Abductor Pollicis Brevis
Hand · Upper Limb
The abductor pollicis brevis is a superficial muscle of the thenar eminence, the fleshy mound at the base of the thumb. It arises from the flexor retinaculum and the tubercles of the scaphoid and trapezium and inserts on the lateral base of the proximal phalanx of the thumb. It abducts the thumb, moving it forward and away from the palm at right angles to it. It is supplied by the recurrent branch of the median nerve (C8, T1); this branch is compromised in carpal tunnel syndrome, so the muscle becomes weak and the thenar eminence visibly wastes.
Origin, Insertion, Action & Nerve
Origin
Flexor retinaculum and tubercles of scaphoid and trapezium
Insertion
Lateral base of proximal phalanx of thumb
Action
Abduction of thumb
Nerve
Recurrent branch of median nerve (C8, T1)
Attachments explained
The Abductor 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
Flexor retinaculum and tubercles of scaphoid and trapezium
Insertion
Lateral base of proximal phalanx of thumb
Action & function
When the Abductor Pollicis Brevis contracts, it produces the following movement: Abduction of thumb.
As part of the Hand 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 Brevis receives its nerve supply from the Recurrent branch of median nerve (C8, T1). This nerve carries fibres from spinal segment(s) C8, T1.
Because a muscle can only contract when its nerve is intact, injury to the Recurrent branch of median nerve or to its spinal roots (C8, T1) can weaken or paralyse the Abductor Pollicis Brevis, impairing the movements it normally produces (abduction of thumb). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Abductor Pollicis Brevis (the OIANS method)
Learn abductor pollicis brevis as the most superficial of the three thenar muscles, the fleshy pad you can feel at the base of the thumb. Its name gives the action, thumb abduction, and its origin on the flexor retinaculum and carpal tubercles keeps it anchored to the wrist side of the palm.
The clinical anchor is carpal tunnel syndrome. The recurrent branch of the median nerve supplies the thenar muscles, so median nerve compression at the wrist weakens thumb abduction and wastes the thenar eminence. Testing thumb abduction against resistance is a bedside check of this exact muscle and nerve.
Frequently asked questions
Where is the Abductor Pollicis Brevis located?
The Abductor Pollicis Brevis is a muscle of the Hand group, located in the Upper Limb.
What is the origin of the Abductor Pollicis Brevis?
Flexor retinaculum and tubercles of scaphoid and trapezium
What is the insertion of the Abductor Pollicis Brevis?
Lateral base of proximal phalanx of thumb
What movements does the Abductor Pollicis Brevis produce?
Abduction of thumb
What nerve supplies the Abductor Pollicis Brevis?
Recurrent branch of median nerve (C8, T1)
Is the Abductor Pollicis Brevis free to study in OIANS?
Yes. The Abductor 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 Abductor Pollicis Brevis
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