ORIGINAL ARTICLES

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

R Rugulies^1,2 and N Krause³

¹ National Research Centre for the Working Environment, Copenhagen, Denmark
² Institute of Public Health, University of Copenhagen, Denmark
³ Department of Medicine, Division of Occupational and Environmental Medicine, University of California at San Francisco, USA

Correspondence to:
Dr R Rugulies, National Research Centre for the Working Environment, Lersø Parkallé 105, DK-2100 Copenhagen, Denmark; rer{at}nrcwe.dk

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. The effect of ERI on the incidence of compensated low back and neck injuries was examined in a 7.5-year follow-up study among 1179 San Francisco transit operators.

Methods: Data from medical examination and a survey on working conditions and health were linked to administrative workers’ compensation databases. HRs 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 1 SD increase in ERI was associated with compensated low back (HR 1.13, 95% CI 1.02 to 1.26) and neck injuries (HR 1.14, 95% CI 1.02 to 1.27) after adjusting for gender, age, 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 an HR of 1.32 (95% CI 0.94 to 1.86) for low back injuries and an HR of 1.66 (95% CI 1.16 to 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 to 1.46 for a 1 SD increase in ERI) than for less severe injuries (HR 1.11, 95% CI 0.96 to 1.28). For neck injuries, stronger relationships were found for less severe injuries (HR 1.15, 95% CI 1.02 to 1.29) than for more severe injuries (HR 1.10, 95% CI 0.86 to 1.41).

Conclusions: ERI is associated with low back and neck injuries in San Francisco transit operators independently of individual worker characteristics, physical workload, ergonomic problems, baseline pain and job strain. Effect sizes differ by injury severity.

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