Atlanto-axial instability in children with Down syndrome.

One hundred fifty-eight patients with Down syndrome underwent roentgenologic examinations of the cervical spine in neutral position, in hyperflexion, and in hyperextension. Fifteen children with Down syndrome were found to have a distance between the joint surfaces of 5 mm and more. The majority of these children were asymptomatic, one child displayed hyperactive deep tendon reflexes and two children were symptomatic and underwent surgery.