The axis ring: a forgotten semiologic sign in the detection of low odontoid fractures.

The axis ring is a very important sign in the detection of low odontoid fractures. It can be the only radiological sign of a type III (low) odontoid fracture in a polytraumatised patient. As these are unstable fractures, their detection is important, even before a spiral CT is performed. Tracheal tube placement in patients with type III odontoid fractures should be performed very carefully to prevent displacement of the fracture. This sign, which has been published more than once in the radiological literature, seems to be not so well known by the physicians nor by a lot of radiologists. We can call it a forgotten semiologic sign. It is not even mentioned in the ATLS (Advanced Trauma Life Support) criteria for evaluation of the cervical spine.