Extensor carpi ulnaris originates from lateral epicondyle and ulna, extending and adducting wrist.
The extensor carpi ulnaris is a long, thin muscle in the posterior compartment of the forearm. It plays a key role in wrist extension and ulnar deviation (adduction). Despite its name, it is innervated by the posterior interosseous nerve (a branch of the radial nerve), not the ulnar nerve. It is essential for stabilizing the wrist during powerful hand movements such as gripping or lifting.
The extensor carpi ulnaris is located on the medial (ulnar) side of the posterior forearm. It originates from the lateral epicondyle and posterior border of the ulna and runs down the forearm to insert on the base of the fifth metacarpal.
The muscle has a fusiform belly and a long tendon that passes through a dedicated compartment beneath the extensor retinaculum.
The extensor carpi ulnaris contributes to:
Supplied by the posterior interosseous nerve (C7–C8), a continuation of the deep branch of the radial nerve after it passes through the supinator muscle.
The extensor carpi ulnaris is the most medial of the wrist extensors. It lies lateral to the flexor carpi ulnaris (on the anterior side) and medial to the extensor digiti minimi and extensor digitorum on the dorsal side. Its tendon runs in a fibrosseous tunnel on the dorsal aspect of the ulna.
The tendon of the extensor carpi ulnaris is visible and palpable on the dorsal-ulnar aspect of the wrist during wrist extension and ulnar deviation. It becomes more prominent with resisted movements.
The extensor carpi ulnaris develops from the dorsal extensor muscle mass of the forearm, originating from paraxial mesoderm. Its posterior interosseous nerve innervation aligns with its derivation from the extensor group.
In some mammals, the extensor carpi ulnaris acts primarily as a flexor rather than an extensor. In humans, it retains its name due to historical convention, although it functions in wrist extension and adduction.