Upper limb

Flexor Pollicis Longus

Musculus flexor pollicis longus

Origin

Anterior surface of the radius and the interosseous membrane

Insertion

Base of the distal phalanx of the thumb

Function

Flexes the interphalangeal joint and the MCP joint of the thumb

Innervation

Median nerve (anterior interosseous nerve), C8–T1

Movement & chain

Essential for a fine pincer grip between thumb and index finger, working together with flexor pollicis brevis.

Palpation

The tendon is palpable on the volar side of the thumb, proximal to the IP joint, during active resisted thumb flexion.

Clinical

Can be involved in a 'jersey finger' equivalent of the thumb, and is a point of interest in carpal tunnel syndrome because the tendon runs through the tunnel.

Segmental innervation

Median nerve (AIN), C8–T1.

In clinical practice

Tendon rupture is tested clinically by having the patient flex the IP joint of the thumb against resistance while the MCP joint is fixed.

Region in the model

Upper limb