Extensor carpi radialis brevis muscle

Origin and insertion

Extensor carpi radialis brevis originates from the lateral epicondyle of humerus via the common extensor tendon. This is a common origin that it shares with the extensor digitorum, extensor digiti minimi and extensor carpi ulnaris muscles. Some fibers also originate from the lateral intermuscular septum, a thick aponeurosis that covers the muscle itself, and from the radial collateral ligament.

The muscle courses inferiorly, giving off a long tendon in the middle of the forearm which descends towards the dorsal hand. The tendon passes through a groove on the posterior surface of radius, deep to the extensor retinaculum. After traversing the extensor retinaculum space, the tendon inserts into the posterior aspect of the base of the third metacarpal bone.

Relations

Extensor carpi radialis brevis is located in the radial (lateral) part of the forearm, sitting deep to extensor carpi radialis longus.

As its name suggests, extensor carpi radialis brevis is the shortest of these two muscles.

Its tendon courses deep to abductor pollicis and extensor pollicis brevis before passing under the extensor retinaculum on the dorsal aspect of the hand.

At the retinaculum level, the tendon is medial to that of extensor carpi radialis longus muscle.

Innervation

Extensor carpi radialis brevis is innervated directly by the radial nerve (C5- C8), or sometimes from its deep branch/posterior interosseous nerve. The radial nerve stems from the posterior cord of the brachial plexus.

Blood supply

The muscle is vascularized by the radial recurrent artery, radial artery and deep brachial artery (via its radial collateral branch).

Function

Extensor carpi radialis brevis works together with extensor carpi ulnaris and extensor carpi radialis longus to extend the hand at the wrist joint. This action is vital in a sequence of muscle contractions needed for clenching a fist or making a grip. When performing these functions, wrist extension blocks the flexor muscles from on acting upon the hand. Instead, flexors act only on the digits, thereby flexing them and producing an effective hand grip, such as that seen in a tennis backhand.

When the extensor carpi radialis brevis muscle contracts together with extensor carpi radialis longus and flexor carpi radialis, it contributes to producing hand abduction (radial deviation).