Suspensory ligament injuries are relatively common in dressage horses, but there is little scientific information available on their causes. A recent study by researchers at the Animal Health Trust in Newmarket, England, examined the possible link between movement patterns at the collected and extended trot, and risk for suspensory ligament injuries.

Scientists used a high-speed camera to capture four Warmbloods working in collected and extended trot on three different surfaces. Each horse wore brushing boots fitted with inertial motion sensors and markers at five points on the hind legs to aid in video analysis.

The results demonstrated that when horses performed the collected trot across all three surfaces tested, there was a decrease in speed and stride length (measured in meters) but an increase in stride duration (measured in seconds) compared to extended trot.

Conversely, in the extended trot, horses showed an increase in flexion of the hock and extension of the fetlock when the limb was in contact with the ground. This suggests that there might be more strain placed on the suspensory ligament at extended trot compared to the collected trot, the team relayed. The authors suggested that this could be because the horse is moving over a greater distance at a greater speed at extended trot, increasing relative protraction and retraction of the hind limb, putting more strain on the soft tissue structures of the leg.

This might be particularly problematic for young horses in dressage training, as there is industry pressure for these horses to demonstrate extended paces–particularly if they are extravagant movers–but these young animals might not have sufficient muscular strength to support this movement, the team relayed.

"They key aspect in terms of young horses is to ensure that they are trained slowly and correctly to build up core muscle strength and not pushed to demonstrate extravagant paces before they have the strength through their body to support their limbs," said Vicki Walker, BSc, MSc and study author. "Any new exercises should be introduced slowly and only undertaken for very short periods initially."

For all dressage horses, it’s important to ensure the surface you ride on is level and stable, as other studies suggest that the gait of the horse is influenced by characteristics of the surface and that certain characteristics can increase the risk of injury. These could be exacerbated when the horse is working on a new surface, as it is likely to be less coordinated and tire more easily, the team said

"In order to protect horses from overload injury, it is important to avoid spending too long in any single exercise and not to repeat any single exercise too many times, especially when the horse is becoming tired," said Walker. "At the extended trot in particular, there may be considerable forces on the limbs, so it is important that the horse is coordinated … it may be safer to avoid performing extended trot when a horse is getting tired at the end of a session."

The study, "The effect of collection and extension on tarsal flexion and fetlock extension at trot," will appear in an upcoming issue of the Equine Veterinary Journal. The abstract is available online.