Pronator quadratus sign
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:
- muscle strain or hematoma
- inflammatory conditions
- infectious conditions, e.g. osteomyelitis, cellulitis
- septic arthritis of the wrist
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 MacEwan in 1964 3.
- 1. Moosikasuwan JB. The pronator quadratus sign. Radiology. 2007;244 (3): 927-8. doi:10.1148/radiol.2443042063 - Pubmed citation
- 2. Soto JA, Lucey B. Emergency Radiology: The Requisites. Mosby. ISBN:0323054072. Read it at Google Books - Find it at Amazon
- 3. Doyle JR, Botte MJ. Surgical Anatomy of the Hand and Upper Extremity. Lippincott Williams & Wilkins. (2003) ISBN:0397517254. Read it at Google Books - Find it at Amazon
- 4. Loesaus J, Wobbe I, Stahlberg E, Barkhausen J, Goltz JP. Reliability of the pronator quadratus fat pad sign to predict the severity of distal radius fractures. (2017) World journal of radiology. 9 (9): 359-364. doi:10.4329/wjr.v9.i9.359 - Pubmed