Does the third cervical vertebra need to be rimmed for odontoid screwing? A hypothetical study of anatomic landmarks.

Background The superoanterior portion of the third cervical vertebra may need to be rimmed during anterior odontoid screw fixation procedures. We, therefore, retrospectively evaluated radiological data to analyze the anatomical relation between the second and third cervical vertebra of the patients who were operated by an anterior cervical approach with respect to the question if odontoid screw fixation would have been possible without rimming or not. Patients and methods Patients in whom the anterior approach for cervical disc prolapse and/or cervical stenosis was used between 2008 and 2010 were included in this study. The odontoid screw angle, and the angle between the lower second and the upper third cervical vertebral endplate were measured on intraoperative cervical lateral radiographs. If the screw line passed through the superior anterior portion of the third vertebral body, it was determined that the third cervical vertebra would have been needed to be rimmed if odontoid screwing would have been planned. Results 100 patients were included. There were 50 males and 50 females with a mean age of 47.9 years (mean +/- SD: 47.9 +/- 12.6 years). The mean odontoid screw angle, and the angle between the lower second and the upper third cervical vertebral endplate were 65.61 degrees +/- 3.75 degrees and 15.24 degrees +/- 4.85 degrees (nonparallel vertebral endplates only), respectively. The odontoid screw angle, in which the third cervical vertebra would not have been needed to be rimmed, was 63.87 degrees +/- 2.84 degrees. In addition, the odontoid screw angle in which the third cervical vertebra would have been needed to be rimmed was 67.28 degrees +/- 3.77 degrees. Conclusion The odontoid screw angle may be easily measured on lateral radiographs. In cases in which the odontoid screw angle is 67.28 degrees +/- 3.77 degrees or higher, the superoanterior portion of the third cervical vertebra would be needed to be rimmed for proper screw fixation of odontoid fractures.