Longitudinal associations between dorsal carpal and third metacarpal bone morphology in Thoroughbred foals during...

The carpal and third metacarpal (MC3) bones of the equine forelimb undergo morphological adaptation during early growth, influenced by developmental and mechanical factors. However, the longitudinal interactions between dorsal carpal morphology and MC3 structural characteristics have not been fully characterized. Improved understanding of these relationships may help identify morphological indicators associated with bone injury risk before training.

To examine the longitudinal associations between dorsal carpal angular morphology and MC3 diaphyseal parameters in growing Thoroughbred foals.

Twenty Thoroughbred foals were followed from within two weeks after birth to 14 months of age. Dorsopalmar carpal and lateromedial MC3 radiographs were obtained at two-month intervals. Two dorsal carpal angular parameters and three MC3 parameters (dorsal cortical width, total bone length, and a radiographic index representing relative dorsal cortical thickening and structural adaptation previously associated with peak strain at the dorsal midshaft) were measured using ImageJ software. Linear mixed-effects models were applied, with foal identity as a random effect and age and limb side as fixed effects.

Both dorsal carpal parameters were positively associated with MC3 length, dorsal cortical width, and radiographic index. The strongest association was observed between proximal dorsocranial inclination and the radiographic index (2.55 ± 0.25° per unit increase; p < 0.001).

These findings demonstrate significant longitudinal associations between dorsal carpal angulation and MC3 structural parameters during early limb development. While this pattern is consistent with mechanical adaptation, the observational study design does not permit direct causal inference or differentiation between growth-related and exercise-related loading effects.