Occupational lifting, carrying, pushing, pulling loads and risk of surgery for subacromial impingement syndrome: a register-based cohort study

AIM: The aim was to examine exposure–response relations between surgery for subacromial impingement syndrome (SIS) and intensities of lifting/carrying and pushing/pulling loads during a 10-year time window. METHODS: We conducted a register-based cohort study (2003–2008), comprising persons born in Denmark (1933–1977) with ≥5 years of work experience (N=2 374 403). Information on surgery for SIS was retrieved from the Danish National Patient Register (N=14 188). Occupational mechanical exposures comprising lifting/carrying loads ≥10 kg and pushing/pulling loads ≥50 kg were assessed by combining individual register-based job codes with our expert-based Shoulder job exposure matrix. We created three intensity-specific exposure duration variables by dividing the intensity for lifting/carrying and pushing/pulling loads into three categories (low, medium and high), and summed up number of years in each exposure category for a 10-year time window. The associations were analysed using logistic regression technique equivalent to discrete survival analysis. RESULTS: The adjusted OR (OR(adj)) increased with both exposure duration and intensity of lifting/carrying and pushing/pulling. For lifting/carrying, the OR(adj) reached a maximum of 1.78 (95% CI 1.66 to 1.89), 2.52 (95% CI 2.32 to 2.74) and 2.96 (95% CI 2.53 to 3.47) after 10 years of exposures for the three exposure intensities. For pushing/pulling, maximum OR(adj) was 1.44 (95% CI 1.31 to 1.58), 1.68 (95% CI 1.58 to 1.79) and 1.72 (95% CI 1.50 to 2.00), respectively. CONCLUSION: We found exposure–response relations for lifting/carrying and pushing/pulling across the 10-year time window. The risk was especially pronounced for lifting/carrying compared with pushing/pulling. We did not find indications of safe exposure intensities.