Occupational and Environmental Medicine 1997;54:90-95

METHODOLOGY Series editors: T C Aw, A Cockcroft, R McNamee

Diagnostics of hand-arm system disorders inworkers who use vibrating tools

Gosta Gemne

AbstractA hand-arm vibration syndrome occursin some workers who use hand heldvibrating tools. It is recognised to consistof white fingers, diffusely distributed fin-ger neuropathy, pain in the arm andhand, and a small excess risk ofosteoarthrosis from percussion to thewrist and elbow. Carpal tunnel syndromeis mainly due to ergonomic factors otherthan vibration, but certain factors relatedto vibration may contribute to its devel-opment. A decrease in muscle powerinduced by vibration, and excessive hear-ing deficit have been postulated. Theassessment of a disorder suspected ofbeing induced by vibration includesdeciding whether there is a disorder and,if so, whether the symptoms can becaused by vibration. To decide whetherthe symptoms can be caused by vibrationepidemiological documentation and path-ogenically reasonable theories must exist.A causal diagnosis finally requires an epi-demiological decision whether or not thefactual exposure has elicited the patient'ssymptoms. Epidemiological data on thequantitative association between vibra-tion and excessive risks of white fingersand diffusely distributed neuropathy areincomplete. The symptomatic diagnosisof white fingers is still mainly based onanamnestic information. Available labo-ratory tests are incapable of grading theseverity of individual cases. Recordingthe finger systolic blood pressure duringcold provocation is a method of sympto-matic diagnosis with reasonable levels ofspecificity, sensitivity, and predictivevalue. For diffusely distributed neuropa-thy these levels are lower than desired.Electrodiagnostic tests for carpal tunnelsyndrome have sufficient validity. Properexposure evaluation must be based on anappreciation ofthe character ofthe vibra-tion as well as effective duration andintermittency. If this is not taken intoaccount, the number of hours of exposureand intensity of vibration are likely to benon-commensurable variables, and thesimple product of them is a questionabledose measure. Separate models for riskevaluation of vascular and neurologicaldisorders related to work with differenttools and processes will have to be estab-lished. Ongoing research to obtain fur-

ther data on exposure-response relationsfor neurological disturbances begins toyield encouraging results.

(Occup Environ Med 1997;54:90-95)

Keywords: carpal tunnel syndrome; epidemiology;hand-arm vibration syndrome; risk evaluation models;vibration white fingers

Disorders suspected of being induced byvibration need to be assessed in three ways.Firstly, it must be found whether there isindeed a disorder. This is done on the basis ofclinical and laboratory findings compared withepidemiological knowledge about the normalvariation of the variables studied. Secondly, itmust be decided whether the symptoms couldbe caused by vibration. For this, there must bereasonable theories on the pathogenic mecha-nisms. Again, epidemiological documentationis necessary, which can be found in studies onthe occupational group to which the patientbelongs, concerning not only vibration butalso other factors in the work environment thatmay cause the symptoms.

Thirdly (only if the first two types of assess-ment are positive) it must be decided whetherthe factual exposure has been harmful enoughto elicit the patient's symptoms. This requiresan evaluation of the intensity and other char-acteristics of the vibration in a way that ismeaningful for the disorder in question.Unfortunately, the methods available for thesetasks have several shortcomings.

What disorders may be caused byvibration?There is no complete agreement as to whatdisorders may be caused by vibration fromhand held tools (hand-arm vibration).However, current opinion favours the follow-ing general picture. 1-2

HAND-ARM VIBRATION SYNDROMEThe symptoms that are possibly related tovibration are collectively referred to as thehand-arm vibration syndrome.

Disturbance offinger skin circulationDisturbance of the circulation in the skin offingers (elicited by exposure to cooling of thehand or general body) in the form of reducedblood flow occurs in the most exposed parts of

74 RAdmansgatan,S-113 60 Stockholm,SwedenG GemneCorrespondence to:Professor Gosta Gemne,74 Radmansgatan, S-1 13 60Stockholm, Sweden.Accepted 1 August 1996

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Diagnostics ofhand-arm system disorders in workers who use vibrating tools

the hand (vibration white finger (VWF); sec-ondary Raynaud's phenomenon due to vibra-tion). This disorder may be due to acombination of sympathetic hyperactivity anda lesion to structures and functions in the wallsof blood vessels in the skin.

Diffusely distributedfinger neuropathyThis disorder may be caused by damage tonerve fibres and receptors by direct mechani-cal influence of vibration or impeded bloodcirculation or both.

Pain in the arm and hand developing duringwork with low frequency toolsPain in and around joints and the often con-comitant restriction of movements may be dueto excessive strain caused by the loading ofmuscles and tendons, or by osteoarthrosis ofthe joints caused by shocks from percussivetools. Vibration may contribute to this disor-der by increasing muscle and joint load.

Carpal tunnel syndromeThere is less agreement on the causal relationbetween exposure to hand-arm vibration andcarpal tunnel syndrome. This disorder consistsof a typically nocturnal paraesthesia in thethree radial fingers and the radial half of thefourth finger with numbness and sometimespain. The symptoms arise from compressionof the median nerve as it passes to the handthrough the wrist. As the syndrome has alsobeen found among people who are notexposed to vibration but perform repetitive,forceful movements with or without a handheld tool, it is not specific to vibration. Theseergonomic factors, in most cases, seem to bethe main cause of carpal tunnel syndrome.4Some work with vibrating tools, however,requires stressful postures of the wrist and ahard grip on the tool handle. This may con-tribute to the development of carpal tunnelsyndrome by prolonging static work, increas-ing nerve compression, and eliciting harmfulischaemia of the nerve.

Other possible effects of vibrationA direct effect of vibration on muscles has alsobeen postulated to result in decreased musclepower.56 Finally, a hearing deficit that cannotbe ascribed to exposure to noise alone hasbeen described in workers exposed to vibra-tion of the hands or arms.7 10 It may be aneffect of enhanced sympathetic hyperactivity,perhaps particularly associated with impulsevibration, that harms cochlear cells.

METHODS OF ASSESSMENTWhite fingersThe assessment of the presence of white fin-gers is mainly based on the anamnestic infor-mation received from the patient. The typicalsymptom of vibration white finger is a coldinduced, patchy blanching of the skin of thefingers (Raynaud's phenomenon) due toobstruction of blood flow (vasospasm) to theskin of the fingers that have been mostexposed to vibration.' The attack is commonlytriggered by cooling of the fingers or, espe-

cially, the whole body in a way that is experi-enced as disagreeable. The blanching is con-nected with a reduction of skin sensitivity inthe affected fingers and usually lasts until thebody is properly warmed. It is sometimes fol-lowed, upon the return of the blood flow, by asensation of throbbing in the fingers.The available tests to ascertain whether

there is a Raynaud's phenomenon, unfortu-nately, are not entirely objective. Straight-forward immersion of the hand in cold waterin the laboratory to see if the phenomenon canbe provoked often fails in patients who indis-putedly have a history of white fingers. This,presumably, is due to the absence in the experi-mental conditions of some decisive factor orfactors. The results of temperature measure-ments made in this way often do not permit anunequivocal interpretation of the presence orabsence of obstruction to blood flow. With anegative test result-that is, if the mostexposed fingers do not blanch in the typicalpatchy way, or if the temperature of the skin ofthe finger is not abnormally reduced-theexistence of white finger cannot be excluded.As the results of skin temperature measure-

ments during simple cold water provocationseem to depend on unknown and partlyuncontrollable factors, this method has seriouslimitations for screening purposes. An attemptto reduce the shortcomings of cold provoca-tion tests has been made"12 by automatingand standardizing the recording of so calledchronothermograms and by the collection oflarge quantities of data from population sam-ples that may pass as normal values. Furtherpromising results can be expected from thisproject, when some epidemiological uncertain-ties have been resolved.

So far, the best way of making objective acold induced reduction of blood flow in theskin of the finger is the method of criticalopening pressure. It consists of recording thefinger systolic blood pressure during coldprovocation.13-15 A positive outcome in theform of a reduction of the blood pressure inthe skin of the finger (at 15'C finger coolingtemperature) by more than 40% of its originalvalue after correction for changes in the bloodpressure of the arm has been considered suit-able for the differentiation between absence orpresence of vasospasm.'6 17 The critical open-ing pressure method has been found to havelevels of specificity, sensitivity, and predictivevalue high enough to be of use for diagnosis ofsymptoms in individual people.1718 The limitfor abnormal reduction in blood pressure inthe skin of the fingers, however, depends onwhether general body cooling is used as well asfinger cooling, and on room temperature.'9This rather time consuming method requireswell established laboratory procedures andskilled personnel, which makes it less suitablefor the purpose of screening large occupationalgroups.The clinical and laboratory diagnostics of

vascular symptoms suspected of being inducedby hand-arm vibration2021 have been recentlyevaluated by an international panel.22 Thescreening methods available were scrutinised.

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It was concluded that a medical interview isstill the best method for diagnosing white fin-gers triggered by cold. None of the existingcooling tests are capable of grading the sever-

ity ofVWF in individual cases.

Neurological disturbancesDiffusely distributed neuropathy-Neurologicaldisturbances in the fingers may be demon-strated in many workers exposed to vibrationwith methods for assessing vibration and tem-perature perception thresholds.23 23 The sensi-tivity, specificity, and predictive values of testsfor diffusely distributed neuropathy, however,are all lower than required for use in screeningor for aetiological diagnosis,2627 and furtherresearch is urgently needed.The pathogenesis of diffusely distributed

neuropathy remains unclear. Direct mechani-cal influence of vibration may result in struc-tural and functional damage. Anatomicalchanges have been reported in animal nerves

after exposure to vibration, among themepineural oedema28 and certain reversible alter-ations of unmyelinated fibres.29 In the work on

unmyelinated fibres, a nerve more proximal tothe site of vibration, however, showed no

changes. Loss of myelinated nerve fibres and,among other changes, Schwann cell prolifera-tion have also been shown in biopsies of skin ofthe fingers directly exposed to vibration fromhand held tools.30 31 However, epidemiologicaldata on the prevalence of all these lesions inpeople exposed to vibration are lacking.

Carpal tunnel syndrome-The median nerve,

together with the nine finger flexor tendons,pass through the carpal tunnel in the wrist.2Compression of this nerve produces carpaltunnel syndrome, which typically presents as

nocturnal paraesthesia with numbness and,sometimes, pain. The main pathogenesis ofthis disorder may be repeated mechanicalinsult from the flexor tendons. In certain handpostures, the tendon movements reduce thetunnel width causing nerve compression, per-haps aggravated by flexor tendon synovitis.32 33

It has been suggested34 that exposure to vibra-tion may produce anatomical changes whichmake the nerve more susceptible to additionaltrauma from compression, the so called condi-tioning lesion phenomenon.With these possible mechanisms it is not

surprising that the occurrence of carpal tunnelsyndrome is increased in occupations thatinvolve manual labour with or without handheld tools, especially work involving repetitivewrist movements and strenuous work.435 Ameta-analysis of occupational groups withincreased prevalence of carpal tunnel syn-drome has indicated that physical work load,not vibration, is the main risk factor.4

Electrodiagnostic tests of sensory and motornerve conduction can identify carpal tunnelsyndrome reasonably well,27 but so far no stud-ies have been able to make an aetiological dis-tinction between exposure to vibration andwork with hand held tools.

Musculoskeletal disturbancesWork with hand held vibrating tools involves

several factors that may influence the muscles,tendons, and joints of the hand-arm system.Painful conditions in the wrist and elbowregion are therefore common in several occu-pational groups with considerable load on thehand-arm system. Percussive vibration fromchisel hammers also causes repeated shocks tothe wrist and elbow joints. In the long run, thismay damage the joint surfaces and causedegeneration, the sequelae of which are knownas osteoarthrosis. Accordingly, as described in areview of bone and joint disorders in workerswho use hand held vibrating tools,36 a smallbut detectable excessive occurrence of osteo-arthrosis of the elbow has been convincinglyshown among coal miners in the Ruhr districtwho use chisel hammers.

Vibration from percussive tools may con-tribute in other ways to locomotor distur-bances: the contraction that automaticallyoccurs in a muscle exposed to vibration, thetonic vibration reflex,3738 as well as a harmfulfeedback through several neural pathways,39increased muscle tension, and joint load.The diagnosis of osteoarthrotic conditions

rests upon radiography, but the causal connec-tion with vibration in individual cases can sel-dom be established. Among other things, thisis because these changes are fairly common inmiddle aged men. Restrictions of movementscan be objectively assessed, but pain (an aetio-logically multifactorial condition) cannot.

THE QUESTION OF CAUSALITYThe causal connection in a person between adisorder and exposure to vibration rests on thebasis of a probability evaluation. The probabil-ity is increased if epidemiological studies havebeen able to show an excessive risk for thatparticular disorder in the occupational groupto which the patient belongs (compared withpertinent subgroups of the general popula-tion). This, unfortunately, applies only towhite fingers and, partly, to diffusely distrib-uted neuropathy in the hands, and even so themagnitude of the causal relation is incom-pletely documented. An important reason forthis deficiency is the fact already mentionedthat the pathogenic mechanisms are largelyunknown.

If it is pathogenically and epidemiologicallyreasonable that the symptoms of a particularpatient may have been caused by vibration,one further decisive step is required to estab-lish causality. It consists of assessing in aquantitative way how and to what extent thispatient has been exposed to vibration, which isessentially a question of evaluating the dose ofexposure. No aetiological diagnosis is possiblewithout a reasonably certain knowledge aboutthe quantitative relation between the dose (orwhatever measure is used) and the response tovibration in terms of presence and severity ofthe symptoms in question. Although results ofepidemiological studies on some occupationalgroups have prompted attempts to establishdose-response relations,40A3 these have largelyfailed or have had limited validity.44A46 It isespecially troublesome that different tools andwork processes definitely seem to require sepa-

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rate models for risk evaluation. Also, in alllikelihood, there are different relations for vas-cular and neurological disorders.

If the concept of dose is used to evaluateexposure, attention must be paid to the follow-ing questions.

Effective exposure-Ideally, this is only thatpart of the vibration which actually reaches thetarget organ. However, it is often difficult toidentify the tissue within the hand-arm systemwhere the lesion is producing the symptoms.In any case, only that time each day should beconsidered when the tool is in close enoughcontact with the hand for substantial vibrationto be absorbed. This is most often consider-ably less than the estimation by the worker,and careful time studies are therefore a pre-requisite for a meaningful dose measure.

Duration-For how many days a week,weeks a year, and for how many years haseffective exposure to vibration occurred?

Internittency-Did the work contain breakssignificantly long enough to allow recoveryfrom the harmful influence of vibration to takeplace?

Vibration character-What was the characterof the vibration (frequency, percussive, ornon-percussive, etc)?A seemingly straightforward way of evaluat-

ing dose is to multiply the total number ofhours of effective exposure by a figure thattells something about vibration intensity-forinstance, 12 000 hours times the accelerationof, say, 10 m/s2. However, if intermittency isnot taken into account, these two variables arelikely to be non-commensurable and a dosemeasure determined in this way is thereforelikely to be misguiding.The time factor may influence exposure-

response relations in different ways. In a com-parison between predicted and observedoccurrence of white fingers among dockyardworkers,47 no particular model for time depen-dency was found to yield a good explanationfor the relation. The results did not confirmthat the frequency weighting or the timedependency as given in the current standardfor the measurement of vibration exposure,ISO 5349,49 are appropriate.The methods recommended in the current

standard are only partly supported by scien-tific observation,4'3 49 and no warning is giventhat the methods may require change withimproved knowledge49; amendments such aschanges in time dependency and frequencyweighting seem necessary.

There is as yet only sparse epidemiologicalevidence of the beneficial effect of intermit-tency in the vibration exposure, but simplephysiological deliberations tell us that thereshould be such an effect because of the chancefor recovery of organ function before perma-nent damage has been done. The ISO 5349,however, does not consider this idea.A disadvantage has been pointed out49 with

the use of energy equivalent magnitude, re-commended with the tacit assumption thatvariations in exposure to vibration during theworking day are unimportant. Without anychange in vibration magnitude, the same four

hour energy equivalent exposure may comefrom one continuous exposure or from acumulative exposure of the same total dura-tion produced by individual exposures thateach last a few seconds and are separated byrest periods. It is concluded that the potentialharmfulness may not be the same in the twoexposures.Some of the deficiences of the risk predic-

tion model in the annex A of ISO 5349, areepidemiological and statistical.44 They con-cern overestimation of risk caused by the useof latency as an effect variable, underestima-tion because a possible healthy worker effectwas ignored, and diagnostic uncertainties. Aswell as the fact that the effects of differentaxes of vibration and contact forces have notbeen taken into account in the construction ofthe standard itself,9' the accuracy and scien-tific background of the model can be ques-tioned on several other grounds.4446 Manyfactors contribute to the effects of vibration onthe hand, and it has been pointed out50 thatthe individual or combined effects of thesefactors are not easily discernible from areanalysis of average values contained in pub-lished data. The statistical techniques neededto identify the relations require access to theraw data for each exposed person.Predictions, furthermore, should not beexpected to be accurate because of the widevariation between subjects within the manyvariables, and the absence of standardisedmeans for combining (or averaging) the differ-ent exposure patterns of individual peoplewithin a group.

In summary, it is clear that it is not possibleto specify the accuracy of the risk predictionmodel discussed here,5' and that separatemodels will have to be established52 for vascu-lar and neurological disorders in work withdifferent tools and work processes.

Ongoing studies on exposure-responserelations-There are encouraging studiesgoing on that may advance our knowledge ofthe all important relation between occurrenceor severity of neurological symptoms and theexposure to vibration.

In a study on neurological disturbances inthe hands of workers who use grinders andchipping hammers,53 the frequency of peoplewithout symptoms was found to decrease withincreasing cumulative exposure to vibration.In the group with the strongest exposure, 12%of the workers had severe symptoms of dif-fusely distributed neuropathy with an oddsratio of 6-4 (95% confidence interval 1-9 to21) when non-exposed workers were used asreference.

In a follow up study on the same cohort,54vibrotactile perception thresholds at frequen-cies between 8 and 500 Hz were measured.The result did not show a clear relationbetween exposure to vibration and individualvibrotactile deficiency, and it was not possibleto establish an exposure-response relation onthe basis of the present results alone.However, a fourfold increase in the relativerisk for deteriorated vibrotactile sensitivitywas found at frequencies above 40 Hz, when

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the group with greatest exposure was com-pared with non-exposed workers.

In an epidemiological study of stonework-ers,55 symptoms of VWF were found to bestrongly related to exposure to vibration, and amonotonic exposure-response relation couldbe shown. Although caution was expressedthat the findings were based on a cross sec-tional study, a relatively simple relation wassuggested. Its time dependency is such that, ifvibration magnitude were doubled, a halvingof the years of exposure would be required toproduce the same prevalence.

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51 Anonymous. The quantitative relationships between expo-sure and disturbances induced by hand-arm vibration-astatement. In: Gemne G, Brammer AJ, Hagberg M,Lundstrom R, Nilsson T, eds. Proceedings of the StockholmWorkshop 94. Hand-arm vibration syndrome: diagnosticsand quantitative relationships to exposure. NIOH, Solna,Sweden: Arbete och Halsa 1995;5:199.

52 Report from discussions in a working group. In: Gemne G,Brammer AJ, Hagberg M, Lundstrom R, Nilsson T, eds.Proceedings of the Stockholm Workshop 94. Hand-arm vibra-tion syndrome: diagnostics and quantitative relationships toexposure. NIOH, Solna, Sweden: Arbete och Halsa1995;5:195-8.

53 Lundstrom R. Burstrom L, Hagberg M, Nilsson T. Theoccurrence of sensorineural disorders and their relation-ship to vibration exposure. In: Gemne G, Brammer AJ,Hagberg M, Lundstrom R, Nilsson T, eds. Proceedings ofthe Stockholm Workshop 94. Hand-arm vibration syndrome:diagnostics and quantitative relationships to exposure. NIOH,Solna, Sweden: Arbete och Halsa 1995;5:47-58.

54 Lundstrom R, Nilsson T, Burstrom L, Hagberg M. Vibro-tactile perception sensitivity and its relation to hand-armvibration exposure. Centr Eur J Public Health 1996;3(suppl):62-5.

55 Bovenzi M. Relationship between vibration exposure andthe occurrence of VWF among stoneworkers. In: GemneG, Brammer AJ, Hagberg M, Lundstrom R, Nilsson T,eds. Proceedings of the Stockholm Workshop 94. Hand-armvibration syndrome: diagnostics and quantitative relationshipsto exposure. NIOH, Solna, Sweden: Arbete och Halsa1995;5:1-10.

Occupational and Environmental Medicine and theelectronic age

OEM has an Email address which is100632.3615@compuserve.com. We wel-come contact by Email, including letters tothe editor. Some of our reviewers alreadysend us their reports by Email, helping tospeed up the peer review process.We are moving towards electronic pub-

lishing and for some months now we havebeen asking authors to send us their revisedpapers on disk as well as a hard copy. I amdelighted to report that nearly all our

authors are managing to comply with thisrequest. Oddly enough, the few authorswho have not sent us a disk version of theirrevised papers have been almost exclusivelyfrom the United Kingdom. I would beinterested in suggestions for why this mightbe. Perhaps United Kingdom basedauthors read our correspondence andinstructions less assiduously? Watch forrevised Instructions to Authors.

The Editor

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