Intraoperative Neurophysiological Monitoring in Anterior Lumbar Interbody Fusion Surgery

Intraoperative somatosensory evoked potential (SEP) monitoring: an updated position statement by the American Society of Neurophysiological Monitoring

Somatosensory evoked potentials (SEPs) are used to assess the functional status of somatosensory pathways during surgical procedures and can help protect patients' neurological integrity intraoperatively. This is a position statement on intraoperative SEP monitoring from the American Society of Neurophysiological Monitoring (ASNM) and updates prior ASNM position statements on SEPs from the years 2005 and 2010. This position statement is endorsed by ASNM and serves as an educational service to the neurophysiological community on the recommended use of SEPs as a neurophysiological monitoring tool. It presents the rationale for SEP utilization and its clinical applications. It also covers the relevant anatomy, technical methodology for setup and signal acquisition, signal interpretation, anesthesia and physiological considerations, and documentation and credentialing requirements to optimize SEP monitoring to aid in protecting the nervous system during surgery.

Intraoperative neuromonitoring as real-time diagnostic for cerebral ischemia in endovascular treatment of ruptured brain aneurysms

OBJECTIVE

To evaluate the diagnostic accuracy of intraoperative neurophysiological monitoring (IONM) during endovascular treatment (EVT) of ruptured intracranial aneurysms (rIA).

METHODS

IONM and clinical data from 323 patients who underwent EVT for rIA from 2014-2019 were retrospectively reviewed. Significant IONM changes and outcomes were evaluated based on visual review of data and clinical documentation.

RESULTS

Of the 323 patients undergoing EVT, significant IONM changes were noted in 30 patients (9.29%) and 46 (14.24%) experienced postprocedural neurological deficits (PPND). 22 out of 30 (73.33%) patients who had significant IONM changes experienced PPND. Univariable analysis showed changes in somatosensory evoked potential (SSEP) and electroencephalogram (EEG) were associated with PPND (p-values: <0.001 and <0.001, retrospectively). Multivariable analysis showed that IONM changes were significantly associated with PPND (Odd ratio (OR) 20.18 (95%CI:7.40-55.03, p-value: <0.001)). Simultaneous changes in both IONM modalities had specificity of 98.9% (95% CI: 97.1%-99.7%). While sensitivity when either modality had a change was 47.8% (95% CI: 33.9%-62.0%) to predict PPND.

CONCLUSIONS

Significant IONM changes during EVT for rIA are associated with an increased risk of PPND.

SIGNIFICANCE

IONM can be used confidently as a real time neurophysiological diagnostic guide for impending neurological deficits during EVT treatment of rIA.

Utility of transcranial motor-evoked potential changes in predicting postoperative deficit in lumbar decompression and fusion surgery: a systematic review and meta-analysis

PURPOSE

The primary aim of this study was to evaluate whether TcMEP alarms can predict the occurrence of postoperative neurological deficit in patients undergoing lumbar spine surgery. The secondary aim was to determine whether the various types of TcMEP alarms including transient and persistent changes portend varying degrees of injury risk.

METHODS

This was a systematic review and meta-analysis of the literature from PubMed, Web of Science, and Embase regarding outcomes of transcranial motor-evoked potential (TcMEP) monitoring during lumbar decompression and fusion surgery. The sensitivity, specificity, and diagnostic odds ratio (DOR) of TcMEP alarms for predicting postoperative deficit were calculated and presented with forest plots and a summary receiver operating characteristic curve.

RESULTS

Eight studies were included, consisting of 4923 patients. The incidence of postoperative neurological deficit was 0.73% (36/4923). The incidence of deficits in patients with significant TcMEP changes was 11.79% (27/229), while the incidence in those without changes was 0.19% (9/4694). All TcMEP alarms had a pooled sensitivity and specificity of 63 and 95% with a DOR of 34.92 (95% CI 7.95-153.42). Transient and persistent changes had sensitivities of 29% and 47%, specificities of 96% and 98%, and DORs of 8.04 and 66.06, respectively.

CONCLUSION

TcMEP monitoring has high specificity but low sensitivity for predicting postoperative neurological deficit in lumbar decompression and fusion surgery. Patients who awoke with new postoperative deficits were 35 times more likely to have experienced TcMEP changes intraoperatively, with persistent changes indicating higher risk of deficit than transient changes.

LEVEL OF EVIDENCE II

Diagnostic Systematic Review.

Neuromonitoring Identifies Occlusion of Femoral Artery in STA-MCA Bypass Procedure: A Case Report

Intraoperative neurophysiological monitoring (IONM) is a technique used to assess the somatosensory and gross motor systems during surgery. While it is primarily used to detect and prevent surgically induced nervous system trauma, it can also detect and prevent injury to the nervous system that is the result of other causes such as trauma or ischemia that occur outside of the operative field as a result of malpositioning or other problematic physiologic states. We present a case study where a neuromonitoring alert altered the surgical procedure, though the alert was not correlated to the site of surgery. A 69-year-old male with a history of bilateral moyamoya disease and a left middle cerebral artery infarct underwent a right-sided STA-MCA bypass and encephaloduroarteriosynangiosis (EDAS) with multimodal IONM. During the procedure, the patient experienced a loss of motor evoked potential (MEP) recordings in the right lower extremity. Blood pressure was elevated, which temporarily restored the potentials, but they were lost again after the angiography team attempted to place an arterial line in the right femoral artery. The operation was truncated out of concern for left hemispheric ischemia, and it was later discovered that the patient had an acute right external iliac artery occlusion caused by a fresh thrombus in the common femoral artery causing complete paralysis of the limb. This case highlights the importance of heeding IONM alerts and evaluating for systemic causes if the alert is not thought to be of surgical etiology. IONM can detect adverse systemic neurological sequelae that is not necessarily surgically induced.

Prevention of Neurological Deficit With Intraoperative Neuromonitoring During Anterior Lumbar Interbody Fusion

STUDY DESIGN

This was a retrospective cohort study.

OBJECTIVE

While intraoperative neuromonitoring (IONM) has been increasingly used in spine surgery to have a real-time evaluation of the neurological injury, we aim here to assess its utility during anterior lumbar interbody fusion (ALIF) and its association with postoperative neurological deficit.

SUMMARY OF BACKGROUND DATA

ALIF is a beneficial surgical approach for patients with degenerative disease of the lower lumbar spine who would benefit from increased lordosis and restoration of neuroforaminal height. One risk of ALIF is iatrogenic nerve root injury. IONM may be useful in preventing this injury.

MATERIALS AND METHODS

We performed a retrospective cohort study of 111 consecutive patients who underwent ALIF at a tertiary care academic center by 6 spine surgeons. We aimed to describe the association between IONM, postoperative weakness, and factors that predispose our center to using IONM.

RESULTS

The 111 patients had a median age of 62 years [interquartile range (IQR): 53-69 y]. Neuromonitoring was used in 67 patients (60.3%) and not used in 44 patients. Seven neuromonitoring patients had IONM changes during the surgery. Three of these patients' surgeries featured intraoperative adjustments to reduce iatrogenic neural injury. The IONM cohort underwent significantly more complex procedures [5 levels (IQR: 3-7) vs. 2 levels (IQR: 2-5), P=0.001]. There was no difference in rates of new or worsened postoperative weakness (IONM: 20.6%, non-IONM: 20.5%).

CONCLUSIONS

We demonstrate evidence of the potential benefits of IONM for patients undergoing ALIF. Intraoperative changes in neuromonitoring signals resulted in surgical adjustments that likely prevented neurological deficits postoperatively. IONM was protective so that more complex surgeries did not have a higher rate of postoperative weakness.

Intraoperative neuromonitoring during surgery for lumbar stenosis

The indications for neuromonitoring during lumbar stenosis surgery are defined by the risks associated with patient positioning, the approach, decompression of neural elements, deformity correction, and instrument implantation. The routine use of EMG and SEP alone during lumbar stenosis surgery is no longer supported by the literature. Lateral approach neuromonitoring with EMG only is also suspect. Lumbar stenosis patients often present with multiple co-morbidities which put them at risk during routine pre-surgical positioning. Frequently encountered morbid obesity and/or diabetes mellitus may play a role in monitorable and preventable brachial plexopathy after "superman" positioning or femoral neuropathy from groin pressure after prone positioning, for example. Deformity correction in lumbar stenosis surgery often demands advanced implementation of multiple neuromonitoring modalities: EMG, SEP, and MEP. Because the bulbocavernosus reflex detects the function of the conus medullaris and sacral somato afferent/efferent fibers of the cauda equina, it may also be recorded. The recommendation to record pedicle screw thresholds has become more nuanced as surgeon dependence on 3D imaging, navigation, and robotics has increased. Neuromonitoring in lumbar stenosis surgery has been subject mainly to uncontrolled case series; prospective cohort trials are also needed.

Diagnostic Accuracy of SSEP Changes During Lumbar Spine Surgery for Predicting Postoperative Neurological Deficit: A Systematic Review and Meta-Analysis

STUDY DESIGN

This study is a meta-analysis of prospective and retrospective studies identified in PubMed, Web of Science, and Embase with outcomes of patients who received intraoperative somatosensory-evoked potential (SSEP) monitoring during lumbar spine surgery.

OBJECTIVE

The objective of this study is to determine the diagnostic accuracy of intraoperative lower extremity SSEP changes for predicting postoperative neurological deficit. As a secondary analysis, we evaluated three subtypes of intraoperative SSEP changes: reversible, irreversible, and total signal loss.

SUMMARY OF BACKGROUND DATA

Lumbar decompression and fusion surgery can treat lumbar spinal stenosis and spondylolisthesis but carry a risk for nerve root injury. Published neurophysiological monitoring guidelines provide no conclusive evidence for the clinical utility of intraoperative SSEP monitoring during lumbar spine surgery.

METHODS

A systematic review was conducted to identify studies with outcomes of patients who underwent lumbar spine surgeries with intraoperative SSEP monitoring. The sensitivity, specificity, and diagnostic odds ratio (DOR) were calculated and presented with forest plots and a summary receiver operating characteristic curve.

RESULTS

The study cohort consisted of 5607 patients. All significant intraoperative SSEP changes had a sensitivity of 44% and specificity of 97% with a DOR of 22.13 (95% CI, 11.30-43.34). Reversible and irreversible SSEP changes had sensitivities of 28% and 33% and specificities of 97% and 97%, respectively. The DORs for reversible and irreversible SSEP changes were 13.93 (95% CI, 4.60-40.44) and 57.84 (95% CI, 15.95-209.84), respectively. Total loss of SSEPs had a sensitivity of 9% and specificity of 99% with a DOR of 23.91 (95% CI, 7.18-79.65).

CONCLUSION

SSEP changes during lumbar spine surgery are highly specific but moderately sensitive for new postoperative neurological deficits. Patients who had postoperative neurological deficit were 22 times more likely to have exhibited intraoperative SSEP changes.Level of Evidence: 2.

Roles of multimodal intra-operative neurophysiological monitoring (IONM) in percutaneous endoscopic transforaminal lumbar interbody fusion: a case series of 113 patients

Background

Despite the wide use of intraoperative neurophysiological monitoring (IONM) in spinal surgeries, the efficacy of IONM during percutaneous endoscopic transforaminal lumbar interbody fusion (PE-TLIF) surgery in detecting postoperative neurological deficits has not been well characterized.

Methods

MIONM data from 113 consecutive patients who underwent PE-TLIF surgeries between June 2018 and April 2020 were retrospectively reviewed. Postoperative neurological deficits were documented and analyzed, and the efficacy and specificity of various IONM techniques were compared.

Results

Of the 113 consecutive patients, 12 (10.6%) with IONM alerts were identified. The MIONM sensitivity and specificity were 100 and 96.2%, respectively. The frequency of neurological complications, including minor deficits, was 6.2% (n = 7); all of the neurological complications were temporary. The ability of single IONM modalities to detect neurological complications varied between 25.0 and 66.6%, whereas that of all modalities was 100%.

Conclusions

MIONM is more effective and accurate than unimodal monitoring in assessing nerve root function during PE-TLIF surgeries, reducing both neurological complications and false-negative findings. We recommend MIONM in PE-TLIF surgeries.

Vulnerability of the L5 nerve root during anterior lumbar interbody fusion at L5-S1: case series and review of the literature

OBJECTIVE

Nerve root injuries associated with anterior lumbar interbody fusion (ALIF) are uncommonly reported in the literature. This case series and review aims to describe the etiology of L5 nerve root injury following ALIF at L5-S1.

METHODS

The authors performed a single-center retrospective review of prospectively collected data of patients who underwent surgery between 2017 and 2019 who had postoperative L5 nerve root injuries after stand-alone L5-S1 ALIF. They also reviewed the literature with regard to nerve root injuries after ALIF procedures.

RESULTS

The authors report on 3 patients with postoperative L5 radiculopathy. All 3 patients had pain that improved. Two of the 3 patients had a neurological deficit, one of which improved.

CONCLUSIONS

Stretch neuropraxia from overdistraction is an important cause of postoperative L5 radiculopathy after L5-S1 ALIF. Judicious use of implants and careful preoperative planning to determine optimal implant sizes are paramount.

Neurologic Complications in Monitored versus Unmonitored Image-Guidance Assisted Posterior Lumbar Instrumentation

BACKGROUND

Intraoperative neurophysiologic monitoring (IOM) has been used clinically since the 1970s and is a reliable tool for detecting impending neurologic compromise. However, there are mixed data as to whether long-term neurologic outcomes are improved with its use. We investigated whether IOM used in conjunction with image guidance produces different patient outcomes than with image guidance alone.

METHODS

We reviewed 163 consecutive cases between January 2015 and December 2018 and compared patients undergoing posterior lumbar instrumentation with image guidance using and not using multimodal IOM. Monitored and unmonitored surgeries were performed by the same surgeons, ruling out variability in intersurgeon technique. Surgical and neurologic complication rates were compared between these 2 cohorts.

RESULTS

A total of 163 patients were selected (110 in the nonmonitored cohort vs. 53 in the IOM cohort). Nineteen signal changes were noted. Only 3 of the 19 patients with signal changes had associated neurologic deficits postoperatively (positive predictive value 15.7%). There were 5 neurologic deficits that were observed in the nonmonitored cohort and 8 deficits observed in the monitored cohort. Transient neurologic deficit was significantly higher in the monitored cohort per case (P < 0.0198) and per screw (P < 0.0238); however, there was no difference observed between the 2 cohorts when considering permanent neurologic morbidity per case (P < 0.441) and per screw (P < 0.459).

CONCLUSIONS

The addition of IOM to cases using image guidance does not appear to decrease long-term postoperative neurologic morbidity and may have a reduced diagnostic role given availability of intraoperative image-guidance systems.

Intraoperative Neuromonitoring and Lumbar Spinal Instrumentation: Indications and Utility

Multimodal intraoperative neurophysiologic monitoring (IONM) can be utilized as an adjunct to lumbar spinal instrumentation in order to aid with avoidance of neurologic complications. The most commonly utilized modalities include somatosensory-evoked potentials, motor-evoked potentials, and electromyography. Somatosensory-evoked potentials (SSEPs) allow for continuous assessment of the dorsal columns of the spinal cord and are therefore most useful during procedures with a posterior approach to the cervical and thoracic spine. Motor-evoked potentials (MEPs) and electromyography (EMG) can be applied intermittently to assess motor nerve function. The utility of each individual modality can be largely dependent on the surgical approach. Approaches to lumbar spinal instrumentation can be generally categorized as anterior, lateral, and posterior. For lateral approaches, electromyography can be helpful in identifying neural structures crossing the surgical field to prevent injury. In posterior and anterior approaches, somatosensory-evoked potentials and motor-evoked potentials can be used to assess nerve injury during and after maneuvers for decompression and instrumentation. Additionally, during the placement of pedicle screws, direct stimulation with triggered electromyography can be used to detect the pedicle cortex's breach. The efficacy of intraoperative neuromonitoring is dependent on prompt and accurate recognition of changes in signals. This is then followed by accurate recognition of the cause for these changes and appropriate responses by the surgeon, anesthesiologist, and monitoring personnel to correct the change.

Diagnostic Accuracy of Somatosensory Evoked Potential Monitoring in Evaluating Neurological Complications During Endovascular Aneurysm Treatment

BACKGROUND

Somatosensory evoked potential (SSEP) monitoring is used extensively for early detection and prevention of neurological complications in patients undergoing many different neurosurgical procedures. However, the predictive ability of SSEP monitoring during endovascular treatment of cerebral aneurysms is not well detailed.

OBJECTIVE

To evaluate the performance of intraoperative SSEP in the prediction postprocedural neurological deficits (PPNDs) after coil embolization of intracranial aneurysms.

METHODS

This population-based cohort study included patients ≥18 years of age undergoing intracranial aneurysm embolization with concurrent SSEP monitoring between January 2006 and August 2012. The ability of SSEP to predict PPNDs was analyzed by multiple regression analyses and assessed by the area under the receiver operating characteristic curve.

RESULTS

In a population of 888 patients, SSEP changes occurred in 8.6% (n = 77). Twenty-eight patients (3.1%) suffered PPNDs. A 50% to 99% loss in SSEP waveform was associated with a 20-fold increase in risk of PPND; a total loss of SSEP waveform, regardless of permanence, was associated with a greater than 200-fold risk of PPND. SSEPs displayed very good predictive ability for PPND, with an area under the receiver operating characteristic curve of 0.84 (95% CI 0.76-0.92).

CONCLUSION

This study supports the predictive ability of SSEPs for the detection of PPNDs. The magnitude and persistence of SSEP changes is clearly associated with the development of PPNDs. The utility of SSEP monitoring in detecting ischemia may provide an opportunity for neurointerventionalists to respond to changes intraoperatively to mitigate the potential for PPNDs.

Repeated sugammadex reversal of muscle relaxation during lumbar spine surgery with intraoperative neurophysiological multimodal monitoring

Intraoperative neurophysiological monitoring during spine surgery is usually acomplished avoiding muscle relaxants. A case of intraoperative sugammadex partial reversal of the neuromuscular blockade allowing adequate monitoring during spine surgery is presented. A 38 year-old man was scheduled for discectomy and vertebral arthrodesis throughout anterior and posterior approaches. Anesthesia consisted of total intravenous anesthesia plus rocuronium. Intraoperatively monitoring was needed, and the muscle relaxant reverted twice with low dose sugammadex in order to obtain adequate responses. The doses of sugammadex used were conservatively selected (0.1mg/kg boluses increases, total dose needed 0.4mg/kg). Both motor evoqued potentials, and electromyographic responses were deemed adequate by the neurophysiologist. If muscle relaxation was needed in the context described, this approach could be useful to prevent neurological sequelae. This is the first study using very low dose sugammadex to reverse rocuronium intraoperatively and to re-establish the neuromuscular blockade.

Anterior lumbar spine surgery: a systematic review and meta-analysis of associated complications

BACKGROUND CONTEXT

The anterior approach to the lumbar spine is increasingly used to accomplish various surgical procedures. However, the incidence and risk factors for complications associated with anterior lumbar spine surgery (ALS) have not been fully elucidated.

PURPOSE

To identify and document types of complications and complication rates associated with ALS, determine risk factors for these events, and evaluate the effect of measures used to decrease complication rates.

STUDY DESIGN

Systematic review and meta-analysis.

METHODS

A systematic review of the English-language literature was conducted for articles published between January 1992 and December 2013. A MEDLINE search was conducted to identify articles reporting complications associated with ALS. For each complication, the data were combined using a generalized linear mixed model with a binomial probability distribution and a random effect based on the study. Predictors used were the type of procedure (open, minimally invasive, or laparoscopic), the approach used (transperitoneal vs. retroperitoneal), use of recombinant bone morphogenetic protein-2, use of preoperative computed tomography angiography (CTA), and the utilization of an access surgeon. Open surgery was used as a reference category.

RESULTS

Seventy-six articles met final inclusion criteria and reported complication rates in 11,410 patients who underwent arthrodesis and/or arthroplasty via laparoscopic, mini-open, and open techniques. The overall complication rate was 14.1%, with intraoperative and postoperative complication rates of 9.1% and 5.2%, respectively. Only 3% of patients required reoperation or revision procedures. The most common complications reported were venous injury (3.2%), retrograde ejaculation (2.7%), neurologic injury (2%), prosthesis related (2%), postoperative ileus (1.4%), superficial infection (1%), and others (1.3%). Laparoscopic and transperitoneal procedures were associated with higher complication rates, whereas lower complication rates were observed in patients receiving mini-open techniques. Our analysis indicated that the use of recombinant bone morphogenetic protein-2 was associated with increased rates of retrograde ejaculation; however, there may be limitations in interpreting these data. Data regarding the use of preoperative CTA and an access surgeon were limited and demonstrated mixed benefit.

CONCLUSIONS

Overall complication rates with ALS are relatively low, with the most common complications occurring at a rate of 1% to 3%. Complication rates are related to surgical technique, approach, and implant characteristics. Further randomized controlled trials are needed to validate the use of preventative measures including CTA and the use of an access surgeon.