Extensor carpi ulnaris

In human anatomy, the extensor carpi ulnaris is a skeletal muscle located on the ulnar side of the forearm. The extensor carpi ulnaris acts to extend and adduct at the carpus/wrist from anatomical position.

Being an extensor muscle, extensor carpi ulnaris is located on the posterior side of the forearm.

Origin and insertion

It originates from the lateral epicondyle of the humerus and the posterior border of the ulna, and crosses the forearm to the ulnar (medial) side to insert at the base of the 5th metacarpal.

Action

The extensor carpi ulnaris extends the wrist, but when acting alone inclines the hand toward the ulnar side; by its continued action it extends the elbow-joint.

The muscle is a minor extensor of the carpus in carnivores, but has become a flexor in ungulates. In this case it would be described as ulnaris lateralis.

Innervation

Despite its name, the extensor carpi ulnaris is innervated by the posterior interosseous nerve (C7 and C8), the continuation of the deep branch of the radial nerve. It would therefore be paralyzed in an injury to the posterior cord of the brachial plexus.

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