Open Reduction of Irreducible Atlantoaxial Dislocation by Transoral Anterior Atlantoaxial Release and Posterior Internal Fixation

In Brief Study Design. A retrospective study of surgical outcome of 33 patients with irreducible atlantoaxial dislocation (IAAD). Objective. To evaluate the safety efficacy of one stage anterior release and posterior fixation and fusion to reduce and stabilize IAAD. Summary of Background Data. The traditional treatment of symptomatic IAAD is ventral decompression by transoral approach. This procedure is accompanied with high morbidity and mortality. It does not correct the swan neck deformity, which could precipitate the degenerative changes in the lower cervical spine. Our hypotheses were that it is the contraction of the muscles, ligaments, and capsules of atlantoaxial joint that prevent reduction, and that most of IAADs might be reduced by anterior atlantoaxial joint release without the odontoid resection, and that further reduction and stabilization might be achieved by special posterior fixation. Methods. A consecutive series of 33 patients with IAAD were surgically treated. Dislocation or reduction was assessed before surgery, immediately after surgery, and at the final follow-up. Etiology, instrumentation, levels fused, and complications were documented. All patients were assessed clinically for neurologic recovery by Odom's method. Results. The mean age was 32 years (range, 7–63 years). The pathology included os odontoideum in 8 patients, occipitalization of C1 in 19 patients, malunion of odontoid fracture in 5, and relaxation of transverse ligament of atlas in 1. Twenty five patients presented neurologic signs and symptoms. Anterior release was performed without odontoid resection in all cases. Four patients underwent transarticular C1–C2 screw fixation, 3 had C1–C2 pedicle screw and plate fixation, and 26 required occipitocervical fixation. Twenty-five cases resulted in an anatomic reduction, 8 had partial reduction. Complication included one dysphagia and two nasal phonations. The mean follow-up period was 33.7 months (range, 24–55 months). There was no pseudarthrosis, and all but 1 of the patients with neurologic deficit showed improvement. Conclusion. This series has demonstrated the safety and efficacy of the transoral anterior atlantoaxial release in the reduction of IAAD. Most of the so-called irreducible/fixed AAD could become reducible after anterior release without odontoid resection. The posterior short-segment atlantoaxial or occipitocervical fixation, especially the plate screw instrumentation, could achieve further reduction and provide immediate stabilization. One-stage anterior release and posterior instrumentation and fusion are a safe and reliable operation in experienced hands. In irreducible atlantoaxial dislocation, it is the contraction of anterior longitudinal ligament, anterior paraspinal muscles, and the capsule of the lateral mass that prevent the reduction. Most of the soa333called irreducible/fixed atlantoaxial dislocation could become reducible after anterior soft tissue release without odontoid resection.