Pronator Quadratus Muscle – Anatomy, Nerve Supply

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Pronator Quadratus Muscle – Anatomy, Nerve Supply

Pronator Quadratus Muscle 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 anterior interosseous artery.

Structure of Pronator Quadratus Muscle

Its fibres run perpendicular to the direction of the arm, running from the most distal quarter of the anterior ulna to the distal quarter of the radius. It has two heads: the superficial head originates from the anterior distal aspect of the diaphysis (shaft) of the ulna and inserts into the anterior distal diaphysis of the radius, as well as its anterior metaphysis. The deep head has the same origin, but inserts proximal to the ulnar notch.[rx] It is the only muscle that attaches only to the ulna at one end and the radius at the other end.

Anatomy of Pronator Quadratus Muscle

Pronator quadratus
  • Origin: distal ulna
  • Insertion: distal radius
  • Action: pronation of the forearm
  • Innervation: median nerve

Origin and Insertion of Pronator Quadratus Muscle

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.

Nerve Supply of Pronator Quadratus Muscle

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.

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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 of Pronator Quadratus

Pronation of forearm (Pronatio antebrachii)
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. Moreover, this muscle can be absent in some humans, however, that does not affect the action of pronation very notably, as the pronator teres does the major role in that action.

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.

References

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