Atlantoaxial subluxation is simply the loss of normal alignment between the atlantoaxial (C1) and cardinal (C2) joints due to various reasons. Clinically, atlantoaxial subluxation often occurs due to congenital, trauma, upper respiratory tract infection and other factors, such as head and neck deviation, neck pain and even neurological damage. When 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, overlapping of cervical vertebrae and maxillofacial bone structures, even in the open position. Therefore, it is often necessary to take atlantoaxial CT scan + three-dimensional reconstruction to clarify. Measurement Two important values are measured on the lateral cervical X-ray: 1) atlanto-dental interspace distance (ADI), the normal ADI is 3mm for adults and 4mm for pediatrics, and the atlantoaxial subluxation is abnormal when it exceeds the above value. 2) atlantoaxial reserve clearance (SAC), which is the measurement of the distance between the posterior margin of the odontoid process of the cardinal vertebrae and the anterior margin of the posterior arch of the atlantoaxial vertebrae. In adults, spinal cord compression occurs when the SAC is 14mm or less, 15-17mm may cause spinal cord compression, and 18mm or more does not cause spinal cord compression. Fielding’s classification: Type I: simple rotational displacement with the dentate process as the fulcrum and no forward displacement; Type II: rotational displacement with the lateral articular process as the fulcrum and forward displacement of 3-5mm; Type III: rotational displacement with forward displacement of more than 5mm; Type IV: rotational displacement with backward displacement; Type V: rotational displacement with backward displacement; Type V: rotational displacement with backward displacement; Type V: rotational displacement with backward displacement; Type V: rotational displacement with backward displacement; Type V: rotational displacement with backward displacement. Indications for surgery: 1, nerve involvement; 2, forward displacement; 3, if the deformity persists for more than three months and cannot be obtained and maintained; 4, deformity recurrence after at least 6 weeks of conservative treatment with braking.