[New methods for measuring atlanto-axial vertical subluxation in rheumatoid arthritis by MR imaging].

We proposed two new methods of measuring atlanto-axial vertical dislocation in rheumatoid arthritis by MR imaging. One is the distance from the subdental synchondrosis of the axis to the diameter of the ring of the atlas. The other is the distance from the midpoint of the anteroposterior ends of the inferior margin of the axis to the diameter of the ring of the atlas. Values were also determined by the Ranawat method and the Redlund-Johnell method. There was good correlation between values determined by the new methods and those determined by the Ranawat method and Redlund-Johnell method.