Pronator quadratus sign

Last revised by Mostafa Elfeky on 13 Mar 2024

The pronator quadratus sign, also known as MacEwan sign, can be an indirect sign of distal forearm trauma. It relies on displacement of the fat pad that lies superficial to the pronator quadratus muscle as seen on a lateral wrist radiograph.

Displacement, anterior bowing, or obliteration of the fat plane in the setting of trauma may indicate a distal radius or ulna fracture. Various studies have described a high specificity but wide-ranging sensitivity for fracture ranging from 26-98%; thus a negative pronator quadratus sign does not exclude a fracture 1,2,4.

On lateral wrist radiographs, the pronator fat pad normally appears as a thin radiolucent triangle, with its base attached to the palmar surface of the distal radius 1,2. It is observed ~90% of the time 1. One study has suggested <8 mm (female) and 9 mm (male) on lateral x-rays as a cut-off for normal 4.

It was first described by Douglas W MacEwan (fl. 2021) 6, a Canadian radiologist, in 1964 3,5.

In the absence of trauma, there are other causes for a positive pronator quadratus sign:

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