Anconeus – Origin, Insertion, Nerve Supply, Function

Anconeus Muscle is a triangular-shaped muscle originating posterior to the lateral epicondyle of the humerus and then fanning out broadly for an insertion base on the proximal part of the posterolateral side of the ulna. Cadaveric studies showed a mean length and width of approximately 9 to 10 cm (range, 6 to 12 cm) and 3 to 3.5 cm (range, 1.5 to 5 cm), respectively. The muscle length is approximately one-third the length of the ulna. The muscle is mainly vascularized from the medial collateral artery and the recurrent posterior interosseous artery. It is innervated through a branch derived from the radial nerve that travels beside the medial collateral artery to the muscle. The anconeus muscle functions as an accessory extensor beside the triceps brachii and possibly contributes to posterolateral elbow stability during forearm rotation.

Anatomy of Anconeus

Anconeus- The anconeus is located in the superficial region of the forearm posterior compartment and is blended with the triceps brachii.

• Function: Extension of the forearm, stabilization of elbow joint
• Origin: Lateral epicondyle of humerus
• Insertion: Olecranon process and posterior ulna
• Innervation: Radial nerve (C7, C8, T1)
• Attachments: Originates from the humerus and attaches to the ulna.
• Actions: Moves the ulna during pronation and extends the forearm at the elbow.

Origin and Insertion of Anconeus

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 is a continuation of the triceps brachii muscle, due to their fibers often being partially or completely blended together.

Nerve Supply of Anconeus

The anconeus is innervated by a branch of the radial nerve (cervical roots 7 and 8)^[rx] from the posterior cord of the brachial plexus called the nerve to the anconeus. The somatomotor portion of radial nerve innervating anconeus bifurcates from the main branch in the radial groove of the humerus. This innervation pattern follows the rules of innervation of the musculature of the posterior forearm (extensor) compartment by the radial nerve.

Blood Supply

• 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.
• The anconeus is supplied by the middle collateral artery from the profunda brachial artery.^[rx]

Functions of Anconeus

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 the 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.
• Its role in elbow extension is trivial in humans. It assists in the extension of the elbow, where the triceps brachii is the principal agonist and supports the elbow in full extension.^[rx] It also prevents the elbow joint capsule from being pinched in the olecranon fossa during the extension of the elbow. Anconeus also abducts the ulna and stabilizes the elbow joint. Anconeus serves to make minute movements with the radius on the ulna. In making slight abduction of the ulna, it allows any finger to be used as an axis of rotation of the forearm.

Furthermore, the anconeus tenses the dorsal joint capsule of the humeroulnar joint, thus preventing damage during hyperextension of the forearm.

References

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