Measurement of pedicle of the axis and its clinical significance

Objective: This study was undertaken to quantitatively measure the range and external dimensions of the pedicle of the axis, and to provide the anatomic basis for pedicle screws fixation in up-cervical spine operation. Methods: The width and height of the pedicle of the axis were measured respectively at 55 adult dry axis specimens, while the obliquity of the pedicle of the axis on transverse plane and sagittal plane were surveyed. Results: The mean width of the pedicle of the axis was (8.22±1.48)mm, the mean height was (8.24±0.86)mm, and the obliquities of the pedicle of the axis on transverse plane and sagittal plane were 36.57°±3.18°and 26.79°±2.10°, separately. Conclusion: This study reports the detailed quantitative evaluation of the external dimensions and the ranges of the pedicle of the axis. On the basis of this study, it can be concluded that there is enough space for C2 pedicle screw in posterior up-cervical fixation. But the diameter of the C2 pedicle screw should be less than 3.5 mm. Furthermore, the trajectory of the fixation screw should be 27° anterosuperior in sagittal plane and 37° inward in the transverse plane.