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Atlantoaxial instability and Down syndrome.

Since Spitzer and co-workers1 described "forward displacement of the atlas on the axis" in persons with Down syndrome 25 years ago, approximately 30 reports have been published on atlantoaxial instability, subluxation, and dislocation in patients with this chromosomal disorder. In previous epidemiologic studies, the prevalence of atlantoaxial instability in persons with Down syndrome was found to be between 9% and 31%.1-4 In our recent large-scale investigation, we found that, of 404 patients with Down syndrome, 53 (13.1%) had asymptomatic atlantoaxial instability and six (1.5%) had symptomatic atlantoaxial subluxation.5 Atlantoaxial instability has come into the lime-light during the past few years primarily because of regulations published by Special Olympics, Inc, concerning the participation of individuals with Down syndrome in Special Olympic sports activities.6