C1-2 and C2-3 Instability in the Presence of Hypoplastic Posterior Elements of C2 Vertebra: Report of 2 Cases.

Abstract

We present 2 cases involving a previously unreported clinical situation in which basilar invagination, atlantoaxial instability, and C2-3 instability were associated with a bifid posterior arch of the axis bone. Two young males presented with limb weakness, spasticity, and paresthesias. Both patients had altered voice quality, with reduced and thin volume, and difficulty sleeping supine. Radiologic imaging showed an absence of the posterior elements of the C2 vertebrae. The C3 spinous process mimicked the C2 spinous process in shape and size. C1-2 and C2-3 posterior fixations were performed. C1-2 and C2-3 fixation resulted in firm fixation of the region and a remarkable clinical recovery. The most significant features were an immediate postoperative improvement in voice quality and the ability to sleep comfortably in the supine position.