The timing and distribution of strains around the surface of the midshaft of the third metacarpal bone during treadmill exercise in one Thoroughbred racehorse.

The research studied the timing and distribution of strains around the surface of the third metacarpal bone (in the lower leg), specifically in a thoroughbred horse while running on a treadmill.

Research Objective and Method

• This study aimed to verify that the midshaft dorsal cortex of the third metacarpal bone experienced higher compressive strains during fast running compared to the medial or lateral cortices. It also sought to show that the strain peak appeared earlier in the hoof-down phase of the stride on the dorsal cortex than the other cortices.
• Methodologically, the data for the research was collected from a 3-year-old Thoroughbred mare. Rosette strain gauges were implanted onto the medial, lateral, and dorsal surfaces of the cannon bone’s midshaft. This allowed for strain data to be gathered during treadmill exercise, and a hoof switch was used to determine when the hoof was in the stance phase.

Results of the Research

• The results showed that peak compressive strains on the dorsal surface of the third metacarpal bone were in proportion to the exercise’s speed and typically occurred at around 30% of the stance.
• The peak compressive strains on the medial surface reached a maximum at a speed around 10 m/s and were found to occur at mid-stance.
• The timing and size of peak compressive strains on the lateral surface varied between strides across all exercise speeds, but the strains remained less than -2000 microstrains.

Conclusions Drawn

• The research concluded that the timing of peak compressive strains on the dorsal cortex could be linked to the deceleration of the limb after hoof impact. It suggests that exercise speed and turning are the main determinants of the strain size.
• The study supports previously published but undiscussed data from other labs, demonstrating that peak compressive strains on the medial surface occur at mid-stance, possibly relating to body weight support.
• The strains on the lateral cortex occurred at different times and could be associated with the maintenance of balance as well as the support of body weight.
• Ultimately, understanding the loading of the third metacarpal bone will be beneficial for determining the causes of damage to it and potential preventative strategies to help avoid injury.