Prospective validation of a low-back disorder risk model and assessment ofergonomic interventions associated with manual materials handling tasks

The evaluation of low-back disorder risk associated with materials handling tasks can be performed using a variety of assessment tools. Most of these tools vary greatly in their underlying logic, yet few have been assessed fo r their predictive ability. It is important to document how well an assessm ent tool realistically reflects the job's injury risk, since only valid and accurate tools can reliably determine whether a given ergonomic interventi on will result in a future reduction in back injuries. The goal of this stu dy was to evaluate how well a previously reported low-back disorder (LBD) r isk assessment model (Marras et al. 1993) could predict changes in LBD inju ry rates as the physical conditions to which employees are exposed were cha nged. Thirty-six repetitive materials handling jobs from 16 different compa nies were included in this prospective cohort study. Of these 36 jobs, 32 u nderwent an ergonomic intervention during the observation period, and four jobs in which no intervention occurred served as a comparison group. The tr unk motions and workplace features of 142 employees performing these jobs w ere observed both before and after workplace interventions were incorporate d. In addition, the jobs' LBD rates were documented for these pre- and post -intervention periods. The results indicated that a statistically significa nt correlation existed between changes in the jobs' estimated LBD risk valu es and changes in their actual low-back incidence rates over the observatio n period. Linear and Poisson regression models also were developed to predi ct a change in a job's incidence rate and the number of LBD on a job respec tively, as a function of the job's risk change using this assessment model. Finally, this prospective study showed which ergonomic interventions consi stently reduced the jobs' mean low-back incidence rates. These results supp ort use of the LBD risk model to assess accurately a job's potential to lea d to low-back injuries among its employees.