Effect of bovine bone constituents on broadband ultrasound attenuation measurements

Broadband ultrasound attenuation (BUA) has been found to correlate positively with bone mineral density (BMD) measured by dual-energy X-ray absorptiometry. However, because there is a significant amount of unexplained variation in this correlation, it has been suggested that BUA might also provide information about bone structure. The purpose of this study was to determine the contribution of bone mineral and organic matrix to BUA and BMD measurements. The influence of sample length on both BUA and BMD was also investigated by normalizing these measurements to length. BUA (Walker Souix, 575+) and BMD (Lunar DPX) values were obtained on bicortical cores removed from 12 bovine femoral necks. BMD and BUA measurements were repeated on the samples after: (1) mechanical removal of the cortices; (2) defatting using a 2:1 chloroform:methanol solution; and (3) decalcifying using formic acid. The data demonstrate that the cortical component of the bone contributes significantly to BMD. We found that 41.7% of the normalized BMD reflect cortical bone. Defatting the samples did not affect BUA. Decalcifying the trabecular bone while maintaining an intact collagenous structure significantly reduces BUA by 89% and BMD by 96% compared to the whole core samples. Normalizing BMD and BUA to sample length, in cases where large variation is present, does influence the correlation between the variables. We conclude that BUA is influenced mainly by the presence of bone mineral, whereas the presence of the organic matrix contributes very little to BUA.