Interfacetal intra-articular spacers: Emergence of a concept.

Atlantoaxial joint instability can be identifi ed by facetal malalignment or even by direct observation and bone handling during surgery. We have recently classifi ed the diagnosis of atlantoaxial instability and basilar invagination on the basis of facetal malalignment and instability.[6,7] We observe that there may be instability even when the atlantodental interval is not aff ected and even when there is no evidence of cord alterations or changes. Atlantoaxial instability that is diagnosed only by clinical evaluation and by manual manipulations and without any radiological abnormality has been termed by us as central or axial atlantoaxial instability.[6,7] Intra-articular spacers can be deployed for all forms of atlantoaxial instability.