What is Tendinitis? Tendinitis is inflammation of a tendon. Tendons are the tissues that connect your muscles to your bones. Tendinitis causes pain near the affected joint. Ankle tendinitis is when this occurs in one of the tendons around your ankle. What Causes Ankle Tendinitis? Tendon inflammation (tendinitis) can occur due to overuse, repetitious activity, trauma, bio-mechanical asymmetries, strength deficits/imbalances, …