The utility of MRI in the evaluation of odontoid fractures.

STUDY DESIGN

Retrospective radiographic review.

OBJECTIVE

The purpose of this study was to reassess the utility of magnetic resonance imaging (MRI) in the assessment of type II and shallow type III odontoid fractures.

SUMMARY OF BACKGROUND DATA

The authors of previous studies have reported a 10% incidence of transverse atlantal ligament (TAL) injury with odontoid fractures and suggested that all odontoid fractures be evaluated preoperatively with MRI.

METHODS

A retrospective radiographic review was performed on all odontoid fractures treated with anterior screw fixation from 1987 to 2006. Patients were not screened for TAL injury with MRI or dynamic radiographs before surgery. Each patient had dynamic studies using intraoperative fluoroscopy after screw placement. Evidence of TAL injury was also evaluated on follow-up radiographs by measuring the atlantodental interval (ADI) on neutral, flexion, and extension films. For the purpose of this study, an ADI>3 mm indicated possible TAL injury. Neutral follow-up radiographs were available for 77 patients (mean follow-up, 17.5 mo), and flexion/extension films were available for 34 patients (mean follow-up, 16.4 mo). The mean ADI of the patients with neutral films was 1.1 mm (range=0.5 to 2.1 mm). The mean ADI of the patients with flexion/extension films was 1.2 mm (range=0.6 to 1.8 mm) for flexion and 1.2 mm for extension (range=0.5 to 2.8 mm). There was no evidence of atlantoaxial instability to suggest TAL disruption.

CONCLUSIONS

The results of our study demonstrate that the patients with type II and shallow type III odontoid fractures do not require MRI screening for TAL injury. We found no cases of patients with late instability to suggest that a TAL injury was missed.