elbow An example of a hinge joint (uniaxial) with movement essentially limited to flexion and extension. The condyles at the lower end of the humerus in the upper arm articulate with the heads of both the radius and the ulna in the lower arm. Twisting movements of the lower arm (pronation and supination) are possible because the top end (the head) of the radius can rotate against the lower end of the humerus. Flexion of the elbow is achieved by action of the biceps muscle, which shortens and bulges, a muscle often shown to advantage in the classic pose of the body builder. Extension involves the triceps muscle, and when fully extended the arm should be in a straight line — the elbow angle at 180 degrees. This joint can also hyperextend; this is much more common in females than in males. Another difference in females is that the lower arms tend to be bent slightly more outwards when extended at the elbow (valgus carrying angle), thus clearing the hips, which are broader than in men. The most common problems associated with the elbow are colloquially described as ‘tennis elbow’ or ‘golfer's elbow’. However, these are not really a dysfunction of the elbow joint itself, but arise from over-indulgence in the named activity, or some equivalent muscular effort. Over-activity, particularly if the sport is not practised regularly, can result in small tears of the fibres in the tendons of muscles which are anchored at the lower end of the humerus (at the epicondyles), resulting in inflammation in this region (epicondylitis). Characteristically there is pain at this site which is aggravated by gripping or twisting movements. Treatment may involve a local injection of anti-inflammatory agents (steroids).

William R. Ferrell

See also joints; skeleton.