| Pronator quadratus muscle | |
|---|---|
| Anterior view of left forearm. Deep muscles. (Pronator quadratus visible at bottom-center right.) | |
| Latin | musculus pronator quadratus |
| Gray's | subject #125 449 |
| Origin | medial, anterior surface of the ulna |
| Insertion | lateral, anterior surface of the radius |
| Artery | anterior interosseous artery |
| Nerve | median nerve (anterior interosseous nerve) |
| Actions | pronates the forearm |
| Antagonist | Supinator muscle |
Pronator quadratus is a square shaped muscle on the distal forearm that acts to pronate (turn so the palm faces downwards) the hand.
As it is on the anterior side of the arm, it is innervated by a branch of the median nerve, the anterior interosseous nerve (roots C8 and T1 with T1 being primary). Arterial blood comes via the interosseous artery.
Its fibers run perpendicular to the direction of the arm, running from the most distal quarter of the anterior ulna to the distal quarter of the anterior radius. It is the only muscle that attaches only to the ulna at one end and the radius at the other end.
When pronator quadratus contracts, it pulls the lateral side of the radius towards the ulna, thus pronating the hand. Its deep fibers serve to keep the two bones in the forearm bound together. It also aids in wrist extension.
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