Prediction of mechanical properties of the human calcaneus by broadband ultrasonic attenuation

Abstract

Broadband ultrasonic attenuation (dB MHz cm-1, nBUA) was determined for specimens from 20 human calcanei, along with apparent density, elasticity (Young's modulus), and compressive strength. The calcanei were modified to provide "whole" (only soft tissue removed), "core" (mediolateral cores corresponding to in vivo measurement region), "can" (cortical end plates removed from core), and "def" (core defatted) samples. The nBUA values for the various modifications were highly correlated. The presence of the cortical endplates creates a significant nBUA, probably due to complex phase interactions. nBUAcan was a good predictor of elasticity (R2 = 75.7%) and strength (R2 = 73.6%). Apparent density was a better predictor of the mechanical variables than nBUA, with R2 values of 88.5% for elasticity and 87.6% for strength. The morphological anisotropy defined by "fabric" for the specimens was extremely uniform. The coefficient of variation in nBUA (40.5%) and compressive strength (64.4%) was significantly greater than for apparent density (23.5%) and fabric (6.7%). It is well known that a power law relationship exists between apparent density and elasticity or strength in cancellous bone. An interesting finding in this work is that there also appears to be a power law relationship between nBUA and apparent density, with an exponent of approximately 2, which, in the light of clinical implications, warrants further investigation.