title: Medially-shifted rather than high-riding vertebral arteries preclude safe pedicle screw insertion.
abstract: We enrolled 100 patients who underwent preoperative CT angiography before cervical spine instrumentation and investigated the morphology of the C2 pedicle from the perspective of pedicle screw (PS) trajectory using volume rendering and multiplanar reconstruction. The narrowest portion of the pedicle was identified as the pedicle isthmus. Safe C2 PS insertion was regarded to be not feasible when the height of the medullary cavity of the pedicle isthmus and/or width of the medullary cavity of the pedicle isthmus was ⩽4mm. Forty-five (22.5%) pedicles were ⩽4mm in width, and safe insertion of a PS was determined to be not feasible. Among these, seven pedicles were ⩽4mm in both height and width. The remaining 38 pedicles were ⩽4mm in width with heights >4mm. There was no pedicle with a width >4mm and height <4mm. In other words, short pedicles were always concomitantly narrow. Therefore, the seven pedicles ⩽4mm in both height and width were considered to be morphologically narrow. The heights of the pedicle isthmus were not limited by the vertebral artery groove (VAG) and safe C2 PS insertion can be considered feasible where the VAG is marginally cranial, whereas the widths of the pedicle isthmus are limited by the VAG. Therefore, safe C2 PS insertion is precluded only when the VAG courses cranially and medially. It is a medially-shifted, rather than a high-riding, vertebral artery that precludes safe C2 PS insertion. Therefore to avoid vertebral artery injury an axial CT scan, parallel to the pedicle axis, should be evaluated before C2 PS insertion.
authors.affiliation: Department of Orthopaedic Surgery, Chiba University Graduate School of Medicine, 1-8-1 Inohana, Chuou-ku, Chiba 260-8670, Japan. Electronic address: makisatoshi@hotmail.com.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Maki
authors.affiliation: Department of Orthopaedic Surgery, Chiba University Graduate School of Medicine, 1-8-1 Inohana, Chuou-ku, Chiba 260-8670, Japan.
authors.forename: Masao
authors.initials: M
authors.lastname: Koda
authors.affiliation: Department of Orthopaedic Surgery, Chiba University Graduate School of Medicine, 1-8-1 Inohana, Chuou-ku, Chiba 260-8670, Japan.
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Iijima
authors.affiliation: Department of Orthopaedic Surgery, Chiba University Graduate School of Medicine, 1-8-1 Inohana, Chuou-ku, Chiba 260-8670, Japan.
authors.forename: Takeo
authors.initials: T
authors.lastname: Furuya
authors.affiliation: Department of Orthopaedic Surgery, Chiba University Graduate School of Medicine, 1-8-1 Inohana, Chuou-ku, Chiba 260-8670, Japan.
authors.forename: Taigo
authors.initials: T
authors.lastname: Inada
authors.affiliation: Department of Orthopaedic Surgery, Chiba University Graduate School of Medicine, 1-8-1 Inohana, Chuou-ku, Chiba 260-8670, Japan.
authors.forename: Koshiro
authors.initials: K
authors.lastname: Kamiya
authors.affiliation: Department of Orthopaedic Surgery, Chiba University Graduate School of Medicine, 1-8-1 Inohana, Chuou-ku, Chiba 260-8670, Japan.
authors.forename: Mitsutoshi
authors.initials: M
authors.lastname: Ota
authors.affiliation: Department of Orthopaedic Surgery, Chiba University Graduate School of Medicine, 1-8-1 Inohana, Chuou-ku, Chiba 260-8670, Japan.
authors.forename: Junya
authors.initials: J
authors.lastname: Saito
authors.affiliation: Department of Orthopaedic Surgery, National Hospital Organization Chiba Medical Center, Chiba, Japan.
authors.forename: Akihiko
authors.initials: A
authors.lastname: Okawa
authors.affiliation: Department of Orthopaedic Surgery, Chiba University Graduate School of Medicine, 1-8-1 Inohana, Chuou-ku, Chiba 260-8670, Japan.
authors.forename: Kazuhisa
authors.initials: K
authors.lastname: Takahashi
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan.
authors.forename: Masashi
authors.initials: M
authors.lastname: Yamazaki
mesh_terms: D001368:Axis, Cervical Vertebra / Q000033:anatomy & histology* / Q000601:surgery*; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D065289:Pedicle Screws; D013123:Spinal Fusion / Q000295:instrumentation; D014057:Tomography, X-Ray Computed; D014711:Vertebral Artery / Q000033:anatomy & histology* / Q000000981:diagnostic imaging
keywords: Anatomy; Atlantoaxial transarticular screw; C2 pedicle screw; Cervical spine; Computed tomographic angiography; High-riding vertebral artery