title: Computed tomographic evaluation of the normal adult odontoid. Implications for internal fixation.
abstract: METHODS
  Computed tomography scans of the dens were performed on patients who had no atlantoaxial pathology.
  
  
  OBJECTIVE
  To determine whether one or two screws is optimal for fracture fixation and whether two screws can always negotiate the intramedullary odontoid cavity.
  
  
  BACKGROUND
  Fixation of Type II dens fractures traditionally has used C1-C2 posterior wiring and fusion. Two screws placed across an odontoid fracture as a method of rigid internal fixation also has been described. However, it is not known whether two screws can always negotiate the odontoid canal.
  
  
  METHODS
  Ninety-two consecutive computerized tomography scans of the dens were performed on adults who had no atlantoaxial pathology. Measurements were taken from the scan and compared with the cross-sectional diameter of two odontoid screws.
  
  
  RESULTS
  The critical diameter for the placement of two 3.5-mm cortical screws with tapping was 9.0 mm. This dimension was present in 95% of the patients studied.
  
  
  CONCLUSIONS
  Correct orientation of the computerized tomography scanner is critical for accurate measurements. Two 3.5-mm screws can be used in internal fixation of Type II dens fractures in 95% of the patients if the inner cortex is tapped.
authors.affiliation: Department of Orthopaedic Surgery, S.U.N.Y. Downstate Medical Center, Brooklyn, USA.
authors.forename: R C
authors.initials: RC
authors.lastname: Nucci
authors.forename: S
authors.initials: S
authors.lastname: Seigal
authors.forename: A A
authors.initials: AA
authors.lastname: Merola
authors.forename: J
authors.initials: J
authors.lastname: Gorup
authors.forename: K J
authors.initials: KJ
authors.lastname: Mroczek
authors.forename: J
authors.initials: J
authors.lastname: Dryer
authors.forename: R I
authors.initials: RI
authors.lastname: Zipnick
authors.forename: T R
authors.initials: TR
authors.lastname: Haher
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001863:Bone Screws; D005260:Female; D005593:Fracture Fixation, Internal / Q000379:methods*; D050723:Fractures, Bone / Q000000981:diagnostic imaging* / Q000601:surgery; D006801:Humans; D008297:Male; D008875:Middle Aged; D009809:Odontoid Process / Q000000981:diagnostic imaging* / Q000293:injuries / Q000601:surgery; D013123:Spinal Fusion; D014057:Tomography, X-Ray Computed