The elbow is a hinge type joint consisting of three bones - the humerus, the ulna, and the radius. The humerus (arm bone) forms the hinge along with the ulna of the forearm. This joint allows for the flexion and extension of the elbow joint. This joint is very stable and a large amount of force is required to dislocate it. The radius also articulates with the humerus - this joint allows for the rotation of your hand - supination (palm up), pronation (palm down). Many muscle groups attach about the elbow. Injuries to these muscle groups can lead to lateral epicondylitis (tennis elbow) and medial epicondylitis (golfer's elbow)