Abstract：Objective To investigate the safety of posterior atlantoaxial transarticular screw combined with atlas pedicle screw fixation in Chinese. Methods CT data of upper cervical spine in 48 patients were collected from Ningbo No.6 Hospital, including 26 males and 22 females aged 26-58 years ［(37.3±13.5)years］. All CT data was transformed into 3D dimensional model and inserted with virtual screws by Mimics 19.0. Firstly, the vertical plane P1 and the horizontal plane P2 of the atlas were built in those atlantoaxial models, secondly the atlantoaxial transarticular screw S0 was inserted by Margel method, and its insertion point was located at 3 mm lateral and 2 mm cephalad in the C2 inferior articular process. Finally, four atlas pedicle screws were inserted at the midline of atlas lateral mass. The four screws are inserted as follows. S1: the screw was tangent to the lateral side of the S0 or the medial of the atlas pedicle. S2: the screw was tangent to the lateral wall of the atlas pedicle. S3: the screw was tangent to the upper wall of the atlas pedicle. S4: the screw was tangent to the inferior wall of the atlas pedicle. The angles between S1,S2 and P1 as the camber angle, and the angle between S3, S4 and P2 as the gantry angle were measured. Then the safety range of camber angle and gantry angle were calculated, and the screw length of S1, S2, S3 and S4 was measured. In all models, the camber angle and gantry angle of the screws were adjusted an interval of 2°, the number of successful cases was calculated and the success rate of insertion was calculated. Results All 3D models were inserted successfully. The minimum value, maximum value and safety range of the camber angle of atlas pedicle screws were (-6.7±5.2)°, (10.4± 4.3)°, (17.1±3.7)°, respectively; and of the gantry angle were (-0.5±3.5)°, (11.0±5.8)°, (11.5±4.9)°, respectively. The length of screw placement was S1:(31.1±2.4)mm, S2:(28.3±2.5)mm, S3:(29.2±3.8)mm, S4:(29.6±3.0)mm, respectively (P<0.05). When the camber angle was from -1°to 5°, the success rate of screw placement was 87.5%; when inserting with 2° camber angle, the success rate was 100%; when the gantry angle was 5°, the success rate was 93.8%. Conclusion The posterior atlantoaxial transarticular screw combined with atlas pedicle screw can achieve satisfy insertion length and success rate.
