Prevalence of radiographic changes in forelimb digits and metacarpophalangeal joints of South African endurance racehorses.

The research studies the prevalence of certain types of bone and joint changes seen in the forelimbs of South African endurance racehorses, in this fastest growing discipline, using radiographic images. Conclusions about these changes could assist equine vets in managing these horses.

Objective and Methodology

• The key aim of this research is to explore the frequency of radiographic changes in the front digits and metacarpophalangeal joints (MCP) of South African endurance racehorses. Despite endurance riding being the second-most popular discipline under the Fédération Equestre Internationale (FEI), there have been no prior studies investigating this issue in South Africa.
• The study involved 100 endurance racehorses registered with ERASA. These horses were volunteered by their owners for the study, and radiographs of their forelimb digits and MCP were taken during the 2018-2019 racing season.
• Each distal forelimb (the lower part of the front limb) of the participating horses was radiographed from seven different standard views. These radiographic images were then reviewed independently by three observers, enabling the assessment of inter-rater reliability (IRR) and the calculation of a point prevalence, which refers to the proportion of a population affected by a specific condition at a given point in time.

Findings

• Data analysis showed that a significant proportion of horses exhibited variations from standard limb structure, suggesting potential issues that could affect their performance or wellbeing. The most prevalent issues were those categorised as potential signs of dorsopalmar hoof imbalance (observed in 95% of horses) and a diversion from a straight digital axis (found in 91% of horses), respectively.
• Osteoarthritis, a common degenerative joint condition, was found in a lower than expected percentage of horses in the proximal (16%) and distal (7%) interphalangeal joints — the joints between the different segments of the horses’ digits. Additionally, it was noted that a large percentage of horses showed signs of MCP joint osteoarthritis (28%), with 10% of these cases being bilateral, affecting both limbs.
• Interestingly, while the hoof-distal-phalanx-ratio of 86% of horses was more than 25%, these horses showed no other signs of chronic laminitis, a painful condition affecting the feet. This suggests that this ratio might not be a reliable indicator of chronic laminitis in this specific population of horses.
• Ossification (hardening) of the ungular cartilages was observed in 69% of the horses, affecting one or both of their distal phalanges (the last bone in the digit).

Conclusions

• This study provides valuable information about the radiographic changes found in the distal front limbs of South African endurance racehorses. It reveals the presence of significant structural changes, despite not making connections with horse age, speed, or the number of competitive kilometers ridden.
• This prevalence data can help equine practitioners better evaluate and manage horses exhibiting these changes, potentially improving outcomes for affected animals.
• Moreover, this work may serve as a solid basis for future research on the relationship between these alterations and performance in endurance racing.