Insertion Angle of Pedicle Screws in the Subaxial Cervical Spine: The Analysis of Computed Tomography-Navigated Insertion of Pedicle Screws

STUDY DESIGN: Four orthopedic spine surgeons measured the radiological parameters of pedicle screws in the cervical spine using a postoperative computed tomography (CT) scan. PURPOSE: This study analyzed the insertion angle of CT-navigated insertion of pedicle screws in the subaxial cervical spine and classified them according to their position. OVERVIEW OF LITERATURE: Overall, a pedicle transverse angle of 33.6°–50.2° with a mean angle of 45° relative to the midline has been reported in the literature. METHODS: The insertion angles of 87 pedicle screws inserted using CT-based navigation in the subaxial cervical spine were measured in the postoperative CT. The screw positioning was determined according to the modified Gertzbein and Robbins classification. RESULTS: Total 89.3% (n=78) of the pedicle screws inserted using CT-based navigation showed good placement. The mean insertion angle of the pedicle screws that showed good positioning was 29.9°±9.9°. The pedicle screws showing bad positioning had a mean insertion angle of 26.8°±10.5° (p=0.157). The interobserver reliability showed a reliable measurement intraclass correlation coefficient: 0.994 (95% confidence interval, 0.992–0.996). CONCLUSIONS: The present results show that the insertion angle of the pedicle screws in the subaxial cervical spine was smaller than the actual pedicle transverse angle, as per the literature. One reason for this discrepancy could be that the navigation systems allow the insertion of cervical pedicle screws with a lower convergence.