Spinal cord monitoring in patients with spinal deformity and neural axis abnormalities: a comparison with adolescent idiopathic scoliosis patients

Accuracy of Intraoperative Neuromonitoring in the Diagnosis of Intraoperative Neurological Decline in the Setting of Spinal Surgery-A Systematic Review and Meta-Analysis

STUDY DESIGN

Systematic review and meta-analysis.

OBJECTIVES

In an effort to prevent intraoperative neurological injury during spine surgery, the use of intraoperative neurophysiological monitoring (IONM) has increased significantly in recent years. Using IONM, spinal cord function can be evaluated intraoperatively by recording signals from specific nerve roots, motor tracts, and sensory tracts. We performed a systematic review and meta-analysis of diagnostic test accuracy (DTA) studies to evaluate the efficacy of IONM among patients undergoing spine surgery for any indication.

METHODS

The current systematic review and meta-analysis was performed using the Preferred Reporting Items for a Systematic Review and Meta-analysis statement for Diagnostic Test Accuracy Studies (PRISMA-DTA) and was registered on PROSPERO. A comprehensive search was performed using MEDLINE, EMBASE and SCOPUS for all studies assessing the diagnostic accuracy of neuromonitoring, including somatosensory evoked potential (SSEP), motor evoked potential (MEP) and electromyography (EMG), either on their own or in combination (multimodal). Studies were included if they reported raw numbers for True Positives (TP), False Negatives (FN), False Positives (FP) and True Negative (TN) either in a 2 × 2 contingency table or in text, and if they used postoperative neurologic exam as a reference standard. Pooled sensitivity and specificity were calculated to evaluate the overall efficacy of each modality type using a bivariate model adapted by Reitsma et al, for all spine surgeries and for individual disease groups and regions of spine. The risk of bias (ROB) of included studies was assessed using the quality assessment tool for diagnostic accuracy studies (QUADAS-2).

RESULTS

A total of 163 studies were included; 52 of these studies with 16,310 patients reported data for SSEP, 68 studies with 71,144 patients reported data for MEP, 16 studies with 7888 patients reported data for EMG and 69 studies with 17,968 patients reported data for multimodal monitoring. The overall sensitivity, specificity, DOR and AUC for SSEP were 71.4% (95% CI 54.8-83.7), 97.1% (95% CI 95.3-98.3), 41.9 (95% CI 24.1-73.1) and .899, respectively; for MEP, these were 90.2% (95% CI 86.2-93.1), 96% (95% CI 94.3-97.2), 103.25 (95% CI 69.98-152.34) and .927; for EMG, these were 48.3% (95% CI 31.4-65.6), 92.9% (95% CI 84.4-96.9), 11.2 (95% CI 4.84-25.97) and .773; for multimodal, these were found to be 83.5% (95% CI 81-85.7), 93.8% (95% CI 90.6-95.9), 60 (95% CI 35.6-101.3) and .895, respectively. Using the QUADAS-2 ROB analysis, of the 52 studies reporting on SSEP, 13 (25%) were high-risk, 10 (19.2%) had some concerns and 29 (55.8%) were low-risk; for MEP, 8 (11.7%) were high-risk, 21 had some concerns and 39 (57.3%) were low-risk; for EMG, 4 (25%) were high-risk, 3 (18.75%) had some concerns and 9 (56.25%) were low-risk; for multimodal, 14 (20.3%) were high-risk, 13 (18.8%) had some concerns and 42 (60.7%) were low-risk.

CONCLUSIONS

These results indicate that all neuromonitoring modalities have diagnostic utility in successfully detecting impending or incident intraoperative neurologic injuries among patients undergoing spine surgery for any condition, although it is clear that the accuracy of each modality differs.PROSPERO Registration Number: CRD42023384158.

The adjunct use of descending neurogenic-evoked potentials when transcranial motor-evoked potentials degrade into warning criteria in pediatric spinal deformity surgery: minimizing false-positive events

PURPOSE

This studies objective was to evaluate the utility of descending neurogenic-evoked potentials (DNEPs) in the setting of transcranial motor-evoked potentials (TCeMEPs) degradation into warning criteria during pediatric spinal deformity surgery.

METHODS

An institutional spinal cord monitoring database was queried to identify all primary and revision pediatric spinal deformity cases, < / = 21 years of age performed from 1/2006 to 12/2021, in which TCeMEPs were the primary motor tract assessment modality which degraded into warning criteria, with subsequent initiation of adjunct DNEPs.

RESULTS

Fourteen surgical cases (0.42%; 3351 total cases) in fourteen patients met inclusion criteria. Mean age was 13.2 years (7.5-21.3).

DIAGNOSES

syndromic (n = 7), kyphosis (n = 3), congenital (n = 2), and idiopathic (n = 2). Three-column osteotomies (3CO)were done in eight patients. TCeMEPs degraded into warning criteria during screw placement (n = 7), 3CO performance/closure (n = 4), or deformity correction (n = 3). DNEPs were present in all cases of warning-criteria TCeMEPs and one case had degradation of DNEPs. Intraoperative Stagnara wake-up tests were performed in only 2/14 cases, with one transient new neurologic deficit (NND). In this specific scenario, DNEPs sensitivity was 50%, specificity 100%, positive predictive value 100%, and negative predictive value 92% to detect aNND.

CONCLUSION

DNEPs were useful in assessing spinal cord function in the setting of TCeMEP data degradation in complex pediatric deformity surgeries. DNEPs demonstrated a higher specificity and positive predictive value in this clinical setting than TCeMEPs when assessing long-term neurologic function after surgery. Based on this small cohort, DNEPs appear to be a useful adjunct modality to TCeMEPs, in this challenging clinical scenario.

Temporary Flexible Rods for Correction of Severe Pediatric Spinal Deformity

Surgical correction of large, rigid scoliotic and kyphotic curves carries an increased risk of perioperative complications, such as neurological injury and excessive blood loss, compared with correction of less severe curves. Titanium temporary flexible rods (TFRs), designed for pediatric long bone fracture fixation, may be helpful as adjuncts to achieve gradual, stepwise intraoperative correction of severe pediatric spinal deformities. A retrospective review was conducted of spinal fusion cases for pediatric scoliosis or kyphosis at our institution that used TFRs as a correction technique from 2007 to 2019. Patients underwent posterior spinal fusion with predominantly pedicle screw instrumentation. Intraoperatively, a non-contoured titanium elastic nail was temporarily positioned in the screws unilaterally to achieve partial correction while the contralateral side was instrumented. Then, the TFR was removed and replaced with a permanent rod. Thirty-four patients with severe spinal deformities underwent posterior spinal fusion. Seventeen had scoliosis (mean major Cobb angle, 89.3°) and 17 had kyphosis (mean T5-T12 kyphosis, 73.8°). Idiopathic deformity was the most common etiology; neuromuscular, syndromic, and postsurgical causes contributed to the remainder of cases. All patients had Ponte osteotomies. Four patients (11.8%) had neuromonitoring alerts, 1 of which was related to insertion of the TFR; all were reversible. For patients with scoliosis, the mean postoperative Cobb angle measured 40.2° (53.6% correction). For patients with kyphosis, the mean postoperative T5-T12 angle measured 43.3° (30.4° of correction). TFRs appear to be helpful adjuncts for correction of severe pediatric spinal deformities, facilitating gradual intraoperative correction in a single-stage operation. Neuromonitoring alerts are common but reversible. [Orthopedics. 2023;46(4):234-241.].

Longitudinal electrophysiological changes after mesenchymal stem cell transplantation in a spinal cord injury rat model

Transcranial electrically stimulated motor-evoked potentials (tcMEPs) are widely used to evaluate motor function in humans and animals. However, the relationship between tcMEPs and the recovery of paralysis remains unclear. We previously reported that transplantation of mesenchymal stem cells to a spinal cord injury (SCI) rat model resulted in various degrees of recovery from paraplegia. As a continuation of this work, in the present study, we aimed to establish the longitudinal electrophysiological changes in this SCI rat model after mesenchymal stem cell transplantation. SCI rats were established using the weight-drop method. The model rats were transvenously transplanted with two types of mesenchymal stem cells (MSCs), one derived from rat cranial bones and the other from the bone marrow of the femur and tibia bone, 24 h after SCI. A phosphate-buffered saline (PBS) group that received only PBS was also created for comparison. The degree of paralysis was evaluated over 28 days using the Basso–Beattie–Bresnahan (BBB) scale and inclined plane task score. Extended tcMEPs were recorded using a previously reported bone-thinning technique, and the longitudinal electrophysiological changes in tcMEPs were investigated. In addition, the relationship between the time course of recovery from paralysis and reappearance of tcMEPs was revealed. The appearance of the tcMEP waveform was earlier in MSC-transplanted rats than in PBS-administered rats (earliest date was 7 days after SCI). The MEP waveforms also appeared at approximately the same level on the BBB scale (average score, 11 points). Ultimately, this study can help enhance our understanding of the relationship between neural regeneration and tcMEP recording. Further application of tcMEP in regenerative medicine research is expected.

Use of transcranial motor-evoked potentials to provide reliable intraoperative neuromonitoring for the Charcot-Marie-Tooth population undergoing spine deformity surgery

PURPOSE

Intraoperative neuromonitoring (IONM) has historically been difficult to obtain in patients with Charcot-Marie-Tooth (CMT) disease. Transcranial motor-evoked potentials (TcMEPs) have been found to be safe and effective for other spinal deformity patients. Our objective was to determine the effectiveness of TcMEP monitoring in patients with CMT.

METHODS

An IRB-approved, retrospective review of CMT patients undergoing spinal deformity surgery assessing TcMEP, somatosensory-evoked potential (SSEP), and neurogenic motor evoked potential (NMEP) IONM was performed. A 2:1 matched cohort control group of idiopathic spinal deformity patients was used. A waveform grading system was applied to review baseline TcMEP reliability and quality, which was validated via intraclass correlation coefficient amongst five raters.

RESULTS

Twenty-three CMT patients (26 surgical cases) were identified. The use of TcMEP improved the ability to obtain baseline IONM when compared to SSEP (83% vs. 20%; p < 0.001) and NMEP (83% vs. 18%; p = 0.003). Baseline monitoring was obtained less often for CMT patients using SSEP (20% vs. 100%; p < 0.001) and TcMEP (83% vs. 100%; p = 0.111) compared to idiopathic patients. Sweep length (time from stimulation waveform evaluation) and maximum stimulation voltage were higher in the CMT group (289 ms vs. 111 ms p = 0.007 and 740 V vs. 345 V p = 0.089, respectively).

CONCLUSION

TcMEP monitoring significantly improves the ability to provide IONM for CMT patients undergoing spinal deformity surgery. Utilizing longer sweep lengths enhances the ability to attain baseline TcMEP readings, allowing surgeons to more safely proceed with surgery for these complex patients.

LEVEL OF EVIDENCE

Therapeutic-Level III.

Does Navigation Make Spinal Fusion for Adolescent Idiopathic Scoliosis Safer? Insights From a National Database

STUDY DESIGN

Retrospective Cohort.

OBJECTIVE

To evaluate the effect of computer-assisted navigation (NAV) on rates of complications and reoperations after spinal fusion (SF) for adolescent idiopathic scoliosis (AIS) using a nationally representative claims database.

SUMMARY OF BACKGROUND DATA

Significant controversy surrounds the reported benefits of NAV in SF for AIS. Previous studies have demonstrated decreased rates of pedicle screw breaches with NAV compared to free-hand methods but no impact on complication rates. Thus, the clinical utility of NAV remains uncertain.

METHODS

Analyses were performed using the IBM MarketScan databases. Patients aged 10 to 18 undergoing SF for AIS were grouped by use of NAV. Patients with nonidiopathic scoliosis were excluded. Univariate and risk-adjusted multivariate analyses were performed. Primary outcomes were neurological complications, any medical complications, and reoperations. Secondary outcomes included adjusted total reimbursements and length of stay.

RESULTS

A total of 12,046 patients undergoing SF for AIS were identified, and 8640 had 90-day follow-up. NAV was used in 467 patients (5.4%), increasing from 2007 to 2015. After risk adjustment, the odds for any complication within 90 days were lower with NAV (OR = 0.61, P = 0.025), but neurological complications were unrelated to NAV (P = 0.742). NAV was not associated with reoperation within 90 days (P = 0.757) or 2 years (P = 0.095). We observed a $25,038 increase in adjusted total reimbursements (P < 0.001) and a 0.32-day decrease in length of stay (P = 0.022) with use of NAV.

CONCLUSION

In this national sample, NAV was associated with a lower rate of total complications but no change in rates of neurological complications or reoperations. In addition, NAV was associated with a large increase in total payments, despite a modest decrease in hospital stay. Considering the increasing popularity of NAV, this study provides important context regarding the utility of NAV for AIS.Level of Evidence: 3.

Feasibility and diagnostic accuracy of intra-operative monitoring of motor evoked potentials in children <2 years of age undergoing tethered cord surgery: results in 100 children

OBJECTIVE

This study documents the monitorability using different anesthesia regimes and accuracy of muscle motor evoked potentials (mMEPs) in children ≤2 years of age undergoing tethered cord surgery (TCS).

METHODS

Intraoperative mMEP monitoring was attempted in 100 consecutive children, ≤2 years of age, undergoing TCS. MEP monitoring was done under 4 different anesthetic regimes: (Total intravenous anesthesia (TIVA); balanced anesthesia with sevoflurane and ketamine; balanced anesthesia with isoflurane and ketamine; and balanced anesthesia with sevoflurane). Factors analyzed for their effect on monitorability were: age, neurological deficits, type of anesthesia, and the number of pulses used for stimulation.

RESULTS

Baseline mMEPs were obtained in 87% children. Monitorability of mMEPs was similar in children ≤1 year and 1-2 years of age (85.7% and 87.5%). In multivariate analysis, anesthesia regime was the only significant factor predicting presence of baseline mMEPs. Children undergoing TIVA (p=0.02) or balanced anesthesia with a combination of propofol, sevoflurane, and ketamine (p=0.05) were most likely to have baseline mMEPs. mMEPs had a sensitivity of 97.4%, specificity of 96.4%, negative predictive value of 98.2% and accuracy of 96.8%.

CONCLUSIONS

Baseline mMEPs were obtained in >85% of children ≤2 years of age including those who had motor deficits. TIVA and balanced anesthesia with sevoflurane and ketamine are ideal for mMEP monitoring. mMEPs have a high accuracy although, false positive and false negative results can occasionally be experienced.

Tetanic stimulation of the peripheral nerve augments motor evoked potentials by re-exciting spinal anterior horn cells

Tetanic stimulation of the peripheral nerve, immediately prior to conducting transcranial electrical stimulation motor evoked potential (TES-MEP), increases MEP amplitudes in both innervated and uninnervated muscles by the stimulated peripheral nerve; this is known as the remote augmentation of MEPs. Nevertheless, the mechanisms underlying the remote augmentation of MEPs remain unclear. Although one hypothesis was that remote augmentation of MEPs results from increased motoneuronal excitability at the spinal cord level, the effect of spinal anterior horn cells has not yet been investigated. We aimed to investigate the effect of tetanic stimulation of the peripheral nerve on spinal cord anterior horn cells by analyzing the F-wave. We included 34 patients who underwent elective spinal surgeries and compared the changes in F-waves and TES-MEPs pre- and post-tetanic stimulation of the median nerve. F-wave analyses were recorded by stimulating the median and tibial nerves. TES-MEPs and F-wave analyses were compared between baseline and post-tetanic stimulation time periods using Wilcoxon signed-rank tests. A significant augmentation of MEPs, independent of the level corresponding to the median nerve, was demonstrated. Furthermore, F-wave persistence was significantly increased not only in the median nerve but also in the tibial nerve after tetanic stimulation of the median nerve. The increased F-wave persistence indicates an increase of re-excited motor units in spinal anterior horn cells. These results confirm the hypothesis that tetanic stimulation of the peripheral nerve may cause remote augmentation of MEPs, primarily by increasing the excitability of the anterior horn cells.

Clinical Relevance of Preoperative MRI in Adolescent Idiopathic Scoliosis: Is Hydromyelia a Predictive Factor of Intraoperative Electrophysiological Monitoring Alterations?

STUDY DESIGN

This was a prospective cohort study.

OBJECTIVES

The main objectives of this study were to evaluate the prevalence and clinical relevance of neuroaxial anomalies in adolescent idiopathic scoliosis (AIS) patients as well as to evaluate different clinical and radiologic variables as potential predictors of the presence of a magnetic resonance imaging (MRI) abnormality.

SUMMARY OF BACKGROUND DATA

The usefulness of preoperative magnetic resonance imaging in AIS is still debated in the literature as well as the clinical relevance of the neuroaxial anomalies detected.

MATERIALS AND METHODS

We performed an analysis on 88 patients affected by AIS with normal neurological examination undergoing a posterior arthrodesis intervention. Patients were stratified according to the presence and type of neuroaxial abnormalities and were compared by age, sex, Risser grading, Lenke curve type, coronal and sagittal curve parameters, presence of alterations at intraoperative neuromonitoring, and "pain" and "function" scores at the SRS-22 test.

RESULTS

Neuroaxial abnormalities were reported in 23 patients (26.14%): 14 hydromyelias, 7 syringomyelias, 1 case of Chiari I syndrome, and 1 case of spinal ependymoma. Age, sex, Risser grading, curve type, and coronal and sagittal curve parameters did not differ between normal patients and patients with any neuroaxial abnormality. Alterations of motor-evoked potential/somatosensory-evoked potential monitoring during surgery were reported in 23 patients; the difference in their incidence between normal (20%) and hydromyelia (64%) patients was significant (P<0.01). In evaluating the subareas of the SRS-22 test, we found that the "function" scores differed significantly by comparing normal (21.5±1.6) and hydromyelia (20.4±1.8) patients (P<0.05).

CONCLUSIONS

The prevalence of neuroaxial abnormalities in AIS patients is relatively high, but we could not identify any definitive clinical or radiologic predictor of their presence. Hydromyelia was correlated with intraoperative motor-evoked potential/somatosensory-evoked potential electrophysiological alterations.

A Novel Posterior Rod-Link-Reducer System Provides Safer, Easier, and Better Correction of Severe Scoliosis

STUDY DESIGN

Retrospective review.

OBJECTIVES

To compare the Cobb >75° scoliosis correction obtained using a novel Rod-Link-Reducer (RLR) system versus traditional corrective techniques (TCT) in patients with severe adolescent idiopathic scoliosis (AIS).

SUMMARY OF BACKGROUND DATA

Current implant strategies provide for good correction, especially for moderate curves; however, severe scoliosis continues to be challenging to obtain correction in a safe and effective manner.

METHODS

A novel correction device was developed so that two provisional rods are placed on the convex side of the scoliosis proximally and distally, which are then linked to an external reduction device termed the RLR. A retrospective analysis was performed to compare the RLR versus the TCT in patients with curve >75° with the diagnosis of AIS with respect to the radiographic outcomes, operative time, intraoperative blood loss, complications, and SRS-30 scores of a minimum 2-year follow-up.

RESULTS

A total of 36 patients were evaluated (RLR-18, TCT-18). The data sets were similar for age, gender, coronal Cobb, curve flexibility, and follow-up period. The mean preoperative Cobb for the RLR group was 91.7° (76°-113°) and 91.8° (78°-108°) for the TCT group. The mean coronal Cobb correction rate was significantly greater for the RLR group (73.1% vs. 56.6%, p < .0001). The mean operative time was 74.8 minutes shorter in the RLR group (316.6 minutes vs. 391.4 minutes, p = .03). There were 2 late-developing infections and 3 intraoperative neuro-monitoring changes during the correction maneuvers in the TCT group compared with none in the RLR group (p = .02).

CONCLUSION

In a matched cohort, the use of the RLR exhibited greater coronal Cobb correction, shorter operative time, and was less likely to have critical neuro-monitoring changes compared with the TCT group. The RLR provides safer and improved correction for severe curves without adding surgical risk.

LEVEL OF EVIDENCE

Level III.

Is a persistent central canal a risk factor for neurological injury in patients undergoing surgical correction of scoliosis?

Background

Scoliosis patients with associated syringomyelia are at an increased risk of neurological injury during surgical deformity correction. The syrinx is therefore often addressed surgically prior to scoliosis correction to minimize this risk. It remains unclear if the presence of a persistent central canal (PCC) within the spinal cord also poses a similar risk. The aim of this study is to determine whether there is any evidence to suggest that patients with a PCC are also at a higher risk of neurological injury during surgical scoliosis correction.

Methods

Eleven patients with a PCC identified on pre-operative magnetic resonance imaging who had undergone correction of adolescent idiopathic scoliosis (AIS) over a 7-year study period at our institution were retrospectively identified. The incidence of abnormal intra-operative spinal cord monitoring (SCM) traces in this group was in turn compared against 44 randomly selected age- and sex-matched controls with no PCC who had also undergone surgical correction of AIS during the study period. Fisher’s exact test was applied to determine whether there was a significant difference in the incidence of abnormal intra-operative SCM traces between the two groups.

Results

Statistical analysis demonstrated no significant difference in the incidence of abnormal intra-operative SCM signal traces between the PCC group and the control group.

Conclusions

This study demonstrates no evidence to suggest a PCC increases the risk of neurological complications during scoliosis correction. We therefore suggest that surgical correction of scoliosis in patients with a PCC can be carried out safely with routine precautions.

Intra-operative MEP monitoring can work well in the patients with neural axis abnormality

PURPOSE

To explain the intra-operative transcranial motor evoked potential (MEP) monitoring can work well in patients with neural axis abnormality (NAA).

METHODS

One hundred eighteen consecutive NAA and 334 adolescent idiopathic scoliosis (AIS) patients who underwent spinal deformity surgery between June 2010 and April 2013 in our spine center were included. The MEP data including the success rate of obtaining a baseline, amplitude, sensitivity and specificity were analyzed.

RESULTS

High-efficiency MEPs baseline could be obtained in 117/118 NAA (74 congenital scoliosis, 32 neuromuscular scoliosis, 8 adult scoliosis, 3 congenital kyphoscoliosis and 1 neurofibromatosis scoliosis) and 334 AIS cases. They had an approximate level in success rate of MEPs baseline (99.2 vs. 99.7 %) and MEPs amplitude (317 μV, n = 118; vs. 312 μV, n = 334). The sensitivity and specificity for MEP were 100 and 98.2 % in patients with NAA. And the MEPs amplitude value fitted positive-skewed distribution in both of NAA and AIS.

CONCLUSIONS

Intraoperative MEP monitoring can be used accurately and satisfactorily in NAA patients and show no difference compared with AIS.

Spinal Cord Monitoring With Transcranial Motor Evoked Potentials in Patients With Neural Axis Abnormalities Undergoing Spinal Deformity Surgery

STUDY DESIGN

Retrospective, case-control study.

OBJECTIVES

To report the effectiveness of transcranial motor evoked potentials (TcMEPs) in patients undergoing scoliosis surgery with neural axis abnormalities (NAAs).

SUMMARY OF BACKGROUND DATA

Transcranial motor evoked potentials are a safe and sensitive modality to identify impending spinal cord injury in adolescent idiopathic scoliosis (AIS). Previous studies have analyzed somatosensory evoked potentials (SSEPs) and neurogenic motor evoked potentials in NAA patients, but to our knowledge, no study has addressed the use of TcMEPs in these patients.

METHODS

We performed an institutional review board-approved retrospective review of a consecutive series of patients with NAA at a single institution and compared them with a consecutive series of AIS patients undergoing scoliosis surgery with spinal cord monitoring using TcMEP and SSEP. We compared the ability to obtain baseline data and the incidence of critical changes in TcMEPs and SSEPs between groups and examined a correlation with postoperative neurologic deficits.

RESULTS

We compared 38 patients with NAA (15 Chiari malformations, 12 syrinx, 7 tethered cords, and 4 spinal cord tumors) with 184 patients with AIS. The age was similar and preoperative curve magnitude was greater in the NAA group. Good baseline data were obtained less frequently in the NAA group for TcMEPs (94.7% vs. 100%; p < .001) and SSEPs (89.5% vs. 100%; p < .001). There was no statistical difference in critical deviation from baseline in the NAA group for TcMEPs (3 of 38 [7.9%] vs. 5 of 184 [2.7%]; p = .120) or SSEPs (0 of 38 vs. 3 of 184 [1.6%] (p = .430). There were no postoperative neurologic deficits in the NAA or AIS group.

CONCLUSIONS

The ability to obtain baseline spinal cord monitoring in patients with NAA approaches that of an AIS group and accurately identifies impending neurologic deficits with high sensitivity. Surgeons should be confident that TcMEP baseline data can be obtained in patients with spinal cord pathology and should trust critical changes in TcMEPs intraoperatively to prevent spinal cord injury.

A review of intraoperative monitoring for spinal surgery

BACKGROUND

Intraoperative neurophysiologic monitoring (IONM) is a technique that is helpful for assessing the nervous system during spine surgery.

METHODS

This is a review of the field describing the basic mechanisms behind the techniques of IONM. These include the most often utilized trancranial motor evoked potentials (Tc-MEPs), somatosensory evoked potentials (SSEPs), and stimulated and spontaneous EMG activity. It also describes some of the issues regarding practices and qualifications of practitioners.

RESULTS

Although the anatomic pathways responsible for the Tc-MEP and SSEP are well known and these clinical techniques have a high sensitivity and specificity, there is little published data showing that monitoring actually leads to improved patient outcomes. It is evident that IONM has high utility when the risk of injury is high, but may be only marginally helpful when the risk of injury is very low. The monitoring team must be well trained, be able to provide the surgeon feedback in real time, and coordinate activities with those of the surgical and anesthesia teams.

CONCLUSIONS

Although IONM is a valuable technique that provides sensitive and specific indications of neurologic injury, it does have limitations that must be understood. Maintaining a high quality of practice with appropriately trained personnel is critical.

[Intraoperative electrophysiological monitoring with evoked potentials]

During the last 30 years intraoperative electrophysiological monitoring (IOEM) has gained increasing importance in monitoring the function of neuronal structures and the intraoperative detection of impending new neurological deficits. The use of IOEM could reduce the incidence of postoperative neurological deficits after various surgical procedures. Motor evoked potentials (MEP) seem to be superior to other methods for many indications regarding monitoring of the central nervous system. During the application of IOEM general anesthesia should be provided by total intravenous anesthesia with propofol with an emphasis on a continuous high opioid dosage. When intraoperative MEP or electromyography guidance is planned, muscle relaxation must be either completely omitted or maintained in a titrated dose range in a steady state. The IOEM can be performed by surgeons, neurologists and neurophysiologists or increasingly more by anesthesiologists. However, to guarantee a safe application and interpretation, sufficient knowledge of the effects of the surgical procedure and pharmacological and physiological influences on the neurophysiological findings are indispensable.

Management of severe spinal deformity: scoliosis and kyphosis

STUDY DESIGN

Review of the literature and author';s experience with the treatment of severe spinal deformity.

OBJECTIVE

To define the anatomic and physiologic challenges in treating severe spinal deformity and to describe the preoperative, intraoperative, and postoperative strategies to achieve the optimal safe result.

SUMMARY OF BACKGROUND DATA

Severe pediatric spinal deformity is a relatively uncommon condition that often arises following treatment of early onset scoliosis. Patients most often present with severe clinical and radiographic deformity with poor pulmonary function. In contrast to the more common adolescent idiopathic scoliosis which is a primary spinal deformity, patients with severe spine deformity have the added chest wall deformity which may need to be addressed at the time of treatment. Previous literature has identified the challenges in the treatment of these patients and the higher risk for complications.

METHODS

A literature review and review of the author's personal experience in the treatment of these patients was performed. An assessment of the preoperative, intraoperative, and postoperative factors leading to an optimal result was analyzed and reported.

RESULTS

The early evaluation should include a multidisciplinary approach from the orthopaedic surgeon, pulmonologist, anesthesiologist, and perhaps the neurologist to provide a baseline assessment. Advanced imaging of the spine with computed tomography is useful especially when previous surgery has been performed and/or when plain radiography is limited. Magnetic resonance imaging of the spinal cord and brain stem is important to ensure that no neural axis abnormalities are present and can determine if spinal cord compression is present. Severe spinal deformity should be distinguished from the more common adolescent idiopathic scoliosis deformity in that both the spine and the chest wall are affected. Preoperative halo-gravity traction is an invaluable tool to improve the flexibility of the spine and chest, to improve pulmonary function, and to stress the spinal cord while the patient is awake and provides feedback as to the neurologic assessment. Surgical treatment should be divided into 3 phases. First, anchor placement which should be predominantly pedicle screws placed in a segmental fashion and also use of reduction screws when performing vertebral column resections. Second, steps should be performed to increase the flexibility of the spine and chest with incremental releases from simple posterior soft tissue releases to posterior facet resections, to vertebral column resections for the most severe deformity. The third phase is the correction of the spine and chest wall deformity. Many strategies can be used to correct these deformities and relies on good anchor point fixation and good releases of the spine and chest wall. Provisional rod fixation is critical when performing resection of the spine to allow for safe correction of the deformity. Improvements in the clinical and radiographic appearance, pulmonary function, and self image are often dramatic.

CONCLUSION

The treatment of severe spinal deformity is challenging and requires careful assessment of the patient by the orthopaedic surgeon, anesthesiologist, pulmonologist, and neurologist especially when neurologic deficits are present. Proper planning and execution of the correct surgical procedure for the surgeon provides an outstanding life-changing result in these patients.

Intraoperative electrophysiological monitoring in spine surgery

STUDY DESIGN

Review of the literature with analysis of pooled data.

OBJECTIVE

To assess common intraoperative neuromonitoring (IOM) changes that occur during the course of spinal surgery, potential causes of change, and determine appropriate responses. Further, there will be discussion of appropriate application of IOM, and medical legal aspects. The structured literature review will answer the following questions: What are the various IOM methods currently available for spinal surgery? What are the sensitivities and specificities of each modality for neural element injury? How are the changes in each modality best interpreted? What is the appropriate response to indicated changes? Recommendations will be made as to the interpretation and appropriate response to IOM changes.

SUMMARY OF BACKGROUND DATA

Total number of abstracts identified and reviewed was 187. Full review was performed on 18 articles.

METHODS

The MEDLINE database was queried using the search terms IOM, spinal surgery, SSEP, wake-up test, MEP, spontaneous and triggered electromyography alone and in various combinations. Abstracts were identified and reviewed. Individual case reports were excluded. Detailed information and data from appropriate articles were assessed and compiled.

RESULTS

Ability to achieve IOM baseline data varied from 70% to 98% for somatosensory-evoked potentials (SSEP) and 66% to 100% for motor-evoked potentials (MEP) in absence of neural axis abnormality. Multimodality intraoperative neuromonitoring (MIOM) provided false negatives in 0% to 0.79% of cases, whereas isolated SSEP monitoring alone provided false negative in 0.063% to 2.7% of cases. MIOM provided false positive warning in 0.6% to 1.38% of cases.

CONCLUSION

As spine surgery, and patient comorbidity, becomes increasingly complex, IOM permits more aggressive deformity correction and tumor resection. Combination of SSEP and MEP monitoring provides assessment of entire spinal cord functionality in real time. Spontaneous and triggered electromyography add assessment of nerve roots. The wake-up test can continue to serve as a supplement when needed. MIOM may prove useful in preservation of neurologic function where an alteration of approach is possible. IOM is a valuable tool for optimization of outcome in complex spinal surgery.

Evaluation of reliability of post-tetanic motor-evoked potential monitoring during spinal surgery under general anesthesia

STUDY DESIGN

A prospective research.

OBJECTIVE

Compare the reliability of post-tetanic motor-evoked potential (p-MEP) monitoring in the detection of motor injury during spinal surgery with that of conventional MEP (c-MEP).

SUMMARY OF BACKGROUND DATA

Myogenic MEPs are sensitive to suppression by anesthetics and neuromuscular blockade. Recently, we reported a new technique for MEP recording, called "p-MEP" in which MEP amplitude can be enlarged by tetanic stimulation of peripheral nerve before transcranial stimulation in comparison with that of c-MEP. The purpose of this study is to compare the reliability of p-MEP monitoring in the detection of motor injury during spinal surgery with that of c-MEP.

METHODS

Eighty patients undergoing elective spinal surgery were enrolled in the study. Both c-MEP and p-MEP monitoring were performed throughout the operation in each patient. For recording c-MEPs, transcranial electrical train of five pulses stimulation with an interstimulus interval of 2 milliseconds was performed and compound muscle action potentials were bilaterally recorded from abductor pollicis brevis, abductor hallucis, tibialis anterior, and soleus muscles. For recording p-MEPs, tetanic stimulation (50 Hz, 50 mA, 5 sec) was applied to the left median nerve and bilateral tibial nerves 1 second before transcranial stimulation and compound muscle action potentials were recorded from the same muscles. The false positive, false negative, and accuracy of MEP monitoring in the detection of change in motor function were compared between p-MEP and c-MEP.

RESULTS

At the baseline, success rates of baseline c-MEP and p-MEP recording were 66.3% (53/80) and 92.5% (74/80), respectively. The false positive, false negative, and accuracy of p-MEP monitoring were 0%, 0%, and 100%, respectively, whereas c-MEP were 4%, 20%, and 95%, respectively.

CONCLUSION

The results indicate that p-MEP is a more reliable method to detect changes in motor function during spinal surgery under general anesthesia in comparison with c-MEP.

Predictive value of intraoperative neurophysiological monitoring during cervical spine surgery: a prospective analysis of 1055 consecutive patients

Object

Despite the growing use of multimodal intraoperative monitoring (IOM) in cervical spinal surgery, limited data exist regarding the sensitivity, specificity, and predictive values of such a technique in detecting new neurological deficits in this setting. The authors sought to define the incidence of significant intraoperative electrophysiological changes and new postoperative neurological deficits in a cohort of patients undergoing cervical surgery.

Methods

The authors conducted a prospective analysis of a consecutive series of patients who had undergone cervical surgery during a 5-year period at a university-based neurosurgical unit, in which multimodal IOM was recorded. Sensitivity, specificity, positive predictive values (PPVs), and negative predictive values (NPVs) were determined using standard Bayesian techniques. The study population included 1055 patients (614 male and 441 female) with a mean age of 55 years.

Results

The IOM modalities performed included somatosensory evoked potential (SSEP) recording in 1055 patients, motor evoked potential (MEP) recording in 26, and electromyography (EMG) in 427. Twenty-six patients (2.5%) had significant SSEP changes. Electromyographic activity was transient in 212 patients (49.6%), and 115 patients (26.9%) had sustained burst or train activity. New postoperative neurological deficits occurred in 34 patients (3.2%): 6 had combined sensory and motor deficits, 7 had new sensory deficits, 9 had increased motor weakness, and 12 had new root deficits. Of these 34 patients, 12 had spinal tumors, of which 7 were intramedullary. Overall, of the 34 new postoperative deficits, 21 completely resolved, 9 partially resolved, and 4 had no improvement. The deficits that completely resolved did so on average 3.3 months after surgery. Patients with deficits that did not fully resolve (partial or no improvement) were followed up for an average of 1.8 years after surgery.

Somatosensory evoked potentials had a sensitivity of 52%, a specificity of 100%, a PPV of 100%, and an NPV of 97%. Motor evoked potential sensitivity was 100%, specificity 96%, PPV 96%, and NPV 100%. Electromyography had a sensitivity of 46%, specificity of 73%, PPV of 3%, and an NPV of 97%.

Conclusions

Combined neurophysiological IOM with EMG and SSEP recording and the selective use of MEPs is helpful for predicting and possibly preventing neurological injury during cervical spine surgery.