Glenosphere disengagement: a potentially serious default in reverse shoulder surgery.

UNLABELLED: Implant failure is a serious complication in reverse shoulder arthroplasty. We determined the incidence of glenosphere disengagement in a cohort of 479 reverse shoulder prostheses (468 Delta III [DePuy International Ltd, Leeds, UK], 11 Aequalis [Tornier, Grenoble, France]). We also determined whether disengagement adversely affected clinical outcomes. The minimum followup was 12 months (mean, 28.6 months; range, 12-72 months). Disengagement of the glenosphere occurred in 16 of 479 shoulders (3.2%). In 13 patients, the disengagement was partial (clear step-off between the baseplate and the glenosphere) and was not associated with a poor functional outcome with this short-term followup. In three patients, the disengagement led to a fracture of the central screw, leading to a complete disengagement of the glenosphere from the baseplate, necessitating revision in two; the third refused revision. Partial disengagement was seen in five of 11 Aequalis prostheses (45.4%) and eight of 468 Delta III prostheses (1.7%). The three total disengagements with central screw breakage all occurred in Delta III prostheses. We believe differences in the type of locking screws may explain the differences observed between the two types of reverse prostheses. LEVEL OF EVIDENCE: Level III, retrospective study. See the Guidelines for Authors for a complete description of levels of evidence.