title: Estimation of odontoid process posterior inclination, odontoid height, and pB-C2 line in the adult population.
abstract: OBJECTIVE
  Posterior odontoid process inclination has been associated with Chiari malformation Type I in the pediatric population. There are varying reports to support a reliable range of odontoid inclination angles in control adults. The purpose of this study is to estimate the normal measurements in adults for odontoid retroflexion, retroversion, height, and the pB-C2 line (a line drawn through the odontoid tip from the ventral dura perpendicular to a second line from drawn the basion to the inferoposterior aspect of C-2 vertebral body) to establish a normative reference in this population.
  
  
  METHODS
  After obtaining institutional review board approval, the authors performed a retrospective analysis of non-contrast enhanced cervical spine CT scans obtained in 150 consecutive control adults. Three neuroradiologists measured odontoid retroflexion, odontoid retroversion, odontoid height, and the pB-C2 line. The cohort was divided into sex and two age groups. Comparisons of the means with unpaired 2-tailed t-test were performed.
  
  
  RESULTS
  A total of 125 subjects met the inclusion criteria; 80 were men and 45 were women (mean age 52 years, range 18-89 years). The odontoid retroflexion angle ranged from 70° to 89° (mean 79.3° ± 4.9°), and the odontoid retroversion angle ranged from 57° to 87° (mean 71.9° ± 5.3°). The range and mean of odontoid height were 17-27 mm and 22 ± 1.8 mm, respectively. The mean pB-C2 line was 6.5 ± 2.1 mm with a range of 0-11.2 mm. The results were also compared with previously published pediatric data.
  
  
  CONCLUSIONS
  The current study demonstrates that the odontoid process in adults is anatomically different from that in children: it is longer, more posteriorly inclined, and has a greater pB-C2 line. Therefore, utilization of these parameters with previously published cutoffs in the pediatric population is not appropriate for surgical planning in adults.
authors: Division of Neuroradiology, Department of Radiology, and.
authors: Ziyad L
authors: ZL
authors: Khaleel
authors: David A
authors: DA
authors: Besachio
authors: Erica F
authors: EF
authors: Bisson
authors: Lubdha M
authors: LM
authors: Shah
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001139:Arnold-Chiari Malformation / Q000000981:diagnostic imaging; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009809:Odontoid Process / Q000000981:diagnostic imaging*; D011859:Radiography