Kinetics and kinematics of the equine hind limb: in vivo tendon loads and force plate measurements in ponies.

This study measures the loads on various tendons in a pony’s hind leg during movement by implanting strain gauges, recording the results alongside ground force data and high-speed film. The results were then analysed post-mortem to better understand the relationship between strain and tendon loads, indicating the key points in movement where different tendons experienced peak loads.

Objective of the study

• The main goal of this study was to determine the load experienced by different tendons in the hind leg of a pony during motion. Specifically, the focus was on the suspensory ligament, the deep digital flexor tendon, superficial digital flexor tendon, and long digital extensor tendon.

Methodology

• Implanted strain gauges were put into application, which contained silicone rubber tubes filled with mercury, to make precise measurements of the strain experienced by the tendons.
• Alongside, force plate measurements and high-speed film recordings were made while the ponies were walking to simultaneously document the ground reaction forces and visual evidence of movement.
• The researchers undertook tension-strain tests post-mortem to understand the relationship between strain measurements and actual tendon loads.

Findings

• The suspensory ligament and the two flexor tendons experienced loading primarily during the stance phase (when the hoof is on the ground carrying weight). The extensor tendon, on the other hand, faced loading mostly during the swing phase (when the hoof is in the air).
• The suspensory ligament experienced peak loads of around 4.6 N/kg of body weight, tracking well with the vertical component of ground reaction force.
• The deep digital flexor tendon saw maximal loading during the latter half of the stance phase, with peak load reaching about 6.7 N/kg.
• The superficial digital flexor tendon faced peak load of approximately 4.1 N/kg at the onset of the stance phase, while the long digital extensor tendon had a maximum load of about 0.3 N/kg during the swing phase.
• Torque analysis using ground reaction force vector, limb conformation, and geometric configuration confirmed the tendon load measurements, showing that the recorded tendon loads matched the ground reaction forces.

Implications

• This study provides insights into the handling of loads by different tendons in the hind limb of a pony during movement. Understanding the biomechanics of equine motion could have implications for veterinary medicine, specifically for preventing and treating movement or load-bearing related injuries in horses.