Flexor Pollicis Brevis

Origin, Insertion, Action & Nerve

Attachments explained

The Flexor 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.

Action & function

When the Flexor Pollicis Brevis contracts, it produces the following movement: Flexes the thumb at the metacarpophalangeal joint.

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 Flexor Pollicis Brevis receives its nerve supply from the Recurrent branch of the median nerve (superficial head) and deep branch of the ulnar nerve (deep head).

Because a muscle can only contract when its nerve is intact, injury to the Recurrent branch of the median nerve can weaken or paralyse the Flexor Pollicis Brevis, impairing the movements it normally produces (flexes the thumb at the metacarpophalangeal joint). This is why knowing the innervation is central to localising nerve lesions in clinical practice.

How to study the Flexor Pollicis Brevis (the OIANS method)

Learn flexor pollicis brevis as the short thumb flexor of the thenar eminence, bending the thumb at the metacarpophalangeal joint (in contrast to flexor pollicis longus in the forearm, which reaches the tip). Its two heads straddle the boundary between the median and ulnar nerve territories in the hand.

That dual nerve supply is the point most worth remembering: the superficial head runs on the median nerve like its thenar neighbours, while the deep head runs on the ulnar nerve like adductor pollicis. This split makes the muscle a neat illustration of where the two nerves meet in the thumb.

Frequently asked questions

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