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Dual-energy X-ray absorptiometry (DXA) is the most common method for determining bone mineral density (BMD) in the proximal femur. However, there remain questions concerning the contribution of cortical and cancellous bone to this technology in the proximal femur. The purpose of this investigation was to identify structural and compositional characteristics of human bone in the proximal femur that significantly influence DXA BMD measurements. Twenty-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 performed on each specimen with a Hologic QDR-2000 densitometer. Direct measurements were determined from proximal femoral sections for cancellous bone (volume fraction, ash fraction, cancellous cross-sectional area and percent cancellous cross-sectional area), cortical bone (thickness, ash fraction, porosity, cortical cross-sectional area and percent cortical cross-sectional area) and anteroposterior thickness. These parameters were compared with the associated DXA measurements by means of simple and multiple regressions. Cancellous volume fraction was the best predictor of variability of DXA measurements for both the neck and trochanter, with an R2 of 0.87 and 0.76, respectively (p < 0.0001). There was only a minor influence of cortical factors such as thickness (neck and trochanter R2 = 0.51 and 0.42, respectively, p < 0.001) and trochanteric cross-sectional area (R2 = 0.21, p < 0.05). Although the accuracy for determining specific components of the proximal femur was low, the DXA BMD measurement was a strong predictor of cancellous bone factors, but not cortical bone factors that have been shown to change significantly with age.

The purpose of this investigation was to directly define the age-related intrafemoral variations in cancellous bone density, bone mineralization and rate of bone loss in a cadaveric population of Caucasian female femoral necks and trochanters. Forty-three Caucasian female femora were obtained and divided into premenopausal, postmenopausal and elderly age groups. The neck and trochanter were removed, and cores of cancellous bone were taken from the superior, middle and inferior regions; volume fraction and ash fraction were determined for each core. The cancellous bone volume fraction of the neck was significantly greater than that of the trochanter, as was that of the inferior region of the neck compared with the superior and middle regions at all age groups (p<0.05). The mean neck/trochanter and neck inferior/superior volume fraction ratios did not change with age; however, the variance increased with age (p<0.001). This increasing variability with age suggests that there may be a subpopulation of individuals within the elderly Caucasian population with a significantly different intrafemoral bone density distribution than was present prior to menopause. This study identified no mineralization changes with age in the cancellous bone of the proximal femur (p>0.05). The influence of increased neck/trochanter and neck inferior/superior ratios on femoral neck integrity and fracture prediction is of interest and requires further investigation.