External epicondylitis of the humerus, commonly known as tennis elbow. The main clinical manifestation is pain on the lateral side of the elbow joint, which can be aggravated by forceful fist clenching and forearm rotation and elbow extension (e.g. towel twisting, floor sweeping, etc.), and multiple local pressure pains without abnormal appearance. External humeral epicondylitis, commonly known as tennis elbow, is a painful inflammation of the tendons on the outside of the elbow. The pain is caused by repetitive force on the muscles responsible for the dorsal extension of the wrist and fingers. The patient may experience pain on the outside of the elbow when gripping or lifting objects with force.