Does matching glenosphere size to patient height improve outcomes following reverse total shoulder arthroplasty?

Abstract

Optimal biomechanics in reverse total shoulder arthroplasty (rTSA) are still a topic of debate. Although larger glenospheres have been linked with a theoretical improvement in the range of movement, results from clinical studies are mixed. We hypothesised that matching glenosphere diameter to patient height would result in greater improvements in post-operative range of motion (ROM) and patient-reported outcomes (PROMs). An international database of rTSAs was analysed. After exclusions, 3318 rTSA patients were classified as short (<158 cm), average (158–173 cm) or tall(>173 cm). Outcomes were stratified for glenosphere size (small≤38 mm, large≥40 mm). Results were compared preoperatively and at 2 years. In short patients glenosphere diameter had no statistically significant impact on the degree of post-operative improvement for any ROM or PROM. Average height patients treated with small glenospheres had significantly more improvement in internal rotation (1.3 vs 1.0, p = 0.01), VAS pain (5.3 vs 4.8, p = 0.002), American Shoulder and Elbow Surgeons (47.8 vs 45.2, p = 0.03) and Shoulder Arthroplasty Smart (30.9 vs 28.2, p = 0.01) but significantly less improvement in constant score (31.7 vs 35.3, p = 0.009). Tall patients treated with small glenospheres had significantly more improvement in external rotation (21.2 vs 16.4, p = 0.01) and VAS pain scores (4.7 vs 4.3, p = 0.04). While most significant differences favoured small glenospheres, the magnitude of these differences was small. Overall, patients of all heights can expect similar clinical improvements irrespective of glenosphere size.