Extensor carpi radialis brevis

The extensor carpi radialis brevis is a forearm extensor muscle that helps control wrist movement. It's shorter and thicker than its neighbor, the extensor carpi radialis longus, and lies slightly deeper and more medial to it.

Origin

The extensor carpi radialis brevis muscle has several points of origin:

• Primarily from the lateral epicondyle of the humerus via the common extensor tendon (shared with other forearm extensors).

• Additional fibers arise from the radial collateral ligament of the elbow joint.

• It also originates from a strong aponeurosis covering its surface and from the intermuscular septa that separate it from nearby muscles.

Course

The muscle belly extends distally down the forearm, remaining deep to the extensor carpi radialis longus and superficial to the supinator muscle. Its fibers transition into a flat tendon around the middle of the forearm. This tendon runs closely alongside the longus tendon. Together, they pass beneath the tendons of three deeper extensor muscles near the wrist: first, the abductor pollicis longus and extensor pollicis brevis, followed by the extensor pollicis longus. Finally, both tendons then pass under the extensor retinaculum before reaching their insertions on the metacarpal bones.

Insertion

The tendon of the extensor carpi radialis brevis primarily inserts onto the dorsal (back) aspect of the base of the third metacarpal bone, though it can sometimes send slips to the second metacarpal as well.

Innervation

The muscle is most commonly innervated by the deep branch of the radial nerve, also known as the posterior interosseous nerve.

Actions

The actions of the extensor carpi radialis brevis are extension and abduction (radial deviation) of the wrist. It plays an important role in providing dynamic stabilization to the wrist during gripping actions and repetitive wrist movements.