Intraoperative Neurophysiologic Monitoring for Degenerative Cervical Myelopathy

Integration of MRI and somatosensory evoked potentials facilitate diagnosis of spinal cord compression

This study aimed to integrate magnetic resonance imaging (MRI) and related somatosensory evoked potential (SSEP) features to assist in the diagnosis of spinal cord compression (SCC). MRI scans were graded from 0 to 3 according to the changes in the subarachnoid space and scan signals to confirm differences in SCC levels. The amplitude, latency, and time-frequency analysis (TFA) power of preoperative SSEP features were extracted and the changes were used as standard judgments to detect neurological function changes. Then the patient distribution was quantified according to the SSEP feature changes under the same and different MRI compression grades. Significant differences were found in the amplitude and TFA power between MRI grades. We estimated three degrees of amplitude anomalies and power loss under each MRI grade and found the presence or absence of power loss occurs after abnormal changes in amplitude only. For SCC, few integrated approach combines the advantages of both MRI and evoked potentials. However, integrating the amplitude and TFA power changes of SSEP features with MRI grading can help in the diagnosis and speculate progression of SCC.

Efficacy of Intraoperative Neuromonitoring during the Treatment of Cervical Myelopathy

Objective The accuracy of intraoperative neuromonitoring (IONM) during surgery for cervical spondylotic myelopathy (CSM) to detect iatrogenic nervous system injuries while they are reversible remains unknown. We evaluated a cohort of patients who had IONM during surgery to assess accuracy.

Methods Patients who underwent surgical treatment of CSM that included IONM from January 2018 through August 2018 were retrospectively identified. A standardized protocol was used for operative management. Clinical changes and postoperative neurological deficits were evaluated.

Results Among 131 patients in whom IONM was used during their procedure, 42 patients (age 58.2 ± 16.3 years, 54.8% males) showed IONM changes and 89 patients had no change. The reasons for IONM changes varied, and some patients had changes detected via multiple modalities: electromyography (n = 25, 59.5%), somatosensory-evoked potentials (n = 14, 33.3%), motor evoked potentials (n = 13, 31.0%). Three patients, all having baseline deficits before surgery, had postoperative deficits. Among the 89 patients without an IONM change, 4 showed worsened postoperative deficits, which were also seen at last follow-up. The sensitivity of IONM for predicting postoperative neurological change was 42.86% and the specificity was 68.55%. However, most patients (124, 94.7%) in whom IONM was used showed no worsened neurological deficit.

Conclusions IONM shows potential in ensuring stable postoperative neurological outcomes in most patients; however, its clinical use and supportive guidelines remain controversial. In our series, prediction of neurological deficits was poor in contrast to some previous studies. Further refinement of clinical and electrophysiological variables is needed to uniformly predict postoperative neurological outcomes.

Need for head and neck repositioning to restore electrophysiological signal changes at positioning for cervical myelopathy surgery

OBJECTIVE

To evaluate the incidence of significant intraoperative electrophysiological signal changes during surgical positioning, and to assess the effectiveness of head and neck repositioning on the restoration of signals, among patients undergoing surgery for cervical myelopathy.

MATERIAL AND METHODS

We used multimodal intraoperative monitoring (somatosensory [SEP] and motor evoked potentials [MEP] and spontaneous electromyography) before and after patients' positioning in a consecutive cohort of 103 patients operated for symptomatic cervical myelopathy. Significant changes were defined as>50% attenuation in amplitude or>10% increase in latency of SEP, or abolishment or 50-80% attenuation of MEP.

RESULTS

Out of 103 patients (34.9% female, median age 54.5 years) 88 underwent laminectomy (85.4%) and 15 (14.6%) anterior approach. At the time of positioning, signal alterations occurred in 44 patients (42.7%), yet only 11 patients (10.7%) showed alarming changes. Immediate neck repositioning of these resulted in complete (n=6) or partial (n=4) restoration of potentials, yielding no postoperative deficits. The patient in which signals could not be restored after repositioning resulted in added postoperative deficit. The accuracy (true positives plus true negatives) of monitoring to detect new neurological deficits was 99.0% (102/103) for the entire cohort, and 100% (11/11) for those showing significant changes at the moment of positioning. Overall, only 1 patient, with non-significant SEP attenuation, experienced a new postoperative deficit, yielding a 0.97% rate of false negatives.

CONCLUSION

Among patients undergoing surgery for cervical myelopathy, 10.7% showed alarming electrophysiological signal changes at the time of positioning. Immediate repositioning of the neck resulted in near always restoration of potentials and avoidance of added neurological damage. Complete or partial restoration of potentials after repositioning yielded no postoperative deficits.

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.

Optimizing the Application of Surgery for Degenerative Cervical Myelopathy [AO Spine RECODE-DCM Research Priority Number 10]

STUDY DESIGN

Literature Review (Narrative).

OBJECTIVE

To introduce the number 10 research priority for Degenerative Cervical Myelopathy: Individualizing Surgery.

METHODS

This article summarizes the current recommendations and indications for surgery, including how known prognostic factors such as injury time, age, disease severity, and associated comorbidities impact surgical outcome. It also considers key areas of uncertainty that should be the focus of future research.

RESULTS

While a small proportion of conservatively managed patients may remain stable, the majority will deteriorate over time. To date, surgical decompression is the mainstay of treatment, able to halt disease progression and improve neurologic function and quality of life for most patients. Whilst this recognition has led to recommendations on when to offer surgery, there remain many uncertainties including the type of surgery, or timing in milder and/or asymptomatic cases. Their clarification has the potential to transform outcomes, by ensuring surgery offers each individual its maximum benefit.

CONCLUSION

Developing the evidence to better guide surgical decision-making at the individual patient level is a research priority for Degenerative Cervical Myelopathy.

Degenerative cervical myelopathy: Neuroradiological, neurophysiological and clinical correlations in 27 consecutive cases

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New insight into prognostic factors for recovery of clinical function following posterior decompression for degenerative cervical myelopathy.

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An increase of IOM amplitude of at least 50% coupled with preoperative T2-only and diffuse T2 signal changes on MRI is a positive prognostic factors for clinical improvement 6 months after surgery.

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Clinical improvement at 6 months follow-up can be expected in patients with T1 hypo intensity if a diffuse border of the lesion on T2 images is present.

Motor Bur Milling State Identification via Fast Fourier Transform Analyzing Sound Signal in Cervical Spine Posterior Decompression Surgery

Objectives

To investigate the real‐time sensitive feedback parameter of the motor bur milling state in cervical spine posterior decompression surgery, to possibly improve the safety of cervical spine posterior decompression and robot‐assisted spinal surgeries.

Methods

In this study, the cervical spine of three healthy male and three healthy female pigs were randomly selected. Six porcine cervical spine specimens were fixed to the vibration isolation system. The milling state of the motor bur was defined as the lamina cancellous bone (CA), lamina ventral corticalbone (VCO), and penetrating ventral cortical bone (PVCO). A 5‐mm bur milled the CA and VCO, and a 2‐mm bur milled the VCO and PVCO. A miniature microphone was used to collect the sound signal (SS) of milling lamina which was then extracted using Fast Fourier Transform (FFT). When using 5‐mm and 2‐mm bur to mill, the CA, VCO, and PVCO of each specimen were continuously collected at 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 kHz frequencies for SS magnitudes. The study randomly selected the SS magnitudes of the CA and VCO continuously for 2 s at 1, 2, 3, 4, and 5 kHz frequencies for statistical analyses. When milling the VCO to the PVCO, we randomly collected the SS magnitudes of the VCO for consecutive 2 s and the SS magnitudes of continuous 2 s in the penetrating state at 1, 2, 3, 4, and 5 kHz frequencies for statistical analyses. The independent sample t‐test was used to compare the SS magnitudes of different milling states extracted from the FFT to determine the motor bur milling state.

Results

The SS magnitudes of the CA and VCO of all specimens extracted from the FFT at 1, 2, and 3 kHz were statistically different (P < 0.01); three specimens were not statistically different at a specific FFT‐extracted frequency (first specimen at 5 kHz, SS magnitudes of the CA were [25.94 ± 8.74] × 10⁻³, SS magnitudes of the VCO were [28.67 ± 12.94] × 10⁻³, P = 0.440; second specimen at 4 kHz, SS magnitudes of the CA were [23.79 ± 7.94] × 10⁻³, SS magnitudes of the VCO were [24.78 ± 4.32] × 10⁻³, P = 0.629; and third specimen at 5 kHz, SS magnitudes of the CA were [16.76 ± 6.20] × 10⁻³, SS magnitudes of the VCO were [17.69 ± 6.44] × 10⁻³, P = 0.643).The SS magnitudes of the VCO and PVCO of all the specimens extracted from the FFT at each frequency were statistically different (P < 0.001).

Conclusions

Based on the FFT extraction, the SS magnitudes of the motor bur milling state between the CA and VCO, the VCO and PVCO were significantly different, confirming that the SS is a potential sensitive feedback parameter for identifying the motor bur milling state. This study could improve the safety of cervical spine posterior decompression surgery, especially of robot‐assisted surgeries.

Need for head and neck repositioning to restore electrophysiological signal changes at positioning for cervical myelopathy surgery

OBJECTIVE

To evaluate the incidence of significant intraoperative electrophysiological signal changes during surgical positioning, and to assess the effectiveness of head and neck repositioning on the restoration of signals, among patients undergoing surgery for cervical myelopathy.

MATERIAL AND METHODS

We used multimodal intraoperative monitoring (somatosensory [SEP] and motor evoked potentials [MEP] and spontaneous electromyography) before and after patients' positioning in a consecutive cohort of 103 patients operated for symptomatic cervical myelopathy. Significant changes were defined as>50% attenuation in amplitude or>10% increase in latency of SEP, or abolishment or 50-80% attenuation of MEP.

RESULTS

Out of 103 patients (34.9% female, median age 54.5 years) 88 underwent laminectomy (85.4%) and 15 (14.6%) anterior approach. At the time of positioning, signal alterations occurred in 44 patients (42.7%), yet only 11 patients (10.7%) showed alarming changes. Immediate neck repositioning of these resulted in complete (n=6) or partial (n=4) restoration of potentials, yielding no postoperative deficits. The patient in which signals could not be restored after repositioning resulted in added postoperative deficit. The accuracy (true positives plus true negatives) of monitoring to detect new neurological deficits was 99.0% (102/103) for the entire cohort, and 100% (11/11) for those showing significant changes at the moment of positioning. Overall, only 1 patient, with non-significant SEP attenuation, experienced a new postoperative deficit, yielding a 0.97% rate of false negatives.

CONCLUSION

Among patients undergoing surgery for cervical myelopathy, 10.7% showed alarming electrophysiological signal changes at the time of positioning. Immediate repositioning of the neck resulted in near always restoration of potentials and avoidance of added neurological damage. Complete or partial restoration of potentials after repositioning yielded no postoperative deficits.

Study protocol for an observational study of cerebrospinal fluid pressure in patients with degenerative cervical myelopathy undergoing surgical deCOMPression of the spinal CORD: the COMP-CORD study

INTRODUCTION

Degenerative cervical myelopathy (DCM) is a disabling spinal disorder characterised by sensorimotor deficits of upper and lower limbs, neurogenic bladder dysfunction and neuropathic pain. When suspected, cervical MRI helps to reveal spinal cord compression and rules out alternative diagnoses. However, the correlation between radiological findings and symptoms is weak. Cerebrospinal fluid pressure (CSFP) analysis may complement the appreciation of cord compression and be used for intraoperative and postoperative monitorings in patients undergoing surgical decompression.

METHODS AND ANALYSIS

Twenty patients diagnosed with DCM undergoing surgical decompression will receive standardised lumbar CSFP monitoring immediately before, during and 24 hours after operation. Rest (ie, opening pressure, CSF pulsation) and stimulated (ie, Valsalva, Queckenstedt's) CSFP-findings in DCM will be compared with 20 controls and results from CSFP monitoring will be related to clinical and neurophysiological findings. Arterial blood pressure will be recorded perioperatively and postoperatively to calculate spinal cord perfusion pressure and spinal vascular reactivity index. Furthermore, measures of CSFP will be compared with markers of spinal cord compression by means of MR imaging.

ETHICS AND DISSEMINATION

The study protocol conformed to the latest revision of the Declaration of Helsinki and was approved by the local Ethics Committee of the University Hospital of Zurich (KEK-ZH number PB-2016-00623). The main publications from this study will cover the CSFP fluid dynamics and pressure analysis preoperative, perioperative and postoperative correlated with imaging, clinical scores and neurophysiology. Other publications will deal with preoperative and postoperative spinal perfusion. Furthermore, we will disseminate an analysis on waveform morphology and the correlation with blood pressure and ECG. Parts of the data will be used for computational modelling of cervical stenosis.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov Registry (NCT02170155).

Extramuscular Recording of Spontaneous EMG Activity and Transcranial Electrical Elicited Motor Potentials in Horses: Characteristics of Different Subcutaneous and Surface Electrode Types and Practical Guidelines

Introduction

Adhesive surface electrodes are worthwhile to explore in detail as alternative to subcutaneous needle electrodes to assess myogenic evoked potentials (MEP) in human and horses. Extramuscular characteristics of both electrode types and different brands are compared in simultaneous recordings by also considering electrode impedances and background noise under not mechanically secured (not taped) and taped conditions.

Methods

In five ataxic and one non-ataxic horses, transcranial electrical MEPs, myographic activity, and noise were simultaneously recorded from subcutaneous needle (three brands) together with pre-gelled surface electrodes (five brands) on four extremities. In three horses, the impedances of four adjacent-placed surface-electrode pairs of different brands were measured and compared. The similarity between needle and surface EMGs was assessed by cross-correlation functions, pairwise comparison of motor latency times (MLT), and amplitudes. The influence of electrode noise and impedance on the signal quality was assessed by a failure rate (FR) function. Geometric means and impedance ranges under not taped and taped conditions were derived for each brand.

Results

High coherencies between EMGs of needle-surface pairs degraded to 0.7 at moderate and disappeared at strong noise. MLTs showed sub-millisecond simultaneous differences while sequential variations were several milliseconds. Subcutaneous MEP amplitudes were somewhat lower than epidermal. The impedances of subcutaneous needle electrodes were below 900 Ω and FR = 0. For four brands, the FR for surface electrodes was between 0 and 80% and declined to below 25% after taping. A remaining brand (27G DSN2260 Medtronic) revealed impedances over 100 kΩ and FR = 100% under not taped and taped conditions.

Conclusion

Subcutaneous needle and surface electrodes yield highly coherent EMGs and TES-MEP signals. When taped and allowing sufficient settling time, adhesive surface-electrode signals may approach the signal quality of subcutaneous needle electrodes but still depend on unpredictable conditions of the skin. The study provides a new valuable practical guidance for selection of extramuscular EMG electrodes. This study on horses shares common principles for the choice of adhesive surface or sc needle electrodes in human applications such as in intraoperative neurophysiological monitoring of motor functions of the brain and spinal cord.

Degenerative cervical myelopathy - update and future directions

Degenerative cervical myelopathy (DCM) is the leading cause of spinal cord dysfunction in adults worldwide. DCM encompasses various acquired (age-related) and congenital pathologies related to degeneration of the cervical spinal column, including hypertrophy and/or calcification of the ligaments, intervertebral discs and osseous tissues. These pathologies narrow the spinal canal, leading to chronic spinal cord compression and disability. Owing to the ageing population, rates of DCM are increasing. Expeditious diagnosis and treatment of DCM are needed to avoid permanent disability. Over the past 10 years, advances in basic science and in translational and clinical research have improved our understanding of the pathophysiology of DCM and helped delineate evidence-based practices for diagnosis and treatment. Surgical decompression is recommended for moderate and severe DCM; the best strategy for mild myelopathy remains unclear. Next-generation quantitative microstructural MRI and neurophysiological recordings promise to enable quantification of spinal cord tissue damage and help predict clinical outcomes. Here, we provide a comprehensive, evidence-based review of DCM, including its definition, epidemiology, pathophysiology, clinical presentation, diagnosis and differential diagnosis, and non-operative and operative management. With this Review, we aim to equip physicians across broad disciplines with the knowledge necessary to make a timely diagnosis of DCM, recognize the clinical features that influence management and identify when urgent surgical intervention is warranted.

High-Risk Surgical Maneuvers for Impending True-Positive Intraoperative Neurologic Monitoring Alerts: Experience in 3139 Consecutive Spine Surgeries

BACKGROUND

Intraoperative neurologic monitoring (IONM) has become an essential component for decreasing the incidence of spinal cord injury during spine surgeries. Many high-risk surgical maneuvers that result in significant IONM alerts have not been reported systematically. Our objective was to thoroughly summarize some common high-risk surgical points associated with IONM alerts in various spine surgeries.

METHODS

Between November 2010 and April 2017, 62 patients with true-positive IONM alerts from 3139 spine surgeries were enrolled. Transcranial motor evoked potentials, somatosensory evoked potentials, and free-run electromyography were used for IONM. All 62 patients were identified as true-positive IONM cases.

RESULTS

Of 3139 patients, 101 demonstrated significant IONM changes-62 true-positive cases, 14 false-positive cases, and 25 indeterminate IONM results. IONM alerts most often occurred in thoracic screw placement (n = 10, 16.1%), osteotomy (n = 22, 35.5%), correction (n = 19, 30.6%), and spinal cord decompression (n = 11, 17.8%). Appropriate timely measures are indicated in response to IONM alerts during high-risk surgical maneuvers. Ten (10/62, 16.1%) patients showed permanent postoperative neurologic deficits.

CONCLUSIONS

IONM alerts are often associated with some specific high-risk surgical maneuvers. Careful and timely observation is crucial.