Comparison between femoral bone mineral parameters assessed by QCT and dual X-ray densitometry

The aim of this study was to assess the agreement between different femoral bone mineral measures and their agreement with some biomechanical parameters. By means of quantitative CT (QCT) and dual X-ray absorptiometry (DXA), measurements were made in different locations of 33 pairs of human femur specimens. There was a principal distinction between bone density as measured by QCT and bone mass as measured by QCT and DXA. Bone mass measured by QCT and the bone mineral content (BMC) measured by DXA are true mass parameters. However, bone mineral density (BMD) as measured by DXA agreed substantially better with the mass measures than with the densities. The mass measures, including the BMD, had good agreements with each other, with a common reference parameter and with the biomechanical parameters. The QCT densities had, on the average, poor agreements with each other, with the other bone mineral measures (including the MBDs), and with the mechanical parameters. The gender differences were less for the QCT densities than for the mass parameters, whereas in this regard the BMDs were intermediate. All measures had approximately similar reproducibilities. Although all mass measures, including the BMDs, seemed to agree with a general structural property of the femur, the bone densities seemed to have local variations, probably to adapt the calcium distribution and bone geometry to local biomechanical requirements. We suggest that BMD should be denoted “mass per projected area” to avoid any misconceptions concerning the nature of this parameter.