Biomechanical Properties of the Equine Third Metacarpal Bone: In Vivo Quantitative Ultrasonography Versus Ex Vivo Compression and Bending Techniques

An experiment was conducted to (1) assess equine cortical bone status in vivo by quantitative ultrasonography (QUS); (2) evaluate certain mechanical properties of the third metacarpal bone (McIII) and to characterize its regional variation along the bone; and (3) compare the in vivo results with the ex vivo mechanical tests on the same bone. Eight adult mares were assessed with a QUS device on the midsection of the right McIII (dorsal and lateral regions). Cortical bone samples from the dorsal and lateral regions of both McIII were collected postmortem and tested in compression and bending. Values of speed of sound (SOS) on the lateral region were higher than for the dorsal one (P < .0001), but they were linearly correlated (r = 0.803; P < .05). In compression, the maximum stress (σmax) was influenced by bone region and bone section, and an interaction was found between these two effects (P < .01). Samples from the dorsal region were stiffer than samples from the lateral region (P < .0001), and lower values of the Young's modulus (E) were obtained on the McIII distal sections (P < .05). Lower bending strength was observed in the distal section of the bone compared with the proximal and the midsection (P < .01). In vivo SOS measurements on the dorsal region were highly correlated with the E obtained from ex vivo compression tests (r2 = 0.92; P = .0002). These results suggest that QUS could be used as a noninvasive method in the assessment of equine cortical bone mechanical properties.