Structural characterization of subchondral bone in the distal aspect of third metacarpal bones from Thoroughbred racehorses via micro–computed tomography.

This research investigates the microstructure of subchondral bone in the lower part of the metacarpal bones of Thoroughbred racehorses, using micro-computed tomography. It reports significant differences in bone structure based on the severity of bone disease.

Objective and Methods of the Study

• The research was conducted to assess the microstructure of the subchondral bone (SCB) and trabecular bone (TBB) in the lower posterior part of metacarpal bones (MC3s) in Thoroughbred racehorses. The aim was to understand the changes that have occurred due to different stages of SCB disease.
• 12 pairs of MC3s were collected from Thoroughbred racehorses that were euthanized for different reasons. These samples were from horses with mild or severe SCB disease ascertained using micro-CT.
• Sections of the SCB plate and TBB were cut and examined using three-dimensional micro-CT. Various parameters such as apparent bone mineral density (aBMD), true BMD (tBMD), bone volume fraction (BVF), trabecular thickness (TBT), trabecular separation (TBS), and connectivity (CN) were calculated for each sample.

Results of the Study

• Condyles showed higher densities for aBMD, tBMD, BVF, and TBT, but lower TBS compared to the sagittal ridge.
• In the samples with mild SCB disease, SCB plate showed higher aBMD, TBT, and CN, but lower TBS compared to TBB. This indicates that the bone had become thicker and denser with less pore space (or separation).
• In samples with severe SCB disease, the TBB showed higher aBMD and tBMD, and a lower TBS than those with mild disease. The values were similar to the SCB plate from horses with severe disease, indicating comparable changes in bone structure with disease progression.

Conclusions

• The micro-CT examination revealed that the SCB microstructure of the lower posterior part of equine metacarpal condyles varied with the severity of the bone disease. Initial changes (sclerosis or hardening of the bone) were found in the SCB plate of the condyles. As the disease progression became severe, sclerosis was also found invading the condylar TBB.
• The findings from this study spotlight the importance of early detection and management of SCB disease in racehorses, as this can have significant implications on their health and performance.