The costal hook sign is a chest x-ray feature seen in some cases of flail chest. It represents the rotation of a fractured rib along its long axis, something that is only possible if a second fracture is present along its length, even if the second fracture is not visible 1.
- 1. Jackson A, Fields JM, Wong-You-Chong JJ. The costal hook: an indicator of occult flail segment in chest trauma. European journal of radiology. 13 (1): 69-71. Pubmed