The limits of intraoperative fluoroscopic navigation

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Jeff McConnell

Whilst intraoperative fluoroscopic navigation may offer a number of benefits to spinal surgery, uptake in the field is still relatively low. Jeff McConnell talks to Spinal
 News
 International about the limits of this technology.

What can intraoperative fluoroscopic navigation enable physicians to achieve?

 

There is an important difference, here, between fluoroscopic imaging and fluoroscopic navigation. I use fluoroscopic imaging frequently to localise bony anatomy to assist in placing pedicle screws percutaneously in the spine. It is truly “real-time” imaging. A disadvantage is that the images obtained are two-dimensional. Capturing these images also leads to radiation exposure. Fluoroscopic navigation can be done in different ways, all based on obtaining anteroposterior and lateral fluoroscopic images using an aftermarket reference frame attached to the C-arm. The images are then correlated using computer software with a pre-operative computed tomography (CT) scan. The simplest software system that I have seen simply requires the surgeon to plot screw direction with triangulation, and then line up the starting point on the skin with fluoroscopy. As long as you maintain the proper angle of trajectory, then placement should be successful. This can be fiddly, and it takes time to plot each screw. This seems less accurate to me.

What are the main problems associated with the use of this technology?

 

The main problem with live fluoroscopic imaging is the radiation that both patient and surgeon are exposed to, particularly the cumulative life-time dose that surgeons receive. CT-based navigation—such as with an O-arm—is better for the surgeon, but there remains a significant radiation dose for the patient. Navigation is also based on the patient’s position when the scan was done.  If the spine moves relative to the reference frame then accuracy is compromised. In the case of percutaneous surgery, or surgery involving multiple levels, O-arms are not as useful or accurate. In my opinion, CT-based computer navigation systems and robotic systems are not completely accurate when you are interested in the 1–3mm range.

What risks are associated with intraoperative exposure to radiation?

 

Radiation brings a cancer risk for both patient and surgeon. This accumulates over time for the surgeon. Thyroid cancer and lymphoid cancers are the most common. Even a single whole spine preoperative CT scan can increase a patient’s risk of cancer.

 

The risk of breast cancer is higher in women who had repeated spine X-rays as adolescents when monitored for scoliosis during growth. Such risks have been fairly well mitigated by the fact that X-ray machines today are more efficient, and the cumulative doses from digital X-rays are magnitudes less.

What do physicians need to keep in mind when using these kinds of navigation systems?

 

Sometimes a combination of direct vision, tactile feedback and navigation is the best way to minimise problems. I like the PediGuard (SpineGuard) technology, for example, as it provides both tactile and directional auditory feedback, and can help to prevent pedicle bone perforation. I use it an adjunct to neuromonitoring in deformity cases and for one- or two- level fusion cases in the lumbar spine it can eliminate the need for monitoring altogether.

When using navigation systems, physicians must understand the level of accuracy required prior to starting each procedure, and the level of accuracy your navigation system will provide. Surgeons should be familiar with how to do surgery in an open fashion without navigation, should the computer fail or operate incorrectly. Navigation does not perform the surgery for you and does not eliminate complications.  Navigation does not make a less experienced surgeon better.

Jeff McConnell is a spinal and orthopaedic surgeon at OAA Orthopaedic Specialists, Allentown, USA, and a clinical assistant professor of surgery at Pennsylvania State University, Hershey, USA