Atlantooccipital instability in Down syndrome.

Atlantooccipital instability is an uncommon and usually lethal result of major trauma. Nontraumatic cases of instability at this site are rare. We report the findings in two children with Down syndrome who have striking atlantooccipital subluxation demonstrated on flexion and extension radiographs. Since there is increasing radiologic evaluation of cervical spine stability in patients with Down syndrome who wish to participate in athletic activities, the status of the atlantooccipital joint needs careful assessment, especially after cervical fusion for C1-C2 instability.