title: Frameless stereotaxy for anterior spinal procedures.
abstract: OBJECTIVE
  Intraoperative image guidance provides real-time three-dimensional visualization and has been successfully applied in many posterior spinal procedures. The feasibility of applying these techniques to anterior spinal surgery has not been studied systematically because the anterior spine, in contrast to the posterior spine, lacks distinct anatomical landmarks for registration. The authors sought to evaluate the practicality of performing stereotaxy in the anterior spine in a cadaveric model.
  
  
  METHODS
  Unilateral C4-L4 pedicle screws were placed posteriorly in three cadaveric specimens to serve as unknown markers within each vertebral body. The specimens then underwent computerized tomography (CT) scanning, and the CT data were transferred to an optical tracking system. The anterior surface of the spine was registered for use with the stereotactic system by using a paired point-matching technique. Attached to a surgical drill, K-wires were placed under stereotactic guidance in a tip-to-tip orientation with the posterior pedicle screws. A second postoperative CT scan was obtained, and accuracy was determined by measuring the distance between the tips of the K-wire and pedicle screw. The K-wires were placed tip to tip with pedicle screw markers in 57 vertebral levels. The mean registration error was 1.47+/-0.04 mm, and when combined with the universal instrument registration error of 0.7 mm yielded an overall registration error of 2.17+/-0.04 mm. The mean tip-to-tip distance for all K-wires placed was 2.46+/-0.23 mm. The difference between the mean tip-to-tip distance and overall registration error was not statistically significant (p > 0.05), indicating that the K-wires were placed within the expected range of error.
  
  
  CONCLUSIONS
  The results of this study confirmed the feasibility of performing anterior stereotactic procedures throughout the spine. The accuracy of the findings in this study indicates that anterior stereotaxy should be applicable in clinical practice.
authors.affiliation: Division of Neurosurgery, University of California at Los Angeles Medical Center, USA.
authors.forename: L T
authors.initials: LT
authors.lastname: Holly
authors.forename: O
authors.initials: O
authors.lastname: Bloch
authors.forename: C
authors.initials: C
authors.lastname: Obasi
authors.forename: J P
authors.initials: JP
authors.lastname: Johnson
mesh_terms: D000328:Adult; D001863:Bone Screws; D001864:Bone Wires; D002102:Cadaver; D005240:Feasibility Studies; D006801:Humans; D013131:Spine / Q000601:surgery*; D013238:Stereotaxic Techniques; D014057:Tomography, X-Ray Computed