Hello there! It’s Matt from Kenhub, and in this tutorial, we will be discussing the pronator quadratus. The pronator quadratus muscle is one of the three deep flexors of the forearm lying at the ventral forearm as you see on this image. They run under the flexor digitorum superficialis close to the radius and ulna and, for that reason, they are difficult to palpate.
The pronator quadratus muscle arises from the distal end of the ulna on the anterior surface and extends horizontally to the radius attaching at the anterior margin at the distal quarter of the radius giving the muscle a square-shaped appearance. The pronator quadratus is the deepest muscle in the anterior forearm.
The median nerve serves as the innervation for the pronator quadratus. The innervating branch, the anterior interosseus nerve, arises approximately 5 cm underneath the medial epicondyle of the humerus from the median nerve.
The deep flexors of the forearm are mainly responsible for flexion of the hand and finger joints. The pronator quadratus pulls the radius medially thus causing pronation at the radioulnar joint. So, this muscle is not so hard to remember. It is a square-shaped muscle. Think quad that pronates the radioulnar joint. So, pronator quadratus makes sense.
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