3-D Image Guidance to Improve Surgical Outcomes

Maps show the lay of the land. A global positioning system (GPS) can pinpoint a location in relation to the larger map. In spine surgery, CT and MRI scans are the anatomic maps, and image-guidance technology is the GPS, telling surgeons the exact positions of their instruments as they operate. The instruments are equipped with light-emitting diodes that send signals to a camera connected to a computer. The computer then uses triangulation to compute the location of the instrument on the patient's anatomy and integrate it into the MRI image on a screen in the operating room. The integrated image may be 2- or 3-dimensional, depending on the type of image-guidance system used.

Developed in the early 1990s, image guidance is a real-time navigation system that continues to improve outcomes for surgical procedures involving the spine, including spinal reconstruction. Barry D. Birch, M.D., a Mayo Clinic neurosurgeon in Phoenix/Scottsdale, Arizona, notes, "It is also useful for tumor location in both the brain and the spine." William E. Krauss, M.D., his neurosurgery colleague at Mayo Clinic in Rochester, Minnesota, adds, "It's often difficult for the surgeon to ascertain the exact position of hands and instruments during procedures to correct degenerative or congenital deformities or when repairing traumatic injuries, but image-guidance greatly improves navigation capabilities."

Operating Room
Set-up

Eric W. Nottmeier, M.D., a neurosurgeon at Mayo Clinic in Jacksonville, Florida, demonstrated just how much image guidance can increase safety in a recent retrospective study. In 1,200 spinal screws placed using 3-D image guidance, there were no vascular, visceral, or spinal cord injuries, and the incidence of injury to the nerve roots was less than 1%. In the literature, the incidence of injury associated with conventional techniques can occur in up to 11% of cases.

In the upper thoracic spine, screw malposition rates are as high as 41%, in part because of the small size of the pedicles and difficulty visualizing the anatomy with lateral fluoroscopy. In Dr. Nottmeier's current study of upper thoracic pedicle screws, 146 screws have been placed in the upper thoracic spine using 3-D image guidance with a 6.9% incidence of minor screw breach of the pedicle, which was of no clinical consequence.

At Mayo Clinic's 3 locations, neurosurgeons have seen improved outcomes with image guidance. Dr. Krauss states, "Since we started using the 3-D system in Rochester 2 years ago, we have not had a single misplaced screw." Dr. Birch notes some other advantages. "Not as many x-rays or scans are needed before the procedure. Without an x-ray or fluoroscopy unit in the field, the surgeon's radiation exposure is reduced, and from an ergonomic standpoint, it is much more comfortable to operate."

Recently, Dr. Nottmeier described a new minimally invasive fusion surgery technique using 3-D image guidance. Application of translaminar facet screws to stabilize the spine can be performed with either an open or a percutaneous approach. Often, posterolateral or dorsal facet joint fusion performed at the same time improves outcomes. However, the combined procedure has only been possible with an open approach. Using a minimally invasive percutaneous approach, Dr. Nottmeier has placed facet screws with concurrent dorsal facet fusion resulting in 360° fusion.

A Screenshot from the Image-Guidance System

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As image guidance continues to advance the practice of spine surgery, other technologies are being developed to work in concert with it. Dr Krauss notes, "The next step, something we're working on at Mayo Clinic, is the development of robotic systems to automate screw placement and other aspects of the procedure."