Little Leaguer's elbow occurs in young baseball players who throw the ball too hard or too often (for example, more than 80 times twice a week). The growing part of the elbow, called the growth center (physis), widens and enlarges a part of the elbow bone called the medial epicondyle of the humerus. Muscles of the forearm that are used to throw the ball constantly pull on the medial epicondyle during throwing and pull the soft growth center apart. In severe cases, a young player may tear through the soft growth center and detach the medial epicondyle from the upper arm bone.

Symptoms include swelling and pain on the inside (medial) part of the elbow. Arm motion may be decreased because of pain.

Treatment for mild to moderate cases of Little Leaguer's elbow includes rest, coaching on the proper way to throw the ball, and physical therapy. Severe cases require surgical repair. Recovery may take 6 weeks to 6 months, depending on the severity of the injury.