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Ulnar bow sign

Last revised by Dr Ammar Haouimi on 30 Jul 2022

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 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.

The normal ulnar bow has been reported as 0.01 ± 0.1 mm. The ulnar bow sign represents the abnormal plastic deformity present if the maximum ulnar bow is >1 mm 1,3.

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Cases and figures

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