Do constrained liners (in a 145° onlay implant) provide any benefit? A matched retrospective study.

Abstract

The purpose of this study was to compare the outcomes of primary reverse total shoulder arthroplasty (rTSA) using constrained liners (in a 145° onlay implant, Equinoxe [Exactech]) with primary rTSA using standard liners with a minimum 1-year follow-up. A total of 836 primary rTSA patients were analyzed in this study. Patients treated with constrained liners (n = 209) were cross-matched 1:3 for age, gender, glenosphere diameter, and follow-up duration and compared with 627 patients who underwent primary rTSA with standard liners. Study endpoint was at 1 year. Outcomes were analyzed preoperatively and at the latest follow-up. Patient characteristics, postoperative range of motion (ROM), patient-reported outcomes (PROs), complications and revisions were recorded. There was no statistically significant changes in improvement in pain (-4.9 vs. -5.1; P = .356), ROM (abduction, 45.7° vs. 47.9°, P = .522; forward elevation, 44.0° vs. 50.8°, P = .057; internal rotation score 1.0 vs. 1.1, P = .709; and external rotation, 17.9° vs. 16.7°, P = .543), or PROs (American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form [ASES] score, 44.5 vs. 43.7, P = .107; and Shoulder Arthroplasty Smart [SAS] score, 27.5 vs. 30.0, P = .052) between the constrained and standard liner cohorts at minimum 1-year follow-up. However, the constrained liner rTSA cohort had a significantly higher rate of adverse events (6.2% vs. 2.7%, P = .012), including a higher rate of scapular notching (15.6% vs. 8.8%, P = .015). The use of constrained liners in primary rTSA demonstrated no significant difference in the change in pain, abduction, forward elevation, external and internal rotation scores, ASES scores, and SAS scores at minimum 1-year follow-up. There was no significant difference in forward elevation or abduction compared with standard liners. However, we observed that the overall rate of adverse events, including scapular notching, were significantly higher in the constrained liner cohort. Long-term clinical and radiographic follow-up is necessary to fully elucidate the durability of these results. At this time, it is unclear if constrained liners have any benefit in rTSA.