Prediction of incident hip fracture with the estimated femoral strength by finite element analysis of DXA Scans in the study of osteoporotic fractures

Abstract

A bone fractures only when loaded beyond its strength. The purpose of this study was to determine the association of femoral strength, as estimated by finite element (FE) analysis of dual-energy X-ray absorptiometry (DXA) scans, with incident hip fracture in comparison to hip bone mineral density (BMD), Fracture Risk Assessment Tool (FRAX), and hip structure analysis (HSA) variables. This prospective case-cohort study included a random sample of 1941 women and 668 incident hip fracture cases (295 in the random sample) during a mean ± SD follow-up of 12.8 ± 5.7 years from the Study of Osteoporotic Fractures (n = 7860 community-dwelling women ≥67 years of age). We analyzed the baseline DXA scans (Hologic 1000) of the hip using a validated plane-stress, linear-elastic finite element (FE) model of the proximal femur and estimated the femoral strength during a simulated sideways fall. Cox regression accounting for the case-cohort design assessed the association of estimated femoral strength with hip fracture. The age-body mass index (BMI)-adjusted hazard ratio (HR) per SD decrease for estimated strength (2.21; 95% CI, 1.95-2.50) was greater than that for total hip (TH) BMD (1.86; 95% CI, 1.67-2.08; p < 0.05), FN BMD (2.04; 95% CI, 1.79-2.32; p > 0.05), FRAX scores (range, 1.32-1.68; p < 0.0005), and many HSA variables (range, 1.13-2.43; p < 0.005), and the association was still significant (p < 0.05) after further adjustment for hip BMD or FRAX scores. The association of estimated strength with incident hip fracture was strong (Harrell's C index 0.770), significantly better than TH BMD (0.759; p < 0.05) and FRAX scores (0.711-0.743; p < 0.0001), but not FN BMD (0.762; p > 0.05). Similar findings were obtained for intracapsular and extracapsular fractures. In conclusion, the estimated femoral strength from FE analysis of DXA scans is an independent predictor and performs at least as well as FN BMD in predicting incident hip fracture in postmenopausal women.

Keywords: DXA; FINITE ELEMENT ANALYSIS; HIP FRACTURE; OSTEOPOROSIS.

Figure 1

The DXA-based FE model of the proximal femur showing the loading conditions that simulates sideways fall: impact forces applied to the greater trochanter, the distal end fixed and femoral head restrained in the vertical direction. The image intensity demonstrates the distribution of elastic modulus in GPa.