Pronator quadratus

The pronator quadratus muscle is a flat, quadrilateral muscle located in the distal forearm, forming a key part of the deep layer of the anterior compartment.

Origin

It originates from the medial border and anterior surface of the distal one-fourth of the ulna.

Insertion

Its fibers extend laterally to insert onto the lateral border and anterior surface of the distal one-fourth of the radius.

The pronator quadratus lies deep to the flexor digitorum profundus and flexor pollicis longus muscles, with these flexors overlying it in the distal forearm.

Innervation

The muscle is innervated by the anterior interosseous nerve, a branch of the median nerve, which enters the muscle on its deep surface in the distal forearm.

Actions

The pronator quadratus is the primary muscle responsible for pronation of the forearm, and it also contributes to stabilization of the distal radioulnar joint.