title: Feasibility of laminar screw placement in the upper thoracic spine: analysis using 3-dimensional computed tomographic simulation.
abstract: METHODS
  Evaluation using 3-dimensional screw trajectory software and computed tomographic scans.
  
  
  OBJECTIVE
  To investigate the anatomic feasibility of laminar screw placement in the upper thoracic spine compared with pedicle screw placement.
  
  
  BACKGROUND
  Although laminar screws have been suggested as an alternative to pedicle screws in the upper thoracic spine, previous anatomic feasibility studies have some limitations.
  
  
  METHODS
  Four types of screws were simulated from T1 to T6: unilaminar screw (US), superior bilaminar screw (SBS), inferior bilaminar screw (IBS), and pedicle screw (PS). Maximum allowable screw dimensions and the success rates of 4.5-mm screw placement were compared for each level. Laminar screw dimensions with more than 90% success rate at each level were determined for reference.
  
  
  RESULTS
  Computed tomographic scans of 132 patients were analyzed. Laminar screw diameters gradually increased from T1 (4.4-5.4 mm, for each type) to T6 (4.8-6.7 mm), whereas PS diameter steeply declined from T1 (5.9 mm) to T4 (3.4 mm) and then leveled off. At T1, PS had greater success rate of 4.5-mm screw placement than laminar screws (US > IBS > SBS); at T2, US had greater success rate than IBS, followed by PS and SBS; and at T3 to T6, laminar screws (US > IBS > SBS) had greater success rate than PS in all comparisons. Except for SBS at T1, laminar screw diameters with more than 90% success rates were between 3.5 and 5.0 mm.
  
  
  CONCLUSIONS
  In view of their anatomic feasibility, laminar screws can be a viable alternative to PSs in the upper thoracic spine. Particularly at T3 to T6 where the pedicle width is inherently small, the success rates of laminar screw placement were significantly and consistently higher than those of PS placement. The comparable success rates of laminar screws using commercially available screw sizes further emphasize their potential clinical use.
authors: Spine Center and Department of Orthopaedic Surgery, Seoul National University College of Medicine and Seoul National University Bundang Hospital, Sungnam, Korea.
authors: Mary Ruth Alfonso
authors: MR
authors: Padua
authors: Jin S
authors: JS
authors: Yeom
authors: Huynh Thong
authors: HT
authors: Em
authors: Ho-Joong
authors: HJ
authors: Kim
authors: Bong-Soon
authors: BS
authors: Chang
authors: Choon-Ki
authors: CK
authors: Lee
authors: K Daniel
authors: KD
authors: Riew
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001863:Bone Screws / Q000145:classification* / Q000592:standards*; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D008297:Male; D008875:Middle Aged; D019637:Orthopedic Procedures / Q000295:instrumentation* / Q000379:methods; D015203:Reproducibility of Results; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D014057:Tomography, X-Ray Computed / Q000379:methods; D055815:Young Adult