From the case:
Ulnar bow sign (illustration)
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Illustrations on the assessment of the ulnar bow sign.
Case Discussion
The ulnar bow sign is used to identify a bowing fracture of the ulna, which can be missed if not sought out properly, usually in the context of a traumatic radial head dislocation. The greatest distance from the ulna cortex to a line drawn from the distal metaphysis to the olecranon should be <1 mm.