Bone properties as estimated by mineral density, ultrasound attenuation, and velocity

Quantitative ultrasound (QUS) analysis of bone has been suggested to have a level of performance equal to dual-energy X-ray absorptiometry (DXA) for the assessment of fracture risk. In this study, QUS and DXA measurements were conducted on bovine trabecular bone in vitro using commercially available clinical instruments. The samples were then mechanically tested to obtain Young's modulus and ultimate strength. In addition, QUS and DXA parameters of the human calcaneus (n = 34) were measured in vivo. The measurements revealed a significant effect of bovine bone size on broadband ultrasound attenuation (BUA) and speed of sound (SOS) in vitro. By normalizing the DXA and QUS results with bone thickness we could systematically improve their ability to predict bone strength. However, in bovine trabecular bone, BUA showed no significant linear correlation with either bone mineral density (BMD), Young's modulus, or ultimate strength. This finding may be typical of only high-density and low-porosity bovine bone. We significantly improved prediction of ultimate strength by combining density and ultrasound velocity results as compared with assessments of volumetric BMDvol (p < 0.05) or SOS (p < 0.001) alone. However, the improvement was not significant if BMDvol, instead of wet density, was used. Altogether, 88% of the variation in the ultimate strength of bovine bone could be explained by combined density and ultrasound velocity. In vivo, SOS showed a weak negative correlation with heel width (r = -1.350). The in vivo measurements also showed a close correlation for BUA with BMD in the human calcaneus. This suggests that BUA is more suitable for quantitative analysis of low-density trabecular bone.