In the sagittal plane, divide the odontoid process into three equal parts, “stations,” and determine the level at which the anterior arch of C1 falls
Station I: anterior arch of C1 falls at the superior third (normal) Station II: anterior arch of C1 falls at middle third (mild) Station III: anterior arch of C1 falls at inferior third (severe)
Ranawat criterion
Distance between the center of the C2 pedicle and the transverse axis of C1 measured along the axis of the odontoid process
Measurements less than 15 mm (males) or 13 mm (females) are indicative of CS
Redlund-Johnell criterion
The distance between the inferior margin of C2 vertebral body and a line drawn from the posterior tip of the hard palate to the caudal cortical margin of the occiput (McGregor Line)
Measurements less than 34 mm (males) or 29 mm (females) are indicative of CS
