Dislocation of the Atlas in Mongolism

Anumber of roentgenographic manifestations of mongolism have already been described. Attention has been called to abnormalities of the cranial bones ((1, 3–5) and to characteristic features of the pelvis and hips (2). The purpose of this paper is to call attention to yet another finding, dislocation of the atlas, which appears to be significantly frequent in this disease. We recently observed such a dislocation in a ten-year-old mongoloid female who was referred to The University of Michigan Medical Center, Ann Arbor, Mich., because of accelerated skeletal maturation. The atlanto — odontoid distance measured 8 mm in the neutral position (Fig. 1). There were no symptoms or signs referable to the cervical spine and no history of trauma or other condition (8–10) which might explain this abnormality. It was therefore of interest to learn whether atlas dislocation was particularly common among mongoloid children. Method Cervical spine films of 18 mongoloids were obtained in neutral and flexion positions. Four patients were seen at the University Hospital and 14 were from the Coldwater State Institution and Training School, Coldwater, Mich. The target-film distance was 60 in. Strict attention was paid to proper positioning, the head being held in position during the exposure. Laminagrams were obtained in one case. In none was there a history of previous trauma, rheumatoid arthritis, or related diseases. Results The atlanto-odontoid interval was measured at the inferior aspect of the anterior atlanto-odontoid joint as shown in Fig. 1, B. The measurements and the respective ages of these patients are given in Table 1. The figures are uncorrected for magnification. In 4 cases the atlantoodontoid interval was greater than 5 mm. In 9 others this measurement was 4 mm or greater. In 3, in whom the atlantoodontoid distance was 4 mm or less, the atlas nevertheless appeared tilted laterally, particularly in flexion (Fig. 2). The significance of this finding is uncertain. It may indicate atlanto-axial instability despite the normal atlanto-odontoid distance, since one alar ligament can be expected to tighten in lateroflexion. Such tightening would serve to restrict the degree of forward displacement of the atlas in cases of insufficiency of the transverse ligament (11). In a 56-year-old mongoloid with an atlanto-odontoid measurement of 9 mm (Fig. 3) there was narrowing of the disks at C2-3 and C3-4 with vertebral end-plate erosion at the former site. This may have been degenerative in nature, but its significance is uncertain. There was no history of trauma or rheumatoid or infectious arthritis. There were 3 patients with spina bifida of Cl and 2 others in whom this was suspected. Discussion Spitzer et al. in a study of the skull, teeth, and lenses in mongolism, briefly mentions observing anterior atlas displacement in 9 of 29 cases but did not give measurements or other details (5).