The change in third metacarpal mid-diaphyseal radiographic dimensions in Thoroughbred foals through growth

Changes in the third metacarpal (MC3) mid-diaphyseal dimensions were measured radiographically in young Thoroughbred racehorses through race training and found to be associated with a higher risk of shin soreness. However, it is still unclear whether such negative MC3 morphologies are set congenitally or through development.

To quantify MC3 bone dimensional changes through growth.

Longitudinal.

Twenty privately owned Thoroughbred foals were radiographed bimonthly from birth to 14 months of age. Four linear MC3 parameters (proximodistal MC3 length, mid-diaphyseal dorsal and palmar cortical bone thickness, and dorsopalmar medullary width) were measured using ImageJ on lateromedial radiographs. Associations with age (growth), MC3 length, differences between left and right limbs, and between sexes were analysed separately using a linear mixed effects model.

The dorsal cortical bone thickness showed a positive linear relationship with growth (0.4 $\pm$ 0.02 mm per month, p < 0.001, 95% CI [0.37, 0.44]) while the medullary width did not change. The relative thickness of the dorsal cortical bone thickness compared with the medullary cavity width and palmar cortical bone thickness also increased through growth (0.2 $\pm$ 0.01 mm per month, p < 0.001, 95% CI [0.14, 0.19]). The dorsal cortical bone thickness was positively associated with MC3 length (0.07 $\pm$ 0.0001 mm per mm increase in MC3 length, p < 0.001, 95% CI [0.05, 0.08]) and the relative thickness of the dorsal cortical bone thickness (RI) to the rest of the diaphyseal parameters (0.02 $\pm$ 0.01 per mm increase in MC3 length, p = 0.01, 95% CI [0.01, 0.03]).

A limited number of foals were included with similar breeding.

The mid-diaphyseal dorsal cortical bone thickness and proportions could be measured to monitor musculoskeletal development and identify foals at increased risk of shin soreness or those that are immature or otherwise need more time before the commencement of fast training.