Ulnar head of extensor carpi ulnaris

At a glance

English

Ulnar head of extensor carpi ulnaris

Latin (TA2)

Caput ulnare extensoris ulnaris carpi

System

Muscle

Region

Upper limb

Side

Paired, left and right

About the ulnar head of extensor carpi ulnaris

Extensor carpi ulnaris is the most medial muscle of the superficial layer on the back of the forearm. It has two heads. The humeral head comes from the lateral epicondyle of the humerus through the common extensor tendon; the ulnar head is the second, lower origin, taken from the back of the ulna. The two heads unite into a single belly that runs down the ulnar side of the forearm.

The ulnar head arises through a shared aponeurosis from the posterior border of the ulna, the ridge felt under the skin from the olecranon down the forearm. Flexor carpi ulnaris and flexor digitorum profundus attach to the same aponeurosis, so the three muscles share an anchoring sheet. Below, the joined muscle gives way to a tendon that passes in a groove beside the ulnar styloid process, inside its own compartment under the extensor retinaculum, and ends on the tubercle at the base of the fifth metacarpal.

Because the ulnar head is fixed to the forearm rather than the elbow, it lets the muscle pull on the wrist with less influence from the elbow position. With flexor carpi ulnaris, extensor carpi ulnaris bends the hand towards the little-finger side; with the radial wrist extensors, it straightens the wrist. It also steadies the wrist during a firm grip, holding it in slight extension so the finger flexors work at good length.

Its tendon lies in a fibro-osseous groove beside the small head at the lower end of the ulna and forms part of the support of the distal radio-ulnar joint and the triangular fibrocartilage complex. In sports with forceful wrist rotation, such as tennis or golf, the sheath can tear and the tendon may snap out of its groove, giving painful clicking on the outer side of the wrist.

Attachments, action and supply

Origin

Posterior border of the ulna, through an aponeurosis shared with flexor carpi ulnaris and flexor digitorum profundus.

Insertion

With the humeral head, by one tendon on the tubercle at the base of the fifth metacarpal.

Action

Extends the wrist and moves the hand towards the ulnar side; steadies the wrist during grip.

Nerve supply

Posterior interosseous nerve, from the deep branch of the radial nerve (C7, C8).

Blood supply

Posterior interosseous artery and branches of the ulnar artery.