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

Abstract

IntroductionReverse 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. MethodsPatients 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. ResultsTwo-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. ConclusionsPCAP 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.