title: Radiographic measurements of C-2 in patients with atlas assimilation.
abstract: OBJECTIVE
  The object of this study was to evaluate the radiographic characteristics of C-2 using multiplanar CT measurements for anchor screw placement in patients with C-1 assimilation (C1A). Insertion of a C-2 pedicle screw in the setting of C1A is relatively difficult and technically demanding, and there has been no report about the optimal sizes of the pedicles and laminae of C-2 for screw placement in C1A.
  
  
  METHODS
  An institutional database was searched for all patients who had undergone cervical CT scanning and cervical spine surgery between April 2006 and December 2012. Two neurosurgeons reviewed the CT scans from 462 patients who met these criteria, looking for C1A and other anomalies of the craniocervical junction such as high-riding vertebral artery (VA), basilar invagination, and VA anomaly. The routine axial images were reloaded on a workstation, and reconstruction CT images were used to measure parameters: the minimum width of bilateral pedicles and laminae and the length of bilateral laminae of the atlas.
  
  
  RESULTS
  Seven patients with C1A were identified, and 14 sex-matched patients without C1A were randomly selected from the same database as a control group. The mean minimum pedicle width was 5.21 mm in patients with C1A and 7.17 mm in those without. The mean minimum laminae width was 5.29 mm in patients with C1A and 6.53 mm in controls. The mean minimum pedicle and laminae widths were statistically significantly smaller in the patients with C1A (p < 0.05).
  
  
  CONCLUSIONS
  In patients with C1A, the C-2 bony structures are significantly smaller than normal, making C-2 pedicle screw or translaminar screw placement more difficult.
authors.affiliation: Department of Neurosurgery, Aichi Medical University, Aichi;
authors.forename: Tatsuro
authors.initials: T
authors.lastname: Aoyama
authors.forename: Muneyoshi
authors.initials: M
authors.lastname: Yasuda
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Yamahata
authors.forename: Mikinobu
authors.initials: M
authors.lastname: Takeuchi
authors.forename: Masahiro
authors.initials: M
authors.lastname: Joko
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Hongo
authors.forename: Masakazu
authors.initials: M
authors.lastname: Takayasu
mesh_terms: D000368:Aged; D001863:Bone Screws; D016022:Case-Control Studies; D001270:Cervical Atlas / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D002574:Cervical Vertebrae / Q000033:anatomy & histology / Q000000981:diagnostic imaging* / Q000601:surgery*; D006801:Humans; D008297:Male; D008875:Middle Aged; D019635:Neurosurgical Procedures; D009929:Organ Size; D011857:Radiographic Image Interpretation, Computer-Assisted; D014057:Tomography, X-Ray Computed / Q000379:methods*
keywords: C-1 assimilation; C-1 lateral mass screw; C-2 pedicle screw; C-2 translaminar screw; C1A = C-1 assimilation; VA = vertebral artery; cervical spine; computed tomography; occipitocervical fixation