Computed Tomographic Evaluation of the Sagittal Ridge of the Third Metacarpal Bone in Young Thoroughbred Racehorses: A Longitudinal Study.

This study examines changes in the metacarpophalangeal joint, a common area for injuries among racehorses, using computed tomography. It tracked changes in 40 young Thoroughbred horses over time, noting that bone issues tended to heal during early training and were not associated with lameness.

Objective and Methodology

• The primary objective of the study was to observe any changes in the sagittal ridge (SR) of the third metacarpal bone in young Thoroughbred racehorses, and whether these changes were associated with lameness or other racing difficulties.
• The study followed 40 Thoroughbred yearlings at the outset of the study. The subjects were then re-examined twice with about six months between each assessment.
• Computed tomographic examinations were carried out with the horses in a standing position. The research team carried out both subjective and objective analyses.
• They examined the Hounsfield Unit (HU) values across eight radial segments as well as the location, size, and shape of any hypoattenuating lesions – signs of lower x-ray attenuation which may indicate tissue damage or other pathology.

Key Findings

• The study found that the mean HU values were higher six months after the first examination, indicating an increase in bone density. There was no difference in the mean HU values between the second and third examinations.
• Morphology of the SR showed hypoattenuating lesions in 41.3% of limbs at the first examination, which decreased slightly at subsequent examinations, indicating these lesions present at the outset of training tended to heal or reduce in size with time.
• All hypoattenuating lesions were located in the dorsodistal aspect of the SR. The most common shapes of these lesions were those elongated proximodistally and those extending towards trabecular bone.
• Despite these findings, these hypoattenuating lesions were not associated with lameness in the horses studied. Thus, the common belief that radiological abnormalities in the SR resulted in joint effusion, lameness, and reduced sales prices was not supported in this study.

Conclusion

• This research suggests that young Thoroughbred racehorses can develop bone lesions in the early stages of training, but these issues are temporary and tend to resolve on their own during continued training.
• Furthermore, these bone abnormalities were not associated with lameness or other hindrance in racing performance, challenging some common beliefs in the equine industry.