Muscles pronating the forearm

Pronator teres

Pronator quadratus

Brachioradialis

Pronator quadratus

Pronator quadratus is a fleshy, quadrangular muscle lying within the flexor compartment of the forearm. It passes transversely from the lower quarter of the anterior surface of the ulna to the lower quarter of the anterior surface of the radius. Some of its deeper fibres attach to the triangular area above the ulnar notch of the radius.

Nerve supply

Pronator quadratus is supplied by the anterior interosseus branch of the median nerve, root value C8, T1. The skin overlying the muscle is supplied by roots C6, 7, 8.

Action

Pronator quadratus initiates pronation of the forearm. The transverse nature of its fibres allows the lower ends of the radius and ulna to be held together when upward pressure is applied, for example when the hand is weight-bearing. It therefore protects the inferior radio-ulnar joint.

Palpation

Pronator quadratus is difficult to palpate because of its deep position, but if firm pressure is applied between the long flexor tendons in the lower part of the forearm, contraction of the muscle may be felt when it acts against resistance.