If the decision is made to apply gentle adjusting procedures, the response of the patient should be carefully monitored. If an adverse reaction occurs, an alternative procedure should be considered. Other variations may also occur in the upper cervical spine. An increase may be due to congenital absence of the transverse ligament as seen in Down syndrome. Although previously considered of little clinical significance, increased participation by such children in athletic activity requires careful assessment of the upper cervical spine.
Variations also occur in the development of the odontoid process.
The tip of the dens develops from an ossification center which appears at age two and unites at 10 to 12 years. If such union does not occur, a terminal ossicle remains. If the dens remains ununited at its base, the condition is termed as os odontoideum. Hypoplasia or congenital absence of the dens may also occur, resulting in an unstable articulation. In cases of instability caused by absence of rupture of the transverse ligament, or instability caused by variations in the development of the odontoid process, caution must be employed.