Prevalence of subchondral bone pathological changes in the distal metacarpi/metatarsi of racing Thoroughbred horses.

The research investigates the rate and extent of minor bone damage in the lower fore and hind limbs of Thoroughbred racehorses, and examines any associations with the horse’s training history. The study concludes that subchondral bone damage is very common among the examined racehorses, and that the amount of damage tends to increase the longer the horse’s racing career.

Objective and Methods of the Study

• The study’s objective was to examine the frequency and magnitude of subchondral (beneath the cartilage) bone damage in the distal (lower) metacarpi/tarsi (forelimb/hindlimb) of Thoroughbred racehorses. Furthermore, it aimed to ascertain any correlation between such injuries and the training history of the horses.
• Postmortem examinations were carried out on the metacarpi/metatarsi of Thoroughbred racehorses. Samples from both the forelimbs and hindlimbs of separate horse cohorts were obtained for this purpose.
• The severity of palmar/plantar osteochondral disease (POD), a degenerative disorder of the bones and joints, was graded in the limb samples. In the forelimb samples, microfracture density in the condylar subchondral bone was determined using backscattered scanning electron microscopy.
• Various observations, such as identification of horizontal subchondral bone fractures and quantification of empty osteocyte lacunae (spaces in the bone that were once home to bone cells), were made in the hindlimb samples.

Results of the Study

• A high prevalence of gross POD was found: 65.8% in the forelimb and 57.8% in the hindlimb samples.
• Microfractures were found in the forelimbs of 97.4% of the horses. The density of these microfractures in the forelimbs was found to increase with age and the number of race starts.
• Empty osteocyte lacunae were observed in the subchondral bone of the hindlimbs in 97.7% of the horses. These are spaces where bone cells were once present, suggesting cell death or damage.

Conclusions of the Study

• Pathological changes to the subchondral bone were found to be very common in the Thoroughbred racehorses subjected to postmortem examinations in this study.
• The accumulation of damage to the subchondral bone was found to be greater with a longer duration of the horse’s career, indicating that these injuries are likely due to fatigue of the bone over time.