The lateralization and distalization shoulder angles are important determinants of clinical outcomes in reverse shoulder arthroplasty

Background: Reverse shoulder arthroplasty (RSA) designs vary in the lateralization and distalization geometry, which may affect functional outcomes. The purpose was to determine the effect of RSA lateralization and distalization on final functional outcomes by using the "lateralization shoulder angle" (LSA) and the "distalization shoulder angle" (DSA). Methods: Forty-six consecutive patients who underwent RSA for cuff tear arthropathy were retrospectively evaluated. Functional outcome and radiographs were evaluated at a minimum of 2 years postoperatively and compared between implants with or without glenoid lateralization and with or without humeralsided lateralization. Anteroposterior shoulder radiographs were used to evaluate the LSA and DSA. Results: Both angles showed substantial to almost perfect intrarater and inter-rater agreement. Higher LSA values were found in more lateralized RSAs (P =.027), and values between 75 degrees and 95 degrees were correlated with better active external rotation (quadratic regression analysis R-2 = 0.553, P <.001). Postoperative active anterior elevation (R-2 = 0.2, P =.008), Constant (r(s) = 0.29, P =.05), and Activities of Daily Living Requiring External Rotation scores (r(s) = 0.4 P =.007) had a positive correlation with the LSA. The quadratic regression analysis also showed that a DSA between 40 degrees and 65 degrees resulted in better active anterior elevation (R-2 = 0.4, P <.001) and abduction (R-2 = 0.4, P <.001). The negative correlation between the LSA and DSA (r(s) = -0.7, P <.001) revealed that, according to the implant used, the more distally the RSA is placed the less lateralization is achieved. Conclusions: The LSA and the DSA are reproducible measurements that may be used to estimate "lateralization and distalization" after RSA. These measurements are correlated with postoperative clinical outcomes. (C) 2018 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved.