Tendonitis is an inflammatory (swelling) disease of the tendons. Tendons are tough but flexible bands of fibrous tissue that connect the muscles to the bones. If the tendon becomes swollen, it will become irritated by the action of the muscles and movement will be painful.
Tendonitis can occur in any tendon in the body, especially in the ankle (Achilles or posterior tibia tendon), wrist, kneecap, elbow or shoulder.