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.
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Measurement
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.
Interpretation
- 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.
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