Risk factors for neurophysiological events related to intraoperative halo-femoral traction in spinal deformity surgery.

PURPOSE: This study identifies risk factors for neurophysiological events caused by intraoperative halo-femoral traction (IOHFT) in patients with adolescent idiopathic scoliosis (AIS), and neuromuscular scoliosis (NMS). METHODS: Neurophysiological integrity was monitored using motor evoked potentials (MEPs). IONM event was defined as a decreased MEP amplitude of more than 80% of baseline in, at least, one muscle. Time between application of IOHFT and event, affected muscles, surgical stage, and time between removal of IOHFT and recovery of MEPs were described. Characteristics (age, height, weight, diagnosis, Cobb angle, and flexibility of the curve) of patients with and without IOHFT-events were compared using analysis of variance. Binary logistic regression analyses were performed to identify predictors. RESULTS: The study included 81 patients (age 15.6 ± 2.4 years, 53 females, AIS: n = 47, NMS n = 34). IOHFT-events occurred in 11 patients (13%; AIS n = 4, NMS n = 7). IOHFTevents affecting all limbs occurred pre-incision in NMS. Events affecting only the legs occurred during all stages of surgery. Patients with IOHFT-events were smaller (p = 0.009) and had stiffer curves (p = 0.046). Height was a predictor (odds ratio, 0.941; 95% confidence interval = 0.896-0.988). All MEPs recovered after removing IOHFT. CONCLUSION: Neurophysiologic events due to IOHFT were common, with the majority in patients with NMS. A shorter stature was a risk factor, and larger Cobb angle and stiffer curve were associated with IOHFT-events. Events occurred at any stage of surgery and involved upper and lower limbs. With an adequate response on IOHFT events, none of the patients had postoperative neurological impairments due to IOHFT.

Evaluation of the diagnostic value of transcranial electrical stimulation (TES) to assess neuronal functional integrity in horses.

Medical imaging allows for the visualization of spinal cord compression sites; however, it is impossible to assess the impact of visible stenotic sites on neuronal functioning, which is crucial information to formulate a correct prognosis and install targeted therapy. It is hypothesized that with the transcranial electrical stimulation (TES) technique, neurological impairment can be reliably diagnosed. Objective: To evaluate the ability of the TES technique to assess neuronal functional integrity in ataxic horses by recording TES-induced muscular evoked potentials (MEPs) in three different muscles and to structurally involve multiple ancillary diagnostic techniques, such as clinical neurological examination, plain radiography (RX) with ratio assessment, contrast myelography, and post-mortem gross and histopathological examination. Methods: Nine ataxic horses, showing combined fore and hindlimb ataxia (grades 2-4), were involved, together with 12 healthy horses. TES-induced MEPs were recorded bilaterally at the level of the trapezius (TR), the extensor carpi radialis (ECR), and tibialis cranialis (TC) muscles. Two Board-certified radiologists evaluated intra- and inter-sagittal diameter ratios on RX, reductions of dorsal contrast columns, and dural diameters (range skull-T1). Post-mortem gross pathological and segmental histopathological examination was also performed by a Board-certified pathologist. Results: TES-MEP latencies were significantly prolonged in both ECR and TC in all ataxic horses as opposed to the healthy horses. The TR showed a mixed pattern of normal and prolonged latency times. TES-MEP amplitudes were the least discriminative between healthy and ataxic horses. Youden's cutoff latencies for ataxic horses were 24.6 ms for the ECR and 45.5 ms for the TC (sensitivity and specificity of 100%). For healthy horses, maximum latency values were 22 and 37 ms, respectively. RX revealed spinal cord compression in 8 out of 9 involved ataxic horses with positive predictive values of 0-100%. All ataxic horses showed multi-segmental Wallerian degeneration. All pathological changes recorded in the white matter of the spinal cord were widely dispersed across all cervical segments, whereas gray matter damage was more localized at the specific segmental level. Conclusion: TES-MEP latencies are highly sensitive to detect impairment of spinal cord motor functions for mild-to-severe ataxia (grades 2-4).

Minimally Invasive Posterior Spinal Nonfusion Surgery in Patients With Adolescent Idiopathic Scoliosis Using a Bipolar One-Way Self-Expanding Rod System: Protocol for a Single-Center Clinical Cohort Study.

BACKGROUND: The current surgical treatment for patients diagnosed with progressive and severe adolescent idiopathic scoliosis (AIS) consists of the correction of the spinal curvature, followed by posterior spinal fusion (PSF). However, research has uncovered short- and long-term complications of posterior spinal fusion in patients with AIS. Minimally invasive growing rod techniques have successfully been used to treat patients with early-onset scoliosis and neuromuscular scoliosis. It may be questioned if minimally invasive posterior spinal nonfusion (PSnF) surgery with bipolar instrumentation can be used for the treatment of AIS. OBJECTIVE: This study will be performed to monitor the efficacy and safety of PSnF surgery by using a commercially available Conformité Européenne-certified spinal implant consisting of bilateral bipolar one-way self-expanding rods (OWSER) for the treatment of patients diagnosed with AIS. METHODS: In 14 selected patients with AIS with Lenke 1-6 curves, minimally invasive PSnF surgery with the OWSER system is performed after the failure of conservative treatment (curve progression of >5° within 1 year). The patients are over 7 years of age, with a major Cobb angle of ≥30°, sufficient flexibility, and a Risser stage of ≤2. Patients will be followed over time, according to the standard medical care. Efficacy will be measured using radiological and patient satisfaction assessments and safety will be determined by the amount of perioperative complications. RESULTS: Patient inclusion started on November 17, 2021 and we hope to finalize patient inclusion by the beginning of 2025. The first results will be expected by the beginning of 2024. CONCLUSIONS: Minimally invasive PSnF in patients with AIS is presented as a less invasive surgical technique that prevents the progression of the scoliotic curve and that allows minor posture correction of coronal imbalance. This will be the first study to examine whether the PSnF bipolar OWSER instrumentation will be the next generation of surgical instrumentation in AIS. TRIAL REGISTRATION: ClinicalTrials.gov NCT04441411; https://clinicaltrials.gov/study/NCT04441411. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID): DERR1-10.2196/47222.

Trapezius Motor Evoked Potentials From Transcranial Electrical Stimulation and Transcranial Magnetic Stimulation: Reference Data, Characteristic Differences and Intradural Motor Velocities in Horses.

Reason for Performing Study: So far, only transcranial motor evoked potentials (MEP) of the extensor carpi radialis and tibialis cranialis have been documented for diagnostic evaluation in horses. These allow for differentiating whether lesions are located in either the thoraco-lumbar region or in the cervical myelum and/or brain. Transcranial trapezius MEPs further enable to distinguish between spinal and supraspinal located lesions. No normative data are available. It is unclear whether transcranial electrical stimulation (TES) and transcranial magnetic stimulation (TMS) are interchangeable modalities. Objectives: To provide normative data for trapezius MEP parameters in horses for TES and TMS and to discern direct and indirect conduction routes by neurophysiological models that use anatomical geometric characteristics to relate latency times with peripheral (PCV) and central conduction velocities (CCV). Methods: Transcranial electrical stimulation-induced trapezius MEPs were obtained from twelve horses. TES and TMS-MEPs (subgroup 5 horses) were compared intra-individually. Trapezius MEPs were measured bilaterally twice at 5 intensity steps. Motoneurons were localized using nerve conduction models of the cervical and spinal accessory nerves (SAN). Predicted CCVs were verified by multifidus MEP data from two horses referred for neurophysiological assessment. Results: Mean MEP latencies revealed for TES: 13.5 (11.1-16.0)ms and TMS: 19.7 (12-29.5)ms, comprising ∼100% direct routes and for TMS mixed direct/indirect routes of L:23/50; R:14/50. Left/right latency decreases over 10 > 50 V for TES were: -1.4/-1.8 ms and over 10 > 50% for TMS: -1.7/-3.5 ms. Direct route TMS-TES latency differences were 1.88-4.30 ms. 95% MEP amplitudes ranges for TES were: L:0.26-22 mV; R:0.5-15 mV and TMS: L:0.9 - 9.1 mV; R:1.1-7.9 mV. Conclusion: This is the first study to report normative data characterizing TES and TMS induced- trapezius MEPs in horses. The complex trapezius innervation leaves TES as the only reliable stimulation modality. Differences in latency times along the SAN route permit for estimation of the location of active motoneurons, which is of importance for clinical diagnostic purpose. SAN route lengths and latency times are governed by anatomical locations of motoneurons across C2-C5 segments. TES intensity-dependent reductions of trapezius MEP latencies are similar to limb muscles while MEP amplitudes between sides and between TES and TMS are not different. CCVs may reach 180 m/s.

Comparison of Muscle MEPs From Transcranial Magnetic and Electrical Stimulation and Appearance of Reflexes in Horses.

INTRODUCTION: Transcranial electrical (TES) and magnetic stimulation (TMS) are both used for assessment of the motor function of the spinal cord in horses. Muscular motor evoked potentials (mMEP) were compared intra-individually for both techniques in five healthy horses. mMEPs were measured twice at increasing stimulation intensity steps over the extensor carpi radialis (ECR), tibialis cranialis (TC), and caninus muscles. Significance was set at p < 0.05. To support the hypothesis that both techniques induce extracranially elicited mMEPs, literature was also reviewed. RESULTS: Both techniques show the presence of late mMEPs below the transcranial threshold appearing as extracranially elicited startle responses. The occurrence of these late mMEPs is especially important for interpretation of TMS tracings when coil misalignment can have an additional influence. Mean transcranial motor latency times (MLT; synaptic delays included) and conduction velocities (CV) of the ECR and TC were significantly different between both techniques: respectively, 4.2 and 5.5 ms (MLT TMS --MLT TES ), and -7.7 and -9.9 m/s (CV TMS -CV TES ). TMS and TES show intensity-dependent latency decreases of, respectively, -2.6 (ECR) and -2.7 ms (TC)/30% magnetic intensity and -2.6 (ECR) and -3.2 (TC) ms/30V. When compared to TMS, TES shows the lowest coefficients of variation and highest reproducibility and accuracy for MLTs. This is ascribed to the fact that TES activates a lower number of cascaded interneurons, allows for multipulse stimulation, has an absence of coil repositioning errors, and has less sensitivity for varying degrees of background muscle tonus. Real axonal conduction times and conduction velocities are most closely approximated by TES. CONCLUSION: Both intracranial and extracranial mMEPs inevitably carry characteristics of brainstem reflexes. To avoid false interpretations, transcranial mMEPs can be identified by a stepwise latency shortening of 15-20 ms when exceeding the transcranial motor threshold at increasing stimulation intensities. A ring block around the vertex is advised to reduce interference by extracranial mMEPs. mMEPs reflect the functional integrity of the route along the brainstem nuclei, extrapyramidal motor tracts, propriospinal neurons, and motoneurons. The corticospinal tract appears subordinate in horses. TMS and TES are interchangeable for assessing the functional integrity of motor functions of the spinal cord. However, TES reveals significantly shorter MLTs, higher conduction velocities, and better reproducibility.

Extramuscular Recording of Spontaneous EMG Activity and Transcranial Electrical Elicited Motor Potentials in Horses: Characteristics of Different Subcutaneous and Surface Electrode Types and Practical Guidelines.

INTRODUCTION: Adhesive surface electrodes are worthwhile to explore in detail as alternative to subcutaneous needle electrodes to assess myogenic evoked potentials (MEP) in human and horses. Extramuscular characteristics of both electrode types and different brands are compared in simultaneous recordings by also considering electrode impedances and background noise under not mechanically secured (not taped) and taped conditions. METHODS: In five ataxic and one non-ataxic horses, transcranial electrical MEPs, myographic activity, and noise were simultaneously recorded from subcutaneous needle (three brands) together with pre-gelled surface electrodes (five brands) on four extremities. In three horses, the impedances of four adjacent-placed surface-electrode pairs of different brands were measured and compared. The similarity between needle and surface EMGs was assessed by cross-correlation functions, pairwise comparison of motor latency times (MLT), and amplitudes. The influence of electrode noise and impedance on the signal quality was assessed by a failure rate (FR) function. Geometric means and impedance ranges under not taped and taped conditions were derived for each brand. RESULTS: High coherencies between EMGs of needle-surface pairs degraded to 0.7 at moderate and disappeared at strong noise. MLTs showed sub-millisecond simultaneous differences while sequential variations were several milliseconds. Subcutaneous MEP amplitudes were somewhat lower than epidermal. The impedances of subcutaneous needle electrodes were below 900 Ω and FR = 0. For four brands, the FR for surface electrodes was between 0 and 80% and declined to below 25% after taping. A remaining brand (27G DSN2260 Medtronic) revealed impedances over 100 kΩ and FR = 100% under not taped and taped conditions. CONCLUSION: Subcutaneous needle and surface electrodes yield highly coherent EMGs and TES-MEP signals. When taped and allowing sufficient settling time, adhesive surface-electrode signals may approach the signal quality of subcutaneous needle electrodes but still depend on unpredictable conditions of the skin. The study provides a new valuable practical guidance for selection of extramuscular EMG electrodes. This study on horses shares common principles for the choice of adhesive surface or sc needle electrodes in human applications such as in intraoperative neurophysiological monitoring of motor functions of the brain and spinal cord.

Influence of the Montage of Stimulation Electrodes for Intraoperative Neuromonitoring During Orthopedic Spine Surgery.

PURPOSE: In transcranial electrical stimulation, induced motor evoked potentials (MEPs) are influenced by the montage of stimulation electrodes. Differences are to be examined between coronal and sagittal stimulation. METHODS: Forty-five patients with idiopathic scoliosis were included. Coronal and sagittal montages were obtained by electrode placement at C3C4 and Cz'F using large contact electrodes. Corkscrew and short needle electrodes were additionally placed at C3C4 in five patients. Voltage motor thresholds (MTvoltage) and MEP amplitudes at 2 times MTvoltage (MEP2MTvoltage) were obtained of upper and lower extremity muscles. Differences of MTvoltage and MEP2MTvoltage at Cz'F and C3C4 and between electrodes were analyzed. RESULTS: MEP2MTvoltage benefits from coronal positioning. Correlations between MTvoltage and impedance were not significant for large electrodes at Cz'F, very low for C3C4, and high for short needles or corkscrew electrodes. MTvoltage of short needles and corkscrews was up to 200% higher compared with MTvoltage of long needles. MTcurrent is increased by 20% to 30% and 2% to 10% for the arm and leg muscles, respectively. CONCLUSIONS: Biphasic stimulation at C3C4 is advised when constant voltage stimulation is used to monitor the spinal cord during orthopedic spine surgery. MTvoltage of corkscrew and small needle electrodes are highly sensitive to electrode impedances.

The Percentage of Amplitude Decrease Warning Criteria for Transcranial MEP Monitoring.

Muscle motor evoked potentials (MEPs) from transcranial electrical stimulation (TES) became a standard technique for monitoring the motor functions of the brain and spinal cord at risk during spinal and brain surgery. However, a wide range of criteria based on the percentage of amplitude decrease is used in practice. A survey of the current literature on clinical outcome parameters reveals a variety of percentages in a range of 30% to 100% (50% to 100% spinal procedures) with no consensus. The interpretation of muscle MEPs is hampered by their sensitivity to many interfering factors. Trial-to-trial MEP variations may partly be reduced by controllable parameters of which TES parameters are in the hands of the neuromonitorist. We propose an operational model based on basic neurophysiologic knowledge to interpret the characteristics of MEP-TES voltage curves and predict the influences of the location on the sigmoid voltage curve on spontaneous MEP-variations and influences of factors affecting the voltage curve. The model predicts a correlation between the slope, expressed by a gain, and variations of muscle MEP amplitudes. This complies with two case examples. The limited specificity/sensitivity of warning criteria based on the percentage of amplitude reduction can possibly be improved by developing standards for set-up procedures of TES paradigms. These procedures include strategies for desensitizing MEPs for variations of controllable parameters. The TES voltage or current is a feasible controlling parameter and should be related to the motor threshold and the onset of the supramaximal level being landmarks of MEP-voltage functions. These parameters may offer a valuable addition to multicenter outcome studies.

Movement Along the Spine Induced by Transcranial Electrical Stimulation Related Electrode Positioning.

STUDY DESIGN: A prospective, nonrandomized cohort study. OBJECTIVE: To describe a technique quantifying movement induced by transcranial electrical stimulation (TES) induced movement in relation to the positioning of electrodes during spinal deformity surgery. SUMMARY OF BACKGROUND DATA: TES induced movement may cause injuries and delay surgical procedures. When TES movements are evoked, muscles other than those being monitored any adjustments in stimulation protocols and electrode positioning may be expected to minimize movement whereas preserving quality of monitoring. In this study, seismic evoked responses (SER) induced through TES were studied at different electrode positions. METHODS: Intraoperative TES-motor evoked potentials were carried out in 12 patients undergoing corrective spine surgery. Accelerometer transducers recorded SER in two directions at four different locations of the spine for TES-electrode montage groups Cz-Fz and C3-C4. A paired t test was used to compare the means of SER and the relationship between movement and TES electrode positioning. RESULTS: SERs were strongest in the upper body. All mean SERs values for the Cz-Fz group were up to five times larger when compared with the C3-C4 group. However, there were no differences between the C3-C4 and Cz-Fz groups in the lower body locations. Both electrode montage groups showed a gradual stepwise reduction in all mean SER values along the spine from the cranial to caudal region. For the upper body locations, there were no significant associations between SER and both montages; in contrast, a significant association SER was demonstrated in the lumbar region. CONCLUSION: At supramaximum levels, movements resulting from multipulse TES are likely caused by relatively strong contractions from muscles in the neck resulting from direct extracranial stimulation. When interchanging electrode montages in individual cases, the movement in the neck may become reduced. At lumbar levels transcranial evoked muscle contractions dominate movement in the surgically exposed areas. LEVEL OF EVIDENCE: 4.

Multimodality intraoperative neuromonitoring in extreme lateral interbody fusion. Transcranial electrical stimulation as indispensable rearview.

PURPOSE: To optimize intraoperative neuromonitoring during extreme lateral interbody fusion (XLIF) by adding transcranial electrical stimulation with motor evoked potential (TESMEP) to previously described monitoring using spontaneous EMG (sEMG) and peripheral stimulation (triggered EMG: tEMG). METHODS: Twenty-three patients with degenerative lumbar scoliosis had XLIF procedures and were monitored using sEMG, tEMG and TESMEP. Spontaneous and triggered muscle activity, and the MEP of 5 ipsilateral leg muscles, 2 contralateral leg muscles and 1 arm muscle were monitored. RESULTS: During XLIF surgery decreased MEP amplitudes were measured in 9 patients and in 6 patients sEMG was documented. In 4 patients, both events were described. In 30 % of the cases (n = 7), the MEP amplitude decreased immediately after breaking of the table and even before skin incision. After reduction of the table break, the MEP amplitudes recovered to baseline. In two patients, the MEP amplitude deteriorated during distraction of the psoas with the retractor, while no events were reported using sEMG and tEMG. Repositioning of the retractor led to recovery of the MEP. CONCLUSIONS: Monitoring the complete nervous system during an XLIF procedure is found to be helpful since nerve roots, lumbar plexus as well as the intradural neural structures may be at risk. TESMEP has additional value to sEMG and tEMG during XLIF procedure: (1) it informed about otherwise unnoticed events, and (2) it confirmed and added information to events measured using sEMG.

Single dose of fluoxetine increases muscle activation in chronic stroke patients.

OBJECTIVES: This pilot study explores the influence of a single dose of fluoxetine (20 mg) on the muscle activation patterns and functional ability of the muscles in the lower part of the arm in chronic stroke patients. METHODS: A crossover, placebo-controlled clinical trial was conducted in 10 patients. After administration of either a single dose of fluoxetine (20 mg) or a placebo, muscle activation of the lower arm was measured during maximum (isometric) force of the musculus flexor carpi radialis and musculus extensor carpi radialis. Delay times, grip strength, and Motricity Index were measured to assess functional ability. RESULTS: After fluoxetine intake, a significant increase in activation was found in both agonist and antagonist muscles of the paretic arm (P < 0.05). This increase did not influence the motor function. CONCLUSIONS: In this pilot study, it was found that fluoxetine influences motor output in chronic stroke patients. Therefore, fluoxetine may influence motor recovery after stroke. Additional studies have to be conducted to explore the effects of fluoxetine on motor recovery after stroke.