Kinematic analysis of dynamic shoulder motion in patients with reverse total shoulder arthroplasty.
Patients that have undergone reverse total shoulder arthroplasty (rTSA) can achieve active shoulder elevation up to 138°. This goes hand in hand with a substantially altered anatomy and subsequent changes in biomechanical properties, which in turn may lead to considerable changes in kinematics of the shoulder girdle.
This study employed an electromagnetic tracking system in order to collect kinematic data on the glenohumeral joint and assess scapulothoracic motion in a group of 17 patients that had undergone rTSA and an asymptomatic control group. Subjects performed a testing sequence consisting of elevation in the sagittal, coronal and scapular plane; this was repeated holding a weight of 2 lb and again holding a weight of 4 lb.
In healthy shoulders, scapulothoracic rotation contributed minimally during lower angles of elevation and increased during higher angles of elevation. The contribution of scapulothoracic rotation in rTSA shoulders was relatively consistent during the entire range of motion.
In both groups, the scapulohumeral rhythm (SHR), i.e. the ratio between glenohumeral motion and scapulothoracic rotation, remained greater than 1.62, indicating that glenohumeral elevation in all cases contributed more to shoulder elevation that scapulothoracic motion. The addition of hand weights led to a significant decrease in SHR, particularly at lower angles > From Kwon et al., J Shoulder Elbow Surg 21 (2012) 1184-1190. All rights reserved to the Journal of Shoulder and Elbow Surgery Board of Trustees.
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