The evaluation of 2 patients with increased motion of their occiput on their atlas stimulated a search for the normal relationship of this articulation in flexion and extension. Flexion-extension lateral roentgenograms from 20 normal volunteers were evaluated. The normal range of horizontal translation in flexion and extension as measured from the basion of the occiput to the tip of the odontold was found to be no more than 1 mm. Of the 2 patients with excessive motion between the occiput and the atlas, one had an associated congenital fusion of C1ndash;2 and C3ndash;4; the other patient had congenital fusion of C2ndash;3. Both presented with subjective complaints of weakness in the extremities with motion of the cervical spine and neck pain with occipital radiation. Rellef in both patients was obtained by posterior fusion from the occiput to C2. While the cause of this excessive motion is not clear, it is proposed that a high cervical fusion produces more stress at the atlanto-occipital articulation which gradually causes the ligaments to stretch, resulting in hypermobility. It is recommended that any patient with a high congenital fusion of the cervical spine should be followed very closely; and with any subjective complaints, flexion-extension roentgenograms should be obtained, with careful attention directed to the occipitoatiantal joint.
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