title: Accuracy of cervical pedicle screw placement using the funnel technique.
abstract: METHODS
  This was a cadaver study assessing the accuracy of cervical pedicle screw placement.
  
  
  OBJECTIVE
  To evaluate the accuracy of the funnel technique of screw placement.
  
  
  BACKGROUND
  Although excellent results have been reported in clinical studies, with no major neurovascular injuries, several cadaveric studies have shown a high pedicle perforation rate during screw placement.
  
  
  METHODS
  Ten fresh frozen cervical spines (C2-C7) were used (120 pedicles, 20 pedicles per level). The average specimen age was 79.6 years (range 65-97); the average height was 159 cm (range 155-175). The male-to-female ratio was 3:7. Pedicle width and angulation were measured on preoperative axial computed tomography (1-mm slices). By use of four bony landmarks and the funnel technique, screws were placed under direct vision. Critical perforations (documented contact of a screw with, or an injury to, a spinal cord, nerve root, or vertebral artery) and noncritical perforations (a perforation with no critical contact) were recorded.
  
  
  RESULTS
  In seven pedicles (5.8%) the procedure was aborted because of a small or nonexistent pedicle medullary canal. Ninety-four pedicle screws (83.2%) were placed correctly, whereas 11 pedicles (9.7%) had noncritical perforations and 8 pedicles (7.1%) had critical perforations. The majority of the critical and noncritical perforations were at C3, C4, and C5.
  
  
  CONCLUSIONS
  Axial computed tomography is necessary for the preoperative planning. Because of the small diameter and steep angulation of cervical pedicles, every spine surgeon who intends to use pedicle screws should first master the technique on cadavers.
authors.affiliation: Department of Orthopaedic Surgery, University of Missouri, Columbia 65212, USA. KaraikovicE@health.missouri.edu
authors.forename: E E
authors.initials: EE
authors.lastname: Karaikovic
authors.forename: W
authors.initials: W
authors.lastname: Yingsakmongkol
authors.forename: R W
authors.initials: RW
authors.lastname: Gaines
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001863:Bone Screws / Q000009:adverse effects; D002102:Cadaver; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D005260:Female; D006801:Humans; D008297:Male; D009985:Orthopedics / Q000379:methods* / Q000592:standards*; D013119:Spinal Cord Injuries / Q000209:etiology; D014057:Tomography, X-Ray Computed