In situ femoral dual-energy X-ray absorptiometry related to ash weight, bone size and density, and its relationship with mechanical failure loads of the proximal femur

The objective of this study was to directly compare in situ femoral dual-en ergy X-ray absorptiometry (DXA) and in vitro chemical analysis lash weight and calcium) with mechanical failure loads of the proximal femur, and to de termine the influence of bone size (volume) and density on mechanical failu re and DXP-derived areal bone mineral density (BMD, in gl cmi). We performe d femoral DXA in 52 fixed cadavers (age 82.1 +/- 9.7 years; 30 male, 22 fem ale) with intact skin and soft tissues. The femora were then excised, mecha nically loaded to failure in stance phase configuration, their volume measu red with a water displacement method (proximal neck to lesser trochanter), and the ash weight and calcium content of this region determined by chemica l analysis. The correlation coefficient between the bone mineral content (m easured in situ with DXA) and the ash weight was r = 0.87 (standard error o f the estimate = 16%), the ash weight allowing for a better prediction of f emoral failure loads (r = 0.78; p<0.01) than DXA (r = 0.67; p<0.01). The fe moral volume (r = 0.61; p<0.01), but not the volumetric bone density (r = 0 .26), was significantly associated with the failure load. The femoral bone volume had a significant impact (r = 0.35; p< 0.01) on the areal BMD (DXA), and only 63% of the variability of bone volume could be predicted (based o n the basis of body height, weight and femoral projectional bone area. The results suggest that accuracy errors of femoral DXA limit the prediction of mechanical failure loads, and that the influence of bone size on areal BMD cannot be fully corrected by accounting for body height, weight and projec ted femoral area.