Extensor Pollicis Longus
Forearm · Upper Limb
The extensor pollicis longus is a deep extensor of the thumb whose tendon forms the posterior (ulnar) border of the anatomical snuffbox. It arises from the posterior surface of the middle of the ulna and the interosseous membrane and inserts on the base of the distal phalanx of the thumb. It extends the distal phalanx of the thumb at the interphalangeal joint and, using the dorsal tubercle of the radius (Lister's tubercle) as a pulley, helps draw the whole thumb backward. It is supplied by the posterior interosseous nerve (C7, C8); its tendon may rupture after a distal radius fracture.
Origin, Insertion, Action & Nerve
Origin
Posterior surface of the middle ulna and interosseous membrane
Insertion
Base of the distal phalanx of the thumb
Action
Extends the distal phalanx of the thumb at the interphalangeal joint
Nerve
Posterior interosseous nerve (C7–C8)
Attachments explained
The Extensor Pollicis Longus is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.
Origin
Posterior surface of the middle ulna and interosseous membrane
Insertion
Base of the distal phalanx of the thumb
Action & function
When the Extensor Pollicis Longus contracts, it produces the following movement: Extends the distal phalanx of the thumb at the interphalangeal joint.
As part of the Forearm group of the Upper Limb, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.
Nerve supply & clinical relevance
The Extensor Pollicis Longus receives its nerve supply from the Posterior interosseous nerve (C7–C8). This nerve carries fibres from spinal segment(s) C7, C8.
Because a muscle can only contract when its nerve is intact, injury to the Posterior interosseous nerve or to its spinal roots (C7, C8) can weaken or paralyse the Extensor Pollicis Longus, impairing the movements it normally produces (extends the distal phalanx of the thumb at the interphalangeal joint). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Extensor Pollicis Longus (the OIANS method)
Fix extensor pollicis longus as the long thumb extensor, the only one reaching the distal phalanx, so it alone straightens the tip of the thumb. Its tendon hooks around Lister's tubercle on the radius, which acts as a pulley and redirects its pull, and it forms the ulnar border of the anatomical snuffbox.
The clinical detail to attach is tendon rupture after a distal radius (Colles) fracture, because the tendon runs over the injured bone and its pulley. Pairing this longus with the brevis (which stops at the proximal phalanx) makes the difference in reach memorable.
Frequently asked questions
Where is the Extensor Pollicis Longus located?
The Extensor Pollicis Longus is a muscle of the Forearm group, located in the Upper Limb.
What is the origin of the Extensor Pollicis Longus?
Posterior surface of the middle ulna and interosseous membrane
What is the insertion of the Extensor Pollicis Longus?
Base of the distal phalanx of the thumb
What movements does the Extensor Pollicis Longus produce?
Extends the distal phalanx of the thumb at the interphalangeal joint
What nerve supplies the Extensor Pollicis Longus?
Posterior interosseous nerve (C7–C8)
Is the Extensor Pollicis Longus free to study in OIANS?
Yes. The Extensor Pollicis Longus is free in OIANS: its full origin, insertion, action and nerve details are open to everyone in the Muscle Directory, and because it belongs to the Upper Limb it is also covered by the free Quiz and Flashcard decks. The other regions, the "All Muscles" deck, and the Progress and Explore tools are unlocked with a one-time Lifetime purchase.
Related muscles
Study the Extensor Pollicis Longus
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