Neuromonitoring of an experimental model of clip compression on the spinal nerve root to characterize acute nerve root injury.
OBJECTIVE
To evaluate the sensitivity of an electro-monitoring method in acute nerve root injury, and to determine a proposed criterion for irreversible electrophysiologic degradation.


METHODS
Acute nerve root injury was induced by a clip compression model in rabbits, mimicking nerve root injury by a transpedicular screw. A common neuromonitoring technique, spinal somatosensory-evoked potential, was used to study the electrophysiologic change during the procedure.


BACKGROUND
With the advent of the transpedicular screw system, increased risk of injury to the spinal root because of the passage of screws is not unexpected. Although both an experimental model and a clinical application in intraoperative neuromonitoring of spinal cord function have been established, the value of neuromonitoring of an acute spinal root injury remains obscure. Several neurophysiologic surveillance techniques have been used successfully to monitor the potential injury to the spinal cord during orthopedic procedures around the spinal cord 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 screws.


METHODS
Experimental acute nerve root injury was induced in rabbits by direct hemostatic clip compression on the nerve root (S1) during different time intervals. Spinal somatosensory-evoked potential elicited by stimulating the sciatic nerve and recorded from a needle electrode at the L6-L7 interspinous ligament was monitored immediately before and after compression.


RESULTS
Spinal somatosensory-evoked potential is sensitive enough to detect the compromise of a single nerve root and that a decrease in the amplitude is the most reliable and sensitive sign. With this model, there was a statistically significant correlation between the compression time and reduction of amplitude and delay of latency. The criterion for irreversible electrophysiologic change was an amplitude loss of more than 20% and a delay in latency immediately after nerve root compression.


CONCLUSIONS
It was concluded 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.
Jou
I M
IM
Department of Orthopedics, National Cheng-Kung University Hospital, Tainan, Taiwan, Republic of China.
Lai
K A
KA
D000818:Animals; D001863:Bone Screws / Q000009:adverse effects*; D004195:Disease Models, Animal; D004869:Equipment Safety; D005073:Evoked Potentials, Somatosensory; D007431:Intraoperative Complications / Q000175:diagnosis; D007796:Laminectomy; D008159:Lumbar Vertebrae / Q000601:surgery; D008297:Male; D009408:Nerve Compression Syndromes / Q000175:diagnosis / Q000209:etiology / Q000503:physiopathology*; D011817:Rabbits; D012584:Sciatic Nerve / Q000502:physiology; D012680:Sensitivity and Specificity; D013126:Spinal Nerve Roots / Q000293:injuries* / Q000473:pathology / Q000503:physiopathology