title: Morphologic evaluation of the thoracic vertebrae for safe free-hand pedicle screw placement in adolescent idiopathic scoliosis: a CT-based anatomical study.
abstract: OBJECTIVE
  To evaluate the morphologic characteristics of the thoracic pedicle with regard to safe free-hand thoracic pedicle screw placement, based on multi-planar reconstruction CT images.
  
  
  METHODS
  Thirty adolescent idiopathic scoliosis (AIS) patients who had undergone posterior corrective surgery for major thoracic curve were included in this study. Reconstructed CT axial images at each thoracic vertebra were used to measure: (1) the shortest distance from an entry point to the ventral cortex of the lamina (critical distance), and (2) the distance from the entry point to the tangent of the spinal canal at the medial wall of the pedicle (safe distance). The critical length was defined as the distance between the critical distance and the safe distance. The distance from the entry point to the medial wall breach site (breach distance) was measured on post-operative CT images.
  
  
  RESULTS
  The mean critical distance was 9.3 ± 1.1 mm. The critical distance of vertebrae from different levels was relatively constant, between 8.1 and 10.1 mm. The mean safe distance was 15.2 ± 1.3 mm. The safe distance of vertebrae from different levels was also relatively constant, between 14.5 and 16 mm. The mean critical length was 5.9 ± 1.0 mm. The critical length of vertebrae between T3 and T12 was relatively constant, ranging from 5 to 6.5 mm. The mean breach distance was 12.3 ± 1.3 mm and the each breach always recognized between the critical distance and the safe distance.
  
  
  CONCLUSIONS
  The risk of pedicle medial wall perforation increases as the pedicle probe advances beyond the critical distance of 8-10 mm from the entry point, while it decreases entering into the safe distance at 14.5-16 mm. These parameters were relatively constant even in the most rotated vertebrae at T9 or those with the narrowest pedicle at T7 or T4.
authors: Department of Orthopedic Surgery, Keio University School of Medicine, 35 Shinanomachi, Shinjuku, Tokyo, 160-8582, Japan.
authors: Guanyu
authors: G
authors: Cui
authors: Kota
authors: K
authors: Watanabe
authors: Naobumi
authors: N
authors: Hosogane
authors: Takashi
authors: T
authors: Tsuji
authors: Ken
authors: K
authors: Ishii
authors: Masaya
authors: M
authors: Nakamura
authors: Yoshiaki
authors: Y
authors: Toyama
authors: Kazuhiro
authors: K
authors: Chiba
authors: Lawrence G
authors: LG
authors: Lenke
authors: Morio
authors: M
authors: Matsumoto
mesh_terms: D000293:Adolescent; D001863:Bone Screws; D002648:Child; D005260:Female; D006801:Humans; D008297:Male; D015588:Observer Variation; D019637:Orthopedic Procedures; D012016:Reference Values; D012600:Scoliosis / Q000601:surgery*; D013904:Thoracic Vertebrae / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000601:surgery*; D014057:Tomography, X-Ray Computed