Tendinitis also called tendonitis is inflammation of a tendon. A tendon is a a strong, cord-like structure that connects muscles to bones. Tendinitis is usually a short-term, acute inflammatory condition commonly involving the tendons of the shoulder, elbow, wrist, hip, knee, or ankle. Tendinitis is often caused by repetitive overuse. Some of the most common types of tendinitis include: Tennis elbow, golfer's elbow, patellar tendinitis, and Achilles tendinitis. Pain can be quite severe, often occurring suddenly. The pain is worse when you move or stress the tendon. The pain can radiate and be far from a joint. It can develop into a chronic condition called tendinosis and/or tendon tear, but not when treated promptly.