What is Tennis Elbow? Tennis elbow, also known as lateral epicondylitis, is a common condition that causes pain on the outside of the elbow. Despite the name, you don’t have to play tennis to develop it. Tennis elbow happens when the tendons that attach your forearm muscles to the elbow become irritated or damaged. These tendons help control wrist and hand movements. When they are overused or strained, small tears can develop, leading to pain, tenderness, and weakness. Everyd