Extensor Carpi Ulnaris

Original Editor - Rania Nasr Top Contributors - Rania Nasr, Kim Jackson, Nikhil Benhur Abburi, Wanda van Niekerk, Aya Alhindi and Alicia Fernandes

Description

The extensor carpi ulnaris muscle 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.

Origin

The extensor carpi ulnaris muscle originates from the lateral epicondyle of the distal humerus and the posterior aspect of the ulna.

Insertion

It inserts onto the dorsal base of the fifth metacarpal after passing through the sixth compartment of the extensor retinaculum.

Nerve

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 the brachial plexus by way of the posterior cord which has contributions from the spinal nerve roots of C5 to T1.

Artery

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.

Function

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.

Clinical Relevance

The extensor carpi ulnaris is an important muscle in the activity of the wrist and forearm that contributes not only to the extension and adduction of the wrist but also to its medial stability. It is most commonly injured in athletes subject to forceful wrist movements. Repetitive flexion and extension of the wrist can lead to tenosynovitis due to the irritation of the tendon and the sheath that holds it in place. Overuse can also lead to tendinopathy of the muscle tendon in which there can be thickening and painful stiffness of the tendon with minimal structural damage. Continued excessive stress on the tendon can cause structural damage which can lead to a partial tear.

Assessment

An accurate clinical history and assessment is essential for diagnosis of ECU tendon disorders. The timing of onset of symptoms discriminates between acute and chronic causes. Mechanical symptoms at the moment of onset are also common descriptors in this condition. Patients will use words such as ‘snap’, ‘pop’ or ‘tear’ in an acute sheath disruption. In some cases, episodes of tendon subluxation are excruciatingly painful. In others the subluxation may be entirely asymptomatic and may be easily reproduced by the patient. Palpation along the length of the ECU tendon (starting distally at its insertion into the base of the fifth metacarpal to ensure palpation of the correct structure) will reveal tenderness accurately localised to that structure. Pain on resisted active extension with ulnar deviation is pathognomic of an ECU condition. Weakness is frequently associated with pain. Painless weakness is likely to represent a complete rupture of the ECU tendon.

In equivocal or difficult cases, ultrasound (US) or MRI are the imaging modalities of choice to supplement the clinical diagnosis of ECU tendinopathy and instability. Conventional X-rays are not routinely required.

Treatment

Acute tendinosis of the ECU usually responds to non-operative measures of rest, activity modification, splintage (in a position of 30° wrist extension and ulnar deviation) or, occasionally, immobilisation in a short-arm plaster cast in the same position for a 3-week period.

Rehabilitation strategies are based on the severity of tendinopathy.5 Treatment of the early reactive phase consists of load management and isometric exercises until the pain settles (typically over 5–10 days). Load can then be increased in stages. Ibuprofen is thought to be a helpful adjunct during this phase.

In chronic tendinopathy, without a sudden increase in pain, a combination of load management, eccentric work, isometrics and strength exercises are likely to help.

If symptoms are not relieved by non-operative measures an injection of steroid into the fibro-osseous sheath should be considered.