Extensor Carpi Ulnaris Muscle Anatomy

Location & Overview

The extensor carpi ulnaris is located in the posterior compartment of the forearm and plays an important role in movements of the wrist. This muscle extends from the elbow to the base of the little finger. It is situated in the most medial part of the extensor compartment of the forearm. At the wrist, the extensor carpi ulnaris runs within its tendinous sheath, passing underneath the extensor retinaculum. The extensor retinaculum is a fibrous band on the back of the wrist.^[1,2]

The extensor carpi ulnaris forms part of a group of extensor muscles located in the superficial layer of the posterior compartment of the forearm. This group includes the brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, and extensor digiti minimi. Several of these muscles share an attachment at or near the lateral epicondyle via the common extensor tendon, although brachioradialis and extensor carpi radialis longus have more proximal attachments on the lateral supracondylar ridge. As these muscles approach their distal insertion sites, they are firmly bound by the extensor retinaculum.^[1,2,3]

In relation to other muscles, the extensor carpi ulnaris’ superior fibers are located medial to the anconeus muscle, a small triangular-shaped muscle at the back of the lower elbow. The flexor carpi ulnaris is also medial to the extensor carpi ulnaris. Located lateral to the extensor carpi ulnaris are the extensor digiti minimi and extensor digitorum muscles.^[1,2]

Origin & Insertion

The extensor carpi ulnaris has two heads at its proximal end: the humeral head and the ulnar head. The humeral head is attached to the lateral epicondyle of the humerus via the common extensor tendon, while the ulnar head originates from a common aponeurosis linked to the posterior border of the ulna. This shared common extensor tendon provides an anchor for the deep fascia of the forearm and also serves as a base for other muscles, including the extensor carpi radialis brevis, extensor digitorum, and extensor digiti minimi.^[2,1,4]

From its origin points, the extensor carpi ulnaris travels down the forearm toward the wrist. It passes under the extensor retinaculum, extending to its insertion point on the base of the fifth metacarpal (little finger).^[2,1,4]

Action & Function

When the extensor carpi ulnaris muscle contracts, it helps extend the wrist joint. This movement elevates the hand, allowing it to move away from the palm side of the forearm. The extensor carpi ulnaris muscle works in coordination with other extensor muscles of the wrist during this movement, such as the extensor carpi radialis longus and extensor carpi radialis brevis.^[1,5,4]

In addition to extension, the extensor carpi ulnaris contributes to adduction of the wrist, a movement that draws the hand toward the midline of the body. In simple terms, this means that the wrist bends toward the little-finger side. In this action, it works with the flexor carpi ulnaris muscle, which is a key flexor and adductor muscle of the wrist located in the anterior compartment of the forearm.^[1,5,4]

Furthermore, when the extensor carpi ulnaris contracts simultaneously with the extensor carpi radialis longus and extensor carpi radialis brevis, it assists in providing medial stability to the wrist.^[1,5,4]

Innervation

The extensor carpi ulnaris muscle primarily receives its innervation from the posterior interosseous nerve, a branch of the radial nerve. The posterior interosseous nerve carries fibers from spinal nerve roots C7 and C8.^[2,3,4]

The radial nerve, from which the posterior interosseous nerve arises, originates from the brachial plexus, specifically the posterior cord. This complex network of nerves lies in the shoulder region, and the brachial plexus receives contributions from spinal nerve roots C5 to T1.^[2,3,4]

Blood Supply

Blood is mainly supplied to the extensor carpi ulnaris muscle via the ulnar artery. The ulnar artery is a significant branch of the brachial artery, which deviates near the antecubital fossa, the region in front of the elbow, and proceeds to supply the medial aspect of the extensor carpi ulnaris muscle. The ulnar artery and the ulnar nerve often follow a similar path.^[2,3,4]

In addition to the ulnar artery, the extensor carpi ulnaris muscle receives an additional blood supply from the posterior interosseous artery. The posterior interosseous artery usually arises from the common interosseous artery, a branch of the ulnar artery, and supplies muscles in the posterior compartment of the forearm, including the extensor carpi ulnaris.^[2,3,4]