Correlation of quantitative ultrasound measurements with material properties and bone mineral density in the equine metacarpus

This study explored the relationship between speed-of-sound (SOS) measurements and the material properties of metacarpal bones in order to validate a device that uses linear unicortical transmission of ultrasound. SOS, ultimate tensile strength and modulus of elasticity were determined at nine experimental sites. Measurements of SOS and bone mineral density were collected at three of the nine experimental sites. Twenty-five equine metacarpal (MC3) bones were used. Micro-computerized tomography was used to validate testing protocols. SOS measurements were highly site- and horse-dependent. One or more statistically significant correlations were found with ultimate tensile strength, modulus of elasticity and bone mineral density in four of the nine experimental sites. A previously described pattern of high lateral and medial cortical stiffness and SOS was found in the mid-diaphysis that correlated with bone mineral density (r2=0.25, P<0.01) and modulus of elasticity (r2=0.14, P<0.05). SOS and ultimate tensile strength correlated strongly in the distal dorsal metacarpus (r2=0.47, P<0.001). Lateral and medial distal-level sites just above the fetlock joint had a variable amount of cancellous bone, reducing the ultimate strength of these sites. The study indicates that quantitative ultrasound is sensitive to differences in the quality of equine metacarpal bone, so this technique may be useful for monitoring adaptation to exercise and bone development.