title: Accuracy of free-hand pedicle screws in the thoracic and lumbar spine: analysis of 6816 consecutive screws.
abstract: BACKGROUND
  Pedicle screws are used to stabilize all 3 columns of the spine, but can be technically demanding to place. Although intraoperative fluoroscopy and stereotactic-guided techniques slightly increase placement accuracy, they are also associated with increased radiation exposure to patient and surgeon as well as increased operative time.
  
  
  OBJECTIVE
  To describe and critically evaluate our 7-year institutional experience with placement of pedicle screws in the thoracic and lumbar spine using a free-hand technique.
  
  
  METHODS
  We retrospectively reviewed records of all patients undergoing free-hand pedicle screw placement without fluoroscopy in the thoracic or lumbar spine between June 2002 and June 2009. Incidence and extent of cortical breach by misplaced pedicle screw was determined by review of postoperative computed tomography scans. We defined breach as more than 25% of the screw diameter residing outside of the pedicle or vertebral body cortex.
  
  
  RESULTS
  A total of 964 patients received 6816 free-hand placed pedicle screws in the thoracic or lumbar spine. Indications for hardware placement were degenerative/deformity disease (51.2%), spondylolisthesis (23.7%), tumor (22.7%), trauma (11.3%), infection (7.6%), and congenital (0.9%). A total of 115 screws (1.7%) were identified as breaching the pedicle in 87 patients (9.0%). Breach occurred more frequently in the thoracic than the lumbar spine (2.5% and 0.9%, respectively; P < .0001) and was more often lateral (61.3%) than medial (32.8%) or superior (2.5%). T4 (4.1%) and T6 (4.0%) experienced the highest breach rate, whereas L5 and S1 had the lowest breach rate. Eight patients (0.8%) underwent revision surgery to correct malpositioned screws.
  
  
  CONCLUSIONS
  Free-hand pedicle screw placement based on external anatomy alone can be performed with acceptable safety and accuracy and allows avoidance of radiation exposure encountered in fluoroscopic techniques. Image-guided assistance may be most valuable when placing screws between T4 and T6, where breach rates are highest.
authors.affiliation: Johns Hopkins Spinal Column Biomechanics and Surgical Outcomes Laboratory, Department of Neurosurgery, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
authors.forename: Scott L
authors.initials: SL
authors.lastname: Parker
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: McGirt
authors.forename: S Harrison
authors.initials: SH
authors.lastname: Farber
authors.forename: Anubhav G
authors.initials: AG
authors.lastname: Amin
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Rick
authors.forename: Ian
authors.initials: I
authors.lastname: Suk
authors.forename: Ali
authors.initials: A
authors.lastname: Bydon
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Sciubba
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Wolinsky
authors.forename: Ziya L
authors.initials: ZL
authors.lastname: Gokaslan
authors.forename: Timothy F
authors.initials: TF
authors.lastname: Witham
mesh_terms: D001863:Bone Screws; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae; D008297:Male; D008875:Middle Aged; D019637:Orthopedic Procedures / Q000295:instrumentation / Q000379:methods*; D012189:Retrospective Studies; D013123:Spinal Fusion / Q000295:instrumentation / Q000379:methods*; D013904:Thoracic Vertebrae