BACKGROUND: Lateralization shoulder angle (LSA) and distalization shoulder angle (DSA) are 2 parameters that have been described for a better planification of arthroplasty, but the range of these angles is very wide. The purpose of this study was to investigate the best combination in terms of lateralization and distalization to optimize the outcome of reverse total shoulder arthroplasty (RTSA) for cuff tear arthropathy (CTA) with a functional deltoid. METHODS: This retrospective cohort study, conducted between 2014 and 2018 at a specialized shoulder unit in Paris, focused on patients exclusively treated with RTSA for CTA, ensuring a minimum follow-up of 1 year. The primary outcome measure was the American Shoulder and Elbow Surgeons (ASES) score. Secondary outcome measures included range of motion and patient-reported outcomes at the final follow-up, such as the Constant score, Subjective Shoulder Value, Simple Shoulder Test, and visual analog scale. Optimal RTSA outcomes were delineated by scores surpassing the patient's acceptable symptom state for ASES, set in literature at 76. Patients were categorized into 2 groups based on ASES scores at the last follow-up: those below and those above 76. The capabilities of LSA and DSA to predict the outcome of interest were assessed, and the corresponding optimal thresholds for having a better outcome were calculated using the receiver operating characteristic curve. RESULTS: Sixty-two patients with a mean age of 74.51 ± 6.79 years were included in the study. Correlation analysis revealed a significant medium correlation between ASES and both LSA (r = -0.43, P = .001) and DSA (r = 0.39, P = .002). The DSA of patients with ASES >
76 was 48.55° ± 12.44° with an interquartile range (IQR) of 39.5°-57.5°, as compared with the lower value for patients with ASES <
76, which was 37.82° ± 9.8° (IQR: 32°-46.5°, P = .009). Similarly, the LSA of patients with ASES >
76 was 86.43° ± 11.4° (IQR: 79.5°-93.5°), as compared with the higher value for patients with ASES <
76, which was 100.09° ± 7.63° (IQR: 93°-105.5°, P <
.001). The receiver operating characteristic curve confirmed LSA and DSA as good predictors for the ASES outcome, with areas under the curve of 0.851 and 0.741, respectively. The optimal LSA should be no more than 90.5° (sensitivity = 100%, specificity = 67.7%). The optimal DSA should be no less than 37.5° (sensitivity = 78.4%, specificity = 63.6%). CONCLUSION: The LSA and DSA could represent a helpful tool to optimize the clinical outcomes of an adaptable RTSA in CTA with a functional deltoid and a complete passive range of motion.