Neurophysiological detection of impending spinal cord injury during scoliosis surgery

Neurophysiologic monitoring can predict iatrogenic injury during acetabular and pelvic fracture fixation

BACKGROUND

Nerve injury during acetabular and pelvic fracture fixation can have devastating consequences for trauma patients already in a compromised situation.

QUESTIONS/PURPOSES

This study aims to evaluate the efficacy of multimodality intraoperative neurophysiologic monitoring during acetabular and pelvic fracture fixation in identifying emerging iatrogenic nerve injury.

METHODS

Sixty patients were retrospectively identified after surgical fixation following acetabular or pelvic fracture. Neuromonitoring during surgery was performed using three different modalities, transcranial electric motor evoked potential (tceMEP), somatosensory evoked potential (SSEP), and electromyographic (EMG) monitoring. Each modality was evaluated for sensitivity and specificity of detecting an intraoperative nerve injury.

RESULTS

tceMEP monitoring was found to be 100% sensitive and 86% specific at detecting an impending nerve injury. The sensitivity and specificity of SSEP were 75% and 94%, while EMG sensitivity was unacceptably low at 20% although specificity was 93%.

CONCLUSIONS

Multimodality neuromonitoring of transcranial electric motor and peroneal nerve somatosensory evoked potentials with or without spontaneous EMG monitoring is a safe and effective method for detecting impending nerve injury during acetabular and pelvic surgery.

Delayed postoperative neurological complication in a patient with congenital kyphoscoliosis: recovered by revision of the 4-rod instrumentation technique: case report

The authors report a case of progressive congenital kyphoscoliosis in which the patient, a boy, originally underwent combined anterior and instrumented posterior spinal fusion at the age of 7 years and 3 months. Early proximal junctional kyphosis and implant failure mandated proximal extension of implants with 2 new rods connected to the old caudad short rods. At the 3-year follow-up, clinical and CT assessment revealed a thoracolumbar pseudarthrosis for which the patient underwent a 2-stage procedure without complication. Recordings of somatosensory evoked potentials intraoperatively were normal. Twelve hours after surgery, his neurological status started to progressively deteriorate. The patient was brought to the operating room, and the initially achieved correction was reversed by an apex-only exposure of the 4-rod system. After surgery the patient started to show progressive improvement in his neurological function. A final myelography was performed and showed free passage of the dye without evidence of obstruction. Clinically, the patient continued to improve and at his 3-month follow-up had near-complete resolution of his neurological deficits. Findings on his physical examination were normal at the final 12-year follow-up. Despite normal findings on intraoperative neuromonitoring, a delayed neurological deficit can occur after complex spine reconstruction. Preoperative risk assessment, surgical approach, and instrumentation deserve careful attention. Advantages of a 4-rod construct are discussed in this case.

Intraoperative motor evoked potential monitoring - a position statement by the American Society of Neurophysiological Monitoring

The following intraoperative MEP recommendations can be made on the basis of current evidence and expert opinion: (1) Acquisition and interpretation should be done by qualified personnel. (2) The methods are sufficiently safe using appropriate precautions. (3) MEPs are an established practice option for cortical and subcortical mapping and for monitoring during surgeries risking motor injury in the brain, brainstem, spinal cord or facial nerve. (4) Intravenous anesthesia usually consisting of propofol and opioid is optimal for muscle MEPs. (5) Interpretation should consider limitations and confounding factors. (6) D-wave warning criteria consider amplitude reduction having no confounding factor explanation: >50% for intramedullary spinal cord tumor surgery, and >30-40% for peri-Rolandic surgery. (7) Muscle MEP warning criteria are tailored to the type of surgery and based on deterioration clearly exceeding variability with no confounding factor explanation. Disappearance is always a major criterion. Marked amplitude reduction, acute threshold elevation or morphology simplification could be additional minor or moderate spinal cord monitoring criteria depending on the type of surgery and the program's technique and experience. Major criteria for supratentorial, brainstem or facial nerve monitoring include >50% amplitude reduction when warranted by sufficient preceding response stability. Future advances could modify these recommendations.

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.

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.

Responding to neuromonitoring changes in 3-column posterior spinal osteotomies for rigid pediatric spinal deformities

STUDY DESIGN

Retrospective review of prospectively collected data on the neuromonitoring changes recorded during a consecutive series of cord level 3-column posterior spinal osteotomies for the correction of rigid pediatric spinal deformities in children between 2005 and 2012.

OBJECTIVE

To review the neuromonitoring changes observed during the performance of these procedures, to highlight the high-risk steps, and to describe actions taken to avert major neurological injury.

SUMMARY OF BACKGROUND DATA

Significant motor evoked potentials (MEP) changes are common during the performance of spinal osteotomies in children. The real-time intraoperative information provided by MEPs can provide the necessary information to direct key surgical decisions.

METHODS

The neuromonitoring changes occurring during the performance of 37 3-column, cord level, posterior spinal osteotomies in 28 patients were recorded. The procedures were divided, for comparative purposes, into 2 groups based on the presence or absence of alerts. A decrease in somatosensory evoked potentials and transcranial MEPs greater than 50% of baseline was considered an alert. Alerts were classified chronologically as type I: prior to decompression, type II: occurring during decompression and bone resection, type III: occurring after osteotomy closure.

RESULTS

Somatosensory evoked potential alerts occurred in 3 patients, all of whom had significant MEP alerts. There were 2 type I, 15 type II, and 6 type III MEP alerts. Increasing blood pressure improved MEPs in all with the exception of 8 type II and 4 type III. The unresponsive 8 type II alerts were treated with osteotomy closure with the expectation that spinal shortening would decompress the spinal cord and improve spinal cord perfusion. The unresponsive 4 type III alerts all responded to reopening, manipulation, and subsequent reclosure of the osteotomy either with a cage or less correction. There were 5 immediate postoperative motor deficits. No patient had a permanent deficit.

CONCLUSION

Changes unresponsive to increasing blood pressure occurring during decompression and bone resection (type II) responded well to osteotomy closure. Unresponsive changes during osteotomy closure (type III) were treated successfully with opening the osteotomy, cage adjustment, and less correction.

[Neurophysiological monitoring during surgery]

BACKGROUND

Intraoperative neurophysiological monitoring has become increasingly important in interventions involving risk of damage to the nervous system. We aim to provide an overview of possibilities and limitations on the use of intraoperative neurophysiological methods.

METHOD

The article is based on a review of relevant textbooks and articles from own literature archives and selective searches in PubMed, combined with the authors' own clinical experience.

RESULTS

Intraoperative neurophysiological monitoring includes both continuous monitoring of neural tissue and localisation of vital neurological structures. This monitoring can reduce the risk of damage to nerves and neural pathways and is used most frequently in scoliosis and neurosurgical operations. The need for neurophysiological monitoring influences the choice of anaesthesia, as some anaesthetics affect the monitoring.

INTERPRETATION

Intraoperative neurophysiological monitoring is dependent on good cooperation between neurophysiologists, surgeons, anaesthetists and the other specialities involved.

A complete gonadal dysgenesis case with mental retardation, congenital hip dislocation, severe vertebra rotoscoliosis, pectus excavatus, and spina bifida occulta

BACKGROUND

46,XY, or Swyer syndrome, is a complete gonadal dysgenesis. Patients usually presents with primary amenorrhea with underdeveloped secondary sex characteristics. Phenotypes of these patients are female. In this report, a Swyer syndrome case is reported with novel clinical features that are classified as connective tissue disorders. This case and the 2 other previously reported Swyer syndrome cases with ascendant aortic aneurysm and diaphragmatic hernia are suggest that the Y chromosome has an important role in the structure of connective tissue.

CASE

Here we report a case of a 17-year-old with clinical features of 46,XY complete gonadal dysgenesis including external female genitalia, hypoplastic uterus, hypergonadotrophic hypogonadism, incomplete secondary sex characterics, primary amenorrhea, and normal male karyotype. In addition, she had mild mental retardation, severe rotoscoliosis, pectus excavatus, spina bifida occulta, hip dislocation, and long, slender extremities. She had a rudimentary uterus and streak gonads; after giving her cyclic estrogen and progesterone pills, she was able to menstruate.

SUMMARY AND CONCLUSION

In this report, a Swyer syndrome case was discussed regarding clinical features, especially those are not characteristic for Swyer syndrome after a review of the literature.

Significant change or loss of intraoperative monitoring data: a 25-year experience in 12,375 spinal surgeries

STUDY DESIGN

Retrospective.

OBJECTIVE

The purpose of this study was to report the spectrum of intraoperative events responsible for a loss or significant change in intraoperative monitoring (IOM) data.

SUMMARY OF BACKGROUND DATA

The efficacy of spinal cord/nerve root monitoring is demonstrated in a large, single institution series of patients, involving all levels of the spinal column (occiput to sacrum) and all spinal surgical procedures.

METHODS

Multimodality IOM included somatosensory-evoked potentials, descending neurogenic-evoked potentials, neurogenic motor-evoked potentials, and spontaneous and triggered electromyography. A total of 12,375 patients who underwent surgery for spinal pathology between January 1985 and December 2010 were reviewed. There were 59.3% female patients (7178) and 40.7% male patients (5197). Procedures by spinal level were as follows: cervical 29.7% (3671), thoracic/thoracolumbar 45.4% (5624), and lumbosacral 24.9% (3080). Age at the time of surgery was as follows: older than 18 years, 72.7% (242/8993) and younger than 18 years, 27.3% (144/3382). A total of 77.8% (9633) patients underwent primary surgical procedures and 22.2% (2742) patients underwent revision surgical procedures.

RESULTS

A total of 406 instances of IOM data change/loss occurred in 386 of 12,375 (3.1%) patients. Causes for data degradation/loss included the following: instrumentation (n = 131), positioning (n = 85), correction (n = 56), systemic (n = 49), unknown (n = 24), and focal spinal cord compression (n = 15). Data loss/change was seen in revision (6.1%/167 patients) surgical procedures more commonly than in primary procedures (2.3%/219 patients; P < 0.0001). Data improvement was demonstrated by 88.7% (n = 360) after intervention versus 11.3% (n = 46) with no improvement in IOM data. One patient with improved data after intervention versus 14 with no improvement despite intervention had a permanent neurological deficit (P < 0.0001).

CONCLUSION

IOM data identified 386 (3.1%) patients with loss/degradation of data in 12,375 spinal surgical procedures. Fortunately, in 93.3% of patients, intervention led to data recovery and no neurological deficits. Reduction from a potential (worst-case scenario) 3.1% (386) of patients with significant change/loss of IOM data to a permanent neurological deficit rate of 0.12% (15) patients was achieved (P < 0.0001), thus confirming efficacy of IOM.

Validity of somatosensory evoked potentials as early indicators of neural compromise in rat model of spinal cord compression

OBJECTIVE

To determine the percentage change in somatosensory evoked potential amplitude and the duration of spinal cord compression that can be tolerated intraoperatively in a rat model before there are significant post-operative functional deficits.

METHODS

Thirty two adult male Wistar rats were divided into four groups according to the percentage of induced SSEP signal loss; all animals had pre-operative functional testing. Following surgical placement of a balloon catheter in the thoracic sub-laminar space, SSEPs were recorded while the spinal cord was compressed by inflation of the balloon. The recordings were terminated after a different percentage loss of SSEP amplitude in each group. Functional behavioral testing was repeated after 24 h.

RESULTS

Only the group wherein the catheter was left inflated for 15 min after a complete (100%) loss of SSEP amplitude showed a significant deterioration in functional testing as compared to pre-operative baseline values. Functional testing remained normal for the groups in which termination of spinal cord compression occurred immediately after a decrease of SSEP amplitude to 50% or 100%.

CONCLUSIONS

SSEP loss of up to 100% can be tolerated in a rat model of spinal cord compression as long as the compression is terminated immediately after the SSEP decrease is detected. Prolonged spinal cord compression, with concomitant SSEP decrease, can result in post-operative functional deficits despite mitigating procedures to remove the compression.

SIGNIFICANCE

This study is an important first step in providing basic science evidence for the establishment of acceptable "alarm criteria" during spinal surgery.

Concurrent tethered cord release and growing-rod implantation-is it safe?

Study Design Retrospective case series from one institution with a comparison control group. Objective To evaluate the safety of concomitant tethered cord release and growing-rod insertion in individuals with early onset scoliosis. Methods We retrospectively reviewed patients who underwent concurrent tethered cord release and growing-rod insertion. We compared our data to a comparison control group of eight patients who underwent staged tethered cord release and growing-rod insertion. Results We identified three patients meeting criteria. There were no neurological complications in the three patients who underwent concomitant surgery. Average immediate postoperative curve correction was 43.3 degrees (47.6%). We identified seven patients who underwent staged surgery from a multicenter prospective database. No neurological complications were reported, and average immediate postoperative correction was 35.1 degrees (46.2%). Conclusion We believe that concurrent tethered cord release and growing-rod insertion can be performed safely with the use of multimodality neurophysiological monitoring techniques.

A survey of current controversies in scoliosis surgery in the United Kingdom

STUDY DESIGN

A 10-point questionnaire was constructed to identify the philosophy of surgeons on various aspects of scoliosis surgery, such as choice of implant, bone graft, autologous blood transfusion, cord monitoring, and computer-assisted surgery. Comparisons were then made with recommendations published in the spinal literature.

OBJECTIVE

To determine certain aspects of the current practice of scoliosis surgery in the United Kingdom.

SUMMARY OF BACKGROUND DATA

Guidelines for good clinical practice in spinal deformity surgery are available in the United Kingdom but do not cover a number of controversial issues.

METHODS

Consultants and fellows attended the 2009 British Scoliosis Society meeting. Fifty questionnaires were completed by 45 consultants and 5 fellows.

RESULTS

All pedicle screw constructs favored by 25 of 50, hybrid 24 of 50 (1 undecided). Posterior construct of fewer than 10 levels, 20 of 50 would not cross-link, 11 of 50 used 1, and 19 of 20 used 2 or more. More than 10 levels 17 of 50 considered cross-links unnecessary, 4 of 50 used 1 and 29 of 50 used 2 or more. Eighty-eight percent preferred titanium alloy implants, whereas others used a mixture of stainless steel and cobalt chrome. When using bone graft, respondents used bone substitutes (24), iliac crest graft (14), allograft (12) and demineralized bone matrix (9) in addition to local bone. Ten of 50 would use recombinant bone morphogenetic protein (3 for revision cases only). Thirty-nine of 50 routinely used intraoperative cell salvage and 4 of 50 never used autologous blood. All used cord monitoring: sensory (19 of 50), motor (2 of 50), and combined (29 of 50). None used computer-aided surgery. Twenty-six operated alone, 12 operated in pairs, and 12 varied depending on type of case.

CONCLUSION

This survey shows interesting variations in scoliosis surgery in the United Kingdom. It may reflect the conflicting evidence in the literature.

Apical vertebral derotation in the posterior treatment of adolescent idiopathic scoliosis: myth or reality?

INTRODUCTION

Direct apical vertebral rotation represents an important goal of posterior surgery for thoracic adolescent idiopathic scoliosis (AIS), so as to obtain a better cosmetic effect and to avoid posterior thoracoplasty. However, the real effectiveness in correction of vertebral rotation, using posterior only procedures, is still open to debate. The aim of the present study is to compare the correction of axial apical rotation obtained with direct rotation procedure versus simple concave rod rotation, in patients treated by posterior fusion for thoracic AIS using pedicle screw-only construct.

MATERIALS AND METHODS

A retrospective review was performed on a total of 62 consecutive patients (one single institution, three different surgeons) affected by AIS, who had undergone a posterior spinal fusion with pedicle screw-only instrumentation between January 2005 and April 2008 at the reference center. All cases presented a main thoracic curve (Lenke type 1 and 2). The angle of rotation (RAsag) of the apical vertebra was measured from the preoperative and last follow-up axial CT. According to the derotation procedure, two groups were identified: a direct vertebral rotation group (DR group; n = 32 patients) and a simple concave rod rotation group (No-DR group; n = 30 patients). There were no statistical differences between the two groups, in terms of age, Risser's sign, curve patterns, Cobb main thoracic (MT) curve magnitude and flexibility, extension of fusion, offset measurements on the coronal plane and sagittal preoperative contour.

RESULTS

All 62 patients were reviewed at an average follow-up of 3.7 years (range 2.5-4.2 years). The DR group compared to the No-DR group showed a significantly better final correction of apical vertebral rotation (DR 63.4 % vs. No-DR 14.8 %; p < 0.05) and a greater final correction (61.3 vs. 52.4 %; p < 0.05) with better maintenance of the initial correction (-1.7° vs. -1.9°; ns) of the main thoracic curve. Concerning the coronal balance, there was the same aforementioned trend of better results in the DR group, with less final apical MT vertebra translation (DR 2.2 cm vs. No-DR 4.1 cm), greater overall change (preop-final) of lower instrumented vertebra (LIV) coronal tilt (-14.9° vs. -11.1°; p < 0.05); the final global coronal balance (C7-S1) resulted quite better in DR group, but without a significant difference. The T5-T12 kyphosis angle was quite similar in both group before surgery (DR 16.8° vs. No-DR 17.5°) and was little lower at final follow-up evaluation in direct vertebral rotation group (14.5° vs. 16.5°). The T10-L2 sagittal alignment angle was similar in each group before surgery (12.5° in DR vs. 11.8° in No-DR), and at the latest follow-up averaged 5.3° versus 8.2°, respectively. Lumbar lordosis was similar in each group before surgery (DR -42° vs. No-DR -44.1°) and at the final follow-up evaluation (-45.9° vs. -43.2°). At the latest follow-up, SRS-30 and SF-36 findings were similar between the two groups. The complication rate was higher in the simple concave rod rotation group (13.3 vs. 9.3 %), related in two cases to thoracoplasty, which was never utilized in direct rotation patients.

CONCLUSIONS

The direct vertebral rotation obtained significantly better final results, when compared to simple concave rod rotation, both concerning correction of apical vertebral rotation and magnitude of MT curve. On the other hand, the DR group presented a little reduction in T5-T12 kyphosis at follow-up, in comparison with concave rod rotation procedure. Both procedures were found to be satisfying from patients' perspective. Nevertheless overall complication rate was higher in the simple concave rod rotation group, related mainly to thoracoplasty (2 cases), which was never necessary in direct rotation patients.

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.

Warning thresholds on the basis of origin of amplitude changes in transcranial electrical motor-evoked potential monitoring for cervical compression myelopathy

STUDY DESIGN

A retrospective analysis of prospectively collected data from consecutive patients undergoing transcranial electrical motor-evoked potential (TCE-MEP: compound muscle action potentials) monitoring during cervical spine surgery. OBJECTIVE.: To divide the warning threshold of TCE-MEP amplitude changes on the basis of origin into the spinal tract and spinal segments and decide warning thresholds for each.

SUMMARY OF BACKGROUND DATA

The parameter commonly used for the warning threshold in TCE-MEP monitoring is wave amplitude, but amplitude changes have not been examined by anatomical origin.

METHODS

Intraoperative TCE-MEP amplitude changes were reviewed for 357 patients with cervical myelopathy. Most of the patients were monitored by transcranial electrical stimulated spinal-evoked potential combined with TCE-MEP. The warning threshold of TCE-MEP was taken as waveform disappearance. For each patient, amplitude changes were separated, according to origin, into the spinal tract and spinal segments and compared with clinical outcome.

RESULTS

Assessable TCE-MEP waves were obtained in 350 cases. Disappearance of TCE-MEP waves, which were innervated by the spinal levels exposed to the surgical invasion, was seen in 11 cases. Disappearance of TCE-MEPs, which were innervated by the spinal levels inferior to them, was seen in 43 cases. There was no postoperative motor deficit in those cases. However, such deficits caused by spinal segment injury were seen in 2 cases, which showed that intraoperative amplitude decreased to 4.5% and 27%.

CONCLUSION

If we had established the warning threshold as 30% of the control amplitude, we would likely have prevented both cases of postoperative motor deficits, but 106 (30.3%) cases would have become positive cases. If we had established the warning threshold separately as wave disappearance for the spinal tract and 30% of the control amplitude for the spinal segments, sensitivity and specificity would have been 100% and 83.7%, respectively. Dividing the warning threshold on the basis of origin of amplitude changes could reduce false-positive cases and prevent intraoperative injuries.

Spinal cord infarction remote from maximal compression in a patient with Morquio syndrome

Morquio syndrome, or mucopolysaccharidosis type IV, is a rare enzyme deficiency disorder and results in skeletal dysplasia. Odontoid dysplasia is common among affected patients, resulting in atlantoaxial instability and spinal cord compression. Surgical treatments include decompression and prophylactic fusion, during which intraoperative neuromonitoring is important to alert the surgical team to changes in cord function so that they can prevent or mitigate spinal cord injury. This report describes a 16-year-old girl with Morquio syndrome who developed paraplegia due to thoracic spinal cord infarction during foramen magnum and atlantal decompression. This tragic event demonstrates the following: 1) that patients with Morquio syndrome are at risk for ischemic spinal cord injury at levels remote from areas of maximal anatomical compression while under anesthesia in the prone position, possibly due to impaired cardiac output; 2) the significance of absent motor evoked potential responses in the lower limbs with preserved upper-limb responses in an ambulatory patient; 3) the importance of establishing intraoperative neuromonitoring baseline assessments prior to turning patients to the prone position following induction of anesthesia; and 4) the importance of monitoring cardiac output during prone positioning in patients with chest wall deformity.

Pedicle screw placement with O-arm and stealth navigation

Various navigation systems are available to aid pedicle screw placement. The O-arm replaces the need for fluoroscopy and generates a 3-dimensional volumetric dataset that can be viewed as transverse, coronal, and sagittal images of the spine, similar to computed tomography (CT) scanning. The dataset can be downloaded to the Stealth system (Medtronic Navigation, Louisville, Colorado) for real-time intraoperative navigation.The main objectives of the current study were to assess (1) accuracy of pedicle screw placement using the O-arm/Stealth system, and (2) time for draping, positioning of the O-arm, and screw placement. Of 188 screws (25 patients), 116 had adequate images for analysis. The average time for O-arm draping was 3.5 minutes. Initial O-arm positioning was 6.1 minutes, and final positioning was 4.9 minutes. Mean time for screw placement, including O-arm draping and positioning and array attachment, was 8.1 minutes per screw. Mean time for screw placement alone was 5.9 minutes per screw. Screw placements on final O-arm images were on average 3.14 mm deeper than on the snapshot navigation images. Three screws (2.6%) breached the medial cortex, and 3 screws (2.6%) were misaligned and did not follow the pilot hole trajectory.The use of the O-arm/Stealth system was associated with a low rate of pedicle screw misalignment. The time to place screws was less than previously reported with CT navigation, but longer than conventional techniques. It is important to be aware of the potential discrepancy between snapshot navigation images and actual screw placement on final O-arm images. Our findings suggest that final screw positions may be deeper than awl positions appear on navigation images.

Intraoperative monitoring in pediatric orthopedic spinal surgery: three hundred consecutive monitoring cases of which 10% of patients were younger than 4 years of age

STUDY DESIGN

Analysis of a prospective series of 300 consecutive cases undergoing intraoperative monitoring in pediatric orthopedic spinal surgery, of which 10% were children younger than 4 years.

OBJECTIVE

Determine feasibility and performance of intraoperative monitoring in children younger than 4 years. Analyze distinct physiopathologic mechanisms of relevant alerts.

SUMMARY OF BACKGROUND DATA

There are few studies in the literature concerning the intraoperative monitoring of children younger than 4 years. During childhood, the development of sensori-motor pathways is dominated by two coexisting phenomena, which have opposite effects: maturation decreasing latencies and height increasing them.

METHODS

We used intraoperative somatosensory-evoked potentials and neurogenic mixed evoked potentials with a flexible bipolar epidural electrode. Uniform total intravenous anesthesia was used.

RESULTS

Values of sensitivity and specificity of the monitoring showed slight differences between patients younger than 4 years versus older patients. There was no false-negative outcome. Various tendencies were highlighted. There were more true positive alerts for secondary etiologies than for idiopathic ones, for revision spinal surgeries than for index ones, and for boys than for girls. There were no more true positive alerts for children younger than 4 years than for older patients whereas the proportion of hemivertebrae was obviously greater for the younger group. Relevant monitoring alerts were more frequent in case of kyphoscoliosis. This is highlighted in case reports.

CONCLUSION

In some cases of kyphoscoliosis, during a posterior-based vertebral column resection, monitoring changes were corrected by positioning a rod that allowed correction of the position of the spine in the sagittal plane. Intraoperative spinal cord monitoring can be performed in children younger than 4 years and allows real-time assessment of spinal functional integrity.

Neurophysiological changes in deformity correction of adolescent idiopathic scoliosis with intraoperative skull-femoral traction

STUDY DESIGN

Retrospective review of 36 consecutive patients undergoing coronal plane deformity correction with intraoperative skull-femoral traction between 2005 and 2008 with motor evoked potential (MEP)/somatosensory evoked potential monitoring.

OBJECTIVE

To determine the prevalence and significance of neurophysiological changes with intraoperative skull-femoral traction in adolescent idiopathic scoliosis.

SUMMARY OF BACKGROUND DATA

Intraoperative skeletal traction can be associated with spinal cord stretching and ischemia with resultant electrophysiological changes. The prevalence and risks of such changes and their clinical significance is unknown.

METHODS

Thirty-seven procedures involving 36 patients (27 females and 9 males) with a mean age of 14.8 (12-18) years were divided into two groups on the basis of the presence (group 1, n = 18 procedures) or absence (group 2, n = 19) of significant MEP changes with surgery. They were compared with patients undergoing correction without traction (group 3).

RESULTS

Significant differences among the groups were observed in mean preoperative Cobb angle (86° vs. 70° vs. 59°), mean intraoperative posttraction Cobb angle (50.0° vs. 34.6°), traction index (0.41 vs. 0.50), flexibility index (0.14 vs. 0.27 vs. 0.25), and presence of primary lumbar curves (0% vs. 32% vs. 14%). Initial onset of MEP amplitude loss (group 1) occurred at a mean of 94 (1-257) minutes from the onset of surgery, was bilateral in 13 procedures, and improved at a mean of 5.5 (1-29) minutes after decreasing or removing the traction. At closure, complete bilateral recovery to baseline was observed in 10 procedures, recovery to >50% baseline in five, and recovery to <50% baseline in three procedures. There were no neurologic deficits in this series.

CONCLUSION

Intraoperative traction is associated with frequent changes in MEP monitoring. The thoracic location of the major curve, increasing Cobb angle, and rigidity of major curve are significant risk factors for changes in MEP with traction. The presence of any MEP recordings irrespective of its amplitude at closure was associated with normal neurological function. Somatosensory evoked potential monitoring did not correlate with the traction induced MEP amplitude changes.

The contribution of an electronic conductivity device to the safety of pedicle screw insertion in scoliosis surgery

STUDY DESIGN

Retrospective, controlled clinical study.

OBJECTIVE

To evaluate the contribution of an electronic conductivity device (ECD) to the safety of pedicle screw insertion in pediatric scoliosis surgery.

SUMMARY OF BACKGROUND DATA

The implantation of pedicle screws in spinal deformity correction surgery has evolved into the currently predominant fixation technique. Methodologies for optimizing placement of pedicle screws are fluoroscopy, electromyography, and intraoperative image-based navigation. A hand-held ECD was recently introduced.

METHODS

Pedicle screw insertion was analyzed in 248 pediatric scoliosis patients (idiopathic, congenital, neuromuscular, syndromatic). Group I included 150 procedures without the aid of the ECD and group II included 98 ECD-aided procedures. The two groups were matched by age, sex, etiology, Cobb angle, and surgical criteria. Data on screw position and concomitant neuromonitoring alarms were compared. Group I consisted of patients operated with both the hybrid construct and pedicle screw instrumentation, while group II consisted of patients operated solely with pedicle screws. Both groups were operated on by a single surgeon with the same neurophysiologic methodology. Clinically relevant misplaced pedicle screws were established by intraoperative monitoring alarms concomitant with pedicle screw insertion.

RESULTS

A total of 1270 pedicle screw placements were analyzed in group I and compared with 1400 pedicle screw placements in group II. Neuromonitoring alarms concomitant with screw placement occurred in 10 procedures in group I (6.6%) compared with 3 in group II (3.0%). The contribution of the electronic device to reducing the number of neurophysiologic alarms was significant (P = 0.048, Fisher exact test). Nine of the 13 monitoring alarms (69%) were associated with implantation adjacent to the apex of the spinal curve.

CONCLUSION

The use of an ECD significantly reduced the incidence of clinically relevant misplaced screws in a variety of scoliosis patients, thereby increasing the safety of pedicle screw implantation.

Hemivertebra resection in children, results after single posterior approach and after combined anterior and posterior approach: a comparative study

PURPOSE

To compare the results after hemivertebra resection through a single posterior approach and through a combined anterior and posterior approach.

METHODS

This is a retrospective study on patients treated by hemivertebra resection with monosegmental instrumentation for congenital scoliosis at a single institution. The patients were divided into two groups according to the surgical approach. Both groups were compared for curve correction, complication rate and perioperative data. Paired samples T test was used for statistical evaluation.

RESULTS

Twenty-five consecutive patients were included. In 12 cases the hemivertebra resection was performed through a single posterior approach (SPA) and in 13 via a combined anterior and posterior approach (CAPA). Curve correction was similar in both groups (59 vs. 55%, p>0.05). Duration of surgery (272 vs. 319 min) and postoperative mechanical ventilation were shorter in the SPA group (5 vs. 30 h), but did not reach statistical significance (p>0.05). Significant blood loss necessitating blood transfusion was observed in six patients operated through an SPA and in 8 patients operated through a CAPA. The duration of the ICU management (1 vs. 3 days) and the hospital stay (12 vs. 19 days) were significantly shorter in the SPA group (p<0.05). Less surgery related general complications were observed in the SPA group (0 vs. 38%).

CONCLUSIONS

Similar correction of the main and the compensatory curves can be achieved with single posterior and combined anterior and posterior hemivertebra resection. Benefits of the SPA are lower complication rate and shorter recovery period.

Transcranial electric motor evoked potential monitoring during spine surgery: is it safe?

STUDY DESIGN

Retrospective review.

OBJECTIVE

To report on the safety of repetitive transcranial electric stimulation (RTES) for eliciting motor-evoked potentials during spine surgery.

SUMMARY OF BACKGROUND DATA

Theoretical concerns over the safety of RTES have hindered broader acceptance of transcranial electric motor-evoked potentials (tceMEP), despite successful implementation of spinal cord monitoring with tceMEPs in many large spine centers, as well as their apparent superiority over mixed-nerve somatosensory-evoked potentials (SSEP) for detection of spinal cord injury.

METHODS

The records of 18,862 consecutive patients who met inclusion criteria and underwent spine surgery with tceMEP monitoring were reviewed for RTES-related complications.

RESULTS

This large retrospective review identified only 26 (0.14%) cases with RTES-related complications; all but one of these were tongue lacerations, most of which were self-limiting.

CONCLUSIONS

The results demonstrate that RTES is a highly safe modality for monitoring spinal cord motor tract function intraoperatively.

The prevention of neural complications in the surgical treatment of scoliosis: the role of the neurophysiological intraoperative monitoring

Iatrogenic spinal cord injury is the most feared complication of scoliosis surgery. The importance of combined somatosensory evoked potentials (SEP) and motor evoked potentials (MEP) monitoring during spine surgery is well known. The current authors retrospectively evaluated the results of neurophysiological intraoperative monitoring (IOM) in a large population of patients who underwent surgical treatment for spinal deformity. Intraoperative monitoring of SEPs and transcranial electrical stimulation MEPs (TES-MEP) was performed in 172 successive patients who underwent surgical treatment of idiopathic (128 pts), congenital (15 pts) or syndromic (29 pts) scoliosis. The first 106 patients (Group 1) underwent only SEP monitoring, while the other 66 patients (Group 2) underwent combined SEP and TES-MEP monitoring, when the technique was introduced in the current authors' institution. Halogenate anaesthesia (Sevoflurane, MAC 0.6-1.2) was performed in Group 1 cases, total intravenous anaesthesia (Propofol infusion, 6-10 mg/kg/h) in Group 2 patients. A neurophysiological "alert" was defined as a reduction in amplitude (unilateral or bilateral) of at least 50% for SEPs and of 65% for TES-MEPs compared with baseline. In Group 1, two patients (1.9%) developed postoperative neurologic deficits following surgical correction of spinal deformity, consisting of permanent paraparesis in one case and transient paraparesis secondary to spinal cord ischaemia in the other. Twelve patients presented intraoperative significant changes of neurophysiological parameters that improved following corrective actions by surgeons and anaesthesiologists, and did not show any postoperative neurologic deficits. In ten cases the alert was apparently unrelated to surgical manoeuvres or to pharmacological interventions and no postoperative neurologic deficits were noted. Considering the patients of Group 2, two patients (3.0%) presented transient postoperative neurologic deficits preceded by significant intraoperative changes in SEPs and TES-MEPs. In five cases a transient reduction in the amplitudes of SEPs (1 patient) and/or TES-MEPs (5 patients) was recorded intraoperatively with no postoperative neurologic deficits. In conclusion, in the current series of 172 patients the overall prevalence of postoperative neurologic deficit was 2.3% (4 patients). When combined SEP and TES-MEP monitoring was performed, the sensitivity and specificity of IOM for sensory-motor impairment was 100 and 98%, respectively. Combined SEP and TES-MEP monitoring must be regarded as the neurophysiological standard for intraoperative detection of emerging spinal cord injury during corrective spinal deformity surgery. Early detection affords the surgical team an opportunity to perform rapid intervention to prevent injury progression or possibly to reverse impending neurologic sequelae.

Concomitant hypertension, bradycardia, and loss of transcranial electric motor evoked potentials during pedicle hook removal: report of a case

Neurophysiologic monitors in the form of transcranial electric motor evoked potentials (tceMEPs) and somatosensory evoked potentials (SSEPs) have become widely used modalities to monitor spinal cord function during major orthopedic spine procedures. In combination with invasive and non-invasive clinical monitoring and an anesthesia information management system (AIMS), we promptly recognized an acute change in hemodynamic and neurophysiologic parameters, managed intraoperative spinal cord contusion, and successfully minimized iatrogenic injury to the spinal cord during corrective spine surgery.

Successful monitoring of transcranial electrical motor evoked potentials with isoflurane and nitrous oxide in scoliosis surgeries

STUDY DESIGN

This is a case series studying the efficacy of concomitant inhalational anesthesia and transcranial electrical motor-evoked potential (tceMEP) monitoring in spinal deformity surgery.

OBJECTIVE

To determine the affects of inhalational anesthesia on the efficacy of tceMEP monitoring.

SUMMARY OF BACKGROUND DATA

Inhalational agents inhibit transmission of evoked potentials from the motor cortex. Consequently, many authors have recommended using total intravenous anesthesia during motor-evoked potential monitoring.

METHODS

A total of 247 consecutive patients, aged 1 to 83 years (156 patients <22 years), undergoing spinal fusion for scoliosis, excluding those with history of seizure or myelopathy, were monitored with tceMEP intraoperatively. Isoflurane with or without nitrous oxide (per anesthesiologist preference) was administered with vecuronium and i.v. agents including propofol and/or narcotic. Vecuronium was titrated for a goal of 2/4 twitches, and isoflurane was decreased (if necessary) to a maximum level at which tceMEP responses were monitorable (patient specific). Patients were grouped according to whether they received nitrous oxide and the anesthetic depth at which responses were monitored (<0.5, 0.5-0.9, 1-1.4, and >1.5 MAC).

RESULTS

A total of 232 (94%) patients received nitrous oxide. Of these patients, responses were obtained throughout the case in 20 (8.6%) at <0.5 MAC, 118 (50.9%) at 0.5 to 0.9 MAC, 85 (36.6%) at 1 to 1.4 MAC, and 9 (3.9%) at >1.5 MAC. Of the remaining 15 (6%) who received no nitrous oxide, responses were monitored in 3 (20%) at <0.5 MAC, 10 (66.7%) at 0.5 to 0.9 MAC, 2 (13.3%) at 1 to 1.5 MAC, and 0 at >1.5 MAC. No false-positive and 1 true-positive (transient) loss of responses occurred. No operations resulted in postoperative motor deficit.

CONCLUSION

Although isoflurane and nitrous oxide diminish tceMEP responses, reliable monitoring can still be accomplished while using significant levels of inhalational anesthetic agents.

Impact of multimodal intraoperative monitoring during correction of symptomatic cervical or cervicothoracic kyphosis

OBJECT

surgical correction of symptomatic cervical or cervicothoracic kyphosis involves the potential for significant neurological complications. Intraoperative monitoring has been shown to reduce the risk of neurological injury in scoliosis surgery, but it has not been well evaluated during surgery for cervical or cervicothoracic kyphosis. In this article, the authors review a cohort of patients who underwent kyphosis correction with multimodal intraoperative monitoring (MIOM).

METHODS

twenty-nine patients were included in the study. Preoperative and postoperative Cobb angles were measured to determine the extent of correction. Multimodal intraoperative monitoring consisted of somatosensory evoked potentials, transcranial motor evoked potentials (tMEPs), and electromyography activity. Sensitivity, specificity, positive predictive values (PPVs), and negative predictive values (NPVs) were assessed for each monitoring modality.

RESULTS

the mean patient age was 58.0 years, and 20 patients were female. The mean pre- and postoperative sagittal Cobb angles were 41.3° and 7.3°, respectively. A total of 8 intraoperative monitoring alerts were observed. Transcranial MEPs yielded a sensitivity of 75%, specificity of 84%, PPV of 43%, and NPV of 95%. Somatosensory evoked potentials had a sensitivity of 25%, specificity of 96%, PPV of 50%, and NPV of 88%. Electromyography resulted in a sensitivity of 0%, specificity of 93%, PPV of 0%, and NPV of 96%. Changes in tMEPs led to successful intervention in 2 cases. There was 1 case in which a C-8 palsy occurred without any changes in MIOM.

CONCLUSIONS

in contrast to sensitivity and PPV, specificity and NPV were generally high in all 3 monitoring modalities. Both false-positive and false-negative results occurred. Transcranial MEP monitoring was the most useful modality and appeared to allow successful intervention in certain cases. Larger, prospective comparative studies are necessary to determine whether MIOM truly decreases the rate of neurological complications and is therefore worth the added economic cost and intraoperative time.

Establishing a standard of care for neuromonitoring during spinal deformity surgery

STUDY DESIGN

Literature review.

OBJECTIVE

This article presents a critical examination of standard of care (SOC) related to intraoperative neurophysiologic monitoring during spine surgery. Definition of SOC and its applications in the surgical setting is accompanied by discussions on SOC for neuromonitoring, credentialing of neuromonitoring personnel, off-site remote monitoring, and unattended surgeon-controlled neuromonitoring devices.

METHODS

A literature review of neuromonitoring and SOC over the past 10 years was performed. This information, in conjunction with the author's experience and evidence-based medicine, was used to formulate a framework for critique and discussion.

CONCLUSION

An appropriate SOC as it relates to neuromonitoring is difficult to devise because of national variance with regard to qualifications of neurophysiologic technical and professional personnel, different levels of training and certification, and anesthesia protocols. A unified group of surgeons working in collaboration with a multidisciplinary group of experienced doctoral level nonphysician and physician professional surgical neurophysiologists is needed to define a protocol for providing and interpreting such data. In addition to ensuring that only the most qualified and experienced personnel are delivering and/or interpreting neuromonitoring services, surgeons, hospital administrators, and insurance company medical directors need to understand the different service delivery models and their respective strengths and limitations with particular attention to the qualifications and competencies of all respective parties. Only then can a well-defined SOC be established, thus improving the treatment of surgical patients for whom neuromonitoring is required.

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.

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

BACKGROUND CONTEXT

The use of neurophysiologic monitoring during anterior and posterior cervical decompression procedures in patients with spondylotic myelopathy remains controversial. The ideal neurophysiologic monitoring modality of choice is also highly debated.

PURPOSE

The purpose of this study was to evaluate the utility of neurophysiologic monitoring with only somatosensory-evoked potentials (SSEPs) in a consecutive series of laminoplasty procedures with regard to the detection of new postoperative neurologic deficits.

STUDY DESIGN

Retrospective case series.

PATIENT SAMPLE

Eighty consecutive patients who underwent a posterior cervical laminoplasty were reviewed.

OUTCOME MEASURES

We analyzed intraoperative SSEP amplitude and latency changes from baseline with regard to the development of new postoperative neurologic deficits.

METHODS

We retrospectively reviewed 80 patients who underwent a posterior cervical "open-door" laminoplasty with a standard SSEP neurophysiologic monitoring protocol. Intraoperative SSEP amplitude and latency changes from baseline ("alerts") were analyzed with regard to the development of new postoperative neurologic deficits.

RESULTS

Baseline SSEP values were obtained in all patients. There were five (6%) procedures that had SSEP alerts. All alerts occurred shortly after the lamina was hinged open. Four patients with SSEP alerts developed new postoperative neurologic deficits, including three unilateral upper extremity motor and sensory deficits and one complete spinal cord injury. In the immediate postoperative period, our experience with SSEP monitoring demonstrated 4 true-positive, 75 true-negative, and 1 false-positive monitoring results.

CONCLUSIONS

In this series of laminoplasty procedures, SSEP neurophysiologic monitoring had a high sensitivity and specificity for predicting new neurologic deficits in the early postoperative period. Somatosensory-evoked potentials are an effective tool for spinal cord monitoring when performing a posterior cervical laminoplasty procedure.

Validity and reliability of intraoperative monitoring in pediatric spinal deformity surgery: a 23-year experience of 3436 surgical cases

STUDY DESIGN

This was a 23-year retrospective study of 3436 consecutive pediatric orthopedic spinal surgery patients between 1995 and 2008.

OBJECTIVE

To demonstrate the effectiveness of multimodality electrophysiologic monitoring in reducing the incidence of iatrogenic neurologic deficit in a pediatric spinal surgery population.

SUMMARY OF BACKGROUND DATA

The elective nature of many pediatric spinal surgery procedures continues to drive the need for minimizing risk to each individual patient. Electrophysiologic monitoring has been proposed as an effective means of decreasing permanent neurologic injury in this population.

METHODS

A total of 3436 consecutive monitored pediatric spinal procedures at a single institution between January 1985 and September 2008 were reviewed. Monitoring included somatosensory-evoked potentials, descending neurogenic-evoked potentials, transcranial electric motor-evoked potentials, and various nerve root monitoring techniques. Patients were divided into 10 diagnostic categories. True-positive and false-negative monitoring outcomes were analyzed for each category. Neurologic deficits were classified as transient or permanent.

RESULTS

Seven of 10 diagnostic groups demonstrated true positive findings resulting in surgical intervention. Seventy-four (2.2%) potential neurologic deficits were identified in 3436 pediatric surgical cases. Seven patients (0.2%) had false-negative monitoring outcomes. These patients awoke with neurologic deficits undetected by neuromonitoring. Intervention reduced permanent neurologic deficits to 6 (0.17%) patients. Monitoring data were able to detect permanent neurologic status in 99.6% of this population. The ratio of intraoperative events to total monitored cases was 1 event every 42 surgical cases and 1 permanent neurologic deficit every 573 cases.

CONCLUSION

The combined use of somatosensory-evoked potentials, transcranial electric motor-evoked potentials, descending neurogenic-evoked potentials, and electromyography monitoring allowed accurate detection of permanent neurologic status in 99.6% of 3436 patients and reduced the total number of permanent neurologic injuries to 6.

False negative and positive motor evoked potentials in one patient: is single motor evoked potential monitoring reliable method? A case report and literature review

STUDY DESIGN

A case report and literature review.

OBJECTIVE

To report a false negative and delayed positive motor-evoked potential (MEP) in 1 patient.

SUMMARY OF BACKGROUND DATA

An unreliable MEP can result in fatal outcomes because surgeons have recently begun to depend on the MEP for intraoperative decision-making.

METHODS

We report a case of a false MEP during scoliosis surgery that showed false negative and positive MEPs during a series of operations.

RESULTS

A 23-year-old man with a history of spondyloepiphyseal dysplasia presented with severe kyphoscoliosis. The initial neurologic examination did not reveal any neurologic abnormalities. Surgical correction and fusion were performed with transcranial MEP monitoring. During the entire procedure, the MEP did not reveal any signs of cord injury. However, lower limb paralysis and paresthesia was observed when the patient awakened. After 2 additional surgical procedures to recover the neurologic deficit, the MEP did not show any signs of cord injury but the patient's neurologic status had recovered slightly. At postoperative day 8, the neurologic status recovered, and a third operation was performed to fix the long rods. However, there were abnormal amplitudes in both lower limbs but the patient's neurologic status was almost normal.

CONCLUSION

From our experience of false negative and positive MEP in 1 patient, it is concluded that undesirable events can occur with use of MEP in scoliosis or other spinal surgery. Therefore, we warn the surgeons too heavily rely on the MEP monitoring, and propose a further prospective study as well as use of alternative method that can improve the reliability of single MEP.

Bilateral femoral artery ischemia detected by multimodality neuromonitoring during posterior scoliosis surgery: a case report

STUDY DESIGN

Case report.

OBJECTIVE

To report a case of a bilateral femoral artery ischemia detected by neuromonitoring during posterior scoliosis surgery and to review relevant literature regarding this rare complication.

SUMMARY OF BACKGROUND DATA

Lower extremity ischemia is a potentially devastating risk of posterior spinal surgery. Ischemia can be a result of thrombotic occlusion or vascular compression during patient positioning. Multimodality neuromonitoring, increasingly used to prevent neurologic injury, can also detect hypoperfusion to the extremities. To date, there have been no reports of bilateral lower extremity ischemia detected by multimodality neuromonitoring during posterior spine surgery.

METHODS

A 15-year-old boy with adolescent idiopathic scoliosis underwent posterior spinal fusion with instrumentation. Intraoperative changes in somatosensory-evoked potentials and motor-evoked potentials were noted 1 hour into the case, before instrumentation or the reduction maneuver. After trouble shooting methods did not localize a technical cause for the changes, the patient's lower extremities were noted to be hypoperfused and pulseless.

RESULTS

The patients was repositioned and lower extremity perfused improved. Palpable distal pulses were detected. Neuromonitoring signals returned to baseline and the surgery completed. The patient had no postoperative neurologic or vascular deficits.

CONCLUSION

Lower extremity ischemia secondary to prone positioning is a rare risk of posterior spinal surgery. This is the first case report of this potentially devastating, but preventable complication detected by multimodality neuromonitoring.

Role of motor-evoked potential monitoring in conjunction with temporary clipping of spinal nerve roots in posterior thoracic spine tumor surgery

BACKGROUND CONTEXT

The vascular supply of the thoracic spinal cord depends on the thoracolumbar segmental arteries. Because of the small size and ventral course of these arteries in relation to the dorsal root ganglion and ventral root, they cannot be reliably identified during surgery by anatomic or morphologic criteria. Sacrificing them will most likely result in paraplegia.

PURPOSE

The goal of this study was to evaluate a novel method of intraoperative testing of a nerve root's contribution to the blood supply of the thoracic spinal cord.

STUDY DESIGN/SETTING

This is a clinical retrospective study of 49 patients diagnosed with thoracic spine tumors. Temporary nerve root clipping combined with motor-evoked potential (MEP) and somatosensory-evoked potential (SSEP) monitoring was performed; additionally, postoperative clinical evaluation was done and reported in all cases.

METHODS

All cases were monitored by SSEP and MEPs. The nerve root to be sacrificed was temporarily clipped using standard aneurysm clips, and SSEP/MEP were assessed before and after clipping. Four nerve roots were sacrificed in four cases, three nerve roots in eight cases, and two nerve roots in 22 cases. Nerve roots were sacrificed bilaterally in 12 cases.

RESULTS

Most patients (47/49) had no changes in MEP/SSEP and had no neurological deficit postoperatively. One case of a spinal sarcoma demonstrated changes in MEP after temporary clipping of the left T11 nerve root. The nerve was not sacrificed, and the patient was neurologically intact after surgery. In another case of a sarcoma, MEPs changed in the lower limbs after ligation of left T9 nerve root. It was felt that it was a global event because of anesthesia. Postoperatively, the patient had complete paraplegia but recovered almost completely after 6 months.

CONCLUSIONS

Temporary nerve root clipping combined with MEP and SSEP monitoring may enhance the impact of neuromonitoring in the intraoperative management of patients with thoracic spine tumors and favorably influence neurological outcome.

The evidence for intraoperative neurophysiological monitoring in spine surgery: does it make a difference?

OBJECTIVE

The objective of this article was to undertake a systematic review of the literature to determine whether IOM is able to sensitively and specifically detect intraoperative neurologic injury during spine surgery and to assess whether IOM results in improved outcomes for patients during these procedures.

SUMMARY AND BACKGROUND DATA

Although relatively uncommon, perioperative neurologic injury, in particular spinal cord injury, is one of the most feared complications of spinal surgery. Intraoperative neuromonitoring (IOM) has been proposed as a method which could reduce perioperative neurologic complications after spine surgery.

METHODS

A systematic review of the English language literature was undertaken for articles published between 1990 and March 2009. MEDLINE, EMBASE, and Cochrane Collaborative Library databases were searched, as were the reference lists of published articles examining the use of IOM in spine surgery. Two independent reviewers assessed the level of evidence quality using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) criteria, and disagreements were resolved by consensus.

RESULTS

A total of 103 articles were initially screened and 32 ultimately met the predetermined inclusion criteria. We determined that there is a high level of evidence that multimodal IOM is sensitive and specific for detecting intraoperative neurologic injury during spine surgery. There is a low level of evidence that IOM reduces the rate of new or worsened perioperative neurologic deficits. There is very low evidence that an intraoperative response to a neuromonitoring alert reduces the rate of perioperative neurologic deterioration.

CONCLUSION

Based on strong evidence that multimodality intraoperative neuromonitoring (MIOM) is sensitive and specific for detecting intraoperative neurologic injury during spine surgery, it is recommended that the use of MIOM be considered in spine surgery where the spinal cord or nerve roots are deemed to be at risk, including procedures involving deformity correction and procedures that require the placement of instrumentation. There is a need to develop evidence-based protocols to deal with intraoperative changes in MIOM and to validate these prospectively.

Major intraoperative neurologic monitoring deficits in consecutive pediatric and adult spinal deformity patients at one institution

STUDY DESIGN

Retrospective review.

OBJECTIVE

The purpose of this study was to assess the preoperative neurologic risk in a consecutive series of spinal deformity patients undergoing correction surgery at one institution.

SUMMARY OF BACKGROUND DATA

During spinal deformity correction surgery, neurologic monitoring techniques are commonly applied to reduce the risk of neurologic deficits. While previous studies have demonstrated risk factors for neurologic changes in the setting of spinal surgery, these involved long time spans and heterogeneous patient populations.

METHODS

Of 301 cases performed over 1 year, 281 cases were monitorable. Patients were grouped according to diagnosis: neuromuscular (NM) scoliosis, Sagittal Plane deformity, and Scoliosis. Demographic and surgical data were collected for neurologically monitorable patients. Coronal and sagittal parameters were measured using digital images of radiographs. Neurologic status was measured with somatosensory-evoked potentials and/or motor-evoked potentials.

RESULTS

Primary NM scoliosis cases had the highest incidence of neurologic monitoring changes (NMC) (10%) while revision sagittal plane deformity had the second highest (9.8%). Sensitivity and specificity were both 100%. Overall incidence of neurologic deficit was 1.1%. Of the 13 NMCs patients, 3 patients had persistent neurologic deficit. Majority of NMCs occurred before deformity correction. In patients with NM scoliosis, NMCs increased with hybrid constructs with wires (P < 0.01). In patients with scoliosis, NMCs increased with increased body mass index, estimated blood loss, operative time, and postoperative coronal thoracolumbar curve magnitude (P < 0.04). In patients with primarily sagittal plane deformity, NMCs increased with preoperative proximal curve, postoperative proximal and thoracolumbar curves, and postoperative kyphosis and lordosis (P < 0.04).

CONCLUSION

Primary NM scoliosis and revision sagittal plane deformities appear to carry greatest incidence of NMCs during surgical intervention. Most observed NMCs did not result in a permanent neurologic deficit. Neuromonitoring should be assessed throughout the entire surgical procedure. This study may aid surgeons and patients to better assess neurologic risks related to spinal deformity surgery.

Multimodal intraoperative neuromonitoring in corrective surgery for adolescent idiopathic scoliosis: Evaluation of 354 consecutive cases

BACKGROUND

Multimodal intraoperative neuromonitoring is recommended during corrective spinal surgery, and has been widely used in surgery for spinal deformity with successful outcomes. Despite successful outcomes of corrective surgery due to increased safety of the patients with the usage of spinal cord monitoring in many large spine centers, this modality has not yet achieved widespread popularity. We report the analysis of prospectively collected intraoperative neurophysiological monitoring data of 354 consecutive patients undergoing corrective surgery for adolescent idiopathic scoliosis (AIS) to establish the efficacy of multimodal neuromonitoring and to evaluate comparative sensitivity and specificity.

MATERIALS AND METHODS

The study group consisted of 354 (female = 309; male = 45) patients undergoing spinal deformity corrective surgery between 2004 and 2008. Patients were monitored using electrophysiological methods including somatosensory-evoked potentials and motor-evoked potentials simultaneously.

RESULTS

Mean age of patients was 13.6 years (+/-2.3 years). The operative procedures involved were instrumented fusion of the thoracic/lumbar/both curves, Baseline somatosensory-evoked potentials (SSEP) and neurogenic motor-evoked potentials (NMEP) were recorded successfully in all cases. Thirteen cases expressed significant alert to prompt reversal of intervention. All these 13 cases with significant alert had detectable NMEP alerts, whereas significant SSEP alert was detected in 8 cases. Two patients awoke with new neurological deficit (0.56%) and had significant intraoperative SSEP + NMEP alerts. There were no false positives with SSEP (high specificity) but 5 patients with false negatives with SSEP (38%) reduced its sensitivity. There was no false negative with NMEP but 2 of 13 cases were false positive with NMEP (15%). The specificity of SSEP (100%) is higher than NMEP (96%); however, the sensitivity of NMEP (100%) is far better than SSEP (51%). Due to these results, the overall sensitivity, specificity and positive predictive value of combined multimodality neuromonitoring in this adult deformity series was 100, 98.5 and 85%, respectively.

CONCLUSION

Neurogenic motor-evoked potential (NMEP) monitoring appears to be superior to conventional SSEP monitoring for identifying evolving spinal cord injury. Used in conjunction, the sensitivity and specificity of combined neuromonitoring may reach up to 100%. Multimodality monitoring with SSEP + NMEP should be the standard of care.

Thoracolumbar spinal deformity: Part II. Developments from 1990 to today: historical vignette

In the first part of this 2-part historical review, the authors outlined the early diagnostic and therapeutic strategies used in the management of spinal deformity. In this second part, they expand upon those early innovations and further detail the advances from 1990 to the modern era.

Neurologic risk in growing rod spine surgery in early onset scoliosis: is neuromonitoring necessary for all cases?

STUDY DESIGN

Retrospective case series from a multicenter database.

OBJECTIVE

To evaluate the risk of neurologic injury during growing rod surgeries and to determine whether intraoperative neuromonitoring is necessary for all growing rod procedures.

SUMMARY OF BACKGROUND DATA

Although the use of growing rod constructs for early-onset spinal deformity has become a commonly accepted treatment, the incidence of neurologic events during growing rod surgeries remains unknown.

METHODS

We reviewed data from a multicenter database on 782 growing rod surgeries performed in 252 patients. VEPTR devices and any constructs with rib attachments were excluded. A questionnaire was sent to all surgeons contributing cases requesting detailed information about all neurologic events associated with any growing rod surgery.

RESULTS

There were 782 growing rod surgeries performed on 252 patients including 252 primary growing rod implantations, 168 implant exchanges, and 362 lengthenings. Five hundred sixty-nine of 782 (73%) cases were performed with neuromonitoring. Only one clinical injury occurred in the series, resulting in an injury rate of 0.1% (1/782). This deficit occurred during an implant exchange while attempting pedicle screw placement, and resolved within 3 months. There were 2 cases with neuromonitoring changes during primary implant surgeries (0.9%, 2/231), 1 change during implant exchanges (0.9%, 1/116), and 1 neuromonitoring change during lengthenings (0.5%, 1/222). The single monitoring change that occurred during a lengthening was in a child with an intracanal tumor who also had a monitoring change during the primary surgery. There are anecdotal cases (outside this study group series) of neuromonitoring changes during simple lengthenings in children with uneventful primary implantations.

CONCLUSION

Based on our study, the largest reported series of growing rod surgeries, the rate of neuromonitoring changes during primary growing rod implantation (0.9%) and exchange (0.9%) justifies the use of intraoperative neuromonitoring during these surgeries. As there were no neurologic events in 361 lengthenings in patients with no previous neurologic events, the question may be raised as to whether intraoperative neuromonitoring is necessary for simple lengthenings in these patients. However, caution should be maintained when interpreting our results as anecdotal cases of neurologic changes from simple lengthenings do exist outside of this series.

Instrumentation and fusion for congenital spine deformities

STUDY DESIGN

A retrospective clinical review.

OBJECTIVE

To review the use of modern instrumentation of the spine for congenital spinal deformities.

SUMMARY OF BACKGROUND DATA

Spinal instrumentation has evolved since the advent of the Harrington rod. There is a paucity of literature, which discusses the use of modern spinal instrumentation in congenital spine deformity cases. This review focuses on modern instrumentation techniques for congenital scoliosis and kyphosis.

METHODS

A systematic review was performed of the literature to discuss spinal implant use for congenital deformities.

RESULTS

Spinal instrumentation may be safely and effectively used in cases of congenital spinal deformity.

CONCLUSION

Spinal surgeons taking care of children with congenital spine deformities need to be trained in all aspects of modern spinal instrumentation.

Neurologic injury in the surgical treatment of idiopathic scoliosis: guidelines for assessment and management

Iatrogenic spinal cord injury resulting from surgical treatment of spinal deformity is a relatively uncommon but devastating complication. Publications on the prevalence of spinal cord injury following surgery are numerous, but no definitive review with clinically pertinent treatment guidelines exists. Methods to reduce the risk of neurologic complications with scoliosis surgery include adequate patient evaluation and preoperative planning, intraoperative preparation, intraoperative neuromonitoring, and postoperative management. Treatment algorithms may be useful in the clinical setting to manage intraoperative or postoperative neurologic injury.

Monitoring of nerve root injury using transcranial motor-evoked potentials in a pig model

STUDY DESIGN

Animal experiment using transcranial motor-evoked potentials (tcMEPs) in a pig model.

OBJECTIVE

To validate measurement of tcMEPs from multiple myotomes in a pig model and determine the capacity to detect injury to a single nerve root.

SUMMARY OF BACKGROUND DATA

The ability of intraoperative neuromonitoring methods to give information about a single nerve root remains poorly understood. Reports suggest that tcMEPs may be a reliable and accurate method to detect nerve root injury. An animal model to study the sensitivity and specificity of this technique has yet to be validated.

METHODS

Transcranial stimulation was delivered through customized electrodes placed in burr holes over the motor cortex in 7 pigs. Spontaneous and evoked muscle potential activity was recorded in 5 myotomes (rectus femoris, vastus lateralis, vastus medialis, tibialis anterior, and gastrocnemius) bilaterally. After unilateral exposure of the L3-S1 nerve roots, sequential ligations were performed. The tcMEP responses from all myotomes were measured after ligation of each nerve root.

RESULTS

Robust MEP responses (range, 37-1165 mV) were achieved in all monitored myotomes. Significant decreases in tcMEP amplitudes occurred in specific myotomes after ligation of the corresponding nerve root. Consistent and substantial decreases were observed after L3 and L5 ligations in rectus femoris (48%) and tibialis anterior (67%), respectively.

DISCUSSION

Our results validate monitoring of tcMEPs in multiple myotomes to detect nerve root injury in pigs. This model may be used for further study of the use of tcMEPs to detect predictors and risk factors of nerve root injury during spinal surgery.