Tennis elbow (lateral epicondylitis) is inflammation of the tendons of the muscle attachment at the outer side of the elbow. This condition most commonly occurs between 40 and 50 years of age but can occur at other ages.
Repeated overloading causes small tears to the tendon attachments to the bone. The body’s attempt to heal this creates an inflammatory response which results in thickened scar tissue.
Pain on the outer side of the elbow characterizes tennis elbow, whereas pain on the inside of the elbow is known as golfer's elbow (medial epicondylitis).
Epicondylitis pain may sometimes spread to the forearm and wrist. Lateral epicondylitis symptoms occur when tightening the wrist and hand extensor muscles, for example when picking up an object with the palm facing downwards; medial epicondylitis symptoms occur when flexing the wrist and hand, for example when swinging a golf club.
Image 1: Tennis elbow (Lateral epicondylitis)