'Atlas shrugged': congenital lateral angular irreducible atlantoaxial dislocation: a case series of complex variant...

The commonly described congenital atlanto-axial dislocation and Basilar-Invagination is antero-posterior or rotational or vertical plane. However, congenital dislocation in lateral plane has received scant attention. The purpose of this manuscript is to describe this unusual entity and discuss its management.

The clinic-radiological feature of seven patients with congenital lateral angular AAD (CLAAAD) were studied and managed. The unilateral C1 facet had subluxed lateral to C2-3 complex. The C1 and C2 facets were drilled comprehensively and repositioned with distraction, placement of metallic spacers and facet manipulation after insertion of screws. The post operative outcome was studied.

The presentation is usually with neck tilt (progressive in 3) and/or progressive spastic quadriparesis. The mean C1-2 tilt was 25.2°. C1 was bifid in six patients. C1 lateral mass was assimilated with occipital condyle on dislocated side in and the other side was normal (6 patients). The dislocated C1-2 joint was abnormally oblique as compared to contralateral side. The relationship of occiput and C1 was normal. Correction of dislocation and lateral tilt was achieved in all patients with subsequent correction of neck tilt and deficits. One patient required reoperation.

The acute angulation of joint on one side and near normal on other side leads to differential vertical movement, further accentuated by splaying of bifid C1. The entity is seen in young patients and often present with neck tilt and spastic quadriparesis. Management requires reshaping the joints and facet manipulation. If the reshaping is inappropriate, the joint is likely to redislocate before fusion occurs.