The anconeus muscle belongs to the superficial extensor compartment, along with the brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi and extensor carpi ulnaris muscles.
In this article, we will discuss the anatomy and function of the anconeus muscle.
Lateral epicondyle of humerus
|Insertion||Lateral surface of olecranon|
|Action||Assists in forearm extension at the elbow joint;
Stabilization of elbow joint
|Innervation||Radial nerve (C7-C8)|
|Blood supply||Posterior interosseous recurrent artery|
Origin and insertion
The anconeus muscle originates by a tendon on the dorsal aspect of the lateral epicondyle of the humerus, just proximal to the common extensor tendon. Its tendon lies deep to the muscle belly of extensor carpi radialis longus and is partially attached to the dorsal capsule of the humeroulnar joint.
The anconeus tendon spreads out obliquely and medially into a wide muscle belly, and inserts at the lateral surface of the olecranon of the ulna and the adjoining posterior surface of the ulnar shaft. Some authors consider the anconeus as a continuation of the triceps brachii muscle, due to their fibers often being partially or completely blended together.
Due to its superficial location, the anconeus can be easily palpated at the lateral side of the forearm near the elbow, especially during pronation and supination movements.
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The anconeus muscle is supplied by the recurrent interosseous branch of the posterior interosseous artery, along with contributions from the small number of musculocutaneous perforators.
Functionally, the anconeus is a continuation of the triceps brachii muscle, exhibiting the same action at the elbow. Thereby, its contraction leads to the extension of the forearm.
Due to its long attachment on the ulna, it is believed that the anconeus has the additional function of abducting the ulna, especially during pronation movements of the forearm. This action is essential for stabilizing the ulna and allowing the rotatory movement of the forearm in activities such as using a screwdriver.
Furthermore, the anconeus tenses the dorsal joint capsule of the humeroulnar joint, thus preventing damage during hyperextension of the forearm.
An anatomical variation of the anconeus is found in up to one third of all humans. Even though most are harmless, there is one variation which can be considered clinically relevant, namely the anconeus epitrochlearis muscle.
This variant of the anconeus muscle originates at the medial epicondyle of the humerus, thus crossing the ulnar groove of the bone. Since the ulnar nerve courses in this groove, in cases of hypertrophy (e.g. in weightlifters), the anconeus epitrochlearis can cause a compression of the ulnar nerve. This results in numbness of the ulnar side of the hand, the little and ring fingers, as well as pain in the elbow (cubital tunnel syndrome).