1 Principles of Navigated Pedicle Screw Placement
Abstract
Treatment of spinal pathology often necessitates spinal instrumentation. The methods used for spinal instrumentation have changed significantly of the past decade. Most of the recent advancements in spinal instrumentation involve technology that allows the surgeon to place pedicle screws with minimal risk of complications. This chapter is a review of the steps a surgeon should take in order to reduce the risk of complication and to establish an efficient workflow in the operating room.
1.1 Introduction
The evolution of spinal instrumentation has improved significantly over the last few decades with transpedicular instrumentation becoming the favored tool of the spine surgeon for a wide variety of spinal stabilization procedures. However, new techniques in any surgical specialty also come with new complications. The rate of misplaced pedicle screws ranges from 14 to 55% with standard nonnavigated insertion techniques. Approximately 7% of these misplaced screws result in neurological injury. 1 , 2 , 3
Introduction of navigation techniques for spinal instrumentation came about around 1995 with the goal of improving instrumentation placement accuracy and reduced injury to neurovascular structures. 4 The advantages of spinal navigation for pedicle screw placement have been reported in multiple studies. 5 , 6 The use of image guidance systems has proven to reduce the number of pedicle breaches to less than 5%. 7 , 8
The purpose of this chapter is to discuss operative planning for cases that utilize navigation for posterior spinal instrumentation and discuss various types of image-guided systems available on the market.
1.2 Consideration for Operative Planning
1.2.1 Operating Room Setup
When utilizing intraoperative navigation systems there are a number of factors that should be considered prior to bringing the patient to the operating room. First is the region of the spine that is being instrumented (i.e., cervical, thoracic, thoracolumbar, lumbar, or lumbosacral). Each region requires a different positioning technique and different strategies for placement of registration trackers to minimize registration error.
The patient’s body habitus is another factor that should be considered prior to the operative intervention. Obese patients have increased soft tissue, which can create difficulties in positioning, beam penetration, exposure of the operative site, line-of-sight requirements for navigation systems, and the limited ability to maneuver the registering devices for accurate navigation. 8
Selection of the appropriate operative table is of utmost importance. Some of the most common operative tables include radiolucent Wilson frame and Jackson OSI table. There should be consideration for any special attachments for cervical cases in which the head should be fixated to the table to ensure accurate registration.
1.3 Types of Image-Guided Navigation
1.3.1 2D Navigation
This method utilizes fluoroscopic anteroposterior and lateral images that are acquired during surgery with a tracker affixed to the patient. The navigation system tracks the relative position of known instruments with respect to the patient and generates a synthetic view of these instruments in the fluoroscopic images. The advantages of this system are its speed, decreased radiation exposure, and ease of use. However, the next-generation three-dimensional (3D)-guided navigation systems have been shown to have better accuracy.
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