Objective To investigate the clinical effects of the posterior atlantoaxial pedicle screw fixation combined with unilateral axial spinous process and lamina screws and allogeneic bone graft for atlantoaxial instability.Methods From March 2010 to April 2014,data of 10 patients with atlantoaxial instability who had undergone atlanto-axial vertebral pedicle fixation and interbody fusion combined with posterior atlanto-axial spines lamina nails were retrospectively analyzed.There were 6 males and 4 females with an average age of 39 (range,16-62) years old.The inclusion criteria was atlantoaxial instability together with unilateral vertebral artery segment high cross deformity (7 patients) or atlantoaxial joint break bad involving unilateral pedicle (7 patients).3 patients have spinal cord disease symptoms and physical signs,both suffered limited neck mobility and pain.The VAS scores were 1-8,with an average of 3.70±2.11.Preoperative X-ray,CT three-dimensional reconstruction and MRI were collected.X-ray and CT examination were performed 7 d and 1,3,6,12 months after operation to evaluate the internal fixation and bone grafting fusion.Results There's no occurrence of cervical spinal cord and vertebral artery injury.Screws were successfully implanted.1 case's incision occurred infiltration liquid 3 days after operation.For allograft rejection consideration,we changed the plan,and the infiltrating stopped 5 days later.Other incisions were all primary healing.VAS scores were 1.01±0.89 after operation,which was significantly reduced.X-ray showed good recovery of cervical sequence after the operation,and CT revealed 1 patient with atlas pedicle screw in the medial cortex damage.Spinal canal was without infringing,and the other screw positions were normal.6 months after operation,X-ray or CT examination both showed bony fusion.Conclusion Atlantoaxial pedicle screw fixation combined with unilateral axial spinous process and lamina screws and allograft bone graft fusion for the treatment of atlantoaxial instability can observe good clinical effects.