The Extensor carpi radialis brevis is shorter and thicker than the longus, beneath which it can be found.
It arises from the lateral epicondyle of the humerus, by a tendon common to it and the three following muscles; from the radial collateral ligament of the elbow-joint; from a strong aponeurosis which covers its surface; and from the intermuscular septa between it and the adjacent muscles.
The fibres end approximately at the middle of the forearm in the form of a flat tendon, which is closely connected with that of the extensor carpi radialis longus, and accompanies it to the wrist; it passes beneath the Abductor pollicis longus and Extensor pollicis brevis, beneath the extensor retinaculum, beneath the dorsal carpal ligament, and inserts into the lateral dorsal surface of the base of the third metacarpal bone, with a few fibres inserting into the medial dorsal surface of the second metacarpal bone.
Under the dorsal carpal ligament the tendon lies on the back of the radius in a shallow groove called Lister's tubercle, to the ulnar side of that which lodges the tendon of the Extensor carpi radialis, longus, and separated from it by a faint ridge.
Like all the muscles in the posterior forearm, ECR brevis is supplied by a branch of the radial nerve.
It is an extensor, and an abductor of the hand at the wrist joint. That is, it serves to manipulate the wrist so that the hand moves away from the palm and towards the thumb. The muscle, like all extensors of the forearm, can be strengthened by exercise that resist its extension. A wrist roller can be used and reverse wrist curls with dumbbells can performed.
Bones of left forearm. Posterior aspect.
Bones of the left hand. Dorsal surface.
Cross-section through the middle of the forearm.
Posterior surface of the forearm. Deep muscles.
Transverse section across distal ends of radius and ulna.
Transverse section across the wrist and digits.
The mucous sheaths of the tendons on the back of the wrist.
