title: Safe Zone of Posterior Screw Insertion for Talar Neck Fractures on 3-Dimensional Reconstruction Model.
abstract: OBJECTIVE
  To investigate the optimal posterior screw placement and the geometry of safe zones for screw insertion in the talar neck.
  
  
  METHODS
  Computed tomography data for 15 normal feet were imported into Mimics 10.01 software for 3-dimensional reconstruction; 4.0-mm-diameter screws were simulated from the lateral tubercle of the posterior process of the talus to the talar head. The range of screw paths trajectories and screw lengths at nine locations that did not breach the cortex of the talus were evaluated. In addition, the farthest (point a) and nearest point (point b) of the safe zone to the subtalar joint at each location, the anteversion angle (angle A), which is parallel to the sagittal plane, and the horizontal angle (angle B), which is perpendicular to the sagittal plane, were measured.
  
  
  RESULTS
  The safe zone was mainly between the 30% location and the 60% location; the width of each safe zone was 13.6° ± 1.4°; the maximum height of each safe zone was 7.8° ± 1.2°. The height of the safe zone was lowest at the 30% location (4.5°) and highest at the 50% location (7.3°). The mixed safe zone of all tali was between the 50% location and the 60% location. When a screw was inserted at point a, the safe entry distance (screw length) ranged from 48.8 to 49.5 mm, and when inserted to point b, the distance ranged from 48.2 to 48.9 mm. And inserting a 48.7 mm screw, 5.6° laterally and 7.4° superiorly, from the lateral tubercle of the posterior process of the talus towards the talar head is safest.
  
  
  CONCLUSIONS
  The safe zone of posterior screw fixation have been defined applying to most talus, assuming the fractures are well reduced, this may strengthen the stability, shorten the operation time and reduce the incidence of surgical complications.
authors.affiliation: Department of Orthopaedics and Traumatology, Nanfang Hospital, Southern Medical University, Guangzhou, China.
authors.forename: Jian-Qun
authors.initials: JQ
authors.lastname: Wu
authors.affiliation: Department of Cardiology, School of Medicine, The Second Affiliated Hospital, Zhejiang University, Hangzhou, China.
authors.forename: Sheng-Hui
authors.initials: SH
authors.lastname: Ma
authors.affiliation: Department of Orthopaedics, The Third Hospital of Guangzhou Medical University, Guangzhou, China.
authors.forename: Song
authors.initials: S
authors.lastname: Liu
authors.affiliation: Department of Orthopaedics and Traumatology, Nanfang Hospital, Southern Medical University, Guangzhou, China.
authors.forename: Cheng-He
authors.initials: CH
authors.lastname: Qin
authors.affiliation: Department of Orthopaedics and Traumatology, Nanfang Hospital, Southern Medical University, Guangzhou, China.
authors.forename: Dan
authors.initials: D
authors.lastname: Jin
authors.affiliation: Department of Orthopaedics and Traumatology, Nanfang Hospital, Southern Medical University, Guangzhou, China.
authors.forename: Bin
authors.initials: B
authors.lastname: Yu
mesh_terms: D000328:Adult; D001863:Bone Screws; D005593:Fracture Fixation, Internal / Q000295:instrumentation / Q000379:methods; D050723:Fractures, Bone / Q000000981:diagnostic imaging / Q000601:surgery*; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008297:Male; D013628:Talus / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000293:injuries* / Q000601:surgery*; D014057:Tomography, X-Ray Computed / Q000379:methods; D055815:Young Adult
keywords: Posterior to anterior; Safe zone; Screw; Talar neck fracture