The contribution of cortical and cancellous bone to dual-energy X-ray absorptiometry measurements in the female proximal femur

Dual-energy X-ray absorptiometry (DXA) is the most common method for determ ining bone mineral density (BMD) in the proximal femur. However, there rema in questions concerning the contribution of cortical and cancellous bone to this technology in the proximal femur. The purpose of this investigation w as to identify structural and compositional characteristics of human bone i n the proximal femur that significantly influence DXA BMD measurements. Twe nty-four femora were obtained at autopsy from Caucasian females ranging in age from 17 to 92 years (mean +/- SD, 61 +/- 25 years). DXA scans were perf ormed on each specimen with a Hologic QDR-2000 densitometer. Direct measure ments were determined from proximal femoral sections for cancellous bone (v olume fraction, ash fraction, cancellous cross-sectional area and percent c ancellous cross-sectional area), cortical bone (thickness, ash fraction, po rosity, cortical cross-sectional area and percent cortical cross-sectional area) and anteroposterior thickness. These parameters were compared with th e associated DXA measurements by means of simple and multiple regressions. Cancellous volume fraction was the best predictor of Variability of DXA mea surements for both the neck and trochanter, with an R-2 of 0.87 and 0.76, r espectively (p <0.0001). There was only a minor influence of cortical facto rs such as thickness (neck and trochanter R-2 = 0.51 and 0.42, respectively , p <0.001) and trochanteric cross-sectional area (R-2 = 0.21, p <0.05). Al though the accuracy for determining specific components of the proximal fem ur was low, the DXA BMD measurement was a strong predictor of cancellous bo ne factors, but not cortical bone factors that have been shown to change si gnificantly with age.