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Electromagnetic Field-Based Image-Guided Spine Surgery Part One: Results of a Cadaveric Study Evaluating Lumbar Pedicle Screw Placement

Sagi, H. C. MD*; Manos, R. MD2; Benz, R. MD3; Ordway, N. R. MS, PE4; Connolly, P. J. MD4

doi: 10.1097/01.BRS.0000087851.51547.00

Study Design. Human cadaveric.

Objectives. Compare the accuracy of electromagnetic field (EMF)-based image-guided lumbar pedicle screw insertion to conventional techniques using anatomic landmarks, and fluoroscopy.

Background. Image-guided surgical systems that aid in spinal instrumentation seek to minimize radiation exposure and improve accuracy. EMF tracking-based image-guidance was developed in the hopes of eliminating line-of-sight restrictions seen with other systems.

Materials and Methods. Sixteen fresh-frozen human cadavers were randomly allocated into three groups. Pedicle screws were inserted from L1 to L5 using only anatomic landmarks in group 1, fluoroscopy in group 2, and image-guidance in group 3. Insertion and total fluoroscopic time were recorded. Anatomic dissections were performed to assess screw placement.

Results. Accuracy was 83%, 78%, and 95% for groups 1, 2, and 3, respectively. However, image-guided pedicle screw placement resulted in a 5% critical perforation rate whereas anatomic and fluoroscopic placement resulted in a 15% and 22% critical perforation rate, respectively. The average degree of perforation was 1.5 mm with image guidance, and 3.8 mm with fluoroscopic guidance (P < 0.05). Fluoroscopy time and insertion time per screw were not improved using image guidance.

Conclusions. Our study has shown that when EMF tracking was used for image-guided lumbar pedicle screw placement, accuracy was improved and the incidence and degree of cortical perforations that may place neurovascular structures at risk was also reduced. Current system requirements for set-up and image acquisition, however, do add time to the procedure, and when factored in, do not yet result in a decrease in the use of fluoroscopy or screw insertion time.

From *University of California San Francisco-Fresno, Fresno, CA;

2Naval Medical Center, San Diego, CA;

3Fort Collins, CO; and

4SUNY Upstate Medical University, Syracuse, NY

Acknowledgment date: January 22, 2002.

Revision date: October 30, 2002.

Acceptance date: January 14, 2003.

Address correspondence to H. Claude Sagi, MD, University Medical Center, Fourth Floor, Department of Orthopaedics, 445 South Cedar Avenue, Fresno, CA 93702; e-mail:

Partial funding and assistance was provided by Visualization Technology, Inc. and Synthes, USA.

© 2003 Lippincott Williams & Wilkins, Inc.