Pronator quadratus sign

Last revised by Assoc Prof Craig Hacking on 29 Apr 2021

The pronator quadratus 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.

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 to 98%; thus a negative pronator quadratus sign does not exclude fracture 1,2,4.

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

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 4, has suggested a cut-off of <8 mm (female) and 9 mm (male) on lateral x-rays as a cut-off for normal.

It was first described by MacEwan in 1964 3.

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Cases and figures

  • Case 1: normal
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  • Case 1: annotated
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  • Case 2: anterior bowing
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  • Case 3: displacement
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  • Case 4
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  • Case 5
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  • Case 6
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