Anatomic suitability of the C1-C2 complex for pedicle screw fixation.

Abstract

A computed tomography (CT) study of 60 consecutive patients (120 sides) was performed to assess suitability for either transarticular or pedicle screw fixation. A C1 lateral mass and C2 pedicle screw fixation with a rigid cantilever beam system has been described. The anatomic constraints relevant for this technique have not. Fifty consecutive patients underwent standard CT of the cervical spine. Pedicle and transarticular screw trajectories were plotted, and the maximum safe diameter for screw placement was determined for each trajectory. Also, trajectories were plotted in 10 additional patients with known craniocervical junction abnormalities using three-dimensional (3-D) imaging and computer-aided navigation tools. Screw placement was considered feasible if a 4-mm diameter trajectory could be plotted without impingement on neural or vascular structures. Four-millimeter diameter pedicle screws could be placed in 91 of 100 C2 pedicles in the CT studies and in 20 of 20 pedicles in the 3-D studies. Four-millimeter diameter C1-C2 transarticular screws could be placed in 94 of 100 sides in the CT study and in 19 of 20 sides in the 3-D study. Four sides could tolerate a C2 pedicle screw and not a transarticular screw; the opposite situation existed in five sides. Placement of screws into C1 was not an issue in any patient. The mean maximum diameter of potential transarticular screws was 6.5 mm, and the mean maximum diameter of the pedicle screws was 5.3 mm (P < 0.01). C1-C2 pedicle screw fixation is a technique that appears to be widely applicable and may represent an alternative fixation technique in selected patients.