Clinical accuracy of computer-assisted two-dimensional fluoroscopy for the percutaneous placement of lumbosacral pedicle screws

Bheeshma Ravi, Ali Zahrai, Raja Rampersaud
Spine 2011 January 1, 36 (1): 84-91

STUDY DESIGN: Clinical case series.

OBJECTIVE: The primary objective of this study was to evaluate the clinical accuracy of computer-assisted two-dimensional fluoroscopy (2D-CAS) for the percutaneous placement of lumbosacral pedicle screws.

SUMMARY OF BACKGROUND DATA: Loss of visual anatomic landmarks and reduced tactile feedback increases the risk of pedicle screw misplacement by when using minimally invasive (MIS) percutaneous techniques. However, objective data on screw misplacement in this scenario is lacking.

METHODS: A MIS-2D-CAS technique (FluoroNav) was used for the placement of pedicle screws in 41 consecutive patients undergoing MIS-interbody instrumented fusion. Postoperative computerized tomography (CT) was obtained in all patients at 6 months after surgery and was evaluated by 3 observers. The relative position of the screw to the pedicle was graded regarding pedicle breach (I, no breach; II, <2 mm; III, 2-4 mm; IV, >4 mm), breach direction, vertebral body perforation and screw trajectory. Interobserver reliability of CT grading was assessed with kappa statistics.

RESULTS: A total of 161 screws were placed. No neurologic, vascular, or visceral injuries occurred. About 37 (23%) screws breached the pedicle. The majority (83.8%, 31/37) of breaches were graded II. There were 5 Grade III and 1 Grade IV breaches. Medial versus lateral breaches occurred in 30% (11/37) and 60% (22/37), respectively; 10% (4/37) of the breaches were superior. Overall, 8 (5%) vertebral body breaches occurred. Of the pedicle screws, 19 (12%) had trajectories that deviated from acceptable, with the majority being medial (16/19, 84%). Fluoroscopy time for screw placement was typically less than 20 seconds total per case. There was 1 clinically significant breach at L5 (III, medial) which resulted in a L5 radiculopathy. Kappa statistics showed excellent overall agreement between reviewers (k = 0.73-0.92; 90%-96% agreement).

CONCLUSION: The two-dimensional (2D) virtual fluoroscopy is a clinically acceptable option for percutaneous placement of pedicle screws. However, this technique requires cautious application and is particularly vulnerable to axial trajectory errors.

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