Effect of deltoid volume on range of motion and patient-reported outcomes following reverse total shoulder arthroplasty in rotator cuff-intact and rotator cuff-deficient conditions

BACKGROUND: Deltoid muscle function is paramount to the success of reverse total shoulder arthroplasty. The purpose of this study was to investigate the role of deltoid volume on shoulder range of motion and patient-reported outcomes following reverse total shoulder arthroplasty in rotator cuff-intact and rotator cuff-deficient conditions. METHODS: Retrospective review of records identified 107 patients who met inclusion criteria. The rotator cuff integrity was evaluated by two musculoskeletal-trained radiologists. Volumetric deltoid measurements were calculated from preoperative computed tomography or magnetic resonance imaging scans. Satisfactory outcomes were defined as forward elevation of at least 135°, external rotation of at least 35°, and American Shoulder and Elbow Surgeons and Single Assessment Numerical Evaluation scores of at least 70. RESULTS: Mean total deltoid muscle volume was significantly higher in patients with satisfactory forward elevation (57.8 ± 18.1 cm³) versus unsatisfactory forward elevation (48.6 ± 19.5 cm³) (p = 0.013). When separated by rotator cuff integrity, total deltoid volume was significantly higher (p = 0.030) in patients who achieved satisfactory forward elevation in the rotator cuff-deficient group but not the rotator cuff-intact group (p = 0.533). DISCUSSION: Preoperative deltoid volume directly correlated with achieving satisfactory forward elevation after reverse total shoulder arthroplasty in rotator cuff-deficient conditions and may be one factor in determining the ability to achieve satisfactory outcomes in the rotator cuff-deficient patient.