Tendonitis is characterized by inflammation of the tendon. It is either traumatic origin or the result of a clearing of the horse. Tendon injury may be more or less important. It can range from a simple inflammation and thickening of the tendon to a change in the tendon structure with a tear of the tendon fibers. Depending on the type of tendon concerned (perforated, perforating, hanger ...) and the importance of the injury, the horse may or may not have a lamness; the diagnosis is not always easy because some times no deformation is visible. The diagnosis is a diagnostic ultrasound or magnetic resonance.