Extensor pollicis longus muscle
Extensor pollicis longus is part of the deep extensors of the forearm together with extensor pollicis brevis, abductor pollicis longus, extensor indicis and supinator muscles. It is located on the posterior aspect of forearm, extending from the middle third of the ulna, and adjacent interosseous membrane, to the distal phalanx of the thumb.
As the name of the muscle suggests, the main function of this muscle is extension of the thumb at the metacarpophalangeal and interphalangeal joints. Also, this muscle participates in extension and abduction of the wrist joint.
|Origin||Posterior surface of middle third of ulna and interosseus membrane|
|Insertion||Posterior aspect of base of distal phalanx of thumb|
|Action||Wrist joints: Weak hand extension
Metacarpophalangeal and interphalangeal joint of thumb: Thumb extension
|Innervation||Posterior interosseous nerve (C7, C8)|
|Blood supply||Posterior interosseous artery, anterior interosseous artery|
In this article, we will discuss the anatomy and function of the extensor pollicis longus muscle.
Origin and insertion
Extensor pollicis longus originates from the middle third of the posterior surface of ulna, mostly along its radial border. This attachment extends onto the adjacent interosseous membrane, and is situated proximal to the origin of extensor indicis muscle. From here, the muscle belly runs obliquely in a radial direction, towards the lateral aspect of the wrist joint. The muscle ends in a tendon that passes deep to extensor retinaculum and travels across the posterolateral aspect of the hand to insert onto the base of the distal phalanx of the thumb.
More specifically, the tendon of extensor pollicis longus forms what is referred to as an extensor expansion (or dorsal aponeurosis) as it is joined by the tendon of abductor pollicis brevis laterally and adductor pollicis medially. Together, this aponeurosis forms the extensor mechanism of the thumb.
Extensor pollicis longus is a deep muscle of the posterior aspect of forearm extending over the distal aspect of interosseous membrane and distal radioulnar joint. It is initially deep to the extensor digitorum, medial to abductor pollicis longus and lateral to extensor indicis, with the posterior interosseous artery and nerve running across the posterior aspect of the muscle. The relatively long tendon of extensor pollicis longus traverses the tendons of extensor carpi radialis longus and extensor carpi radialis brevis in the distal aspect of hand.
At the level of the radiocarpal joint, the tendon of extensor pollicis longus sits medial to that of extensor pollicis brevis, which collectively form a depression (when the thumb is extended) known as the anatomical snuffbox.
Extensor digitorum is innervated by posterior interosseous nerve which is a continuation of a deep branch of radial nerve (root value C7 and C8).
Extensor pollicis brevis receives its blood supply from the posterior interosseous artery and perforating branches of the anterior interosseous artery.
The main action of extensor pollicis longus is extension of the thumb at the metacarpophalangeal and interphalangeal joints. Extension at the metacarpophalangeal joint occurs in synergy with extensor pollicis brevis muscle. When the thumb reaches the full extension or abduction, extensor pollicis longus can also assist in adduction of the thumb.
Owing to the fact that their tendons cross the distal radioulnar joint, the extensors of thumb may assist in the supination of the forearm, as well as extension and abduction of the wrist joint.
Inflammation or a rupture of extensor pollicis longus tendon is commonly referred to as "drummer's paralysis". This condition is most commonly caused by blunt mechanical injuries to the wrist area or a simple overuse of the extensor pollicis longus muscle. It is most commonly seen in drummers, sculptors, blacksmiths or waiters. This condition results in weakness of extensor pollicis longus, which is presented as an incomplete extension of the thumb.