Pronator quadratus
Pronator quadratus is a flat, square muscle across the lower front of the forearm that turns the palm downward.
At a glance
- English
- Pronator quadratus
- Latin (TA2)
- Pronator quadratus
- System
- Muscle
- Region
- Upper limb
- Side
- Paired, left and right
About the pronator quadratus
Pronator quadratus is the deepest muscle on the front of the forearm. It is a flat, roughly square sheet stretched across the lower quarter of the radius and ulna, lying directly on the bones and the interosseous membrane, under the tendons of the long finger and thumb flexors.
It arises from an oblique ridge on the lower front of the ulna and from the medial part of that surface. Its fibres run across, slightly downward and laterally, and attach to the lower quarter of the anterior radius and to its anterior border. In most people the muscle has two layers. The superficial layer runs straight between the bones, while the deeper layer reaches the area near the distal radioulnar joint.
It is the main pronator of the forearm, the first to act whenever the palm is turned down, with pronator teres joining in for speed or force. Its deep layer also binds the lower radius and ulna together, steadying the distal radioulnar joint, especially when the hand bears weight. The anterior interosseous nerve ends by entering its deep surface, and the anterior interosseous artery supplies its blood.
Surgeons lift this muscle off the radius when fixing fractures of the lower radius with a plate on the front of the bone, and then lay it back to cover the plate. A fat pad in front of it shows on a side radiograph; if the pad is displaced, a hidden wrist fracture may be present. Testing pronation with the elbow fully bent puts pronator teres at a disadvantage and checks this muscle and its nerve on their own.
Attachments, action and supply
- Origin
- Oblique ridge and medial part of the anterior surface of the lower ulna.
- Insertion
- Anterior surface and anterior border of the lower quarter of the radius.
- Action
- Pronates the forearm and holds the lower radius and ulna together.
- Nerve supply
- Anterior interosseous nerve, from the median nerve (C7, C8).
- Blood supply
- Anterior interosseous artery.
Anthromica
See the pronator quadratus where it really sits, with every layer of the body around it.
- Every layer, one body. Peel from muscle to bone, nerve, vessel and organ, and turn it any way.
- English and Latin. Every structure named the way your exam names it.
- Quiz until it sticks. Short drills on the structures you keep missing.
Free to start. No card.
