Preoperative planning and inferior glenosphere overhang increases the odds of achieving high internal rotation after Univers reverse total shoulder arthroplasty.

Background: Despite advances in surgical technique and implant design, internal rotation (IR) after reverse total shoulder arthroplasty (rTSA) continues to be relatively unpredictable. The purpose of this study was to compare patient characteristics, use of 3-dimensional computed tomography (3D CT)-based preoperative planning, and postoperative implant position between patients with high or low IR after rTSA.

Methods: A retrospective review was performed of a multicenter prospectively collected database on patients who underwent primary rTSA (Univers Revers; Arthrex, Inc.) from 2016-2021 with a minimum 2-year follow-up. Patients were selected for a comparative analysis who either achieved high IR (T12 or better) or low IR (below the hip) postoperatively. Baseline demographics and postoperative radiographs were evaluated for association with IR. Implant position was assessed on radiographs for lateralization shoulder angle (LSA), distalization shoulder angle (DSA), inferior glenosphere overhang, and coracoid-to-glenosphere distance. Regression analyses were performed on component and clinical variables to assess for factors predictive of high vs. low IR.

Results: A total of 344 rTSAs were eligible, of which 98 patients met criteria for the high-IR group and 50 met criteria for the low-IR group. Decreased body mass index (BMI) (odds ratio [OR] 1.14, 95% confidence interval [CI] 1.01-1.30, P = .044), high preoperative IR (OR 1.30, 95% CI 1.02-1.66, P = .034), and surgery on the dominant arm (OR 5.38, 95% CI 1.31-22.1, P = .019) correlated with an increased odds of high IR. The use of 3D CT-based preoperative planning was associated with having high IR (OR 9.69, 95% CI 1.83-51.3, P = .008). Radiographically, increased DSA (OR 1.09, 95% CI 1.02-1.16, P = .012) and increased inferior glenoid overhang (OR 1.39, 95% CI 1.07-1.80, P = .013) were associated with a greater chance of being in the high-IR group.

Conclusion: Although specific baseline patient characteristics influence the ability to obtain high IR after rTSA including increased preoperative IR, decreased BMI, and surgery on the dominant arm, there are several factors within the surgeon's control. The use of 3D CT-based preoperative planning greatly increases the odds of obtaining increased postoperative IR. More precisely, mindful implant positioning including inferior glenosphere overhang and slight distalization increased postoperative IR. Therefore, the use of 3D CT-based preoperative planning may be considered in order to carefully and consciously position the glenosphere to slightly increase distalization and inferior overhang in order to optimize IR. However, further evaluation with regard to 3D planned position and postoperative outcomes are required.