Flexor Pollicis Brevis

Hand · Upper Limb

Located in the Hand of the Upper Limb, the Flexor Pollicis Brevis is a key muscle for anatomy study. It arises from Tubercle of the trapezium, trapezoid, capitate, and flexor retinaculum and attaches to Base of the proximal phalanx of the thumb (radial side). Its chief action is that it flexes the thumb at the metacarpophalangeal joint. Innervation is provided by the Recurrent branch of the median nerve (superficial head) and deep branch of the ulnar nerve (deep head).

Origin, Insertion, Action & Nerve

Origin

Tubercle of the trapezium, trapezoid, capitate, and flexor retinaculum

Insertion

Base of the proximal phalanx of the thumb (radial side)

Action

Flexes the thumb at the metacarpophalangeal joint

Nerve

Recurrent branch of the median nerve (superficial head) and deep branch of the ulnar nerve (deep head)

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.

Origin

Tubercle of the trapezium, trapezoid, capitate, and flexor retinaculum

Insertion

Base of the proximal phalanx of the thumb (radial side)

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)

OIANS stands for Origin, Insertion, Action and Nerve, the four facts that uniquely define every skeletal muscle. To learn the Flexor Pollicis Brevis, work through them in order: picture its origin, trace the muscle to its insertion, reason out the action that shortening between those two points must create, then add the nerve that drives it.

Most students remember the Flexor Pollicis Brevis fastest by linking its action back to its attachments rather than memorising each fact in isolation. Once the origin and insertion make sense, the action usually follows logically.