September 2000

Spinal Navigation

Medicine

By Yudhijit Bhattacharjee

Accuracy is critical to all surgeries, particularly those involving the nervous system, where the slightest error can cause permanent damage. While neurosurgeons operating on the brain have dramatically improved surgical accuracy over the last several years, similar advances in surgeries involving the spinal cord have proven more vexing. One reason is that while surgeons can navigate inside the skull using an external reference-a head ring fixed to the cranium-it's far more difficult for them to find their way about when doing spinal operations. As a result, there is a significantly high misplacement rate associated with the fixing of screws in the spine-a common procedure to correct deformities and fractures.

To improve that statistic, neurosurgeons at the Jena College of Medicine in Jena, Germany, have developed the first spinal navigation technique that employs CT scans obtained during the surgery. Such real-time imaging has been used for cranial navigation, and the German physicians successfully applied the strategy to spinal surgery by using a mobile CT scanner and small titanium screws implanted in the vertebrae as markers. By touching each of these titanium screws with a pointing device, the surgeon can achieve perfect registration, which means the CT image on display is perfectly aligned with the region being operated upon.

All the instruments used in the surgery are fitted with light-emitting diodes, and the procedure is recorded by an infrared camera. A tracking device fixed on the spine keeps account of the movements made by the patient during surgery-just the breathing can disturb the registration-and allows the navigation system to update its images five to 10 times every second. "The surgeon gets an almost real-time picture of the region of interest, along with the position of all the instruments," says Kristian Ebmeier, a member of the team that developed the system.

The technique isn't necessary for all types of spinal surgeries, says Iain H. Kalfas, head of spinal surgery at The Cleveland Clinic Foundation. However, Kalfas expects the advance will "be helpful" to fix fractures or address tumors and deformities.