Analysis of the subchondral microarchitecture of the distopalmar aspect of the third metacarpal bone in racing Thoroughbreds

Luis M. Rubio-Martínez, DVM, PhD, DVSc; Antonio M. Cruz, DVM, MVM, MSc, DrMedVet; Dean Inglis, PhD; Mark B. Hurtig, DVM, MVSc
American Journal of Veterinary Research
October 2010

Objective—To determine the anisotropic characteristics of the microarchitecture of the subchondral bone (SCB) plate and trabecular bone (TBB) of the distopalmar aspect of the metacarpal condyles in horses with different stages of SCB disease.

Sample Population—12 third metacarpal bone pairs from racing Thoroughbreds euthanized for diverse reasons.

Procedures—Both metacarpi were collected from horses with SCB changes that were mild (sclerosis and focal radiolucencies; n = 6) or severe (multifocal radiolucencies and articular surface defects; 6). Sample blocks of SCB plate and TBB were collected from the distopalmar aspect of both condyles and the sagittal ridge and examined via 3-D micro-computed tomography at 45-?m isotropic voxel resolution. For each sample, the angle between the principal orientation of trabeculae and the sagittal plane and the degree of anisotropy (DA) were calculated from mean intercept length measurements.

Results—Condylar samples had significantly lower angle (mean, 8.9°; range, 73° to 10.9°) than sagittal ridge samples (mean, 40.7°; range, 33.6° to 49.2°), TBB had significantly higher DA (mean ± SE, 1.75 ± 0.04) than SCB plate (1.29 ± 0.04), and mildly diseased TBB had higher DA (1.85 ± 0.06) than severely diseased TBB (1.65 ± 0.06).

Conclusions and Clinical Relevance—The highly ordered appearance of trabeculae within the condyles supports the concept that joint loading is primarily transmitted through the condyles and not the sagittal ridge. The sharp changes in the trajectories of the SCB trabeculae at the condylar grooves may be indicative of hypothetical tensile forces at this location contributing to the pathogenesis of condylar fractures.

Large animal: