Effort-reward imbalance and incidence of low back and neck injuries in San Francisco transit operators

Reiner Rugulies ^1* and Niklas Krause ²

¹ National Research Centre for the Working Environment, Denmark
² Division of Occupational and Environmental Medicine, University of California, San Francisco, United States

^* To whom correspondence should be addressed. E-mail: rer{at}nrcwe.dk.

Accepted 9 November 2007

Abstract

Objectives: Effort-reward imbalance (ERI) has been associated with musculoskeletal disorders in cross-sectional and case-control studies but no longitudinal studies have been published yet. We examined the effect of ERI on the incidence of compensated low back and neck injuries in a 7.5-year follow-up study among 1,179 San Francisco transit operators. Methods: Data from medical examination and a survey on working conditions and health were linked to administrative workers’ compensation databases. Hazard ratios (HR) for first low back and first neck injury were calculated with multivariate Cox regression models. Additional analyses accounted for severity of injury based on medical diagnosis. Results: A one standard deviation increase in ERI was associated with compensated low back (HR=1.13, 95% CI: 1.02-1.26) and neck injuries (HR=1.14 (95% CI: 1.02-1.27) after adjusting for age, gender, height, weight, years of professional driving, weekly driving hours, vehicle type, ergonomic problems, pain at baseline, and job strain. The highest quartile of ERI showed a HR of 1.32 (95% CI: 0.94-1.86) for low back injuries and a HR of 1.66 (95% CI: 1.16-2.38) for neck injuries after adjustment for all covariates. The associations between ERI and low back injury were stronger for more severe injuries (HR=1.23, 95% CI: 1.03-1.46 for a one standard deviation increase in ERI) than for less severe injuries (HR=1.11, 95% CI: 0.96-1.28). For neck injuries, stronger relationships were found for less severe injuries (HR=1.15, 95% CI: 1.02-1.29) than for more severe injuries (HR=1.10, 95% CI: 0.86-1.41). Conclusions: ERI is associated with low back and neck injuries in San Francisco transit operators independent of individual worker characteristics, physical workload, ergonomic problems, baseline pain, and job strain. Effect sizes differed by injury severity.

Keywords: Musculoskeletal disorders, Psychosocial factors, Stress, psychological, low back pain, neck pain

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