Abductor Pollicis Longus
Forearm · Upper Limb
The abductor pollicis longus is a deep extensor-compartment muscle that helps position the thumb. It arises from the posterior surfaces of the ulna, radius, and interosseous membrane and inserts on the base of the first metacarpal. It abducts and extends the thumb at the carpometacarpal joint, drawing it away from the palm. It is supplied by the posterior interosseous nerve (C7, C8). Its tendon forms the anterior (palmar) border of the anatomical snuffbox and, with extensor pollicis brevis, is involved in de Quervain's tenosynovitis.
Origin, Insertion, Action & Nerve
Origin
Posterior surfaces of ulna, radius, and interosseous membrane
Insertion
Base of 1st metacarpal
Action
Abduction and extension of thumb at carpometacarpal joint
Nerve
Posterior interosseous nerve (C7, C8)
Attachments explained
The Abductor 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 surfaces of ulna, radius, and interosseous membrane
Insertion
Base of 1st metacarpal
Action & function
When the Abductor Pollicis Longus contracts, it produces the following movement: Abduction and extension of thumb at carpometacarpal 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 Abductor 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 Abductor Pollicis Longus, impairing the movements it normally produces (abduction and extension of thumb at carpometacarpal joint). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Abductor Pollicis Longus (the OIANS method)
Read the name for the action: it abducts the thumb, and being longus it reaches the base of the first metacarpal, drawing the whole thumb away from the palm. Grouping the three deep outcropping thumb muscles (this one with extensor pollicis brevis and longus) as they emerge from the forearm helps organise them.
Two landmarks make it memorable: its tendon forms the palmar border of the anatomical snuffbox, and, with extensor pollicis brevis, it is the tendon pair inflamed in de Quervain's tenosynovitis. Tying the muscle to the snuffbox and that overuse syndrome cements both its position and its clinical relevance.
Frequently asked questions
Where is the Abductor Pollicis Longus located?
The Abductor Pollicis Longus is a muscle of the Forearm group, located in the Upper Limb.
What is the origin of the Abductor Pollicis Longus?
Posterior surfaces of ulna, radius, and interosseous membrane
What is the insertion of the Abductor Pollicis Longus?
Base of 1st metacarpal
What movements does the Abductor Pollicis Longus produce?
Abduction and extension of thumb at carpometacarpal joint
What nerve supplies the Abductor Pollicis Longus?
Posterior interosseous nerve (C7, C8)
Is the Abductor Pollicis Longus free to study in OIANS?
Yes. The Abductor 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 Abductor Pollicis Longus
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