Subscapularis repair in reverse total shoulder arthroplasty: a systematic review and descriptive synthesis of cadaveric biomechanical strength outcomes.

Hypothesis/Background: There is no consensus on whether to repair the subscapularis in the setting of reverse total shoulder arthroplasty (rTSA). There have been an assortment of studies showing mixed results regarding shoulder stability and postoperative strength outcomes when looking at subscapularis repair in rTSA. The purpose of this systematic review was to investigate differences in biomechanical strength outcomes of cadaveric subscapularis repair vs. no repair in rTSA.Increased force will be required to move the shoulder through normal range of motion (ROM) in cadaveric rTSA shoulders with the subscapularis repaired when compared with no subscapularis repair. Methods: A comprehensive literature review was conducted in accordance with the 2009 Preferred Reporting Items for Systematic Review and Meta-Analysis statement. The databases used to search the keywords used for the concepts of subscapularis, reverse total shoulder arthroplasty, and muscle strength were PubMed (includes MEDLINE), Embase, Web of Science, Cochrane Reviews and Trials, and Scopus. Original, English-language cadaveric studies evaluating rTSA and subscapularis management were included, with subscapularis repair surgical techniques and strength outcomes being evaluated for each article meeting inclusion criteria. Results: The search yielded 4113 articles that were screened for inclusion criteria by 4 authors. Two articles met inclusion criteria and were subsequently included in the final full-text review. A total of 11 shoulders were represented between these 2 studies. Heterogeneity of the data across the 2 studies did not allow for meta-analysis. Hansen et al found that repair of the subscapularis with rTSA significantly increased the mean joint reaction force and the force required by the posterior deltoid, total deltoid, infraspinatus, teres minor, total posterior rotator cuff, and pectoralis major muscles. Giles et al found that rotator cuff repair and glenosphere lateralization both increased total joint load. Conclusion: The present review of biomechanical literature shows that repair of the subscapularis in the setting of rTSA can effectively restore shoulder strength by increasing joint reactive forces and ROM force requirements of other rotator cuff muscles and of the deltoid muscle. Available biomechanical evidence is limited, and further biomechanical studies evaluating the strength of various subscapularis repair techniques are needed to evaluate the effects of these techniques on joint reactive forces and muscle forces required for ROM.