Extensor Carpi Radialis Brevis

Origin

The extensor carpi radialis brevis muscle originates from the:

- lateral epicondyle of humerus, via the common extensor tendon;

- radial collateral ligament of elbow joint;

- adjacent intermuscular septa;

- aponeurosis that surrounds the muscle.

The common extensor tendon is the combined tendon for four of the six superficial muscles in the posterior compartment of the forearm, which are the:

- extensor carpi radialis brevis muscle;

- extensor digitorum muscle;

- extensor digiti minimi muscle;

- extensor carpi ulnaris muscle.

Insertion

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

Key Features & Anatomical Relations

The extensor carpi radialis brevis 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 brevis muscle. Within the hand, the tendon of extensor carpi radialis brevis then travels inferomedially to its insertion site.

The extensor carpi radialis brevis muscle is located:

- anterior to the extensor digitorum and abductor pollicis longus muscles;

- posterior to the extensor carpi radialis brevis muscle;

- lateral to the supinator 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 brevis muscle is involved in multiple actions:

- extends the hand at the radiocarpal (wrist) joint, which occurs when the extensor carpi radialis longus 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 longus and flexor carpi radialis muscles contract simultaneously with it.

The extensor carpi radialis brevis 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).

List of Clinical Correlates

- Lateral epicondylitis (tennis elbow)

References

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