The classification of arch of posterior atlas and anatomic study of the pedicle screw fixation

Objective: To study the classification of the arch of posterior atlas and the methods of the pedicle screw fixation. Methods: 48 dry atlas specimens were measured the relative anatomic data with an electronic caliper. Results: The mean height and width of the atlas mass at the entry point were 12.40±1.12 mm and 12.40±1.12 mm, and that of atlas pedicle were 4.56±1.82 mm and 7.89±1.10 mm respectively. 17% (8 cases) specimens' mean height of the pedicle under the groove for vertebral artery at the entry path were less than 3.5 mm (the screw diameter), and 4%(2 cases) of it were less than 1.75 mm (the screw semidiameter). Conclusions: To those patients whose arches of posterior atlas are not high enough to be put in the pedicle screw. We can partly drill through or pass the posterior arch to achieve the pedicle screw fixation. The entry point should be ascertained by preoperative 3D CT restitution and the exploration during the operation.