Lateralization of the Humerus in Reverse Total Shoulder Arthroplasty: Can Preoperative Planning Software Predict Postoperative Lateralization and Does Lateralization Influence Outcomes?

ABSTRACT

INTRODUCTION: 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 CT 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 predicted or actual change-in-arm-position correlates with patient-reported outcomes or complications. METHODS: Patients undergoing RTSA underwent preoperative 3D CT 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 (RCAP-LHO). 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: Two-hundred-and-fifty patients were eligible for this study including 189 patients reaching the one-year clinical follow-up point and 144 patients reaching the two-year clinical follow-up point. One-year and two-year follow-up rates were 89 percent and 91 percent, respectively. The mean PCAP was 3+5 mm and RCAP-LHO was 1+8 mm. There was moderate correlation between PCAP and RCAP-LHO. There was weak correlation between increased PCAP lateralization and higher WOOS and ASES at two years and improvement from baseline to 2 years in WOOS. There was very weak correlation between increased PCAP lateralization and improvement compared to baseline in 1 year SANE and improvement compared to baseline in 2 year SANE. There was 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 to baseline in patients with a lateralized PCAP compared to a medialized or neutral PCAP. There was superior 2-year WOOS, improvement in WOOS from baseline to 2-year follow-up, and SANE at 2-years in patients with a lateralized RCAP-LHO compared to 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 compared to 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 were the same or better in patients with a lateralized change-in-arm-position compared to those that were medialized or remained neutral. A lateralized change-in-arm-position did not result in increased overall complications and was protective against postoperative instability.