The pronator quadratus is a flat, square muscle binding the distal radius and ulna together, acting as the primary pronator at low speeds and stabiliser of the distal radioulnar joint throughout forearm rotation. Its position deep to the flexor tendons at the wrist makes it visible on MRI but not palpable clinically. Bruising and swelling of the pronator quadratus fat pad on lateral wrist radiograph is an indirect sign of occult distal radius fracture.
| Origin | Anterior surface of the distal quarter of the ulna |
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| Insertion | Anterior surface of the distal quarter of the radius |
| Nerve Supply | Anterior interosseous nerve (C8, T1) |
| Blood Supply | Anterior interosseous artery |
| Actions | Pronation of the forearm — the primary pronator at low loads and speeds; Stabilises the distal radioulnar joint during forearm rotation |
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At low forearm rotation speeds it is the primary pronator, with the pronator teres being recruited increasingly at higher speeds and loads. Its stabilising effect on the DRUJ is important for wrist loading tasks.
Anterior interosseous nerve syndrome specifically paralyses pronator quadratus, FPL, and index FDP, and the degree of pronation weakness (tested with the elbow fully flexed to eliminate pronator teres contribution) helps localise the lesion. Pronator quadratus disruption during volar plate fixation of distal radius fractures impairs DRUJ stability and wrist pronation strength, justifying its repair during fracture surgery.
The pronator quadratus is not palpable as it lies deep to the flexor tendons at the distal forearm. It is assessed functionally by measuring forearm pronation strength with the elbow fully flexed.
Tearing or disruption during distal radius fracture or its fixation producing DRUJ instability and pronation weakness, managed with repair at the time of fracture fixation.
