title: Safe angle scope for posterior atlanto-occipital transarticular screw fixation.
abstract: OBJECTIVE
  To study the technical parameters related to, and explore the clinical significance of, posterior atlanto-occipital transarticular screw fixation.
  
  
  METHODS
  Posterior implantation of Kirschner wires via the atlanto-occipital joint was performed on 20 dry bone specimens with complete atlanto-occipital joints. The angle of the Kirschner wire was measured on a postimplantation x-ray. Three-dimensional computed tomographic reconstruction of the atlanto-occipital joint of 30 healthy adults was performed to measure the simulative safety range for screw placement in posterior atlanto-occipital transarticular screw fixation. The procedure was then conducted on 12 fresh cadaver occipitocervical specimens. X-rays and 3-dimensional computed tomographic reconstruction were performed postsurgery to verify exact screw positioning.
  
  
  RESULTS
  The ideal angles for screw placement were cephalocaudal angle in the sagittal plane of 53.3 +/- 3.4 degrees, mediolateral angle in the coronal plane of 20.0 +/- 2.6 degrees, a maximum allowable cephalocaudal angle of 74.6 +/- 2.8 degrees (67.9-80.5 degrees), a minimum allowable cephalocaudal angle of 24.9 +/- 1.9 degrees (22.1-29.4 degrees), a maximum allowable mediolateral angle of 40.5 +/- 2.9 degrees (31.1-49.4 degrees), and a minimum allowable mediolateral angle of 0.7 +/- 1.6 degrees (-4.1-5.9 degrees). Surgery simulation in the fresh cadaver specimens indicated that this safe scope is reliable.
  
  
  CONCLUSIONS
  There is a safe scope for the angle of the screw placement in posterior atlanto-occipital transarticular screw fixation. Posterior transarticular screw fixation can be safely performed for occipitocervical fusion fixation when utilizing careful screw placement.
authors.affiliation: Department of Orthopedics, Changzheng Hospital, Second Military Medical University, The People's Liberation Army Orthopaedic Institute, Shanghai, China.
authors.forename: Wangjun
authors.initials: W
authors.lastname: Yan
authors.forename: Chengshi
authors.initials: C
authors.lastname: Zhang
authors.forename: Xuhui
authors.initials: X
authors.lastname: Zhou
authors.forename: Xiongsheng
authors.initials: X
authors.lastname: Chen
authors.forename: Wen
authors.initials: W
authors.lastname: Yuan
authors.forename: Lianshun
authors.initials: L
authors.lastname: Jia
mesh_terms: D001268:Atlanto-Axial Joint / Q000601:surgery*; D001269:Atlanto-Occipital Joint / Q000601:surgery*; D001863:Bone Screws; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008297:Male; D008875:Middle Aged; D013118:Spinal Cord Diseases / Q000601:surgery; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods; D014057:Tomography, X-Ray Computed / Q000379:methods; D016896:Treatment Outcome