357 - Occiput, C1, and C2 Instrumentation

Abstract

The atlantoaxial joint is the most mobile and potentially the most unstable joint of the body. Acute atlantoaxial dislocation is associated with severe pain and spasm of muscles of the nape of the neck and a varying range of neurological deficits. On the other hand, chronic or longstanding atlantoaxial dislocation is associated with subtle and relentlessly progressive symptoms and neurological deficits and a host of secondary and natural protective musculoskeletal and neural alterations that are aimed to limit or reduce the effects of potential or manifest atlantoaxial instability and compression of neural structures between bones. Basilar invagination, Klippel-Feil abnormality, bone fusions, platybasia, Chiari formation, and syringomyelia are some such secondary manifestations of chronic atlantoaxial instability. Instability of the atlantoaxial joint is the nodal point of pathogenesis of the entire structural alteration, and atlantoaxial stabilization is the treatment. The atlantoaxial joint can be unstable even when the facets of atlas and axis are in alignment and there is no neural or dural compression. Such instability is referred to as central or axial atlantoaxial instability. Direct facet fixation using screws in the lateral masses of the atlas and axis after opening of the articulation, denuding of articular cartilage, and packing of the articular cavity with bone graft provides an opportunity to achieve solid arthrodesis.