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Tag: Dr. John Porter

SEP as a Sensory Pathway Integrity Check

Over the past two decades, intraoperative spinal cord monitoring has matured into a widely used clinical tool. It is used when the spinal cord is at risk for damage during a surgery. This includes orthopedic, neurosurgical, and certain cardiothoracic procedures.

Endoscpic spine surgery is technically feasible, and often produces excellent clinical and neurological results. Somatosensory Evoked Potential (SEP) testing has been used in surgery as a measure of peripheral and central nervous system integrity in humans and animals. SEP baseline and post-operative measurements may document both preexisting conditions and operative outcomes when elements of the central and peripheral nervous system are at risk for compromise.

Compared with alternative techniques such as dermatomal SEP and Motor evoked potentials, SEP techniques are used most widely and generally accepted. SEP studies have also been shown to reduce surgical morbidity. A large multicenter study has shown that continuous intraoperative SEP monitoring reduces postoperative paraplegia by more than 50-60%.

Method for SEP collection is presented, results are discussed, and clinical correlation is provided in 100 patients.

Percutaneous Selective Endoscopic Discectomy and Thermal Annuloplasty

The history of low back pain and sciatica date back to ancient times. Domenico Cotugno first described “sciatica” in its classic terminology in 1764 and believed that pain was generated by the nerve itself. The big three V’s: Valliex, Virchow and Von Luschka introduced the possibility of structure referred pain in the 1800’s. With the advent of x-rays one hundred years ago, imaging of spinal anatomy allowed correlation of anatomic findings to conditions that explained the origin of low back pain.

SEP as A Sensory Pathway Integrity Check in Patients Undergoing Lumbar Endoscopic Spine Surgery Using the Yeung Endoscopic Spine System


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.

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