Neurophysiological monitoring of spinal cord function during spinal deformity surgery: 2020 SRS neuromonitoring information statement

Biomechanical analysis of spinal cord injury during scoliosis correction surgery

Introduction: Surgical correction is a common treatment for severe scoliosis. Due to the significant spinal deformation that occurs with this condition, spinal cord injuries during corrective surgery can occur, sometimes leading to paralysis. Methods: Such events are associated with biomechanical changes in the spinal cord during surgery, however, their underlying mechanisms are not well understood. Six patient-specific cases of scoliosis either with or without spinal complications were examined. Finite element analyses (FEA) were performed to assess the dynamic changes and stress distribution of spinal cords after surgical correction. The FEA method is a numerical technique that simplifies problem solving by replacing complex problem solving with simplified numerical computations. Results: In four patients with poor prognosis, there was a concentration of stress in the spinal cord. The predicted spinal cord injury areas in this study were consistent with the clinical manifestations of the patients. In two patients with good prognosis, the stress distribution in the spinal cord models was uniform, and they showed no abnormal clinical manifestations postoperatively. Discussion: This study identified a potential biomechanical mechanism of spinal cord injury caused by surgical correction of scoliosis. Numerical prediction of postoperative spinal cord stress distribution might improve surgical planning and avoid complications.

Delayed paraparesis after posterior spinal fusion for congenital scoliosis: a case report

INTRODUCTION

Although multimodal intraoperative neuromonitoring (IONM), which has high sensitivity and specificity, is typically performed during spinal deformity surgery, neurological status may deteriorate with delay after surgical maneuvers. Here, we report a rare case of delayed postoperative neurological deficit (DPND) that was not detected by IONM during posterior spinal fusion (PSF) for congenital scoliosis.

CASE PRESENTATION

A 14-year-old male presented with congenital scoliosis associated with T3 and T10 hemivertebrae. Preoperative Cobb angle of proximal thoracic (PT) and main thoracic (MT) curves were 50° and 41°, respectively. PSF (T1-L1) without hemivertebrectomy was performed, and the curves were corrected to 31° and 21° in the PT and MT curves, respectively, without any abnormal findings in IONM, blood pressure, or hemoglobin level. However, postoperative neurological examination revealed complete loss of motor function. A revision surgery, release of the curve correction by removing the rods, was immediately performed and muscle strength completely recovered on the first postoperative day. Five days postoperatively, PSF was achieved with less curve correction (36° in the PT curve and 26° in the MT curve), without postoperative neurological deficits.

DISCUSSION

Possible mechanisms of DPND in our patient are spinal cord ischemia due to spinal cord traction caused by scoliosis correction and spinal cord kinking by the pedicle at the concave side. Understanding the possible mechanisms of intra- and postoperative neural injury is essential for appropriate intervention in each situation. Additionally, IONM should be continued to at least skin closure to detect DPND observed in our patient.

Neuromonitoring for spine surgery in children

Neuromonitoring or electrophysiologic monitoring is now an essential component of pediatric spine surgery due to the high number of spinal deformity indications in asymptomatic patients, for whom any neurological complication would be disastrous. Technological advances have led to the development of compact monitors that allow surgeons themselves to monitor the motor evoked potentials (MEP) perioperatively. This shift happened because it was difficult to always have a neurophysiologist in the operating room. Unfortunately, this also means that multimodal monitoring (sensory, mixed, D-wave, electromyography, pedicle screws) is much more difficult to implement. There are absolute indications, such as any spinal deformity without neurological deficit and relative indications, which are more difficult to interpret. Technical incidents frequently occur before the start of the surgery. If no replacement device is available, the procedure must be cancelled unless the patient's life or function are at risk. At least two monitoring systems should be available at every facility to avoid having to cancel surgery for purely technological reasons. Once the surgical procedure has started, the absence of MEP recruitment curves in the upper and lower limbs is likely due to the anesthesia depth; the surgery should be stopped until this problem is corrected. When there is a true intraoperative alert (MEPs disappear in the lower limbs only), we propose taking the following steps, depending on whether the spine is stable or unstable: remove the causal implant, remove all hardware, preserve any stabilization devices, initiate an intraoperative wake-up test, verify conditions under which the intervention should continue. Level of evidence: V.

Utility of intraoperative neurophysiological monitoring in detecting motor and sensory nerve injuries in pediatric high-grade spondylolisthesis

BACKGROUND CONTEXT

Intraoperative neuromonitoring (IONM) during surgical correction of spinal deformity has been shown to reduce iatrogenic injury in pediatric and adult populations. Although motor-evoked potentials (MEP), somatosensory-evoked potentials (SSEP), and electromyography (EMG) have been shown to be highly sensitive and specific in detecting spinal cord and nerve root injuries, their utility in detecting motor and sensory nerve root injury in pediatric high-grade spondylolisthesis (HGS) remains unknown.

PURPOSE

We aim to assess the diagnostic accuracy and therapeutic impact of unimodal and multimodal IONM in the surgical management of HGS.

STUDY DESIGN/SETTING

Retrospective cohort study.

PATIENT SAMPLE

Pediatric patients undergoing posterior spinal fusion (PSF) for treatment of HGS.

OUTCOME MEASURES

Data on patient demographics, spinopelvic and spondylolisthesis parameters, and the presence of pre-and postoperative neurological deficits were collected.

METHODS

Intraoperative MEP, SSEP, and EMG alerts were recorded. Alert criteria were defined as a change in amplitude of more than 50% for MEP and/or SSEP, with or without change in latency, and more than 10 seconds of sustained EMG activity. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy were calculated for each modality and the combination of MEP and SSEP. The 95% confidence intervals (CIs) were calculated using the exact (Clopper-Pearson) method.

RESULTS

Fifty-four pediatric patients with HGS undergoing PSF between 2003 and 2021 in a single tertiary center were included. Seventy-two percent (39/54) of patients were female; the average age of patients was 13.7±2.3 years. The sensitivity of MEP in detecting new postoperative neurologic deficit was 92.3% (95% CI [64.0-99.8]), SSEP 77.8% (95% CI [40.0-97.2]), EMG 69.2% (95% CI [38.6-90.9]), and combination MEP and SSEP 100% (95% CI [73.5-100]). The specificity of MEP was 80.0% (95% CI [64.4-91.0]), SSEP 95.1% (95% CI [83.5-99.4]), EMG 65.9% (95% CI [49.4-79.9]), and combination MEP and SSEP 82.9% (95% CI [67.9-92.9]). The accuracy of SSEP was 92.0% (95% CI [80.8%-97.8%]), and the combination of MEP and SSEP was 86.8% (95% CI [74.7%-94.5%]). Twelve (22.2%) patients had a new motor or sensory deficit diagnosed immediately postoperatively. Nine patients made a full recovery, and 3 had some neurologic deficit on final follow-up.

CONCLUSION

Unimodal IONM using SSEP and MEP alone were accurate in diagnosing sensory and motor nerve root injuries, respectively. The diagnostic accuracy in predicting motor and sensory nerve injuries in pediatric HGS improved further with the use of multimodal IONM (combining MEP and SEP). We recommend the utilization of multimodal IONM in all HGS PSF surgeries.

The role of intraoperative neurophysiological monitoring in intramedullary spinal cord tumor surgery

Intramedullary tumors are a class of central nervous system tumors with an incidence of 2 to 4%. As they are located very deep and frequently cause postoperative neurological complications, surgical resection is difficult. In recent years, many surgeons have performed electrophysiological monitoring to effectively reduce the occurrence of postoperative neurological complications. Modern electrophysiological monitoring technology has advanced considerably, leading to the development of many monitoring methods, such as SSEPs, MEPs, DCM, and EMG, to monitor intramedullary tumors. However, electrophysiological monitoring in tumor resection is still being studied. In this article, we discussed the different monitoring methods and their role in monitoring intramedullary tumors by reviewing previous studies. Intratumorally tumors need to be monitored for a summary of the condition of the patient. Only by using various monitoring methods flexibly and through clear communication between surgeons and neurophysiological experts can good decisions be made during surgery and positive surgical results be achieved.

Intraoperative neurophysiological monitoring in scoliosis surgery: literature review of the last 10 years

INTRODUCTION

Patients with spinal deformities undergoing corrective surgery are at risk for iatrogenic spinal cord injury (SCI) and subsequent neurological deficit. Intraoperative neurophysiological monitoring (IONM) allows early detection of SCI which enables early intervention resulting in a better prognosis. The primary aim of this literature review was to search if there are threshold values of TcMEP and SSEP in the literature that are widely accepted as alert during IONM. The secondary aim was to update knowledge concerning IONM during scoliosis surgery.

METHOD

PubMed/MEDLINE and Cochrane library electronic databases were used to search publication from 2012 to 2022. The following keywords were used: evoked potential, scoliosis, surgery, intraoperative monitoring and neurophysiological. We included all studies dealing with SSEP and TcMEP monitoring during scoliosis surgery. Two authors reviewed all titles and abstracts to identify studies that met the inclusion criteria.

RESULTS

We included 43 papers. Rates of IONM alert and neurological deficit varied from 0.56 to 64% and from 0.15 to 8.3%, respectively. Threshold values varied from a loss of 50 to 90% for TcMEP amplitude, whereas it seems that a loss of 50% in amplitude and/or an increase of 10% of latency is widely accepted for SSEP. Causes of IONM changes most frequently reported were surgical maneuver.

CONCLUSION

Concerning SSEP, a loss of 50% in amplitude and/or an increase of 10% of latency is widely accepted as an alert. For TcMEP, it seems that the use of highest threshold values can avoid unnecessary surgical procedure for the patient without increasing risk of neurological deficit.

Intraoperative neuromonitoring in non-idiopathic pediatric scoliosis operated with minimally fusionless procedure: A series of 290 patients

BACKGROUND

One of the worst complications of surgery for spinal deformity is postoperative neurological deficit. Multimodal intraoperative neuromonitoring (IONM) can be used to detect impending neurological injuries. This study aimed to analyze IONM in non-idiopathic scoliosis using a minimally invasive fusionless surgical technique.

METHODS

This retrospective, single-center study was performed from 2014 to 2018. Patients with non-idiopathic scoliosis who underwent a minimally invasive fusionless procedure and had at least 2 years of follow-up were included. IONM was performed using a neurophysiological monitoring work station with somatosensory evoked potentials (SSEP) and neurogenic mixed evoked potentials (NMEP).

RESULTS

A total of 290 patients were enrolled. The mean age at surgery was 12.9±3 years. The main etiology was central nervous system (CNS) disorders (n=139, 48%). Overall, 35 alerts (11%) in the SSEP and 10 (7%) in the NMEP occurred. There were two neurological deficits with total recovery after 6 months. There were no false negatives in either SSEP or NMEP, although there was one false positive in SSEP and two false positives for NMEP in the group without signal recovery. There was no significant relationship between the incidence of SSEP or NMEP loss and age, body mass index (BMI), number of rods used, upper instrumented vertebrae (p=0.36), lower instrumented vertebrae, or type of surgery. A preoperative greater Cobb angle was associated with a significantly higher risk of NMEP loss (p=0.02). In CNS patients, a higher BMI was associated with a statistically significant risk of NMEP loss (p=0.004). The use of a traction table was associated with a higher risk of signal loss (p=0.0005).

CONCLUSION

A preoperative higher Cobb angle and degree of correction were associated with a significant risk of NMEP loss. In CNS scoliosis, a higher BMI was associated with a significant risk of NMEP loss. The use of a traction table was associated with a higher risk of signal loss.

Mechanism of dexmedetomidine preconditioning on spinal cord analgesia in rats with functional chronic visceral pain

Purpose:

To analyze the effect and mechanism of dexmedetomidine (DEX) analgesia pretreatment on functional chronic visceral pain in rats.

Methods:

Rats were divided into six groups: W1, W2, W3, W4, W5, and W6. The behavioral changes and electrophysiological indexes of rats in each group before and after DEX treatment were detected.

Results:

The levels of abdominal withdrawal reflex (AWR) in W5 and W6 groups were significantly lower than those in group W3, while the levels of thermal withdrawal latency (TWL) and mechanical withdrawal threshold (MWT) were significantly higher than those in group W3 (p < 0.05). The electromyographic signals of W1, W5, and W6 groups showed little fluctuation, while those of groups W2, W3, and W4 showed obvious fluctuation. TLR4 mRNA expression, IRF3, P65, and phosphorylation levels in W4, W5, and W6 groups were significantly lower than those in group W2 (p < 0.05).

Conclusions:

Dexmedetomidine epidural anesthesia pretreatment could significantly inhibit visceral pain response in rats with functional chronic visceral pain, and its mechanism was related to the activation of TLR4 in spinal dorsal horn tissue of rats and the activation inhibition of IRF3 and P65 in the downstream key signals.

Natural language processing for automated surveillance of intraoperative neuromonitoring in spine surgery

We sought to develop natural language processing (NLP) methods for automated detection and characterization of neuromonitoring documentation from free-text operative reports in patients undergoing spine surgery. We included 13,718 patients who received spine surgery at two tertiary academic medical centers between December 2000 - December 2020. We first validated a rule-based NLP method for identifying operative reports containing neuromonitoring documentation, comparing performance to standard administrative codes. We then trained a deep learning model in a subset of 993 patients to characterize neuromonitoring documentation and identify events indicating change in status or difficulty establishing baseline signals. Performance of the deep learning model was compared to gold-standard manual chart review. In our patient population, 3,606 (26.3%) patients had neuromonitoring documentation identified using NLP. Our NLP method identified notes containing neuromonitoring documentation with an F1-score of 1.0, surpassing performance of standard administrative codes which had an F1-score of 0.64. In the subset of 993 patients used for training, validation, and testing a deep learning model, the prevalence of change in status was 6.5% and difficulty establishing neuromonitoring baseline signals was 6.6%. The deep learning model had an F1-score = 0.80 and AUC-ROC = 1.0 for identifying change in status, and an F1-score = 0.80 and AUC-ROC = 0.97 for identifying difficulty establishing baseline signals. Compared to gold standard manual chart review, our methodology has greater efficiency for identifying infrequent yet important types of neuromonitoring documentation. This method may facilitate large-scale quality improvement initiatives that require timely analysis of a large volume of EHRs.

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 CONTEXT

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 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.

PURPOSE

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) versus a regimen balanced with volatile inhalational and intravenous agents.

STUDY DESIGN

Baseline 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 SAMPLE

Age 18 and older. Fellowship support for 65,000 for year 2021.

OUTCOME MEASURES

Percent monitorability and amplitudes of baseline MEPs.

METHODS

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.

RESULTS

At 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%).

CONCLUSIONS

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.

The use of three rods in correcting severe scoliosis

PURPOSE

The three-rod technique, utilising a short apical concavity rod is an option to achieve controlled correction in severe scoliosis. We describe this technique, the complications encountered, and the long-term outcomes.

METHOD

All paediatric patients who had at least 2 years follow-up after undergoing corrective surgery for scoliosis ≥ 100° using 3 parallel rods were included. Radiographs were assessed to evaluate the correction and clinical records examined for any loss of correction, complications, revision procedures or neuromonitoring events.

RESULTS

Twenty-five patients met the inclusion criteria. Four underwent prior anterior fusion to prevent crankshaft phenomenon. The mean angle of the deformity was 112.0° (range 100.3-137.1). Mean maximal kyphosis was 48.8° (range 11.4-78.8°) and mean curve flexibility 4.4% (range 0-37.0%). Intraoperative traction achieved an average of 70.4% (95% CI 56.6-84.1%). Nine patients (39%) showed a reduction in MEPs during definitive surgery. All returned to within 75% of baseline by the end of surgery. All patients had normal postoperative neurology. One patient underwent removal of hardware for late infection. The mean overall Cobb correction was 55.7° (95% CI 50.2-61.2°), equating to 50.2% (95% CI 44.9-55.4%) of the mean initial deformity. Thoracic kyphosis reduced by a mean of 18.2° (95% CI 12.8-23.6°).

CONCLUSION

Our series suggests that three-rod constructs are able to safely and effectively achieve 50% correction of severe scoliosis.

Intraoperative neuromonitoring practice patterns in spinal deformity surgery: a global survey of the Scoliosis Research Society

PURPOSE

Although multimodal IONM has reached a widespread use, several unresolved issues have remained in clinical practice. The aim was to determine differences in approaches to form a basis for taking actions to improve patient safety globally.

METHODS

A survey comprising 19 questions in four sections (demographics, setup, routine practices and reaction to alerts) was distributed to the membership of the SRS.

RESULTS

Of the estimated 1300 members, 205 (~ 15%) completed the survey. Respondent demographics reflected SRS member distribution. Most of the respondents had > 10 years of experience. TcMEP and SSEP were available to > 95%. Less than 5% reported that a MD/PhD with neurophysiology background routinely examines patients preoperatively, while 19% would consult if requested. After an uneventful case, 36% reported that they would decrease sedation and check motor function if the patient was to be transferred to ICU intubated. Reactions to dropped signals that recovered or did not fully recover varied between attempting the same correction to aborting the surgery with no rods and returning another day, with or without implant removal. After a decrease of signals, 85.7% use steroids of varied doses. Of the respondents, 53.7% reported using the consensus-created checklist by Vitale et al. Approximately, 14% reported never using the wake-up test while others use it for various conditions.

CONCLUSION

The responses of 205 experienced SRS members from different regions of the world showed that surgeons had different approaches in their routine IONM practices and in the handling of alerts. This survey indicates the need for additional studies to identify best practices.