Evaluation des facteurs de risque de troubles musculo-squelettiques: Comparaison de methodes d'observation et perception des travailleurs

The prevalence of musculoskeletal disorders (MSDs) in workplaces is a major problem. According to the recently published Enquête sur les conditions de travail, d'emploi et de santé et de sécurité du travail, one in five Quebeckers (20,5%) suffer from MSDs. MSDs represent 38% of all injuries compensated by Quebec's worker compensation board. Given the significant impacts of MSDs, industries need to work on prevention. The scientific literature shows that intervention to reduce exposure to MSD risk factors is the best prevention strategy. Recent literature in ergonomics offers a variety of observation methods for MSDs risk factors assessment. Some were developed with the intention of supporting industry-led MSDs prevention efforts and provide important guidelines for the implementation of occupational health and safety strategies. Yet, the existing literature showcases little applied research that tests these methods in the field to compare the results they produce.;This doctoral thesis performs a comparative analysis of results obtained from 11 methods of MSDs risk factors assessment based on observation, and studies the relationship between the declaration of pain and perceptions of workers regarding the assessment of their workstations. The results of 21 indices from the 11 observation-based methods are compared in homogeneous groups. In total, 224 workstations were evaluated, involving 567 different tasks in 18 firms from various sectors of the economy. Data were gathered using video and measurements taken at the workstations. A questionnaire on the musculoskeletal pain experienced in various body regions, during the 12 months and seven days prior to the data collection, was also administered to employees participating in the study.;The first article of this doctoral thesis compares the results obtained from methods most likely to be used by practitioners when assessing risk factors for MSDs of the back. Six methods are analyzed: the QEC (Quick Exposure Check), the Ergonomic Workplace Analysis of the FIOH (Finnish Institute of Occupational Health), 3D SSPP, 4D WATBAK, A Guide to Manual Materials Handling by Mital et al. (1997) and the EN 1005-3 standard. The second article focuses on two groups of methods. In a first group, the methods assessing upper limbs risk factors are compared with each other (ACGIH HAL, Job Stain Index, OCRA, QEC, and the EN 1005-3 standard). In a second group, more general MSDs risk assessment methods are compared (FIOH's Ergonomic Workplace Analysis, QEC, RULA, and REBA). The results are compared using three risk categories (low, moderate, high).;Results reveal significant differences between methods in determining the level of risk. Among the methods compared in pairs, almost half evaluating the risk on the back showed differences of two risk level categories for one workstation out of five. Comparison of the methods from homogeneous groups reveals discrepancies between the methods that are sometimes significant within the same group. No pair of methods seems in perfect agreement. The results presented in the studies show that a workstation may be considered at risk by one method and not by another. These results illustrate the potentially important consequences of choosing a method for determining priorities in the context of a screening intervention in a company. The analysis of methods based on the identification of priorities (i.e. workstations that are considered most at risk by a method) has shown that some methods requiring less effort can produce similar results regarding the identification of the workstations that are at risk. Results also show that some methods should be preferred to others if a more conservative approach is sought.;The third study compares the evaluation of risk factors related to ergonomics for workers with and without musculoskeletal pain. FIOH's Ergonomic Workplace Analysis was used by workers and by an expert for the evaluation of the workstations. Also, the ergonomic quality of the workstation and the need to make changes were graded on a visual analogue scale (VAS). The results show that those who reported pain in the seven days prior to the assessment evaluated their workstations more negatively than subjects who reported no pain, while the expert found no difference between the workstations of the two groups.;The results of our study show that the opinion of the worker is less reliable since it depends on the presence of pain or not. However, even if this information is a ‘subjective' opinion of the worker, it supplies information that is otherwise difficult to obtain with a method based solely on observation. The results of this research help practitioners to have a much better idea of what to expect when they choose one method over another to perform the evaluation of a workstation. Considering these results, research should continue to develop decision making aids for choosing a method to evaluate MSDs risk factors.