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 DXA scans, with incident hip fracture in comparison to hip BMD, 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 yrs from the Study of Osteoporotic Fractures (n=7860 community-dwelling women ≥67 yr of age). We analyzed the baseline DXA scans (Holgoic 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-BMI-adjusted hazard ratio (HR) per SD decrease for estimated strength (2.21, 95% CI 1.95–2.50) was greater than that for 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 intra- and extra-capsular 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.

Study of sex differences in the association between hip fracture risk and body parameters by DXA-based biomechanical modeling

“…assuming the plane-stress approach, i.e., considering that proximal femur is a plate with a constant thickness [65,66]. Then, isotropic inhomogeneous material properties were derived from vBMD using the empirical equations of Morgan and colleagues [67,68] …”

“…If FRI is greater than one, the patient is in a high risk of hip fracture. The femoral strength was then derived as the onset impact force that causes the FRI exceeding one [65,66]. This was calculated by scaling the impact force by the factor FRI as:…”

“…An image-processing algorithm, that combined edge detection and thresholding, was used to segment the proximal femur. A subject-specific thickness of the proximal femur was first derived as [65,66]:…”

A biomechanical sorting of clinical risk factors affecting osteoporotic hip fracture

“…In vitro studies have demonstrated that QCTbased FEA significantly improves the prediction of bone strength than densitometric measures [225,229]. Reported clinical studies has shown FEA estimated bone strength is indeed an independent fracture risk predictor [230,231]. However, the incremental contribution made by FEA over BMD in discriminating fracture cases is still marginal and the role of FEA in routine clinical examination of fracture risk has not been established.…”

“…FEA itself has no ability to predict the risk of fall and the types of fall. In finite element modeling of hip fractures, sideways fall from standing height or single-leg stance loading conditions are mostly used [8,230,231]. However, real-world accident falls are much more complicated.…”