Impact of Reverse Total Shoulder Arthroplasty on Scapulohumeral Rhythm: A Systematic Review and Meta-Analysis.

Background: Scapulohumeral rhythm (SHR) describes the relative contributions of the humerus and scapula to total shoulder motion and is defined as the ratio of glenohumeral elevation (GH) to scapulothoracic (ST) upward rotation. The impact of reverse total shoulder arthroplasty (rTSA) on scapular kinematics and SHR has not been fully elucidated. The purpose of the present study was to perform a systematic review and meta-analysis of the literature to compare SHR among patients following rTSA and asymptomatic controls.

Methods: A literature search was performed by querying PubMed, EMBASE, and the Cochrane computerized databases to identify studies that assess SHR, or the relationship of GH elevation to ST upward rotation, in patients after rTSA. Study quality was assessed using the MINORS criteria. Quantitative review was performed for studies that reported either SHR directly, or reported GH and ST rotation. Differences in scapulohumeral rhythm were compared between different ranges of humeral elevation including rest-30°, 30-60°, 60-90°, and the total arc of elevation.

Results: Twenty-seven studies comprised of 464 patients who underwent rTSA were included in the final analysis for review. Among the studies included, 19 (70%) directly assessed SHR. The average SHR across all elevation ranges in the scapular plane was 1.6 (range: 0.8-2.7). The average SHR in the rest-30°, 30-60°, and 60-90° degree elevation arc ranges were 4.3 (range: 0.8-34), 2.0 (range: 0.7-4), and 1.8 (range: 0.8-3), respectively. Compared to controls, patients who underwent rTSA had greater ST upward rotation, quantified as a significantly lower SHR (1.9 vs. 3.2, p=0.0238).

Conclusion: There is an increased contribution of ST rotation relative to GH motion throughout arm elevation following rTSA compared to asymptomatic shoulders. The average SHR was lowest between 60-90° of arm elevation compared to the other measured ranges of arm elevation, indicating a greater contribution of scapulothoracic rotation required at higher angles of arm elevation. Further investigations are needed to determine the clinical implications of greater scapulothoracic motion in patients following rTSA, as well as the biomechanical causes and consequences of this alteration in scapular kinematics.