Extensor carpi radialis brevis muscle
Extensor carpi radialis brevis is a fusiform muscle found in the lateral part of the posterior forearm. Together with anconeus, brachioradialis, extensor carpi radialis longus, extensor digitorum, extensor digiti minimi and extensor carpi ulnaris, it belongs to the superficial forearm extensor group.
Crossing the elbow and wrist joints from their posterior aspects, these muscles produce extension at one or both of these joints. The specific action of extensor carpi radialis brevis is to extend and abduct the hand at the wrist joint.
||Lateral epicondyle of humerus (common extensor tendon)|
|Insertion||Posterior aspect of base of metacarpal bone 3|
|Action||Wrist joints: Hand extension, hand abduction (radial deviation)|
|Innervation||Radial nerve (C5- C6)|
|Blood supply||Radial recurrent artery, radial artery, deep brachial artery|
This article will discuss the anatomy and function of extensor carpi radialis brevis.
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.
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.
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.
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).