Craniovertebral abnormalities in Down's syndrome.

The ligamentous laxity associated with atlantoaxial subluxation has been assumed as a normal occurrence in 15-20% of Down's syndrome patients. The occipitoatlantoaxial instability that accompanies this entity has been poorly recognized. The medical records and radiographic findings of 18 symptomatic patients with Down's syndrome and cervicomedullary compromise were reviewed (1979-1991). All patients were evaluated prospectively under protocol for abnormalities of the cranial vertebral junction. There were 11 males and 7 females (age 3-42). 'Fixed' atlantoaxial luxation was seen in 8 (5 developed precipitous onset of cervical medullary compression). Occipitoatlantoaxial instability was present in 9 and associated rotary luxation in 9. The average predental space was 8 mm in the neutral position in 18 individuals. Two adolescents had previously undergone atlantoaxial dorsal fusion with subsequent progressive basilar invagination due to unrecognized occipitoatlantal instability. An os odontoideum was seen in 3 patients. Irreducible invagination in 2 was treated with anterior decompression followed by dorsal occipital cervical fixation. The occipital cervical fixation was utilized in 10 individuals. Atlantoaxial dorsal fusion was made in 7 and 2 patients with acute rotary luxation of C1 and C2 were treated with immobilization. Halo immobilization in two individuals following a dorsal occipital cervical fixation produced an anterior fusion at the cranial vertebral complex indicating active vertebral ligamentous pathology. The review focuses on increased incidence of occiput cervical instability in the spectrum of craniovertebral junction abnormalities associated with Down's syndrome. A large percentage has an odontoid ossicle probably as a result of repeated minor trauma. The results of surgical stabilization have been shown to be excellent.