title: Application of three-dimensional model in the management of irreducible atlanto-axial dislocation.
abstract: OBJECTIVE
  The aim of this study was to describe the application of the rapid prototyping (RP) life-size 3-dimensional model used to improve accuracy of screw insertion in irreducible atlanto-axial dislocation (IAD).
  
  
  METHODS
  The study included 10 patients with IAD. All patients were assessed using the Japanese Orthopedic Association (JOA) score. Radiographs, MRI and CT were conducted during the preoperative and postoperative procedure. A 3D RP model was created for each patient. The model was used to obtain detailed information of each pedicle and used as an intraoperative reference. Assisted by the model, transoral atlanto-axial reduction plate fixation was performed in each case.
  
  
  RESULTS
  The average operation time was 145 (range: 90 to 180) minutes and average blood loss was 120 (range: 60 to 250) ml. JOA scores improved after surgery. All 40 transoral pedicle/lateral mass screws were placed without serious complications or internal fixation failure. Postoperative radiographs and CT scan showed 38 transoral pedicle/lateral mass screws located in the pedicle tracts. Satisfactory reduction was achieved in 95% of screws. Two screws perforated the lateral wall of the C2 pedicles in an extremely narrow pedicle case. No neurologic sequelae or vertebral artery injury were detected.
  
  
  CONCLUSIONS
  The RP technique is effective and reliable in achieving an accurate and safe screw insertion during IAD surgery, especially in anatomically abnormal cases.
authors.affiliation: Department of Orthopedics, Fujian Provincial Hospital, Fuzhou, China; Department of Orthopedics, Liu-Hua-Qiao Hospital, Guangzhou, China.
authors.forename: Xi
authors.initials: X
authors.lastname: Lin
authors.affiliation: Department of Orthopedics, Liu-Hua-Qiao Hospital, Guangzhou, China.
authors.forename: Fu Zhi
authors.initials: FZ
authors.lastname: Ai
authors.affiliation: Department of Orthopedics, Liu-Hua-Qiao Hospital, Guangzhou, China.
authors.forename: Qing Shui
authors.initials: QS
authors.lastname: Yin
authors.affiliation: Department of Orthopedics, Liu-Hua-Qiao Hospital, Guangzhou, China.
authors.forename: Hong
authors.initials: H
authors.lastname: Xia
authors.affiliation: Department of Orthopedics, Liu-Hua-Qiao Hospital, Guangzhou, China.
authors.forename: Zeng Hui
authors.initials: ZH
authors.lastname: Wu
authors.affiliation: Department of Orthopedics, Liu-Hua-Qiao Hospital, Guangzhou, China.
authors.forename: Xiang Yang
authors.initials: XY
authors.lastname: Ma
mesh_terms: D000293:Adolescent; D000328:Adult; D001268:Atlanto-Axial Joint / Q000000981:diagnostic imaging* / Q000293:injuries / Q000601:surgery*; D016063:Blood Loss, Surgical; D001860:Bone Plates; D001863:Bone Screws; D003198:Computer Simulation; D005260:Female; D005593:Fracture Fixation, Internal / Q000379:methods; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D016268:Internal Fixators; D004204:Joint Dislocations / Q000000981:diagnostic imaging* / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D061646:Operative Time; D011182:Postoperative Care / Q000379:methods; D011300:Preoperative Care / Q000379:methods; D011859:Radiography; D012189:Retrospective Studies; D016896:Treatment Outcome