Does glenosphere size impact shoulder rotational range of motion after reverse shoulder arthroplasty? A retrospective cohort study

Abstract

Background/objectives: Improving shoulder range of motion (ROM), including functional internal rotation (fIR) after reverse shoulder arthroplasty (RSA), is crucial for the patient's daily activity. We aimed to investigate the potential differences in shoulder ROM and fIR after RSA based on the glenosphere size (36 mm vs. 39 mm) and to evaluate if increasing the glenosphere size affects shoulder ROM and fIR.

Methods: A retrospective analysis was performed on patients who had RSA with a minimum follow-up of 2 years postoperatively. A 36 mm or 39 mm glenosphere was utilized based on surgeon preference. Functional outcomes were evaluated using the constant score (CS) and simple shoulder value (SSV). Shoulder ROM assessment included evaluating passive and active external rotation (ER) and forward elevation, while fIR was assessed and classified into type I if the hand was blocked to the buttock, type II lumbar sliding, and type III smooth motion. Type I was non-functional, while types II and III were functional.

Results: A total of 222 patients were eligible for inclusion, having a mean age of 72 ± 8 years; 109 had a glenosphere 36 mm (Group 1), and 113 had a glenosphere 39 mm (Group 2). After a mean follow-up of 24.7 ± 4.1 months, the overall CS significantly improved from 42.8 ± 15.3 preoperatively to 73.4 ± 11.8 at the last follow-up (p < 0.01), and the SSV increased from 43.6 ± 16.7 to 79.7 ± 13.2 (p < 0.01), however, patients in group 2 had higher values in the strength component of the Constant Score (11.4 ± 6.1 vs. 8.7 ± 4.7, p < 0.01) and better active ER (29.6 ± 19.8 vs. 22.2 ± 20.7, p < 0.01), with no significant difference in the remaining parameters. Functional categories (Type II or III at last follow-up) of fIR were achieved in 79 (72.5%) and 79 (69.9%) of the patients in groups 1 and 2, respectively, with no significant difference between both groups (p = 0.32). For active ER, sphere size 39 and preoperative active ER were significantly associated with the last follow-up active ER values (p value < 0.01), while age, gender, and BMI did not show a significant effect. In contrast, the last follow-up fIR was not affected by any of the variables, including the glenosphere size.

Conclusions: A larger glenosphere (39 mm vs. 36 mm) was associated with a slightly better active ER; however, the glenosphere size did not affect the fIR. Preoperative ER ROM and larger glenosphere size were significantly associated with improved last follow-up shoulder ER. Regardless of the glenosphere size, all patients achieved satisfactory functional outcomes at the last follow-up compared to their baseline values.

Keywords: Functional internal rotation; Glenosphere size; Range of motion; Reverse shoulder arthroplasty.