Monitoring of nerve root injury using transcranial motor-evoked potentials in a pig model.
METHODS
Animal experiment using transcranial motor-evoked potentials (tcMEPs) in a pig model.


OBJECTIVE
To validate measurement of tcMEPs from multiple myotomes in a pig model and determine the capacity to detect injury to a single nerve root.


BACKGROUND
The ability of intraoperative neuromonitoring methods to give information about a single nerve root remains poorly understood. Reports suggest that tcMEPs may be a reliable and accurate method to detect nerve root injury. An animal model to study the sensitivity and specificity of this technique has yet to be validated.


METHODS
Transcranial stimulation was delivered through customized electrodes placed in burr holes over the motor cortex in 7 pigs. Spontaneous and evoked muscle potential activity was recorded in 5 myotomes (rectus femoris, vastus lateralis, vastus medialis, tibialis anterior, and gastrocnemius) bilaterally. After unilateral exposure of the L3-S1 nerve roots, sequential ligations were performed. The tcMEP responses from all myotomes were measured after ligation of each nerve root.


RESULTS
Robust MEP responses (range, 37-1165 mV) were achieved in all monitored myotomes. Significant decreases in tcMEP amplitudes occurred in specific myotomes after ligation of the corresponding nerve root. Consistent and substantial decreases were observed after L3 and L5 ligations in rectus femoris (48%) and tibialis anterior (67%), respectively.


CONCLUSIONS
Our results validate monitoring of tcMEPs in multiple myotomes to detect nerve root injury in pigs. This model may be used for further study of the use of tcMEPs to detect predictors and risk factors of nerve root injury during spinal surgery.
Department of Orthopaedic Surgery, University of California, San Francisco, CA, USA.
James M
JM
Mok
Russ
R
Lyon
Jeremy A
JA
Lieberman
Jordan M
JM
Cloyd
Shane
S
Burch
D000818:Animals; D004558:Electric Stimulation; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D008026:Ligation; D008159:Lumbar Vertebrae / Q000294:innervation; D023421:Models, Animal; D016343:Monitoring, Intraoperative / Q000379:methods*; D018482:Muscle, Skeletal / Q000294:innervation; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013126:Spinal Nerve Roots / Q000502:physiology* / Q000601:surgery*; D013552:Swine