Atlantoaxial instability in Down's syndrome: clinical and radiological screening.

One hundred and thirty children with Down's syndrome were screened for the presence of atlantoaxial instability, using both clinical examination and radiographs of the cervical spine taken in flexion and hyperextension views. Seven children were found to have radiological evidence of atlantoaxial instability, with an atlanto-dens interval greater than 5.0 mm in one or all positions. Although a full clinical history was obtained from the attending parent and each child underwent a complete neurological examination, there were no factors detected which differentiated between those with radiological evidence of atlantoaxial instability and those with a normal atlantodens distance. It is recommended that children with Down's syndrome be screened twice, at the ages of 5-10 years and at 15 years.