BACKGROUND
This cadaveric study compared efficacy and safety of an electromagnetic (EM) guidance system versus conventional fluoroscopy for percutaneous pedicle screw fixation. As percutaneous pedicle screw fixation becomes increasingly common in spinal surgery, intraoperative imaging systems that maximize efficiency while minimizing radiation exposure and inaccurate trajectories will be progressively more important. Published studies have validated the safety of percutaneous screw fixation using conventional fluoroscopic guidance and frameless optical stereotaxy, though EM guidance systems have not been evaluated for percutaneous placement in the lumbosacral spine. The aim of the study was to evaluate the clinical applicability of an EM system for minimally invasive spine fusion in the lumbosacral spine.

METHODS
Five human cadaveric specimens underwent bilateral lumbosacral percutaneous screw fixation from L1 to S1 using conventional anteroposterior (AP) and lateral fluoroscopic techniques on one side and 2-dimesional (2D) EM guidance on each matching side. Intraoperative efficiency was evaluated, and pedicle, vertebral, and critical breach rates were assessed on postoperative computed tomography (CT).

RESULTS
Overall mean fluoroscopy time per screw was 58.9 ± 44.7 seconds for conventional fluoroscopy compared to 27.4 ± 13.5 seconds for electromagnetic guidance (P = .0003). Pedicle, vertebral, and critical breach rates for the L1-S1 were 32.1%, 10.7%, and 25.0% for conventional fluoroscopy and 42.8%, 10.7%, and 14.1% for electromagnetic guidance (difference not statistically significant [ns]). In comparing critical breaches in the lumbar spine (L1-L5), there was a significant difference between 2-D EM guidance (0) and CF guidance (6) (P = .02).

CONCLUSIONS
Two-dimensional EM navigation provides a modality for lumbosacral percutaneous pedicle screw fixation that is more efficient and safer than conventional fluoroscopy. This data provides a foundation for further clinical trials of this technology.

Level of Evidence
Level 5 – Bench Research

Key Words Minimally invasive spine fusion, percutaneous pedicle screw fixation, electromagnetic guidance. SAS Journal. Winter 2008;2:43–47. DOI: SASJ-2007-0105-RR

Justin F. Fraser, MD, Ron Von Jako, MD, John A. Carrino, MD, MPH, and Roger Härtl, MD

From Department of Neurological Surgery, Weill Medical College of Cornell University, New York Presbyterian Hospital, New York, NY (Fraser and Härtl); Surgical Development Leader, GE Healthcare Surgery (Von Jako); and Division of Musculoskeletal Radiology, Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD (Carrino)

Ron Von Jako, MD, is an employee and shareholder in GE Healthcare Surgery. Cadaveric specimens were provided by GE Healthcare Surgery. Drs. Fraser, Carrino, and Härtl are not paid employees and do not receive personal stipends from GE Healthcare Surgery.

Address correspondence to Roger Härtl, MD, Department of Neurological Surgery, Weill Medical College of Cornell University, New York Presbyterian Hospital, 525 E. 68th St., Box 99, New York, NY 10021, (email: roger@hartlmd.net)

This manuscript was submitted June 17, 2007, and accepted for publication November 20, 2007.