Multimodal Intraoperative Neuromonitoring Research Articles

Intraoperative Neuromonitoring During Lateral Lumbar Interbody Fusion.

ObjectiveTo review the evidence for the use of electromyography (EMG), motor-evoked potentials (MEPs), and somatosensory-evoked potentials (SSEPs) intraoperative neuromonitoring (IONM) strategies during lateral lumbar interbody fusion (LLIF), as well as discuss the limitations associated with each technique. MethodsA comprehensive review of the literature and compilation of findings relating to clinical studies investigating the efficacy of EMG, MEP, SSEP, or combined IONM strategies during LLIF. ResultsThe evidence for the use of EMG is mixed with some studies demonstrating the efficacy of EMG in preventing postoperative neurologic injuries and other studies demonstrating a high rate of postoperative neurologic deficits with EMG monitoring. Multimodal IONM strategies utilizing MEPs or saphenous SSEPs to monitor the lumbar plexus may be promising strategies based on results from a limited number of studies. ConclusionThe use of traditional EMG during LLIF remains without consensus. There is a growing body of evidence utilizing multimodal IONM with MEPs or saphenous SSEPs demonstrating a possible decrease in postoperative neurologic injuries after LLIF. Future prospective studies, with clear definitions of neurologic injury, that evaluate different multimodal IONM strategies are needed to better assess the efficacy of IONM during LLIF.

240. Utility of intraoperative neuromonitoring alerts relating to adverse outcomes in spine surgery: a study of 289 patients

<h3>BACKGROUND CONTEXT</h3> Although rare, one of the most problematic complications during spine surgery is neurologic injury with subsequent deficit. The use of multimodal intraoperative neuromonitoring (MIOM) during spine surgery provides the surgical team with real-time assessment of the neurological physiology and function. MIOM is thought to be sensitive and specific for identifying perioperative neurological injury in spinal surgery especially deformity surgery. However, results from recent studies have cast doubt on the effectiveness of certain MIOM techniques in detecting neurological injury in spine surgery patients. <h3>PURPOSE</h3> The purpose of this study was to improve spine surgery patient safety and outcomes by minimizing the incidence of postoperative new neurological deficits correlated to intraoperative neuromonitoring alerts from two neuromonitoring signals: motor evoked potentials (MEPs) and somatosensory evoked potentials (SSEPs). <h3>STUDY DESIGN/SETTING</h3> A multicenter, multisurgeon prospective quality improvement initiative that was performed in conjunction with neuro alert (NA) monitoring services. All data was retrospectively analyzed. <h3>PATIENT SAMPLE</h3> A total of 289 patients who (1) received nondeformity lumbar (45%), cervical (45%) or thoracic (10%) surgery between July 2018 and July 2019 and (2) underwent SSEP and MEP monitoring throughout the entire surgery. <h3>OUTCOME MEASURES</h3> This study investigated the incidence of immediate postoperative (≤ 48 hours) new neurological deficits. sensitivty, specificity, postive predictive value (PPV), and negative predictive value (NPV) was calculated for the SSEP and MEP signals. <h3>METHODS</h3> This study was a multicenter, multisurgeon prospective quality improvement initiative that was performed in conjunction with neuro alert (NA) monitoring services. All neuromonitoring was carried out in accordance with the guidelines set forth by the American Academy of Neurology and the American Board for Neurophysiological Monitoring Programs. Two commonly used MIOM signals were tracked: somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs). Intraoperative data were recorded using a paper data collection tool. SSEP and MEP signal changes were classified as alerts based on the following best practices guidelines outlined in the literature: 50% or greater decrease in signal amplitude and/or a 10% or greater increase in signal latency with no signal recovery. Immediate postoperative (≤ 48 hours) new neurological deficit status was assessed for all patients. Neurological deficit information was recorded via paper during a postoperative physical exam that all physicians conducted on the patient within 48 hours after surgery. The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for the SSEP and MEP signals were calculated. <h3>RESULTS</h3> SSEP and MEP neuromonitoring data was analyzed for 289 patients who (1) received non-deformity lumbar (45%), cervical (45%) or thoracic (10%) surgery between July 2018 and July 2019 and (2) underwent SSEP and MEP monitoring throughout the entire surgery. A total of 22 MEP and 16 SSEP alerts were triggered. Ninety percent (20) of MEP alerts occurred during anterior cervical discectomy and fusion (ACDF) procedures; one MEP alert was triggered during a posterior cervical fusion and one MEP alert was triggered during a lumbar laminectomy. 56% (9) of SSEP alerts occurred during transforaminal lumbar interbody fusion procedures while 25% (4) occurred during ACDFs and 19% (3) occurred during lumbar laminectomy surgeries. MEP and SSEP alerts were most frequently triggered during the decompression surgical step (45% and 25%, respectively). There were 6 instances (n = 6) of new neurological deficits that occurred within 48 hours postsurgery. These deficits were as follows: foot drop (n = 1), leg weakness (n = 1), arm weakness (n = 2), bilateral paraparesis (n = 1) and unilateral paraparesis (n = 1). The patient who developed unilateral paraparesis was myelopathic. All other patients with new neurological deficits did not have a history of myelopathy. The MEP alert should have been triggered for all 6 patients, however the signal was only alerted in the patient who developed bilateral paraparesis and in one patient who developed arm weakness. In 4/6 patients, MEP alerts were not triggered but a new neurological deficit occurred, resulting in a false negative rate of 67% and a sensitivity of 33%. In addition, MEPs had a specificity of 92.4%, PPV of 11% and NPV of 98.5%. The SSEP signal showed 100% sensitivity and displayed a specificity, PPV and NPV of 95.2%, 12.5% and 100%, respectively. <h3>CONCLUSIONS</h3> The MEP signal had a low sensitivity of 33%, which differed greatly from that of the SSEP signal (100%). The specificity, PPV and NPV were comparable between the SSEPs and MEPs. The PPV was low for both signals. Results indicate that the accuracy of SSEP and MEP alerts in detecting new neurological deficits in spine surgery patients immediately postsurgery is questionable. The effectiveness of these two intraoperative neuromonitoring techniques in identifying neurological injury seems uncertain and needs to be explored further. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs

244. Impact of inhalational anesthetic agents on the baseline monitorability of motor evoked potentials (MEPs) during spine surgery: A review of 22,755 cervical and lumbar procedures

<h3>BACKGROUND CONTEXT</h3> During spine surgery, motor evoked potentials (MEPs) are often utilized to monitor both spinal cord function and spinal nerve root or plexus function. While there are reports evaluating the impact of anesthesia on the reliability of MEPs to monitor spinal cord function, less is known about the impact of anesthetics on the ability of MEPs to monitor spinal nerve root and plexus function. <h3>PURPOSE</h3> To compare the baseline monitorability and amplitude of MEPs during cervical and lumbar procedures between two cohorts based on the maintenance anesthetic regimen: a total intravenous anesthesia (TIVA) vs a regimen balanced with volatile inhalational and intravenous agents. <h3>STUDY DESIGN/SETTING</h3> Baseline MEP data from a total of 16,559 extradural cervical and 6,196 lumbar spine procedures utilizing multimodality intraoperative neuromonitoring (IONM) including MEPs between January 2017 and March 2020 were obtained from a multi-institutional database. Two cohorts were delineated based on the anesthetic regimen: a TIVA cohort and a balanced anesthesia cohort. <h3>PATIENT SAMPLE</h3> Age 18 and older. <h3>OUTCOME MEASURES</h3> Percent monitorability and amplitudes of baseline MEPs. <h3>METHODS</h3> The baseline monitorability of each muscle MEP was evaluated by the IONM team in real time and recorded in the patient's electronic medical record. The relation between anesthetic regimen and baseline monitorability was estimated using mixed effects logistic regression, with distinct models for cervical and lumbar procedures. Subsets of cervical and lumbar procedures from each anesthesia cohort in which all MEPs were deemed monitorable were randomly selected and the average peak-to-trough amplitude of each muscle MEP was retrospectively measured. Mixed-effects linear regression models were estimated (one each for cervical and lumbar procedures) to assess possible differences in average amplitude associated with anesthesia regimen. <h3>RESULTS</h3> At the time of surgery, baseline MEPs were reported as monitorable from all targeted muscles in 86.8% and 83.0% of cervical and lumbar procedures, respectively, for the TIVA cohort, but were reported as monitorable in just 59.3% and 61.0% of cervical and lumbar procedures, respectively, in the Balanced cohort, yielding disparities of 27.5% and 22.0%, respectively. The model-adjusted monitorability disparity between cohorts for a given muscle MEP ranged from 0.2% -16.6% but was smallest for distal intrinsic hand and foot muscle MEPs (0.2%-1.1%) and was largest for proximal muscle MEPs (deltoid: 10.8%, biceps brachii: 8.8%, triceps: 13.0%, quadriceps: 16.6%, gastrocnemius: 7.8%, and tibialis anterior: 3.7%) where the monitorability was significantly decreased in the Balanced cohort relative to the TIVA cohort (P < 0.0001). Relative to the TIVA cohort, the model-adjusted amplitude of an MEP in the Balanced cohort was smaller for all muscles measured, ranging from 27.5%-78.0% smaller. Relative to the TIVA cohort, the model-adjusted amplitude of an MEP was significantly decreased (P <0.01) in the Balanced cohort for the most proximal muscles (percent smaller: deltoid: 74.3%, biceps: 78.0%, triceps: 54.9.0%, quadriceps: 54.8%). <h3>CONCLUSIONS</h3> TIVA is the preferred anesthetic regimen for optimizing MEP monitoring during spine surgery. Inhalational agents significantly decrease MEP monitorability and amplitudes for most muscles, and this effect is especially pronounced for proximal limb muscles such as the deltoid, biceps, triceps, and quadriceps. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.

Impact of inhalational anesthetic agents on the baseline monitorability of motor evoked potentials during spine surgery: a review of 22,755 cervical and lumbar procedures

BACKGROUND CONTEXTDuring spine surgery, motor evoked potentials (MEPs) are often utilized to monitor both spinal cord function and spinal nerve root or plexus function. While there are reports evaluating the impact of anesthesia on the ability of MEPs to monitor spinal cord function, less is known about the impact of anesthesia on the ability of MEPs to monitor spinal nerve root and plexus function. PURPOSETo compare the baseline monitorability and amplitude of MEPs during cervical and lumbar procedures between two cohorts based on the maintenance anesthetic regimen: a total intravenous anesthesia (TIVA) versus a regimen balanced with volatile inhalational and intravenous agents. STUDY DESIGNBaseline MEP data from a total of 16,559 cervical and 6,196 lumbar extradural spine procedures utilizing multimodality intraoperative neuromonitoring (IONM) including MEPs between January 2017 and March 2020 were obtained from a multi-institutional database. Two cohorts for each region of spine surgery were delineated based on the anesthetic regimen: a TIVA cohort and a Balanced anesthesia cohort. PATIENT SAMPLEAge 18 and older. Fellowship support for 65,000 for year 2021. OUTCOME MEASURESPercent monitorability and amplitudes of baseline MEPs. METHODSThe baseline monitorability of each muscle MEP was evaluated by the IONM team in real-time and recorded in the patient's electronic medical record. The relation between anesthetic regimen and baseline monitorability was estimated using mixed effects logistic regression, with distinct models for cervical and lumbar procedures. Subsets of cervical and lumbar procedures from each anesthesia cohort in which all MEPs were deemed monitorable were randomly selected and the average peak-to-trough amplitude of each muscle MEP was retrospectively measured. Mixed-effects linear regression models were estimated (one each for cervical and lumbar procedures) to assess possible differences in average amplitude associated with anesthesia regimen. RESULTSAt the time of surgery, baseline MEPs were reported monitorable from all targeted muscles in 86.8% and 83.0% of cervical and lumbar procedures, respectively, for the TIVA cohort, but were reported monitorable in just 59.3% and 61.0% of cervical and lumbar procedures, respectively, in the Balanced cohort, yielding disparities of 27.5% and 22.0%, respectively. The model-adjusted monitorability disparity between cohorts for a given muscle MEP ranged from 0.2% to 16.6% but was smallest for distal intrinsic hand and foot muscle MEPs (0.2%–1.1%) and was largest for proximal muscle MEPs (deltoid: 10.8%, biceps brachii: 8.8%, triceps: 13.0%, quadriceps: 16.6%, gastrocnemius: 7.8%, and tibialis anterior: 3.7%) where the monitorability was significantly decreased in the Balanced cohort relative to the TIVA cohort (p<.0001). Relative to the TIVA cohort, the model-adjusted amplitude of an MEP in the Balanced cohort was smaller for all muscles measured, ranging from 27.5% to 78.0% smaller. Relative to the TIVA cohort, the model-adjusted amplitude of an MEP was significantly decreased (p<.01) in the Balanced cohort for the most proximal muscles (Percent smaller: deltoid: 74.3%, biceps: 78.0%, triceps: 54.9%, quadriceps: 54.8%). CONCLUSIONSTIVA is the preferred anesthetic regimen for optimizing MEP monitoring during spine surgery. Inhalational agents significantly decrease MEP monitorability and amplitudes for most muscles, and this effect is especially pronounced for proximal limb muscles such as the deltoid, biceps, triceps, and quadriceps.

The Utility of Multimodal Intraoperative Neuromonitoring in Spine Surgery: Case Series from a Lower-Middle-Income Country Perspective

Multimodal intraoperative neuromonitoring (IOM) using somatosensory-evoked potentials and motor-evoked potentials is a sensitive and specific tool for detecting intraoperative neurologic injury during spine surgery. This study aimed to evaluate the use of multimodal IOM in a lower-middle-income country (LMIC) during cervical and thoracic spine surgery in order to prevent and predict new postoperative neurologic deficits early on. This is the first report of multimodal IOM application in LMICs. The neurophysiologist raised the cutoff warning criteria of 50 patients who underwent surgery for different cervical and thoracic pathologies to decrease postoperative neurologic deficits. We retrospectively reviewed the medical charts and neuromonitoring traces of these patients followed by calculating the sensitivity, specificity, positive predictive value, and negative predictive value of combined IOM for postoperative neurologic deficit occurrence. A significant relationship was found between the reversibility of alerts and the development of new postoperative deficits (P < 0.001). There was no relationship between the cause of alerts and the reversibility of those alerts after corrective measures were carried out (P= 0.455), or the frequency of alerts and the development of new deficits postoperatively (P= 0.578). Sensitivity, specificity, positive predictive value, and negative predictive value of combined somatosensory-evoked potential and motor-evoked potential monitoring were 100%, 80%, 62.5%, and 100%, respectively. Because of the limited experience and the many technical difficulties faced in LMICs, we found that this cutoff limit resulted in more false-positive warnings but helped to avoid any false-negative results, thus enhancing the safety of surgery.

Multimodality Intraoperative Neuromonitoring in Lateral Lumbar Interbody Fusion: A Review of Alerts in 628 Patients.

Retrospective review of private neuromonitoring databases. To review neuromonitoring alerts in a large series of patients undergoing lateral lumbar interbody fusion (LLIF) and determine whether alerts occurred more frequently when more lumbar levels were accessed or more frequently at particular lumbar levels. Intraoperative neuromonitoring (IONM) databases were reviewed and patients were identified undergoing LLIF between L1 and L5. All cases in which at least one IONM modality was used (motor evoked potentials (MEP), somatosensory evoked potentials (SSEP), evoked electromyography (EMG)) were included in this study. The type of IONM used and incidence of alerts were collected from each IONM report and analyzed. The incidence of alerts for each IONM modality based on number of levels at which at LLIF was performed and the specific level an LLIF was performed were compared. A total of 628 patients undergoing LLIF across 934 levels were reviewed. EMG was used in 611 (97%) cases, SSEP in 561 (89%), MEP in 144 (23%). The frequency of IONM alerts for EMG, SSEP and MEPs did not significantly increase as the number of LLIF levels accessed increased. No EMG, SSEP, or MEP alerts occurred at L1-L2. EMG alerts occurred in 2-5% of patients at L2-L3, L3-L4, and L4-L5 and did not significantly vary by level (P = .34). SSEP and MEP alerts occurred more frequently at L4-L5 versus L2-L3 and L3-L4 (P < .03). IONM may provide the greatest utility at L4-L5, particularly MEPs, and may not be necessary for more cephalad LLIF procedures such as at L1-L2.

Anaesthesia and multimodality intraoperative neuromonitoring in carotid endarterectomy. Chronological evolution and effects on intraoperative neurophysiology.

Contingency data was retrospectively collected to evaluate the historical and current ability to provide multimodality intraoperative neurophysiological monitoring during carotid endarterectomy under two conditions: total intravenous anaesthesia (TIVA) and low dose halogenated anaesthesia (SEVO). 229 patients were monitored during carotid endarterectomy procedures under general anaesthesia between 2012 and 2020. 121 Patients were monitored with SEVO at a minimum alveolar concentration less than 0.7 and 108 were monitored using TIVA, according to common anaesthetic practice standards in our hospital across the years. Multimodality IONM was established with electroencephalography, somatosensory evoked potentials and motor evoked potentials. As compared to TIVA, patients monitored with SEVO showed significantly higher motor evoked potential thresholds (313.52 ± 77.74 SEVO and 218.93V ± 103.2V TIVA p < 0.05) and lower reproducibility. Electroencephalography and somatosensory evoked potentials showed no significant differences among the groups. When using SEVO, multimodality intraoperative neurophysiological monitoring during carotid endarterectomy could mask or miss a motor isolated change in patients in spite of low dose minimum alveolar concentration and of apparently adequate electroencephalography and somatosensory evoked potentials for monitoring. Given these difficulties, we believe the chronological transfer to TIVA could have improved our ability to establish multimodality intraoperative neurophysiological monitoring during carotid endarterectomy in recent times.

Intraoperative Neuromonitoring in Patients with Intradural Extramedullary Spinal Cord Tumor: A Single-Center Case Series

Intradural extramedullary spinal cord tumors (ID-EMSCT) make up 40% of all spinal neoplasms. Resection of these tumors is mostly conducted using intraoperative neuromonitoring (IONM). However, the literature shows heterogenous data on its added value for ID-EMSCT. The aim of this study is to define sensitivity and specificity of IONM in ID-EMSCT resection and to study possible correlations between preoperative, intraoperative, and postoperative variables and neurologic outcomes after ID-EMSCT resection. Data of patients undergoing ID-EMSCT surgeries with IONM from January 2012 until July 2019 were examined. Using neurologic status 6 weeks and 1 year postoperatively, sensitivity and specificity for IONM were calculated. IONM test results and neurologic outcomes were paired to preoperative, intraoperative, and postoperative parameters. Data of 78 patients were analyzed. 6 weeks postoperatively, 14.10% of patients had worse neurologic status, decreasing to 9.84% 1 year postoperatively. Multimodal IONM showed a sensitivity of 0.73 (95% confidence interval [CI], 0.39-0.94) and a specificity of 0.78 (95% CI, 0.66-0.87) after 6 weeks, and a sensitivity of 1.00 (95% CI, 0.54-1.00) and a specificity of 0.71 (95% CI, 0.57-0.82) after 1 year. IONM yielded high to perfect sensitivity and high specificity. However, IONM signals did not always determine the extent of resection, and false-positive results did not always result in incomplete tumor resections, because of surgeons overruling IONM. Therefore, IONM cannot fully replace clinical judgment and other perioperative information.

Is routine intraoperative neuromonitoring necessary in growing rod lengthening procedures? A retrospective, observational study.

To investigate whether intraoperative neuromonitoring (IONM) may be avoided in growing rod lengthening procedures in early onset scoliosis (EOS). A total of 636 primary growing rod surgeries and lengthening procedures were performed in 112 patients with EOS. Traditional growing rods (TGR) or magnetically controlled growing rods (MCGR) were implanted and subsequent lengthening procedures were done at stipulated intervals. Combined multi-modality IONM was used in all index surgeries-but was only used in lengthening procedures in patients with existing spinal cord abnormality or a history of neurosurgical procedure for the same, patients with prior history of a neuromonitoring alert in their index surgery and when lengthening was accompanied by an implant exchange/revision. All the remaining growing rod lengthening procedures were carried out without IONM. Hospital records and operation notes were retrospectively reviewed with focus on details of neurological events/complications. In 112 primary growing rod applications (TGR = 96, MCGR = 16) and 524 lengthening procedures (TGR = 444, MCGR = 80), intraoperative neuromonitoring 'alerts' were encountered in 6/112 index surgeries and temporary postoperative neurological deficits were seen in 2/112 index surgeries. No intraoperative neuromonitoring event or postoperative neurological complication was encountered in 524 lengthening procedures-irrespective of whether they were carried out along with implant exchange, or in patients with spinal cord abnormality or prior neuromonitoring event during index surgery. While IONM should be used in primary growing rod application surgeries, its use may be avoided in lengthening and implant exchange procedures in a resource-limited setting. Level 3.

Technological advancements that can be adopted for performing a safe vertebral column resection

Recent technological advancements have reduced the risks involved in vertebral column resection (VCR) with a wide range of tools that can be adopted. We intend to highlight the importance of these tools for performing a safe VCR. The patient, a 35-year-old man, presented with hyperkyphotic thoracic spine and symptomatic thoracic myelopathy. Radiological evaluation showed anterior wedging and fused T6-T7 vertebra, resulting in a gibbus deformity causing significant canal stenosis. Hence, T3-T10 posterior stabilization, T5-T8 decompression, and T6-T7 VCR and anterior column reconstruction were planned. We used recent technological advancements such as: (1) three-dimensional printed spine model for preoperative planning, (2) multimodal intraoperative neuromonitoring, (3) ultrasonic bone debulking, and (4) computed tomography–based image-guided spinal navigation. These advancements have made spine surgery relatively safer, predictable, and precise. Moreover, the field is constantly evolving. Hence, adapting to these advancements and utilizing it in complex scenarios are highly beneficial.

Utility of motor evoked potentials to diagnose and reduce lower extremity motor nerve root injuries during 4,386 extradural posterior lumbosacral spine procedures

BACKGROUND CONTEXTMotor evoked potentials (MEPs) have excellent sensitivity for monitoring the functional integrity of the lateral corticospinal tract of the spinal cord. The sensitivity for nerve root function, however, is not as well established; consequently, MEPs are often not utilized for posterior extradural spine procedures distal to the conus. Spontaneous electromyography (sEMG) and somatosensory evoked potentials (SSEPs) are often included for these procedures, but their limited sensitivity has been well documented. Given the risk of motor nerve root injuries during spine procedures, and specifically increased vulnerability of the L4 and L5 nerves, the sensitivity of MEPs was evaluated for diagnostic accuracy and therapeutic impact. PURPOSETo determine the diagnostic sensitivity of MEPs during lumbosacral spine procedures and the potential therapeutic impact of the resolution of MEP alerts. STUDY DESIGNA total of 4,386 posterior extradural lumbosacral spine procedures utilizing multimodality intraoperative neuromonitoring (IONM) with sEMG, SSEPs, and MEPs were abstracted from a multi-institutional database. All cases took place between October 2015 and October 2017. No external funding was provided. OUTCOME MEASURESSensitivity and specificity, as well as positive and negative likelihood ratios for new postoperative neurologic deficits were calculated for each modality individually as well as when combined (multimodality). PATIENT SAMPLEAge 18 and older METHODSData entered in the electronic medical record were analyzed. Alerts to sEMG activity, decreases in SSEP amplitude, or decreases in MEP amplitude were documented as well as the status of the alerts at closure: resolved or unresolved. The presence of an sEMG alert or an unresolved MEP or SSEP alert at closure was considered a positive diagnostic result, and these results were assessed relative to presence of new immediate onset neurologic deficits as documented in the electronic record. RESULTSThe sensitivity and specificity of multimodality IONM for new immediate-onset lower extremity motor deficits were 100.0% (95% confidence interval: [64.6, 100.0]) and 92.2% (91.1, 93.1), respectively. Looking at the modalities in isolation, the sensitivity of MEPs was considerably better than either lower extremity sEMG or posterior tibial nerve SSEPs: 100.0% (78.5, 100.0) versus just 14.3% (4.0, 39.9) and 28.6% (8.2, 64.1), respectively. Surprisingly, the specificity of lower extremity MEPs was better than sEMG, 97.9% (97.5, 98.3) versus 95.4% (94.7, 96.0) (χ2=43.0, p<.001). The specificity of lower extremity SSEPs was 99.0% (98.5, 99.3). Only 4.4% of all procedures had a lower extremity MEP alert. There were 14 significant new nerve root injuries and all 14 had unresolved MEPs at closure. Total 85.7% of those nerve root injuries were dorsiflexion foot drop injuries and all had unresolved tibialis anterior MEP alerts. Although the overall rate of nerve root injuries was 0.32% (14/4,386), the rate for procedures with unresolved isolated tibialis anterior MEP alerts was 44.4% (12/27). The therapeutic impact is evident in the 2.0% of cases (87/4,386) with lower extremity MEP alerts that were able to be fully resolved by closure and for which the rate of injury was zero. CONCLUSIONSThe diagnostic accuracy of MEPs for anterior tibialis-related nerve root dysfunction supports the inclusion of this modality during routine posterior extradural lumbosacral procedures, especially when the L4 or L5 nerve roots are at risk. Moreover, therapeutic interventions that lead to the resolution of MEP alerts avert postoperative neurologic injuries.

Evolving Indications for Neuromonitoring in Spinal Surgery: What and When to Monitor

Intraoperative neuromonitoring (IONM) is utilized during spine surgery to help prevent intraoperative neurologic injury. The first reported use of IONM in humans occurred more than four decades ago. Since its initial inception, technological advances such as the ability to monitor afferent sensory pathways and efferent motor pathways has greatly improved the efficiency and accuracy of IONM. Clinical research has established the superiority of multimodal IONM over unimodal techniques. However, controversy still exists regarding the most appropriate use of IONM. Currently, the surgeon is responsible for the interpretation of neuromonitoring alerts with the assistance of technicians and neurologists. Furthermore, the surgeon must determine the interventions necessary to mitigate neurologic risk according to such alerts. To that end, this chapter provides a historical context for IONM, reviews the physiologic mechanisms of common IONM modalities and examines the clinical evidence for IONM use.

Multimodality Intraoperative Neuromonitoring in Severe Thoracic Deformity Posterior Vertebral Column Resection Correction

Multimodal intraoperative neuromonitoring (IONM) has been proposed as an effective way to reduce permanent neurologic injury during spinal deformity surgery. However, few studies have reported evoked potential changes at different surgical stages of thoracic posterior vertebral column resection (PVCR). A total of 82 cases with severe thoracic deformity (Yang's A type) treated by PVCR in a single institution between January 2010 and March 2015 were reviewed. Multimodal IONM including somatosensory evoked potential, motor evoked potential, and descending neurogenic evoked potential was performed for real-time assessment of spinal cord function during surgery. The risk factors of neuromonitoring events at different surgical stages were documented and analyzed. Multimodal IONM was successfully performed in all 82 cases. Thirty-nine neuromonitoring events presented in 27 (32.9%) cases. Neurologic monitoring events were more likely to occur in patients with larger scoliosis and kyphosis, longer osteotomy closure distance, more Halo gravity traction, more screw insertion, and higher PVCR segments. The reasons for monitoring changes included 6 events during screw insertion, 20 during osteotomy, 9 during osteotomy gap closure, and 4 during deformity correction. New postoperative neurologic deficits were observed in 11 (13.4%) cases including 1 incomplete paraplegia, 8 transient cord deficits, and 2 nerve root injuries. Multimodal IONM can effectively identify neurologic deficits throughout surgery. Osteotomy and osteotomy gap closure are the surgical stages with the highest neurologic risks during PVCR procedures. It is imperative to improve dexterity since the majority of neuromonitoring events are caused by surgical techniques.

Intraoperative Neuromonitoring (IONM): Is There a Role in Metastatic Spine Tumor Surgery?

A retrospective design. We aim to report our experience with multimodal intraoperative neuromonitoring (IONM) in metastatic spine tumor surgery (MSTS). IONM is considered as standard of care in spinal deformity surgeries. However, limited data exist about its role in MSTS. A total of 135 patients from 2010 to 2017, who underwent MSTS with IONM at our institute, were studied retrospectively. After excluding seven with no baseline signals, 128 patients were analyzed. The data collected comprised of demographics, pre and postoperative American Spinal Injury Association (ASIA) grades and neurological status, indications for surgery, type of surgical approach. Multimodal IONM included somatosensory-evoked potentials (SSEPs), transcranial electric motor-evoked potentials (tcMEP), and free running electromyography (EMG). The 128 patients included 61 males and 67 females with a mean age of 61 years. One hundred sixteen underwent posterior procedures; nine anterior and three both. The frequency of preoperative ASIA Grades were A = 0, B = 0, C = 10, D = 44, and E = 74 patients. In total, 54 underwent MSTS for neurological deficit, 66 for instability pain, and 8 for intractable pain.Of 128 patients, 13 (10.2%) had significant IONM alerts, representing true positives; 114 true negatives, one false negative, and no false positives. Among the 13 true positives, four (30%) underwent minimally invasive and nine (70%) open procedures. Eight (69.2%) patients had posterior approach. Seven (53.84%) true positive alerts were during decompression, which resolved to baseline upon completion of decompression, while five (38.46%) were during instrumentation, which recovered to baseline after adjusting/downsizing the instrumentation, and one (8.3%) during lateral approach, which reversed after changing the plane of dissection. Of the seven patients without baseline, five were ASIA-A and two were ASIA-C. The sensitivity, specificity, positive, and negative predictive values were 99.1%, 100%, 100%, and 92.9%, respectively. Multimodal IONM in MSTS helped in preventing postoperative neurological deficit in 9.4% of patients. Its high sensitivity and specificity to detect intraoperative neurological events envisage its use in ASIA-grade D/E patients requiring instrumented decompression. 3.

Wednesday, September 26, 2018 1:00 PM – 2:00 PM Navigation and Intraoperative Monitoring: 45. Neuromonitoring signal changes in cervical spine surgery: when is it significant?

BACKGROUND CONTEXT Modern cervical spine surgeries utilizes intraoperative neuromonitoring (IONM) in the form of motor evoked potential (MEP), somatosensory evoked potential (SSEP) and electromyography (EMG). However, with a sensitivity ranging from 0% to 100% and specificity ranging from 27% to 100%, there is a need to differentiate between true and false positive signal changes to better supplement intraoperative management. PURPOSE To compare the incidence of neurological deficits in sustained, bimodal intraoperative neuromonitoring (MEP and SEP) signal drops to that of unimodal or transient changes in cervical spine surgeries. STUDY DESIGN/SETTING Retrospective cohort study. PATIENT SAMPLE A total of 257 cases of cervical spine surgery with multimodal neuromonitoring in 3 hospitals in Singapore between 2013 and 2017. OUTCOME MEASURES Incidence of neurological deficits in 3 different patterns of neuromonitoring signal changes. Sensitivity and specifity of MEP and SSEP in cervical spine surgeries. METHODS A retrospective review of IONM and clinical records of all cervical spine surgeries in three hospitals between 2013 and 2017. The procedures were performed by fellowship trained spine surgeons and multimodal IONM was used in all cases. Clinical records were evaluated by two clinicians who were not involved in the patients' management. IONM records of MEP and SSEP were reviewed by a trained neurophysiology technologist. Results were grouped into three groups. In Group 0, there were unimodal signal drops that were transient and resolved back to baseline by the end of surgery. In Group 1, there were sustained unimodal signal changes while in Group 2, there were sustained drops in both the MEP and SSEP. RESULTS A total of 257 cases were reviewed and 207 cases were analyzed after exclusions. A total of 52/207 (25.1%) cases had IONM changes. A total of 10/207 (4.3%) of cases were in Group 0, while Group 1 had 35/207 (16.9%) of cases. 7/207 (3.4%) of cases were in Group 2. Group 0 and 1 had no neurological deficits, while in Group 2, 2/7 (28.6%) had neurological deficits. Both MEP and SSEP were 100% sensitive. SSEP had a specificity of 96.6%, while MEP had a lower specificity at 76.6%. CONCLUSIONS Our study shows that by grouping the signal changes into transient or sustained, and unimodal or bimodal, we are able to better predict which signal drops are significant, thereby allowing for improved intraoperative decision making. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.

S125. Degree of resolution of neuromonitoring alerts predicts the likelihood of neurological deficits in extradural cervical spine surgery: Review of 30,921 procedures

Introduction Multimodality intraoperative neuromonitoring (IONM) is frequently used during extradural spine surgery. Further understanding about the clinical significance of the reversibility of IONM alerts may provide guidance regarding the need to alter the intraoperative surgical technique. We asked whether the presence of an IONM alert, and the degree to which it resolved intraoperatively, predicted the likelihood of a postoperative neurological deficit. Methods We performed a retrospective review of a multi-institutional database to analyze a series of 30,921 consecutive extradural cervical spine procedures performed between October 2015 and October 2017 at 517 U.S. institutions. Within each case, the presence or absence of an IONM alert was recorded, as well as the degree of resolution at the conclusion of surgery for those cases with one or more alerts (fully resolved, partially resolved, unresolved). Presence or absence of a neurological deficit was recorded in the postoperative period. Relative odds of new-onset post-operative neurological deficit according to IONM alert resolution status were assessed using a random effects logistic regression model controlling for patient age, gender, number of vertebral levels addressed, surgical approach (anterior (A), posterior (P), or combined A/P), anesthesia regimen, trauma status, surgeon, surgical neurophysiologist, and hospital. Results There were 785, 497, and 2332 cases with no, partial, or full resolution of alerts, respectively. After controlling for all of the above named factors, we found that relative to cases with no IONM alerts, cases with alerts had significantly higher risk of neurologic deficit following an expected relative risk gradient. Cases with fully resolved IONM alerts were more than twice as likely to experience a deficit (OR = 2.5, 95%CI: 1.3–4.9, p Conclusion Degree of resolution of IONM alerts helps to predict the likelihood of a neurological deficit in the postoperative setting in patients undergoing extradural spine surgery. While risk of a neurological deficit is highest when alerts do not resolve, there is also a slightly increased risk of a neurological deficit with full resolution. Awareness of these relationships helps the surgical team make decisions intraoperatively, and allows the surgeon to counsel the patient.

Technique and advantages of multimodal intraoperative neuromonitoring for complex spinal interventions in older patients

Complex spinal surgery in elderly patients mostly treats degenerative spine alterations. The use of multimodal intraoperative neuromonitoring (IONM) has proven to be auseful tool to recognize neural deterioration during such operations. Elderly patients often have preexisting neural impairment, which leads to difficulties in deriving some potentials or can even lead to not obtaining any potentials at all. For reliable benefits from IONM acombined use of monitoring and mapping methods as well as the right choice of methods according to the spine level to be treated and adefinition of the neural structures in danger is needed. This article intends to explain IONM methods in procedures treating degenerative spine alterations in acomprehensive way and to show our point of view on pedicle stimulation. Readers should be motivated to deepen their knowledge in these methods and to gain confidence and experience to increase the safety of these operations for the benefit of our patients.

Early experience of placing image-guided minimally invasive pedicle screws without K-wires or bone-anchored trackers.

OBJECTIVE Image guidance for spine surgery has been reported to improve the accuracy of pedicle screw placement and reduce revision rates and radiation exposure. Current navigation and robot-assisted techniques for percutaneous screws rely on bone-anchored trackers and Kirchner wires (K-wires). There is a paucity of published data regarding the placement of image-guided percutaneous screws without K-wires. A new skin-adhesive stereotactic patient tracker (SpineMask) eliminates both an invasive bone-anchored tracker and K-wires for pedicle screw placement. This study reports the authors' early experience with the use of SpineMask for "K-wireless" placement of minimally invasive pedicle screws and makes recommendations for its potential applications in lumbar fusion. METHODS Forty-five consecutive patients (involving 204 screws inserted) underwent K-wireless lumbar pedicle screw fixation with SpineMask and intraoperative neuromonitoring. Screws were inserted by percutaneous stab or Wiltse incisions. If required, decompression with or without interbody fusion was performed using mini-open midline incisions. Multimodality intraoperative neuromonitoring assessing motor and sensory responses with triggered electromyography (tEMG) was performed. Computed tomography scans were obtained 2 days postoperatively to assess screw placement and any cortical breaches. A breach was defined as any violation of a pedicle screw involving the cortical bone of the pedicle. RESULTS Fourteen screws (7%) required intraoperative revision. Screws were removed and repositioned due to a tEMG response < 13 mA, tactile feedback, and 3D fluoroscopic assessment. All screws were revised using the SpineMask with the same screw placement technique. The highest proportion of revisions occurred with Wiltse incisions (4/12, 33%) as this caused the greatest degree of SpineMask deformation, followed by a mini midline incision (3/26, 12%). Percutaneous screws via a single stab incision resulted in the fewest revisions (7/166, 4%). Postoperative CT demonstrated 7 pedicle screw breaches (3%; 5 lateral, 1 medial, 1 superior), all with percutaneous stab incisions (7/166, 4%). The radiological accuracy of the SpineMask tracker was 97% (197/204 screws). No patients suffered neural injury or required postoperative screw revision. CONCLUSIONS The noninvasive cutaneous SpineMask tracker with 3D image guidance and tEMG monitoring provided high accuracy (97%) for percutaneous pedicle screw placement via stab incisions without K-wires.

Demographic Trends in the Use of Intraoperative Neuromonitoring for Scoliosis Surgery in the United States.

Intraoperative neuromonitoring (ION), such as motor-evoked potential (MEP), somatosensory evoked potentials (SSEP), and electromyography (EMG), is used to detect impending neurological injuries during spinal surgery. To date, little is known about the trends in the use of ION for scoliosis surgery in the United States. A retrospective review was performed using the PearlDiver Database to identify patients that had scoliosis surgery with and without ION from years 2005 to 2011. Demographic information (such as age, gender, region within the United States) and clinical information (such as type of ION and rates of neurological injury) were assessed. There were 3618 patients who had scoliosis surgery during the study period. Intraoperative neuromonitoring was used in 1361 (37.6%) of these cases. The number of cases in which ION was used increased from 27% in 2005 to 46.9% in 2011 (P < .0001). Multimodal ION was used more commonly than unimodal ION (64.6% versus 35.4%). The most commonly used modality was combined SSEP and EMG, while the least used modality was MEP only. Neurological injuries occurred in 1.8 and 2.0% of patients that had surgery with and without ION, respectively (P = .561). Intraoperative neuromonitoring was used most commonly in patients <65 years of age and in the Northeastern part of the United States (age P = .006, region P < .0001). The use of ION for scoliosis surgery gradually increased annually from 2005 to 2011. Age and regional differences were noted with neuromonitoring being most commonly used for scoliosis surgery in nonelderly patients and in the Northeastern part of the United States. No differences were noted in the risk of neurological injury in patients that had surgery with and without ION. Although the findings from this study may seem to suggest that ION may not influence the risk of neurologic injury, this result must be interpreted with caution as inherently riskier surgeries may utilize ION more, leading to an actual reduction in injuries more dramatic than observed in this study.

47. Rate of complications due to non-idiopathic scoliosis spine surgery: The key role of multimodal intraoperative neuromonitoring and mapping

Aim of this study was to evaluate the role of multimodal intraoperative neuromonitoring and mapping (IONM) for detection of intraoperative and postoperative complications in a series of patients with non-idiopathic scoliosis (NI-S). We reviewed IONM records of 32 patients with NI-S (neurofibromatosis, Duchene muscular dystrophy, spinal muscular atrophy, Haberland, Goldenhair, Prader Willi syndrome, mucopolisaccaridosis, tetraparesis, congenital myopathy and neuropathy, achondroplasia, spinal tumor, diastematomyelia) with a mean age at surgery of 14 years (range, 6–25 years), who underwent posterior fusion with instrumentation surgery for spinal deformity. IONM with somatosensory evoked potentials (SSEP), transcranial motor evoked potentials (TcMEP) and pedicle screw mapping was performed. IONM using at least two modalities was attempted in all patients. No false-negative results were present. We recorded a high incidence of TcMEP alarm cases (14/32, 43.7%): increase of TcMEP threshold stimulation or samplification morphology/drop amplitude in 13 cases, TcMEP loss only in one case. Among these patients, postoperative motor deficit (true positive) was transient in 3/14, and permanent in 1/14. The surgical treatment in NI-S is burdened by a large number of complications, more than idiopathic scoliosis. IONM is safe and effective to minimize the incidence of new onset neurological deficit.