DO QUANTITATIVE ULTRASOUND MEASUREMENTS REFLECT STRUCTURE INDEPENDENTLY OF DENSITY IN HUMAN VERTEBRAL CANCELLOUS BONE

Ultrasonic measurements were made in three orthogonal directions on 70 vertebral bone cubes. Apparent density (rho) was determined, and micr ocomputed tomography was used to derive a range of microstructural par ameters. Qualitatively different ultrasonic behavior was observed in t he craniocaudal (CC) axis, in which two distinct waves propagated. In this direction, only attenuation correlated strongly with rho (r(2) = 80%), whereas, in the anteroposterior (AP) and mediolateral (ML) axes, there were significant correlations between all ultrasonic parameters and rho (r(2) = 57% - 79%), Microstructural parameters were, in gener al, correlated with ultrasonic properties, but when adjusted for rho, few significant relationships remained and the additional variance exp lained by individual microstructural parameters was relatively small ( < 25% for CC axis, < 3% for AP, 0% for ML), In stepwise regression ana lysis including rho and all of the microstructural parameters, rho rem ained the primary determinant of ultrasonic properties in the transver se axes: Combinations of structural parameters explained, at most, an additional of 6% of the variability in ultrasonic properties in the AP axis, but failed to contribute significantly in the ML axis. In the C C axis, structural parameters played a greater role, but the pattern o f associations was complex and the predictive power of the models was generally much less than that for the transverse axes. These data indi cate that the ability of ultrasound to reflect aspects of trabecular s tructure is strongly dependent on the direction in which ultrasonic me asurements are made, and provide only qualified support for the hypoth esis that ultrasound reflects cancellous bone structure independently of bone density. (C) 1998 by Elsevier Science Inc. All rights reserved .