Clinical and radiographic outcomes of reverse shoulder arthroplasty performed with 40 mm polyethylene glenospheres vs. 36 mm cobalt chrome glenospheres at minimum 2-years follow-up.

INTRODUCTION: Most reverse total shoulder arthroplasty utilise a cobalt chrome (CoCr) glenosphere with a polyethylene liner. The Lima Shoulder Modular Replacement (SMR)™ platform has inverted the materials to potentially decrease polyethylene debris when the humeral liner contacts the scapula. METHODS: This retrospective, multi-centre study was conducted to examine the equivalence of the Lima SMR™ 40 mm highly cross-linked polyethylene (XLPE) glenospheres to the 36 mm CoCr glenospheres, examining patients from 2013 to 2022 with a minimum of 2-year clinical and radiographic follow-up. RESULTS: 199 patients were investigated: 107 with the XLPE glenosphere and 92 with the CoCr glenosphere. At 2-year follow-up, there was no significant difference in Oxford Shoulder scores (p = 0.081). There were more areas of glenoid radiolucency in the CoCr group (n = 18 zones in eight patients) at 2 years (z = -2.04, p = 0.04). There was no significant difference in notching (16% in the XLPE group, 20% in CoCr group (p = 0.190)). Two patients in the XLPE group were revised and five in the CoCr group. DISCUSSION: XLPE glenosphere outcomes were largely equivalent to a CoCr glenosphere at 2 years. While the XLPE glenosphere had fewer major complications, this could be attributed to other factors including the larger diameter, rather than the polyethylene glenosphere. LEVEL OF EVIDENCE: Level III - retrospective comparative study.