LBP:1.3 in univariateanalysis, not sig inmultivariate
No association Õ Õ Sedentary work anddisc degeneration:24.6 (1.5-409)
Sitting and LBP:females: 1.7(1.1-2.6)
Risk factors(combined)
Occupation: NS Õ Õ In workers withpresent S, theyoccurred mostfrequently whilelifting loads and whilein bended postures:no risk estimate
Õ Driving vs. Mixedwork: 2.3 (0.8-6.2)
Driving and LBP:males: 1.7 (1.0-2.9)
Psychosocialfactors
Work dissatisfaction:2.4, p=0.02
LBP and worry andfatigue at end ofwork day: p<0.0001
Dissatisfaction withwork tasks: p<0.05
Õ Õ Õ Õ Õ
Individual /other factorsconsidered
Female gender: 2.16, p=0.001;increasing age: 2.0, p=0.001
LBP and standing:p<0.01
NS for sitting,standing, walking, orrepetitive work
Current back Spositively correlatedwith height and age.
Õ Õ
Duration ofemployment
Õ Õ Õ Current back Spositively correlatedwith length ofexperience intransport work.
Õ Õ Õ
Dose/response
Õ Õ Õ Õ Õ Õ Õ
Õ Not studied.ADL Activities of daily living.CS Cross-sectional.F Force.Hrs Hours.LBP Low-back disorders.LBP Low-back pain.LBS Low-back symptoms.MMPI Minnesota Multiphasic Personality Inventory.MS Musculoskeletal.
N No.NHANESNational Health and Nutrition Examination Survey.NR Not reported.NS Not statistically significant.OWASOVAKO working posture analysis system.PE Physical examination.R Repetition.S Symptoms.Sig. Statistically significant.WBV Whole body vibration.
Y Considered (yes).
C-59