Early radiographic findings are not associated with instability for reverse total shoulder arthroplasty with the Perform metaphyseal-fixated humeral stem

Background: Humeral stems in reverse total shoulder arthroplasty (rTSA) have moved toward shorter metaphyseal fixed stems in recent years to preserve bone stock and reduce the risks of stress shielding and stem loosening. However, shorter stems may be at higher risk for stem malalignment, which may impact clinical outcomes such as instability. The purpose of this study was to examine early radiographic outcomes and their relationship to instability, utilizing the Perform metaphyseal-fixated humeral stem for rTSA. Methods: This is a retrospective review of a consecutive series of patients undergoing primary rTSA by a single surgeon for the 2-year period after adoption of a new shorter metaphyseal fixed humeral stem. Standardized radiographs were analyzed at 2 weeks post-operatively and at final follow-up (minimum 1 year). Initial radiographs were analyzed for humeral stem alignment, metaphyseal fill ratio, and distance from stem tip to greater tuberosity. Final x-rays were analyzed for stem alignment, distance from stem tip to greater tuberosity, and humeral loosening. Subsidence of the humeral implant was calculated based on vertical and angular stem changes between the initial and final radiographs. Logistic regression was used to analyze surgical and radiographic parameters associated with subsidence and instability. Results: = .0189). None of the studied radiographic variables was a significant predictor of instability. All 8 shoulders with instability were performed for either massive rotator cuff tear or cuff tear arthropathy. No shoulders had evidence of radiographic loosening. Conclusion: In this study of rTSA with the Perform metaphyseal-fixated humeral stem, radiographic parameters including stem alignment and subsidence were not predictors of instability. No stems had radiographic loosening. Established patient risk factors for instability, including diagnosis of rotator cuff tear, remain key risk factors even with newer metaphyseal fixed stems. These findings highlight the importance of patient selection, understanding the nuances of the system, and refining surgical technique when using a new implant to optimize outcomes.