Comparison of distal extremity magnetic resonance imaging findings in Australian racing Standardbreds and Thoroughbreds.

Introduction: Foot-related lameness is common in Standardbred and Thoroughbred racehorses. Magnetic resonance imaging (MRI) provides information on both the soft tissue and osseous structures of the distal extremity. The aim of this study was to determine whether abnormalities identified on distal limb MRI differed between these two racehorse populations.

Materials and methods: The records of Standardbred and Thoroughbred racehorse distal extremity MRI examinations conducted at Camden Equine Centre and Ballarat Veterinary Practice between 2013 and 2023 were retrieved. Horses were included if pain causing lameness had been localised to the foot using perineural or intra-articular analgesia. MRI abnormalities of the structures within the distal extremity were recorded and comparisons made between the two groups.

Results: There was a significant difference in the rate of occurrence of certain MRI abnormalities between the Thoroughbred and Standardbred racehorse populations, including distal phalangeal fractures, proximal phalangeal short tau inversion recovery (STIR) hyperintensity (distal aspect), the presence and severity of ungular cartilage ossification, abnormalities of the navicular bone distal border synovial invaginations/vascular channels and navicular bone distal border fragments. The presence of distal extremity STIR hyperintensity and fractures was significantly higher in Standardbred compared to Thoroughbred racehorses when these findings were grouped and considered in combination.

Conclusion: There were many similarities in the distal extremity MRI abnormalities identified in lame Australian Standardbred and Thoroughbred racehorses. However, distal phalangeal fractures, ungular cartilage ossification and distal extremity STIR hyperintensity were identified in significantly more in Standardbred than Thoroughbred racehorses.