PREDICTIVE VALUE OF PROXIMAL FEMORAL BONE DENSITOMETRY IN DETERMININGLOCAL ORTHOGONAL MATERIAL PROPERTIES

Models which are based on non-invasive bone measurements may in the fu ture be able to successfully identify individual subjects at an increa sed risk for hip fracture; thus, we designed a study to determine the usefulness of dual-energy X-ray absorptiometry (DXA) and quantitative computed tomography (QCT) in predicting the local material properties of human proximal femoral cancellous bone. There has been some disagre ement in the scientific literature regarding appropriate predictive mo dels for local material properties of cancellous bone. We sought to co nfirm that density-mechanical property relationships were consistent f rom subject to subject, and that three-dimensional QCT measurements we re stronger predictors of mechanical properties than two-dimensional D XA results. Linear and power fit relationships between these densitome tric measures and material properties were also examined to determine which were more appropriate. Bone cubes from specific regions of highl y oriented trabeculae were analyzed separately to determine if cube or ientation had an effect on mechanical properties independent of bone d ensity. Ten pairs of ex vivo femurs (five male, five female; age 30-93 , mean age 62) were prepared such that specific anatomic planes were v isible radiographically. Both QCT and DXA measurements were made on al l 20 femurs. Cancellous bone cubes were obtained proceeding along two distinct directions from the proximal end of each femur pair. Unexpect edly, the density-modulus relationships among these ten donors were fo und to be significantly different at p < 0.01 (83% of the tests were d ifferent at p < 0.0001). Density-strength regressions were also signif icantly different at p < 0.01, but this effect was not as consistent n or as statistically significant. In general, the QCT method did not pr oduce predictions of local cancellous bone material properties superio r to the DXA method. The linear and power fit models appeared to produ ce consistent results, with neither being obviously more advantageous. These density measurements explained at best 30-40% of the variance i n modulus and 50-60% of the variance in ultimate stress. The orientati on of cancellous cubes in the principal compressive trabeculae region was a significant contributor to mechanical properties (p = 0.0001) in dependent of bone density. This finding was not as dramatic in the fem oral neck cancellous bone region. (C) 1996 Elsevier Science Ltd.