Restoration of External Rotation by Sequential Glenoid Lateralization Based on Body Size in Reverse Shoulder Arthroplasty

Abstract

Background: Although reverse shoulder arthroplasty (RSA) for rotator cuff arthropathy reliably restores anterior elevation (AE), restoration of external rotation (ER) had been unreliable using traditional Grammont-type designs, which has been addressed by lateralizing the center of rotation. This study investigated whether sequential lateralization based on the intraoperatively measured glenoid-humeral axis interval (GHI) results in better outcomes than RSA with a uniform amount of lateralization irrespective of the GHI. Methods: Fifty-four shoulders were treated with a nonlateralized Grammont-type implant between 2016 and 2018 (group A). Forty shoulders were treated with the same Grammont-type implant with 8.0-mm-thick bony increased offset (BIO) between 2014 and 2016 (group B). Fifty consecutive shoulders were treated with a different Grammont-type implant with glenoid-side prosthetic lateralization based on the GHI between 2019 and 2020 (group C). Group C was further stratified into 3 subgroups: group C1 (GHI < 20.0 mm, n = 12) was lateralized by +3.4 mm; C2 (20.0 ≤ GHI ≤ 24.0 mm, n = 25), by +5.4 mm; and C3 (GHI > 24.0 mm, n = 13), by +7.4 mm. Active ER with the arm at the side (ER0) and abducted to 90° (ER90) as well as functional outcomes including active AE and Constant and UCLA scores were evaluated at 2 years postoperatively. Results: The mean age, height, and body mass index and the percentage of male patients were not significantly different between groups A, B, and C. However, the patients in subgroup C1 were the shortest (151.3 ± 3.9 cm) and most elderly (77.5 ± 4.1 years) and had the highest proportion of female patients (91.7%). The patients in subgroup C3 were the tallest (161.1 ± 5.6 cm) and had the highest proportion of male patients (69.2%). ER0, ER90, and the Constant score were significantly larger in group C than in group A. AE, ER0, and the Constant and UCLA scores were significantly larger in group C than in group B. Conclusions: Rather than using a single ideal offset, the optimal lateralization may be better determined according to the body size, the muscle volume, or perhaps the excursion of the musculotendinous unit of each individual patient. Level of Evidence: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.