Harris or axis ring: an aid in diagnosing low (type 3) odontoid fractures.

OBJECTIVE: To present our experience of diagnosing fractures of the odontoid process on lateral radiographs of the cervical spine that show the Harris (axis) ring. DESIGN: Retrospective study. SETTING: Teaching hospital, Belgium. SUBJECTS: 12 patients with multiple injuries, including cervical spine, 8 of them unconscious or uncooperative. INTERVENTIONS: Cross table lateral view of the cervical spine. MAIN OUTCOME MEASURE: Identification of otherwise hidden type 3 axial fractures. RESULTS: Diagnosis of low odontoid fractures in all cases. CONCLUSION: The Harris ring is disrupted in low odontoid fractures and intact in fractures of the odontoid process. Awareness of this sign will allow diagnosis of otherwise hidden axial fractures.