Dislocation following reverse total shoulder arthroplasty

Background The etiology of instability following reverse total shoulder arthroplasty (RTSA) remains incompletely understood. The purpose of this study was to describe the shared characteristics, etiologies, and outcomes of early and late dislocations requiring operative revision. Methods We identified all patients at our institution who underwent operative revision of an RTSA for instability. Baseline demographic, clinical, and radiographic data were collected. Standardized outcome scores were collected preoperatively and at final follow-up. Characteristics of dislocations that occurred less than 3 months postoperatively (early) were compared with those that occurred more than 3 months postoperatively (late). Results Twenty-two patients met the criteria, and follow-up was obtained on 19 patients at 4.9 ± 2.5 years, with 14 early and 5 late dislocations. Most patients in both groups were men, were aged over 70 years, and had a history of shoulder surgery. On analysis of instability etiology, 68% had inadequate soft-tissue tensioning (10% due to partial axillary nerve injuries). The remaining patients had asymmetric liner wear, mechanical liner failure, or impinging heterotopic ossification. Asymmetric liner wear accounted for 60% of late dislocations. Recurrent instability after revision was present in 29% of early and 40% of late dislocators. Discussion No significant differences in outcomes or recurrence rates were found for early and late dislocations. Of the late dislocations, 80% had evidence of adduction impingement, via either heterotopic ossification or asymmetric polyethylene wear. Post-RTSA instability had 2 distinct etiologies: (1) instability due to inadequate soft-tissue tensioning and/or axillary nerve palsy and (2) instability due to impingement or liner failure.