What is Tennis Elbow? Tennis Elbow, (clinically referred to as lateral epicondylalgia), is a localised degenerative tendon condition affecting the muscles attaching to the bony prominence on the outer edge of the elbow. It is the most common injury in the adult elbow, and usually progresses very gradually over a period of time, often from history of repetitive use and overloading of the muscles around the elbow and arm. Occasionally lateral epicondylalgia pain can involve a m