Atlantoaxial subluxation (AAS) with os odontoideum is more unstable than AAS without it. We investigated the surgical results of symptomatic AAS with os odontoideum. Eleven males and 16 females (mean age: 38 years) underwent surgery. Fifteen patients showed myelopathy (mean JOA score: 9.4), and 12 had only local symptoms without myelopathy. Three parameters on the lateral radiographs (minimum diameter in flexion, maximum diameter in extension and atlanto-axial angle in flexion and extension) were measured preoperatively, and the instability index was calculated. Manipulation (18) or anterior release (3) reduced AAS in 21 patients. Posterior atlanto-axial fusion and bone graft were performed with wiring (9), transarticular screw fixation with wiring (9), and Olerud Cervical fixation (3). In 6 patients, AAS was not reduced and occipito-cervical fusion was performed. Correction loss and union rate were investigated on the postoperative lateral radiograph. The mean follow-up was 5 years and 4 months. There was no significant difference between preoperative radiological values and clinical symptoms. The mean JOA score improved to 13.0 after surgery, and the improvement rate was 52.3%. Four patients treated with wiring showed correction loss. Three of them developed non-union and required re-operation. Bone union was achieved with other fixations.
