
The main muscle that becomes injured in lateral epicondylitis is the extensor carpi radials brevis. The injury can consist of inflammation, partial tearing or sometimes even a complete tear.

Lateral epicondylitis or "tennis elbow" involves the muscles that extend or bring back the wrist. These muscles and where they originate from become inflammed or injured when this injury occurs. The pain in typically over the lateral or outer part of the elbow and can sometimes radiate down the outer forearm.