Application of laminar screws to posterior fusion of cervical spine: Measurement of the cervical vertebral arch diameter with a navigation system

STUDY DESIGN. Morphometric analysis. OBJECTIVE. For safe and solid fixation, it is necessary to measure the diameter of the vertebral arch to ascertain whether or not screws can be used and if so, the appropriate size of screws to be used. SUMMARY OF BACKGROUND DATA. Cervical pedicle screws are the most biomechanically stable screws. However, their use carries a high risk of neurovascular complications during screw insertion. In 2004, a new method to avoid such vertebral artery injuries was reported by insertion of screws with crosswise to the lamina of C2. For safe and solid fixation, it is necessary to measure the diameter of the vertebral arch to ascertain whether or not screws can be used and if so, the appropriate size of screws to be used. There is no report of the diameter of the vertebral arch by a navigation system. METHODS. Morphometric analysis was performed on 42 patients who had undergone a CT scan of the cervical spine for either surgery or diagnostic purposes. To examine the possibilities to insert laminar screws, the diameter of the vertebral arch was measured using a navigation system. RESULTS. The diameter of the vertebral arch in C2 was the largest in the cervical spine, individual differences ranging between 0.8 and 8.4 mm. In C2, insertion of screws with a diameter of 3 mm was possible in 80% of males and 63% of females. As for screws with a diameter of 4 mm, insertion was possible in 50% of the males and 24% of the females in C2. In C2, gender had a significant effect, but left-right differences and height did not. CONCLUSION. Laminar screws are useful as they can prevent vascular injuries, but a preoperative evaluation is necessary.