Tendon and Ligament Injuries in the Horse

By Liz Devine, DVM, MS, DACVS-LA, Pilchuck Veterinary Hospital

Tendon and ligament injuries are relatively common in the horse. These soft tissues carry the load during exercise when the fetlock joint is hyperextended and they support the joints of the distal limb. During exercise, tendons stretch when the leg is bearing weight, and it has been shown that these structures can stretch as much as 10% to 12% of their length before rupture. Horses at maximal exercise will stretch their tendons to this point and beyond, which explains how tendon injuries can be so prevalent. However, plenty of horses working at less than maximal exercise still have tendon injuries. The exact mechanism of this type of tendon injury is likely due to repeated damage which causes subclinical tendonitis, or damage to the tendon that does not manifest itself with clinical signs of lameness. In these cases, one inconsistent step or hyperextension of the fetlock can lead to soft-tissue injury.

Success of therapy for tendon and ligament lesions depends greatly on having an accurate diagnosis. Lameness exams are essential for the localization of the individual’s lameness and for determining the severity of the condition. It is extremely important to have a complete lameness exam, including regional anesthesia, to make this diagnosis. Nerve blocks, or the infiltration of a numbing agent over a peripheral nerve, allow the clinician to determine precisely where the lameness is coming from. Radiographs (X-rays), ultrasound and MRI are diagnostic tools that allow the clinician to make an exact diagnosis.  

An understanding of the way that the body repairs tendon injuries is an important part of developing a treatment plan. Tendons are made of a combination of collagen, proteins and water. These are arranged in fibers that run parallel to the long axis of the leg. When injured, there is an initial inflammatory phase that lasts for about one to two weeks. During this time, there is a significant amount of swelling, hemorrhage and cellular inflammatory response. Clinically, this phase can be recognized by a rapid onset of lameness and swelling in the distal limb that is centered over the soft-tissue structures in the limb. The reparative phase begins a few days after injury and lasts for a few weeks. This phase consists of the body laying down some initial scar tissue in the lesion. The scar tissue that fills the defect is unorganized and is not as strong as the initial collagen fibers. The remodeling phase begins a few months after injury and continues for over a year after initial injury. During this time, controlled exercise can help the scar tissue to remodel to be stronger, but it is still relatively inelastic compared to the adjacent normal tendon. Re-injury after soft-tissue damage is common and often occurs near the initial lesion.

There are multiple treatment options for tendon and ligament injury. Severity and chronicity of the lesion, as well as cost, are some of the major factors that help guide the clinician toward the varying treatment choices. If your horse has a tendon or ligament injury, it is important to develop a partnership with your veterinarian to decide what therapy will be best for you and your horse.

Located in Snohomish, Pilchuck Veterinary Hospital offers comprehensive wellness and preventive equine care, including 24/7 emergency. Call 360.568.3111 for more information.

Article added 8.11.14