Analysis of 3-Dimensional Course of the Intra-axial Vertebral Artery for C2 Pedicle Screw Trajectory

Study Design. A retrospective radiological study. Objective. To analyze the course of intra-axial vertebral artery (IAVA) and evaluate the relationship between the 3-dimensional (3D) courses for IAVA with respect to safe trajectory for C2 pedicle screw (C2PS). Summary of Background Data. The VA at the level of C2 has a distinct 3D course. The traditional concept of "high riding (HR)" VA was based on sagittal plane but does not provide all the 3D course of IAVA for safe C2PS placement. However, 3D course of IAVA has not been previously analyzed. Methods. Three-dimensional, vascular-enhanced computed tomographic scans on the cervical spine of 100 patients, 200 IAVA (male to female ratio = 50:50; mean age, 58.4 yr) were analyzed. (1) The arterial parameters including (1) " medial-shifting (MS)" (A: lateral, B: neutral, C: medial to C3 transverse foramen [TF]) and (2) "HR" (0: below C2TF, 1 within C2TF, 2: above C2TF) of IAVA was measured. (2) The bony parameters including pedicle diameter, medial convergence angle, and sagittal angle of C2PS were measured. Correlation between the arterial and bony parameters, differences between sex, laterality, dominance of VA, and age were analyzed. Results. MS (grade A, 37.5%; B, 37%; and C, 25.5%) and HR (grade 0 in 34%, 1 in 42%, and 2 in 24%) showed significant correlation with each other (P < 0.001). The main patterns of IAVA were A-0 (26%), B-1 (26.5%), and C-2 (18.5%). Higher grade of MS and HR showed significantly smaller pedicle diameter, larger medial convergence angle, and smaller sagittal angle (P < 0.001). Female sex and older age are factors that showed significantly higher grade of MS and HR (P < 0.001). Conclusion. Tortuosity of IAVA was greater in the female sex and it also increased with aging. The different IAVA courses significantly influenced the pedicle diameter and the safe trajectory for C2PS; therefore, these factors should be considered before planning C2 pedicle screw placement.