Distal forelimb radiographic bone morphology in Thoroughbred foals during the first 10 months post-partum. Part 1:...

The risk of carpal injury in racehorses may be related to the morphology, yet whether carpal morphologies are set from birth or change through growth remains unclear.

To quantify carpal bone changes through growth.

Twenty privately owned Thoroughbred foals born between January 2022 and May 2023 were radiographed bimonthly from birth to 10 months of age. Imprint training was used to take radiographs safely without chemical restraints. Fifteen individual and 11 relative angular carpal parameters were measured using ImageJ on dorsopalmar radiographs of the carpus at zero degrees of vertical and horizontal rotation. Associations with age (growth), sex and the differences between left and right limbs were analysed separately using a linear mixed effects model.

Six individual carpal parameters changed with age (radial carpal joint [RCJ], Prx.dor. radial carpal [Cr], Prx.Cu, Dis.dor. third carpal [C3], Dis.pal.C3 and Dis.pal. intermediate carpal), and one was influenced by side, that is higher in the left carpus (Dis.pal.Cr). Seven relative parameters changed with age, and one relative parameter was influenced by side, that is higher in the left (Ra.met-RCJ). The proximo-dorsal bone surface angle of Cr and disto-dorsal bone surface angle of C3 became flatter over time, which may be associated with the re-direction of the load towards the sagittal carpal plane. Sex did not influence any of the carpal parameters, nor did the combined effect of age, side of the limb and sex.

Specific individual and relative angular carpal parameters changed significantly over time and some differed between the left and right limb, whereas other parameters did not change. The steeper carpal bone angles achieved proximally with the parameters that did change may improve stability by redirecting the load more medially through the carpus and the proximal and distal bones.