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Extensor pollicis brevis muscle

Origins, insertions, innervation and function of the extensor pollicis brevis muscle.

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Hey there everybody! It’s Matt from Kenhub, and in this tutorial, we will discuss the extensor pollicis brevis. The extensor pollicis brevis muscle is one of the five deep extensors of the forearm. This group of muscles can be easily palpated as they form the surface of the distal forearm and the wrist. The extensor pollicis longus lies on the medial side of the abductor pollicis longus and is found on the dorsal side of the forearm. The extensor pollicis brevis originates more distally at the posterior side of the radius and the interosseus membrane and has its insertion at the base of the proximal phalanx of the thumb.

Like all extensors of the forearm, this muscle is innervated by a deep branch of the radial branch which you’re seeing here highlighted in green on this image. The radial nerve divides into a superficial branch and deep branch at the height of the radial head. While the superficial branch runs along the brachioradialis, the deep branch continues between the two layers of the supinator. There, it penetrates the supinator muscle and branches off as the posterior interosseus nerve which is responsible for the innervation of almost all deep extensors.

A triangular depression lies at the radial side of the dorsum of the hand which becomes even more prominent during hand extension. It is commonly referred to as the anatomical snuffbox or radial fossa. The depression is framed by the radius and both the tendons of the extensor pollicis longus and of the extensor pollicis brevis.

The main function of the deep extensors is to move the joints of the hand and fingers. The extensor pollicis brevis extends and abducts the thumb in the saddle and at the metacarpophalangeal joints, which also leads to a radial deviation at the wrist.

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