Predicting the onset of knee pain: results from a two year prospective study of new workers.

OBJECTIVES: To determine the relative contribution of work-related mechanical (injury) factors and psychosocial factors to the onset of a new episode of knee pain in a cohort of newly employed workers. METHODS: A prospective cohort study of newly employed workers from twelve diverse occupational settings in England (The New Worker Study). 859 newly employed workers, free of knee pain, were identified. Information about occupational mechanical factors (manual handling and postural activities), the occupational physical environment, and psychological and psychosocial factors was collected by self-completion questionnaire. Participants were followed up after 12 and 24 months to identify cases of knee pain onset. Generalised estimating equations were used to estimate the risk of new onset knee pain, with respect to the exposures previously measured. RESULTS: In total, over the two-year follow-up period, there were 108 cases of new onset knee pain. Mechanical load, postural factors, psychological distress and work-place psychosocial factors all influenced the risk of new onset knee over the two-year follow-up period. On multivariable analysis, two factors remained independently predictive of knee pain onset: lifting or carrying heavy weights in one hand, and the level of general psychological distress. CONCLUSION: This paper demonstrates that psychological factors are important, in addition to mechanical (injury) factors as risk factors for knee pain onset, in a population of young newly employed workers.