Vibration syndrome and vibration in pedestal

British Journal of Industrial Medicine 1983 ;40:426-433

Vibration syndrome and vibration in pedestalgrinding

J STARCK,' M FARKKILA,3 S AATOLA,' I PYYKKO,4 AND 0 KORHONEN2

From the Departments ofIndustrial Hygiene and Toxicology' and Occupational Medicine,2 Institute ofOccupational Health, and the Department ofNeurology,3 University of Helsinki, Helsinki, Finland, and theDepartment of Otorhinolaryngology,4 University Hospital of Lund, Lund, Sweden

ABSTRAcr At one Finnish foundry all the workers had typical symptoms of vibration inducedwhite finger (VWF) after they began using a new type of pedestal grinding machine. The objec-tives of this study were to establish the severity of the symptoms and the difference in vibrationexposure between the new and the old machines. Vibration detection thresholds and grip forceswere measured, as well as the vibration in the casting and in the wrist simultaneously. The mean

latency for VWF among the grinders was 103 months after the change of pedestal grindingmachines. All the grinders had numbness in their hands. The vibration detection threshold was

significantly higher for the grinders than for their referents. At the same circle speed, the new

wheels caused vibration levels up to 12 dB more than the old wheels. The circle speed had a slightinfluence on the vibration. The vibration levels of light (0.5 kg) casting were up to 25 dB higherthan the heavy (5 kg) casting. The use of a pneumatic pressing device decreased the vibrationlevels in the wrist by 5-10 dB. The increase in vibration, which occurred when the new wheelswere taken into use, was too small to explain such a dramatic outbreak of VWF. This led to theconclusion that some other feature such as the impulse character of the vibration also contributedto the effects of vibration.

Exposure to occupational vibration can be thecause of different symptoms in the hands and arms.These symptoms-circulatory disturbances in thefingers, paraesthesias of the hands and arms, degen-eration of the bones and joints, and diminished mus-cle force-comprise a disease entity known as vibra-tion syndrome.1 2 The somewhat independentoccurrence of these symptoms in vibration syn-drome points to the possibility that each of thesecomponents may arise by an independent mechan-ism.23 Opinions vary on this matter, however.4-6The best documented symptom is the periodic cir-culatory disturbances in the fingers-that is, vibra-tion induced white finger (VWF). As both numbnessof the hands and arms and muscles weakness aredifficult to evaluate, only a few epidemiologicalstudies have investigated these symptoms.7

Agate et al and Agate were among the first toobserve severe VWF among pedestal grinders.89 Intheir studies 71-86% of the grinders suffered from

Received 23 June 1982Accepted 3 August 1982

VWF after a mean latency of 23 months. VWF wassevere; and after the cessation of such work, VWFtended to progess rather than regress. Since thenother investigators have confirmed these findings.Pyykko observed extremely severe VWF amongFinnish knife grinders.'0 VWF affected all the work-ers and occurred after a latency of, on average, ninemonths. Pelmear et al reported an outbreak ofVWFamong grinders after silicon carbide wheels werereplaced by zirconium wheels." 12 The outbreak ofVWF, which occurred after a latency of six months,affected all the grinders and was severe. Althoughdifferent explanations have been proposed, no con-vincing evidence has so far been found to explainwhy pedestal grinders are so liable to vibrationinduced disease.

Pedestal grinding is still used at several foundriesto clean small castings. At one Finnish foundry newwheels composed of zirconium were taken into usein 1977. After a working period of about one year,all the workers using the new pedestal grindingwheels suffered from VWF. This led us to measurethe levels of vibration generated by the wheels, to

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Vibration syndrome and vibration in pedestal grinding

conduct medical examinations of the foundry work-ers, and to propose technical modifications.

Subjects

All 12 grinders (mean age 30, range 26-55) workingwith grinding wheels were examined at the Instituteof Occupational Health in Helsinki. A medical his-tory was taken to get information on the grinders'symptoms in the hands and arms and their generalstate of health, and a clinical examination was car-ried out. The;hration of exposure to vibration wasestimated in hours.'3 As control subjects for themeasurements of vibration detection thresholds, 20healthy men (mean age 33, range 25-59) wereexamined. The control subjects were not occupa-tionally exposed to vibration in their work.

Methods

PEDESTAL GRINDINGThe castings were cleaned manually. One pedestalgrinding machine was supplied with a pneumaticdevice used to press the casting against the wheel.The operator still had to be in contact with the cas-ting, but strong pressing and holding forces were nolonger necessary. The weight of the casting variedbetween 0-5 kg and 10 kg.The pedestal grinding machine was locally con-

structed. The circle speed of the grinding wheel was48 mIs, and it was kept constant with a variator. Inconnection with this study the technical propertiesof the grinding wheels used before and after 1977were evaluated. The roughness, hardness, and bondof the two wheels were the same; but before 1977the abrasing material was corundum (normal corun-dum) and after 1977 it was zirconium-corundummixed with silica. The eccentricity of each of thegrinding wheels was measured in addition to thecircle speed.

HAND GRIP FORCEThe hand grip force was measured with a straingauge dynamometer.4 The subject maximally com-pressed the handle repeatedly in time with anaudiosignal. One cycle consisted of a grip lasting fortwo seconds, followed by a two second relaxation,and the cycle was repeated 20 times.4 Measurementswere taken from both hands, both with vibration ofa vertical direction at 80 Hz sinusoidal frequencyand without vibration. The angle of the lower armwas 450 from the horizontal plane.

VIBRATION DETECTION THRESHOLDPsychophysical vibration detection threshold valueswere measured from the fingertip of the third finger

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of the left hand for sinusoidal vibration at six fre-quencies (16,31-5, 63,125, 250, and 500 Hz).'4 Thevibrating head, which was circular and had a diam-eter of 2-6 mm, leaned on the fingertip at a constantforce of 0*20 N. The vibration, measured by anaccelerometer (B&K 4371) placed between the vi-bration exciter (B&K 4291) and the vibrating head,was recorded on a level recorder (B&K 2306). Theacceleration of the vibrating head was automaticallyincreased from zero at a speed of 3 dB per second.When the subject felt the vibration, he pressed aswitch in 1bisright hand; this brought the vibration tozero again. The threshold value at each frequencywas measured three times, and the results were cal-culated as the mean of these three values.For the psychophysical vibration detection

threshold, adaptation was measured from the finger-tip of the third finger of the left hand, at a frequencyof 250 Hz. During the measurement of adaptation,the examiner manually adjusted different amp-litudes of vibration, and the subject was asked toreport when he perceived vibration and when he didnot. The recording was done during three minutes.After three minutes the circulation of blood in theleft hand was interrupted for three minutes furtherwith a sphygmomanometric pressure of 120 mm Hg.Three values were analysed from the adaptation

measurements: the first value at the beginning, thesecond at the end of the third minute, and the thirdat the end of the sixth minute (under ischaemic con-ditions). Each value was the mean of three detectionthreshold values during 40 s. The block diagram ofthe instrumentation of the measurements of thepsychophysical vibration detection threshold and ofadaptation is shown in fig 1. The vibration detectionthreshold and the adaptation values, expressed indecibels, are based on the reference values indicatedin formula (1).The temperature of the fingertip was measured

with a T-type thermocouple at the beginning and atthe end of all the measurements and also betweenthe measurements of the vibration detection thres-hold and adaptation.

VIBRATION MEASUREMENTSVibration was measured for different types of grin-ding wheels at the most- commonly used, constantcircle speed of 48 m/s. Measurements were alsomade at circle speeds of 45, 40, and 35 m/s. Theoperator was the same during all the measurements.The vibration levels generated during two differenttypes of castings weighing 0*5 and 5 kg weremeasured. The directions for simultaneous recor-dings of vibration and the measuring sites were: (1)casting in vertical (tangential to the wheel) and hori-zontal (radial to the wheel) directions, and from the

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Starck, Farkkila, Aatola, Pyykko, and Korhonen

Fig 1 Block diagram ofinstrumentationfor measurements ofvibration detectionthresholds and adaptation to vibration.

B&K 2635 B&K 2306

Balance

operator' s left wrist in the direction of the lower armand (2) from the stalk of the sharpener in the verti-cal and horizontal direction, and from the operator sleft wrist in the direction of the lower arm.A metal piece was welded to the casting, and a

triaxial accelerometer (B&K 4321) was fastened toit with a screw. For the measurement of vibration inthe wrist, the transducer (B&K 4366) was fastenedto a plastic module with a screw. The module, whichwas adjusted to fit against the styloid process of thewrist, was held in place with a tightener and a plasticsupport.'3 15The time required to clean one casting, which was

only a few seconds, was too short for reliable vibra-tion measurements. Therefore, the sample time wasextended to 20 s. The sample was recorded on a taperecorder (B&K 7003) for further analysis. The fre-quency range of the recordings was between 2 and1000 Hz. The recording was replayed on a real timeanalyser (B&K 2131) controlled by a computer(TEK 4052), and displayed as the average 1/3octave spectrum of 20 spectra. The averaging timein the analyser was 0-5 s corresponding with thesampling intervals of the spectra in the computer.The corresponding total acceleration level and thestandard deviation were calculated for each 1/3octave. The vibration levels (L) were based on theformula (1)

L = 20 log (a/a.) (dB) (1)where ao = 0-438 x 10-3 ms-2 and a = themeasured acceleration ms-2.The block diagram of the instrumentation is pre-

sented in fig 2.

STATISTICAL METHODSThe statistical significance of the mean values detec-ted between the grinders and the control subjectswas tested with Student's t test for independentsamples at the frequencies of 63, 125, and 250 Hz.The statistical significance of the difference of meangrip forces, right hand v left hand, and with v with-out vibration, was tested with two-way analyses ofvariance (ANOVA). The statements of statisticalsignificance were based on the probability value of p< 0*05.

Results

HISTORY OF VIBRATION SYNDROME ANDASSOCIATED DISORDERSAll the grinders had a history of VWF. The totalduration of exposure for grinding work was, onaverage, 9200 hours (range 3100-19 400), and theduration of exposure before the wheels werechanged was 7800 hours (range 2800-12 700).None of the grinders had VWF before the wheels

AcceLero jCharge

meters -jampLifiers Q

B&K 4321 B&K 2635 B&K 7003B&K 4366

Cette Fig 2 Block diagram ofinstrumentationm / (a) in the field (b) in the laboratory.

S Analyser Computer Line Facit 4554

B& K 7003 B&TK2131 Tektronix 40513Cop Tektronix 4631

Sinegenerator

B&K 1023

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were changed. The latency for VWF after the wheelswere changed was, on average, 1100 hours; this cor-responded to a working period of 10-3 months (SD4-5 months). All the men experienced their mostrecent attack of VWF during the week beforeexamination. The disease had started in the righthand in 10 men, in the left hand in one, and bilater-ally in one. On examination, the disease of fivemen was bilateral, six men had it only in the righthand, and one had it only in the left hand. The meanduration of an attack of VWF was 10-5 min (+ SD4-0 min) in indoor conditions. Eleven subjectsexperienced attacks of VWF daily, and 11 alsoexperienced them in summer.

All the subjects also had numbness in their hands,which disturbed their sleep. The hand grip force wassubjectively diminished in six men. Five experiencedpain in their wrists, elbows, or shoulders; eight hadcontracture of the palmar fascia of fingers IV and V,and four of them had a Dupuytren's contracture.Two had mild arterial hypertension treated withmetoprolol or propranolol; their blood pressure wasnormal during the examination.

HAND GRIP FORCEThe curves of the compression and relaxation of theleft hand without simultaneous vibration did not dif-fer (F(1) 0-46, p = 0.3) from the curves of theright hand. During simultaneous vibration, the com-pression forces of the right hand were diminished.The difference between the curves with and withoutvibration was statistically significant (F(1) = 7*1, p< 0-01) (fig 3). The corresponding difference in theleft hand was not significant (F(1) = 025, p = 0-6).Thus reduced compression force in connection with

50-

Grippingforce

unit )

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simultaneous vibration was detected in the handmore affected by VWF.

VIBRATION DETECTION THRESHOLDFour of the 12 grinders did not feel the 95 dB maxi-mum vibration level of the equipment at 500 Hz.Two did not feel the 96 dB maximum vibration levelat 250 Hz. Figure 4 shows the means of the vibrationdetection thresholds for control subjects and forgrinders. The grinders' vibration detection thresholdvalues were significantly greater than those of thecontrol subjects (t = 6-2 - 8-9, p < 0-001) at all testfrequencies. Three grinders lost their sense of vibra-tion during adaptation measurements: one beforethree full minutes and two before six full minutes ofmeasuring time. Because five men were totallyeliminated during the adaptation measurements, nostatistical tests of adaptation were conducted.

Skin temperatures were evaluated for all men atthe beginning and at the end of the test. No statisti-cally significant differences were found between thegrinders and the control subjects.

VIBRATION OF THE GRINDING WHEELSFigure 5 shows the vibration acceleration spectra inradial (Sa) and tangential (Sb) directions measuredfrom a light (0-5 kg) casting. Most measurementsshowed that the grinding wheel with normal corun-dum as the abrasing material had the lowest vibra-tion level. The differences were the greatest (max-imum 12 dB) in the frequency range of 25-160 Hz.The weighted'6 vibration level of the new wheel was

80-fRight hand* Without vibration* With vibration

* Grinders

* Controls

70 -,:ibrationthreshold(dB)

5 17 29 41 53 65 75Time (s)

Fig 3 Curves ofmean muscle fatigue of right hands of 12grinders with standard errors ofmeans.

60-

50 -

63 125Frequency (Hz)

250

Fig 4 Mean values ofvibration detection thresholds for 12grinders and 20 controls with standard errors ofmeans.

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430~~~~~~~~~~~~Starck,Farkkila, Aatola, Pyykk5, and Korhonen

3-5 dB higher than the old wheel. The vibrationlevels in the radial direction were usually 0-10 dBhigher than in the tangential direction. The

100 measured eccentricity was about the same (±+ Odmm) for each wheel.

90 We found that the circle speed had a slight effecton the vibration levels at frequencies above 80 Hz.

Vibration80 4- ~~~~~Below and at 80 Hz, the highest circle speed of 48lvibato80B m/s produced the lowest vibration in zirconiumLeveL(dB) ~~~~~~~wheels. Corundum wheels had the lowest vibration

70 level at a circle speed of 35 m/s and the highestvibration level at a circle speed of 40 mIs. Light (0.5

60 ~~~~~~~~~kg)castings had acceleration levels up to 25 dB60 ~~~~~~~~~~higherthan heavy (5 kg) castings. In the wrist the

vibration measurements yielded somewhat different50 results. As indicated in fig 6, the light casting pro-0 [ irconiumcorundum ~ duced higher vibration levels only in the frequencies

i i ~~~~~~~~~over40 Hz. The total acceleration level in the wrist100 Nracoudmin a light casting was, on average, 3-7 dB higher

than in a heavy casting90 Measurements were taken also from the stalk of

Vibration Z the sharpener for both the zirconium-corundum andLevel (dB) 80 +the corundum wheels. The vibration levels in both

cases were up to 30 dB higher than those measuredin any other working situation. Figure 7 shows the

70-vibration acceleration spectra in the direction ofgrinder's arm when measured from the stalk. It is

60 worth noting that the angle between the arm andstalk was 900, and the direction of the stalk was very

50 near the direction of the radius of the wheel. Thus4 12*5 40 125 400 1250 vibration is almost totally emitted in a vertical direc-

Frequency (Hz) tion during this work phase.Fig 5 Vibration levels when casting were held against When grinding with a pneumatic pressing device,different wheels (a) in radial directions and (b) in the vibration decreases about 5 dB in the frequencytangential directions. range of 40-400 Hz, in both the casting and in the

wrist (fig 8). The vibration level remained almostunchanged below 40 Hz, but it was slightly increased

*Wrist, tight casting*Wrist, heaivy casting +Zirconium-corundum

80 Normal corundum120 -

70-110 -

Vibration 60 Vibrationlevel (dB) level (dB) 100

4 12-5 40 125 400 1250Frequency (Hz)

Fig 6 Vibration levels in wrist, light (0.5 kg) and heavy (5kg) casting.

4 12-5 40 125 1,00 1250Frequency (Hz)

Fig 7 Vi-bration levels when sharpeningzirconium-corundum and normal corundum wheels.

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(e) Casting.normal rnethodCasting.pneumatic pressing

Vibration8Jtevel ( dB ) _

70-

60

50(i) | + Wrist, norrnal rnethod l

Wrist,pneumatic pressing

90

Vibrationlevel (dB)

80

70-

60

1504 12 5 40 125 400 1250

Frequency (Hz)

Fig 8 Vibration levels when pneumatic pressing was used(a) in casting and (b) in wrist.

above 400 Hz. In the wrist the decrease was about 5dB when the frequency was below 12-5 Hz andabout 5-10 dB at the frequencies of 20-125 Hz. Athigher frequencies the vibration level remainedunchanged or increased slightly. Comparison of thetwo different wheel types shows that grinding withcorundum wheel produced vibration levels in thewrist to about 25 dB lower than the zirconium-corundum wheel. The result agrees well with manualcasting. The result indicated that, depending on thetype of grinding wheel, the pneumatic devicedecreased the acceleration of vibration in the wristto the 1/18 or 1/6 of the values measured withoutthe pneumatic device.The standard deviation of each analysis, cal-

culated for 1/3-octave band, ranged from 1 dB to 4dB. The standard deviation for the total level ofacceleration was 3 dB.

Discussion

An outbreak of vibration syndrome occurred amonggrinders after grinding wheels made of corundumhad been changed to wheels made of zirconium-corundum mixed with silica. It is noteworthy thatthese men had been grinding metal castings symp-tom free for years. After the grinding wheels hadbeen changed, all the men became disabled eventhough their working routines were essentially thesame as before. Thus an analysis of the vibrationcharacteristics of the two wheels might discover whygrinding work causes the vibration syndrome andshow the most hazardous characterisics of the vibra-tion spectra.

In agreement with earlier reports8-'2 the grindingof metal castings may cause severe VWF, whichaffects most of the workers after a short latency. Thegrinders' history of attacks of VWF was much thesame as that found among forest workers'°; in thatrespect our results were contradictory to the state-ment of Dart,'7 who in 1946 claimed that vibrationof a high frequency may cause a different type ofVWF. The average latency in the present study was10 months. This appeared exceptionally short whencompared with the latency of about five years repor-ted for lumberjacks.'0 1819 Gurdjian and Walker,bowever, reported that exposure to vibrationincluding high frequency components of vibrationmay cause VWF among workers even after twoweek period of exposure.20 The short latency ofVWF among grinders may indicate that the vibra-tion of grinding work is more hazardous than thevibration of forestry work.The changes in hand grip force measured in the

right hand were similar to the earlier results amonglumberjacks.4 Also, the hand grip forces werereduced only in the affected hand during exposureto vibration. The measurements of vibration detec-tion showed that the grinders' thresholds were muchhigher than the referents. In two cases afterischaemic provocation the thresholds were so highthat end values for the adaptation test could not bedetermined. Our finding of excessive adaptationduring ischaemic condition confirmed the findings ofMarschall et al, who showed that, in workers withVWF the sensory peripheral nerves are highly sus-ceptible to ischaemia.2' The findings concerningchanges in muscle force and in the vibration detec-tion thresholds may be also linked to the peripheralneuropathy associated with vibration syndrome.2223The prevalence of contracture of the palmar fascia

of fingers IV and V was surprisingly high (67%), andDupuytren's contracture was also found among onethird of the grinders. The palmar fascia contracturescan be a predisposing state to Dupuytren's contrac-

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432

ture, and this condition may also be associated withprolonged exposure to vibration, as proposed byTeleky.' It may also, however, be due to the uniformloading of the hand ligaments during grinding work.Conclusive evidence for either of these theories isnot yet available.The comparison of the vibration spectra of grin-

ding and chain sawing indicated that high frequencycomponents were more prominent in grinding workthan in chain sawing. This finding concurred withearlier results.' 24 It has been proposed that the highfrequency components may be hazardous.20 Wecould therefore expect that the differences betweenthe vibration spectra of the old corundum wheelsand the new zirconium-corundum wheels would lieat high frequency vibration.The analysis of vibration showed that the level of

vibration acceleration in the new zirconium-corundum wheels was somewhat higher at the fre-quency range of 100-1000 Hz. The vibration accel-eration measured from the wrists during grindingwas somewhat higher with the new zirconiumwheels; this agreed with the measurements takenfrom the castings. The differences cited above wereslight and could not explain such a dramatic out-break of VWF among grinders. A similar outbreakof VWF among grinders was reported by Pelmear etal. 111 2 In a detailed analysis of the energy spectra,Hempstock and O'Connors concluded that theeccentricity of zirconium wheels is higher than thatof carborundum wheels, and that this eccentricitycauses bouncing on and off the grinding wheels,thereby increasing the vibration.24 Ourmeasurements could not confirm their hypothesis. Infact, the eccentricity and the vibration spectra werethe same for both types of grinding wheelsISO/DIS 5349 ("Guide for the measurement and

the assessment of human exposure to vibrationtransmitted to the hand") proposed limits forhazardous vibration.'6 This proposed standard alsogives limitations for the duration of exposure in theranges of 4-8 h (A), 2-4 h (B), and 30 min-2 h (C)(fig 9). The application of these limits to the grindersshowed that, for the lowest vibration level, durationshould be less than one hour for both the old corun-dum wheel and the new zirconium-corundum wheel.According to the proposed standard, the workingsituation where the vibration is highest (the shar-pening of wheels) should not be permitted at all. It isnoteworthy that the older wheel type did not causeVWF, whereas the new wheel type caused VWF inall the workers. The proposed standard makes nodistinction between the two types of grindingwheels.Our findings led us to conclude that other factors,

in addition to the vibration spectra, made important

Starck, Farkkila, Aatola, Pyykko, and Korhonen

miS2-c1 dB

\ B~110

l0dB A

K0 p100

~905 1~~~~~~~80

2

1FL V ~~~~~~~708 20 50 125 315 800

12-5 315 80 200 500 HzFrequency of 1/3-octave band

Fig 9 Exposure guidelines for acceleration of vibrationaccording to ISOIDIS 5349.

contributions to the hazardous effects of vibration.Vibration spectra are usually analysed in 1/3-

octave or octave bands. Biological receptor systemsapparently do not respond to the signal in a Fouriertransformation manner. On the contrary, the vibra-tion receptor system follows sinusoidal vibration in aphaselocked manner, depending on the receptor sys-tem, at vibration frequencies from 2 Hz to 700 Hz,responding with one spike to one stimulus. Thesame phaselocked response to vibration can beobserved in the cells of the central nervous system inthe cortex and in the cerebellum.25 26 Most studieshave focused on the stimulation of the Pacinian cor-puscles, which are extremely sensitive to vibration.27The same type of responses, however, have beenobserved after stimulation of cutaneous receptors28and muscle spindles.2930The physiological studies have usually been con-

ducted using sinusoidal vibration. Sinusoidal vibra-tion differs from the vibration of occupationalexposures, which consists of randomly occurringspikes. The spike character of vibration reflects itsimpulsiveness and may produce shock waves thatdistort tissues and increase the firing rate of thereceptors. The dynamic processes of the receptorsand the synapses as such may further modify theresponses in the central nervous system and producean awareness of vibration.3' 32 The awareness of vib-ration, which reflects the penetration of vibrationstimulus to consciousness, may thus be one factorthat is coupled with the hazard of vibration.More information about vibration signals are

needed so that the reasons for the present outbreakof vibration syndrome can be clarified. These addi-

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tional data could be obtained by the help of narrowband analysis in the frequency domain. In the timedomain the time history of the vibration signalsexpressed either as histograms or as cumulative dis-tribution functions are analyses that might provebeneficial. The impulse characteristics of vibrationcan be described as the difference between peak andRMS-signals, using the same functions already men-tioned. The analysis of impulse characteristics mightprovide a better approach to the evaluation ofhealth hazards caused by vibration than the cur-rently used 1/3 octave band analysis.

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Kumlin T, Wiikeri M, Sumari P. Radiological changes in carpalbones and metacarpal bones and phalanges caused by chainsaw vibration. Br J Ind Med 1973;30:.71-3.

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Vibration syndrome and vibration in pedestal