Management of craniocervical junction dislocation

The discovery of a craniocervical junction malformation requires management in three steps: (1) The patterns must be recognized using tomographic meas urements (Chamberlain's line, Wackenheim's line). Dynamic flexion-extension studies are necessary to assess stability or instability. Stable patterns range from platybasia to basilar invagination, with gradual deformation, an d are frequently associated with Chiari malformation. Unstable patterns cha racterized by odontoid instability are the equivalent of an odontoid fractu re. The origin is malformative (hypoplasia, aplasia of the dens, os odontoi dum), but the last may be difficult to distinguish from an old odontoid fra cture. They are found in many syndromes (Down, Morquio, etc.). Unstable atl antoaxial patterns with atlas assimilation are hardly reducible; they evolv e toward progressive instability. (2) The neurological consequences must be defined from the clinical features of the spinal cord and the cranial nerv es. Both static and dynamic MRI scans must be performed; in this way identi fication of the neural abnormalities (hydromyelia, Chiari, etc.) and of the osseous compression is possible. (3) The most appropriate operative proced ure must be selected: stable platybasia with a nervous compression by Chiar i is cured only by posterior decompression; odontoid instability is cured b y reduction and posterior fixation, using hooks and autologous bone grafts on the posterior arches of C-l and C-2. Sometimes a transarticular screw fi xation of C1-2 is necessary if there is a defect on the C-l posterior arch. Craniocervical dislocations with assimilation of the atlas require posteri or occipito-vertebral bony fixation with grafts and external halo immobiliz ation or internal fixation with hooks or screws, with anterior transoral de compression in a second step.