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# Pronator quadratus

The pronator quadratus is a square muscle deep in the lower forearm, just above the wrist; it turns the palm down and holds the two bones together.

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## What it is

A flat square muscle across the lower ends of the radius and ulna, deep to the tendons.

## What it does

Turns the palm down and holds the two bones together.

## Key points

- Tested with the elbow fully bent, which slackens [pronator teres](https://durgical.com/en/anatomy/pronator-teres/): weak pronation then points to an anterior interosseous nerve lesion
- Lateral radiograph: the pronator quadratus fat stripe in front of the distal radius bulges or blurs in an occult fracture
- In the volar approach it is lifted off the radius to expose the fracture and, where possible, repaired over the plate

## Key facts

**Origin**
Distal quarter of the anterior ulna

**Insertion**
Distal quarter of the anterior radius

**Action**
Pronates the forearm (starts every pronation); binds radius and ulna

**Nerve**
Anterior interosseous nerve (C8–T1)

**Blood supply**
Anterior interosseous artery

## Relations

**Superficial**
Tendons of [flexor digitorum profundus](https://durgical.com/en/anatomy/flexor-digitorum-profundus/) (FDP) and [flexor pollicis longus](https://durgical.com/en/anatomy/flexor-pollicis-longus/) (FPL); the [radial artery](https://durgical.com/en/anatomy/radial-artery/) runs at its lateral edge and the [median nerve](https://durgical.com/en/anatomy/median-nerve/) lies further forward; between the muscle and these tendons lies the space of Parona, continuous with the deep space of the palm, along which flexor sheath infections spread

**Deep**
The distal [radius](https://durgical.com/en/anatomy/radius/) and [ulna](https://durgical.com/en/anatomy/ulna/), the interosseous membrane and the distal radioulnar joint; the end of the [anterior interosseous nerve](https://durgical.com/en/anatomy/anterior-interosseous-nerve/) and artery run on its deep surface

## How to find it

Not palpable. It is found on imaging, or in the volar approach as a flat square muscle lying directly on the distal radius and ulna just above the wrist once the flexor tendons are retracted.

## Examination

- Resisted pronation with the elbow fully flexed: weakness, with an OK-sign deficit, supports anterior interosseous nerve palsy

## On imaging

On a lateral wrist radiograph a thin fat line lies in front of it; bowing, blurring or loss of this line suggests a fracture not yet visible. Ultrasound and MRI show the muscle lying directly on the bones.

## Clinical notes

- Galeazzi fracture: pronator quadratus rotates the distal radial fragment toward the ulna while [brachioradialis](https://durgical.com/en/anatomy/brachioradialis/) shortens the radius
- Volar plates are kept proximal to the watershed line, under pronator quadratus, to protect the flexor tendons
- Its deep surface carries the terminal anterior interosseous nerve, whose articular branches are cut in partial wrist denervation

## Test yourself

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

## How is the pronator quadratus tested, and why that way?

Resisted pronation with the elbow fully bent, which slackens pronator teres; weakness points to an anterior interosseous nerve lesion.

## What does the pronator quadratus fat stripe show on a lateral wrist radiograph?

It bulges or blurs in front of the distal radius in an occult fracture.

## What role does the pronator quadratus play in a Galeazzi fracture?

It rotates the distal radial fragment toward the ulna, while the brachioradialis shortens the radius.

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

## Its names

**Official Latin (TA2)**
pronator quadratus TA2 2493

**Official Spanish (DeCS)**
Músculo pronador cuadrado

**English (TA2)**
Pronator quadratus

## Related

- [FCR tendon](https://durgical.com/en/anatomy/flexor-carpi-radialis-tendon/)
- [FPL tendon](https://durgical.com/en/anatomy/flexor-pollicis-longus-tendon/)
- [Anterior interosseous nerve](https://durgical.com/en/anatomy/anterior-interosseous-nerve/)
- [Interosseous arteries](https://durgical.com/en/anatomy/interosseous-arteries-of-the-forearm/)
- [Radius](https://durgical.com/en/anatomy/radius/)
- [Ulna](https://durgical.com/en/anatomy/ulna/)

Sources: Terminologia Anatomica (TA2); [Anatomy, Shoulder and Upper Limb, Forearm Muscles](https://www.ncbi.nlm.nih.gov/books/NBK536975/); Anatomía humana (4.ª ed.), tomo 1, cap. 57: Antebrazo. Aparato de la pronosupinación.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/pronator-quadratus/