Ultrasonic determination of the elastic properties of cortical bone: techniques and limitations
Description
A technique for measuring the orthotropic elastic coefficients from a single small, five millimeter, cubic specimen is described in this dissertation. This technique was applied to human and canine femora in order to measure the variation of the elastic properties as a function of anatomical position. The nine orthotropic elastic coefficients are determined by measuring the propagation velocity of a continuous ultrasonic wave. The time delay of propagation of the wave through the specimen, and hence the velocity, is obtained by the measuring the phase shift between the transmitted and received signals The spatial variations of the elastic coefficients measured in this study are the first extensive measurements of the variation of the elastic properties of bone as a function of anatomical position. It was found that the elastic properties of human and canine femora are statistically higher in value towards the proximal end of the femur. The most prominent variation in the elastic properties around the periphery of the femur was a consistent, statistically significant (p < 0.01) decrease in the posterior quadrant of the femur. The maximum values of the measured elastic properties were found in the lateral and medical quadrants, but this result was not found to be as statistically significant (p < 0.05) as the decrease in the posterior quadrant The spatial variation of the elastic properties were found to be very similar for human and canine femora. The mean values of the corresponding elements of the matrix of elastic coefficients for human and canine femora were also found to be very close in value. The similarity in the elastic properties of the femora of these two species is interesting in light of the different loadings to which femora of quadrupeds and bipeds are subjected. The spatial variations of the bone density and bone mineral content were measured in this investigation and found to be similar to the spatial variation of the elastic properties. Positive correlations were found to exist between the elastic properties, the density, and the mineral content for both human and canine cortical bone