Early failure of an inlay modular shoulder arthroplasty for proximal humeral fracture in a retrospective series

Background: Surgical reconstruction of proximal humeral fractures is difficult, and failure may occur leading to revision surgery. The development of convertible modular hemiarthroplasty has the potential to reduce the complexity of revision surgery. The aim of this study was to review the failure rate and modes of an inlay modular humeral hemiarthroplasty prosthesis used for proximal humeral fractures. Methods: A retrospective clinical review of the medical records and X-rays was undertaken. A sawbone model was used to implant a Global FX and a Global Unite convertible hemiarthroplasty to compare differences in height and offset between the prostheses. Results: Six patients (five females, one male) had a Global Unite hemiarthroplasty with a mean age 73.66 years. Four (66%) failed by superior migration at a mean of six months. In vitro sawbones measurement identified the humeral height of the Global Unite was approximately 3 mm higher than the Global FX (the previous model). Conclusion: We experienced a 66% failure rate of the Global Unite by superior migration. Our previous series of Global Fx had a failure rate of 23%. We postulate that the extra height of the Global Unite increases the excursion of the rotator cuff tendons, placing undue tension on the rotator cuff and tuberosity construct predisposing to early failure. We recommend that the consideration be given to downsizing the humeral head and using a smaller body where possible.