Early Mobilization After Reverse Total Shoulder Arthroplasty Is Not Associated With Increased Risk of Acromial and Scapular Stress Fractures: A Retrospective Cohort Study

Background Acromial and scapular spine stress fractures (ASF) are recognized complications following reverse total shoulder arthroplasty (rTSA) and may negatively affect clinical outcomes. The influence of postoperative immobilization duration and timing of rehabilitation on ASF risk remains unclear. This study evaluated whether a shorter postoperative sling immobilization protocol was associated with an increased incidence of ASF following primary rTSA. Methods A retrospective single-centre comparative cohort study was performed including 698 patients who underwent primary rTSA between 2016 and 2022 with a minimum follow-up of 2 years. Patients were managed with either 2-week or 6-week of postoperative sling immobilization according to surgeon preference. The two protocols represented different rehabilitation strategies, with passive shoulder mobilization initiated after 2 or 6 weeks, respectively, followed by progression to active-assisted and active motion and strengthening according to standard institutional practice. ASF was defined as a postoperative acromial or scapular spine fracture confirmed by computed tomography when clinically or radiographically suspected. Fracture-free survival was assessed using Kaplan–Meier analysis. Multivariable Cox proportional hazards regression and Firth penalized Cox regression were performed to evaluate factors associated with ASF risk. Results Thirty-six patients (5.2%) developed an ASF during follow-up. Kaplan–Meier analysis demonstrated no significant difference in fracture-free survival between patients treated with 2-week and 6-week immobilization protocols (log-rank p=0.79). The median time to ASF diagnosis was 107 days (interquartile range, 75–190 days). In multivariable Cox regression analysis, sling duration was not associated with ASF risk (6 weeks vs. 2 weeks: HR 1.22, 95% CI 0.57–2.60, p=0.60). This finding was confirmed in the Firth penalized Cox regression model (HR 0.99, 95% CI 0.83–1.18, p=0.91). Conclusions A shorter postoperative immobilization protocol was not associated with an increased risk of ASF following primary rTSA. These findings suggest that earlier mobilization protocols may be considered without an apparent increase in fracture risk. However, given the retrospective design, surgeon-dependent treatment allocation, and limited number of ASF events, prospective studies are required to confirm these findings and further define patient-specific factors associated with ASF risk. Level of Evidence Level III, Retrospective Cohort Comparison, Treatment Study