Abstract
OBJECTIVE: To investigate whether body mass index (BMI) modifies the association be tween bone mineral density (BMD) and intraoperative fracture risk in cementless hemiarthroplasty. METHODS: Between April 2020 and March 2025, 588 patients who received cementless stems and underwent dual-energy X-ray absorptiometry scans within one week postoperatively were included. Patients were stratified by BMI (≥ 18.5 kg/m (2) versus < 18.5 kg/m (2) ) and young adult mean (YAM) (cutoff: 70%). Fracture risk was compared across groups. Subgroup analyses based on YAM levels and operative parameters were performed in 577 patients with complete data. RESULTS: In underweight patients (BMI < 18.5 kg/m (2) ), lower YAM was associated with higher intraoperative fracture risk ( p = 0.128), whereas no significant association was observed in patients with BMI ≥ 18.5 kg/m (2) ( p = 0.80). Fracture rates increased with lower YAM: 3.97% (≥ 70%), 5.24% (60-69%), 5.88% (50-59%), 6.58% (< 50%), though not statistically significant. Higher BMI was associated with longer operative time and greater blood loss. CONCLUSION: Body mass index modifies the association between BMD and intraoperative fracture risk. Preoperative YAM assessment may help identify underweight patients at higher risk during cementless hemiarthroplasty. Level of Evidence III, therapeutic study.