Reassessment of the craniocervical junction: normal values on CT.

BACKGROUND AND PURPOSE As the standard of care for the evaluation of the cervical spine shifts from plain radiographs to multidetector row CT (MDCT), a re-examination of the normal anatomic relationships of the occipitovertebral articulations is needed. We aimed to define the normal anatomic relationships of craniocervical articulations on MDCT and address any discrepancies with currently accepted ranges of normal on plain radiographs. MATERIALS AND METHODS A total of 200 patients underwent an MDCT scan of the cervical spine with multiplanar reconstructions (MPR). We measured the basion-axial interval (BAI), basion-dens interval (BDI), Powers ratio, atlantodental interval (ADI), and atlanto-occipital interval (AOI) in each patient. After statistical analysis, we compared these values to previously accepted data on plain radiographs. RESULTS Ninety-five percent of the population was found to have a BDI less than 8.5 mm compared with 12 mm on data from plain radiographs. The Powers ratio demonstrated no significant difference compared with data obtained by plain radiographs. Ninety-five percent of the population was found to have an ADI less than 2 mm, compared with 3 mm previously accepted. The AOI demonstrated 95% of the population ranged between 0.5 mm and 1.4 mm. The BAI was difficult to reproduce on CT images. CONCLUSION Normal values for the craniocervical relationships on MDCT are significantly different from the accepted ranges of normal on plain radiographs. We propose these values as normal for the adult population.