Spinal cord injury from electrocautery: observations in a porcine model using electromyography and motor evoked potentials
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We have previously investigated electromyographic (EMG) and transcranial motor evoked potential (MEP) abnormalities after mechanical spinal cord injury. We now report thermally generated porcine spinal cord injury, characterized by spinal cord generated hindlimb EMG injury activity and spinal cord motor conduction block (MEP loss). Electrocautery (EC) was delivered to thoracic level dural root sleeves within 6–8 mm of the spinal cord (n = 6). Temperature recordings were made near the spinal cord. EMG and MEP were recorded by multiple gluteobiceps intramuscular electrodes before, during, and after EC. Duration of EC was titrated to an end-point of spinal motor conduction block (MEP loss). In 5/6 roots, ipsilateral EMG injury activity was induced by EC. In 4/5 roots, EMG injury activity was identified before MEP loss. In all roots, a minimum of 20 s EC and a temperature maximum of at least 57 °C at the dural root sleeve were required to induce MEP loss. Unexpectedly, conduction block was preceded by an enhanced MEP in 4/6 trials. EMG injury activity, preceding MEP loss, can be seen during near spinal cord EC. Depolarization and facilitation of lumbar motor neurons by thermally excited descending spinal tracts likely explains both hindlimb EMG and an enhanced MEP signal (seen before conduction block) respectively. A thermal mechanism may play a role in some unexplained MEP losses during intraoperative monitoring. EMG recordings might help to detect abnormal discharges and forewarn the monitorist during both mechanical and thermal injury to the spinal cord.
KeywordsNeuromonitoring Electromyography Motor evoked potential Electrocautery Thermal spinal cord injury
The authors would like to thank Joyce Wiberg REEG, Angie Talbot, and Michelle Vrieze, CNIM (neuromonitoring technologist) for their capable assistance. They would also like to thank the following for assistance with manuscript preparation: Deanna Aleksandrowicz, Larry Sobaskie, and Carol Garner (medical illustrator).
Conflict of interest
Dr. Skinner and Dr. Transfeldt are royalty bearing for patent through Medtronic Sofamor-Danek. Dr. Mehbod is a consultant for Medtronic Sofamor-Danek. Dr. Rippe, Dr. Wu, Dr. Hsu, and Dr. Erkan have no financial interests to disclose.
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