Free-running Electromyography Research Articles

Multimodal intraoperative neurophysiological monitoring with special emphasis on facial MEPs for facial nerve preservation in vestibular schwannoma surgeries: Surgical nuances and outcome predictability

Multimodal intraoperative neurophysiological monitoring with special emphasis on facial MEPs for facial nerve preservation in vestibular schwannoma surgeries: Surgical nuances and outcome predictability

Extraocular muscle electromyographic recordings for intraoperative monitoring of cranial nerves III, IV, and VI: a single-center experience with intraorbital electrodes.

The objective of this study was to describe the quantitative features of intraoperative electromyographic recordings obtained from cranial nerve III, IV, and VI neuromonitoring using 25-mm intraorbital electrodes, in the larger context of demonstrating the practicality of this technique during neurosurgical cases. A 25-mm-long shaft-insulated intraorbital needle electrode is routinely used at the authors' institution for extraocular muscle (EOM) electromyographic monitoring of the inferior rectus, superior oblique, and/or lateral rectus muscles when their function is at risk. Cases monitored between January 1, 2021, and December 31, 2022, were reviewed for patient demographics, tumor location and pathology, EOMs monitored, pre- and postoperative examination, and complications from electrode placement. Compound muscle action potentials on triggered electromyography, as well as neurotonic discharges on free-run electromyography, were described quantitatively. There were 141 cases in 139 patients reviewed during the 24-month time span, with 278 EOMs monitored (inferior rectus/superior oblique/lateral rectus muscles 68/68/142). Triggered electromyography yielded biphasic or triphasic compound muscle action potentials from EOMs with a mean onset latency of 1.51 msec (range 0.94-3.22 msec), mean maximal peak-to-trough amplitude of 1073.93 μV (range 76.75-7796.29 μV), and high specificity for the channel in nearly all cases. Neurotonic discharges were recorded in 30 of the 278 EOMs (with all 3 muscles represented) and associated with a greater incidence of new or worsened ophthalmoparesis (OR 4.62, 95% CI 1.3-16.4). There were 2 cases of small periorbital ecchymosis attributed to needle placement; additionally, 1 case of needle-related intraorbital hematoma occurred after the review period. The 25-mm shaft-insulated intraorbital electrode facilitates robust and consistent electromyographic recordings of EOMs that are advantageous over existing techniques. Combined with the relative ease of needle placement and low rate of complications, the technique is practical for neuromonitoring during craniotomies.

Ventro-Lateral Meningioma of the Cervico-Thoracic Junction: 2-Dimensional Operative Video.

Meningiomas are one of the most common intradural extramedullary tumors.1 Symptoms often arise from cord compression, with gross total resection leading to the most optimal patient outcomes.2,3 Utilization of intraoperative neurophysiological monitoring can increase patient safety through real-time assessment of neural structures and reduce postoperative neurologic complications.4 In this video, we describe the operative techniques for the resection of a meningioma located at the cervico-thoracic junction. A 43-year-old female patient presented with 6 months of bilateral leg numbness and gait disturbances. MRI of the cervical spine demonstrated a cervical thoracic ventral meningioma causing severe cord compression from the bottom of the C6 lamina to the top of the T1 lamina. Surgical resection with intraoperative neuromonitoring with somatosensory-evoked potentials, motor-evoked potentials, and free-running electromyography was recommended. A partial C6-T1 laminectomy was routinely performed, and the dura was opened using a paramedian approach to allow for maximal tumor visualization. The tumor was carefully dissected and debulked, achieving gross total resection. Postoperatively, the patient experienced improvements in preoperative symptoms with no perioperative complications, and the final pathology confirmed the intradural lesion was a meningioma. This video illustrates the surgical technique and management of a spinal meningioma at the cervico-thoracic junction. Patient consent was obtained for their participation in this surgical video.

Electromyographic predictors of abducens nerve palsy after endoscopic skull base surgery.

Recovery of abducens nerve palsy (ANP) after endoscopic endonasal skull base surgery (ESBS) has been shown to be potentially predicted by postoperative ophthalmological examination. Triggered electromyography (t-EMG) and free-run electromyography (f-EMG) activity provide an intraoperative assessment of abducens nerve function, but associations with long-term ANP outcomes have not been explored. The objective of this study was to describe intraoperative abducens EMG characteristics and determine whether these electrophysiological profiles are associated with immediately postoperative and long-term ANP outcomes after ESBS. The authors conducted a 5-year (2011-2016) retrospective case-control study of patients who underwent ESBS in whom the abducens nerve was stimulated (t-EMG). Electrophysiological metrics were compared between patients with a new postoperative ANP (cases) and those without ANP (controls). Pathologies included chordoma, pituitary adenoma, meningioma, cholesterol granuloma, and chondrosarcoma. Electrophysiological data included the presence of abnormal f-EMG activity, t-EMG stimulation voltage, stimulation threshold, evoked compound muscle action potential (CMAP) amplitude, onset latency, peak latency, and CMAP duration at various stages of the dissection. Controls were selected such that pathologies were similarly distributed between cases and controls. Fifty-six patients were included, 26 with new postoperative ANP and 30 controls without ANP. Abnormal f-EMG activity (28.0% vs 3.3%, p = 0.02) and lack of response to stimulation (27% vs 0%, p = 0.006) were more frequent in patients with immediately postoperative ANP than in controls. Patients with immediately postoperative ANP also had a lower median CMAP amplitude (35.0 vs 71.2 μV, p = 0.02) and longer onset latency (5.2 vs 2.8 msec, p = 0.04). Comparing patients with transient versus persistent ANP on follow-up, those with persistent ANP tended to have a lower CMAP amplitude (12.8 vs 57 μV, p = 0.07) and higher likelihood of not responding to stimulation at the end of the case (45.5% vs 7.1%, p = 0.06). Abnormal f-EMG was not associated with long-term ANP outcomes. The presence of f-EMG activity, lack of CMAP response to stimulation, decreased CMAP amplitude, and increased CMAP onset latency were associated with immediately postoperative ANP. Long-term ANP outcomes may be associated with t-EMG parameters, including whether the nerve is able to be stimulated once identified and CMAP amplitude. Future prospective studies may be designed to standardize abducens nerve electrophysiological monitoring protocols to further refine operative and prognostic utility.

Intraoperative Monitoring of the Facial Nerve during Microvascular Decompression for Hemifacial Spasm.

This review article discusses the clinical significance of intraoperative neurophysiological monitoring (IONM), provides recommendations for monitoring protocols, and considers the interpretation of results in microvascular decompression (MVD) for hemifacial spasm (HFS). The lateral spread response (LSR) is an important monitoring parameter during MVD. It helps to identify the responsible blood vessel and confirms its thorough decompression from the facial nerve. The disappearance of the LSR during surgery is associated with favorable clinical outcomes. Standard and revised monitoring protocols and the confirmation of LSR persistence and disappearance are also discussed. The blink reflex and other facial nerve monitoring modalities, such as free-running electromyography, facial motor evoked potentials, F-waves, and the Z-L response, are further considered.

흉추 종양 수술에서 복직근을 이용한 신경계감시의 가능성: 증례 보고

Intraoperative neurophysiologic monitoring (IONM) has been widely used to prevent nerve damage during spinal tumor surgery. However, when the tumor is located in the thoracic vertebrae, it is impossible to monitor lower motor neurons such as nerve roots by conventional methods. To solve this problem, the rectus abdominis muscle, which is innervated by the thoracic nerve root, can be used. We report a case using the rectus abdominis motor evoked potentials (MEP) and free-running electromyography in a patient with schwannoma located at the T12 thoracic vertebrae. During surgery, a reduction in MEP was seen upon removal of the tumor, but not less than 50%. Neurotonic discharge was seen upon removal of the tumor, but was not sustained. After the operation, the patient did not report any neurological symptoms. This case supports that MEP and free-running electromyography of the rectus abdominis muscle can be feasible for monitoring in thoracic spine surgery.

The effect of intraoperative neurophysiological monitoring on neurological outcomes after spinal tumors operations: A single institution experience

We aim to report our study about using multimodality intraoperative neurophysiological monitoring (IONM) in intradural spinal tumor surgery. This cohort present a retrospective review of the patient who underwent intraspinal tumors surgery at Vajira Center of Excellence in Neurosurgery; between 2005 and 2020. Transcranial motor evoked potentials, somatosensory evoked potentials, and free run electromyography were used for IONM with alarm criteria. Patient record were reviews with preoperative and postoperative neurological outcome measurements; Frankel Grading, McCormick Score, American Spinal Injury Association (ASIA) Grading, Karnofsky Performance Status (KPS) Scale and The Japanese Orthopedic Association (JOA) Score at 1, 6, 12, 24 months after operation. Overall, 104 patients were operated. 77.4 % operations were used IONM. 70.2 % of tumor located at intradural extramedullary (IDEM) space and 16.7 % located at intramedullary space. There were demonstrating statistically significant (p-value < 0.050) improvement between preoperative and postoperative neurological outcome in all follow up time in IONM group. The sensitivity and specificity of alarm IONM to predict early worsening postoperative neurological outcome were 66.7 % and 88.7 %, respectively. IDEM spinal cord tumor surgery are associated with good neurological outcome (OR 0.187 [95 % CI 0.05–0.71]; p-value 0.014). Used of IONM in intradural spinal tumor surgery statistically significant improved postoperative neurological outcome and decrease postoperative neurological deficit. IONM has ability to detect postoperative neurological deficit and poor outcome with fair sensitivity and high specificity. Especially, using of IONM in IDEM have preferable postoperative neurological outcomes.

Confirming a C5 Palsy with a Motor Evoked Potential Trending Algorithm during Insertion of Cervical Facet Spacers: A Case Study

ABSTRACT The use of cervical facet spacers has shown favorable clinical results in the treatment of cervical spondylotic disease; however, there are limited data regarding neurological complications associated with the procedure. This case report demonstrates the specificity of multi-myotomal motor evoked potentials (MEPs) in detecting acute postoperative C5 palsy following placement of facet spacers. A posterior cervical fusion with decompression and instrumentation involving DTRAX (Providence Medical Technology; Lafayette, CA) was used to treat a patient with cervical stenosis and myelopathy. Intraoperative neurophysiological monitoring (IONM) consisting of MEPs, somatosensory evoked potentials (SSEPs), and free-run electromyography (EMG), was used throughout the procedure. Immediately following the placement of the DTRAX spacers at C4-5, a decrease in amplitudes from the right deltoid and biceps MEP recordings (>65%) was detected. All other IONM modalities remained stable; it is noteworthy that there was an absence of mechanically elicited EMG. A novel post-alert regression analysis trending algorithm of MEP amplitudes confirmed the visual alert. This warning along with an intraoperative computed tomography (CT) scan of the cervical spine subsequently resulted in the decision to remove one of the facet spacers. Surgical intervention did not result in recovery of the aforementioned MEP recordings, which remained attenuated at the time of wound closure. Postoperatively, the patient exhibited an immediate right C5 palsy (2/5). A post-surgery application of the trending algorithm demonstrated that it correlated to the visual alert until the end of monitoring.

자발 및 유발 근전도

Intraoperative electromyography (EMG) is known to record compound muscle action potential (CMAP) in response to spontaneous or stimulated cranial nerve or spinal root activation. EMG can detect cranial nerve or spinal nerve root irritation (known as free-running EMG), and may involve electrical stimulation of neural elements or hardware to assess function (known as stimulated or triggered EMG). EMG has a low positive predictive value with high sensitivity, which is particularly useful in the early detection and prevention of pending nerve injury. EMG is one the most useful modalities of intraoperative neuromonitoring (IONM) for monitoring neural function along with sensory and motor evoked potentials during surgery associated with spinal manipulation and cranial nerve involvement.

Free-run electromyography assisted interlaminar endoscopic lumbar disckectomy at L4L5 and L5S1 under general anesthesia

IntroductionInterlaminar Endoscopic Lumbar Disckectomy has been found to offer symptomatic alleviation comparable to open disckectomy while reducing blood loss, postoperative discomfort, complications, hospital stay, and narcotic use. General anesthesia decreases intraoperative stress, but surgeons may not be sure whether they injure nerve roots. Free-run electromyography may protect nerve roots that are thought to be in danger from surgery. MethodsPatients with L4L5 or L5S1 lumbar disc herniation were treated with IELD. EMG was monitored via needle electrodes in lateral vastus lateralis, anterior tibialis, abductor hallucis muscles. Surgeons were asked to halt the surgery and adjust their manipulation right when abnormal EMG appeared on the screen. The severity of signs and symptoms were noted pre- and post-operatively. ResultsIn all 26 cases, the median of visual analogue scale (VAS) of low back pain was 4.5. That of radicular pain was 7. Two patients had motor weakness at L4 or S1 muscles. One patient has sensory loss at L5 dermatome. The level of disc herniation was 46% at L4L5 and 56% at L5S1. The complications included only superficial infection in two patients that were effectively managed with antibiotics. During postoperative follow-up, all patients recovered completely without any neurological deficit. f-EMG signal included uneventful (9 patients), burst/spike (10 patients), A-train (3 patients, and C-train (4 patients) ConclusionFree-run EMG is a protective mean in IELD. All surgeons will profit from this technique in the early stages of their learning curve. To examine the outcomes, further comparative research and prospective, randomized, controlled trials should be undertaken.

Chapter 4 - EMG monitoring

While most neurophysiologists are familiar with electromyography (EMG) for the purpose of clinical diagnostics, this technique also has a long tradition for neuro-monitoring. In short, intra-operative use of EMG can be divided into stimulated EMG on the one hand and monitoring of the free-running EMG and its spontaneous activity on the other hand. Methods for utilization of stimulated EMG are covered elsewhere in this book. This chapter focuses on the monitoring of spontaneous, or, more correctly, "surgically evoked" EMG. The history and underlying physiologic principles of intra-operative EMG are covered in this chapter as well as a detailed overview of the methodology. Building up from the basis of this background, we describe examples of how EMG can be used to help in intra-operative detection of adverse events and also in the prediction of postoperative outcomes. In the opinion of the authors, EMG should not be used as a "standalone" technique in contemporary neuro-monitoring. Most of its significant potential may be realized when it is used in a complementary way together with other modalities, mainly motor evoked potentials. Bearing this in mind, we sketch out how such a complementary setup may be used for improved neuro-monitoring.

WS5.4. EMG Monitoring: Free-Run and Triggered

The recording of compound muscle action potentials (CMAPs) in response to spontaneous or electrically stimulation of the cranial, spinal, peripheral nerves or nerve root activation is known as intraoperative electromyography (EMG). EMG monitoring is widely used in surgeries when the aforementioned neural structures might be at risk. It allows early detection of surgery- related nerve injury so that proper intervention can be accordingly adopted; it also allows confirmation of the functional status of the nerve. The intraoperative monitoring team must thoroughly understand the nervous pathways that require monitoring and mapping in order to develop optimal stimulation and recording strategies for each surgical procedure. Intraoperative EMG testing includes triggered EMG (tEMG) for mapping and free-run EMG (fEMG) for monitoring purposes. Triggered EMG is used to identify the nerves and nerve root, to define a safe entry pathway to access the lesion, or to assess the functional integrity of the nerve so that the surgical plan can be modified accordingly. Clinical applications of tEMG also include confirmation of the placement of pedicle screws during spine surgery and guiding the sectioning of the lumbosacral rootlets during selective dorsal rhizotomy. The following three kinds of stimulation electrodes are available: monopolar, bipolor, and tripolar electrode. Each of the aforementioned electrodes are associated with certain strengths and weakness; thus, they can be used under different circumstances and meets most of our clinical needs. fEMG involves recording spontaneous or evoked muscle activity without interfering with the surgery. It is used as a monitoring tool to detect surgically driven mechanical irritation of the peripheral nerves and motor cranial nerves, hopefully before permanent damage occurs. It also can be applied to detect muscle activity evoked by mechanical irritation of the corticospinal tract and/or alpha motor neurons during brain tumor or intramedullary spinal cord tumor resection. There are three types of fEMG activity, referred to as the A, B and C train. Among them, the A train has been more associated with poor postoperative outcomes, although false-positive and false-negative findings do exist. Thus, the concomitant use of somatosensory and motor evoked potentials will certainly increase the sensitivity and specificity of fEMG.

Intraoperative neuromonitoring during distal femoral extension osteotomy in children with cerebral palsy.

The most common treatment method for a fixed knee flexion contracture more than 10 degrees in cerebral palsy (CP) is distal femoral extension osteotomy (DFEO). However, a serious complication after a DFEO is neurological impairment. Its rates were reported as 5- 40%. Intraoperative neuromonitoring (IONM), widely used in spinal surgery and in other fields, is a valuable tool to define any neurological injury during operation. The aim of our study was to determine surgical steps with risk of neurological injury and to report if precautions would be effective in recovering signal loss. We performed IONM during DFEO of 23 knees of 12 children with CP. IONM was performed by recording somatosensory evoked potentials, transcranial motor evoked potentials and free-run electromyography during defined steps throughout the surgery. Preoperative and postoperative popliteal angles, flexion contractures and physeal posterior distal femoral angles were evaluated. We detected alert signals at osteotomy or manipulation steps of surgeries of all patients. We observed persistent alert signals in two cases (2 out of 23 knees; Group 2). In this group, the action potentials recovered only after 5 and 10 degrees of undercorrection at the osteotomy sites. Alert signals disappeared after a brief period of waiting in other cases. Throughout mean 37 months of follow-up, none of our patients experienced any neurological complication. The study concludes that the surgical steps in DFEO with a higher risk for a neurological complication were the osteotomy and manipulation steps. Alert signals were detected with the help of IONM, and preventive measures were effective in recovering neuromonitoring recordings.

Direct Stimulation of Neural Placode and Nerve Roots in Open Myelomeningocele: The Efficacy of Neural Tube Reconstruction

Introduction: Intraoperative electrophysiological studies are increasingly used in spinal surgery. However, its use in myelomeningocele (MMC) surgery is still not widespread. The aim of this study was to present our experience in neural placode (NP) and nerve root stimulations in newborns with open MMC. Methods: Eight newborns underwent surgical treatment for thoracolumbar and lumbosacral MMCs. Intraoperative neuromonitoring including free-running electromyography and stimulation of NP, nerve roots, and spinal cord were performed in all cases. Stimulation sites and intensities and distal response’s amplitudes and latencies were recorded. Results: Five patients had thoracolumbar and 3 patients had lumbosacral MMC. Two patients had no movements at the lower extremities while the other had some movements. No response on the lower extremities was obtained in only 1 patient. Responses from the nerve root stimulations were more robust and significant than the placode stimulations. Conclusions: It is clear that the NP and nerve roots originating from the placode are mostly functional and should be preserved during the surgery. Intraoperative neuromonitoring and direct stimulation should be performed during the MMC repair in order to obtain a better neurological outcome.

Incidence of peripheral nerve injury in revision total shoulder arthroplasty: an intraoperative nerve monitoring study

The incidence of nerve injuries in revision total shoulder arthroplasty (TSA) is not well defined in the literature and may be higher than that in primary procedures, with 1 study reporting a complication rate of 50% for shoulder revisions. Given that continuous intraoperative nerve monitoring (IONM) can be an effective tool in diagnosing evolving neurologic dysfunction and preventing postoperative injuries, the purpose of this study was to report on IONM data and nerve injury rates in a series of revision TSAs. A retrospective cohort review of consecutive patients who underwent revision TSA was performed from January 2016 to March 2020. Indications for revision included infection (n = 7); failed total arthroplasty and hemiarthroplasty secondary to pain, dysfunction, and/or loose components (n = 36); and periprosthetic fracture (n = 1). Of the shoulders, 32 underwent revision to a reverse TSA, 6 underwent revision to an anatomic TSA, and 6 underwent spacer placement. IONM data included transcranial electrical motor evoked potentials (MEPs), somatosensory evoked potentials, and free-run electromyography. The motor alert threshold was set at ≥80% signal attenuation in any peripheral nerve. Patients were screened for neurologic deficits immediately following surgery, prior to administration of an interscalene nerve block, and during the first 2 postoperative visits. Additional data collection included surgical indication, sex, laterality, age at surgery, procedure performed, body mass index, history of tobacco use, Charlson Comorbidity Index, medical history, and preoperative range of motion. A total of 44 shoulders in 38 patients were included, with a mean age of 63.2 years (standard deviation, 13.0 years). Of the procedures, 22.4% (n = 10) had an MEP alert, with 8 isolated to a single nerve (7 axillary and 1 radial) and 1 isolated to the axillary and musculocutaneous nerves. Only 1 patient experienced a major brachial plexus alert involving axillary, musculocutaneous, radial, ulnar, and median nerve MEP alerts, as well as ulnar and median nerve somatosensory evoked potential alerts. Age, sex, body mass index, Charlson Comorbidity Index, and preoperative range of motion were not found to be significantly different between cases in which an MEP alert occurred and cases with no MEP alerts. In the postoperative period, no minor or major nerve injuries were found whereas distal peripheral neuropathy developed in 4 patients (9.1%). Among 44 surgical procedures, no patients (0%) had a major or minor nerve injury postoperatively and 4 patients (9.1%) complained of distal peripheral neuropathy postoperatively. In this study, we have shown that through the use of IONM, the rate of minor and major nerve injuries can be minimized in revision shoulder arthroplasty.

Anatomic versus reverse shoulder arthroplasty, are nerve injury rates different?

BackgroundThe true incidence of iatrogenic neurological injury following total shoulder arthroplasty (TSA) surgery remains controversial at a cited rate of 1%-18.7%. Additionally, there is a reported incidence of new onset distal peripheral neuropathy (DPN) of 7.1% and 12.3%, for anatomic (aTSA) and reverse (rTSA) shoulder replacements, respectively. The purpose of this present study is to report on nerve injury rates of a large, consecutive series of primary TSA (ie, rTSA and aTSA) performed by one surgeon, utilizing intraoperative neuromonitoring and consistent implant design. MethodsA retrospective cohort review of consecutive patients who underwent primary TSA was performed from January 2016 to March 2020. Intraoperative neuromonitoring data included transcranial electrical motor evoked potentials (MEPs), somatosensory evoked potentials, and free-run electromyography. Motor alert threshold was set at ≥ 80% signal attenuation in any one or more peripheral nerves. Patients were screened for neurological deficits immediately following surgery and in the first 2 postoperative visits. Additional data collection included surgical indication, gender, laterality, age at surgery, procedure performed, body mass index, history of tobacco use, Charlson comorbidity index, past medical history and preoperative range of motion. ResultsA total of 290 consecutive shoulders in 270 patients were included. Ninety-one (31.4%) shoulders underwent aTSA, while 199 (68.6%) underwent rTSA. Patients in the rTSA cohort were significantly older (70.1 vs. 61.3 years; P < .001), had higher Charlson comorbidity index scores (4.3 vs. 3.0; P < .001), and shorter operative time (81.8 vs. 99.7; P < .001). A total of 96 MEP alerts occurred in 65 (22.4%) operations, with a significantly higher proportion of these occurring in patients undergoing aTSA. MEP alerts occurred in 28 (39.8%) aTSA versus 37 (18.5%) rTSA (P = .024). Logistical regression found operative time (P = .003, odds ratio = 1.020 [95%: 1.007-1.033]) was predictive of a MEP alert. The axillary nerve was the most commonly alerted nerve accounting for 61.5% of all alerts. Zero patients had a major or minor nerve injury in this large cohort. Nine patients (3.1%) had DPN in the postoperative period. ConclusionIn 290 surgeries, no (0%) patients had a postoperative major or minor nerve injury, and 9 (3.1%) patients complained of postoperative distal peripheral neuropathy. Patients that had MEP alerts had significantly longer operative times and were more likely to be in the aTSA group compared to the rTSA group. This may be attributed to longer exposure and implantation times on the glenoid side for an anatomic as opposed to a reverse arthroplasty. Level of evidenceLevel III; Retrospective Cohort study.

Clinical Correlation of Intraoperative Neuromonitoring in 319 Individuals Undergoing Posterior Decompression and Fixation of Spine.

This was a prospective study. To correlate improvement in motor evoked potential (MEP) during spine surgery with postoperative clinical improvement. Three hundred fifty-three patients operated for posterior spinal decompression and fixation surgeries were prospectively selected and followed up. Patients who underwent lumbar, dorsal, and cervical surgeries were grouped into-group A, B, and C, respectively. Intraoperative neuromonitoring was done using MEP with free-running electromyography. Improvements in MEP scores were calculated in percentage. Similarly, postoperative improvement in Oswestry disability index (ODI) and visual analog scale (VAS) scores at 3 months were calculated in percentage. Improvements in MEP scores were correlated with clinical improvement using the Spearman ρ test and the r value was calculated to find out the association. Of 353 patients, 319 (250-group A, 38-group B, and 31-group C) were included for the study. VAS and ODI improved significantly from preoperative 8.5±0.8 and 62.9±14.5, to postoperative 2.3±1.1 and 15.9±11.5, respectively, in the entire group. Average preoperative MEP were 127.8±191.0 mV on the right side and 132.3±206.6 mV on the left side, which significantly improved to 163.7±231.2 mV (P=0.0001) and 155.2±219.6 mV (P=0.0001), respectively, showing 157.0% and 178.5% improvement. Correlating MEP improvement with postoperative improvement in ODI showed poor correlation (r=0.088 right and 0.030 left sides). Similarly, correlating MEP improvement with improvement in VAS showed r=0.110 on the right and -0.023 on the left side suggesting poor correlation. Postoperative neurological complications (0.56%) were found in 2 patients in the form of screw malpositioning. Intraoperative neuromonitoring showed significant improvement during posterior decompression and fixation surgery, and reduction in postoperative neurological complication. The study also exhibited significant postoperative clinical improvement. However, improvement in MEP did not correlate with postoperative clinical improvement suggesting that it has no predictive role.

Intraoperative Neurophysiology Monitoring for Spinal Dysraphism

Spinal dysraphism often causes neurological impairment from direct involvement of lesions or from cord tethering. The conus medullaris and lumbosacral roots are most vulnerable. Surgical intervention such as untethering surgery is indicated to minimize or prevent further neurological deficits. Because untethering surgery itself imposes risk of neural injury, intraoperative neurophysiological monitoring (IONM) is indicated to help surgeons to be guided during surgery and to improve functional outcome. Monitoring of electromyography (EMG), motor evoked potential, and bulbocavernosus reflex (BCR) is essential modalities in IONM for untethering. Sensory evoked potential can be also employed to further interpretation. In specific, free-running EMG and triggered EMG is of most utility to identify lumbosacral roots within the field of surgery and filum terminale or non-functioning cord can be also confirmed by absence of responses at higher intensity of stimulation. The sacral nervous system should be vigilantly monitored as pathophysiology of tethered cord syndrome affects the sacral function most and earliest. BCR monitoring can be readily applicable for sacral monitoring and has been shown to be useful for prediction of postoperative sacral dysfunction. Further research is guaranteed because current IONM methodology in spinal dysraphism is still deficient of quantitative and objective evaluation and fails to directly measure the sacral autonomic nervous system.

The use of transcranial motor-evoked potentials, somatosensory-evoked potentials and free-run electromyography for proper placement of paddle leads in chronic pain

Introduction: As an alternative to those patients who cannot be performed an awake spinal cord stimulation (SCS) or had been percutaneously implanted with poor pain relief outcomes, neurophysiological monitoring through transcranial motor evoked potentials (MEPs), somatosensory-evoked potentials (SSEPs) and free-run electromyography (EMG) under general anesthesia allows the correct placement of surgical leads and provide objective responses.Methods: An initial series of 15 patients undergoing SCS implantation for chronic pain. Physiologic midline was determined with 32-channel NIM-Eclipse System equipment. During neurophysiological monitoring, MEPs, SSEPs, EMG and CMAPs were recorded.Results: MEPs, SSEPs, and EMG were able to target spinal cord physiological midline during SCS to all patients. Physiologic midline was deviated in 53% patients. No warning events in SSEPs, MEPs, or EMG were recorded in any patient.Conclusions: Bilateral CMAPs recording allows placement of paddle leads in physiological midline, obtaining an accurate coverage, pain relief and avoid unpleasant or ineffective stimulation postoperatively. While these neurophysiological techniques are generally used to provide information on the state of the nervous system and prevent neurological injury risks during SCS, our work has shown that can accurate direct lead placement.

Intraoperative electrophysiology during single-level selective dorsal rhizotomy: technique, stimulation threshold, and response data in a series of 145 patients.

Selective dorsal rhizotomy (SDR) is effective at permanently reducing spasticity in children with spastic cerebral palsy. The value of intraoperative neurophysiological monitoring in this procedure remains controversial, and its robustness has been questioned. This study describes the authors' institutional electrophysiological technique (based on the technique of Park et al.), intraoperative findings, robustness, value to the procedure, and occurrence of new motor or sphincter deficits. The authors analyzed electrophysiological data of all children who underwent SDR at their center between September 2013 and February 2019. All patients underwent bilateral SDR through a single-level laminotomy at the conus and with transection of about 60% of the L2-S2 afferent rootlets (guided by intraoperative electrophysiology) and about 50% of L1 afferent roots (nonselectively). One hundred forty-five patients underwent SDR (64% male, mean age 6 years and 7 months, range 2 years and 9 months to 14 years and 10 months). Dorsal roots were distinguished from ventral roots anatomically and electrophysiologically, by assessing responses on free-running electromyography (EMG) and determining stimulation thresholds (≥ 0.2 mA in all dorsal rootlets). Root level was determined anatomically and electrophysiologically by assessing electromyographic response to stimulation. Median stimulation threshold was lower in sacral compared to lumbar roots (p < 0.001), and 16% higher on the first operated (right) side (p = 0.023), but unrelated to age, sex, or functional status. Similarly, responses to tetanic stimulation were consistent: 87% were graded 3+ or 4+, with similar distributions between sides. This was also unrelated to age, sex, and functional status. The L2-S2 rootlets were divided (median 60%, range 50%-67%), guided by response to tetanic stimulation at threshold amplitude. No new motor or sphincter deficits were observed, suggesting sparing of ventral roots and sphincteric innervation, respectively. This electrophysiological technique appears robust and reproducible, allowing reliable identification of afferent nerve roots, definition of root levels, and guidance for rootlet division. Only a direct comparative study will establish whether intraoperative electrophysiology during SDR minimizes risk of new motor or sphincter worsening and/or maximizes functional outcome.