Extensor Carpi Radialis Longus

Origin

The extensor carpi radialis longus muscle originates from the:

- inferior one third of the lateral supracondylar ridge of the humerus, which is located inferior to the origin site of the brachioradialis muscle;

- adjacent intermuscular septa.

Insertion

The fibers of the extensor carpi radialis longus muscle travel inferiorly to the hand and insert, via a flat tendon, onto the dorsal aspect of the base of second metacarpal bone.

Key Features & Anatomical Relations

The extensor carpi radialis longus muscle is one of the muscles of the superficial part of the posterior compartment of the forearm. It is a long fusiform type of skeletal muscle.

In the middle of the forearm, the muscle belly gives rise to a flat tendon, which travels inferiorly along the lateral aspect of the forearm towards the lateral aspect of the dorsal radial tubercle. At the wrist, its tendon travels deep to the extensor retinaculum of hand, where it passes through the tendinous sheath of extensor carpi radialis longus muscle. Within the hand, the tendon of extensor carpi radialis longus then travels inferiorly to its insertion site.

The extensor carpi radialis longus muscle is located:

- Anterior to the extensor carpi radialis brevis muscle;

- Posterior to the brachioradialis muscle;

- Lateral to the pronator teres muscle;

- Deep to the tendons of the abductor pollicis longus, extensor pollicis brevis and extensor pollicis longus (at its tendon).

Actions & Testing

The extensor carpi radialis longus muscle is involved in multiple actions:

- extends the hand at the radiocarpal (wrist) joint, which occurs when the extensor carpi radialis brevis and extensor carpi ulnaris muscles contract simultaneously with it;

- abducts the hand at the radiocarpal and midcarpal joints, which occurs when the extensor carpi radialis brevis and flexor carpi radialis muscles contract simultaneously with it.

The extensor carpi radialis longus muscle can be tested by extending and abducting the hand at the radiocarpal and midcarpal joints against resistance while the forearm is held in the pronated position (Standring, 2016).

References

Standring, S. (2016) Gray's Anatomy: The Anatomical Basis of Clinical Practice. Gray's Anatomy Series 41st edn.: Elsevier Limited.