Posterior Compression Distraction Reduction （CDR）Technique in the Treatment of BI-AAD

Inclusion Criteria: * Age between 18-70 * Patients with cervical CT display that atlanto occipital fusion or partial fusion, Atlantoodontoid interval(ADI)\>\>3mm, odontoid tip over Qian line(CL)\>\>3mm. * Agreed to the surgical operation treatment * The patient can carry out clinical follow-up and agree to long-term clinical follow-up * Signed informed consent Exclusion Criteria: * Patients with traumatic atlanto-axial dislocation * Patients with rheumatoid atlantoaxial dislocation * Patients with a history of occipital cervical junction operation * Patients with severe cerebellar tonsillar hernia (reach the C2 margin), needed to remove tonsil of cerebellum * Patients during pregnancy and the postpartum period within 3 months * The life expectancy of \< 1 years * Severe dementia(MMSE\<18) * Severe renal failure (CR \> 2.5mg/dl) * Serious cardiovascular disease (such as unstable angina, heart failure) * Atrial fibrillation and other severe arrhythmia * Without the ability to sign the informed consent