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 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 (FDP) and flexor pollicis longus (FPL); the radial artery runs at its lateral edge and the 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 and ulna, the interosseous membrane and the distal radioulnar joint; the end of the 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 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.
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
Sources: Terminologia Anatomica (TA2); Anatomy, Shoulder and Upper Limb, Forearm Muscles; Anatomía humana (4.ª ed.), tomo 1, cap. 57: Antebrazo. Aparato de la pronosupinación.
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Representative model, for educational purposes only.
