title: A novel radiographic targeting guide for percutaneous placement of transfacet screws in the cervical spine with limited fluoroscopy: A cadaveric feasibility study.
abstract: BACKGROUND
  We describe a technique for percutaneous transfacet screw placement in the cervical spine without the need for lateral-view fluoroscopy.
  
  
  METHODS
  Previously established articular pillar morphometry was used to define the ideal trajectory for transfacet screw placement in the subaxial cervical spine. A unique targeting guide was developed to allow placement of Kirschner wires across the facet joint at 90° without the guidance of lateral-view fluoroscopy. Kirschner wires and cannulated screws were placed percutaneously in 7 cadaveric specimens. Placement of instrumentation was performed entirely under modified anteroposterior-view fluoroscopy. All specimens were assessed for acceptable screw placement by 2 fellowship-trained orthopaedic spine surgeons using computed tomography. Open dissection was used to confirm radiographic interpretation. Acceptable placement was defined as a screw crossing the facet joint, achieving purchase in the inferior and superior articular processes, and not violating critical structures. Malposition was defined as a violation of the transverse foramen, spinal canal, or nerve root or inadequate fixation.
  
  
  RESULTS
  A total of 48 screws were placed. Placement of 45 screws was acceptable. The 3 instances of screw malposition included a facet fracture, a facet distraction, and a C6-7 screw contacting the C7 nerve root in a specimen with a small C7 superior articular process.
  
  
  CONCLUSIONS
  Our data show that with the appropriate radiographic technique and a targeting guide, percutaneous transfacet screws can be safely placed at C3-7 without the need for lateral-view fluoroscopy during the targeting phase. Because of the variable morphometry of the C7 lateral mass, however, care must be taken when placing a transfacet screw at C6-7.
  
  
  CONCLUSIONS
  This study describes a technique that has the potential to provide a less invasive strategy for posterior instrumentation of the cervical spine. Further investigation is needed before this technique can be applied clinically.
authors.affiliation: Department of Orthopaedics, University of Maryland, Baltimore, MD.
authors.forename: David M
authors.initials: DM
authors.lastname: Jackson
authors.affiliation: Department of Orthopaedics, University of Maryland, Baltimore, MD.
authors.forename: Jacqueline E
authors.initials: JE
authors.lastname: Karp
authors.affiliation: Department of Orthopaedic Surgery, George Washington University Hospital, Washington, DC.
authors.forename: Joseph R
authors.initials: JR
authors.lastname: O'Brien
authors.affiliation: Department of Orthopaedic Surgery, Thomas Jefferson University Hospital, Philadelphia, PA.
authors.forename: D Greg
authors.initials: DG
authors.lastname: Anderson
authors.affiliation: Department of Orthopaedics, University of Maryland, Baltimore, MD.
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Gelb
authors.affiliation: Department of Orthopaedics, University of Maryland, Baltimore, MD.
authors.forename: Steven C
authors.initials: SC
authors.lastname: Ludwig
keywords: Cervical spine; Minimally invasive surgery of the spine; Radiographic targeting guide; Transfacet screws