Parameter	Adults	Children
Predental space	3 mm or less	4 to 5 mm or less
C2-C3 pseudosubluxation	3 mm or less	4 to 5 mm or less
Retropharyngeal space	Less than 6 mm at C2, less than 22 mm at C6*	⅓ to ⅔ vertebral body distance anteroposteriorly
Angulation of spinal column at any single interspace level	Less than 11 degrees	Less than 11 degrees
Cord dimension	10 to 13 mm	Adult size by 6 years of age