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Reverse shoulder arthroplasty (RSA) is based on the biomechanical advantages of lengthening the deltoid while medializing its center of rotation (COR). Little evidence exists describing the clinical benefits of these biomechanical advantages. The purpose of this study is to assess the relationship between deltoid lengthening and medialization of the COR with functional outcomes for RSA patients. We retrospectively reviewed patients treated with primary RSA. Radiographic measurements of deltoid length and COR, assessment of forward elevation (FE) and external rotation (ER), and functional outcome scores were obtained pre- and postoperatively. Linear regression analyses were performed to assess the relationship between these radiographic measurements and changes in shoulder functionality. On average, patients improved significantly in function and functional outcome scores. Postoperative COR correlated weakly with postoperative FE. There were weakly negative correlations between increase in acromion to greater tuberosity distance and postoperative FE, and between deltoid lengthening and FE improvement. Our results suggest that deltoid lengthening does not correlate with improvements in active FE or ER. These findings could indicate that change in deltoid length is less important than previously thought. Furthermore, the negative correlations seen could indicate that there is over-tensioning of the deltoid in specific cases. Further studies are needed to better assess the role of deltoid length and other factors that may impact RSA outcomes.

Reverse shoulder arthroplasty (RSA) is an effective surgery for a variety of patients with difficult shoulder pathology. Since postsurgical outcomes are often variable, there has been great effort made to optimize the design and use of these implants. Previous studies demonstrated an association between increased glenosphere size and improved range of motion. The purpose of this study is to assess the relationship between glenosphere size, range of motion, and functional outcome scores. This is a retrospective cohort study of 140 patients (148 shoulders) undergoing reverse shoulder arthroplasty. All patients were assessed pre- and postoperatively for range of motion, Constant score, ASES score, and Subjective Shoulder Value. Improvements in these variables were compared for patients treated with three different glenosphere sizes (36, 40, 42 mm). All groups had a mean improvement in range of motion and functional outcome scores, but there were no statistically significant differences between groups when controlling for preoperative differences. Our findings do not support a strong role for glenosphere size as a singular factor affecting range of motion or patient-reported outcome following RSA. These problems are most likely due to the multifactorial nature of shoulder dynamics. For this reason, assessing the effect a single surgical or biomechanical parameter on function has been challenging.