Flexor pollicis longus
Musculus flexor pollicis longus
Also known as: FPL
A deep forearm flexor from the anterior radius to the distal phalanx of the thumb. It is the only muscle that flexes the thumb's interphalangeal joint.
Overview
FPL arises from the anterior surface of the radius and the adjacent interosseous membrane, sometimes with a slip from the coronoid process. Its tendon passes through the carpal tunnel (the most lateral structure in it) in its own synovial sheath (the radial bursa). It then runs between the two heads of flexor pollicis brevis to the base of the distal phalanx of the thumb. It flexes the thumb IP joint and assists flexion at the MCP and carpometacarpal joints, which is essential for pinch and grip. It is supplied by the anterior interosseous nerve.
Anatomy
- Origin
Anterior surface of the radius and the adjacent interosseous membrane.
- Insertion
Base of the distal phalanx of the thumb (palmar surface).
- Action
Flexion of the phalanges of the thumb.
- Innervation
Anterior interosseous nerve (median nerve).
- Nerve roots
C8–T1 (C7–C8)
- Arterial supply
Anterior interosseous artery.
- Relations
Lies lateral to FDP on the interosseous membrane. Pronator quadratus lies deep to its lower part.
Function
- Flexes the interphalangeal joint of the thumb
- Assists flexion of the thumb MCP and CMC joints
Clinical significance
Flexor sheath infection
Infection in the FPL sheath (radial bursa) can spread through the space of Parona in the distal forearm to the ulnar bursa, producing a "horseshoe abscess".
Compiled from standard anatomy and physiology references — see the Muscular System sources. For education only; not medical advice.