The elbow joint is formed by three bones: the humerus (upper arm), the radius and the ulna.
The elbow joint permits the ulna and radius to be flexed and straightened like a pivot joint. The muscles along the outer border of the forearm are responsible for this.
The tendons transmit the power of the muscles to the bone. They consist of firm, elastic connective tissue. If we repeatedly perform the same movement with a flexed elbow, the tense tendon continually rubs over the elbow bone. This leads to very fine tears and we feel the first twinges of pain in our elbow – at the epicondyle. This is a small bony prominence on the outside of the elbow.