NEUROMONITORING OF AN EXPERIMENTAL-MODEL OF CLIP COMPRESSION ON THE SPINAL NERVE ROOT TO CHARACTERIZE ACUTE NERVE ROOT INJURY

Objectives. To evaluate the sensitivity of an electromonitoring method in acute nerve root injury, and to determine a proposed criterion for irreversible electrophysiologic degradation. Study Design. Acute nerv e root injury was induced by a clip compression model in rabbits, mimi cking nerve root injury by a transpedicular screw. A common neuromonit oring technique, spinal somatosensory-evoked potential, was used to st udy the electrophysiologic change during the procedure. Summary of Bac kground Data. With the advent of the transpedicular screw system, incr eased risk of injury to the spinal root because of the passage of scre ws is not unexpected. Although both an experimental model and a clinic al application in intraoperative neuromonitoring of spinal cord functi on have been established, the value df neuromonitoring of an acute spi nal root injury remains obscure. Several neurophysiologic surveillance techniques have been used successfully to monitor the potential injur y to the spinal cord during orthopedic procedures around the spinal co rd and spinal column. Spinal somatosensory-evoked potential, which has the advantages of high amplitude and quick recording time, is used to detect nerve root impairment during the insertion of transpedicular s crews. Methods, Experimental acute nerve root injury was induced in ra bbits by direct hemostatic clip compression on the nerve root (S1) dur ing different time intervals. Spinal somatosensory-evoked potential el icited by stimulating the sciatic nerve and recorded from a needle ele ctrode at the L6-L7 interspinous ligament was monitored immediately be fore and after compression. Results. Spinal somatosensory-evoked poten tial is sensitive enough to detect the compromise of a single nerve ro ot and that a decrease in the amplitude is the most reliable and sensi tive sign. With this model, there was a statistically significant corr elation between the compression time and reduction of amplitude and de lay of latency. The critical criterion for irreversible electrophysiol ogic change was an amplitude loss of more than 20% and a delay in late ncy immediately after nerve root compression. Conclusions. It was conc luded that spinal somatosensory-evoked potential can provide immediate feedback of nerve root injury and should be considered for use during the dynamic phase of transpedicular screw insertion.