Odontoid Lateral Mass Interval (OLMI) asymmetry and rotary subluxation: a retrospective study in cervical spine injury.

The aim of the study was to evaluate the significance of odontoid lateral mass interval (OLMI) asymmetry on open-mouth view, in neck injury patients who have otherwise normal cervical spine x-rays. Thirteen neck injury patients were reviewed. Average age was 23.5 years (range, 16-30 years) and average follow-up was 15 weeks (range, 6-39 weeks). All the patients, referred from the casualty department, had computed tomography (CT) scans because of the OLMI asymmetry to rule out rotary subluxation. Clinically none of the patients had torticollis. CT scans were reported normal except for OLMI asymmetry, in 11 patients. Two patients were reported as having rotary subluxation and one was found, after normal initial plain films, to have an undisplaced lateral mass fracture of the atlas with bony avulsion of the transverse ligament. The average OLMI asymmetry was 3.1 mm (range, 2-4 mm). The authors concluded that although OLMI asymmetry has low sensitivity and specificity for true subluxation or instability, it may be a sign of significant cervical injury and should be evaluated with CT.