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The Spine Blog

Saturday, July 13, 2019

Image Guided Navigation Technology for Pedicle Screw Insertion

Navigation technology to improve pedicle screw insertion accuracy has been developing rapidly. The most commonly used platform uses an intra-operative CT scan combined with optical markers attached to the patient and instruments in order to track the position of the instruments relative to the spine in real time. Other than the intra-operative CT scan, no other radiation is used during the navigation process. The other technology that is being adopted involves a pre-operative CT scan, creation of  a 3D model on which screw trajectories are planned, and 3D printing of drill guides that fit the patient anatomy. In theory, no intra-operative radiation is necessary to use this technology, though surgeons may intermittently use fluoroscopy to ensure that drill trajectories match the pre-operative plan. The goals of these technologies include accuracy, efficiency, and minimization of radiation to both the patient and operating room team. Cost is another important factor in today's fiscally constrained healthcare environment. In order to evaluate a new navigation system designed for percutaneous screw placement, Dr. Burstrom and colleagues from Sweden performed a pig cadaver study using a system in which an intra-operative CT scan was combined with optical markers placed on the skin and instruments. No navigation array was attached to the spine itself, and the entire spine could be navigated without registering points or moving any of the optical markers. Incisions for the percutaneous screws and screw trajectories were planned using the virtual model based on the CT scan. The pedicle was then cannulated using either a tracked Jamshidi needle or a tracked power drill. A K-wire was then placed through the Jamshidi needle or the drill bit was left in place to allow for accuracy assessment with a post-procedure CT scan. Two experienced neurosurgeons cannulated 78 pedicles, with only 2 clinically significant pedicle breaches. The authors classified these as surgical technique errors related to the needle or drill bit slipping down a sloped surface rather than a navigation error. They found an average error at the entry point of 1.7 mm (maximum 5.7 mm) and 2 mm (maximum 6.4 mm) at the tip of the screw. Mean angular error was less than 2 degrees.

The authors have done a nice job evaluating and quantifying a system designed to navigate percutaneous pedicle screw placement. This system seems to have the advantage of using optical markers placed on the skin rather than a fixed navigation array that needs to be relatively close to the site of navigation and can be bumped during surgery, resulting in a loss of accuracy. Technology is rapidly evolving in this realm, and hopefully we will soon have systems that are accurate, require minimal radiation exposure, and fit seamlessly into the flow of an operation. The current technology requiring intra-operative CT scan and the use of an array fixed to the spine adds significant time to the operation and provides a relatively limited field that can be navigated prior to having to move the array and repeat a CT scan. The 3D printed drill guides are an appealing technology, though the current cost of this technique is bordering on prohibitive. Additionally, it requires aggressive removal of soft tissue for the jigs to fit appropriately, and this is at odds with MIS philosophy. The current paper serves as a good proof of concept in the lab. We await further clinical validation of the system. It seems likely that the current available navigation technology is in its infancy, and hopefully the technology available in ten years from now will combine accuracy, efficiency, and radiation reduction in ways we can only imagine now.

Please read Dr. Burstrom's article on this topic in the August 1 issue. How do you currently use navigation and screw guidance technology in your practice? Let us know by leaving a comment on The Spine Blog.

Adam Pearson, MD, MS

Associate Web Editor