The diagnostic accuracy of somatosensory evoked potentials in evaluating neurological deficits during 1036 posterior spinal fusions

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

STUDY DESIGN

Systematic review and meta-analysis.

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Diagnostic Value of Multimodal Intraoperative Neuromonitoring by Combining Somatosensory-With Motor-Evoked Potential in Posterior Decompression Surgery for Thoracic Spinal Stenosis

Background

Intraoperative neuromonitoring (IONM) has become an increasingly essential technique in spinal surgery. However, data on the diagnostic value of IONM in predicting impending postoperative neurological deficits (PONDs) for patients who underwent posterior decompression surgery for thoracic spinal stenosis (TSS) are limited. Furthermore, patients who are at the highest risk of waveform changes during the surgery remain unknown. Our purpose was to (1) assess the diagnostic accuracy of IONM by combining somatosensory-evoked potential (SSEP) with motor-evoked potential (MEP) in predicting PONDs for patients who underwent the surgery and (2) identify the independent risk factors correlated with IONM changes in our study population.

Methods

A total of 326 consecutive patients who underwent the surgery were identified and analyzed. We collected the following data: (1) demographic and clinical data; (2) IONM data; and (3) outcome data such as details of PONDs, and recovery status (complete, partial, or no recovery) at the 12-month follow-up visit.

Results

In total, 27 patients developed PONDs. However, 15, 6, and 6 patients achieved complete recovery, partial recovery, and no recovery, respectively, at the 12-month follow-up. SSEP or MEP change monitoring yielded better diagnostic efficacy in predicting PONDs as indicated by the increased sensitivity (96.30%) and area under the receiver operating characteristic (ROC) curve (AUC) value (0.91). Only one neurological deficit occurred without waveform changes. On multiple logistic regression analysis, the independent risk factors associated with waveform changes were as follows: preoperative moderate or severe neurological deficits (p = 0.002), operating in the upper- or middle-thoracic spinal level (p = 0.003), estimated blood loss (EBL) ≥ 400 ml (p < 0.001), duration of symptoms ≥ 3 months (p < 0.001), and impairment of gait (p = 0.001).

Conclusion

Somatosensory-evoked potential or MEP change is a highly sensitive and moderately specific indicator for predicting PONDs in posterior decompression surgery for TSS. The independent risks for IONM change were as follows: operated in upper- or middle-thoracic spinal level, presented with gait impairment, had massive blood loss, moderate or severe neurological deficits preoperatively, and had a longer duration of symptoms.

Clinical Trial Registration

[http://www.chictr.org.cn]; identifier [ChiCTR 200003 2155].

The incidence of stroke post neck dissection surgery and perioperative management

BACKGROUND

Head and neck surgery encompasses major vessels, raising the concern of life-threatening complications such as stroke.

METHODS

Databases at UPMC were queried to identify patients with both neck dissections and stroke from January 1st, 2004, to October 1st, 2020. A retrospective chart review was performed to identify patients who experienced a stroke within 30 days of a neck dissection.

RESULTS

Search of a UPMC database for carotid artery stenosis (CAS), transient ischemic attack (TIA), and stroke identified 20,527 patients. After matching with the Head and Neck Tumor Registry patients, 41 of 4230 patients with a neck dissection also had a stroke, TIA, or CAS in their lifetime. One patient, with multiple risk factors, despite pre-operative precautions, had a stroke 2 days post neck dissection in the setting of carotid occlusion from hypercoagulability of malignancy and intraoperative vessel injury. The patient subsequently underwent a carotid thrombectomy and vein patch repair and has had no additional cerebrovascular accidents.

CONCLUSION

Although the incidence of stroke post neck dissection is minimal, patients with multiple risk factors for stroke should be managed carefully to prevent deleterious outcomes.

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.

Roadmap for Motor Evoked Potential (MEP) Monitoring for Patients Undergoing Lumbar and Lumbosacral Spinal Fusion Procedures

MEPs are recommended for patients undergoing lumbar and lumbosacral procedures in which intraoperative neuromonitoring (IONM) is being utilized. While electromyography (EMG) provides critical nerve root proximity information, spontaneous EMG discharges are relatively poor at reliably diagnosing spinal nerve root dysfunction. In contrast, research indicates that MEPs are both sensitive and specific in diagnosing evolving spinal nerve root dysfunction. There is conflicting evidence, however, and it must be emphasized that the value of adding MEPs is only realized when practices and techniques are optimized. The ideal anesthetic plan is an optimized total intravenous anesthetic (TIVA) regimen. Selection of appropriate anesthetics and dosing is important for optimizing baseline response amplitudes and promoting diagnostic confidence in analyzing signal changes. An adaptive set of alert criteria that account for baseline amplitude and morphology fluctuations should guide the determination of significant signal change. The therapeutic impact of accurate diagnostic information depends on the timeliness of diagnosis and intervention. Prior to the start of surgery, a plan to obtain MEPs at least once every 10 minutes during the active part of the procedure and after every significant surgical maneuver should be agreed upon, and the intervention plan should include but not be limited to possible removal of hardware and release of retraction or distractive forces. In summary, MEPs can improve monitoring of at-risk nerve root function, but the accuracy and therapeutic impact of such monitoring depend on perioperative planning and communication that optimize use of this modality.

Optimal "Low" Pedicle Screw Stimulation Threshold to Predict New Postoperative Lower-Extremity Neurologic Deficits During Lumbar Spinal Fusions

OBJECTIVE

Previous studies have shown that pedicle screw stimulation thresholds ≤6-8 mA yield a high diagnostic accuracy of detecting misplaced screws. Our objective was to determine the optimal "low" stimulation threshold to predict new postoperative neurologic deficits and identify additional risk factors associated with deficits.

METHODS

We included patients with complete pedicle screw stimulation testing who underwent posterior lumbar spinal fusion surgeries from 2010-2012. We calculated the diagnostic accuracy of pedicle screw responses of ≤4 mA, ≤6 mA, ≤8 mA, ≤10 mA, ≤12 mA, and ≤20 mA to predict new postoperative lower-extremity (LE) neurologic deficits. We used multivariate modeling to determine the best logistic regression model to predict LE deficits and identify additional risk factors. Statistics software packages used were Python3.8.5, NumPy 1.19.1, Pandas 1.1.1, and SPSS26.

RESULTS

We studied 1179 patients who underwent 8584 pedicle screw stimulations with somatosensory evoked potential and free-run electromyographic monitoring for posterior lumbar spinal fusion. Twenty-five (2.1%) patients had new LE neurologic deficits. A stimulation threshold of ≤8 mA had a sensitivity/specificity of 32%/90% and a diagnostic odds ratio/area under the curve of 4.34 [95% confidence interval: 1.83, 10.27]/0.61 [0.49, 0.74] in predicting postoperative deficit. Multivariate analysis showed that patients who had pedicle screws with stimulation thresholds ≤8 mA are 3.15 [1.26, 7.83]× more likely to have postoperative LE deficits while patients who have undergone a revision lumbar spinal fusion surgery are 3.64 [1.38, 9.61]× more likely.

CONCLUSIONS

Our results show that low thresholds are indicative of not only screw proximity to the nerve but also an increased likelihood of postoperative neurologic deficit. Thresholds ≤8 mA prove to be the optimal "low" threshold to help guide a correctly positioned pedicle screw placement and detect postoperative deficits.

Diagnostic Accuracy of Thresholds Less Than or Equal to 8 mA in Pedicle Screw Testing During Lumbar Spine Procedures to Predict New Postoperative Lower Extremity Neurological Deficits

STUDY DESIGN

Retrospective observational study.

OBJECTIVE

It has been shown that pedicle screw stimulation thresholds less than or equal to 8 mA yield a very high diagnostic accuracy of detecting misplaced screws in spinal surgery. In our study, we determined clinical implications of low stimulation thresholds.

SUMMARY OF BACKGROUND DATA

Posterior lumbar spinal fusions (PSF), using pedicle screws, are performed to treat many spinal pathologies, but misplaced pedicle screws can result in new postoperative neurological deficits.

METHODS

Patients with pedicle screw stimulation testing who underwent PSF between 2010 and 2012 at the University of Pittsburgh Medical Center (UPMC) were included in the study. We evaluated the sensitivity, specificity, and diagnostic odds ratio (DOR) to determine how effectively low pedicle screw responses predict new postoperative lower extremity neurological deficits.

RESULTS

One thousand one hundred seventy nine eligible patients underwent 8584 pedicle screw stimulations with lower extremity somatosensory evoked potentials (LE SSEP) monitoring for lumbar fusion surgery. One hundred twenty one of these patients had 187 pedicle screws with a stimulation response at a threshold less than or equal to 8 mA. Smoking had a significant correlation to pedicle screw stimulation less than or equal to 8 mA (P = 0.012). A threshold of less than or equal to 8 mA had a sensitivity/specificity of 0.32/0.90 with DOR of 4.34 [1.83, 10.27] and an area under the ROC curve (AUC) of 0.61 [0.49, 0.74]. Patients with screw thresholds less than or equal to 8 mA and abnormal baselines had a DOR of 9.8 [95% CI: 2.13-45.17] and an AUC of 0.73 [95% CI: 0.50-0.95].

CONCLUSION

Patients with pedicle screw stimulation thresholds less than or equal to 8 mA are 4.34 times more likely to have neurological clinical manifestations. Smoking and LE deficits were shown to be significantly correlated with pedicle screw stimulation thresholds less than or equal to 8 mA. Low stimulation thresholds result in a high specificity of 90%. Pedicle screw stimulation less than or equal to 8 mA can serve as an accurate rule in test for postoperative neurological deficit, warranting reevaluation of screw placement and/or replacement intraoperatively.Level of Evidence: 3.

Utility of motor evoked potentials to diagnose and reduce lower extremity motor nerve root injuries during 4,386 extradural posterior lumbosacral spine procedures

BACKGROUND CONTEXT

Motor evoked potentials (MEPs) have excellent sensitivity for monitoring the functional integrity of the lateral corticospinal tract of the spinal cord. The sensitivity for nerve root function, however, is not as well established; consequently, MEPs are often not utilized for posterior extradural spine procedures distal to the conus. Spontaneous electromyography (sEMG) and somatosensory evoked potentials (SSEPs) are often included for these procedures, but their limited sensitivity has been well documented. Given the risk of motor nerve root injuries during spine procedures, and specifically increased vulnerability of the L4 and L5 nerves, the sensitivity of MEPs was evaluated for diagnostic accuracy and therapeutic impact.

PURPOSE

To determine the diagnostic sensitivity of MEPs during lumbosacral spine procedures and the potential therapeutic impact of the resolution of MEP alerts.

STUDY DESIGN

A total of 4,386 posterior extradural lumbosacral spine procedures utilizing multimodality intraoperative neuromonitoring (IONM) with sEMG, SSEPs, and MEPs were abstracted from a multi-institutional database. All cases took place between October 2015 and October 2017. No external funding was provided.

OUTCOME MEASURES

Sensitivity and specificity, as well as positive and negative likelihood ratios for new postoperative neurologic deficits were calculated for each modality individually as well as when combined (multimodality).

PATIENT SAMPLE

Age 18 and older METHODS: Data entered in the electronic medical record were analyzed. Alerts to sEMG activity, decreases in SSEP amplitude, or decreases in MEP amplitude were documented as well as the status of the alerts at closure: resolved or unresolved. The presence of an sEMG alert or an unresolved MEP or SSEP alert at closure was considered a positive diagnostic result, and these results were assessed relative to presence of new immediate onset neurologic deficits as documented in the electronic record.

RESULTS

The sensitivity and specificity of multimodality IONM for new immediate-onset lower extremity motor deficits were 100.0% (95% confidence interval: [64.6, 100.0]) and 92.2% (91.1, 93.1), respectively. Looking at the modalities in isolation, the sensitivity of MEPs was considerably better than either lower extremity sEMG or posterior tibial nerve SSEPs: 100.0% (78.5, 100.0) versus just 14.3% (4.0, 39.9) and 28.6% (8.2, 64.1), respectively. Surprisingly, the specificity of lower extremity MEPs was better than sEMG, 97.9% (97.5, 98.3) versus 95.4% (94.7, 96.0) (χ²=43.0, p<.001). The specificity of lower extremity SSEPs was 99.0% (98.5, 99.3). Only 4.4% of all procedures had a lower extremity MEP alert. There were 14 significant new nerve root injuries and all 14 had unresolved MEPs at closure. Total 85.7% of those nerve root injuries were dorsiflexion foot drop injuries and all had unresolved tibialis anterior MEP alerts. Although the overall rate of nerve root injuries was 0.32% (14/4,386), the rate for procedures with unresolved isolated tibialis anterior MEP alerts was 44.4% (12/27). The therapeutic impact is evident in the 2.0% of cases (87/4,386) with lower extremity MEP alerts that were able to be fully resolved by closure and for which the rate of injury was zero.

CONCLUSIONS

The diagnostic accuracy of MEPs for anterior tibialis-related nerve root dysfunction supports the inclusion of this modality during routine posterior extradural lumbosacral procedures, especially when the L4 or L5 nerve roots are at risk. Moreover, therapeutic interventions that lead to the resolution of MEP alerts avert postoperative neurologic injuries.

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.