Objective To evaluate the feasibility and efficacy of atlantoaxial fusion by flipping periosteum pedicle occipital outer plate.Methods Between March 2010 and June 2013,27 patients with atlantoaxial instability were treated by atlantoaxial fusion with flipping periosteum pedicle occipital outer plate and combining pedicle screws fixation.There were 16 males and 11 females with the age ranging from 23 to 56 years (with an average of 45.6 years) at time of surgery.There were 12 cases of fresh odontoid fracture with atlantoaxial instability,7 cases of old odontoid fracture combined with uneducable atlantoaxial dislocation,7 cases of congenital loose of odontoid process,and 1 case of rheumatoid arthritis.The visual analog scale (VAS) scores and Frankel grades were respectively used to evaluate the axial neck pain and the neurological deficit,and the results were compared before and after the operation.Bony fusion was observed by the midline sagittal CT scan images.Results All the patients were successfully operated.The operation time was 90 to 140 mins (with an average of 100 mins),and the blood loss was 100 to 600 ml (with an average of 160 ml).All patients were followed up for 18 to 39 months,with an average of 32.6 months.19 cases got solid fusion 3 months after surgery,and 7 cases got solid fusion 6 months after surgery,while 1 case got solid fusion 9 months after surgery.The average VAS score at final follow-up was 2.87± 1.03,which was significantly lower than that preoperatively 7.23± 1.65.Before the operation,nine cases presented spinal nerve function damage.At the final follow up time,7 cases returned to complete normal and 2 cases improved from grade C to grade D according to the Frankel classification.1 case was complicated with veiniplex injury with no heavy blood loss,due to successful hemostasia.Two screws were placed close to the vertebral artery canal,without clinical consequences.Conclusion The flipping periosteum pedicle occipital outer plate as a bone graft is one effective method for atlantoaxial fusion,which got great feasibility and safety.