Minimal Clinically Important Differences for Oxford, Constant, and University of California Los Angeles Shoulder Scores After Reverse Shoulder Arthroplasty to Allow Interpretation of Patient-Reported Outcome Measures and Future Statistical Power Analyses

Purpose: To determine the minimal clinically important difference (MCID) for the ConstanteMurley Score (CMS), University of California Los Angeles (UCLA) Shoulder Score, and Oxford Shoulder Score (OSS) after reverse shoulder arthroplasty. Methods: Patients were prospectively followed up between January 2011 and February 2020. Inclusion criteria was that of patients who underwent reverse shoulder arthroplasty for massive irreparable cuff tear, cuff tear arthropathy, and fractures, with and without previous cuff repair, by a fellowship-trained surgeon. Patients were assessed preoperatively and at 3, 6, and 12 months' postoperatively. Functional outcome was assessed by the CMS, UCLA Shoulder Score, and OSS and the respective MCIDs were determined using simple linear regression in consonance with patient satisfaction and expectation fulfilment. Results: A total of 131 patients were followed up for 12 months. The MCIDs at 3 months for CMS, UCLA Shoulder Score, and OSS were 7.2, 3.3, and 6.9, respectively. At 6 months, the MCIDs for CMS, UCLA Shoulder Score, and OSS were 6.6, 2.4, and 4.7, respectively. At 12 months, the MCIDs for CMS, UCLA Shoulder Score, and OSS were 9.3, 2.9, and 6.6, respectively. Conclusions: CMS, UCLA Shoulder Score, and OSS are valid scores to calculate MCID after reverse shoulder arthroplasty, and the MCID established in this study can be used for the interpretation of these scores to help in statistical power analysis for future studies. Level of Evidence: III, retrospective cohort study.