Mechanical and psychosocial factors predict new onset shoulder pain: a prospective cohort study of newly employed workers

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Abstract
Aim: To test the hypothesis that work related mechanical and psychosocial factors predict new onset shoulder pain in newly employed workers. Methods: Two year prospective study of newly employed workers from 12 diverse occupational settings. At baseline, 1081 subjects provided information on work related mechanical and psychosocial risk factors, and current pain status. Results: In all, 803 (74%) subjects were free from shoulder pain at baseline. Of those, 638 (79%) responded at 12 months and 476 (88%) at 24 months. New onset shoulder pain was reported by 93 (15%) and 73 (15%) subjects respectively. An increased risk of symptom onset was found in subjects reporting mechanical exposures involving heavy weights including lifting with one or two hands, carrying on one shoulder, lifting at or above shoulder level, and pushing or pulling. Working with hands above shoulder level was also predictive of new onset shoulder pain. Of the psychosocial factors examined, the strongest predictor was monotonous work. Those individuals with any other previous pain also had an increased risk of new onset shoulder pain at follow up. In multivariate analysis, lifting heavy weights with one or two hands, pushing or pulling heavy weights, working with hands above shoulder level, and monotonous work were independently associated with new onset shoulder pain. Conclusions: This study supports the hypothesised relation between mechanical risk factors and shoulder pain. In general, work related psychosocial factors were modestly associated with new onset shoulder pain. However, monotonous work was a strong risk factor for new onset shoulder pain.