Detection of postoperative neurologic deficits using somatosensory-evoked potentials alone during posterior cervical laminoplasty

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.

Application of electrophysiological measures in degenerative cervical myelopathy

Degenerative cervical myelopathy (DCM) is one of the leading causes of progressive spinal cord dysfunction in the elderly. Early diagnosis and treatment of DCM are essential to avoid permanent disability. The pathophysiology of DCM includes chronic ischemia, destruction of the blood–spinal cord barrier, demyelination, and neuronal apoptosis. Electrophysiological studies including electromyography (EMG), nerve conduction study (NCS), motor evoked potentials (MEPs) and somatosensory evoked potentials (SEPs) are useful in detecting the presymptomatic pathological changes of the spinal cord, and thus supplementing the early clinical and radiographic examinations in the management of DCM. Preoperatively, they are helpful in detecting DCM and ruling out other diseases, assessing the spinal cord compression level and severity, predicting short- and long-term prognosis, and thus deciding the treatment methods. Intra- and postoperatively, they are also useful in monitoring neurological function change during surgeries and disease progression during follow-up rehabilitation. Here, we reviewed articles from 1979 to 2021, and tried to provide a comprehensive, evidence-based review of electrophysiological examinations in DCM. With this review, we aim to equip spinal surgeons with the basic knowledge to diagnosis and treat DCM using ancillary electrophysiological tests.

Intraoperative Neuromonitoring Use Patterns in Degenerative, Nondeformity Cervical Spine Surgery: A Survey of the Cervical Spine Research Society

STUDY DESIGN

A cross-sectional survey study.

OBJECTIVE

To determine the neuromonitoring (NM) usage patterns among cervical spine surgeons when performing degenerative, nondeformity cervical spine surgery.

SUMMARY OF BACKGROUND DATA

Intraoperative NM is frequently used in spine surgery. Although there is literature to support the use of NM in deformity surgery, its utility in degenerative cervical spine surgery remains unclear.

MATERIALS AND METHODS

A survey was distributed to members of the Cervical Spine Research Society to assess practice patterns of NM use during degenerative cervical spine surgery. The survey consisted of 17 multiple choice questions. The first 3 questions focus on practice experience. The remaining 14 questions pertain to NM practice patterns in the setting of radiculopathy and myelopathy.

RESULTS

Significantly more surgeons routinely (>75% of the time) used NM for myelopathy versus radiculopathy (64% vs. 38%, P<0.001). Private practitioners were overall more likely to use NM than academicians (55% vs. 28%, P=0.007 for radiculopathy; 75% vs. 57%, P=0.09 for myelopathy). No significant difference in NM usage was found comparing neurosurgeons and orthopedic spine surgeons. The most commonly cited primary reasons for NM usage were prevention of positioning/hypotension-related neurological complications, and medicolegal protection.

CONCLUSIONS

Routine NM use during degenerative cervical surgery is significantly more common in myelopathy and is thought to be of more value than in radiculopathy. However, the most common reasons for usage were to provide medicolegal cover and to mitigate neurological complications related to positioning/hypotension, rather than to protect against direct surgical events. These findings contrast the prevailing notion that NM is beneficial in reducing complications related to events occurring in the surgical site when performing spinal deformity correction. We believe that these data provide an important baseline for informing best practice guidelines and further study regarding appropriate NM use for degenerative, nondeformity, cervical spine surgery.

What is the predictive value of intraoperative somatosensory evoked potential monitoring for postoperative neurological deficit in cervical spine surgery?-a meta-analysis

BACKGROUND CONTEXT

Cervical decompression and fusion surgery remains a mainstay of treatment for a variety of cervical pathologies. Potential intraoperative injury to the spinal cord and nerve roots poses nontrivial risk for consequent postoperative neurologic deficits. Although neuromonitoring with intraoperative somatosensory evoked potentials (SSEPs) is often used in cervical spine surgery, its therapeutic value remains controversial.

PURPOSE

The purpose of the present study was to evaluate whether significant SSEP changes can predict postoperative neurologic complications in cervical spine surgery. A subgroup analysis was performed to compare the predictive power of SSEP changes in both anterior and posterior approaches.

STUDY DESIGN

The present study was a meta-analysis of the literature from PubMed, Web of Science, and Embase to identify prospective/retrospective studies with outcomes of patients who underwent cervical spine surgeries with intraoperative SSEP monitoring.

PATIENT SAMPLE

The total cohort consisted of 7,747 patients who underwent cervical spine surgery with intraoperative SSEP monitoring.

METHODS

Inclusion criteria for study selection were as follows: (1) prospective or retrospective cohort studies, (2) studies conducted in patients undergoing elective cervical spine surgery not due to aneurysm, tumor, or trauma with intraoperative SSEP monitoring, (3) studies that reported postoperative neurologic outcomes, (4) studies conducted with a sample size ≥20 patients, (5) studies with only adult patients ≥18 years of age, (6) studies published in English, (7) studies inclusive of an abstract.

OUTCOME MEASURES

The sensitivity, specificity, diagnostic odds ratio (DOR), and likelihood ratios of overall SSEP changes, reversible SSEP changes, irreversible SSEP changes, and SSEP loss for predicting postoperative neurological deficit were calculated.

RESULTS

The total rate of postoperative neurological deficits was 2.50% (194/7,747) and the total rate of SSEP changes was 7.36% (570/7,747). The incidence of postoperative neurological deficit in patients with intraoperative SSEP changes was 16.49% (94/570) while only 1.39% (100/7,177) in patients without. All significant intraoperative SSEP changes had a sensitivity of 46.0% and specificity of 96.7% with a DOR of 27.32. Reversible and irreversible SSEP changes had sensitivities of 17.7% and 37.1% and specificities of 97.5% and 99.5%, respectively. The DORs for reversible and irreversible SSEP changes were 9.01 and 167.90, respectively. SSEP loss had a DOR of 51.39, sensitivity of 17.3% and specificity 99.6%. In anterior procedures, SSEP changes had a DOR of 9.60, sensitivity of 34.2%, and specificity of 94.7%. In posterior procedures, SSEP changes had a DOR of 13.27, sensitivity of 42.6%, and specificity of 94.0%.

CONCLUSIONS

SSEP monitoring is highly specific but weakly sensitive for postoperative neurological deficit following cervical spine surgery. The analysis found that patients with new postoperative neurological deficits were nearly 27 times more likely to have had significant intraoperative SSEP change. Loss of SSEP signals and irreversible SSEP changes seem to indicate a much higher risk of injury than reversible SSEP changes.

Indication and technical implementation of the intraoperative neurophysiological monitoring during spine surgeries-a transnational survey in the German-speaking countries

BACKGROUND

Intraoperative neurophysiological monitoring is widely used in spine surgery (sIONM). But guidelines are lacking and its use is mainly driven by individual surgeons' preferences and medicolegal advisements. To gain an overview over the current status of sIONM implementation, we conducted a transnational survey in the German-speaking countries.

METHODS

We developed a Web interface-based survey assessing prevalence, indication, technical implementation, and general satisfaction regarding sIONM in German, Austrian, and Swiss spine centers. The electronic survey was performed between November 2017 and April 2018, including both neurosurgical and orthopedic spine centers.

RESULTS

A total of 463 German, 60 Austrian, and 52 Swiss spine centers were contacted with participation rates of 64.1% (Germany), 68.3% (Austria), and 55.8% (Switzerland). Some 75.9% participating neurosurgical spine centers and only 14.7% of the orthopedic spine centers applied sIONM. Motor- and somatosensory-evoked potentials (93.7% and 94.3%, respectively) were the most widely available modalities, followed by direct wave (D wave; 66.5%). Whereas sIONM utilization was low in spine surgeries for degenerative, traumatic, and extradural tumor diseases, it was high for scoliosis and intradural tumor surgeries. Overall, the general satisfaction within the institutional setting regarding technical skills, staff, performance, and reliability of sIONM was rated as "high" by more than three-quarters of the centers. However, shortage of skilled staff was claimed to be a negative factor by 41.1% of the centers and reimbursement was considered to be insufficient by 83.5%.

CONCLUSIONS

sIONM availability was high in neurosurgical but low in orthopedic spine centers. Main modalities were motor/somatosensory-evoked potentials and main indications were scoliosis and intradural spinal tumor surgeries. A more frequent sIONM use, however, was mainly limited by the shortage of skilled staff and restricted reimbursement.

Should evoked potential monitoring be used in degenerative cervical spine surgery? A systematic review

Background

Intraoperative somatosensory evoked potential (SSEP) and transcranial motor evoked potential (tcMEP) monitoring are frequently used in spinal as well as spinal cord surgery for so-called intraoperative neuromonitoring (IONM), while the combination of these techniques is known as concomitant multimodal intraoperative monitoring (MIOM). The aim of this review is to collect available evidence concerning use of IONM and MIOM in cervical decompression surgery in the degenerative setting and attempt to identify the best practice to be advocated.

Materials and methods

A review of the PubMed and MEDLINE databases and Cochrane Central Registry of Controlled Trials was performed. Studies were included if they involved patients who underwent cervical spine decompression surgery for degenerative stenosis with use of IONM or MIOM and where sensitivity/specificity was reported.

Results

In the identified studies, the sensitivity of SSEP was estimated to be between 22 and 100% with constant specificity of 100%. In the included studies, the sensitivity of MEP was estimated to be between 78 and 100% with specificity ranging from 83.2 to 100%.

Conclusions

On the basis of available evidence, MIOM could be a helpful tool in decompression cervical spine surgery in patients affected by degenerative spinal stenosis, since it is associated with high specificity and sensitivity for detection of intraoperative neural damage. However, evidence is still lacking regarding patient selection to identify individuals in whom monitoring is indicated.

Level of evidence

IV (systematic review of studies with LOE II to IV).

Somatosensory Evoked Potentials as a Stand-Alone Tool During Spine Surgery: An Egyptian Preliminary Report

PURPOSE

Monitoring of somatosensory evoked potentials (SSEPs) serves as an early warning system to detect spinal cord injury and is correlated with postoperative sensory findings. It is an indirect indicator of motor function. This study aimed to evaluate the usefulness of intraoperative SSEPs monitoring as a stand-alone tool during spinal surgeries when motor evoked potentials are not available, to prevent and predict new postoperative neurologic deficits. Motor evoked potentials were not used as the equipment needed to record them was not available at the time of this study.

METHODS

This study included 50 patients, aged 14 to 67 years, undergoing extramedullary manipulations, decompression of an epidural abscess or neoplasm, removal of intramedullary tumor, or arteriovenous malformation or spine correction procedures. Somatosensory evoked potentials were analyzed for latency and peak-to-peak amplitude. Critical SSEP changes were defined as a 50% decrease in amplitude or a 10% increase in latency.

RESULTS

Somatosensory evoked potentials had an overall sensitivity of 81.8%, a specificity of 100%, a positive predictive value of 100%, and a negative predictive value of 91.3%.

CONCLUSIONS

Intraoperative SSEPs have proved to be highly sensitive and specific for iatrogenic injury, mechanical stress caused by cord traction/compression, dural traction, lowered systemic blood pressure, and cord hypothermia. The reversibility of intraoperative SSEP changes showed a highly significant relation to the number of cases with new postoperative deficits as well as type and site of pathologic study (P = 0.00, P = 0.01, and P = 0.00, respectively) but not with the level of pathologic study (P = 0.49).

Diagnostic Accuracy of Somatosensory Evoked Potentials in Evaluating New Neurological Deficits After Posterior Cervical Fusions

STUDY DESIGN

This study examined the diagnostic accuracy of significant changes of somatosensory evoked potentials (SSEPs) to evaluate and predict postoperative neurological deficits after posterior cervical fusions (PCF). Eight hundred forty six eligible patients underwent PCF at the University of Pittsburgh Medical Center (UPMC), from 2010 to 2012.

OBJECTIVE

To assess the specificity and sensitivity of intraoperative monitoring in predicting postoperative neurological deficits during PCF.

SUMMARY OF BACKGROUND DATA

We calculated the predictive value, including sensitivity and specificity, of changes in SSEPs to identify neurological deficits postoperatively. We used a receiver operating characteristic (ROC) curve with SSEP categories as cutoff values to further evaluate the diagnostic accuracy of change in SSEPs and postoperative neurological deficit.

METHODS

All patients had preposition baselines and continuous SSEP monitoring throughout the surgery. Statistical analysis was completed using SPSS version 22 (IBM Corp., Armonk, NY).

RESULTS

Age and sex did not influence outcomes. Obesity affected patient outcome. The SSEP categories of significant changes and loss of responses resulted in a sensitivity/specificity of 0.30/0.96 and 0.16/0.98, respectively. The receiver operating characteristic curve has an area under the curve for significant change in/loss of SSEPs of 0.62/0.65 with a 95% confidence interval of 0.525 to 0.714/0.509 to 0.797.

CONCLUSION

Significant SSEP changes during PCF are a very specific but poorly sensitive indicator of postoperative neurological deficits. The odds ratio for significant changes in SSEPs and loss of waveforms was 9.80 and 11.82, respectively, with a 95% confidence interval of 4.695 to 20.46 and 4.45 to 31.41, respectively.

LEVEL OF EVIDENCE

1.

The cutoff value of ossification of posterior longitudinal ligament (OPLL) for early diagnosis of myelopathy using somatosensory evoked potential in cervical OPLL patients

STUDY DESIGN

Retrospective study.

OBJECTIVES

The objective of this study was to find out whether ossification of posterior longitudinal ligament (OPLL) characteristics, including size, shape and subtype, can be used to diagnose myelopathy using somatosensory evoked potential (SEP) in cervical OPLL patients.

SETTING

Yonsei University College of Medicine, Seoul, Korea.

METHODS

We retrospectively reviewed the medical records of 153 cervical OPLL patients who underwent SEP study. OPLL anterior-posterior (AP) diameter, area and involved longitudinal vertebral level were measured. OPLL was classified into subtypes according to longitudinal continuity and shape. Correlation analysis and receiver operating curve were used.

RESULTS

Tibial SEP latency was significantly correlated with OPLL AP diameter (P=0.001), diameter occupying ratio (P=0.019), area (P=0.007), area occupying ratio (P=0.008), involved longitudinal vertebral level (P=0.028) and space available for the spinal cord (P=0.019). The cutoff values that were diagnostic for SEP prolongation suggesting myelopathy were 4.91 mm for OPLL AP diameter, 6.02 mm for space available for the spinal cord, 44.5% for diameter occupying ratio, 63.4 mm² for area, 36.1% for area occupying ratio and level 2 for the involved longitudinal vertebral level.

CONCLUSIONS

Our results revealed that tibial SEP latency was significantly correlated with OPLL size and suggested cutoff values of OPLL diameter (4.91 mm, 44.5%) and area (63.4 mm², 36.1%) for early diagnosis of myelopathy. These results can help to establish treatment plans.

Monitoring of Motor and Somatosensory Evoked Potentials During Spine Surgery: Intraoperative Changes and Postoperative Outcomes

OBJECTIVE

To evaluate whether the combination of muscle motor evoked potentials (mMEPs) and somatosensory evoked potentials (SEPs) measured during spinal surgery can predict immediate and permanent postoperative motor deficits.

METHODS

mMEP and SEP was monitored in patients undergoing spinal surgery between November 2012 and July 2014. mMEPs were elicited by a train of transcranial electrical stimulation over the motor cortex and recorded from the upper/lower limbs. SEPs were recorded by stimulating the tibial and median nerves.

RESULTS

Combined mMEP/SEP recording was successfully achieved in 190 operations. In 117 of these, mMEPs and SEPs were stable and 73 showed significant changes. In 20 cases, motor deficits in the first 48 postoperative hours were observed and 6 patients manifested permanent neurological deficits. The two potentials were monitored in a number of spinal surgeries. For surgery on spinal deformities, the sensitivity and specificity of combined mMEP/SEP monitoring were 100% and 92.4%, respectively. In the case of spinal cord tumor surgeries, sensitivity was only 50% but SEP changes were observed preceding permanent motor deficits in some cases.

CONCLUSION

Intraoperative monitoring is a useful tool in spinal surgery. For spinal deformity surgery, combined mMEP/SEP monitoring showed high sensitivity and specificity; in spinal tumor surgery, only SEP changes predicted permanent motor deficits. Therefore, mMEP, SEP, and joint monitoring may all be appropriate and beneficial for the intraoperative monitoring of spinal surgery.

Exploration of the Intraoperative Motor Evoked Potential

STUDY DESIGN

Prospective study.

OBJECTIVE

The objectives of the study was to (1) seek a relation between motor evoked potential (MEP) and corresponding cervical cord function in cervical compression myelopathy (CCM) and (2) explore a high-sensitive MEP range that can predict the intraoperative monitoring change ahead in cervical spine surgery.

SUMMARY OF BACKGROUND DATA

There have been lots of controversies concerning the application of transcranial MEP in cervical spine surgery.

METHODS

We prospectively investigate 86 consecutive patients with CCM who underwent posterior laminoplasty or laminectomy from December 2012 to September 2014. The 18-point modified Japanese Orthopedic Association (mJOA) score and intraoperative MEP were used for neurological and electrophysiological assessment. Statistical correlation analysis and curve fitting were used to definite the relationship between MEP and corresponding cervical cord function. And a novel concept of high-sensitive MEP range was firstly addressed for predicting the intraoperative monitoring change ahead in CCM.

RESULTS

Our results showed that the preoperative mJOA score of lower extremity presented a significant correlation with MEP parameters in CCM, and the correlation was expressed in an exponential relationship. The monitoring change in CCM often appeared at a high-sensitive MEP range (amplitude <159 μV or latency >36.1 ms). In addition, the high-sensitive MEP ranges not only included MEP degeneration but also a larger number of MEP improvement cases.

CONCLUSION

Intraoperative MEP may imply an exponential correlation with the corresponding cervical cord function in CCM. And we first characterize a high-sensitive MEP range which may indicate high risk for the impending monitoring change during cervical cord decompression and we must watch more closely.

Electrophysiological functional recovery in a rat model of spinal cord hemisection injury following bone marrow-derived mesenchymal stem cell transplantation under hypothermia

Following successful establishment of a rat model of spinal cord hemisection injury by resecting right spinal cord tissues, bone marrow stem cells were transplanted into the spinal cord lesions via the caudal vein while maintaining rectal temperature at 34 ± 0.5°C for 6 hours (mild hypothermia). Hematoxylin-eosin staining showed that astrocytes gathered around the injury site and formed scars at 4 weeks post-transplantation. Compared with rats transplanted with bone marrow stem cells under normal temperature, rats transplanted with bone marrow stem cells under hypothermia showed increased numbers of proliferating cells (bromodeoxyuridine-positive cells), better recovery of somatosensory-evoked and motor-evoked potentials, greater Basso, Beattie, and Bresnahan locomotor rating scores, and an increased degree of angle in the incline plate test. These findings suggested that hypothermia combined with bone marrow mesenchymal stem cells transplantation effectively promoted electrical conduction and nerve functional repair in a rat model of spinal cord hemisection injury.

Increased spinal cord movements in cervical spondylotic myelopathy

BACKGROUND CONTEXT

Magnetic resonance imaging (MRI) is a very useful diagnostic test for cervical spondylotic myelopathy (CSM) because it can identify degenerative changes within the spinal cord (SC), disclose the extent, localization, and the kind of SC compression, and help rule out other SC disorders. However, the relationships between changes in cerebrospinal fluid (CSF) flow, cord motion, the extent and severity of spinal canal stenosis, and the development of CSM symptoms are not well understood.

PURPOSE

To evaluate if changes in the velocity of CSF and SC movements provide additional insight into the pathophysiological mechanisms underlying CSM beyond MRI observations of cord compression.

STUDY DESIGN

Prospective radiologic study of recruited patients.

PATIENT SAMPLE

Thirteen CSM subjects and 15 age and gender matched controls.

OUTCOME MEASURES

Magnetic resonance imaging measures included CSF and SC movement. Cervical cord condition was assessed by the Japanese Orthopaedic Association (JOA) score, compression ratio (CR), and somatosensory evoked potentials (SSEPs) of the tibial and ulnar nerves.

METHODS

Phase-contrast imaging at the level of stenosis for patients and at C5 for controls and T2-weighted images were compared with clinical findings.

RESULTS

Cerebrospinal fluid velocity was significantly reduced in CSM subjects as compared with controls and was related to cord CR. Changes in CSF velocity and cord compression were not correlated with clinical measures (JOA scores, SSEP) or the presence of T2 hyperintensities. Spinal cord movements, that is, cord displacement and velocity in the craniocaudal axis, were increased in CSM patients. Increased SC movements (ie, total cord displacement) both in the controls and CSM subjects were associated with altered spinal conduction as assessed by SSEP.

CONCLUSIONS

This study revealed rather unexpected increased cord movements in the craniocaudal axis in CSM patients that may contribute to myelopathic deteriorations in combination with spinal canal compression. Understanding the relevance of cord movements with respect to supporting the clinical CSM diagnosis or disease monitoring requires further long-term follow-up studies.

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.

Electrophysiological evaluation of sensory and motor pathways after incomplete unilateral spinal cord contusion

OBJECT

Unilateral contusions represent an increasingly popular model for studying the pathways and recovery mechanisms of spinal cord injury (SCI). Current studies rely heavily on motor behavior scoring and histological evidence to make assessments. Electrophysiology represents one way to reliably quantify the functionality of motor pathways. The authors sought to quantify the functional integrity of the bilateral motor and sensory pathways following unilateral SCI by using measurements of motor and somatosensory evoked potentials (MEPs and SSEPs, respectively).

METHODS

Eighteen rats were randomly divided into 3 groups receiving a mild unilateral contusion, a mild midline contusion, or a laminectomy only (control). Contusions were induced at T-8 using a MASCIS impactor. Electrophysiological analysis, motor behavior scoring, and histological quantifications were then performed to identify relationships among pathway conductivity, motor function, and tissue preservation.

RESULTS

Hindlimb MEPs ipsilateral to the injury showed recovery by Day 28 after injury and corresponded to approximately 61% of spared corticospinal tract (CST) tissue. In contrast, MEPs of the midline-injured group did not recover, and correspondingly > 90% of the CST tissue was damaged. Somatosensory evoked potentials showed only a moderate reduction in amplitude, with no difference in latency for the pathways ipsilateral to injury. Furthermore, these SSEPs were significantly better than those of the midline-injured rats for the same amount of white matter damage.

CONCLUSIONS

Motor evoked potential recovery corresponded to the amount of spared CST in unilateral and midline injuries, but motor behavior consistently recovered independent of MEPs. These data support the idea that spared contralateral pathways aid in reducing the functional deficits of injured ipsilateral pathways and further support the idea of CNS plasticity.