Occipito-atlantal translation in Down's syndrome.

Several cases of occipito-atlantal instability have been reported in patients with Down's syndrome. However, standards for radiographic measurement and normal values for translational motion at the occiput-C1 level have not been established for the Down's patient. A retrospective analysis of 102 flexion and extension lateral cervical spine radiographs of 73 patients with Down's syndrome was performed. Patients with congenital cervical spine anomalies, C1-C2 instability, or previous neck surgery were excluded. Occiput-C1 translation was measured by the technique described by Wiesel and Rothman. In normal adult patients, occiput-C1 translation should be no more than 1 mm by this method. Analysis of the data demonstrated a range of 0 to 10 mm, with a mean of 2.62 mm and a standard deviation of +/- 1.94 mm. Only 30 sets of films (29%) representing 27 patients (37%) showed anteroposterior translation of 1 mm or less. This laxity was not dependent on patient age in the current study group. A review of these patients' medical records did not disclose any evidence of impaired neurologic function related to cervical spine instability. The authors' data suggest that the prevalence and magnitude of occipito-atlantal instability in Down's syndrome is greater than previously appreciated.