title: Analysis of 3-dimensional course of the intra-axial vertebral artery for C2 pedicle screw trajectory: a computed tomographic study.
abstract: METHODS
  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).
  
  
  BACKGROUND
  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).
  
  
  CONCLUSIONS
  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.
  
  
  METHODS
  3.
authors.affiliation: *Department of Orthopedic Surgery, Kyung Hee University Hospital at Gangdong, Seoul, Korea †Busan Paik Hospital, Inje University, Busan, Korea; and ‡Cedars Sinai Medical Center, Los Angeles, CA.
authors.forename: Sang-Hun
authors.initials: SH
authors.lastname: Lee
authors.forename: Dae-Hyun
authors.initials: DH
authors.lastname: Park
authors.forename: Sang-Do
authors.initials: SD
authors.lastname: Kim
authors.forename: Dae-Seok
authors.initials: DS
authors.lastname: Huh
authors.forename: Ki-Tack
authors.initials: KT
authors.lastname: Kim
mesh_terms: D000328:Adult; D000368:Aged; D002574:Cervical Vertebrae / Q000601:surgery*; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008297:Male; D008875:Middle Aged; D019637:Orthopedic Procedures / Q000379:methods; D065289:Pedicle Screws; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods; D014711:Vertebral Artery / Q000601:surgery*