Speed of sound reflects Young's modulus as assessed by microstructural finite element analysis

We analyzed the ability of the quantitative ultrasound (QUS) parameter, spe ed of sound (SOS), and bone mineral density (BMD), as measured by dual-ener gy X-ray absorptiometry (DXA), to predict Young's modulus, as assessed by m icrostructural finite element analysis (mu FEA) from microcomputed tomograp hy (mu CT) reconstructions. With mu FEA simulation, all bent elements in th e model ran be assigned the same isotropic Young's modulus; therefore, in c ontrast to mechanical tests, only the trabecular structure plays a role in the determination of the elastic properties of the specimen. SOS, BMB, and mu CT measurements were performed in 15 cubes of pure trabecular bovine bon e in three orthogonal directions: anteroposterior (AP); mediolateral (ML); and craniocaudal (CC). The anisotropy of the architecture was determined us ing mean intercept length (MIL) measurements. SOS, MIL, and Young's modulus (E) values were significantly different in all three directions (p < 0.001 ), with the highest values in the CC direction. There was a strong linear r elationship between E and SOS in each of the three orthogonal directions, w ith r(2) being 0.88, 0.92, and 0.84 (all p < 0.0001) for the CC, Mi,, and A P directions, respectively. The relationship between E and BMD was less str ong, with r(2) being between 0.66 and 0.85 (all p < 0.0001) in the differen t directions. There was also a significant, positive correlation between SO S and BMD in each of the three axes (r(2) being 0.81, 0.42, and 0.92 in the CC, ML, and AP directions, respectively; p < 0.0001). After correction for BMD, the correlations between SOS and E in each of the three directions re mained highly significant (r(2) = 0.77, p < 0.0001 for the AP direction; r( 2) = 0.48, p < 0.001 for the CC direction; r(2) = 0.52, p < 0.005 for the M L direction), After correction for SOS, BMD remained significantly correlat ed with Young's modulus in the AP and CC directions (r(2) = 0.52,p < 0.005; r(2) = 0.30, p < 0.05, respectively), but the correlation in the ML, direc tion was no longer statistically significant In a stepwise regression model , E was best predicted by SOS in each of the orthogonal directions. These o bservations illustrate the ability of the SOS technique to assess the archi tectural mechanical quality of trabecular bone. (C) 2000 by Elsevier Scienc e Inc. All rights reserved.