Radiographic Risk Factors for Scapular Stress Fractures After Reverse Total Shoulder Arthroplasty: A Case-Control Study

Background: – Acromial and scapular spine fractures following reverse total shoulder arthroplasty (rTSA) occur with prevalence rates ranging from 0.8% to 7.2%.^1-5 This study aimed to identify radiographic risk factors for the development of scapular stress fractures following primary rTSA and to provide quantifiable recommendations for surgeons to decrease risk for stress fracture.Methods: – This was an institutional review board‑approved retrospective case-control study. Electronic medical records were screened for patients who underwent a rTSA from 2010 to 2021. Patients with stress fractures were then matched in a 3:1 ratio for a comparison control group. Radiographs were analyzed and compared at multiple time points.Results: – Patients developed a fracture at a median of 3.4 months postoperatively (n = 14, mean age = 76 years, 79% female) and were compared with matched controls who did not (n = 42, mean age = 76 years, 79% female). Minimal radiographical differences were seen except in those who developed a fracture of lower Hamada classification (1 to 3 vs. 4 to 5) preoperatively (P = 0.005) and wider acromion to lateral humerus distance postoperatively (P = 0.034). Regarding pre- to postoperative change, the fracture group had an increase in acromion to lateral humerus distance by 2.3 mm, whereas the control group had a reduction by 3 mm (P = 0.024). These two variables alone were 80.4% accurate in predicting fractures on logistic regression. For the acromion to lateral humerus distance, receiver operator characteristic analysis identified 9.78 mm as the most discriminant cutoff (area under curve = 0.690).Conclusion: – In our study, the distance from the lateral edge of the acromion to the lateral humerus was a useful tool for identifying risk of acromial fracture. Based on these findings, our current practice is to avoid lateralizing beyond an acromion to lateral humerus distance of 10 mm and to use unicortical screw fixation in the superior half of the glenoid to avoid creation of a stress riser in the scapular spine.Level