Prevalence of musculoskeletal disorders at the wrist as a function of angles, forces, repetitiveness and movement velocities

OBJECTIVES: The purpose of this investigation was to study the relationship between the prevalence of musculoskeletal disorders at the wrists and the characteristics of the work conditions in terms of angles, forces, repetitiveness, and movement velocities. METHODS: Nine workplaces were selected and the prevalence of wrist disorders was determined by means of a questionnaire for both arms separately, along with characteristics of the 335 subjects (age, weight, height, seniority). A work analysis was performed on subjects selected at random from each workplace by recording, for both wrists during a representative number of work cycles, the angles both in radial and ulnar deviations and in flexion-extension and the surface electromyogram on the hand flexors of the forearm. Repetitiveness (defined as the number of transitions per minute) and movement velocities (in deviation and flexion-extension) were derived from the recordings of the angles. RESULTS: All the derived variables were highly correlated, greater angles and greater forces being associated with greater velocities and higher repetitiveness. A multivariate linear regression model for the prediction of the prevalence of musculoskeletal disorders of the wrist was constructed (R = 0.904). Height, weight, seniority, angles in radial-ulnar deviation, and forces were significant and independent predictors of the prevalence. CONCLUSIONS: The prevalence of wrist disorders is significantly linked to wrist angles in deviation and to forces exerted. Due to their high correlation with force, the repetitiveness indices and velocities, as defined, do not appear to play an additional role. Further research is needed to find alternative ways of characterizing repetitiveness