Interactions between physical and psychosocial risk factors at work increase the risk of back disorders: an epidemiological approach.

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Abstract
OBJECTIVES: To investigate the possible interactions between physical and psychosocial risk factors at work that may be associated with self reported back disorders. METHODS: 891 of 1514 manual workers, delivery drivers, technicians, customer services computer operators, and general office staff reported risk factors at work and back disorders with a self administered questionnaire (59% return rate). Of the 869 respondents with a valid questionnaire, 638 workers were classified in to one of four exposure groups: high physical and high psychosocial; high physical and low psychosocial; low physical and high psychosocial; and low physical and low psychosocial. Low physical and low psychosocial was used as an internal reference group. The exposure criteria were derived from existing epidemiological publications and models for physical and psychosocial work factors. The frequency and amplitude of lifting and the duration spent sitting while experiencing vibration were used as physical exposure criteria. Ordinal values of mental demands, job control, and social support from managers and coworkers were used as psychosocial exposure criteria. RESULTS: The highest increase in risk was found in the high physical and high psychosocial exposure group for symptoms of back disorders. In the crude and multivariate analyses, a departure from an additive risk model was found for the 7 day prevalence of symptoms of a low back disorder and also for a recurrent back disorder not present before the current job but also experienced in the past 7 days. CONCLUSION: This study suggests that an interaction between physical and psychosocial risk factors at work may exist to increase the risk of self reported back disorders. Ergonomic prevention strategies that aim to minimise the risks of symptoms of work related back disorders should not only focus on physical but also on psychosocial risk factors at work. The greatest benefits are likely to be realised when both physical and psychosocial factors are put right.