We studied six cases of atlanto-axial dislocation treated by occipito cervical instrumentation. The diagnosis was RA in two cases and malignant tumors in four cases. The alignment of the upper cervical spine was severely destroyed in all cases. In the cases of RA, the clinical results and mechanical fixation of the instruments were good, but vertical redislocation between the atlanto-axial joint occurred on rentogenographic examination. Though all cases of malignant tumors died within four months after the operation, the symptomatic evaluation, including relief of pain, was excellent. In conclusion, occipito-cervical fusion with a modified U rod seemed to be the most useful instrumentation in selected cases.
