Extensor carpi radialis longus

The extensor carpi radialis longus is a key muscle in the forearm that lies partly underneath the brachioradialis muscle.

Origin

The extensor carpi radialis longus muscle arises from the lower third of the lateral supracondylar ridge of the humerus, just below where the brachioradialis starts. It also receives some fibers from the lateral intermuscular septum and the common extensor origin (which is the lateral epicondyle of the humerus).

Course

As it travels down the forearm, the extensor carpi radialis longus muscle belly is deep to the brachioradialis and superficial to the extensor carpi radialis brevis. In the distal forearm, its tendon becomes more superficial and lateral. Here, it passes underneath the brachioradialis tendon but remains on the radial side of the extensor carpi radialis brevis tendon. Further down, it ducks beneath the tendons of three deeper thumb muscles: the abductor pollicis longus, the extensor pollicis brevis, and the extensor pollicis longus. Finally, at the wrist, the extensor carpi radialis longus tendon continues its descent under the extensor retinaculum to reach its insertion point.

Insertion

The extensor carpi radialis longus tendon inserts onto the dorsal (back) surface of the base of the second metacarpal bone.

Innervation

The radial nerve innervates the extensor carpi radialis longus. The branch supplying this muscle typically comes off the radial nerve before it splits into its superficial and deep branches, which happens just below the elbow.

Actions

The extensor carpi radialis longus muscle primarily works to extend and abduct (move towards the thumb side) the wrist. It's also crucial for stabilizing the wrist when we grip something or make dynamic wrist movements,