Pronator quadratus muscle
Pronator quadratus is a quadrangular, thin, short and flat muscle lying within the anterior compartment of forearm. It is part of the deep group of forearm flexors, together with flexor digitorum profundus and flexor pollicis longus. These three muscles are overlaid by the superficial group of forearm flexors.
Thanks to your pronator quadratus, you can turn your forearm and palm in order to write or type on a computer. These actions are possible due to nervous transmission by the median nerve which supplies this muscle.
|Origins||Distal anterior surface of ulna|
|Insertion||Distal anterior surface of radius|
|Actions||Proximal radioulnar joint: Forearm pronation|
|Innervation||Median nerve (anterior interosseous nerve, C7, C8)|
|Blood supply||Anterior interosseous artery|
This article will discuss the anatomy and functions of the 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.
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.
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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.
Pronator quadratus produces forearm pronation by acting on the proximal radioulnar joint. 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.