Extensor carpi radialis longus muscle

Origin and insertion

The majority of extensor carpi radialis longus originates from the lateral supracondylar ridge of humerus (distal third) and anterior aspect of the lateral intermuscular septum of the arm. A small portion of its fibers originate from the common extensor tendon attached to the lateral epicondyle of humerus.

The fibers unite into a muscle belly which extends approximately to the middle of the forearm. The muscle belly is then replaced by a flat tendon that travels distally along the lateral surface of the radius, together with the tendon of extensor carpi radialis brevis. Both tendons course towards the radial styloid process, deep to the tendons of abductor pollicis longus and extensor pollicis brevis muscles. Proximal to the wrist, the tendons of extensor carpi radialis longus and brevis pass behind the radial styloid process within a common synovial sheath and continue along the radial groove deep to the extensor retinaculum of the wrist. At this level, the tendon of extensor carpi radialis longus is crossed by the tendon of extensor pollicis longus, after which it inserts on the posterior aspect of the base of the second metacarpal bone. Some tendon slips can insert into the first and third metacarpal bones.

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Relations

Extensor carpi radialis longus is superficial to the deep group of forearm extensors and the belly of the anconeus. The muscle is also lateral to brachialis and is partially overlapped by the brachioradialis.

The radial nerve courses within a deep groove in the elbow, medially to both extensor carpi radialis longus and brachioradialis muscles and laterally to the brachialis. The course of the radial nerve becomes more superficial approximately 10 cm proximal to the radial styloid process, which at this point is travelling between brachioradialis and extensor carpi radialis longus.

Innervation

Extensor carpi radialis longus receives innervation from the radial nerve, with contributions mainly from spinal nerves C5-C8. The radial nerve is a branch of the brachial plexus. 

Blood supply

Extensor carpi radialis longus receives blood supply mainly from the radial artery. It directly supplies the distal part of the muscle, while the rest of the muscle receives blood from one of its radial recurrent branches. The brachial artery also supplies a small portion of the muscle via the radial collateral artery.

Function

Extensor carpi radialis longus primarily acts on the wrist joint to produce two major actions:

• Wrist extension by working synergistically with extensor carpi radialis brevis and extensor carpi ulnaris.
• Hand abduction (radial deviation), with the help of flexor carpi radialis.

Since extensor carpi radialis longus also spans the elbow, the muscle has a minimal contribution to elbow flexion. Together with other forearm extensors, extensor carpi radialis longus plays an important role in hand gripping. In order to achieve an effective grip, the wrist must be maintained in an extended position by the forearm extensors, including the extensor carpi radialis longus. Thereby, wrist flexion is prevented and the contraction force produced by the forearm flexors is transferred to the fingers. If the wrist would not be extended, the forearm flexor tendons would be incapable to shorten sufficiently to produce a functional hand grip.

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For more details about extensor carpi radialis longus and other forearm extensors, including labelling diagrams, take a look below: