Reverse shoulder arthroplasty (RSA) is effective for cuff tear arthropathy, but complications from the Grammont design emphasized humeral lateralization and distalization. Conventional parameters such as the acromio-humeral interval (AHI) and critical shoulder angle (CSA) show inconsistent outcome associations. This study introduces new parameters using the greater tuberosity as a reference: the acromion–greater tuberosity distance (AGT), the greater tuberosity–inferior glenoid/glenosphere distance (GTIG), and the theta angle, formed at their intersection.
Methods
We retrospectively reviewed 60 patients who underwent primary RSA between 2010 and 2019. Clinical outcomes (ROM, Constant-Murley, UCLA, Oxford scores) were assessed pre-operatively and at 2 years. Radiographs were analyzed for AHI, CSA, AGT, GTIG, and theta angle.
Results
GTIG, theta angle, and CSA showed good inter-observer reliability (ICC 0.75–0.88). AHI had no outcome correlation. Absolute GTIG and AGT correlated weakly with forward flexion strength (R = 0.30, p = 0.02 and R = 0.27, p = 0.04 respectively). Change in theta angle correlated with ROM and improved Oxford scores (R = 0.36, p < 0.01 and R = −0.28, p = 0.04 respectively, where lower Oxford score is better). Lastly, absolute CSA demonstrated a negative correlation with ROM, strength, and Constant scores (R = −0.31, p = 0.02; R = −0.28, p = 0.03; and R = −0.31, p = 0.02 respectively).
Conclusion
GTIG and theta angle are reliable radiographic parameters with clinical utility in RSA assessment.
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