C1-2 transarticular screw fixation in high-riding vertebral artery: suggestion of new trajectory.

A significant drawback of atlantoaxial transarticular screw fixation is a potential risk of vertebral artery injury, especially with a high-riding type. The authors propose a relatively safe trajectory in cases of high-riding vertebral artery by using the 3-dimensional computerized tomography image reconstruction programs. Twelve consecutive patients with a pathologic condition in atlantoaxial complex were prospectively analyzed. Five other patients, whose high-riding vertebral arteries were incidentally found during the 3-dimensional computerized tomography performance for other cervical pathologic conditions, were also included. The preoperative screw simulation images, convergence angle, and caudal tilting angle for each screw were obtained from each patient. Of 17 subjects, 7 had high-riding vertebral artery unilaterally and 1 had bilaterally. All 12 patients with pathologic atlantoaxial complex, including 2 unilateral and 1 bilateral high-riding vertebral artery, had atlantoaxial transarticular screw fixation. For these 3 patients, the entry point and the trajectory for screw were moved more superiorly and medially as in cases with C2 pedicle screwing. The mean convergence angle and caudal tilt angle obtained during screw simulation for patients with high-riding vertebral arteries was 17.6 and 38 degrees compared with 21 and 53.3 degrees for patients with normal course of vertebral artery. It was possible to insert transarticular screws safely in patients with high-riding vertebral artery guided by preoperative screw insertion simulation program.