Muscles extending the elbow joint

Triceps brachii

Anconeus

Anconeus

Anconeus is a small triangular muscle situated immediately behind the elbow joint, appearing almost to be part of triceps brachii. It arises from the posterior surface of the lateral epicondyle of the humerus and the adjacent part of the elbow joint capsule. The fibres pass medially and distally to attach to the lateral surface of the olecranon and upper quarter of the posterior surface of the ulna and to the fascia which covers it. 

Nerve supply

Anconeus is supplied by a branch of the radial nerve to the medial head of triceps, root value C7 and 8. The skin over anconeus is supplied by root T1.

Action

Anconeus assists in extension of the elbow joint.

Functional activity

By virtue of its long attachment on the ulna, it is thought that anconeus produces lateral movement(abduction of the ulna) and extension of the bone at its distal end. These movements occur during pronation and are essential if a tool, such as a screwdriver, is being used. Movement of the ulna with respect to the radius allows the axis of pronation and supination to be altered so that the forearm rotates about a single axis and so does not describe an arc. This can be seen on an articulated skeleton. This action allows the rotatory movement of the forearm to be transmitted along the screwdriver into the head of the screw.

Palpation

Anconeus can be palpated between the lateral epicondyle of the humerus and the upper part of the ulna during pronation and supination, particularly if the axis of rotation is maintained through the extended index finger. As a practical exercise, it can be demonstrated that anconeus alters the axis of pronation and supination by making each of the fingers, in turn, the axis of rotation.