Extensor pollicis longus

Origin and insertion?

• Origin (O): posterior surface of the ulna (ulna) and interosseous membrane (membrana interossea). The site of origin is located distal to the abductor pollicis longus muscle (m. abductor pollicis longus).
• Insertion (I): base of the distal phalanx of the thumb.

Topography and tendon course

The muscle is located in the deep layer of the posterior compartment of the forearm. The course of its tendon has several important topographical features:

• The tendon hooks around the dorsal tubercle of the radius (Lister's tubercle).
• It passes into the hand through the 3rd compartment beneath the extensor retinaculum (retinaculum musculorum extensorum). Within this compartment, it is enclosed in its own synovial sheath (vagina tendinis m. extensoris pollicis longi).
• Upon exiting the compartment, the tendon courses toward the dorsum of the thumb, turning sharply in a lateral direction.
• Crossing: on its way to the digit, the tendon crosses superficially (anteriorly) the tendons of the extensor carpi radialis longus and brevis muscles (mm. extensores carpi radiales longus et brevis).

Function

• Extends the distal phalanx of the thumb.
• Participates in the extension of the metacarpophalangeal (first) and carpometacarpal joints of the thumb.
• Takes part in wrist extension.

Blood supply and innervation

• Innervation: supplied by branches of the radial nerve — n. radialis (spinal cord segments C7–C8).
• Blood supply: the muscle receives blood from the posterior interosseous artery (a. interossea posterior) and the radial artery (a. radialis).

Participation in forming the anatomical snuffbox

The tendon of m. extensor pollicis longus is a critical landmark on the radial side of the wrist. It forms the ulnar (medial) boundary of the anatomical snuffbox, a triangular depression visible upon strong abduction of the thumb.

The radial (lateral) boundary of this space is formed by the tendons of m. abductor pollicis longus and m. extensor pollicis brevis. The floor of the snuffbox contains the radial artery (a. radialis), which then passes directly deep to the tendon of the extensor pollicis longus as it travels through the first interosseous space into the palm.

Do not confuse with: extensor hallucis longus

In the lower extremity, there is a similarly named muscle — extensor hallucis longus (m. extensor hallucis longus). It originates from the anterior surface of the fibula, inserts into the distal phalanx of the great toe, extends it, and also participates in extension and supination of the foot. It is innervated by the deep fibular nerve (L4–S1).

Class and exam questions

What else to study on this topic

• Anatomical snuffbox and its contents
• Extensor pollicis brevis muscle (m. extensor pollicis brevis)
• Compartments beneath the extensor retinaculum of the wrist
• Topography of the radial artery (a. radialis)

Other topics in the "Anatomical Structures" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.