Intraoperative neuromonitoring: lessons learned from 32 case events in 2095 spine cases

Clinical Correlation of Intraoperative Neuromonitoring in 319 Individuals Undergoing Posterior Decompression and Fixation of Spine

STUDY DESIGN

This was a prospective study.

OBJECTIVES

To correlate improvement in motor evoked potential (MEP) during spine surgery with postoperative clinical improvement.

MATERIALS AND METHODS

Three hundred fifty-three patients operated for posterior spinal decompression and fixation surgeries were prospectively selected and followed up. Patients who underwent lumbar, dorsal, and cervical surgeries were grouped into-group A, B, and C, respectively. Intraoperative neuromonitoring was done using MEP with free-running electromyography. Improvements in MEP scores were calculated in percentage. Similarly, postoperative improvement in Oswestry disability index (ODI) and visual analog scale (VAS) scores at 3 months were calculated in percentage. Improvements in MEP scores were correlated with clinical improvement using the Spearman ρ test and the r value was calculated to find out the association.

RESULTS

Of 353 patients, 319 (250-group A, 38-group B, and 31-group C) were included for the study. VAS and ODI improved significantly from preoperative 8.5±0.8 and 62.9±14.5, to postoperative 2.3±1.1 and 15.9±11.5, respectively, in the entire group. Average preoperative MEP were 127.8±191.0 mV on the right side and 132.3±206.6 mV on the left side, which significantly improved to 163.7±231.2 mV (P=0.0001) and 155.2±219.6 mV (P=0.0001), respectively, showing 157.0% and 178.5% improvement. Correlating MEP improvement with postoperative improvement in ODI showed poor correlation (r=0.088 right and 0.030 left sides). Similarly, correlating MEP improvement with improvement in VAS showed r=0.110 on the right and -0.023 on the left side suggesting poor correlation. Postoperative neurological complications (0.56%) were found in 2 patients in the form of screw malpositioning.

CONCLUSIONS

Intraoperative neuromonitoring showed significant improvement during posterior decompression and fixation surgery, and reduction in postoperative neurological complication. The study also exhibited significant postoperative clinical improvement. However, improvement in MEP did not correlate with postoperative clinical improvement suggesting that it has no predictive role.

Utility of neuromonitoring during lumbar pedicle subtraction osteotomy for adult spinal deformity

OBJECTIVE

The benefits and utility of routine neuromonitoring with motor and somatosensory evoked potentials during lumbar spine surgery remain unclear. This study assesses measures of performance and utility of transcranial motor evoked potentials (MEPs) during lumbar pedicle subtraction osteotomy (PSO).

METHODS

This is a retrospective study of a single-surgeon cohort of consecutive adult spinal deformity (ASD) patients who underwent lumbar PSO from 2006 to 2016. A blinded neurophysiologist reviewed individual cases for MEP changes. Multivariate analysis was performed to determine whether changes correlated with neurological deficits. Measures of performance were calculated.

RESULTS

A total of 242 lumbar PSO cases were included. MEP changes occurred in 38 (15.7%) cases; the changes were transient in 21 cases (55.3%) and permanent in 17 (44.7%). Of the patients with permanent changes, 9 (52.9%) had no recovery and 8 (47.1%) had partial recovery of MEP signals. Changes occurred at a mean time of 8.8 minutes following PSO closure (range: during closure to 55 minutes after closure). The mean percentage of MEP signal loss was 72.9%. The overall complication rate was 25.2%, and the incidence of new neurological deficits was 4.1%. On multivariate analysis, MEP signal loss of at least 50% was not associated with complication (p = 0.495) or able to predict postoperative neurological deficits (p = 0.429). Of the 38 cases in which MEP changes were observed, the observation represented a true-positive finding in only 3 cases. Postoperative neurological deficits without MEP changes occurred in 7 cases. Calculated measures of performance were as follows: sensitivity 30.0%, specificity 84.9%, positive predictive value 7.9%, and negative predictive value 96.6%. Regarding the specific characteristics of the MEP changes, only a signal loss of 80% or greater was significantly associated with a higher rate of neurological deficit (23.0% vs 0.0% for loss of less than 80%, p = 0.021); changes of less than 80% were not associated with postoperative deficits.

CONCLUSIONS

Neuromonitoring has a low positive predictive value and low sensitivity for detecting new neurological deficits. Even when neuromonitoring is unchanged, patients can still have new neurological deficits. The utility of transcranial MEP monitoring for lumbar PSO remains unclear but there may be advantages to its use.

Prone Position-Induced Quadriceps Transcranial Motor Evoked Potentials Signal Loss-A Case Report

BACKGROUND

Transcranial motor evoked potential (TcMEP) is widely used intraoperatively to monitor spinal cord and nerve root function. To our knowledge, there is no report regarding TcMEP signal loss purely caused by patient positioning during the spinal procedure.

PURPOSE

The objective of this article is to report an intraoperative TcMEP signal loss of a patient with fixed sagittal imbalance posture along with mild hip contractures.

STUDY DESIGN

A retrospective case report.

METHODS

A 57-year-old man had fixed sagittal imbalance and flexed hip contractures. For a reconstruction surgery of T10 to the sacrum/ilium and L5 pedicle subtraction osteotomy (PSO), he was put in a prone position on a Jackson table. In order to accommodate his fixed hip flexion contracture, thigh pads were not used and pillows were placed under his bilateral thighs for cushioning. TcMEPs were used to assess lumbar nerve root function. Ten minutes after incision, bilateral vastus medialis TcMEPs were lost during spine exposure whereas all other data remained normal at baseline. The bilateral lower extremities were repositioned, with the knees flexed into a sling position to increase hip flexion. Five minutes after repositioning, the bilateral vastus medialis TcMEPs gradually improved and maintained baseline amplitude during the remainder of the surgery.

RESULTS

No muscle weakness was detected immediately after surgery. The patient was discharged day 6 postoperatively with markedly improved posture and alignment.

CONCLUSION

Insufficient hip flexion in patients with fixed sagittal imbalance and hip flexion contractures may cause TcMEP signal changes in the quadriceps response. TcMEP monitoring of bilateral lower extremities is highly recommended for patients with sagittal imbalance and hip contractures, with consideration for lower extremity repositioning when data degradation does not correlate with the actual spinal procedure being performed.

Risk Factor Analysis of Change in Intraoperative Neurophysiologic Monitoring During Cervical Open Door Laminoplasty

OBJECTIVE

The aim of this study is to determine the risk factors affecting intraoperative neurophysiologic monitoring (IONM) changes, when such changes take place, and clinical outcomes associated with IONM change during cervical open door laminoplasty (COL) for cervical compressive myelopathy.

METHODS

Between 2010 and 2015, 79 patients who underwent COL with IONM recording were studied. Changes in motor evoked potentials or somatosensory evoked potentials over an alarm criterion were defined as IONM change. Patients with IONM change were assigned to the alarm group, and the others were classified as the control group. Baseline data and radiographic measurements were compared between the 2 groups. Radiologic parameters including maximal compression level (MCL), area and diameter of the spinal canal and ventral compressive lesion, stenosis grade, and occupying ratio of area (ORA) and length at the MCL were measured with magnetic resonance imaging.

RESULTS

Thirteen patients were assigned to the alarm group and 66 patients were assigned to the control group. Multivariate analysis identified ORA at the MCL (odds ratio, 1.520; 95% confidence interval, 1.192-1.37; P = 0.001) as an independent risk factor for IONM change. Immediately after decompression, the IONM change occurred. One of 4 patients who did not fully recover from the IONM change had postoperative motor deficits.

CONCLUSIONS

IONM change during COL occurred immediately after decompression, and a risk factor of IONM change was ORA at the MCL. If the IONM change was not fully recovered, a new motor deficit occurred after COL.

Benefit of Intraoperative Neurophysiological Monitoring in a Pediatric Patient with Spinal Dysmorphism, Split Cord Malformation, and Scoliosis

Intraoperative neurophysiological monitoring (IONM) consists of a group of neurodiagnostic techniques that assess the nervous system's functional integrity during surgical operations. A retrospective analysis of a pediatric female patient was conducted who underwent 12 operations for the correction of scoliosis, tethered cord, and split spinal cord wherein IONM played an important role. From age 3 to 6, she underwent six procedures including a release of the tethered cord, resection of the filum terminale, removal of a T11-T12 bony spur, release of L3 adhesions, repair of subcutaneous meningocele, and correction of scoliosis with a vertical expandable prosthetic titanium rod (VEPTR) technique without the use of IONM. However, a multimodality IONM protocol with somatosensory evoked potentials, transcranial electrical motor evoked potentials (TCeMEP), and an electromyogram was utilized during the later procedures. At age 6 (the seventh procedure), a VEPTR expansion was performed, with loss and recovery of the lower extremity motor evoked potentials. The postoperative magnetic resonance imaging (MRI) showed a partial split cord malformation with retethering of the spinal cord. We repaired her split cord malformation and tethered cord while employing IONM. Using IONM for her operation was crucial because a sudden significant loss of TCeMEP resulted in a cancellation of the procedure; the MRI showed a thick remnant attached to the spinal cord. If the procedure was performed without IONM, we could have missed the underlying pathology, an error that may have resulted in paraplegia. We strongly recommend using IONM during high-risk surgical procedures to help significantly reduce the risk of permanent postoperative complications.

Why No Signals? Cerebral Anatomy Predicts Success of Intraoperative Neuromonitoring During Correction of Scoliosis Secondary to Cerebral Palsy

BACKGROUND

Intraoperative neuromonitoring (IONM) is widely used to reduce postoperative neurological complications during scoliosis correction. IONM allows intraoperative detection of neurological insults to the spinal cord and enables surgeons to react in real time. IONM failure rates can reach 61% in patients with cerebral palsy (CP). Factors decreasing the quality of IONM signals or making IONM impossible in CP patients undergoing scoliosis correction have not been well described.

METHODS

We categorized IONM data from 206 children with CP who underwent surgical scoliosis correction at a single institution from 2002 through 2013 into 3 groups: (1) "no signals," if neither somatosensory-evoked potentials (SSEP) nor transcranial motor-evoked potentials (TcMEP) could be obtained; (2) "no sensory," if no interpretable SSEP were obtained regardless of interpretable TcMEP; and (3) "no motor," if no interpretable TcMEP were obtained regardless of interpretable SSEP. We analyzed preexisting neuroimaging, available for 93 patients, and neurological status of the full cohort against these categories. Statistical analysis of univariate and multivariate associations was performed using logistic regression. Odds ratios (ORs) were calculated with significance set at P<0.05.

RESULTS

Multivariate analysis showed significant associations of periventricular leukomalacia (PVL), hydrocephalus, and encephalomalacia with lack of meaningful and interpretable signals. Focal PVL (Fig. 1) was associated with no motor (OR=39.95; P=0.04). Moderate hydrocephalus was associated with no signals (OR=32.35; P<0.01), no motor (OR=10.14; P=0.04), and no sensory (OR=8.44; P=0.03). Marked hydrocephalus (Fig. 2) was associated with no motor (OR=20.46; P<0.01) and no signals (OR=8.83; P=0.01). Finally, encephalomalacia (Fig. 3) was associated with no motor (OR=6.99; P=0.01) and no signals (OR=4.26; P=0.03).

CONCLUSION

Neuroanatomic findings of PVL, hydrocephalus, and encephalomalacia are significant predictors of limited IONM signals, especially TcMEP.

LEVEL OF EVIDENCE

Level IV.

Multimodal Neuromonitoring During Safe Surgical Dislocation of the Hip for Joint Preservation: Feasibility, Safety, and Intraoperative Observations

Introduction:

Nerve injuries can occur from major hip surgeries, and some may be significant. Our goal was to assess the feasibility and safety of neuromonitoring during hip preservation surgery and the incidence of alerting events during such monitoring.

Methods:

Twenty-five adult patients underwent surgical hip dislocation for femoroacetabular impingement. Upper and lower extremity somatosensory evoked potentials, lower extremity transcranial motor evoked potentials, and lower extremity electromyography were recorded.

Results:

We observed a temporary reduction of the monitored parameters in twelve patients (48%) during surgery. There were no clinically significant neurological deficits postoperatively in any cases.

Discussion:

Neuromonitoring did demonstrate events during hip surgery in our case series. Although it may not be practical to use neuromonitoring in all major hip surgeries, it may be prudent from the perspective of patient safety to use it in high-risk cases, including those requiring prolonged surgical time; in patients with high body mass index, excessive deformity correction, and preexisting neuropathy; and in revision cases, among others.

Intraoperative Use of Neuromonitoring in Multilevel Thoracolumbar Spine Instrumentation and the Effects on Postoperative Neurological Injuries

STUDY DESIGN

Retrospective cohort analysis of a national database between 2005 and 2011.

OBJECTIVE

To investigate the current usage of neuromonitoring in patients undergoing multilevel thoracolumbar spine surgery. We hypothesize that the use of neuromonitoring would be associated with a reduced incidence of postoperative neurological injuries.

SUMMARY OF BACKGROUND DATA

Intraoperative neuromonitoring is a common technique utilized in spine surgery to improve safety and reduce neurological injuries. However, the literature remains unclear in defining the populations that benefit from the use of neuromonitoring.

METHODS

The PearlDiver Medicare database was queried to identify patients undergoing multilevel thoracolumbar spine instrumentation (defined as >3 thoracolumbar levels) from 2005 to 2011. The use of neuromonitoring was identified by Current Procedural Terminology codes. Neurological injuries were identified by codes from the International Classification of Diseases, Ninth Revision.

RESULTS

Within 15,032 patients, the postoperative rate of neurological injury diagnosis was higher when neuromonitoring was used at both 1 week (1.3% vs. 1.0%, P=0.06) and 6 months (5.9% vs. 4.6%, P=0.0005). However, a lower incidence of neurological injury was associated with neuromonitoring in patients undergoing specifically anterior fusion of 4-7 levels, posterior fusion of 7-12 levels, and in adults below 65 years old (P=0.0266, 0.0458, 0.032).

CONCLUSION

Within the total Medicare cohort, the use of neuromonitoring was not associated with a decreased rate of neurological injury in multilevel thoracolumbar instrumentation procedures. This is likely due to the possible selection and detection bias of utilizing neuromonitoring when there is an increased risk of neurological injury based on patient-specific pathology and/or surgical procedure. However, despite the overall potential bias, it was appreciated that in subgroups: age below 65 years old, anterior fusion of 4-7 segments, and posterior fusion of 7-12 segments, there was a statistically significant reduction in the incidence of neurological injuries with neuromonitoring.

LEVEL OF EVIDENCE

Level III.

Intraoperative Neurophysiological Monitoring (IONM) for Cordotomy Procedures

This case illustrates the benefits of utilizing intraoperative neurophysiological monitoring (IONM) for preventing injury to sensory/motor pathways of the spinal cord during a cordotomy procedure to relieve pain. Cordotomy has been used effectively in the treatment of visceral pain but comes with a high risk of damaging motor and sensory pathways due to close proximity of lesion. The subject is a 47-year-old female with a pancoast tumor of the left lung, left brachialplexopathy, and severe neuropathic pain syndrome, refractory to medical therapy. A palliative cordotomy procedure was elected for pain control. Baseline bilateral posterior tibial and median nerve somatosensory evoked potentials (SSEP) were present except in the left upper extremity. Transcranial electric motor evoked potential (TCeMEP) baselines were present in all extremities except the left upper. Total intravenous anesthesia was used. The spine was exposed at C2-C3 and a right single anterolateral cordotomy was performed with an immediate drop in TCeMEPs (70-80% amplitude reduction) in the right upper and right lower extremities. The surgeon decided to stop the cordotomy at that point. Postoperatively, the patient had no sensory or motor deficit. In this patient, TCeMEPs were used effectively to guide the surgeon in preventing damage to the spinal cord that could lead to motor deficits.

Early detection of pedicle screw-related spinal cord injury by continuous intraoperative neurophysiological monitoring (IONM)

Pedicle screw placement has a high risk of damaging the motor and sensory pathways due to the close proximity to the spinal cord and nerve roots. Early detection and prevention of injury can be achieved by utilizing Somatosensory Evoked Potentials (SSEP) and Transcranial electrical Motor Evoked Potentials (TCeMEP) during a scoliosis surgery. A 19-year-old female presented for correction of scoliosis. After intubation, electrodes were placed for upper and lower SSEPs, EMGs and TCeMEPs. Total intravenous anesthesia was used. Baseline SSEP and TCeMEP responses were present in all limbs. Eight pedicle screws were placed. After placing the last screw, TCeMEP signals were lost bilaterally in lower extremities. Surgery was paused. After removing all the screws TCeMEP responses returned to baseline in left lower limb but remained absent in right lower limb. A wake-up test was performed which was positive in her right leg. Blood pressure was increased and bolus of steroids was given. There was no improvement in right lower limb TCeMEP responses. Surgeon was advised to stop the surgery and proceed for MRI and follow-up. SSEP signals remained stable in all four-extremities. The surgical correction was cancelled. MRI revealed intramedullary spinal cord ischemic changes at T11. After extubation, patient was unable to move her right lower extremity with flaccid paralysis. She also complained about severe burning in her left lower extremity. The patient was taken for rehabilitation exercises. One week post-op, she was moving hip flexors and two weeks later had afull motor function, bilaterally. Real-time IONM was useful in early identification of spinal cord injury. Significant changes were seen in TCeMEP, without any change in SSEP. We highly recommend utilizing continuous TCeMEP and SSEP monitoring during pedicle screw placement for prevention of injury to the spinal cord. In this case, the patient would have been paralyzed post-operatively without the use of IONM.