Mechanical properties of subchondral bone in the distal aspect of third metacarpal bones from Thoroughbred racehorses

Objective-To characterize the mechanical properties of subchondral bone (SCB) of the distopalmar aspect of the condyles of the third metacarpal bone (MC3) and their correlations with structural aspects of MC3s in Thoroughbred racehorses. Sample Population-12 pairs of MC3s from Thoroughbred racehorses euthanized for various reasons. Procedures-MC3s were collected from horses with mild (n = 6) and with severe (6) SCB changes, as determined by micro-computed tomography (CT). Specimens of SCB plate and trabecular bone were cut from the distopalmar aspect of condyles and sagittal ridge and examined with 3-dimensional micro-CT Specimens were tested in compression, and elastic modulus, yield stress, yield strain, and toughness were calculated. Apparent and true bone mineral density, bone volume fraction, trabecular thickness, trabecular separation, and connectivity were also calculated. Differences in mechanical properties among various classifications of bone were evaluated. Correlations between structural and mechanical variables were also assessed. Results-No differences were detected between left and right forelimbs. Specimens from condyles had higher values for elastic modulus, yield stress, and toughness than did specimens of sagittal ridge. In SCB with severe changes attributable to SCB disease, SCB plate was weaker and trabecular bone was stronger than in SCB with mild changes. Microstructural and mechanical properties were significantly correlated. Conclusions and Clinical Relevance-A marked gradient in mechanical properties of SCB from horses, which could be involved in the pathogenesis of condylar fractures, was detected. Mechanical properties of SCB from the distal aspect of MC3s can be predicted to some extent via micro-CT (Am J Vet Res 2008;69:1423-1433)