Extensor carpi radialis longus muscle

Structure

It originates from the lateral supracondylar ridge of the humerus, from the lateral intermuscular septum, and by a few fibers from the lateral epicondyle of the humerus.

The fibers end at the upper third of the forearm in a flat tendon, which runs along the lateral border of the radius, beneath the abductor pollicis longus and extensor pollicis brevis; it then passes beneath the dorsal carpal ligament, where it lies in a groove on the back of the radius common to it and the extensor carpi radialis brevis, immediately behind the styloid process.

One of the three muscles of the radial forearm group, it initially lies beside the brachioradialis, but becomes mostly tendon early on. Passing between the brachioradialis and the extensor carpi radialis brevis, this tendon continues into the second tendon compartment together with the latter muscle.

It is inserted into the dorsal surface of the base of the metacarpal of the index finger (second metacarpal).

Innervation

The extensor carpi radialis longus is a wrist extensor that is innervated by the radial nerve, from spinal roots C6 and C7. All other major extensor muscles in the superficial layer of the posterior compartment (the extensor digitorum, extensor carpi radialis brevis, extensor carpi ulnaris, and extensor digiti minimi) are innervated by the posterior interosseous branch of the radial nerve.