I. Definition Atlantoaxial subluxation is simply the loss of normal alignment between the joints of the atlantoaxial spine (C1) and the cardinal spine (C2) due to various causes. Clinically, head and neck deviation, neck pain and even neurological impairment often occur due to congenital, trauma and upper respiratory tract infection. When a conventional X-ray is taken at the time of consultation, it is sometimes difficult to obtain proper X-ray results due to the fixed deformity of the head and the overlap of the cervical spine and maxillofacial bone structures, even in open position. Therefore, it is often necessary to take CT scan of the atlantoaxial spine + 3D reconstruction to clarify. Shao will be the orthopedic department of Shanghai Xinhua Hospital. Two important values are measured on the lateral cervical spine X-ray: 1, atlanto-axial distance (ADI), the normal adult ADI is 3mm, and the pediatric ADI is 4mm, exceeding the above value is abnormal, that is, atlanto-axial dislocation. 2, atlantoaxial reserve clearance (SAC), that is, the measurement of the distance between the posterior edge of the pontine dentition and the anterior edge of the posterior arch of the atlantoaxial spine. In adults, spinal cord compression symptoms occur when the SAC is 14mm or less, while those with 15-17mm have the possibility of spinal cord compression and those with 18mm or more do not have spinal cord compression symptoms. Fielding type I: Simple rotational displacement with the dentate process as the fulcrum, but no forward displacement. Type II: Rotational displacement with lateral articular eminence as the fulcrum with forward displacement of 3-5 mm. Type III: Rotational displacement with forward displacement of more than 5 mm. Type IV: Rotational displacement with backward displacement. Indications for surgery 1.Nerve involvement; 2.Forward displacement; 3.If the deformity persists for more than 3 months and cannot be repositioned and maintained; 4.Recurrence of deformity after at least 6 weeks of conservative treatment with braking.