Ulnar bow sign
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The ulnar bow sign is a radiographic indication of a plastic deformity of the ulna, its assessment is quite useful in the case of a suspected "isolated" radial head dislocation in the pediatric population 1,3.
"Isolated" dislocation of the radial head is almost always in fact associated with a bowing fracture of the ulna 2,3.
Draw a line from the distal ulna to the olecranon on a true lateral forearm radiograph. The ulnar bow is the maximum distance between the drawn line and the dorsal border of the ulna 1,3.
- normal: 0.01 ± 0.1 mm 1, also reported as 1.07 ± 0.7 mm 4
- ulnar bowing: >1 mm
A maximum ulnar bow >1 mm has classically been considered a sign of ulnar bowing 3. However, some authors have reported a normal range of 1.07 ± 0.7 mm 4.
- 1. John M. Flynn, David L. Skaggs, Peter M. Waters. Rockwood and Wilkins' Fractures in Children. (2014) ISBN: 9781451143935 - Google Books
- 2. John A. Herring. Tachdjian's Pediatric Orthopaedics: From the Texas Scottish Rite Hospital for Children. (2013) ISBN: 9781437715491 - Google Books
- 3. Lincoln T & Mubarak S. “Isolated” Traumatic Radial-Head Dislocation. Journal of Pediatric Orthopaedics. 1994;14(4):454-7. doi:10.1097/01241398-199407000-00006 - Pubmed
- 4. Jeong W, Lee D, Kyung B, Lee S. Factors Affecting Assessment of Ulnar Bowing in Radiography. Journal of Pediatric Orthopaedics. 2012;32(1):48-53. doi:10.1097/bpo.0b013e31823db04a - Pubmed