Intraoperative neurophysiologic monitoring: are we really that bad?

Intraoperative Monitoring of Scoliosis Surgery in Young Patients

SUMMARY

Intraoperative neurophysiologic monitoring has added substantially to the safety of spinal deformity surgery correction since its introduction over four decades ago. Monitoring routinely includes both somatosensory evoked potentials and motor evoked potentials. Either modality alone will detect almost all instances of spinal cord injury during deformity correction. The combined use of the two modalities provides complementary information, can permit more rapidly identification of problems, and enhances safety though parallel redundancy should one modality fail. Both techniques are well established and continue to be refined. Although there is room for provider preference, proper monitoring requires attention to technical detail, understanding of the underlying physiology, and familiarity with effects of commonly used anesthetic agents.

Optimizing the methodology for saphenous nerve somatosensory evoked potentials for monitoring upper lumbar roots and femoral nerve during lumbar spine surgery: technical note

The demand for intraoperative monitoring (IOM) of lumbar spine surgeries has escalated to accommodate more challenging surgical approaches to prevent perioperative neurologic deficits. Identifying impending injury of individual lumbar roots can be done by assessing free-running EMG and by monitoring the integrity of sensory and motor fibers within the roots by eliciting somatosensory (SEP), and motor evoked potentials. However, the common nerves for eliciting lower limb SEP do not monitor the entire lumbar plexus, excluding fibers from L1 to L4 roots. We aimed to technically optimize the methodology for saphenous nerve SEP (Sap-SEP) proposed for monitoring upper lumbar roots in the operating room. In the first group, the saphenous nerve was consecutively stimulated in two different locations: proximal in the thigh and distal close to the tibia. In the second group, three different recording derivations (10-20 International system) to distal saphenous stimulation were tested. Distal stimulation yielded a higher Sap-SEP amplitude (mean ± SD) than proximal: 1.36 ± 0.9 µV versus 0.62 ± 0.6 µV, (p < 0.0001). Distal stimulation evoked either higher (73%) or similar (12%) Sap-SEP amplitude compared to proximal in most of the nerves. The recording derivation CPz-cCP showed the highest amplitude in 65% of the nerves, followed by CPz-Fz (24%). Distal stimulation for Sap-SEP has advantages over proximal stimulation, including simplicity, lack of movement and higher amplitude responses. The use of two derivations (CPz-cCP, CPz-Fz) optimizes Sap-SEP recording.

Use of motor evoked potentials during lateral lumbar interbody fusion reduces postoperative deficits

BACKGROUND CONTEXT

Intraoperative neurophysiological monitoring (IONM) has gained rather widespread acceptance as a method to mitigate risk to the lumbar plexus during lateral lumbar interbody fusion (LLIF) surgery. The most common approach to IONM involves using only electromyography (EMG) monitoring, and the rate of postoperative deficit remains unacceptably high. Other test modalities, such as transcranial electric motor-evoked potentials (tcMEPs) and somatosensory-evoked potentials, may be more suitable for monitoring neural integrity, but they have not been widely adopted during LLIF. Recent studies have begun to examine their utility in monitoring LLIF surgery with favorable results.

PURPOSE

This study aimed to evaluate the efficacy of different IONM paradigms in the prevention of iatrogenic neurologic sequelae during LLIF and to specifically evaluate the utility of including tcMEPs in an IONM strategy for LLIF surgery.

STUDY DESIGN/SETTING

A non-randomized, retrospective analysis of 479 LLIF procedures at a single institution over a 4-year period was conducted. During the study epoch, three different IONM strategies were used for LLIF procedures: (1) surgeon-directed T-EMG monitoring ("SD-EMG"), (2) neurophysiologist-controlled T-EMG monitoring ("NC-EMG"), and (3) neurophysiologist-controlled T-EMG monitoring supplemented with MEP monitoring ("NC-MEP").

PATIENT SAMPLE

The patient population comprised 254 men (53.5%) and 221 women (46.5%). Patient age ranged from a minimum of 21 years to a maximum of 89 years, with a mean of 56.6 years.

OUTCOME MEASURES

Physician-documented physiological measures included manual muscle test grading of hip-flexion, hip-adduction, or knee-extension, as well as hypo- or hyperesthesia of the groin or anterolateral thigh on the surgical side. Self-reported measures included numbness or tingling in the groin or anterolateral thigh on the surgical side.

METHODS

Patient progress notes were reviewed from the postoperative period up to 12 months after surgery. The rates of postoperative sensory-motor deficit consistent with lumbar plexopathy or peripheral nerve palsy on the surgical side were compared between the three cohorts.

RESULTS

Using the dependent measure of neurologic deficit, whether motor or sensory, patients with NC-MEP monitoring had the lowest rate of immediate postoperative deficit (22.3%) compared with NC-EMG monitoring (37.1%) and SD-EMG monitoring (40.4%). This result extended to sensory deficits consistent with lumbar plexopathy (pure motor deficits being excluded); patients with NC-MEP monitoring had the lowest rate (20.5%) compared with NC-EMG monitoring (34.3%) and SD-EMG monitoring (36.9%). Additionally, evaluation of postoperative motor deficits consistent with peripheral nerve palsy (pure sensory deficits being excluded) revealed that the NC-MEP group had the lowest rate (5.7%) of motor deficit compared with the SD-EMG (17.0%) and NC-EMG (17.1%) cohorts. Finally, when assessing only those patients whose last follow-up was greater than or equal to 12 months (n=251), the rate of unresolved motor deficits was significantly lower in the NC-MEP group (0.9%) compared with NC-EMG (6.9%) and SD-EMG (11.0%). A comparison of the NC-MEP versus NC-EMG and SD-EMG groups, both independently and combined, was statistically significant (>95% confidence level) for all analyses.

CONCLUSIONS

The results of the present study indicate that preservation of tcMEPs from the adductor longus, quadriceps, and tibialis anterior muscles are of paramount importance for limiting iatrogenic sensory and motor injuries during LLIF surgery. In this regard, the inclusion of tcMEPs serves to compliment EMG and allows for the periodic, functional assessment of at-risk nerves during these procedures. Thus, tcMEPs appear to be the most effective modality for the prevention of both transient and permanent neurologic injury during LLIF surgery. We propose that the standard paradigm for protecting the nervous system during LLIF be adapted to include tcMEPs.

Utilization of intraoperative neuromonitoring throughout the United States over a recent decade: an analysis of the nationwide inpatient sample

BACKGROUND

To identify temporal changes to the demographics and utilization of intraoperative neuromonitoring (IONM) throughout the United States (U.S.).

METHODS

The National Inpatient Sample (NIS) database was queried for IONM of central and peripheral nervous electrical activity (ICD-9-CM 00.94) between 2008 and 2014. The NIS database represents a 20% sample of discharges from U.S. Hospitals, weighted to provide national estimates. Demographic and economic data were obtained which included the annual number of surgeries, age, sex, insurance type, location, and frequency of routine discharge.

RESULTS

The estimated use of IONM of central and peripheral nervous electrical activity increased 296%, from 31,762 cases in 2008 to 125,835 cases in 2014. Based on payer type, privately insured patients (45.0%), rather than Medicare (36.8%) or Medicaid patients (9.2%), were more likely to undergo IONM during spinal procedures. When stratifying by median income for patient zip code, there was a substantial difference in the rates of IONM between low (19.9%) and high-income groups (78.1%). IONM was significantly more likely to be utilized at urban teaching hospitals (72.9%) rather than nonteaching hospitals (25.0%) or rural centers (2.2%).

CONCLUSIONS

Over the last decade, there has been a massive increase of 296% in utilization of IONM during spine surgery. This is likely due to its proven benefit in reducing neurologic morbidity in spinal deformity surgery, while introducing minimal additional risk. While IONM may improve patient care, it is still rather isolated to teaching hospitals and patients from higher income zip codes.

The Recognition, Incidence, and Management of Spinal Cord Monitoring Alerts in Early-onset Scoliosis Surgery

BACKGROUND

The objective of the research was to study the relevance of intraoperative neuromonitoring throughout all stages of surgical management in patients with progressive early-onset scoliosis (EOS).The routine monitoring of spinal cord potentials has gradually become standard of practice among spinal surgeons. However, there is not a consensus that the added expense of this technique necessitates monitoring in all stages of surgical management.

METHODS

A retrospective review of 180 surgical cases of 30 patients with EOS from July 2003 to July 2012 was performed. All monitoring alerts as judged by the neuromonitoring team were identified. Both somatosensory-evoked potentials and transcranial electric motor-evoked potentials were studied and no limiting thresholds for reporting electrophysiological changes were deemed appropriate.

RESULTS

Of 150 monitored cases there were 18 (12%) monitoring alerts. This represented 40% of the patient cohort over the 9-year study period.

CONCLUSIONS

Index versus routine lengthening rate of alerts showed no significant difference in incidence of monitoring alerts. Conversely, several patients whose primary implantation surgeries were uneventful had monitoring alerts later in their treatment course. Intraoperative neuromonitoring is warranted throughout all stages of surgical management of EOS.

LEVEL OF EVIDENCE

Level IV. This study is a retrospective review of surgical cases of 30 patients with EOS.

Intraoperative neurophysiologic monitoring in spine surgery. Developments and state of the art in France in 2011

Intraoperative spinal cord monitoring consists in a subcontinuous evaluation of spinal cord sensory-motor functions and allows the reduction the incidence of neurological complications resulting from spinal surgery. A combination of techniques is used: somatosensory evoked potentials (SSEP), motor evoked potentials (MEP), neurogenic motor evoked potentials (NMEP), D waves, and pedicular screw testing. In absence of intraoperative neurophysiological testing, the intraoperative wake-up test is a true form of monitoring even if its latency long and its precision variable. A 2011 survey of 117 French spinal surgeons showed that only 36% had neurophysiological monitoring available (public healthcare facilities, 42%; private facilities, 27%). Monitoring can be performed by a neurophysiologist in the operating room, remotely using a network, or directly by the surgeon. Intraoperative alerts allow real-time diagnosis of impending neurological injury. Use of spinal electrodes, moved along the medullary canal, can determine the lesion level (NMEP, D waves). The response to a monitoring alert should take into account the phase of the surgical intervention and does not systematically lead to interruption of the intervention. Multimodal intraoperative monitoring, in presence of a neurophysiologist, in collaboration with the anesthesiologist, is the most reliable technique available. However, no monitoring technique can predict a delayed-onset paraplegia that appears after the end of surgery. In cases of preexisting neurological deficit, monitoring contributes little. Monitoring of the L1-L4 spinal roots also shows low reliability. Therefore, monitoring has no indication in discal and degenerative surgery of the spinal surgery. However, testing pedicular screws can be useful. All in all, thoracic and thoracolumbar vertebral deviations, with normal preoperative neurological examination are currently the essential indication for spinal cord monitoring. Its absence in this indication is a lost opportunity for the patient. If neurophysiological means are not available, intraoperative wake-up test is a minimal obligation.

Intraoperative neurophysiological monitoring in spine surgery: indications, efficacy, and role of the preoperative checklist

Spine surgery carries an inherent risk of damage to critical neural structures. Intraoperative neurophysiological monitoring (IONM) is frequently used to improve the safety of spine surgery by providing real-time assessment of neural structures at risk. Evidence-based guidelines for safe and efficacious use of IONM are lacking and its use is largely driven by surgeon preference and medicolegal issues. Due to this lack of standardization, the preoperative sign-in serves as a critical opportunity for 3-way discussion between the neurosurgeon, anesthesiologist, and neuromonitoring team regarding the necessity for and goals of IONM in the ensuing case. This analysis contains a review of commonly used IONM modalities including somatosensory evoked potentials, motor evoked potentials, spontaneous or free-running electromyography, triggered electromyography, and combined multimodal IONM. For each modality the methodology, interpretation, and reported sensitivity and specificity for neurological injury are addressed. This is followed by a discussion of important IONM-related issues to include in the preoperative checklist, including anesthetic protocol, warning criteria for possible neurological injury, and consideration of what steps to take in response to a positive alarm. The authors conclude with a cost-effectiveness analysis of IONM, and offer recommendations for IONM use during various forms of spine surgery, including both complex spine and minimally invasive procedures, as well as lower-risk spinal operations.

Intraoperative spinal cord monitoring during the surgical correction of scoliosis due to cerebral palsy and other neuromuscular disorders

PURPOSE

Patients with neuromuscular scoliosis are at increased risk of neurological deficit post-operatively, but are a difficult population on whom to perform neurophysiological monitoring. We look here at a 7-year sample of our practice in the monitoring of neuromuscular patients.

METHODS

A retrospective chart review was performed for 109 patients who underwent correction of neuromuscular scoliosis within our institution between 2005 and 2011.

RESULTS

Of 109 patients who were identified, intraoperative monitoring was attempted in 66 cases. In eight cases (13 %), no reliable monitoring could be achieved and was therefore abandoned. On nine occasions, there was a significant drop in at least one modality intraoperatively. None of these nine suffered any clinically observable neurological deficit post-operatively. Of the 109 patients, 2 had clinically detectable deficits post-operatively, both of whom had undergone normal intraoperative monitoring.

CONCLUSIONS

The two patients with observable deficit had their instrumentation left in situ after discussion with them and/or parents. Spinal cord monitoring in this population is possible but potentially unreliable. Surgeons will need to carefully consider the use of monitoring in their management of this challenging population.

Outcome of Revision Surgery in Pediatric Spine Deformity Patients

STUDY DESIGN

Retrospective case series.

OBJECTIVES

To report the complications and outcomes of pediatric revision spine surgery and review the surgical indications and treatment methods.

BACKGROUND SUMMARY

Recent reports have shown the necessity of revision spine surgery for pediatric deformities. Many reports have shown the result of revision surgery for pediatric spinal deformity.

MATERIALS AND METHODS

We conducted a retrospective review of 638 patients with pediatric spinal deformity who were treated with surgery from 1996 to 2007. We identified 50 patients who underwent revision spinal fusion surgery with a minimum of 3 years of follow-up.

RESULTS

Mean follow-up was 4 years (range, 3-8.3 years). The diagnosis at index surgery was idiopathic scoliosis in 18 patients, congenital scoliosis in 13, neuromuscular scoliosis in 13, tumor and spinal arteriovenous malformation in 4, burst fracture in thoracic spine in 1, and Scheuermann kyphosis in 1. The primary surgeries were 1 hemi epiphysiodesis, 3 anterior spinal fusions, 4 posterior decompressions, 8 combined anterior and posterior spinal fusions, and 34 posterior spinal fusions. A total of 16 patients had pseudarthrosis, 12 decompensation, 11 progressive kyphosis, 8 crankshaft phenomenon, 2 infections, and 1 junctional degeneration. All 50 reoperations included spinal instrumentation and fusion. The revision surgeries were 2 anterior spinal fusions, 14 posterior fusions, and 34 combined anterior and posterior spinal fusions. Spine arthrodesis was obtained in 98% of patients (49 of 50) and complications occurred in 14% of patients (7 of 50). The Scoliosis Research Society Patient Questionnaire outcomes at the latest follow-up were as follows: total 3.95, function 3.88, pain 3.83, self-image 3.98, and mental health 4.04.

CONCLUSION

Pseudarthrosis was the most common indication for revision surgery, and bony union was achieved in 98% with revision surgery. Despite the complications, pediatric revision spine surgery can achieve successful outcomes.