Rotational subluxation of the atlantoaxial joint was first reported by Corner in 1907 and officially named “atlantoaxial rotation-fixation” by Wortzman in 1968. The disease was not mentioned in China until 1981. At present, the diagnostic criteria are still not uniform and comprehensive. The atlantoaxial spine has no vertebral body and is composed of the anterior and posterior arches, which are in the shape of an annulus. The transverse atlantoaxial ligament is attached to the nodes on the inner surface of the block on both sides, dividing the atlantoaxial foramen into two parts: the anterior part has the odontoid process of the cardinal spine, and the posterior part has the spinal cord. The atlantoaxial joint is a composite joint, consisting of two joints: (1) the lateral atlantoaxial joint, consisting of the left and right inferior atlantoaxial facets and the superior atlantoaxial facets, with the posterior and medial aspects of the joint capsule reinforced by ligaments; (2) the anterior-posterior dentate joint, consisting of the anterior edge of the dentate and the posterior edge of the anterior atlantoaxial arch, and the synovial capsule between the posterior edge of the dentate and the transverse atlantoaxial ligament forming the posterior atlantoaxial joint. The transverse atlantoaxial ligament is thick and tough, connecting the left and right lateral blocks of the atlantoaxial spine and the medial side, and forming a bone fiber structure together with the anterior atlantoaxial arch. The ligament is divided into two parts, the anterior part accommodates the dentate process and the posterior part accommodates the spinal cord and the periosteum, wrapping around and limiting excessive movement of the dentate process and, together with the pterygoid ligament, limiting excessive forward flexion and rotation of the head and keeping the atlantoaxial spine stable. The transverse atlantoaxial ligament is the most important structure in maintaining atlantoaxial stability and is the most important factor in preventing anterior subluxation of the atlantoaxial spine. The role of the transverse atlantoaxial ligament is to keep the anterior atlantoaxial space within normal limits (no more than 3 mm in adults and no more than 4 mm in children). Axial rotation of the atlantoaxial joint is limited by the bilateral pterygoid ligaments, and loss of pterygoid ligament function would imply potential rotational instability of the atlantoaxial joint. The pterygoid ligaments and the annular fibers work together to allow the atlantoaxial joint to rotate freely within a certain range and prevent lateral dislocation of the atlantoaxial joint. In addition, there is a transverse foramen at the base of the atlantoaxial spine, which is not located directly above the transverse foramen of the cardinal spine, but on the posterior side, where the vertebral artery, vertebral vein, and sympathetic nerve pass through; misalignment of the atlantoaxial joint can further misalign the transverse foramen, which is not in a straight line, and cause distortion, extrusion, or compression of the vertebral artery, resulting in poor blood flow to the vertebral artery and inadequate blood supply to the vertebrobasilar artery system. Below the posterior arch of the atlantoaxial vertebrae, there are shallow grooves on each side that meet to form the intervertebral foramen, from which the second pair of cervical spinal nerves penetrate respectively. When the C↓2 nerve is stimulated, it can cause abnormal sensation in the occipital region, and when the forehead is involved, it can cause ipsilateral orbital distention and pain and blurred vision. Further forward misalignment of the atlantoaxial spine can lead to limited spinal stenosis and compression of the cervical medulla, resulting in weakness of the limbs and unstable gait. (1) Inflammation around the atlantoaxial joint, such as infection of the pharynx and upper respiratory tract, rheumatoid, etc., produce congestive edema and exudation of the synovial membrane, causing congestive decalcification of the ligaments, causing ligamentous relaxation and dislocation; inflammation can also cause the ligaments to form folds and affect the reset after rotation, forming a rotational strangulation solid trauma can directly cause tears of the transverse ligaments, pterygoid ligaments or cause inflammatory edema of the bursa and ligaments, resulting in rotational instability of the atlantoaxial joint and causing the atlantoaxial joint to become unstable. Atlantoaxial joint rotational instability and dislocation; atlantoaxial fracture and pivotal dentate fracture can directly cause atlantoaxial dislocation. (2) When the atlantoaxial joint surfaces are symmetrical, the forces are balanced and the joint is more stable. When the atlantoaxial joint surfaces are asymmetrical (i.e., the tilt is not equal and the joint surfaces are not equal in length), the forces on the joint surfaces are not balanced, and the shearing force is large on the side with large tilt and small on the opposite side, which makes the joint in an unstable state and prone to atlantoaxial rotational subluxation. Clinical manifestations (1) rotational locking fixation, i.e. idiopathic oblique neck, neck stiffness, pain, restricted movement, especially restricted rotational movement is obvious. (2) Ischemic symptoms of vertebrobasilar artery, i.e., dizziness, headache, nausea, vomiting and other symptoms. (3) C↓2 spinal nerve irritation symptoms, i.e. abnormal sensation in the occipital collar, neck pain, limited movement, and individual orbital swelling and pain and blurred vision. Symptoms of cervical medullary compression, i.e. weakness of limbs, unstable gait, etc. The diagnosis of atlantoaxial joint rotational subluxation should be based on any of the above clinical symptoms. X-ray diagnosis (a) cervical spine opening orthopantomograph 1. In normal people, the blocks on both sides of the atlantoaxial spine are equal in size, and the gap between the dentate process and the lateral blocks is equal. When the head is turned to the right, the left side of the atlantoaxial block is close to the dentate process and its gap becomes smaller, while the left side of the atlantoaxial block becomes wider and clearer and the right side becomes narrower and blurred. In addition, the left atlantoaxial joint gap becomes wider and the right narrower. The opposite change occurs when the head is rotated to the left. If the difference between the lateral atlantoaxial block and the dentate process remains constant, the diagnosis of atlantoaxial rotational subluxation can be made, except for asymmetric changes in the atlantoaxial gap due to malpositioning of the projection. 2.The two upper articular surfaces of the normal atlantoaxial vertebrae are symmetrical, with their extension lines intersecting on the median axis of the dentate process, and the joint gaps on both sides are symmetrical; with the rotational dislocation of the atlantoaxial vertebrae, the misalignment of the atlantoaxial joint surfaces gradually increases. 3.The spinous process of the atlantoaxial spine does not deviate from the midline when normal, and when the rotation exceeds 50% of the normal range, the spinous process of the atlantoaxial spine deviates from the midline, suggesting rotational dislocation of the atlantoaxial joint. (B) Lateral cervical spine film The atlanto-dental spacing ADI is commonly used, which is the distance between the posterior edge of the anterior atlanto-axial arch and the anterior edge of the dentate process. Atlantoaxial instability can be diagnosed in adults when the ADI is ≥4 mm, and atlantoaxial instability should be highly suspected when it is ≥mm, and the diagnosis should be confirmed by combining with other clinical examination methods. The criteria for atlantoaxial instability in pediatric patients is ADI ≥ 5 mm. (c) Cervical hyperextension and hyperflexion lateral radiographs can show abnormal increase in ADI and better observation of changes in the anterior dentate space, but are generally only suitable for cases without nerve damage and no impairment of consciousness. The atlanto-lateral gap asymmetry in the orthopantomogram cannot be used as a diagnostic basis, and it is necessary to take additional orthopantomograms with a left and right double oblique 15° opening when the difference between the two sides of the atlanto-lateral gap is >3 mm in adults and >5 mm in children. If the atlanto-lateral gap difference still exists and there is misalignment of the atlanto-axial surface, the diagnosis of atlanto-axial rotational subluxation can be confirmed. (d) CT scan has certain advantages for the diagnosis of atlantoaxial subluxation, because it can overcome the anterior-posterior overlap of tissue structures, so that the anatomical relationship of atlantoaxial rotational subluxation can be clearly shown, and the size of the bony spinal canal can be observed, and the spinal cord compression can be indirectly inferred.