Extensor pollicis longus
Musculus extensor pollicis longus
Also known as: EPL
A deep extensor whose tendon hooks around Lister's tubercle to reach the distal phalanx of the thumb. It extends all the thumb joints and forms the posterior (ulnar) border of the anatomical snuffbox.
Overview
EPL arises from the posterior surface of the middle third of the ulna and the interosseous membrane. Its tendon passes alone through the 3rd extensor compartment, turning sharply around the ulnar side of the dorsal (Lister) tubercle of the radius, which acts as a pulley. It then crosses the radial wrist extensors to the base of the distal phalanx of the thumb. It extends the thumb IP joint (the only muscle that does) as well as the MCP and CMC joints, and it helps adduct the extended thumb. It forms the ulnar (posterior) border of the anatomical snuffbox.
Anatomy
- Origin
Posterior surface of the middle third of the ulna and the interosseous membrane.
- Insertion
Dorsal base of the distal phalanx of the thumb.
- Action
Extension of the distal phalanx of the thumb (and the MCP and CMC joints).
- Innervation
Posterior interosseous nerve.
- Nerve roots
C7–C8
- Arterial supply
Posterior interosseous artery.
Function
- Extends the IP, MCP and CMC joints of the thumb
- Assists thumb adduction and wrist extension
Clinical significance
EPL rupture
Attritional or ischaemic rupture at Lister's tubercle, typically weeks after an undisplaced distal radius fracture, or in rheumatoid arthritis. The patient cannot lift the thumb off the table (retropulsion). Treated by extensor indicis tendon transfer.
Compiled from standard anatomy and physiology references — see the Muscular System sources. For education only; not medical advice.