Annals of Occupational Hygiene Advance Access originally published online on September 20, 2004
Annals of Occupational Hygiene 2004 48(7):635-642; doi:10.1093/annhyg/meh054
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© British Occupational Hygiene Society Published by Oxford University Press;
Surveillance Program of Neck and Upper Limb Musculoskeletal Disorders: Assessment Over a 4 Year Period in a Large Company
1 Consultation de Pathologie Professionnelle, Centre Hospitalier Universitaire, F-49033 Angers Cedex, France; 2 Service Médical Inter-entreprise de l'Anjou, 25 Rue Carl Linné, F-49009 Angers, France; 3 INSERM U 88, 14 Rue du Val d'Osne, F 94415 Saint-Maurice Cedex, France
* Author to whom correspondence should be addressed. Tel: +33 2 41353764; fax: +33 2 41353448; e-mail: yvroquelaure{at}chu-angers.fr
Received 19 January 2004; in final form 5 April 2004
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONACKNOWLEDGEMENTSREFERENCES |
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Objective: A company-wide surveillance program for musculoskeletal disorders (MSDs) based on the assessment of health and risk factors was implemented between 1996 and 2000 in a large shoe factory. The study aimed to compare the results of the surveillance program in 1996 and 1997 with the occurrence of MSDs in 2000.
Methods: A health and ergonomic assessment of workstations was performed for 253 workers in 1996. Of these, 166 were examined again in both 1997 and 2000. A set of criteria was used to predict whether or not a job category could be predicted to have a potentially high risk of MSDs in 1996 and 1997 and the results were compared with the incidence rate of MSDs in the job category in 2000.
Results: The criteria based on prevalence data in 1996 were unable to detect the job categories characterized by the occurrence of MSDs in 2000. The criterion based on an incidence rate >1% in 1997 was sensitive and specific. The agreement between the ranking of the job categories according to incidence rate of MSDs in 1997 and 2000 was good (
= 0.57, P = 0.11). Agreement of the prediction based on ergonomic exposure was lower than that based on incidence data.
Conclusion: The efficacy of the surveillance program to predict on a collective basis the job categories in which numerous cases of MSDs occurred in 2000 depended on the decision criteria used. The criteria based on the incidence of MSDs were more reliable to predict the risk of MSDs than those based on prevalence data or on exposure assessment. Because exposure assessment plays a greater role in determining the priorities for ergonomic intervention, surveillance of health and exposure must nevertheless be combined to predict the risk of MSDs in the plant in the short and middle terms.
Keywords: exposure assessment • health assessment • musculoskeletal disorders • risk assessment • surveillance
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONACKNOWLEDGEMENTSREFERENCES |
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It is recommended that company-wide surveillance systems for work-related upper limb musculoskeletal disorders (MSDs) are implemented to determine the most appropriate action for the prevention of MSDs and to assess their efficacy (Rutstein et al., 1983
; Hagberg et al., 1995; Silverstein et al., 1997; Sorock et al., 1997). For this purpose, Hagberg et al. (1995) have proposed a multi-level model for surveillance of MSDs and their risk factors. The first level (level 1) uses questionnaires and checklists, which provide rapid assessment of the situation. The second level (level 2) includes physical examinations and in-depth job analysis by trained health care providers (Hagberg et al., 1995). Few studies are available to assess the predictive value of such collective surveillance methods (Hagberg et al., 1995; Silverstein et al., 1997; Sorock et al., 1997).
In a large shoe factory facing an epidemic of MSDs for many years, a surveillance program was implemented between 1996 and 1997 to identify on a collective basis the jobs with a high risk of MSDs (Roquelaure et al., 2002). For that, the model of surveillance of MSDs proposed by a panel of experts (Hagberg et al., 1995) was used after minor modification to take into account the features of the French occupational health system. The surveillance program therefore combined a level 2 active medical surveillance program and a level 1 active surveillance program for the risk factors. The company's occupational physician conducted the level 2 medical surveillance and two trained ergonomists performed the level 1 active surveillance of the risk factors for each worker.
A previous study based on a 1 year follow-up positively assessed the active surveillance method for MSDs at a collective level in the factory (Roquelaure et al., 2002). The principal purpose of the present study was to assess the predictive value of this surveillance strategy at the level of the company after 3 years.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONACKNOWLEDGEMENTSREFERENCES |
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A cross-sectional study was performed in 1996 to determine the prevalence of the main MSDs in a large modern mechanized shoe factory. This company, in which numerous epidemiological studies on MSDs had previously been conducted (Roquelaure et al., 1997
), was characterized by a high level of technological development and by the stability of the working population for many years (Roquelaure et al., 2002). An initial follow-up study was conducted in 1997 using the same clinical procedure to determine the prevalence and incidence of the disorders after 1 year. A second follow-up study using the same methodology was undertaken 3 years later. Ergonomic assessment of the workstations was conducted in 1996 to evaluate the risk factors of MSDs for each worker. Job site analyses were not performed in 1997 and 2000, but major changes to the job, the task or the workstation were checked in order to be taken into consideration in 1997 and 2000.
Subjects
Six of the 12 production units of the shoe factory, employing 
2000 wage earners, were randomly selected and 20% of the blue-collar workers for each production unit were randomly selected using the payroll rosters. Two hundred and fifty-three of the 1250 blue-collar workers were thus randomly included in the study in 1996. About 10% of these workers had refused to answer a questionnaire about working conditions in 1996 and were not followed up in 1997 and 2000. Moreover, because of the decrease in activity of one production unit due to the economic crisis, only five of the six production units were included in the study in 1997 and 2000. For that reason, only 191 out of the 253 workers examined in 1996 were re-examined by the same physician during a 12 month period in 1997. A second follow-up was conducted 3 years later, allowing 166 of the 191 workers examined both in 1996 and 1997 to be examined again in 2000. Socio-demographic data of the three surveys are reported in Table 1.
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Definition of health outcomes
All were interviewed by the same company occupational physician during the annual compulsory medical examination (1996, 1997 and 2000) using the same procedure (Roquelaure et al., 2002
). The physician was blind to the results of exposure assessment, but aware of the results of the previous health assessment. The clinical procedure consisted of three stages. The worker was first asked about pain and symptoms (tingling, burning, numbness, stiffness, lack of mobility, etc.) in one or both of the upper limbs during the previous 12 months and the previous week. In the next stage, the minimal examination procedure consisted of testing mobility and sensitivity to pressure of the neck, shoulders, elbows and wrists, followed by the sensitivity evaluation and provocation tests of the CTS (Phalen's and Tinel's tests) for each side. Finally, in cases of pain or symptoms in one of the regions of the upper limbs, the physical examination was extended by specific testing for tension neck syndrome, rotator cuff syndrome, lateral epicondylitis, medial epicondylitis, cubital tunnel syndrome, radial tunnel syndrome, Guyon's canal syndrome and hand–wrist tendinitis (Hoppenfeld, 1976). MSDs were considered to have been diagnosed if the results of any one of the three clinical procedures was positive.
The present paper only reports findings regarding the occurrence of one or more of the nine MSDs under review, i.e., tension neck syndrome, rotator cuff syndrome, lateral epicondylitis, medial epicondylitis, cubital tunnel syndrome, radial tunnel syndrome, carpal tunnel syndrome, Guyon's tunnel syndrome and hand–wrist tendinitis. For the case definition of the disorders see Roquelaure et al. (2002). In the following part of the text, the term ‘MSDs’ will refer to ‘one or more of the nine MDSs under review’. The incident cases were defined as the cases of MSDs diagnosed in 2000 in workers free of MSD in 1996 and 1997.
Exposure measurements
Risk factors for MSDs were assessed for each worker by standardized job site work analysis by two experienced ergonomists. The work analysis was performed by questioning and direct observation of the workers using the checklist of Keyserling et al. (1993). The ergonomist was blind as to the medical status of the workers and analysis was performed only for the most frequent work situation when the workers had two or more work situations during a single work analysis. Job rotation between different work situations was recorded. Eighteen risk factors belonging to five classes of ergonomic factors were taken into account by the checklist: repetitiveness (work cycle <30 s; repetition of the same motions/exertions during more than half of the work cycle), local mechanical contact stress (finger; palm; elbow; armpit), forceful manual exertion (weight over 4.5, 2.7, 1 kg; slipping object or tool; pressing or pushing with the thumb; wearing gloves), awkward upper extremity posture (pinch grip; wrist deviation; twisting of the forearm; reaching down and behind the torso; use of elbow above mid-torso level), hand tool usage (vibration exposure; cold; finger trigger motion; unbalanced or jerky tools or objects). The checklist took into account 18 risk factors for each hand. The response mode was dichotomous (‘positive’ versus ‘negative’) for risk factor ‘repetitiveness’ and ‘local mechanical stress’. Ergonomic factors regarding force, posture, equipment and tools had to be present during more than a third of the working cycle to be considered as ‘positive’. The checklist used was strictly the same as that of Keyserling et al. (1993), but the computation of the total score was modified. The score was defined exclusively as the sum of ‘positive’ risk factors, i.e. those present at the workstation during more than a third of the working cycle. The risk factors occuring during less than a third of the working cycle were not taken into account in the present study. The total ergonomic score for right, left and both hands was calculated for each worker and each work situation (Roquelaure et al., 2002).
Most subjects worked full-time and 77% of them were at the same type of workstations during the 4 year follow-up. About 23% (38 subjects) changed job classifications during the 4 year period: 15 workers (9%) during the first year of follow-up and 21 others (13%) between 1997 and 2000. Of the 38 workers who had changed job classifications between 1996 and 2000, the change of job was mainly due to technical or economic reasons (86%) and rarely to the occurrence of MSDs (eight cases). In particular, the number of workers assigned to sewing was reduced during the second part of the follow-up because of a delocalization of a part of the shoe production, while the subjects working on mechanized or manual assembly increased as a result of technological changes in the factory. Moreover, the number of flexible workers increased during the period because of greater flexibility in shoe production. Nevertheless, most of the workers (73%) estimated that their exposure to ergonomic factors had not changed between 1997 and 2000. For some workers, exposure to ergonomic stressors decreased during the period due to implementation of an ergonomic program (Roquelaure et al., 2002). In particular, these workers experienced more frequent rotation between different workstations (28 workers), lower physical (17 workers) or mental (11 workers) loads, lower task repetitiveness (12 workers), less frequent constrained postures (21 workers) and/or less stressful psychosocial factors (12 workers). However, exposure to ergonomic stressors increased for other workers, in particular exposure to physical (25 workers) or mental (17 workers) loads, awkward postures (12 workers) or psychosocial factors (three workers).
Data analysis
Each worker was first classified according to the main workstation used during the year preceding the assessment. For that, a classification of the workstations of the shoe industry were previously validated (Roquelaure et al., 1997, 2002). The titles of these groups of workstations (called here ‘job categories’) were: cutting (21 workers in 1996); preparation of the leather, including supplying pieces of leather (sewing preparation) (23 workers); sewing (67 workers); assembly preparation (12 workers); mechanized assembly, including carding (26 workers); manual assembly (24 workers); pasting (13 workers); finishing, including checking (27 workers) and packing tasks (19 workers) (Table 2). The prevalence rates [PR(1996,1997,2000)] were calculated on the basis of the existing cases of MSD during the year of the survey divided by the total number of workers in the corresponding job category. The incidence rates of MSDs in 1997 were calculated for each job category as the number of MSDs in workers free from any MSDs in 1996 divided by the total number of workers in the corresponding job category. The cases of MSD diagnosed in 2000 in workers free of any MSDs in 1996 and 1997 were computed for each job category. The mean annual incidence rates between 1998 and 2000 [IR(2000)] were calculated as the number of cases of MSD arising during the 36 month period divided by three and by the total number of workers in the corresponding job category.
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The criteria used to predict the occurrence of MSDs were those of the reference book on MSDs (criteria 1, 3, 4 and 5) and those defined during the first follow-up (Roquelaure et al., 2002
):
- Criterion 1. More than a 2-fold difference in the prevalence rate [PR(1996)] of MSDs for the job category compared to the prevalence for the whole sample from the factory.
- Criterion 2. A ratio between the PR(1996) of MSDs in the job category and the PR(1996) for the entire population >1.5.
- Criterion 3. An incidence rate [IR(1997)] of MSDs in the job category >1 per 100 person-years.
- Criterion 4. An incidence rate [IR(1997)] of MSDs more than twice that of the whole sample from the factory.
- Criterion 5. Workers of the job category under review exposed to at least one ergonomic risk factor.
- Criterion 6. A mean ergonomic score of the job category greater than the median value for the whole sample from the factory.
- Criterion 2. A ratio between the PR(1996) of MSDs in the job category and the PR(1996) for the entire population >1.5.
).
The 
2 test and analysis of variance (ANOVA) were used to compare the characteristics of the workers whether they were followed up in 1997 and 2000 or not. The Spearman's rank correlation coefficient () was used to compare the ranking of the job categories according to IR(2000) and the different criteria (1–6) used in 1996 and 1997. The sensitivity (Se) and specificity (Sp) of the different decision criteria were computed in relation to the ranking of the job categories by decreasing order of IR(2000) in 2000. Statistical analysis was performed using the Statistical Package for Social Science software (SPSS for Windows, version 10.0).
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONACKNOWLEDGEMENTSREFERENCES |
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The prevalence rate of MSDs [PR(2000)] remained high (
37%) in the shoe factory in 2000 (Table 2) and included all sectors of the company. PR(2000) did not significantly differ between the job categories (P = 0.4). The prevalence of MSDs was particularly high for four classes of workstations: pasting (56%), cutting (44%), sewing (42%) and assembly preparation (40%) (Table 2). The mean annual incidence of MSDs in 2000 was not significantly different between the job categories (P = 0.7). While no job category had an IR(2000) twice the IR(2000) for the whole sample, IR(2000) was >1% for all job categories, except for assembly preparation and packing. Because 87 workers out of the 253 included in the study in 1996 were not followed up in 2000, the possible effect of selection of workers who were followed up was studied. Age and number of years on the job did not significantly differ between workers who were followed up and those who were not. The PR(1996) was similar between both groups. The distribution of workers between the job categories did not differ significantly in the three surveys. However, the number of flexible workers increased from 1997. The ergonomic scores were higher for the workers who were not followed up in 2000 (8.8 ± 1.6 versus 8.0 ± 2.4, P = 0.03), suggesting exposure to higher ergonomic strains.
The results of the surveillance of health outcomes in 1996, 1997 and 2000 are summarized in Table 3. The surveillance of health outcomes in 1996 and 1997 predicted that several job categories were at high risk of MSDs. The sensitivity of the prevalence criteria 1 and 2 was low since no incident case of MSDs occurred in workers assigned to assembly preparation, which was the only job category predicted to be at high risk. The sensitivity and specificity of the criteria based on incidence data in 1997 was much better than criteria based on prevalence data. In particular, the sensitivity of criterion 3 was good (Se = 1) since all the job categories identified as at high risk in 1997 also had an IR > 1% in 2000. The specificity of this criterion was also good (Sp = 1) since no MSD occurred in job categories classified at low risk (assembly preparation and packing). The correlation between the rankings of IR in 1997 and 2000 was good ( = 0.567, P = 0.11). Agreement between the rankings of IR was particularly good for mechanized assembly, manual assembly, assembly preparation and packing, moderately good for sewing and sewing preparation and low for cutting, pasting and finishing. While the sensitivity of criterion 4 (2-fold difference in IR in 1997) was low (Se = 0.14) with only one of the seven categories identified as at high risk in 1997, this criterion permitted identification of the job category with the highest IR in 2000 (i.e. mechanized assembly).
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Agreement between job categories predicted to have potentially high risk of MSDs on the basis of ergonomic exposure and the occurrence of MSDs 4 years later was lower than the prediction based on incidence data. Criterion 5 (the presence of at least one ergonomic risk factor) was sensitive (Se = 1), since all job categories in which at least one case of MSD occurred in 2000 were identified to have potentially high risk of MSDs in 1996. Nevertheless, the specificity of the criterion was low (Sp = 0) since the two job categories in which no MSD occurred 4 years later were also considered to have potentially high risk of MSDs. Above all, the ranking of job categories by mean ergonomic score and IR(2000) was not congruent (
= –0.092, P = 0.8). Some job categories (mechanized assembly and manual assembly) with a low mean ergonomic score were characterized 4 years later by high IR(2000). On the other hand, some job categories with a high ergonomic score had low IR(2000), in particular assembly preparation and, to a lesser extent, sewing. Agreement between the prediction and the situation in 2000 was higher for prevalence [ = 0.403, P = 0.28 for PR(2000)] than for incidence. The use of a more restrictive ergonomic criterion (ergonomic score over the median value for the whole sample) was not efficient enough to detect job categories at risk of MSDs (Se = 0.43, Sp = 0.5, = 0.600, P = 0.4). In particular, assembly preparation was misclassified and the job categories with the highest IR(2000) were not identified, except for pasting. The agreement between the prediction based on the ranking of mean ergonomic scores and PR(2000) was relatively good ( = 0.8, P = 0.2). |
DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONACKNOWLEDGEMENTSREFERENCES |
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From a methodological point of view, the shoe factory studied was a good example of health and work exposure surveillance. The low worker turnover and the low percentage of flexible workers facilitated surveillance over a relatively long period. Selection for health reasons between the three physical examinations was minimal during the 4 year follow-up since the 166 workers included in this longitudinal study were not selected according to health criteria. Most of the workers lost from follow-up were for economic reasons or due to retirement. Since the technical aspects of the surveillance method have been discussed in a previous paper (Roquelaure et al., 2002
), the discussion will focus on the result of the health and exposure surveillance.
The previous study conducted in the factory demonstrated that the results of the surveillance program after 1 year of follow-up depended on the definition of the criteria to decide whether or not a job category could be considered to have high risk of MSDs (Roquelaure et al., 2002). The present study confirms this result over a longer period of follow-up. Consequently, the implementation of a routine analysis of health and exposure data in a company should be preceded by reflection by the occupational health staff on the rules of decision and it should be kept in mind that decisions based on a health and exposure surveillance program depend largely on the criteria used to define the risk of MSDs.
The criteria for surveillance of the workers' musculoskeletal health status based on prevalence data were not efficient enough to predict the risk of MSDs. Only assembly preparation was identified among the job categories characterized by frequent onset of MSDs in 2000, whatever the threshold chosen. Moreover, the prevalence and incidence rates in assembly preparation should be interpreted with caution because of the small size of this sub-group. It should be borne in mind that the incidence rate during the second follow-up could be underestimated since some of the cases of MSDs that both began and ended in the 3 year period were not taken into account (Leclerc et al., 2001). Nevertheless, the study clearly shows that incidence data are more valid than prevalence data to predict the occurrence of MSDs 3 years later. This confirms the result of the first follow-up study (Roquelaure et al., 2002). In a more general way, incidence data are more relevant since they are less affected by the healthy worker effect than prevalence data. In consequence, the present study suggests placing more emphasis on incidence data than on prevalence data in the surveillance of workers' musculoskeletal health. The criterion based on a threshold of incidence rate of 1% was effective in identifying all types of job categories characterized as having a high risk of MSDs at 3 years. Specificity was relatively good since none of the job categories without onset of MSDs in 2000 were predicted to have high risk in 1997. The study demonstrates that the criterion based on a 2-fold difference in incidence rate (criterion 3) was not effective in predicting the risk of MSDs in the shoe factory. As previously stated, it is more effective to rank workstations from highest to lowest incidence rates of MSDs to determine the level of risk of MSDs rather to define a threshold level of incidence (Roquelaure et al., 2002), since the agreement between the ranking of the job classifications in relation to IR(1997) and the number of cases arising during the second follow-up was fairly good. This suggests the use of incidence data rather than prevalence data in selecting the job categories requiring priority for ergonomic improvement.
Contrary to our hypothesis, the surveillance of work exposure was of lower value than incidence data to detect job categories with high IR of MSDs in 2000. This could be due to the method of ergonomic exposure assessment, which relied on a checklist. Nevertheless, the present study confirms the high sensitivity of the checklist, as observed in several workplaces (Keyserling et al., 1993). In particular, the method of computation of the ergonomic score by which risk factors present for less than a third of the working cycle were not taken into account, contrary to the methodology proposed by Keyserling et al. (1993), did not drastically diminish the sensitivity of the checklist, since at least one ergonomic risk factor for MSDs was identified in almost all job categories. The definition of the decision criteria could also explain the lack of agreement between exposure assessment and occurrence of MSDs 4 years later. Criterion 5 (at least one risk factor) appeared to be too sensitive and not specific enough to allow accurate exposure assessment. Indeed, if all types of job categories with high IR(2000) were predicted to have high risk, two with low IR were also considered at high risk. As explained above, the small number of workers in each job category studied should be borne in mind before drawing general conclusions. Moreover, the high prevalence of disorders during the first follow-up reduced the number of workers free from MSDs and, consequently, available for computation of the incidence rate of MSDs during the second follow-up. This explains the low precision of the estimation of the incidence rate of MSDs in 2000. For example, in the two job categories with IR(2000) = 0, the occurrence of only one case of MSDs would have increased the incidence rate substantially over the threshold value of 1% (12.5 and 20%, respectively). Therefore, the possibility that these two job categories were in reality also at high risk of MSDs cannot be excluded. The sensitivity and specificity of the second ergonomic exposure decision criterion (criterion 6) was fairly low. This criterion, based on the summation of the risk factors of the checklist, was a relatively rough method for exposure measurement and this could explain the low level of agreement with the result of the health surveillance 4 years later. The study confirms that the choice of cut-off value for the ergonomic score has a dramatic effect on the results of exposure surveillance and that it is more effective to rank the types of job classification from highest to lowest ergonomic score. Nevertheless, the agreement between the ranking of the job classifications in relation to the ergonomic score in 1996 and incidence rate in 2000 was relatively poor. As observed during the first year of follow-up, the ergonomic findings were more closely associated with prevalence rate than with incidence rate.
The relatively low agreement between the prediction and the occurrence of MSDs in 2000 could not only be explained by methodological aspects of the surveillance program discussed above but also by the characteristics of the shoe factory. The risk of MSDs was spread throughout the whole factory, as demonstrated by both health and exposure assessments that showed a high risk of MSDs in almost all jobs (Roquelaure et al., 2002). This might explain the difficulty in identifying job categories with a higher risk of disorders than others. Nevertheless, although the prevalence of MSD was high at baseline, the incidence of MSD remained high all along the 4 year follow-up. Since ergonomic exposure was assessed solely in 1996, another explanation might be the occurrence of variations in work exposure over the 4 year period, particularly as a result of the intervention program implemented after the first stage of the surveillance program. The intervention program consisted of both training for workers and supervisors and a wide-scale ergonomic program in production units to reduce the main ergonomic hazards (Roquelaure et al., 2002). Design of workstations was improved in the cutting, sewing, assembly and finishing sectors of the company during the second follow-up study. Changes in work organization were mainly made in the cutting and shoe assembly sectors, including pasting. The methodology of the study did not permit accurate association of the evolution of work exposure between 1997 and 2000 with the incidence rates in each category of job classification in 2000. Nevertheless, the impact of the program on work exposure was probably modest for most workers, since three-quarters of them estimated that their exposure to ergonomic stressors had not changed since 1997. Consequently, the change in exposure is probably not the only explanation for changes in the health situation between the different surveys. The checklist used focused more on risk factors for distal disorders, such as carpal tunnel syndrom and hand–wrist tendinitis, than on risk factors for cervico-brachial disorders. Therefore, the agreement between the ergonomic score and the outcomes in 2000 could have been better if the survey had focused more on distal MSDs. However, the sensitivity/specificity of each item of the checklist was not investigated for distal disorders because of the small number of incident cases of carpal tunnel syndrome and hand–wrist tendinitis in each job classification. Whatever the level of exposure, prevalence and incidence rates in job categories might also fluctuate because of the cyclical evolution of most MSDs (De Marco et al., 1998). Moreover, psychosocial factors which can affect the risk of occurrence of MSDs were not taken into account during the surveillance program (Hagberg et al., 1995).
The study emphasizes the importance of systematic surveillance of MSDs, which is part of the occupational and safety program of this company, to decide the most appropriate ergonomic intervention in the workplace to reduce the occurrence of MSDs in the workforce. It is generally proposed to monitor work exposure for this purpose (Hagberg et al., 1995; Silverstein et al., 1997; Sorock et al., 1997). Several considerations argue in favor of such a strategy (Silverstein et al., 1997). In a general way, monitoring of risk factor exposure is more proactive than assessment of MSDs, in that it does not require workers to be adversely affected. The time to evaluate job classifications can be relatively short, allowing repeated assessment to identify emerging problems and to plan plant prevention. However, evaluation of this surveillance strategy over a 4 year period demonstrates several limitations in the factory studied. The relatively low agreement between work exposure assessment at baseline and the occurrence of MSDs 4 years later suggests combining both health surveillance and risk factor assessment to predict the risk of MSDs, as proposed by Hagberg et al. (1995). Nevertheless, the study demonstrates several limitations of this sophisticated surveillance strategy. In particular, health surveillance cannot be based only on cross-sectional surveys since prevalence data are of limited value to predict the occurrence of MSDs. Health surveillance should therefore collect incidence data, which requires an interval of several months between the implementation of the health surveillance and the drawing up of ergonomic recommendations for the plant safety and ergonomic committee (Sorock et al., 1997). Such a health surveillance strategy is time-consuming and decreases the reactivity of the surveillance method. Moreover, such a strategy can be difficult to implement in small companies. When results are required rapidly, e.g. before the implementation of a prevention program, it would be better to predict the risk of adverse outcome from exposure measurements. Consequently, although health and risk factor surveillance must ideally be combined to predict the risk of MSDs in a company, exposure assessment plays a greater role in objectively determining which hazards the plant safety and ergonomics committee will address (Sorock et al., 1997). In this case, potential hazards could be detected even in small groups of workers, where health surveillance is less effective (Silverstein et al., 1997). Research is therefore needed to define efficient strategies of ergonomic exposure assessment over time, allowing more accurate prediction of the risk of MSDs.
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CONCLUSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONACKNOWLEDGEMENTSREFERENCES |
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The combination of health and risk factor surveillance to predict the risk of MSDs in a large factory was efficient in predicting at a collective level the categories of job classification in which numerous cases of MSDs occurred over a 4 year period. As observed during the first year of the follow-up, the criteria based on the incidence of MSDs were more reliable to predict the risk of MSDs than those based on prevalence data or on exposure assessment.
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ACKNOWLEDGEMENTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONACKNOWLEDGEMENTSREFERENCES |
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The study was supported by the French Health Insurance Fund for Prevention of Occupational risks (CNAM-CRAM Pays-de-la-Loire, grant 1996–2000).
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONACKNOWLEDGEMENTSREFERENCES |
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