Abstract
Background:
Carpal conformation is an important factor in relation to the joint soundness. The equine carpometacarpal joint was reported to have variations in its three palmaromedial articulations. Lacking one or more of these articulations has not been radiographically evaluated in Thoroughbred (TB) and Standardbred (SB) racehorses.
Aim:
The study aimed to identify the prevalence of the variation in the palmaromedial articulation of the carpometacarpal joint (PM-CMCJ) in TB and SB horses. Additionally, to detect the probability of having each of the three articulations within and between the breeds. Finally, to establish an anatomical description for the different patterns of the articulations in these horses.
Methods:
313 dorsopalmar radiographs from 174 horses (117 TB and 57 SB) were used. Three articulations at PM-CMCJ were evaluated based on their presence or absence: the articulations between the second and third carpal bones (C2-C3), the second carpal-second metacarpal (C2-Mc2) and the second and third metacarpal (Mc2-Mc3) bones. Probability of each articulation was determined in the breeds. Depending on the presence/absence of one or more of these articulations in each horse, each group of horses that had the same patterns of the articulation was gathered into one category.
Results:
Prevalence of variation in articulations of PM-CMCJ was identified in about 28% of the horses. SB showed a higher variation than TB throughout the comparisons. C2-C3 articulation was significantly the most common articulation, especially in TB (98%). The most common pattern of articulations (73%) was found in Category I, which had the three articulations whereas 3 horses that grouped in Category VI had no palmaromedial articulations.
Conclusion:
The variations in the articulations of PM-CMCJ in TB and SB racehorse might show a breed association. C2-C3 articulation was considerably the most frequent feature and Category I was the common pattern of articulations in PM-CMCJ. Potential clinical effects of the varied patterns of the articulations require investigation.

Key words: Carpometacarpal joint, Radiology, Standardbreds, Thoroughbreds, Variation