Selection of the screw fixation path in atlas via pedicle of vertebral arch

Aim: To evaluate the feasibility and the safety range of the pedicle screw placement in atlas by different channels and choose the best entry channel. Methods: Fifty-eight( 116 sides) adults of atlas or atlantoaxial lesion were randomly selected,who had a multi-slice spiral CT screening. Three screw fixation pathways in atlas via posterior pedicle of vertebral arch were set up,and the parameters of atlas pedicle including the height,width,lenghth and direction of screw were measured. Results: The differences of anatomic measurements of atlas pedicles between the two sides were not statistically significant( P 0. 05). All the mean width of the atlas pedicle in sagittal direction and the direction of pedicle was8. 21 and 9. 59 mm,respectively,and 3 sides with the width less than 5. 5 mm. The mean height( H1,H2,H3) of the atlas pedicle of vertebral arch was 4. 57,4. 55 and 4. 51 mm,among which,the height less than 3. 5 mm accounted for 11. 21%( 6/58),12. 06%( 7/58) and 12.06%( 7/58). The median inside oblique angle of channel 3 of atlas pedicle screw fixation was 21. 27°,and the median superior inclination angles of 3 channels were 17. 88°,18. 27° and 15. 24°. The mean path length( D1E1,D2E2,D3E3) atlas pedicle were 29. 02,27. 69 and 28. 55 mm. Conclusion: It is more safe to implant screws between channel 2 and channel 3,with the inside oblique angle between 0° ~ 10°,and the mean path length of27. 5 mm.