title: Use of spinous processes to determine the laterally angulated trajectory for placement of lateral mass screws: an image analysis.
abstract: BACKGROUND
  Lateral mass screw placement techniques have been broadly described in the literature. Differences in these techniques are related to entry points, lateral angulations and the cephalocaudal axis.
  
  
  OBJECTIVE
  We evaluated 20 patients who underwent lateral mass screw placement between 2007 and 2009. Computed tomography (CT) scans of the cervical vertebrae were analyzed for each patient.
  
  
  METHODS
  We measured the maximal transition from the midpoint of the lateral mass to a proposed intersection point by a line connecting the corresponding spinous process and outermost rim of the transverse foramen at each level. This determined an optimal entry point during the tip of screw tilted on the same level of spinous process.
  
  
  RESULTS
  The results revealed that a screw entry point less than 3 mm medial to the midpoint of the lateral mass could safely avoid violation of the vertebral artery.
  
  
  CONCLUSIONS
  The current study uses imaging analysis to demonstrate that spinous processes are an intraoperative landmark to aid surgeons in determining safe lateral mass screw trajectories. The limited-scale case results support our prediction from the image analysis. Depending on intraoperative landmarks, lateral mass screws could be safely and comfortably placed with good clinical outcomes.
authors: Department of Neurological Surgery, Tri-Service General Hospital, Taipei 114, Taiwan, China.
authors: Kuan-Yin
authors: KY
authors: Tseng
authors: Chung-Ching
authors: CC
authors: Hsia
authors: Yuan-Hao
authors: YH
authors: Chen
authors: Shin-I
authors: SI
authors: Ma
authors: Chi-Tun
authors: CT
authors: Tang
mesh_terms: D000328:Adult; D000368:Aged; D001863:Bone Screws / Q000009:adverse effects; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D016268:Internal Fixators; D007431:Intraoperative Complications / Q000517:prevention & control; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D019637:Orthopedic Procedures / Q000009:adverse effects / Q000379:methods*; D013131:Spine / Q000000981:diagnostic imaging / Q000601:surgery*; D014057:Tomography, X-Ray Computed; D014711:Vertebral Artery / Q000293:injuries