The extensor carpi radialis longus is one of the muscles of the superficial layer of the posterior compartment of the forearm.

The posterior compartment of the forearm consists of a superficial layer (7 muscles) and a deep layer (5 muscles).

The muscles in the superficial layer include:

The muscles of the superficial layer share a common origin from the lateral epicondyle and lateral supracondylar ridge of the humerus.

All the muscles of the posterior compartment are innervated by the radial nerve.

Origin
  • Distal part of the lateral supracondylar ridge, distal to the origin of the brachioradialis muscle
  • Adjacent lateral intermuscular septum
Insertion
  • Dorsal base of the second metacarpal.
Innervation
  • Radial nerve (before it divides into superficial and deep branches)

Other than the brachioradialis, the rest of the muscles of the superficial layer of the posterior compartment of the forearm are innervated by the posterior interosseus branch of the radial nerve: extensory carpi radialis brevis, extensor digitorum, extensor digiti minimi and extensor carpi ulnaris.

Blood Supply

Radial artery

Antagonist

Flexor carpi ulnaris muscle

Action
  • Extension and abduction at the wrist joint