Response of the Thoroughbred Forelimb to Perturbations Caused by a Change in Ground Surface.

This study explores how changes in ground surface impact the forelimb of Thoroughbred racehorses, using a musculoskeletal model and real-world data from ridden trials. The main findings include that both hard and soft surfaces lead to distinct reactions that may stress different parts of the equine forelimb, potentially causing injuries.

Development of Musculoskeletal Model

• The researchers created a detailed musculoskeletal model of the equine forelimb. It was developed using data from computed tomography (CT) scans as well as knowledge about muscle, tendon and ligament properties.
• The model was fed kinematic data gathered from five Thoroughbred horses ridden in trials under different ground surface conditions.

Testing Conditions and Method

• Horses were ridden at trot and canter on a baseline sand surface. Additionally, two other surfaces — one harder and one softer — were also tested.
• Data was collected for one stance phase on each type of surface. This allowed the researchers to detail how the musculoskeletal system of a horse reacts to sudden changes in the ground underfoot.

Findings: Hard Surface

• The study found that on the harder surface, the upper portion of the horse’s limb became more flexible, as shown by increased shoulder, elbow, and carpal flexion. This demonstrates a level of adaptivity in the horse’s locomotion to adjust for the harder impact.
• Simultaneously, the suspensory ligaments and muscle-tendon units strained less, however, the lacertus fibrosus was strained more, suggesting a redistribution of stress within the limb.

Findings: Soft Surface

• On the softer surface, different adjustments were observed. The horse’s hoof joint flexed more and the elbow was more extended during the initial contact with the ground, which resulted in increased strain to the deep digital flexor (DDF), extensor branches and lacertus fibrosus.
• At the fastest gait, the canter, the coffins flexed more and the fetlocks hyperextended less, reducing strain on the suspensory structures during the initial contact, but increasing it in the subsequent stance phase.

Research Implications

• This research provides a greater understanding of how track surface changes can impact the musculoskeletal system of racehorses.
• Such insights could be used in the future to improve training and riding practices, prevent injuries, and inform the design of racetracks to minimize the risk to the horses.