The epitrochleoanconeus muscle (anconeous epitrochlearis muscle, anconeus-epitrochlearis or anconeus sextus) is a small

accessory muscle An accessory muscle is a relatively rare anatomical variation where duplication of a muscle may appear anywhere in the muscular system. Treatment is not indicated unless the accessory muscle interferes with normal function. Examples are the sterna ...

of the

arm In human anatomy, the arm refers to the upper limb in common usage, although academically the term specifically means the upper arm between the glenohumeral joint (shoulder joint) and the elbow joint. The distal part of the upper limb between th ...

which runs from the back of the inner condyle of the humerus over the ulnar nerve to the

olecranon The olecranon (, ), is a large, thick, curved bony eminence of the ulna, a long bone in the forearm that projects behind the elbow. It forms the most pointed portion of the elbow and is opposite to the cubital fossa or elbow pit. The olecranon ...

. The average prevalence of this muscle is 14.2% in healthy individuals.

Structure

The epitrochleoanconeus is a short striated muscle which originates on the posterior surface of the medial epicondyle of the humerus. The muscle runs over the ulnar nerve, forms an arch over the

cubital tunnel The cubital tunnel is a space of the dorsal medial elbow which allows passage of the ulnar nerve around the elbow. It is bordered medially by the medial epicondyle of the humerus, laterally by the olecranon process of the ulna and the tendinous arc ...

and inserts on the olecranon. It is innervated by the ulnar nerve.

Variation

There are cases where there is no structure at all bridging the space occupied by the epitrochleoanconeus. The muscle tends to be hypertrophied when associated with

cubital tunnel syndrome Ulnar nerve entrapment is a condition where the ulnar nerve becomes physically trapped or pinched, resulting in pain, numbness, or weakness, primarily affecting the little finger and ring finger of the hand. Entrapment may occur at any point from ...

Clinical significance

The presence of the epitrochleoanconeus muscle can lead to ulnar neuropathy, or cubital tunnel syndrome, due to compression of the ulnar nerve. The absence of epitrochleoanconeus muscle or Osborne's ligament can increase the chances of ulnar nerve dislocation.

History

While there were previous identifications of the epitrochleoanconeus in animal studies, under a variety of names, Gruber (1866) seems to offer the first extensive comparative study involving the epitrochleoanconeus in man. This was shortly followed by several accounts by Wood describing his identification of the muscle during a series of dissections in humans along with comparative studies in other animals.

Other animals

In animals with a discrete developed epitrochleoanconeus the muscle acts as an adductor of the olecranon and a supinator of the forearm. A variety of names have been given to this muscle in different species including flexor antebrachii ulnaris, epitrochleo-cubitalis and entepicondylo-ulnaris. The epitrochleoanconius is common amongst

tetrapods Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids (reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct therapsi ...

being found in reptiles, amphibians,

mammals Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur o ...

and birds. The epitrochleoanconeus is found widely amongst mammals having been characterised in the mid 19th century in a variety of species including

two-toed sloth ''Choloepus'' is a genus of xenarthran mammals of Central and South America within the monotypic family Choloepodidae, consisting of two-toed sloths, sometimes also called two-fingered sloths. The two species of ''Choloepus'' (which means "la ...

, duck billed platypus and

echidna Echidnas (), sometimes known as spiny anteaters, are quill-covered monotremes (egg-laying mammals) belonging to the family Tachyglossidae . The four extant species of echidnas and the platypus are the only living mammals that lay eggs and the ...

. Galton (1874) gave an overview of the several species characterised at that point and noted that at least 15 species had been figured with the muscle in Cuvier's "Anatomie comparée" of 1855 but that the muscle was given a wide variety of aliases and was not shown in many species where it should have been seen. The muscle is common in lower primates but has been lost as a discrete muscle in apes, although it has reoccurred in chimpanzees.

References

External links

Epitrochleoanconeus at radiopedia

Cubital tunnel syndrome associated with epitrochleoanconeus at radiopedia
{{Portal bar, Anatomy Muscles of the upper limb Upper limb anatomy Accessory muscle Anatomical variations