A new method of screening for vertical atlantoaxial dislocation.

A new method for the screening and grading of vertical atlantoaxial dislocation is described. The Sakaguchi-Kauppi method is based on a pathologic process in the atlantoaxial joints and the grading system gives a reproducible (interobserver coefficient of variation = 0.062) tool for the screening of vertical dislocation and is also applicable to patients for whom earlier radiographs are not available. There were differences between the results obtained using Redlund's method and the new Sakaguchi-Kauppi method (chi 2 = 44.7, p less than 0.001). This difference stems from the variations in the height of the axis in the normal population and results in a sensitivity and specificity of 84.2% and 90%, respectively, for Redlund's method compared to the new method.