16 Patients undergoing Lumbar Selective Endoscopic Discectomy (SED) using the Y.E.S.S. method was monitored intraoperatively for SEP (somatosensory evoked potentials) and EMG (electromyography) activity. 18 cases were analyzed. Questions: Is Intraoperative Neuromonitoring of SEP and EMG safe, effective and useful in SED cases? What information does it yield, if any?
SEP: On average, the patients experienced a decrease in N1 latency (Cervical, PNS response) of 2.53 msec. The P1 latency, (Cortical, CNS response) the first recordable scalp component of the waveform decreased 1.07 msec, comparing the pre-op values to the post-op studies. Amplitudes measuring the first cortical slope of P1- N2 decreased .01 milliamps on average. N2-P2 slope amplitudes increased 34.79 milliamps.
EMG: Mechanical elicitation of evoked discharges occurred in 6 cases, (33%). Discharges correlated with the action of tapping past the nerve into the disc space with a cannula. EMG neurotonic irritation response patterns were exhibited by 2 patients (11%). In both cases, the EMG returned to baseline after disc material was removed from the nerve area.
Conclusion: SEP monitoring documented the decrease in latency of the initial cervical and cortical responses post operatively. Marginal amplitude decrease of the initial slope of the cortical waveform was noted, but significant increase in 2nd slope amplitude was seen on average. Overall, these latency and amplitude changes reflect measurable recordable improvement of the central and peripheral nervous system pathways when comparing pre-op and post-op values.
EMG monitoring provided additional information to the surgeon regarding the position and irritability of the nerves in the operative area. EMG muscles could be correlated to the level of lumbar spine on x-ray imaging and physician visualization of the nerve in the operative field. No adverse events were reported.
The Method for SEP collection is presented, results are discussed, and clinical correlation is provided in 100 patients.