Correlation of mechanical properties and structure in the subchondral bone of the distopalmar metacarpus in thoroughbred racehorses

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Rubio Martínez, Luis M.

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University of Guelph

Abstract

This thesis is an investigation of the microstructure and the mechanical properties of the subchondral bone of the distopalmar aspect of the metacarpal condyles of racing Thoroughbreds (TBs) by using micro-Computed Tomography ([mu]CT) and compressive mechanical testing. Both metacarpi were collected from TBs with mild (n=6; sclerosis, focal radiolucencies), and with severe (n=6; multi-focal radiolucencies, articular surface defects) SCB changes, as determined by [mu]CT. Sample blocks of 6x6x6 mm including subchondral bone plate (SCBP) and trabecular bone (TBB) were collected from the palmar aspect of both condyles and the sagittal ridge, and examined with 3D [mu]CT. On each sample, Bone Mineral Density (BMD), True Mineral Density (TMD), Bone Volume Fraction (BVF), Trabecular Thickness (Tb.Th), Trabecular Separation (Tb.Sp), and Connectivity (CN) were calculated. Samples were tested in compression, and Elastic Modulus (EM), Yield Stress (YSS), Yield Strain (TSN), and Toughness (AUC) calculated. A partial randomized block (horse) ANOVA factorial design was performed, and adjusted with Tukey analysis. Manova and Pearson's correlation analyses between structural and mechanical variables were performed. Significance was p<=0.05. No differences were found between left and right limbs. Condyles had higher BMD, TMD, BVF, Tb.Th, lower Tb.Sp, and higher EM, YSS and AUC than sagittal ridge. In the mild group, SCBP had higher BMD and lower Tb.Sp than TBB; these values were similar in the severe group. Between groups, TBB in the severe group had higher BMD, lower Tb.Sp than the mild TBB. In the severe group, YSS increased in TBB and decreased in SCBP. EM, YSS and AUC were correlated with TMD, BMD and BVF, and Tb.Th and Tb.Sp with YSS. Structural and mechanical properties of the SCB at distopalmar aspect of the metacarpal condyles in TBs follow an anatomically-related pattern. Severe [mu]CT changes are indicative of bone failure at the SCBP, while TBB strengthens. With both mild and severe [mu]CT changes, there is steep gradient of structural and mechanical properties at the condylar grooves, which could be involved in the pathogenesis of condylar fracture. Mechanical properties of subchondral bone from the distal equine MC3 can be predicted to some extent by using [mu]CT.

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Thoroughbred racehorses, Distopalmar metacarpus, subchondral bone, microstructure, mechanical properties

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