Tendonitis is a medical condition that is characterized by inflammation or irritation of a tendon. Tendons are dense cords of tissue that connect the muscles to the bones and causes the force generated by the muscle to the bone. Tendonitis can happen due to many reasons, including overuse, repetitive motions, and sudden injuries. It mostly affects the tendons in the shoulders, elbows, wrists, knees, and ankles.   The treatment of tendonitis usually involves a combination of lots of rest, ice, compression, and elevating the affected area. Over-the-counter pain relievers may be used to lessen pain and reduce inflammation. It is important to see a doctor if you suspect that you have tendonitis.