STUDY DESIGN Prospective consecutive case series. OBJECTIVE To identify the incidence of undetected vertebral artery groove and foramen violations and arterial injuries during placement of C1 lateral mass and C2 pedicle screws. SUMMARY OF BACKGROUND DATA Although insertion of C1 lateral mass and C2 pedicle screws has become increasingly common, we are unaware of any report that has specifically examined postoperative CT scans with CT angiography to determine the incidence of undetected neurovascular violations during insertion of these screws. METHODS Twenty-three consecutive patients were examined after upper cervical screw fixation was performed under fluoroscopic guidance. In all patients, intraoperative clinical findings, fluoroscopic images, and postoperative radiographs were reviewed. Thin-cut CT scans and CT angiography with multiplanar and three-dimensional reconstruction were used to detect cortical breaches and arterial injuries. RESULTS A total of 85 screws, including 39 C1 lateral mass, 39 C2 pedicle, and 7 C2 laminar screws were inserted. No apparent neurologic or arterial injuries were noted. However, CT scans revealed that 8 C2 pedicle screws (21%) resulted in vertebral artery groove violations. None resulted in arterial injury. Two C1 screws (5%) had errant trajectories. One breached the medial wall of the lateral mass and the other breached the vertebral artery foramen, causing arterial occlusion as seen on CT angiography. None of the violations were detected intraoperatively or on postoperative plain radiographs with the exception of 1 C1 medial breach observed on a postoperative open-mouth view. CONCLUSION Although vertebral artery groove and foramen violations were relatively common on postoperative CT scans, none were detected intraoperatively or on postoperative radiographs. Most alarmingly, 1 vertebral artery injury was undetected intraoperatively. Since a vertebral injury can be potentially catastrophic, this study emphasizes the inherent dangers associated with placement of C1 and C2 screws and underscores the importance of careful postoperative evaluation and surgical technique when inserting these screws.
