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 (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: 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.