Abstract: Objective： To evaluate the clinical result of atlantoaxial reduction and fixation guided by the intraoperative CT. Methods: Sixteen cases were retrospectively studied, including seven males and nine females, with the mean age of 49.9 years. Twelve cases were diagnosed as chronic atlantoaxial instability or dislocation, while four cases as acute odontoid fracture and dislocation. Among the sixteen cases, fourteen underwent atlantoaxial fusion, while two underwent temporary atlantoaxial fixation without fusion. The intraoperative CT was used in the setting of: 1. Evaluating the atlantoaxial reduction before the screw insertion; 2. Guiding the C1 and C2 pedicle drilling (two cases using additional three-dimensional printing drilling template)；3. Evaluating the position of the screws and reduction after the atlantoaxial fixation. In addition, three-dimensional drilling template combined with intraoperative CT was used in two cases. CT scanning frequency was calculated. To evaluate the accuracy rate of screw fixation under the intraoperative CT, 19 cases without the intraoperative CT were studied as the control group. Results: Averaged CT scanning frequency was 1.4 times (Once in eleven cases, twice in four and three times in one). Among the sixteen cases, mal-positioned C1 screws were found and revised in two cases. No spinal cord injury or vertebral artery injury occurred. The follow-up ranged from three to ten months, with the mean of 6.7 months. Fourteen cases achieved solid osseous fusion, and two with temporary fixation had odontoid fracture union. Anatomic reduction was achieved in all the cases. Eleven cases with preoperative myelopathy had postoperative improvement and their mean JOA scores improved from 12.1 to 14.4. To the last follow-up, no hardware complications were found including screw broken, rod broken or fixation loosening. All the screws of intraoperative CT group had good positions. For 19 cases of the control group, there were two cases of mal-positioned screws (10.5%). Conclusion: Advantages of atlantoaxial reduction and fixation guided by the intraoperative CT included: improving the accuracy of the atlantoaxial screws, exactly evaluating the reduction of the atlantoaxial joint, immediately discovering the mal-positioned screws and avoiding the revision surgery. A good clinical result was found in the preliminary study.

Key words: Atlanto-axial joint, Atlantoaxial instability, Atlantoaxial dislocation, Internal fixation, Intraoperative CT, Three-dimensional printing template