Quantitative ultrasound and trabecular architecture in the human calcaneus

Relationships between quantitative ultrasound (QUS), density (bone volume d ensity [BV/TV]), and trabecular architecture were investigated in 69 calcan eal cancellous bone cubes. Ultrasound signal velocity, phase velocity, atte nuation, and broadband ultrasonic attenuation (BUA) measurements were made along the mediolateral axis. Density and architectural parameters were meas ured using microcomputed tomography (mu CT). Density yielded the best corre lations with QUS (r(2) = 73-77%). Of the individual architectural parameter s, correlations with QUS were highest for the Structure Model Index (SMI), a parameter quantifying the relative proportion of rods and plates (r(2) = 57-63%). After adjustment for density, significant associations with QUS re mained for SMI, trabecular spacing (Tb.Sp), and trabecular number (Tb.N), a lthough the variance in QUS attributable uniquely to individual architectur al parameters was at best 4%. In multivariate regression models, combinatio ns of density and architectural parameters explained 76-82% of the variance in QUS, representing an r(2) increase of, at most, 8% compared with using density alone. However, multivariate models using combinations of architect ural parameters alone (i.e., density excluded) also had a good predictive a bility for QUS (r(2) = 73-81%). Thus, although these data show modest but s ignificant density-independent relationships between QUS and trabecular arc hitecture in the human calcaneus for the first time, the causal relationshi ps behind the variation in acoustic properties remain obscure. Given the re lative weakness and complexity of the emerging associations between QUS and architecture, it is prudent to regard QUS measurements in calcaneal bone p rimarily as an indicator of bone density.