A comparison of DXA and CT based methods for estimating the strength of the femoral neck in post-menopausal women

Abstract

Purpose Simple 2-dimensional (2D) analyses of bone strength can be done with dual energy x-ray absorptiometry (DXA) data and applied to large data sets. We compared 2D analyses to 3-dimensional (3D) finite element analyses (FEA) based on quantitative computed tomography (QCT) data. Methods 213 women participating in the Study of Women’s Health across the Nation (SWAN) received hip DXA and QCT scans. DXA BMD and femoral neck diameter and axis length were used to estimate geometry for composite bending (BSI) and compressive strength (CSI) indices. These and comparable indices computed by Hip Structure Analysis (HSA) on the same DXA data were compared to indices using QCT geometry. Simple 2D engineering simulations of a fall impacting on the greater trochanter were generated using HSA and QCT femoral neck geometry; these estimates were benchmarked to a 3D FEA of fall impact. Results DXA-derived CSI and BSI computed from BMD and by HSA correlated well with each other (R= 0.92 and 0.70) and with QCT-derived indices (R= 0.83–0.85 and 0.65–0.72). The 2D strength estimate using HSA geometry correlated well with that from QCT (R=0.76) and with the 3D FEA estimate (R=0.56). Conclusions Femoral neck geometry computed by HSA from DXA data corresponds well enough to that from QCT for an analysis of load stress in the larger SWAN data set. Geometry derived from BMD data performed nearly as well. Proximal femur breaking strength estimated from 2D DXA data is not as well correlated with that derived by a 3D FEA using QCT data.

Trajectories of femoral neck strength in relation to the final menstrual period in a multi-ethnic cohort

“…The composite indices of hip strength employed in this study are structural measures based on macroscopic measurements from DXA scans and ignore microscopic features such as differences in the quality of cancellous mineralization and micro-architecture [33, 34]. We also made the simplifying assumption that mineral mass in the femoral neck is largely in the cortex since details of bone composition are not readily available from DXA scans; however, cross-validation with 3D quantitative computed tomography (QCT)-based strength measures confirm the validity of these DXA-based measures [35], which are also more readily obtainable with substantially less radiation exposure and lower costs than QCT. Although the composite strength indices have not been validated against laboratory measures of mechanical strength, they have been shown to be inversely associated with fracture risk in multiple studies [11, 12, 36, 37].…”

Quantitative Comparison of 2 Dual-Energy X-ray Absorptiometry Systems in Assessing Body Composition and Bone Mineral Measurements

“…In future studies, cross-sectional imaging modalities, such as magnetic resonance imaging (16) and quantitative computed tomography (QCT) (14,15), should be used to provide accurate measure values to compare DXA measurements. Skeletal, lean, fat, and fat-free mass, as well as percent fat, can be measured by magnetic resonance imaging or QCT, whereas BMD and BMC can be measured by QCT.…”

Adult bone strength of children from single-parent families: the Midlife in the United States Study

“…Using those DXA-based measurements, and measured body height and body weight, we calculated composite indices of femoral neck strength that index bone strength relative to the load during a fall using the following formulas [11, 53], which have been validated against 3-dimensional (3D) methods based on quantitative computed tomography [61]: Compression Strength Index = $\frac{{\mathit{BMD}}^{\ast }\mathrm{italicFNW}}{\text{Weight}}$ Bending Strength Index = $\frac{{\mathit{BMD}}^{\ast }{\mathit{FNW}}^2}{{\mathit{FNAL}}^{\ast }italic\text{Weight}}$ Impact Strength Index = $\frac{{\mathit{BMD}}^{\ast }{\mathit{FNW}}^{\ast }\mathrm{italicFNAL}}{{\text{Height}}^{\ast }italic\text{Weight}}$…”