The Effect of Reverse Shoulder Arthroplasty Design and Surgical Indications on Deltoid and Rotator Cuff Muscle Length

Advancements in surgical planning, technique, and prosthesis design have improved adaptation to patient anatomy in reverse total shoulder arthroplasty (rTSA). Postoperative changes in deltoid and rotator cuff muscle length are important and may vary based on preoperative indications and prosthesis selection. The purpose of this study is to demonstrate the changes in deltoid and rotator cuff muscle length for planned rTSA using the spectrum of prosthesis configurations in both GHOA and RCA. Ten shoulder arthroplasty surgeons used preoperative planning software to plan rTSA cases for 20 subjects (10 GHOA, 10 RCA) following surgical guidelines. Each surgeon planned each case using three prosthesis configurations: (1) 8-mm lateralized glenosphere and 135° neck-shaft angle (135+8), (2) 4-mm lateralized glenosphere and 145° neck-shaft angle (145+4), and (3) 0-mm lateralized glenosphere and 155° neck-shaft angle (155+0). Pre- and postoperative deltoid and rotator cuff muscle lengths and percentage-change were calculated and compared between prosthesis configurations within each indication. Different muscle lines of action were included representing the deltoid, subscapularis, infraspinatus, and teres minor. Preoperatively, the RCA cohort had significantly shorter muscle lines of action in the posterior, lateral, and anterior deltoid (P