The common causes of atlantoaxial instability are degeneration, congenital malformations (e.g., dentate synostosis), trauma, and inflammation. Clinical features are stiffness of the neck, reluctance to move the head, and a marked reduction in neck movement, especially when the neck is rotated, which can reduce the amount of normal movement by almost half or more. There is pain in the occipital neck, with significant pressure pain and, in severe cases, an electric shock-like sensation. Fine hand movements are impaired, and the muscle tone of the lower limbs is increased. Knee tendon reflex and Achilles tendon reflex are hyperactive, and walking is unstable. Sensory impairment may include numbness, pain and hypersensitivity in the extremities. Hoffmann’s sign is mostly positive and Babinski’s evidence may be positive.γγγγThe diagnosis of atlanto-anterior spacing is mainly based on the atlanto-anterior spacing of more than 3 mm in adults and more than 4 mm in children on X-ray. Atlantoaxial instability caused by free dentition should be treated surgically as early as possible because of the high risk of spinal cord degeneration and irreversible spinal cord injury if not treated in time, which can be life-threatening in severe cases. The following is a case of a 37-year-old male patient, a fisherman, who came to our hospital from Rizhao City, Shandong Province. He presented to our hospital from Rizhao, Shandong Province with a complaint of neck pain for one month, limited fine movement of the right hand, and MRI showing free dentition, atlantoaxial instability, and spinal cord degeneration. On careful analysis, the patient had probably been suffering from neck discomfort for a long time, but did not pay attention to it until the pain worsened, and was referred to our hospital because of the high risk of upper cervical surgery. We performed a posterior atlantoaxial repositioning and fixation implant fusion, and the patient’s posterior occipital discomfort disappeared after surgery. The surgery served to relieve posterior occipital pain and prevent the aggravation of high cervical marrow injury leading to paralysis and life threatening injury, but it may not be possible to completely reverse the degeneration that already exists in the spinal cord, so for organic atlantoaxial instability caused by free dentition, etc., early surgical treatment should be performed, and once degeneration of the spinal cord occurs, surgical recovery is not very likely. Diagnosis