Extensor Carpi Ulnaris – Anatomy, Nerve Supply, Function

The Extensor Carpi Ulnaris Muscle is located in the posterior compartment of the forearm and primarily functions to extend and adduct the wrist. Its origin lies on the lateral epicondyle of the distal humerus and the posterior aspect of the ulna. It inserts onto the dorsal base of the fifth metacarpal after passing through the sixth compartment of the extensor retinaculum. It receives its innervation from the posterior interosseous nerve and gets its blood supply from the ulnar artery.

Structure

The extensor carpi ulnaris serves to extend and adduct the hand at the wrist and also provides medial stability to the wrist. It is a thin muscle which has fibers originating from both the distal humerus, as a part of the common extensor tendon, as well as the proximal ulna.

Extensor carpi radialis brevis

• Origin: lateral epicondyle of humerus
• Insertion: base of 3rd metacarpal
• Action: extension and abduction of the wrist
• Innervation: radial nerve

Blood Supply of Extensor Carpi Ulnaris

The extensor carpi ulnaris gets its vascular supply primarily from the ulnar artery which branches off of the brachial artery near the antecubital fossa and supplies the medial aspect of the forearm. Due to the muscle’s location in the posterior compartment of the forearm, it also receives some blood supply from the posterior interosseous artery, a posterior branch of the radial artery, that runs between the superficial and deep extensor muscle groups and supplies them both.

The lymphatic drainage of the upper limb consists of both superficial and deep lymphatic vessels. The superficial lymphatic vessels of the hand and forearm ascend the arm along with the superficial veins, such as the basilic vein, and enter the cubital lymph nodes, near the medial epicondyle of the humerus. Superficial lymphatic vessels traveling more proximally to the cephalic vein primarily drain into the apical axillary lymph nodes, though the deltopectoral lymph nodes are another potential site of drainage. The deep lymphatic vessels of the arm and forearm follow the deep veins and end up in the humeral axillary lymph nodes and eventually the subclavian lymphatic trunk.[rx]

Nerves Supply of Extensor Carpi Ulnaris

The muscle receives nerve supply from the posterior interosseous nerve, which is a motor branch of the radial nerve. The radial nerve dives posteriorly through the heads of the supinator muscle in the antecubital fossa to form the posterior interosseous nerve. It innervates the extensor carpi ulnaris muscle in addition to the other muscles in the posterior compartment of the forearm. The radial nerve arises from brachial plexus by way of the posterior cord which has contributions from the spinal nerve roots of C5 to T1.[rx]

Muscles

The extensor carpi ulnaris is one of the extensor muscles of the forearm located in the superficial layer of the posterior compartment of the forearm. It shares this compartment with the brachioradialis, the extensor carpi radialis longus, the extensor carpi radialis brevis, the extensor digitorum, and the extensor digiti minimi. All of these muscles share a common origin on the lateral epicondyle via the common extensor tendon.  As all of these muscles near their distal insertion sites, they are secured by the extensor retinaculum.

Function

The oblique course of extensor carpi ulnaris orientates its direction of pull posterolaterally, meaning that its contraction results with a combined extension and adduction (ulnar deviation) of the hand.

Working together with extensor carpi radialis brevis and extensor carpi radialis longus, the extensor carpi ulnaris muscle contributes to a balanced extension of wrist without deviating the hand in the transverse plane. This action is important for activities of the hand, such as strongly clenching a fist or making a power grip. In this process, extension of the wrist blocks the forearm flexors from on acting upon it. Instead, these flexors remain able to act solely on the digits, flexing them to produce an effective grip such as that seen in a tennis backhand.

Similarly, synergistic action of flexor carpi ulnaris and extensor carpi ulnaris results in balanced adduction (ulnar deviation) of the hand at the wrist. That is, adduction without added flexion or extension. This action is necessary for processes like hammering, throwing, golfing and swinging a baseball bat. Extensor carpi ulnaris also contributes to the stability of the distal radioulnar joint.

References