Pronator quadratus sign
Citation, DOI & article data
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 to 98%; thus a negative pronator quadratus sign does not exclude 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 4, has suggested a cut-off of <8 mm (female) and 9 mm (male) on lateral x-rays as a cut-off for normal.
History and etymology
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:
- 1. Moosikasuwan J. The Pronator Quadratus Sign. Radiology. 2007;244(3):927-8. doi:10.1148/radiol.2443042063 - Pubmed
- 2. Jorge A. Soto, Brian C. Lucey. Emergency Radiology. (2009) ISBN: 9780323054072 - Google Books
- 3. James R. Doyle. Surgical Anatomy of the Hand and Upper Extremity. (2003) ISBN: 9780397517251 - Google Books
- 4. Loesaus J, Wobbe I, Stahlberg E, Barkhausen J, Goltz J. Reliability of the Pronator Quadratus Fat Pad Sign to Predict the Severity of Distal Radius Fractures. World J Radiol. 2017;9(9):359-64. doi:10.4329/wjr.v9.i9.359 - Pubmed
- 5. MacEwan D. Changes Due to Trauma in the Fat Plane Overlying the Pronator Quadratus Muscle: A Radiologic Sign. Radiology. 1964;82(5):879-86. doi:10.1148/82.5.879 - Pubmed
- 6. Manitoba opera (@ManitobaOpera). 2021.11.21. Happy 97th Birthday to Dr. Douglas MacEwan, WWII veteran and Manitoba Arts hero. One year ago today, Dr. MacEwan completed https://twitter.com/ManitobaOpera/status/1458894871125798921 [Accessed 09 January 2022].