The extensor pollicis longus runs obliquely through the third extensor compartment around Lister tubercle on the dorsal radius to reach the thumb tip. Its change of direction around Lister tubercle acts as a pulley, and this bony contact point is the site of EPL rupture, which can occur spontaneously after distal radius fractures even those treated conservatively, from attrition of the tendon against the fracture haematoma and distal radius irregularity.
| Origin | Posterior surface of the middle third of the ulna and adjacent interosseous membrane |
|---|---|
| Insertion | Dorsal surface of the base of the distal phalanx of the thumb |
| Nerve Supply | Posterior interosseous nerve (C7, C8) |
| Blood Supply | Posterior interosseous artery |
| Actions | Extension of the thumb interphalangeal joint; Extension and adduction of the thumb metacarpophalangeal joint; Extension of the wrist |
|---|
By extending the IP joint it lifts the thumb tip away from the palm — the gesture used in a thumbs-up sign — and its loss produces a drooping thumb tip that cannot be straightened against gravity.
Spontaneous EPL rupture after a minimally displaced distal radius fracture occurs in 0.3 to 3 percent of cases, typically presenting 6 to 8 weeks after injury when the haematoma has resolved. The patient notices they can no longer extend the thumb tip. Management is with extensor indicis proprius tendon transfer rather than primary repair, as the remaining tendon ends are too attenuated. EPL rupture also occurs in rheumatoid arthritis from attrition over bony spurs.
The EPL tendon forms the posterior boundary of the anatomical snuffbox between Lister tubercle and the thumb IP joint, clearly visible during full thumb extension (retropulsion) with the hand flat on a table.
Spontaneous tendon rupture after distal radius fracture or from rheumatoid arthritis producing inability to extend the thumb tip, managed with extensor indicis proprius tendon transfer.
