Pittsburgh, September 11, 1997 -- Spine surgeons at the University of Pittsburgh Medical Center (UPMC) report in the September Journal of Neurosurgery that a unique monitoring system used during certain delicate spine surgeries can be an added safeguard against bone and nerve injury.

Some patients with lumbar spinal instability undergo a surgical procedure called lumbar spinal fusion, in which vertebrae in the lower back are fused together with bone screws. The bony structure projecting around each vertebra is called the pedicle and in between are delicate nerves. The proximity of this delicate nerve tissue allows little room for surgical error during the fusion and pedicle bone screw insertion.

"It is not surprising that nerve root injury occurs in as many as 15 percent of these types of operations," said William C. Welch, MD, assistant professor of neurosurgery, co-director of the UPMC's Comprehensive Spine Center and study investigator.

"We evaluated a technique that uses continuous stimulation through an electrified pedicle probe and feeler designed to provide immediate sound feedback of nerve activity during preparation of the pedicle entry site and insertion of the implant screws," said Dr. Welch. "This serves as an early warning system alerting the surgeon if re-direction of the pedicle probe or screw is necessary to avoid nerve root irritation or injury."

The current commonly used monitoring techniques detect nerve and bone injury after the pedicle screws have already been placed in the bone. "This monitoring is helpful, but it may not detect subtle compromises in nerve root function and it does not preclude the possibility of creating nerve root damage during probing or tapping of the pedicle or placement of the screw," said Dr. Welch.

The UPMC study involved the insertion of 164 pedicle bone screws in 32 patients. Feedback via the electrified pedicle probes in appropriate muscle groups was successful in identifying surrounding pedicle bone compromise in four patients. "The evoked stimulation proved to be reliable. This technique may provide an added safeguard during implant placement procedures," the researchers report.

Dr. Welch and his team at the UPMC's Comprehensive Spine Center have been using the evoked stimulation monitoring system for more than five years. They perform about 50 lumbar fusions with pedicle bone screws each year on patients with spinal instability, which can be due to fractures, traumatic injuries or degenerative conditions or following removal of tumors.

Other investigators in the study include: Robert D. Rose, PhD, and Jeffrey R. Balzer, PhD, Center for Clinical Neurophysiology, and George B. Jacobs, MD, University of Medicine and Dentistry, Newark, NJ and University Medical Center, Hackensack, NJ.