Pronator quadratus muscle

Origin and insertion

Pronator quadratus is a flat, short, quadrilateral muscle that originates from the anterior surface of distal shaft of ulna and an aponeurosis that partially covers the muscle. Superficial muscle fibers project laterally and distally towards the anterior surface of distal shaft of radius, where they also insert. Deeper fibers insert superiorly to the ulnar notch of radius.

Relations

Pronator quadratus is the deepest muscle in the anterior (flexor) compartment of forearm. Hence, it is located underneath the remaining deep forearm flexors; flexor digitorum profundus and flexor pollicis longus. Pronator quadratus is located distally in the forearm, covering the interosseous membrane superficially.

The anterior interosseous artery pierces the interosseous membrane proximal to pronator quadratus as it passes from the anterior to the posterior compartment of forearm. A branch of the anterior interosseous artery also descends deep to pronator quadratus on its way towards the palmar arch. The radial artery travels anteriorly to pronator quadratus, while its palmar carpal branch arises close to the distal border of the muscle. The anterior interosseous nerve courses posteriorly to the deep surface of pronator quadratus.

CTA: Master the attachments, innervation and actions of every muscle of the human body in an easy and efficient way using Kenhub’s muscle anatomy and reference charts!

Innervation

Pronator quadratus is innervated by the anterior interosseous nerve of forearm, with contributions mainly from C7 and C8 spinal nerves. The anterior interosseous nerve is a branch of the median nerve, which stems from the brachial plexus.

This quiz challenges you on the flexors of the forearm. Give it a spin!

Blood supply

Pronator quadratus receives arterial blood from the anterior interosseous artery, which stems from the common interosseous artery. The latter is a branch of the ulnar artery.

Functions

Pronator quadratus produces forearm pronation by acting on the radioulnar joints. During this movement, the head of radius pivots around the ulna, turning the palm posteriorly or inferiorly, if the forearm is flexed. This action of pronator quadratus is aided by the pronator teres and brachioradialis muscles.The location of this muscle across the distal forearm attributes it a protective role. When upward pressure is applied during weight-bearing activities, pronator quadratus holds together the distal ends of the radius and ulna, protecting and stabilizing the distal radioulnar joint. It also protects the interosseous membrane during forced and rapid forearm rotations by dissipating the forces pulling on the membrane.