Facet-occiput slope angle: A novel predictor of cage placement feasibility during surgery in basilar invagination patients.

Background And Aim: Direct posterior reduction and manipulation of the C joints, accompanied by placement of spacers, is the state-of-the-art technique for treating basilar invagination (BI) and atlantoaxial dislocation (AAD). The hindrance of occiput to reaching up to the true atlantoaxial facets (AAF) during the surgery remains challenging for cage placement. The aim of this study was to explore an objective and precise method of measuring the effect of the hindrance of occiput to reaching up to the true AAF and cage placement during surgery.