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# EPL

The extensor pollicis longus is a deep forearm muscle whose tendon reaches the thumb tip; it lifts the thumb up and back.

Official name: Extensor pollicis longus

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## What it is

A deep forearm muscle whose tendon goes to the tip of the thumb.

## What it does

Lifts the thumb up and back.

## Key points

- Delayed rupture weeks after a distal radius fracture, often an undisplaced one, from wear and poor blood supply where it turns round Lister's tubercle
- Forms the dorsal border of the anatomical snuffbox
- Retropulsion (lifting the thumb off a flat table) is the reliable test, because the thenar muscles can still extend the IP joint weakly

## Key facts

**Origin**
Middle third of the posterior ulna and interosseous membrane

**Insertion**
Base of the [distal phalanx of the thumb](https://durgical.com/en/anatomy/distal-phalanx-of-the-thumb/)

**Action**
Extends the whole thumb (IP joint); hooks round Lister's tubercle

**Nerve**
[Posterior interosseous nerve](https://durgical.com/en/anatomy/posterior-interosseous-nerve/) (C7–C8)

**Blood supply**
Posterior interosseous artery

## Relations

**Course**
From the back of the [ulna](https://durgical.com/en/anatomy/ulna/) through the third compartment on the ulnar side of Lister's tubercle; it then crosses the [ECRL](https://durgical.com/en/anatomy/extensor-carpi-radialis-longus/) and [ECRB](https://durgical.com/en/anatomy/extensor-carpi-radialis-brevis/) tendons obliquely to reach the thumb

**Medial**
[Extensor indicis](https://durgical.com/en/anatomy/extensor-indicis/) in the deep layer of the forearm; the [extensor digitorum tendons](https://durgical.com/en/anatomy/extensor-digitorum-tendons/) in the fourth compartment

**Lateral**
APL and EPB in the deep extensor layer

**Deep**
The dorsal [radius](https://durgical.com/en/anatomy/radius/) at Lister's tubercle; distally the ECRL and ECRB tendons where it crosses them

## How to find it

With the palm flat on a table, lifting the thumb straight up off it tightens the tendon, which is seen as the dorsal edge of the anatomical snuffbox and can be traced back to Lister's tubercle.

## Examination

- Retropulsion test: inability to lift the thumb off the table with the hand flat indicates EPL rupture, a cut or posterior interosseous nerve palsy

## On imaging

Ultrasound follows it around Lister's tubercle in the third compartment; a rupture is a gap with a retracted end. Classic: late rupture weeks after an undisplaced distal radius fracture, or wear from a protruding dorsal screw. Radiographs show the fracture or screw; ultrasound or MRI shows the tendon. It forms the ulnar border of the anatomical snuffbox.

## Clinical notes

- Extensor indicis to EPL transfer is the classic reconstruction after rupture
- Drill bits or screws that protrude from the back of the radius during volar plating can wear through the tendon
- Attrition rupture also occurs in rheumatoid arthritis

## Anatomical variants

- Rare tendon anomalies, such as a doubled tendon or an extra slip to the index finger, have been described and classified

## Related conditions

- [Distal radius fracture (Colles)](https://durgical.com/en/conditions/distal-radius-fracture/)
- [Scaphoid fracture](https://durgical.com/en/conditions/scaphoid-fracture/)

## Test yourself

Think of the answer, then tap the question to see it.

## Why does the EPL (extensor pollicis longus) rupture weeks after a distal radius fracture?

From wear and poor blood supply where it turns round Lister's tubercle, often after an undisplaced fracture.

## Which test reliably detects EPL rupture, and why is IP extension not enough?

Retropulsion: lifting the thumb off a flat table; the thenar muscles can still extend the IP joint weakly.

## What is the classic reconstruction after EPL rupture?

Transfer of the extensor indicis to the EPL.

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Educational information, not medical advice. For any symptom, see a health professional.

## Its names

**Official Latin (TA2)**
extensor longus pollicis TA2 2516

**Official Spanish (DeCS)**
Músculo extensor largo del pulgar

**English (TA2)**
Extensor pollicis longus

## Related

- [Posterior interosseous nerve](https://durgical.com/en/anatomy/posterior-interosseous-nerve/)
- [Interosseous arteries](https://durgical.com/en/anatomy/interosseous-arteries-of-the-forearm/)
- [EPL tendon](https://durgical.com/en/anatomy/extensor-pollicis-longus-tendon/)
- [Ulna](https://durgical.com/en/anatomy/ulna/)

Sources: Terminologia Anatomica (TA2); [Anatomy, Shoulder and Upper Limb, Hand Extensor Pollicis Longus Muscle](https://www.ncbi.nlm.nih.gov/books/NBK544294/); [Anatomy, Shoulder and Upper Limb: Hand Anatomical Snuff Box](https://www.ncbi.nlm.nih.gov/books/NBK482228/).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/anatomy/extensor-pollicis-longus/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/extensor-pollicis-longus/