Upper limb

Flexor Pollicis Brevis

Musculus flexor pollicis brevis

Origin

Deep head: trapezoid and capitate bones. Superficial head: trapezium bone and flexor retinaculum

Insertion

Base of the proximal phalanx of the thumb, via the lateral sesamoid bone

Function

Flexes the metacarpophalangeal joint of the thumb

Innervation

Deep head: ulnar nerve (deep branch); superficial head: median nerve (recurrent branch), C8–T1

Movement & chain

Works together with opponens pollicis and abductor pollicis brevis during opposition and flexion of the thumb, essential for a fine pinch grip between thumb and index finger.

Palpation

Palpable on the thenar eminence, medial to abductor pollicis brevis, during resisted thumb flexion.

Clinical

In a median nerve lesion (for example carpal tunnel syndrome), the deep head, supplied via the ulnar nerve, often remains functional: this helps localize the lesion.

Segmental innervation

The dual innervation (C8–T1, via both the median and ulnar nerves) makes this muscle clinically useful for differentiating between a median and an ulnar nerve lesion.

In clinical practice

Focus on hand function and edema prevention; ensure IV cannulas and splints maintain functional hand position to prevent joint contractures.

Region in the model

Upper limb