Use of DXA-based finite element analysis of the proximal femur in a longitudinal study of hip fracture



Bone mineral density (BMD) measured by dual-energy X-ray absorptiometry (DXA) is used for clinical assessment of fracture risk; however, measurements that incorporate bone strength could improve predictive ability. The aim of this study was to determine whether bone strength derived from finite element (FE) analysis was associated with hip fracture risk in a longitudinal study. We studied 728 women (mean age 82 years), 182 with subsequent hip fracture. FE models were generated from baseline DXA scans of the hip to determine femoral bone strength and load-to-strength ratio (LSR). The baseline LSR was significantly higher in fracture cases (median 1.1) compared with controls (0.7, p < 0.0001). Femoral strength and BMD were also significantly lower in cases (median 1820 N, 0.557 g/cm2) compared with controls (2614 N, 0.618 g/cm2) both p < 0.0001. Fracture risk increased per standard deviation decrease in femoral strength (odds ratio [OR] = 2.2, 95% confidence interval [CI] 1.8–2.8); femoral neck (FN) BMD (OR = 2.1, 95% CI 1.7–2.6); total hip BMD (OR = 1.8, 95% CI 1.5–2.1); and per SD increase in LSR (OR = 1.8, 95% CI 1.5–2.1). After adjusting for FN BMD, the odds ratio for femoral strength (OR = 1.7, 95% CI 1.2–2.4) and LSR (OR = 1.4, 95% CI 1.1–1.7) remained significantly greater than 1. The area under the curve (AUC) for LSR combined with FN BMD (AUC 0.69, 95% CI 0.64–0.73) was significantly greater than FN BMD alone (AUC 0.66, 95% CI 0.62–0.71, p = 0.004). Strength and LSR remained significant when adjusted for prevalent fragility fracture, VFA, and FRAX score. In conclusion, the DXA-based FE model was able to discriminate incident hip fracture cases from controls in this longitudinal study independently from FN BMD, prior fracture, VFA, and FRAX score. Such an approach may provide a useful tool for better assessment of bone strength to identify patients at high risk of hip fracture who may benefit from treatment to reduce fracture risk. © 2013 American Society for Bone and Mineral Research.