Associations between single and combined occupational mechanical exposures and surgery for subacromial impingement syndrome: a nationwide Danish cohort study

Abstract

Objective: This study aimed to evaluate whether the risk of surgery for subacromial impingement syndrome (SIS) increases with the number of combined occupational mechanical exposures compared with single exposure.

Methods: We reanalyzed data from a register-based cohort study of the entire Danish working population (N=2 374 403) with 14 118 events of surgery for SIS (2003-2008). Exposure information in 10-year windows was obtained by combining occupational codes with a job exposure matrix. For single and combined mechanical exposures, we created three exposure variables of the number of years with specific exposure intensities with or without co-existing mechanical exposures. We used logistic regression as survival analysis.

Results: We found exposure-response relations for duration and intensity of each single mechanical exposure except for repetition. The single effect of arm elevation >90º reached a maximum adjusted odds ratio (OR_adj) of 1.7 [95% confidence interval (CI) 1.5-2.0], which increased to 1.8 (95% CI 1.5-2.0), 2.0 (95% CI 1.9-2.2), and 2.2 (95% CI 2.0-2.5) when combined with repetition, force, and both. When combining repetition with arm elevation >90º, force, and both, OR_adj increased from 1.5 (95% CI 1.3-1.8) to 2.1 (95% CI 1.8-2.4), 2.5 (95% CI 2.4-2.9), and 2.7 (95% CI 2.4-3.0). For force, OR_adj increased from 2.5 (95% CI 2.1-2.9) to 2.6 (95% CI 2.3-2.8), 2.8 (95% CI 2.4-3.2), and 3.0 (95% CI 2.6-3.4).

Conclusion: We found an increased risk of surgery for SIS with the number of combined exposures; the risk was especially pronounced when the combined exposures included force.

Figure 1

Adjusted odds ratios (OR)* with 95% confidence intervals of surgery for subacromial impingement syndrome in relation to duration of exposure (years) at different arm elevation intensities; single or combined with other mechanical exposures across 10-year exposure time windows. Single: Adjusted for the other two arm elevation duration variables, age, sex, region of residence, calendar year at start of follow up, number of follow-up years, and cumulative effects of three other mechanical exposures including hand-arm vibrations. Combined: Adjusted for the other two arm elevation duration variables, age, sex, region of residence, calendar year at start of follow up, number of follow-up years, cumulative exposures of one or two other mechanical exposures including hand-arm vibrations and the 2 variables, which counted years of exposure with one specific mechanical exposure occurring without the other.

Figure 2

Adjusted odds ratios (OR)* with 95% confidence intervals of surgery for subacromial impingement syndrome in relation to duration of exposure (years) at different repetition intensities; single or combined with other mechanical exposures across 10-year exposure time windows. Single: Adjusted for the other two repetition duration variables, age, sex, region of residence, calendar year at start of follow up, number of follow-up years, and cumulative effects of three other mechanical exposures including hand-arm vibrations. Combined: Adjusted for the other two repetition duration variables, age, sex, region of residence, calendar year at start of follow up, number of follow-up years, cumulative exposures of one or two other mechanical exposures including hand-arm vibrations and the two variables, which counted years of exposure with one specific mechanical exposure occurring without the other.

Figure 3

Adjusted odds ratios (OR)* with 95% confidence intervals of surgery for subacromial impingement syndrome in relation to duration of exposure (years) at different force intensities; single or combined with other mechanical exposures across 10-year exposure time windows. Single: Adjusted for the other two force duration variables, age, sex, region of residence, calendar year at start of follow up, number of follow-up years, and cumulative effects of three other mechanical exposures including hand-arm vibrations. Combined: Adjusted for the other two force duration variables, age, sex, region of residence, calendar year at start of follow up, number of follow-up years, cumulative exposures to one or two other mechanical exposures including hand-arm vibrations, and the two variables, which counted years of exposure with one single mechanical exposure occurring without the other.