Outcomes of nonoperative management of acromial stress fractures after reverse shoulder arthroplasty

Introduction: Acromial stress fractures (ASF) and stress reactions (ASR) are common complications after reverse shoulder arthroplasty (RSA), and have been shown to compromise outcomes. The purpose of this study was to determine the functional outcomes of patients with ASF and ASR treated nonoperatively. Methods: A total of 958 patients that underwent RSA were retrospectively reviewed. 43 (4.5%) were found to have ASF and 56 (5.7%) were found to have ASR. ASF were defined by tenderness over the acromion with identified fracture on radiographic imaging, and ASR was defined as tenderness without radiographic evidence of fracture. Functional outcomes were assessed via American Shoulder and Elbow Surgeons (ASES) score, Single Assessment Numeric Evaluation (SANE), Simple Shoulder Test (SST) and VAS (Visual Analog scale) pain at a minimum of 2 years after RSA and one year from diagnosis of acromial pathology. The ASF patients were matched 3:1 to RSA controls without acromial pathology based on age, sex, indication, and implant. Results: Twenty seven ASF and 35 ASR patients met inclusion criteria with a mean follow-up of 50.3 months after surgery (range: 24-108 months). Symptom onset after RSA occurred at 8.1 ± 8.9 months (range: 0.8-49.8) in ASFs and 7.5 ± 6.8 months (range: 1.0-41.3) in ASRs (P =.700). The ASF group included 20 (74%) females with an average age of 71.8 years, and the ASR group included 30 (86%) females with an average age of 72.9 years. ASF patients had inferior outcomes compared to controls in ASES (57.8 vs. 76.0, P =.001), SANE (59.1 vs. 78.8, P =.001), SST (5.1 vs. 7.5, P =.001), and VAS (3.3 vs. 1.2, P =.002). Additionally, ASF patients had significantly worse scores compared to ASR patients by VAS Pain (3.3 vs 1.7, P =.020), ASES (57.8 vs. 76.7, P =.001), SANE (59.1 vs. 81.1, P =.001), and SST (5.1 vs. 7.5, P =.001). Patients with ASR had comparable pain and function to controls in ASES (P =.858), SANE (P =.508), SST (P =.956), and VAS (P =.264) scores. Twenty-one (77.7%) ASF patients experienced fracture displacement and 13 (48.1%) went on to nonunion. Conclusion: Early follow-up of patients treated nonsurgically for ASF after RSA demonstrated worse pain and function compared to controls. The majority demonstrated further displacement after diagnosis and almost half developed a nonunion. Patients with ASR experienced temporary dysfunction with little impact on final outcome. Strategies to prevent and treat ASFs remain an area in need of innovation.