Frameless stereotaxy for anterior spinal procedures

Object. Intraoperative image guidance provides real-time three-dimensional visualization and has been successfully applied in many posterior spinal pr ocedures. The feasibility of applying these techniques to anterior spinal s urgery has not been studied systematically because the anterior spine, in c ontrast to the posterior spine, lacks distinct anatomical landmarks for reg istration. The authors sought to evaluate the practicality of performing st ereotaxy in the anterior spine,in a cadaveric model. Methods. Unilateral C4-L4 pedicle screws were placed posteriorly in three c adaveric 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 surfa ce of the spine was registered for use with the stereotactic system by usin g a paired point-matching technique. Attached to a surgical drill, K-wires were placed under stereotactic guidance in a tip-to-tip orientation with th e posterior pedicle screws. A second postoperative CT scan was obtained, an d 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 vertebr al levels. The mean registration error was 1.47 +/- 0.04 mm, and when combi ned with the universal instrument registration error of 0.7 mm yielded an o verall 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 me an 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 perform ing anterior stereotactic procedures throughout the spine. The accuracy of the findings in this study indicates that anterior stereotaxy should be app licable in clinical practice.