title: Application of laminar screws to posterior fusion of cervical spine: measurement of the cervical vertebral arch diameter with a navigation system.
abstract: METHODS
  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.
  
  
  BACKGROUND
  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.
  
  
  CONCLUSIONS
  Laminar screws are useful as they can prevent vascular injuries, but a preoperative evaluation is necessary.
authors.affiliation: Department of Orthopaedic Surgery, Okayama University Hospital of Medicine and Dentistry, Okayama, Japan. kazu17@md.okayama-u.ac.jp
authors.forename: Kazuo
authors.initials: K
authors.lastname: Nakanishi
authors.forename: Masato
authors.initials: M
authors.lastname: Tanaka
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Sugimoto
authors.forename: Haruo
authors.initials: H
authors.lastname: Misawa
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Takigawa
authors.forename: Kazuo
authors.initials: K
authors.lastname: Fujiwara
authors.forename: Keiichiro
authors.initials: K
authors.lastname: Nishida
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Ozaki
mesh_terms: D001368:Axis, Cervical Vertebra / Q000033:anatomy & histology / Q000473:pathology; D001863:Bone Screws; D002574:Cervical Vertebrae / Q000033:anatomy & histology* / Q000473:pathology / Q000601:surgery; D005260:Female; D006801:Humans; D008297:Male; D011300:Preoperative Care / Q000295:instrumentation* / Q000379:methods*; D012107:Research Design; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods*