Load redistribution after desmotomy of the accessory ligament of the deep digital flexor tendon in adult horses.

This research paper studies the effects on joint moments and load distribution in horses after surgery to remove the accessory ligament of the deep digital flexor tendon. The study found that after surgery, the other tendons in the horse’s limb take on additional load, but do not overload, allowing for continued locomotion.

Methodology

• This study analysed the joint movements of six healthy adult horses before and ten days after the desmotomy of the accessory ligament of the deep digital flexor tendon in their right forelimb. The gaits studied were the walk and the trot.
• Kinematic recordings of the movements of the right forelimb and the lower part of the left forelimb were made using the CODA-3 system, a high-speed, multi-camera motion analysis system.
• At the same time, kinetic recordings of the ground reaction forces of both forelimbs were made using a Kistler force plate, a device designed to measure the forces exerted on the ground during movement.
• Radiographic localisation of markers on both lower limbs allowed for analysis of the movements and forces in the coffin and fetlock joints and the digital flexor tendons.

Results

• The research found that there was no transfer of load from the operated limb to the other one.
• In the operated limb, the total load, or moment arm of the coffin joint (the horse’s equivalent of the human finger or toe joint), decreased substantially due to a reduced vertical ground reaction force during the entire stance phase(when the horse’s foot is on the ground).
• The fetlock joint (the horse’s equivalent of the human knuckle) moment decreased slightly.
• To compensate for the loss of function in the accessory ligament, the superficial digital flexor tendon took a higher load during the midstance phase, while at the end of the stance phase, the load was carried by the deep digital flexor tendon, with an increased load peak just before the “heel off” phase (when the horse lifts its foot off the ground).

Conclusions

• The deep digital flexor tendon wasn’t able to completely compensate for the loss of the accessory ligament. This resulted in a prolonged hyperextension of the fetlock joint and a rapid flexion at the start of the swing phase (when the horse’s foot is off the ground)
• Despite this, the researchers concluded that the load changes were not serious enough to cause overloading of the compensating tendons after the removal of the accessory ligament, allowing normal movement.