Lateralization of the humerus in reverse total shoulder arthroplasty: can preoperative planning software predict postoperative lateralization and does lateralization influence outcomes?

Background: Reverse total shoulder arthroplasty (RTSA) can result in varying amounts of humeral medialization or lateralization. The amount of medial or lateral change-in-arm-position can be predicted using 3D computed tomography planning software. It is not clear if the preoperatively predicted change-in-arm-position correlates with the actual radiographically measured change-in-arm-position or if the predicted or actual change-in-arm-position correlates with patient-reported outcomes or complications. Methods: Patients who received RTSA underwent preoperative 3D computed tomography planning to predict the postoperative medial- to-lateral change-in-arm-position (PCAP). Preoperative and postoperative radiographs were used to calculate the actual medial-to-lateral change-in-arm-position using the measurement of the lateral edge of the greater tuberosity to the lateral edge of the acromion (RCAPLHO). The Western Ontario Osteoarthritis Score (WOOS), American Shoulder and Elbow Surgeons score (ASES), and Single Assessment Numeric Evaluation (SANE) were recorded at baseline, 1 year, and 2 years. Rates of complications were recorded. Results: A total of 250 patients were eligible for this study including 189 patients reaching the 1-year clinical follow-up point and 144 patients reaching the 2-year clinical follow-up point. One-year and 2-year follow-up rates were 89% and 91%, respectively. The mean PCAP was 3 +/- 5 mm and the mean RCAP-LHO was 1 +/- 8 mm. There was a moderate correlation between PCAP and RCAP-LHO. There was a weak correlation between increased PCAP lateralization and higher WOOS and ASES at 2 years and an improvement from baseline to 2 years in WOOS. There was a very weak correlation between increased PCAP lateralization and improvement compared with baseline in 1-year SANE and improvement compared with baseline in 2-year SANE. There was a weak correlation between lateralized RCAP-LHO and 2-year postoperative SANE. There was superior 2-year WOOS, ASES, and SANE, and improvement in SANE at 1 year compared with baseline in patients with a lateralized PCAP compared with a medialized or neutral PCAP. There was superior 2-year WOOS, improvement in WOOS from baseline to 2-year follow-up, and 2-year SANE in patients with a lateralized RCAP-LHO compared with a medialized or neutral RCAP-LHO. Overall complication rates were similar between groups although the dislocation rate in shoulders with a lateralized change-in-arm-position was significantly less than that in shoulders with a medial or neutral change-in-arm-position. Conclusions: PCAP correlated with actual RCAP-LHO. Correlations exist with increased humeral lateralization and improved patient- determined outcomes. Patient-determined outcomes in patients with a lateralized change-in-arm-position were the same as or better than those with a medialized or neutral change-in-arm-position. A lateralized change-in-arm-position did not result in increased overall complications and was protective against postoperative instability. Level of evidence: Level III; Retrospective Cohort Comparison; Prognosis Study (c) 2024 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights are reserved, including those for text and data mining, AI training, and similar technologies.