Tennis elbow, or lateral epicondylitis, is a painful inflammation of the elbow joint caused by repetitive stress (overuse). The pain is located on the outside (lateral side) of the elbow, but may radiate down the back of your forearm. You’ll likely feel the pain when you straighten or fully extend your arm.
The tendon is the part of a muscle that attaches to the bone. Forearm tendons attach the forearm muscles to the outer bone of the elbow. Tennis elbow often occurs when a specific muscle in the forearm — the extensor carpi radialis brevis (ECRB) muscle — is damaged. The ECRB helps raise (extend) the wrist.
Repetitive stress weakens the ECRB muscle, causing extremely tiny tears in the muscle’s tendon at the point where it attaches to the outside of the elbow. These tears lead to inflammation and pain.
These activities may include:
Tennis and other racquet sports
Turning a key
Frequently using a screwdriver, hammer, or a computer
Elbow pain that is mild at first but gradually gets worse
Pain extending from the outside of the elbow down to the forearm and wrist
A weak grip
Increased pain when shaking hands or squeezing an object
Pain when lifting something, using tools, or opening jars