Three-Dimensional Configuration and Morphometric Analysis of the Lateral Atlantoaxial Articulation in Congenital Anomaly With Occipitalization of the Atlas

Study Design. Observational and quantitative study with 3-dimensional (3D) computerized tomographic (CT) analysis. Objective. To establish the 3D configuration and morphometric data of obliquity of the lateral atlantoaxial articulations (LAA) in congenital anomaly with occipitalization. Summary of Background Data. Plane radiographs and normal CT scans cannot clearly demonstrate the configuration of LAA as the hindrance of circumambient bony structures. The morphology of anomalous LAA with occipitalization is underreported. Methods. A series of 63 cases with occipitalization and 20 control subjects underwent thin-slice CT scanning. The 3D configuration of LAA were analyzed and categorized based on the degree of olisthy and inclination orientation of the atlantoaxial articular facets (AAF). The obliquity of the AAF was measured in reconstructed sagittal and coronal planes, respectively. Results. Four types of configuration of LAA with occipitalization were found: type I, characterized by slight anteversion of LAA without olisthy of the inferior and superior facets (16% of 126 sides); type II, characterized by partial olisthy of the 2 facets and evident anteversion of LAA (48%); type III, defined by the separation or complete olisthy of the 2 facets (13%); and type IV, wherein the articular facets sloped dorsally (23%). Forty-eight of 49 cases in the former 3 types wherein AAF sloped ventrally had atlantoaxial dislocation (AAD). All type IV cases wherein AAF sloped dorsally had no AAD. In control subjects, LAA had no evident obliquity of anteversion or retroversion. Conclusion. Instability at the C1-C2 junction in congenital anomaly with occipitalization is likely a direct result of the anteversion of LAA and bony malformation of this region, and it aggratates with the increasing obliquity of anteversion of the AAF. Demonstrating 3D morphological changes of LAA may provide a new means to diagnosis instability in congenital anomaly at craniovertebral junction and a basis for rational surgical treatment.