In human anatomy, the extensor pollicis longus muscle (EPL) is a

skeletal muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of m ...

located dorsally on the

forearm The forearm is the region of the upper limb between the elbow and the wrist. The term forearm is used in anatomy to distinguish it from the arm, a word which is most often used to describe the entire appendage of the upper limb, but which in ...

. It is much larger than the extensor pollicis brevis, the origin of which it partly covers and acts to stretch the

thumb The thumb is the first digit of the hand, next to the index finger. When a person is standing in the medical anatomical position (where the palm is facing to the front), the thumb is the outermost digit. The Medical Latin English noun for thu ...

together with this muscle.

Structure

The extensor pollicis longus arises from the dorsal surface of the ulna and from the interosseous membrane, next to the origins of abductor pollicis longus and extensor pollicis brevis. Passing through the third tendon compartment, lying in a narrow, oblique groove on the back of the lower end of the

radius In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...

,'' Gray's Anatomy'' 1918, see infobox it crosses the wrist close to the dorsal midline before turning towards the thumb using Lister's tubercle on the distal end of the

as a pulley. It obliquely crosses the tendons of the extensores carpi radialis longus and brevis, and is separated from the extensor pollicis brevis by a triangular interval, the anatomical snuff box in which the radial artery is found. At the proximal phalanx, the tendon is joined by expansions from abductor pollicis brevis and adductor pollicis. The tendon is finally inserted on the base of the distal phalanx of the thumb. in length, the tendon passes through a long and superficial

synovial sheath A synovial sheath is one of the two membranes of a tendon sheath which covers a tendon. The other membrane is the outer fibrous tendon sheath. The tendon invaginates the synovial sheath from one side so that the tendon is suspended from the membran ...

which, passing obliquely from the radial border of the forearm into the thumb, extends from the proximal border of the extensor retinaculum to the first carpometacarpal joint. In the synovial sheath a proximal and a distal mesotendon connect the tendon to the floor of the sheath.

Relations

Together with the tendons of the extensor pollicis brevis and the abductor pollicis longus, its tendon crosses the radial artery.

Blood supply

The tendon of extensor pollicis longus is supplied by branches from various arteries. Before the tendon enters its synovial sheath, arteries from the anterior interosseous artery or its muscular branches enter the tendon. The sheath itself is supplied by the posterior ramus of the same artery. In the metacarpal region, beyond the synovial sheath, the tendon is supplied directly from the radial artery. At the phalanges, the tendon forms a dorsal aponeurosis which is supplied by a digital branch of the first

dorsal metacarpal artery The dorsal carpal arch (dorsal carpal network, posterior carpal arch) is an anatomical term for the combination (anastomosis) of dorsal carpal branch of the radial artery and the dorsal carpal branch of the ulnar artery near the back of the wrist. ...

Innervation

The extensor pollicis longus muscle receives innervation from the posterior interosseous nerve (C7 and C8) which is the continuation of the deep branch of the radial nerve.

Function

Extensor pollicis longus extends the terminal phalanx of the thumb. While abductor pollicis brevis and adductor pollicis, both attached to the extensor pollicis longus tendon, can extend the thumb's interphalangeal joint to the neutral position, only extensor pollicis longus can achieve full hyperextension at the interphalangeal joint. This complete extension at the interphalangeal joint is not possible, or considerably more difficult, with the carpal, carpometacarpal, and metacarpophalangeal joints simultaneously extended. Likewise, flexion at the interphalangeal joint by flexor pollicis longus is considerably reduced in wrist flexion. It also applies an extensor force at the metacarpophalangeal joint together with the extensor pollicis brevis and extends and adducts at the carpometacarpal joint of the thumb.

Clinical significance

Injury

Tenosynovitis, inflammatory irritation of the synovial sheath, is relatively common in the third compartment after repetitive activities such as drum playing.

Additional images

Notes

References

* * * * {{Authority control Muscles of the upper limb