Comparison of Shoulder Functions Between Workers With and Without Shoulder Impingement Syndrome

The occurrence of shoulder impingement syndrome (SIS) is associated with the frequent handling and lifting of heavy loads and excessive repetitive work above the shoulder level. Thus, assembly workers have a high prevalence of shoulder injuries, including SIS. The purpose of this study was to investigate differences in shoulder ROM, muscle strength, asymmetry ratio, function, productivity, and depression between workers with and without SIS. Sixty-seven assembly line male workers (35 workers with SIS and 32 workers without SIS) participated in this study. The four shoulder ROMs and the five muscle strengths were measured using a Smart KEMA system. The asymmetry ratios were calculated using the asymmetry ratio formula; shoulder functions were measured using the shoulder pain and disability index (SPADI), disabilities of the arm, shoulder, and hand (DASH), and visual analogue scale (VAS); and Endicott work productivity scale (EWPS). Severity of depression was measured using the Beck depression inventory (BDI). Independent t-tests were performed for statistical analysis. The SPADI, DASH, and VAS values of workers with SIS were significantly higher than those of workers without SIS. Also, workers with SIS had significantly smaller shoulder internal rotation and shoulder abduction compared to workers without SIS. In addition, workers with SIS exhibited significantly lower SIR muscle strength than workers without SIS. Workers with SIS had significantly higher asymmetry ratios in shoulder internal rotation, shoulder external rotation, and elbow flexion muscle strength than workers without SIS. The SPADI and DASH scores, which indicate shoulder function, were higher, and the intensity of self-aware pain was higher in workers with SIS. Also, workers with SIS exhibited reduced SIR and SAB ROMs; decreased SIR muscle strength. Particularly, the asymmetry ratios of SIR, SER, EF muscle strength are good comparable factors for workers with and without SIS. In addition, the asymmetry ratios of shoulder muscle strengths could provide an important baseline comparison for the workers with SIS.