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Anconeus Muscle Anatomy

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Origin
  • Posterior surface of the lateral epicondyle of the humerus
Insertion
  • Lateral aspect of the olecranon
  • Proximal posterior surface of the ulna
Action
  • Assists with elbow extension
Innervation
  • Radial nerve
Blood Supply
  • Branches of the posterior interosseous recurrent artery
Last updated: Estimated Reading Time: 7 min

Location & Overview

The anconeus is a small, triangular muscle located at the posterolateral aspect of the elbow.[1,2] It sits at the junction between the distal arm and the proximal forearm, so it does not fit neatly into a single regional classification.[1,2,3] It is commonly grouped with the superficial posterior (extensor) muscles of the forearm,[1] but it is also described as a distally placed assistant to the triceps brachii in the posterior compartment of the arm.[2]

The muscle may be partially and variably blended with the triceps brachii or with extensor carpi ulnaris.[1] Its tendon of origin lies beneath extensor carpi radialis longus, and its fibers pass across and cover the posterior aspect of the anular ligament (the ring-shaped ligament that holds the radial head in place).[1] The deep surface of the anconeus is closely related to the lateral elbow joint capsule.[2,3] Its primary role is to assist with extension of the elbow.[1,2]

The anconeus should not be confused with a separate accessory muscle called the anconeus epitrochlearis, which is a distinct variant muscle found at the medial side of the elbow in association with the cubital tunnel.[1,4] A meta-analysis by Suwannakhan et al. (2021) reported a pooled prevalence of approximately 14.2% in healthy subjects and 4.5% in cubital tunnel syndrome subjects for this variant muscle.[4]

Anconeus muscle, posterior and lateral views
Pictured here, we can see the anconeus muscle from posterior and lateral views.
posterior muscles of the forearm with labels
Pictured here, we can see the labeled posterior muscles of the forearm.

Origin & Insertion

The anconeus originates from the posterior surface of the lateral epicondyle of the humerus.[1,2] This origin is formed by a separate tendon that sits proximal to the common extensor tendon (the shared tendon from which several forearm extensor muscles arise).[1]

The muscle inserts onto the lateral aspect of the olecranon (the bony prominence at the back of the elbow) and the proximal posterior surface of the ulna.[1,2] The ulnar attachment extends along approximately the proximal quarter of the posterior shaft of the ulna.[1]

Anconeus origin marked in red on the lateral epicondyle of the humerus and the insertion marked in blue on the olecranon and proximal ulna
Here, we can see the anconeus origin marked in red on the posterior surface of the lateral epicondyle of the humerus. The insertion is marked in blue on the lateral aspect of the olecranon and the proximal posterior surface of the ulna.

Action & Function

Elbow extension: The primary action of the anconeus is to assist the triceps brachii in extending the forearm at the elbow joint.[1,2] Although it is a relatively small muscle, its position at the posterolateral elbow allows it to contribute to this movement alongside the much larger triceps.

Elbow extension, the primary action of the anconeus muscle
This image shows an example of elbow extension, which involves straightening the arm at the elbow joint. The opposite of elbow extension is elbow flexion. This is the primary action of the anconeus muscle.

Stabilization of the elbow joint capsule: The anconeus is also thought to help tense the elbow joint capsule during extension, which may prevent the capsule from being pinched between the bones as the elbow straightens.[2] Cadaveric research supports a broader stabilizing role for the muscle at the lateral side of the elbow.[3] However, this function is best considered secondary rather than a firmly established primary action, as the full extent of the muscle’s functional role is not yet completely understood.[1]

Ulnar abduction during pronation: The anconeus may also contribute to abduction of the ulna (a slight lateral movement of the ulna away from the body’s midline) during forearm pronation.[1,2] Electromyographic research supports the idea that different regions of the anconeus may contribute to different functions depending on the task being performed.[5] This action remains context-dependent and should not be treated as a straightforward primary function of the muscle.

Innervation

The anconeus is innervated by the radial nerve.[1,2] The branch to the anconeus is long and descends through the medial head of triceps brachii, partly supplying it along the way, before passing behind the elbow to reach the anconeus.[1] This course has been confirmed by cadaveric dissection studies.[6]

The exact spinal nerve root values for the anconeus are not fully agreed upon between major anatomical references. Some references list C6, C7, and C8,[1] while others list C7, C8, and T1.[2] There is overlap at C7 and C8, but the lower and upper boundaries differ. Jiménez-Díaz et al. (2021) also reported that a secondary branch from the posterior interosseous nerve may enter the anconeus in some individuals, having observed this in 38 of 54 elbows studied.[7] This possible double innervation pattern does not replace the standard radial nerve supply, which was present in all specimens examined in that study.

Radial nerve
Here, we can see the radial nerve highlighted in red, which innervates the anconeus muscle.

Blood Supply

The principal blood supply to the anconeus comes from branches of the posterior interosseous recurrent artery.[1] This artery is a branch of the posterior interosseous artery and courses proximally in the region of the posterolateral elbow.

Schmidt et al. (1999) described additional arterial pedicles reaching the anconeus in a cadaveric study examining the muscle’s potential use as a local flap. These included contributions from the medial collateral artery and the posterior branch of the radial collateral artery, which were found to anastomose (connect) with the posterior interosseous recurrent artery beneath the muscle.[8] These supplementary pedicles are most relevant in surgical contexts such as flap planning, while the posterior interosseous recurrent artery remains the primary named supply for general anatomical purposes.

References

  1. [1] Standring S, editor. Gray’s anatomy: the anatomical basis of clinical practice. 42nd ed. Amsterdam: Elsevier; 2021.
  2. [2] Dalley AF 2nd, Agur AMR. Moore’s clinically oriented anatomy. 9th ed. Philadelphia: Wolters Kluwer; 2023.
  3. [3] Molinier F, Laffosse J-M, Bouali O, Tricoire J-L, Moscovici J. The anconeus, an active lateral ligament of the elbow: new anatomical arguments. Surg Radiol Anat. 2011;33(7):617-621.
  4. [4] Suwannakhan A, Chaiyamoon A, Yammine K, Yurasakpong L, Janta S, Limpanuparb T, et al. The prevalence of anconeus epitrochlearis muscle and Osborne’s ligament in cubital tunnel syndrome patients and healthy individuals: an anatomical study with meta-analysis. Surgeon. 2021;19(6):e402-e411.
  5. [5] Bergin MJG, Vicenzino B, Hodges PW. Functional differences between anatomical regions of the anconeus muscle in humans. J Electromyogr Kinesiol. 2013;23(6):1391-1397.
  6. [6] Maniglio M, Zaidenberg EE, Martinez EF, Zaidenberg CR. The anatomy of the anconeus nerve redefined. J Hand Surg Eur Vol. 2022;47(4):410-414.
  7. [7] Jiménez-Díaz V, Aragonés P, García-Lamas L, Barco-Laakso R, Quinones S, Konschake M, et al. The anconeus muscle revisited: double innervation pattern and its clinical implications. Surg Radiol Anat. 2021;43(10):1595-1601.
  8. [8] Schmidt CC, Kohut GN, Greenberg JA, Kann SE, Idler RS, Kiefhaber TR. The anconeus muscle flap: its anatomy and clinical application. J Hand Surg Am. 1999;24(2):359-369.

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