Lower Geriatric Nutritional Risk Index is associated with increased risk of acromial stress fracture following reverse total shoulder arthroplasty

Background Acromial and scapular spine stress fractures are serious complications following reverse total shoulder arthroplasty (rTSA), and patient-level risk factors may contribute to their development. The Geriatric Nutritional Risk Index (GNRI) is a validated marker of physiologic reserve. The purpose of this study was to evaluate the association between GNRI and postoperative stress fracture after rTSA. We hypothesized that lower GNRI would be associated with increased fracture risk. Methods We performed a retrospective 1:2 age- and sex-matched case-control study of patients undergoing primary rTSA. Forty-five patients who developed postoperative acromial or scapular spine stress fracture were matched to 90 controls without fracture. Demographic variables collected included age, sex, body mass index, diagnosis, and comorbidities. GNRI was calculated preoperatively and postoperatively and analyzed as a continuous variable and using predefined thresholds (<98, <103, <109). Conditional logistic regression adjusted for diagnosis and comorbidities. Receiver operating characteristic (ROC) analysis assessed discriminatory ability. Results A total of 135 patients were included (mean age, 72.8 years; 53% female). Patients with stress fracture had lower preoperative GNRI (107.4 ± 12.4 vs. 114.0 ± 13.9; p=0.007) and postoperative GNRI (105.5 ± 14.9 vs. 114.8 ± 14.5; p=0.001). Postoperative GNRI <109 was more common among fracture patients (60% vs. 30%; p=0.001). In matched multivariable analysis, each 1-point increase in postoperative GNRI was associated with a 5% reduction in fracture odds (odds ratio [OR], 0.95; 95% confidence interval [CI], 0.92–0.99; p=0.015). Postoperative GNRI <109 was independently associated with fracture (OR, 3.64; 95% CI, 1.02–13.02; p=0.047). ROC analysis demonstrated moderate discrimination (area under the curve, 0.70; 95% CI, 0.60–0.79). Conclusion In this matched case-control analysis, lower postoperative GNRI was independently associated with increased risk of acromial and scapular spine stress fracture following rTSA. GNRI may serve as a practical perioperative risk stratification tool in patients undergoing reverse shoulder arthroplasty.