Extensor Pollicis Brevis Muscle – Anatomy, Nerve Supply

Extensor Pollicis Brevis Muscle (EPB) found in current anatomical textbooks describes its origin as the posterior surface of the radius and the adjacent part of the interosseous membrane, distal to the attachment of the abductor pollicis longus (APL). Its tendon is described as inserting into the posterior surface of the base of the proximal phalanx of the thumb after passing under the extensor retinaculum.^[rx] Its primary function is described as extending the metacarpophalangeal joint (MCPJ) of the thumb, with contributions to the abduction of the thumb and carpus, as well as stabilizing the MCPJ of the thumb by integrating into the extensor hood.^[rx,rx]

In human anatomy, the extensor pollicis brevis is a skeletal muscle on the dorsal side of the forearm. It lies on the medial side of, and is closely connected with, the abductor pollicis longus.

Extensor pollicis brevis is a short and slender muscle located in the posterior compartment of the forearm, extending from the posterior surface of the radius to the proximal phalanx of the thumb. It is one of the deep extensors of the forearm, together with the supinator, abductor pollicis longus, extensor pollicis longus and extensor indices muscles.

Structure of Extensor Pollicis Brevis Muscle

The extensor pollicis brevis arises from the ulna distal to the abductor pollicis longus, from the interosseous membrane, and from the dorsal surface of the radius. ^[rx]

Its direction is similar to that of the abductor pollicis longus, its tendon passing the same groove on the lateral side of the lower end of the radius, to be inserted into the base of the first phalanx of the thumb.

Extensor Pollicus Brevis

• Function: Extension of the thumb by acting on the carpometacarpal joint and the metacarpophalangeal joint
• Origin: Dorsal aspects of middle radius and interosseous membrane
• Insertion: Distal phalanx of 1st finger
• innervation: Posterior interosseous nerve (C7, C8)

Origin and Insertion of Extensor Pollicis Brevis Muscle

The tendon passes deep to the extensor retinaculum, between the tendons of abductor pollicis longus and extensor carpi radialis longus. Along with abductor pollicis longus, it is located in the first extensor (dorsal) compartment of the wrist. After passing under the retinaculum, the tendon runs laterally to insert onto the dorsal surface of the base of the proximal phalanx of the thumb.

Function 

In a close relationship to the abductor pollicis longus, the extensor pollicis brevis both extends and abducts the thumb^[rx] at the carpometacarpal and metacarpophalangeal joints.^[rx]

Together with extensor pollicis longus, extensor pollicis brevis is in charge of extension of the thumb in the first metacarpophalangeal joint. It also extends the thumb in the carpometacarpal joint of the thumb. This movement is important in the anatomy of the grip, as it enables letting go of an object. As it crosses the wrist, extensor pollicis brevis also participates in the extension and abduction of this joint.

References

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