An atlantodental interval (ADI) of more than 5 mm on lateral cervical spine radiography indicates instability 1) 2). This is more than the 3-mm adult value because of the increased cartilage content of the odontoid and ring of the atlas in children, as well as the increased ligamentous laxity in children. In extension, overriding of the anterior arch of the atlas on top of the odontoid also can be seen in up to 20% of children 3).