Joint contribution of rotation of the back and repetitive movements to disability pension using job exposure matrix data

Abstract

Background: Heavy physical effort at work has been linked with disability pension, but the contribution of other ergonomic job exposures is less studied. We studied the independent and joint contributions of long-term exposure to (i) rotation of the back and (ii) repetitive movements to disability pension, particularly due to musculoskeletal disorders.

Methods: Exposures were measured with the Helsinki Health Study Job Exposure Matrix during 1996-2005 and linked to register data on employees of the City of Helsinki, Finland (n = 18 585). Outcomes were followed up during 2006-2015. Competing risk survival analyses were performed and synergy indices computed, adjusting for sociodemographic factors.

Results: Long-term exposure to rotation of the back was associated with disability pension due to any cause [age and sex-adjusted subhazard ratio (SHR) 2.39, 95% confidence interval (CI) 1.73-3.30], and specifically disability pension due to musculoskeletal disorders (SHR = 3.39, 95% CI 1.52-7.56) when compared to employees exposed to neither of the two exposures. Repetitive movements alone did not increase the risk of disability pension (all-cause SHR = 1.08, 95% CI 0.84-1.38, musculoskeletal SHR = 1.65, 95% CI 0.91-2.97). Employees with exposure to both rotation of the back and repetitive movements had the highest risk of disability pension due to musculoskeletal disorders (SHR = 5.98, 95% CI 3.85-9.28), but the interaction between exposures was additive rather than synergistic. Adjustment for education diluted the associations by 42-108%.

Conclusion: Long-term exposure to awkward work postures increased the risk of disability pension. Educational inequalities largely account for differences in occupational exposures.