Table 1.

Criteria for cranial settling in rheumatoid

Measurement/Criteria	Description	Definition of abnormal
McRae’s line	Tip of the basion to opisthion	If any portion of the odontoid extends superior to this line
McGregor’s line	Hard palate to caudal aspect of the opisthion	> 4.5 mm of the dens is superior to this line
Chamberlain’s line	Hard palate to the midpoint of the opisthion	> 3 mm of the dens extends superior to this line
Ranawat’s1	Distance from the C2 pedicle to a line bisecting the ring of C1	< 15 mm in males, < 13 mm in females
Redlund-Johnell and Peterson1	Distance from the inferior end plate of C2 to McGregor’s palato-occipital line	< 34 mm in males, < 29 mm in females
Clark’s station of the atlas1	Position of C1 with relation to the body of C2 (divided into thirds)	If C1 extends below the rostral third of C2

¹Recommended criteria by Riew et al[79].