Method of measuring atlantooccipital instability according to Wiesel and Rothman. These lines are drawn on flexion and extension lateral radiographs, and translation should be no more than 1 mm. Atlantal line joins points 1 and 2. Line drawn perpendicular to atlantal line at posterior margin of anterior arch of atlas. Point 3 is basion. x is distance from point 3 to perpendicular line measured in flexion and extension. Difference represents anteroposterior translation.