Association between decreased bone mineral density and Pauwels angle in femoral neck fractures: a cross-sectional study

Background: Progressive osteoporosis reduces the trabecular structures of the proximal femur, whereas the primary compression trabeculae (PCTs) are relatively preserved. We hypothesize that the loss of the vertically oriented PCTs in osteoporosis, which act as a mechanical barrier, affects fracture line propagation and influences the Pauwels angle. This study investigated the association between bone mineral density (BMD) and Pauwels angles in low-energy femoral neck fractures (FNFs).Methods: This cross-sectional study included 150 patients (mean age, 75.3 years; range, 50–94 years) diagnosed with intracapsular FNFs between May 2019 and May 2023. BMD was measured within 1 month of the injury date using dual-energy X-ray absorptiometry, and modified Pauwels angles were assessed using a computed tomography-based multiplanar reconstruction program. Multiple linear regression analysis was performed to evaluate the factors influencing the Pauwels angles. The dependent variable was the Pauwels angle, while the independent variables included sex, age, height, body weight, body mass index, American Society of Anesthesiologists score, Charlson comorbidity index score, smoking status, alcohol use, preinjury walking ability, and femoral neck BMD T-scores.Results: Higher femoral neck BMD T-scores were significantly associated with increased Pauwels angles (β=3.449, P<0.001). Greater body weight was independently associated with increased Pauwels angles (β=0.213, P=0.007).Conclusions: The Pauwels angle demonstrated a significant association with BMD, with lower BMD associated with less steep Pauwels angles. In the absence of BMD measurement, the Pauwels angle may indicate osteoporosis severity in patients with low-energy FNFs.Level of evidence: III.