Anconeus muscle

At a glance

English

Anconeus muscle

Latin (TA2)

Musculus anconeus

System

Muscle

Region

Upper limb

Side

Paired, left and right

About the anconeus muscle

Anconeus is a short, triangular muscle that lies behind the elbow on its outer side, just lateral to the point of the elbow. Its upper fibres are almost continuous with the medial head of triceps, and some anatomists treat it as part of that muscle, while others place it with the back muscles of the forearm. It can be felt as a small soft pad in the triangle between the olecranon, the lateral epicondyle and the head of the radius.

The muscle arises by a short tendon from the back of the humerus's lateral epicondyle. Its fibres spread out medially and downward to a broad attachment on the lateral side of the olecranon and the upper part of the back of the ulna. Its deep surface lies on the back of the elbow joint capsule and the annular ligament around the head of the radius, and some of its fibres attach to the capsule.

Its role in straightening the elbow is small compared with triceps, but it helps, especially at the start of the movement, and it steadies the elbow when the arm is fully straightened. By pulling on the joint capsule it keeps the capsule from getting caught in the olecranon fossa. During turning of the forearm (pronation and supination), it moves the ulna slightly outward, which keeps the axis of rotation in line with the chosen finger. It receives its nerve, the nerve to anconeus, from the radial nerve (C7, C8) high in the arm; this branch runs down within the medial head of triceps. Blood comes mainly from the middle collateral branch of the profunda brachii artery, with help from the recurrent interosseous artery.

Because the nerve to anconeus leaves the radial nerve so far up, the muscle can be weakened by fractures of the humeral shaft or injuries near the elbow that damage the radial nerve. Surgeons use the plane between anconeus and the neighbouring extensor carpi ulnaris as a route to the head of the radius, and the muscle can be moved as a small flap to fill gaps around the elbow.

Attachments, action and supply

Origin

Lateral epicondyle of the humerus, on its back surface.

Insertion

Lateral side of the olecranon and the upper posterior surface of the ulna.

Action

Assists extension of the elbow, stabilises the joint and tenses its capsule; abducts the ulna during pronation.

Nerve supply

Nerve to anconeus, from the radial nerve (C7, C8).

Blood supply

Middle collateral branch of the profunda brachii artery, and the recurrent interosseous artery.