Introduction to Equine Tendon Injury

Equine tendon injuries have been recognized and treated for centuries. In early American texts, poor conformation was considered a primary risk factor. “Tied-in” at the knees and long, weak, and slender pasterns were thought to predispose the horse to injury because of mechanical disadvantage. Any trait that favored fetlock extension such as low heels and long toes was thought to increase a horse’s risk of injury, particularly injury to the superficial digital flexor tendon (SDFT). “Race horses and hunters and horses required to trot at sharp pace for long periods are the most general sufferers.” Injury of the deep digital flexor tendon (DDFT) was recognized less commonly, and causes and risks of injury to the check (accessory) and suspensory ligaments were similar to those currently recognized. Injuries were reported as a strain caused by either tension and repetitive strain or bruising from external trauma. Until use of ultrasonography, diagnosis and localization of tendon injuries relied solely on recognition of lameness and external palpation. The term “bowed tendon” was derived from the shape exhibited by the SDFT or DDFT that is caused by inflammation. Swelling is the hallmark of tendon or ligament injury, but ultrasonography can reveal injuries before pain or swelling are observed or palpated as well as abnormalities of a chronic nature. Differentiating the pain and inflammation from individual tendons and ligaments is possible in the metacarpus and metatarsus unless marked swelling and multiple injuries make separation impossible.