evaluation of occupational knee-joint stress using liquid crystal thermography: a case study

7/29/2019 Evaluation of occupational knee-joint stress using liquid crystal thermography: a case study

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Applied Ergonomics 1994 25(2) 111-115

E v a l u a t io n o f o c c u p a t io n a l k n e e - j o i n t s t re ssu s i n g l i q u i d c r y s t a l t h e r m o g r a p h y : a c a s es t u d yDaniel J. H abes*, A mit Bhattacharya' and Monica Milliron** U S D e p a r t m e n t o f H e al th a n d H u m a n S e rv i ce s , C e n t e r s f o r D i se a s e C o n t r o l a n d P r e v e n t i o n ,Na t iona l I n s t i t u t e f o r Oc c upa t iona l S a f ety a nd He a l th , D iv i s ion o f B iom e d ic a l a nd B e h a v io r a lSc ience , C inc inna t i , OH 45226, USA'Un ive r si t y o f C inc inna t i M e d ic a l S c hoo l , B iom e c ha n ic s - E r gono m ic s La b o r a to r y , C inc inna t i ,OH 45267- -0056, U SA* N ow a t C o n v e rs e , I n c ., O n e F o r d h a m R o a d , N o r t h R e a d i n g , M A 0 1 8 6 4- 2 68 0 , U S AT h i s p a p e r d e s c r i b es a m e t h o d t o d e t e c t k n e e s t re s s u s i n g li q u id c r y st a l t h e r m o g r a p h ya n d p r e s e n t s t h e r e s u lt s o f a ca s e s t u d y i n w h i c h t h e s y s t e m w a s a p p l i e d t o t w o c a r p e ti n s ta l le r s. T h e m e t h o d i n v o l v e s p l a c i n g h e a t - s e n s i t i v e s h e e t s o f f i l m o n t h e k n e e s o fw o r k e r s a t v ar i o us i nt e rv a l s d u r i n g t h e w o r k d a y . T h e t h e r m o g r a p h i c s h e e t s r e a c t t ov a r ia t io n s in h e a t b y c h a n g i n g c o l o u r . T h e m e a s u r e m e n t s a r e t a k e n w i t h t h e w o r k e r ' sk n e e p o s i t i o n e d in a n i l l u m i n a t e d , e n c l o s e d b o x . O n c e t h e p a t c h s t ab i li z es , t h ee x h i b it e d co l o u r s a r e r e c o r d e d w i t h a n 8 m m v i d e o c a m e r a . T h e c o l o u r p a t t e r n ,r a n g in g f ro m b r o w n t o b l u e , p r o v i d e s a t h e r m a l r e c o r d o f w h a t i s b e l i e v e d t o b e k n e es t re s s r e s u l t in g f r o m i n s t a l li n g c a r p e t . T h e t h e r m o g r a p h i c r e c o r d s a r e s t o r e d i nc o m p u t e r m e m o r y f o r s u b s e q u e n t a na ly s is u si n g a n A T & T T A R G A 1 6 v i d e o b o a r d .C u s t o m s o f tw a r e a ll o w s c o m p u t a t i o n o f t h e a r e a o f e a c h d i s ti n c t e o l o u r p a t t e r n a s ap e r c e n t a g e o f to t a l p a t c h s iz e . T h e s e r e c o r d s p r o v i d e a c h a r a c t e ri z a t i o n o f k n e er e s p o n s e ( i n fl a m m a t i o n ) re s u l t in g f r o m t h e b i o m e c h a n i c a l l o a d s u s t a i n e d b y t h e k n e ed u r i n g t h e c a r p e t i n s t a l l a ti o n t a s k .K e y w o r d s : c a r p e t i ns ta ll er s , l i q u i d c r y s t a l t h e r m o g r a p h y , b i o m e c h a n i c a l l o a d , k n e e - j o i n t s tr e s sIntroduct ion

Ava i l a b l e m or b id i ty da t a i nd i c a t e t ha t c a r pe t i n -s t a ll e rs , who r e p r e se n t 0 . 06% o f t he U S w or k f o r c e , fi l e6 . 2% o f a ll wor ke r s ' c om pe nsa t ion c l a im s f o r t r a um a t i ckne e in ju r y , a r a t e ove r 100 t im e s t ha t e xpe c t e d , a ndthe h ighe s t r a t e o f a ny oc c u pa t ion r e po r t i ng suc h c l a im s( NI O S H , 1990 ). Th i s oc c u pa t ion is unusua l i n t ha tb iom e c ha n ic a l s tr e s s is im pos e d on th e l ow e r e x t r e m i tyth r ough kne e l ing a nd , a dd i t i ona l ly , by u s ing the kne eto s t r i ke a t oo l t ha t s t r e t c he s c a r pe t ( B ha t t a c ha r ya e t a l ,1985 ; Thu n e t a l , 1987).

M e th ods f o r a s se s s ing wo r ke r e xpos u r e t o r e pe t i t ivekne e s t r e s s a r e ne e de d a s a f i rs t s t e p t owa r ds r e duc ingthe i nc ide nc e o f kne e d i so r de r s a m ong c a r pe t i n s t a l le r s .The goa l o f t h i s s tudy wa s t o de ve lop a wor ks i t e' d o s i m e t e r ' t o m o n i t o r w o r k e r e x p o s u r e t o r e p e ti t iv eM e n t i o n o f c o m p a n y n a m e s o r p r o d u c t s d o e s n o t c o n s t it u teen d o rsemen t b y t h e N a t i o n a l In s t i t u t e fo r O ccu p a t i o n a l Sa fe t y an dH e a l t h .

k n e e t r a u m a . T h i s d o s i m e t e r c o ul d b e u s e d t o w a r n o rs igna l wo r ke r s t o s top o r m od i f y t he i r wo r k pa t t e r n sb e f o r e i n j u r y t o t h e k n e e o c c u r r e d . T o d e v e l o p a ne f f e c tive wo r k m od i f i c a t i on s tr a t e gy , howe ve r , t her e l a t i o n s h i p b e t w e e n t h e b i o m e c h a n i c a l l o a d o n t h ekne e ( dose ) a n d phys io log ic a l r e a c t ion ( r e sponse ) m us tf i r s t be de t e r m ine d .

Th e pu r po se o f t h i s pa pe r i s t o de sc r ibe a nd i l l u s t ra t ethe r e spon se po r t i on o f suc h a dos im e te r : t he de ve lop -m e n t o f a t he r m ogr a ph ic - ba se d sys t e m f o r qua n t i f y ingpo te n t i a l t r a um a - induc e d in f l a m m a to r y r e a c t ions .M a t e r i a ls a n d m e t h o d s

T h e r m o g r a p h y i s a t e c h n i q u e f o r m e a s u r i n g t h ev a r i at i o n s in h e a t e m i t t e d f r o m t h e b o d y . U n l i k e o t h e re va lua t ive m e thods , suc h a s X- r a ys , t he r m ogr a phyis non- invas ive , pa in less , sa fe , and non- ioniz ing .D e p e n d i n g o n t h e a p p l i c a t i o n , a t h e r m o g r a m c a nind ic a t e a n inc r e a se o r de c r e a se i n body he a t . Them e thod ha s be e n u se d by c l i n i c i a ns t o de t e c t m usc l e

Appl ied Ergonomics 1994 Volume 25 Num ber 2 0 0 0 3 - 6 8 7 0 / 9 4 1 0 21 1 1- -0 5 ~ ) 1 9 94 Bu t t e rw o r t h -H e i n em an n L t d 111


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Evaluation of occupational knee-joint stress: D.J. H abes et altissue response to back pain, to assess nerve rootcompression syndromes of the upper and lower extrem-ities, and to evaluate soft tissue injuries (Dribbon,1983; Pochaczevsky, 1983; Herrick and Herri ck, 1987).

We considered thermography to be a suitable measurefor evaluating the effects of knee stress because of itsconvenience and simplicity, particularly in a fieldsetting. Knee stress among carpet layers arises from therepeated contact and impact forces to the knee thattake place during the installation process. Such mechan-ical stress can result in inflammation and increasedjoint heat due to increased blood flow.

For this application, thermograms were obtainedusing flexible liquid crystal sheets. These elastic polym ersheets are embedd ed with cholesterol derivatives whichselectively reflect polarized light in a narrow region ofwavelengths. The result is a display of colours rangingfrom brown (coldest) to blue (hottest), depending onthe temperature of the contact area. An individualthermographic sheet displays all colours within a rangeof 3 or 4 C. In order to perform the knee temp eratur eassessments described in this paper, a collection ofliquid crystal sheets enabling measurements from 22 Cto 42 C was assembled.M e a s u r e m e n t p r o c e du r eThe intent of the thermographic measures was toshow a progression of thermal responses due tophysical activity; therefore several recordings wererequired at convenient intervals during the workday. Inorder to document the rise in knee temperaturesresulting from the cumulative biomechanical load tothe knee while installing carpet, five recordings weremade at the following times: before work began, atmid-morning and mid-afternoon breaks, just be fore thelunch break, and at the end of the workday.

All thermography measurements were conducted ina draught-free room. To minimize the effects of anydifference between the ambient temperature of thework area and that of the measuring room, each kneewas swabbed with a cool, wet cloth. To ensure that nofever existed, the worker's body temperature wasmeasured with a Feverscan forehead thermometer.When the skin was dry, the worker sat on an adjustablechair and placed his right knee into the opening of abox. The box was a 76 cm x 76 cm table with blackmaterial wrapped around it to exclude ambient light.Two 20 W incandescent/ fluorescent light bars (SylvaniaModel F20T12/1F) were mounted inside the box forillumination. This light arrangement combined the fullcolour-spectrum display capabilities of incandescentlight with th e low-temperature illumination propertiesof fluorescent light. Before taking the measure, alloverhead lights were turned off.

To begin the thermography assessment a liquidcrystal sheet was selected and placed on the suprapatellarportion of the knee (above the kneecap). If the patch ofmaterial remained dark, a sheet with a lower temperaturerange was selected. Similarly, if the patch immediatelyturned green o r blue, a sheet with a higher temperat urerange was used. When the appropriate liquid crystalsheet was identified, it was placed on the knee and left

there until the colour stabilized. This usually tookabout 15 s. Small weights were attached to each cornerof the sheet to ensure good contact with the skin. Theinitial patch in our pilot study was one that beganchanging colours at 25.6 C. The highest knee temperat-ure detected was 30.1 C; thus all measurements werewell within the range of thermography sheets at ourdisposal. When the patch ceased changing colour, theknee colour patterns were recorded for about 15 s usinga video camera (Sony CCD V8AF) mo unted inside thebox, which was located 61 cm from the liquid crystalsheet (Figure 1).

Following the initial measurement, the worker placedhis heel on a footrest moun ted at the rear of the box toobtain a temperature profile of the ground contact(prepatellar) portion of the knee (below the kneecap).The same prgeedure with the liquid crystal patch andvideo camer~t was followed. When all measurementswere completed, the worker removed his leg from thebox. Af ter similar procedures and measu res had beenrepeated for the left leg, the workers proceeded withtheir normal work routine. T he measurements for bothknees were completed in less than 10 min.D a t a - a n a ly s i s p r o c e d u r e sThe videotapes of the liquid crystal sheets werereturned to the laboratory for analysis, An AT&TTruevision Advanced Raster Graphics Adapter(TARGA) 16 video capture-and-display board wasused to digitize the taped images in real time. Before

Ta x . h e i g h t62 crn

6 9 c mFigure t The table and video camera arrangement used tocollect the thermograms. During a measurement, he camera,viewing window and open side of the box are covered withblack cloth to screen out ambient light

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s a v i n g t h e r e c o r d s i n c o m p u t e r m e m o r y , a p r e v i o u s l ysaved f i l e o f a co lour -ca l i b ra t i on cha r t was d i sp l ayed o nt h e c o m p u t e r m o n i t o r so t h a t t h e c o l o u r s c o u l d b ea d j u s t e d t o m a t c h t h o s e o f t h e s a m e c h a r t h e l d i n t h ea n a l y s t' s h a n d . C o m m e r c i al s o f t w a r e , T r u e v i s i o n I m a g eP r o c e s s i n g S o f t w a r e ( T I P S ) , a l l o w e d t h i s c o l o u rca l i b ra t i on t o be made ea s i l y and accura t e ly .A c u s t o m p r o g r a m b y S ci en ti fi c C o m p u t e r T e c h n o -logy , Inc . (C inc inna t i , Oh io ) enab l ed t he s i z e o fd i f f e ren t co lour a rea s on each l i qu id c rys t a l pa t ch t o bec o m p u t e d a s a p e r c e n t a g e o f t o t a l p a t c h a r e a . I n o r d e rf o r t h e p r o g r a m t o m a k e t h e s e c a l c u la t i o n s , t h e a n a l y s tm u s t o u t l i n e t h e a r e a o f e a c h c o l o u r p a t t e r n a n d t h ep e r i m e t e r o f t h e p a t c h w i th a m o u s e . T h e t h e r m o g r a mi s c o m p l e t e d b y a s s ig n in g t e m p e r a t u r e s t o t h e o u t l i n e dc o l o u r a r e a s u s i n g a r e f e r e n c e c h a r t s u p p l i e d b y t h et h e r m o g r a p h i c p a t c h m a n u f a c t u r e r . T h e s e q u e n c e o fa n a l y s e s i s s h o w n i n F i g u r e 2 . W i t h t h i s m e t h o d , t h et e m p e r a t u r e p r o f i l e o f e a c h k n e e w a s c a p t u r e d , c o n -s i s t i ng o f t he r e l a t i ve a rea s o f t he poss ib l e co lour s fo r

e a c h t h e r m o g r a p h y p a t c h .In t ra - a n d i n t er - ra t er re l i a b i l i t y o f t h e me th o dT h e r e p e a ta b i li ty o f th e m e t h o d o f c o m p u t i n g t h es i z e o f t h e v a r i o u s c o l o u r a r e a s w a s c o n s i d e r e d . A ne x p e r i en c e d m e m b e r o f o u r l a b o r a t o r y te a m , w h o u s e dt h e c o m p u t e r m e t h o d t o a n al y s e m o r e t h a n 6 0 t h e r m o -g r a p h y p a t c h e s f o r a d i f f e r e n t p r o j e c t , r e - a n a l y s e d 1 5r a n d o m l y s e l e c t e d p a t c h e s t h a t c o n t a i n e d 4 4 c o l o u rs p o t s . T h e c o m p u t e d c o r r e l a ti o n c o e f f i c i e n t f o r t h e 4 4p a i rs o f n u m b e r s w a s g r e a t e r t h a n 0 . 9 9 , a n d t h ec o e f f i c ie n t o f v a r ia t i o n w a s 7 . 4 % . O n e o f t h e a u t h o r s o ft h is p a p e r ( D J H ) a n a l y s e d f iv e o f t h e s a m e p a t c h e s t h a tt h e l a b o r a t o r y s t a f f m e m b e r h a d r e a n a l y s e d , w h i c hc o n t a i n e d 1 2 c o l o u r a r e a s . T h e c o r r e l a t io n c o e f f i c i e n tf o r t h e t w e l v e p a i r s o f n u m b e r s w a s 0 .9 9 a n d t h ec o e f f i c ie n t o f v a r i a t io n w a s 9 . 0 % . I n n e i t h e r o f t h e t w oa n a l y s e s w a s t h e r e a n y d i s a g r e e m e n t i n t h e c o l o u r o rt h e n u m b e r o f s p o t s o n t h e t h e r m o g r a p h y s h e e t s ;va r i ab i l i t y was due exc lus ive ly t o d i f f e rences i n t he s i z eo f t h e t r a c e s o u t l i n e d b y t h e a n a l y s ts .

Evaluat ion o f occupat ional knee- jo in t st ress: D.J. Habes et alC a s e study description and r e s u l t s

T h e t h e r m o g r a p h y s y s t e m w a s te s t e d a t t h e si te o f al o c al h o t e l u n d e r g o i n g r e n o v a t i o n . T w o c a r p e t- i n s t al l e rt r a d e s m e n v o l u n t e e r e d t o u n d e r g o a d a y o f t e st in g i na c c o r d a n c e w i t h t h e m e a s u r e m e n t s c h e d u l e d e s c r i b e da b o v e . B o t h w e r e e x p e r i e n c e d w o r k e r s , w i th 1 0 a n d 1 1y e a r s a s c a r p e t i n s t a l l e r s , r e s p e c t i v e l y . O w i n g t o t i m ec o n s t r a i n t s a t t h e w o r k s i t e , o n l y t h e r ig h t ( k ic k i n g )k n e e w a s e v a l u a t e d f o r t h e t w o s t u d y p a r t i c i p a n t s .

T h e t w o t r a d e s m e n w e r e a s k e d t o g o a b o u t t h e i rt yp i ca l work ac t i v i t i e s , wh ich i nc luded a mix o fu n l o a d i n g r o ll s o f c a r p e t f r o m t h e d e l i v e r y t r u c k ,c u t t i n g c a r p e t a n d p a d s t o s i z e , l a y i n g t a c k s t r i p a n dm o u l d i n g , a n d s t r e t c h in g c a r p e t ( F i g u r e 3 ). T h e w o r k e r sw e r e n o t o b s e r v e d d u r i ng t h e i r w o r k , n o r w e r ea t t e m p t s m a d e t o q u a n t i f y t h e t im e d i s t r i b u ti o n o f th e s ea c t iv i t ie s d u r i n g t h e w o r k d a y . H o w e v e r , b a s e d o np r e v i o u s j o b a n a l y s e s o n o t h e r c a r p e t i n s t a l l e r s , i t w a se s t i m a t e d t h a t t h e t w o v o l u n t e e r c a r p e t i n s t a l l e r s s p e n ta b o u t 7 5 % o f t h e w o r k d a y o n t he i r k n e e s ( B h a t ta c h a r y ae t a l , 1 9 8 5 ) . T h e i n d i v i d u a l a n d c o m b i n e d r e s u l t s f o r t h eu p p e r k n e e ( s u p r a p at e ll a r ) o n l y o f th e t w o w o r k e r so v e r t h e c o u r s e o f t h e d a y a r e p r e s e n t e d i n F i g u re 4( a ) , ( b ) a n d ( c ) .

T h e e x t e n t o f k n e e t e m p e r a t u r e i n c r e a s e d u r i n g t h ed a y d i f f e r e d b e t w e e n t h e t w o c a r p e t i n s t a l l e r s , b u t t h ed i r e c t i o n o f c h a n g e w a s g e n e r a l l y t h e s a m e f o r e a c h o ft h e m . T h e h o t t e s t t e m p e r a t u r e s ( g r e e n a n d b l u e )i n c r e a s e d s t e a d i l y d u r i n g t h e w o r k d a y , w h e r e a s t h ec o o l e r t e m p e r a t u r e s ( b r o w n a n d t a n ) d e c r e a se d . T h eo n l y e x c e p t i o n t o t h i s t r e n d w a s t h e b e f o r e - l u n c hm e a s u r e f o r w o r k e r 1 an d t h e e n d o f w o r k m e a s u r e f o rw o r k e r 2 . I n e a c h c a s e , th e p e r c e n t a g e o f h o t t e s tt e m p e r a t u r e s d e c r e a s e d s l ig h t ly f r o m t h a t o f th ep r e v i o u s m e a s u r e . F o r t h e a v e r a g e d d a t a ( F i g u r e 4( c ) ) , t h e d i s t r i b u t i o n o f h o t t e s t t e m p e r a t u r e s i n c r e a s e df o r e a c h m e a s u r e t a k e n .O n e n o t a b l e f i n d i n g f o r b o t h s u b j e c t s w a s t h a t f o r t h em e a s u r e s t a k e n a t t h e e n d o f th e d a y , g r e e n a n d b l u e' h o t s p o t s ' s e e m e d t o b e c o n c e n t r a t e d p r i m a r i l y o n a

a b CFigure 2 Com puter analysis sequence of the captured video images: (a ) the raw thermogram; (b) each eolour t raced and codedinto the comp uter (1 = green, 2 -- tan, 3 = blue); (c) summ ary sheet prov ided by the area-computation program

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Evaluation of occupational kn ee-jo int stress ." D.J. Hab es e t a l

a

Figure 3 The ma in activities of a carpet installer: (a) attaching base strip; (b) nailing tack strip to the floor; (c) gluing the pad tothe floor; (d) bringing carpet rolls into the room : (e ) unro lling carpet; (f) stretching carpet into place

p , L ~ : ~ -~ :~ - ~ , ~ . .. .. ~ . . . .. . . - ~ , ~ . . .. . .. . . . . . . .. . . . . . .. . . . 1 9 7 4r e w o r K - - - - , " . . . . . . . . . .. . . . . . . . .. . . ' " ' . . . . . . . . I , , , , , , , , , ~ . . . . . . . . . . .M i m v . . . - . - % n ......... ..................~~, d a . DI;e 16.2

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Figure 4 Bar charts show ing the distribution of thermographypatch colours over the course of the w orkday for: (a) worker1; (b) worker 2; (c) both workers combined

p ort ion o f th e u p p e r k n ee ( su p rap ateUar) th at th ew o r k e r s r e p o r t e d t h e y u s e d t o i m p a c t t h e c a r p e t -s tre tch in g too l .

Th e resu l t s o f th e case s tu d y in d icate th at th e u se o fcon tac t th erm ograp h y , in con ju n ct ion wi th th e an a ly tica lm e t h o d s d e s c r i b e d a b o v e , m a y b e a n e f f e c t i v e a n de x p e d i e n t m e a n s o f o b t a i n i n g q u an t it a t iv e n m m u r e s o fk n e e t e m p e r a t u r e p a t t er n s i n r e s p o n s e t o w o r k i n v o l v i n gth e k n ee . W h i le th e in crease in s i ze o fa ae 'h otsp ots ' onth e k n ees o f th e two vo lu n teer carp e t in s ta l l er s wass tead y an d con s i s ten t over th e cou rse o f th e d ay , th eexac t cau se o f th e in f lam m atory resp on se can n ot b eascer ta in ed from an alys i s o f th e th erm ograp h ic record sa lon e . P rop er cau se -an d -e f fec t in terp re tat ion o f th e

1 1 4 Applied Ergonomics 1994 Volume 25 Number 2


5/5

r e s u lt s m u s t b e m a d e in c o n j u n c t i o n w i t h s e v e r a li m p o r t a n t c o n s i d e r a t i o n s : f o r e x a m p l e , w h e t h e r t h eo b s e r v e d i n f l a m m a t o r y r e s p o n s e w a s d u e t o t h e w o r kt h a t w a s p e r f o r m e d o n t h e d a y o f t e s t i n g , o r t o a p r e -e x i s t i n g k n e e i n f l a m m a t i o n t h a t e a c h w o r k e r h a dd e v e l o p e d o v e r t h e c o u r s e o f t h e i r 1 0 - y e a r c a r e e r s .O t h e r q u e s t i o n s t h a t a r e r ai s e d f r o m t h i s in i ti a l s t u d yi n cl u de w h e t h e r o r n o t r e c o v e r y t o t h e w o r k e r s ' k n e e sw o u l d o c c u r o v e r n ig h t , a n d w h e t h e r w o r k e r s w o u l ddem ons t ra t e s imi l a r pa t t e rns o f i nc rea se s i n kn eet e m p e r a t u r e w h i l e p e rf o r m i n g k n e e - i n t e n s i v e a c t iv i t ie so the r t han ca rpe t i n s t a l l i ng , such a s wa lk ing , s t a i rc l i m b i n g , o r c r o u c h i n g w i t h b e n d e d k n e e . T o a d d r e s ss o m e o f t h e s e c o n c e r n s , a l a rg e r s t u d y i s p l a n n e d .

B a s e d o n t h e p r e s e n t l i m i t e d d a t a , t h r e e c o n c l u s i o n sw e r e d r a w n .1 K n e e t e m p e r a t u r e s a p p e a r t o in c r e a s e c o n s i s t e n t l y asc u m u l a t i v e b i o m e c h a n i ea l l o a d i n g i n c r e a s e s , a n d t h et r e n d i s n o t n o t i c e a b l y a f f e c t e d b y r e s t a n d l u n c hb r e a k s .2 C o n t a c t t h e r m o g r a p h y i s a b l e t o d e t e c t t h e s et e m p e r a t u r e c h a n g e s .3 T h e t h e r m o g r a p h i c s y s t e m d e v e l o p e d f o r u s e i n t h i sf i e l d s t u d y p r o v i d e s a f e a s i b l e m e a n s o f m e a s u r i n gk n e e t e m p e r a t u r e a t t h e w o r k s i t e .T h e e f f e c t i v e u s e o f th e r m o g r a p h y i n p r e v e n t i n g i n j u r yt o c a r p e t l a y e r s ' k n e e s d e p e n d s o n p e r f o r m i n g t h e t y p eo f r e s e a r c h d e s c r i b e d a b o v e , a n d o n d e v i s i n g a m e c h a n -i s m f o r m e a s u r i n g t h e b i o m e c h a n i c a l l o a d s u s t a i n e d b yt h e w o r k e r s o t h a t a d o s im e t e r c a n b e d e v e l o p e d . A f t e r

Evaluat ion o f oc cupat ional knee- jo in t s tress: D.J. Habes et aie s ta b l is h i ng a d o s e - r e s p o n s e r e la t io n s h i p b e t w e e n t h eb i o m e c h a n i c a l l o a d i n g f a c t o r s a n d t h e p h y s i o l o g i c a lr e s p o n s e , t h e d e c i s i o n r u l e s f o r t h e i m p l e m e n t a t i o n o fp r e v e n t i v e w o r k p r a c t i ce s c a n b e f o r m u l a t e d . E x a m p l e so f t h e s e w o r k p r a c t i c e s a r e t h e p r o p e r s c h e d u l in g o fr e s t b r e a k s , r o t a t i n g t o l e s s k n e e - i n t e n s i v e a s p e c t s o fc a r p e t i n s t a ll i ng , a n d i n c r e a s e d u s e o f av a i l a b l e m e c h a n -i z e d t o o l s t o i n s ta l l c a r p e t i n g , s u c h a s a p o w e r s t r e t c h e r .A c k n o w l e d g e m e n t

T h e a u t h o r s w o u l d l ik e t o t h a n k D r K a t h a r y n A .G r a n t f o r h e r a s s i s t a n c e i n d r a w i n g f i g u r e s f o r t h i sp a p e r .

R e f e r e n c e sBhat taeharya , A, Muei ler , M and Putz.Anderson, V 1985'Traumatogenic factors affecting the knees of carpetinstallers' A p p l E r g o n 16 (4), 243--250Dribbon, B S 1983 'Appl ica t ion and v a lue of l iquid crysta l

thermography ' J A m P o d ia t ry AsSo c 7 (8), 400--404Her rick, R T and .Herrick, S K 198 7 'Thermography in thedetec t ion of carpa l tunnel syndrome and oth er compressiveneuropathies ' J H a n d S u r g 12A (5, part 2), 943-949Pochaczevsky, R 1983 'Assessment o f back pa in by contac tthermography of ext remity dermatomes ' Orth o p Rev 12(1), 45-58NIO SH 1990 Pre venting kn ee injuries and disorders in carpetlayers' U S D H H S ( N I O S H ) A l e r t Publication 90-104, MayThun, M , Tanaka , S, Smith, A B, l la lper in , W E, Lee , S T,Luggen, M E and He ss, Evelyn E 1987 'Morbidity fromrepet it ive knee t raum a in carpet and f loor layers ' Br J l n dM e d 4 4 , 611--620

Applied Ergonom ics 1994 Volume 25 N umber 2 11 5

evaluation of occupational knee-joint stress using liquid crystal thermography: a case study

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