In vivo tendon forces in the forelimb of ponies at the walk, validated by ground reaction force measurements.

This research observed the distribution of load over the tendinous structures in the forelimbs of ponies while walking, using implanted strain gauges. The computed tendon forces appeared to be reliable despite some differences likely due to errors in the moment arms.

Study Design and Procedure

• The researchers tested the load distribution over the tendinous structures within the forelimbs of ponies. This involved examining the forces experienced by these tendons during a pony’s walk.
• Strain gauges, which are devices used to measure strain on an object, were implanted into five ponies. They were constructed from a liquid-metal, making them flexible and biocompatible.
• The in vivo signals obtained from these strain gauges were used to calculate the forces exerted on the tendinous structures.

Validation and Results

• The calculated tendon forces were validated by converting them into joint moments and comparing these against calculated moments induced by the ground reaction force.
• On average, the peak force per unit body weight (in Newtons per kilogram) was discovered to be 5.2 N/kg for the superficial digital flexor tendon, 3.8 N/kg for the deep digital flexor tendon, 7.3 N/kg for the distal accessory (check) ligament, and 8.4 N/kg for the third interosseous muscle (suspensory ligament).
• The maximal moment exerted by the tendons around the fetlock joint differed mildly from the maximal ground reaction force moment. For the fetlock joint, this difference was roughly 11%, while for the coffin joint, it was about 17%.

Interpretation and Conclusion

• The relatively minor discrepancies between the tendon force moments and the ground reaction force moments were largely attributed to errors in the moment arms, or the perpendicular distance between the line of application of force and the hinge about which the moment occurs.
• Despite these differences, the calculated tendon forces can still be considered sufficiently reliable, providing valuable insights for further research into equine locomotion and potential areas of injury.