title: [A novel computer-assisted drill template for atlantoaxial pedicle screw placement:a cadaveric experimental study].
abstract: OBJECTIVE
  To validate the accuracy of atlanto-axial pedicle screw placement with a rapid prototyping drill guide template and analyze the factors of screw deviations.
  
  
  METHODS
  Computed tomography (CT) scan was performed in 16 cervical specimens. And three-dimension cervical vertebrae was reconstructed by Mimics software. The ideal trajectory for atlanto-axial pedicle screws was designed with a complementary basal template for posterior surface of atlanto-axial corresponding anatomical structure. Then drill guide template was materialized in a rapid prototyping machine. These templates were used during operation. The entry point and ideal and actual trajectories were measured after matching the positions of preoperative and postoperative specimens at designated coordinate axis.
  
  
  RESULTS
  The average displacement of entry point of left and right C1 pedicle screw in x, y, z axis was (0.14 ± 0.59),(0.31 ± 1.32), (0.27 ± 0.68), (0.23 ± 0.55), (0.43 ± 1.21) and (0.30 ± 0.72) mm. And the average displacement of entry point of left and right C2 pedicle screw in m, n, p axis was (0.25 ± 0.85), (0.52 ± 1.52), (-0.27 ± 0.67), (0.44 ± 0.87), (0.38 ± 1.48), (-0.14 ± 0.62) mm.No statistically significant difference existed (P > 0.05) in deviation of entry point and between ideal and actual trajectories.
  
  
  CONCLUSIONS
  Both human handling and inherent hardware and software factors are main reasons for a deviation of C1-C2 pedicle screw placement assisted by a rapid prototyping drill guide template.Ease of operation and individualized design are the advantages of drill guide template so as to greatly improve the precision of screw placement and reduce screw deviation.
authors.affiliation: Ningbo No.6 Hospital, Ningbo 315040, China. Email: huyong610@163.com.
authors.forename: Yong
authors.initials: Y
authors.lastname: Hu
authors.affiliation: Ningbo No.6 Hospital, Ningbo 315040, China.
authors.forename: Zhen-shan
authors.initials: ZS
authors.lastname: Yuan
authors.affiliation: Ningbo No.6 Hospital, Ningbo 315040, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Xie
authors.affiliation: Ningbo No.6 Hospital, Ningbo 315040, China.
authors.forename: Jian-bing
authors.initials: JB
authors.lastname: Yuan
authors.affiliation: Ningbo No.6 Hospital, Ningbo 315040, China.
authors.forename: Wei-xin
authors.initials: WX
authors.lastname: Dong
authors.affiliation: Ningbo No.6 Hospital, Ningbo 315040, China.
authors.forename: Cheng-tao
authors.initials: CT
authors.lastname: Wang
mesh_terms: D000328:Adult; D001368:Axis, Cervical Vertebra / Q000601:surgery*; D001863:Bone Screws; D002102:Cadaver; D001270:Cervical Atlas / Q000601:surgery*; D002574:Cervical Vertebrae / Q000601:surgery; D005260:Female; D006801:Humans; D016268:Internal Fixators; D008297:Male; D008875:Middle Aged; D025321:Surgery, Computer-Assisted / Q000379:methods*; D035501:Uncertainty