title: Computed tomography-based morphometric analysis of the human occipital condyle for occipital condyle-cervical fusion.
abstract: OBJECTIVE
  Occipital condyle screws serve as an alternative fixation point in occipital-cervical fusion. Their placement requires a thorough understanding of the anatomy of the occipital condyles and associated structures. This study is a CT-based morphometric analysis of occipital condyles as related to occipital condyle-cervical fusion.
  
  
  METHODS
  A total of 170 patients were examined with CT scans of the craniocervical junction at a single institution, for a total of 340 occipital condyles, between March 6, 2006, and July 30, 2006. All CT scans were negative for traumatic, degenerative, and neoplastic pathological entities. Condylar anteroposterior (AP) length, transverse width, height, projected screw angle, and projected screw lengths were measured on an EBW Portal 2.5 CT Viewer Workstation (Philips Electronics). The longest axis in the AP orientation of the occipital condyle was accepted as the length. The transverse width was a line perpendicular to the midpoint of the long axis. The height was measured in the coronal projection that had the thickest craniocaudal portion of the condyle. The screw trajectory started 5 mm lateral to the medial edge of the condyle and a line was directed anteromedially in the longest axis. The angle was measured relative to the sagittal midline. The screw length was measured from the outer cortex of the posterior wall to the outer cortex of the anterior wall.
  
  
  RESULTS
  The mean ± SD values for occipital condyle measurements were as follows: AP length was 22.38 ± 2.19 mm (range 14.7-27.6 mm); width was 11.18 ± 1.44 mm (range 7.4-19.0 mm); height was 9.92 ± 1.30 mm (range 5.1-14.3 mm); screw angle was 20.30° ± 4.89° (range 8.0°-34.0°); and screw length was 20.30 ± 2.24 mm (range 13.0-27.6 mm).
  
  
  CONCLUSIONS
  These measurements correlate with previous cadaveric and radiographic studies of the occipital condyle, and emphasize the role of preoperative planning for the feasibility of placement of an occipital condyle screw.
authors.affiliation: Department of Neurosurgery and Brain Repair, University of South Florida, Tampa, Florida 33606, USA.
authors.forename: Tien V
authors.initials: TV
authors.lastname: Le
authors.forename: Elias
authors.initials: E
authors.lastname: Dakwar
authors.forename: Shannon
authors.initials: S
authors.lastname: Hann
authors.forename: Euclides
authors.initials: E
authors.lastname: Effio
authors.forename: Ali A
authors.initials: AA
authors.lastname: Baaj
authors.forename: Carlos
authors.initials: C
authors.lastname: Martinez
authors.forename: Fernando L
authors.initials: FL
authors.lastname: Vale
authors.forename: Juan S
authors.initials: JS
authors.lastname: Uribe
mesh_terms: D000328:Adult; D001863:Bone Screws; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging* / Q000601:surgery*; D005260:Female; D006801:Humans; D008297:Male; D009777:Occipital Bone / Q000000981:diagnostic imaging* / Q000601:surgery*; D012189:Retrospective Studies; D013123:Spinal Fusion / Q000295:instrumentation; D014057:Tomography, X-Ray Computed