Monitoring superficial peroneal nerve somatosensory evoked potential during L4-5 lumbar root decompression

Neuromonitoring for Proximal Fibular Osteochondroma Excision

BACKGROUND

The peroneal nerve is at risk when excising tumors in the proximal fibula. The rate of nerve injuries during proximal fibular tumor resection varies from 3% to 20%. Our goal was to report our experience with resection of osteochondromas in the proximal fibula and describe the technique and utility of neuromonitoring during excision of proximal fibular osteochondromas (PFO).

METHODS

Patients with a diagnosis of symptomatic PFO who had undergone excision at one institution from 1994 to 2018 were included. An institutional review board-approved retrospective review was performed. Intraoperative neuromonitoring was provided from 2006 on by a single group utilizing a multimodality protocol.

RESULTS

This study contains 29 patients who had excision of osteochondromas in the proximal fibula. Of these 29 consecutively monitored patients, there were 34 involved extremities. Intraoperative neuromonitoring alerts occurred in 10/29 (34.5%) procedures, which included 3 electromyography (EMG) (30%), 2 motor-evoked potential (20%), 1 somatosensory-evoked potential (10%), and 4 alerts with a combination of EMG/motor-evoked potential/somatosensory-evoked potential changes (40%). The interventions that were taken resulted in resolution of the neuromonitoring changes in all procedures. Postoperatively, we noted 2 (6.9%) new mild sensory deficits, which resolved during follow up. There were 3 patients in whom pre-existing sensory-motor deficits improved but not completely after surgery, 1 motor weakness, and 2 with residual paresthesia. In those initially presenting with paresis, there was improvement in 8 of the 8 extremities by the last follow-up visit. Pain as a symptom was resolved in all cases. There were no iatrogenic foot drop injuries. The average follow up was 32.2 months.

CONCLUSIONS

Neuromonitoring during PFO excision demonstrated a high number of alerts, all of which resolved following timely corrective action. The use of neuromonitoring may help decrease the risk of iatrogenic postoperative neurological deficits following fibular osteochondroma surgery.

LEVEL OF EVIDENCE

Level IV.

Dermatomal somatosensory evoked potentials and cortical somatosensory evoked potentials assessment in congenital scoliosis

Background

The aim of this study was to assess the value of dermatomal somatosensory evoked potentials (DSEPs) and cortical somatosensory evoked potentials (SSEPs) in monitoring spinal cord function for patients with congenital scoliosis (CS).

Methods

This retrospective study reviewed the medical records of patients (n = 102) who underwent DSEP (T2-S1 dermatome), of whom 60 were normal subjects and 62 with congenital scoliosis. The study analyzed the latencies and peaks of N1-L, N1-R, P1-L and P1-R recorded by DSEPs of patients’ thoracolumbar dermatomes. To observe the incidence of abnormal DSEPs and SSEPs in CS patients and to analyze the difference in sensitivity and reliability between the two in the examination of scoliosis patients. SPSS 22.0 statistical software package was used to analyze the data, and χ2 test and correlation analysis were used to indicate that the difference was statistically significant, p < 0.05.

Results

Sixty two patients with CS were evaluated with total spine magnetic resonance imaging (MRI). Only 23 patients (37.09%) showed spinal cord malformations in the MRI findings. The DSEP recordings showed a relatively high sensitivity (97.8%) compared to the abnormality rate of SSEPs recordings, and the rates of waveform, latency and amplitude abnormalities were much higher in DSEPs recordings (36.6, 36.3, 24.8%) than in SSEPs recordings (3.2, 22.5, 14.5%). The abnormality rate of DSEP records with and without neurological symptoms was higher than the abnormality rate of SSEP records (100% vs 20, 96.2% vs 44.2%, p<0.05). And in 62 patients with CS, the rate of positive MRI (37.1%) was lower than that recorded by DSEP (79.6% / 57.9%). p < 0.05.

Conclusion

DSEPs are more sensitive to microscopic posterior column dysfunction in patients with CS that cannot be detected by either radiology or routine clinical examination. Preoperative DSEPs assessment is recommended as a baseline examination for intraoperative monitoring and comparison with the postoperative situation. DSEPs recording complements the information obtained from routine clinical and radiological evaluation.

Diagnostic Accuracy of SSEP Changes During Lumbar Spine Surgery for Predicting Postoperative Neurological Deficit: A Systematic Review and Meta-Analysis

STUDY DESIGN

This study is a meta-analysis of prospective and retrospective studies identified in PubMed, Web of Science, and Embase with outcomes of patients who received intraoperative somatosensory-evoked potential (SSEP) monitoring during lumbar spine surgery.

OBJECTIVE

The objective of this study is to determine the diagnostic accuracy of intraoperative lower extremity SSEP changes for predicting postoperative neurological deficit. As a secondary analysis, we evaluated three subtypes of intraoperative SSEP changes: reversible, irreversible, and total signal loss.

SUMMARY OF BACKGROUND DATA

Lumbar decompression and fusion surgery can treat lumbar spinal stenosis and spondylolisthesis but carry a risk for nerve root injury. Published neurophysiological monitoring guidelines provide no conclusive evidence for the clinical utility of intraoperative SSEP monitoring during lumbar spine surgery.

METHODS

A systematic review was conducted to identify studies with outcomes of patients who underwent lumbar spine surgeries with intraoperative SSEP monitoring. The sensitivity, specificity, and diagnostic odds ratio (DOR) were calculated and presented with forest plots and a summary receiver operating characteristic curve.

RESULTS

The study cohort consisted of 5607 patients. All significant intraoperative SSEP changes had a sensitivity of 44% and specificity of 97% with a DOR of 22.13 (95% CI, 11.30-43.34). Reversible and irreversible SSEP changes had sensitivities of 28% and 33% and specificities of 97% and 97%, respectively. The DORs for reversible and irreversible SSEP changes were 13.93 (95% CI, 4.60-40.44) and 57.84 (95% CI, 15.95-209.84), respectively. Total loss of SSEPs had a sensitivity of 9% and specificity of 99% with a DOR of 23.91 (95% CI, 7.18-79.65).

CONCLUSION

SSEP changes during lumbar spine surgery are highly specific but moderately sensitive for new postoperative neurological deficits. Patients who had postoperative neurological deficit were 22 times more likely to have exhibited intraoperative SSEP changes.Level of Evidence: 2.

Transcranial Motor Evoked Potential Alarm Criteria to Predict Foot Drop Injury During Lumbosacral Surgery

STUDY DESIGN

A retrospective cohort analysis.

OBJECTIVE

This study aims to investigate whether waveform alterations in transcranial motor evoked potentials (TCMEPs) can reliably predict postoperative foot drop.

SUMMARY OF BACKGROUND DATA

Nerve injury leading to foot drop is a potential complication of lumbosacral surgery. Very limited data exist on the use of intraoperative TCMEPs to identify iatrogenic foot drop.

METHODS

We retrospectively reviewed neuromonitoring data from 130 consecutive spine surgeries with instrumentation involving L4-S1. TCMEP waveform analysis included amplitude (A), area under the curve (AUC), latency (L), and duration (D). Patient outcomes were correlated with neuromonitoring results. Intraoperative alert criteria were established on the basis of observed intraoperative changes.

RESULTS

Three patients developed severe foot drop with a muscle weakness functional grade ranging from 0/5 to 3/5. Two patients developed a mild foot drop with functional grade 4/5. Twenty-three patients had preoperative weakness in an L5 distribution. One-hundred two patients who had neither preoperative nor postoperative neurological complications served as a control group. Amplitude significantly decreased in patients with a severe postoperative deficit (P = 0.005) as did AUC and duration (P < 0.05). Intraoperative alert criteria defined as a >65% decrease in AUC resulted in a sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of 100%, 91.4%, 12%, and 100%, respectively. When defining an alert criteria as a >50% decrease in amplitude, sensitivity, specificity, PPV, and NPV were 100%, 87.9%, 8.8%, and 100%, respectively.

CONCLUSION

Reduction of TCMEP waveform associated with postoperative severe foot drop can be detected during lumbar surgery. Other waveform parameters such as AUC may predict foot drop better than the amplitude. Additional examinations in larger samples of foot drops are needed to validate these alert threshold findings.

LEVEL OF EVIDENCE

4.

P37 latency mismatch between lateral and midline potentials is influenced by transversal afference

SUMMARY

P37 cortical peak latency registered on Ci' (lateral) is usually approximately 1 millisecond shorter than Cz' (midline) in lower limb somatosensory evoked potential. At the present time, the underlying mechanism that leads to this mismatch remains unknown. Superficial peroneal nerve, posttibial nerve, and sural nerve somatosensory evoked potentials were obtained from 26 anesthetized individuals by using Ci'-Cc', Cc'-Fpz, and Cz'-Fpz recording montages. P37 latency mismatches between the lateral (Ci'-Cc') and midline (Cz'-Fpz) potentials (P < 0.001) were recorded in superficial peroneal nerve, posttibial nerve, and sural nerve somatosensory evoked potentials; all showed shorter Ci'-Cc' P37 latency (1-1.7 milliseconds). However, in individuals who had minimal or no N37 potential on Cc' recording, the mean P37 latencies of Ci'-Cc' and Cz'-Fpz equalized with the P37 latency of Ci'-Cc' approaching to default Cz'-Fpz value. The data showed that N37 seemed to potentiate the P37 latency difference between Ci-Cc' and Cz'-Fpz recordings. We postulate that N37 may preferentially reflect the dipoles of transversal afference; lack of it thereof suggests poor dipole sources primarily perpendicular to the mesial hemisphere.