Kinetic strategies of patients with shoulder impingement syndrome

Abstract

Our aim was to determine whether subjects with shoulder impingement syndrome (SIS) have abnormal multijoint torque patterns compared to healthy subjects during normalized isometric force along specific directions. Subjects had to generate an isometric force corresponding to 40% of the maximal pain-free force. Eight targets were displayed on a monitor (0, 45, 90, 135, 180, 225, 270, and 3158). We calculated shoulder and elbow torques (kinetic strategies) using a biomechanical model. Regardless of the target location, the SIS group succeeded in reaching the target; however, when compared to the healthy subjects, they needed more time to do so, suggesting that SIS may slow down the execution of the kinetic strategies. Moreover, the SIS group produced lower shoulder external/internal torque to reach the targets located at 08 and 2258, and they generated greater abduction/adduction torque for targets located at 0, 135, and 1808. In addition, they had lower elbow extension/flexion torque for the target located at 3158. The investigation of atypical kinetic strategies is essential to provide an understanding of the pathomechanics of the SIS and to develop more effective treatment strategies. Shoulder impingement syndrome (SIS) is an encroachment of the subacromial bursa and the rotator cuff that results from the narrowing of the subacromial space. 1 There are two predominant theories about the cause of impingement. The intrinsic theory suggests that tendon degeneration, due to overuse, tension overload, or trauma lead to muscle weakness and lack of shoulder movements coordination. In contrast, the extrinsic theory proposes that impingement is caused by factors unrelated to the tendon. Despite the controversy regarding the etiology, SIS is a general term related to pathology involving the rotator cuff, biceps tendon, and subacromial bursa. 2 SIS constitutes a medical, social, and economic impairment on society, 3 with diagnosed cases of rotator cuff pathology usually resulting in impaired physical health and lower quality of life. 4 Kinematic changes at the scapula are associated with SIS. 2,5 Moreover, altered dynamic stability of the shoulder is associated with SIS, 6 a decreased rotator cuff contribution during arm elevation associated with an increased contribution of the deltoid, and an altered force production of the deltoid and the supraspinatus or a dysfunctional rotator cuff can result in increased superior translation of the humeral head. 1,5,7 Nonetheless, electromyography results from a limited set of muscles inevitably provide an incomplete picture of coordination disturbances following SIS.During the last decade, the impact of rotator cuff pathology on either isokinetic or isometric strength has been quantified. 4,[8][9][10] Overall, results revealed that patients have lower strength than healthy subjects. But these studies did not measure shoulder internal/ external, adduction/abduction, and flexion/extension and elbow joint torque coupling. Accordingly, the objective of this study was to determ...