Extensor Pollicis Brevis
Forearm · Upper Limb
The extensor pollicis brevis is a deep muscle of the extensor compartment that works on the thumb. It arises from the posterior surface of the radius and the interosseous membrane and inserts on the base of the proximal phalanx of the thumb. It extends the thumb at the metacarpophalangeal and carpometacarpal joints. It is supplied by the posterior interosseous nerve (C7, C8). Its tendon, with that of abductor pollicis longus, forms the anterior border of the anatomical snuffbox and is involved in de Quervain's tenosynovitis.
Origin, Insertion, Action & Nerve
Origin
Posterior surface of the radius and interosseous membrane
Insertion
Base of the proximal phalanx of the thumb
Action
Extends the thumb at the metacarpophalangeal and carpometacarpal joints
Nerve
Posterior interosseous nerve (C7–C8)
Attachments explained
The Extensor Pollicis Brevis 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 radius and interosseous membrane
Insertion
Base of the proximal phalanx of the thumb
Action & function
When the Extensor Pollicis Brevis contracts, it produces the following movement: Extends the thumb at the metacarpophalangeal and carpometacarpal joints.
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 Brevis 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 Brevis, impairing the movements it normally produces (extends the thumb at the metacarpophalangeal and carpometacarpal joints). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Extensor Pollicis Brevis (the OIANS method)
Distinguish the two thumb extensors by how far each reaches: the brevis is short, ending at the proximal phalanx, so it extends the thumb only at the base joints. Learning it next to extensor pollicis longus, which continues to the tip, keeps the pair clearly separated.
Its two clinical landmarks make it stick: with abductor pollicis longus it forms the palmar border of the anatomical snuffbox, and the same tendon pair is inflamed in de Quervain's tenosynovitis. Both facts double as reminders of its position on the radial side of the wrist.
Frequently asked questions
Where is the Extensor Pollicis Brevis located?
The Extensor Pollicis Brevis is a muscle of the Forearm group, located in the Upper Limb.
What is the origin of the Extensor Pollicis Brevis?
Posterior surface of the radius and interosseous membrane
What is the insertion of the Extensor Pollicis Brevis?
Base of the proximal phalanx of the thumb
What movements does the Extensor Pollicis Brevis produce?
Extends the thumb at the metacarpophalangeal and carpometacarpal joints
What nerve supplies the Extensor Pollicis Brevis?
Posterior interosseous nerve (C7–C8)
Is the Extensor Pollicis Brevis free to study in OIANS?
Yes. The Extensor Pollicis Brevis 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 Brevis
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