Metacarpal geometry changes during Thoroughbred race training are compatible with sagittal-plane cantilever bending

Bending of the equine metacarpal bones during locomotion is poorly understood. Cantilever bending, in particular, may influence the loading of the metacarpal bones and surrounding structures in unique ways.

We hypothesised that increased amounts of sagittal-plane cantilever bending may govern changes to the shape of the metacarpal bones of Thoroughbred racehorses during training. We hypothesised that this type of bending would require a linear change to occur in the combined second moment of area of the bones for sagittal-plane bending (I) during race training.

Six Thoroughbred racehorses were used, who had all completed at least 4 years of race training at a commercial stable. The approximate change in I that had occurred during race training was computed from radiographic measurements at the start and end of training using a simple model of bone shape.

A significant (P < 0.001), approximately linear pattern of change in I was observed in each horse, with the maximum change occurring proximally and the minimum change occurring distally.

The pattern of change in I was compatible with the hypothesis that sagittal-plane cantilever bending governed changes to the shape of the metacarpal bones during race training.