Randomized Placebo-Controlled Trial of 60-Day Percutaneous Peripheral Nerve Stimulation Treatment Indicates Relief of Persistent Postoperative Pain, and Improved Function After Knee Replacement

OBJECTIVES

Total knee arthroplasty (TKA) is an effective surgery for end-stage knee osteoarthritis, but chronic postoperative pain and reduced function affect up to 20% of patients who undergo such surgery. There are limited treatment options, but percutaneous peripheral nerve stimulation (PNS) is a promising nonopioid treatment option for chronic, persistent postoperative pain. The objective of the present study was to evaluate the effect of a 60-day percutaneous PNS treatment in a multicenter, randomized, double-blind, placebo-controlled trial for treating persistent postoperative pain after TKA.

MATERIALS AND METHODS

Patients with postoperative pain after knee replacement were screened for this postmarket, institutional review board-approved, prospectively registered (NCT04341948) trial. Subjects were randomized to receive either active PNS or placebo (sham) stimulation. Subjects and a designated evaluator were blinded to group assignments. Subjects in both groups underwent ultrasound-guided placement of percutaneous fine-wire coiled leads targeting the femoral and sciatic nerves on the leg with postoperative pain. Leads were indwelling for eight weeks, and the primary efficacy outcome compared the proportion of subjects in each group reporting ≥50% reduction in average pain relative to baseline during weeks five to eight. Functional outcomes (6-minute walk test; 6MWT and Western Ontario and McMaster Universities Osteoarthritis Index) and quality of life (Patient Global Impression of Change) also were evaluated at end of treatment (EOT).

RESULTS

A greater proportion of subjects in the PNS groups (60%; 12/20) than in the placebo (sham) group (24%; 5/21) responded with ≥50% pain relief relative to baseline (p = 0.028) during the primary endpoint (weeks 5-8). Subjects in the PNS group also walked a significantly greater distance at EOT than did those in the placebo (sham) group (6MWT; +47% vs -9% change from baseline; p = 0.048, n = 18 vs n = 20 completed the test, respectively). Prospective follow-up to 12 months is ongoing.

CONCLUSIONS

This study provides evidence that percutaneous PNS decreases persistent pain, which leads to improved functional outcomes after TKA at EOT.

Effect of percutaneous electrical stimulation with high-frequency alternating currents at 30 kHz on the sensory-motor system

Background

Unmodulated high-frequency alternating currents (HFAC) are employed for producing peripheral nerves block. HFAC have been applied in humans with frequencies up to 20 kHz, whether transcutaneously, percutaneously, or via surgically-implanted electrodes. The aim of this study was to assess the effect of percutaneous HFAC, applied with ultrasound-guided needles at 30 kHz, on the sensory-motor nerve conduction of healthy volunteers.

Methods

A parallel, double-blind, randomized clinical trial with a placebo control was conducted. Percutaneous HFAC at 30 kHz or sham stimulation was applied via ultrasound-guided needles in 48 healthy volunteers (n = 24 in each group) for 20 min. The assessed outcome variables were pressure pain threshold (PPT), mechanical detection threshold (MDT), maximal finger flexion strength (MFFS), antidromic sensory nerve action potential (SNAP), hand temperature, and subjective sensations by the participants. The measurements were recorded pre-intervention, during the stimulation (at 15 min), immediately post-intervention (at 20 min), and 15 min after the end of treatment.

Results

The PPT increased in the active group compared with sham stimulation, both during the intervention [14.7%; 95% confidence interval (CI): 4.4-25.0], immediately post-intervention (16.9%; 95% CI: -7.2-26.5), and 15 min after the end of the stimulation (14.3%; 95% CI: 4.4-24.3) (p < 0.01). The proportion of participants who reported feelings of numbness and heaviness was significantly higher in the active group (46 and 50%, respectively) than in the sham group (8 and 18%, respectively) (p < 0.05). No intergroup differences were observed in the remaining outcome variables. No unexpected adverse effects derived from the electrical stimulation were reported.

Conclusion

Percutaneous stimulation with HFAC at 30 kHz applied to the median nerve increased the PPT and subjective perception of numbness and heaviness. Future research should evaluate its potential therapeutic effect in people with pain.

Clinical trial registration

https://clinicaltrials.gov/ct2/show/NCT04884932, identifier NCT04884932.

Blocking peripheral drive from colorectal afferents by subkilohertz dorsal root ganglion stimulation

ABSTRACT

Clinical evidence indicates dorsal root ganglion (DRG) stimulation effectively reduces pain without the need to evoke paresthesia. This paresthesia-free anesthesia by DRG stimulation can be promising to treat pain from the viscera, where paresthesia usually cannot be produced. Here, we explored the mechanisms and parameters for DRG stimulation using an ex vivo preparation with mouse distal colon and rectum (colorectum), pelvic nerve, L6 DRG, and dorsal root in continuity. We conducted single-fiber recordings from split dorsal root filaments and assessed the effect of DRG stimulation on afferent neural transmission. We determined the optimal stimulus pulse width by measuring the chronaxies of DRG stimulation to be below 216 µs, indicating spike initiation likely at attached axons rather than somata. Subkilohertz DRG stimulation significantly attenuates colorectal afferent transmission (10, 50, 100, 500, and 1000 Hz), of which 50 and 100 Hz show superior blocking effects. Synchronized spinal nerve and DRG stimulation reveals a progressive increase in conduction delay by DRG stimulation, suggesting activity-dependent slowing in blocked fibers. Afferents blocked by DRG stimulation show a greater increase in conduction delay than the unblocked counterparts. Midrange frequencies (50-500 Hz) are more efficient at blocking transmission than lower or higher frequencies. In addition, DRG stimulation at 50 and 100 Hz significantly attenuates in vivo visceromotor responses to noxious colorectal balloon distension. This reversible conduction block in C-type and Aδ-type afferents by subkilohertz DRG stimulation likely underlies the paresthesia-free anesthesia by DRG stimulation, thereby offering a promising new approach for managing chronic visceral pain.

Effect of Percutaneous Electric Stimulation with High-Frequency Alternating Currents on the Sensory-Motor System of Healthy Volunteers: A Double-Blind Randomized Controlled Study

Former studies investigated the application of high-frequency alternating currents (HFAC) in humans for blocking the peripheral nervous system. The present trial aims to assess the effect of HFAC on the motor response, somatosensory thresholds, and peripheral nerve conduction when applied percutaneously using frequencies of 10 kHz and 20 kHz in healthy volunteers. A parallel, placebo-controlled, double-blind, randomized clinical trial was conducted. Ultrasound-guided HFAC at 10 kHz and 20 kHz and sham stimulation were delivered to the median nerve of 60 healthy volunteers for 20 min. The main assessed variables were the maximum isometric flexion strength (MFFS) of the index finger, myotonometry, pressure pain threshold (PPT), mechanical detection threshold (MDT), and sensory nerve action potential (SNAP). A decrease in the MFFS is observed immediately postintervention compared to baseline, both in the 10 kHz group (−8.5%; 95% CI −14.9 to −2.1) and the 20 kHz group (−12.0%; 95% CI −18.3 to −5.6). The between-group comparison of changes in MFFS show a greater reduction of −10.8% (95% CI −19.8 to −1.8) immediately postintervention in the 20 kHz compared to the sham stimulation group. The percutaneous stimulation applying 20 kHz HFAC to the median nerve produces a reversible postintervention reduction in strength with no adverse effects.

Kilohertz-frequency stimulation of the nervous system: A review of underlying mechanisms

BACKGROUND

Electrical stimulation in the kilohertz-frequency range has gained interest in the field of neuroscience. The mechanisms underlying stimulation in this frequency range, however, are poorly characterized to date.

OBJECTIVE/HYPOTHESIS

To summarize the manifold biological effects elicited by kilohertz-frequency stimulation in the context of the currently existing literature and provide a mechanistic framework for the neural responses observed in this frequency range.

METHODS

A comprehensive search of the peer-reviewed literature was conducted across electronic databases. Relevant computational, clinical, and mechanistic studies were selected for review.

RESULTS

The effects of kilohertz-frequency stimulation on neural tissue are diverse and yield effects that are distinct from conventional stimulation. Broadly, these can be divided into 1) subthreshold, 2) suprathreshold, 3) synaptic and 4) thermal effects. While facilitation is the dominating mechanism at the subthreshold level, desynchronization, spike-rate adaptation, conduction block, and non-monotonic activation can be observed during suprathreshold kilohertz-frequency stimulation. At the synaptic level, kilohertz-frequency stimulation has been associated with the transient depletion of the available neurotransmitter pool - also known as synaptic fatigue. Finally, thermal effects associated with extrinsic (environmental) and intrinsic (associated with kilohertz-frequency stimulation) temperature changes have been suggested to alter the neural response to stimulation paradigms.

CONCLUSION

The diverse spectrum of neural responses to stimulation in the kilohertz-frequency range is distinct from that associated with conventional stimulation. This offers the potential for new therapeutic avenues across stimulation modalities. However, stimulation in the kilohertz-frequency range is associated with distinct challenges and caveats that need to be considered in experimental paradigms.

Limited Sensitivity of Hippocampal Synaptic Function or Network Oscillations to Unmodulated Kilohertz Electric Fields

Understanding the cellular mechanisms of kilohertz (kHz) electrical stimulation is of broad interest in neuromodulation including forms of transcranial electrical stimulation, interferential stimulation, and high-rate spinal cord stimulation (SCS). Yet, the well-established low-pass filtering by neuronal membranes suggests minimal neuronal polarization in respond to charge-balanced kHz stimulation. The hippocampal brain slice model is among the most studied systems in neuroscience and exhaustively characterized in screening the effects of electrical stimulation. High-frequency electric fields of varied amplitudes (1–150 V/m), waveforms (sinusoidal, symmetrical pule, asymmetrical pulse) and frequencies (1 and10 kHz) were tested. Changes in single or paired-pulse field EPSPs (fEPSP) in CA1 were measured in response to radial-directed and tangential-directed electric fields, with brief (30 s) or long (30 min) application times. The effects of kHz stimulation on ongoing endogenous network activity were tested in carbachol-induced γ oscillation of CA3a and CA3c. Across 23 conditions evaluated, no significant changes in fEPSP were resolved, while responses were detected for within-slice control direct current (DC) fields; 1-kHz sinusoidal and pulse stimulation (≥60 V/m), but not 10 kHz, induced changes in oscillating neuronal network. We thus report no responses to low-amplitude 1-kHz or any 10-kHz fields, suggesting that any brain sensitivity to these fields is via yet to be-determined mechanism(s) of action which were not identified in our experimental preparation.

Partial high frequency nerve block decreases neuropathic signaling following chronic sciatic nerve constriction injury

OBJECTIVE

High frequency (HF) block can quickly and reversibly stop nerve conduction. We hypothesized HF block at the sciatic nerve would minimize nociception by preventing neuropathic signals from reaching the central nervous system.

APPROACH

Lewis rats were implanted with a constriction cuff and a distal cuff electrode around their right sciatic nerve. Tactile sensitivity was evaluated using the 50% paw withdrawal threshold determined using Chaplan's method for von Frey monofilaments. Over the course of 49 days, the 50% paw withdrawal threshold was measured 1) before HF block, 2) during HF block (50 kHz, 3 Vpp), and 3) after HF block. Gait was observed and scored before and during block. At end point, HF block efficacy was directly evaluated using additional cuff electrodes to elicit and record compound neural action potentials across the HF blocking cuff.

MAIN RESULTS

At days 7 and 14 days post-operation, tactile sensitivity was significantly lower during HF block compared to before and after block (p < 0.005). Additionally, an increase in gait disability was not visually observed during HF block.

SIGNIFICANCE

HF block can reduce tactile sensitivity in a limb with a neuropthic injury in a rapidly reversible fashion.

Quantitative comparisons of block thresholds and onset responses for charge-balanced kilohertz frequency waveforms

OBJECTIVE

There is growing interest in delivering kilohertz frequency (KHF) electrical signals to block conduction in peripheral nerves for treatment of various diseases. Previous studies used different KHF waveforms to achieve block, and it remains unclear how waveform affects nerve block parameters.

APPROACH

We quantified the effects of waveform on KHF block of the rat tibial nerve in vivo and in computational models. We compared block thresholds and onset responses across current-controlled sinusoids and charge-balanced rectangular waveforms with different asymmetries and duty cycles.

MAIN RESULTS

Sine waves had higher block thresholds than square waves, but used less power at block threshold. Block threshold had an inverse relationship with duty cycle of rectangular waveforms irrespective of waveform asymmetry. Computational model results were consistent with relationships measured in vivo, although the models underestimated the effect of duty cycle on increasing thresholds. The axonal membrane substantially filtered waveforms, the filter transfer function was strikingly similar across waveforms, and filtering resulted in post-filtered rms block thresholds that were approximately constant across waveforms in silico and in vivo. Onset response was not consistently affected by waveform shape, but onset response was smaller at amplitudes well above block threshold. Therefore, waveforms with lower block thresholds (e.g. sine waves or square waves) could be more readily increased to higher amplitudes relative to block threshold to reduce onset response. We also observed a reduction in onset responses across consecutive trials after initial application of supra-block threshold amplitudes.

SIGNIFICANCE

Waveform had substantial effects on block thresholds, and the amplitude relative to block threshold had substantial effects on onset response. These data inform choice of waveform in subsequent studies and clinical applications, enhance effective use of block in therapeutic applications, and facilitate the design of parameters that achieve block with minimal onset responses.

20-kHz alternating current stimulation: effects on motor and somatosensory thresholds

BACKGROUND

High frequency alternating current (HFAC) stimulation have been shown to produce a peripheral nerve conduction block. Currently, all the studies applying HFAC stimulation in clinical studies, have employed frequencies below 10 kHz. The main aim of this work was to investigate the neuromodulatory effect of transcutaneous 20 kHz stimulation on somatosensory and pain thresholds, and maximal handgrip strength.

METHODS

A randomized, crossover, single-blinded, placebo-controlled trial was conducted following recruitment of fourteen healthy volunteers. Transcutaneous stimulation at 20 kHz and sham stimulation were applied over the ulnar and median nerves of fourteen healthy volunteers for 20 min. Maximal handgrip strength (MHS), mechanical detection threshold (MDT) and pressure pain threshold (PPT) were registered prior to, during (15 min), immediately after the end (20 min), and 10 min following stimulation.

RESULTS

The 20 kHz stimulation showed a lower MHS during the stimulation at the 15 min (30.1 kgs SE 2.8) and at 20 min (31.8 kgs, SE 2.8) when compared to sham stimulation (35.1 kgs, SE 3.4; p < 0.001 and 34.2 kgs, SE 3.4; p = 0.03, respectively). The 20 kHz stimulation resulted in a slight increase in MDT at 15 min (0.25 mN; 0.25-2.00) when compared to the sham stimulation (0.25 mN; 0.25-0.25; p = 0.02), and no effects were showed for PPT.

CONCLUSIONS

High-frequency stimulation at 20 kHz suggests a partial block of nerve activity. Studies in subjects with neurological disorders characterized by nerve hyperactivity are needed to confirm the clinical impact of this non-invasive electrical stimulation technique.

TRIAL REGISTRATION

NCT, NCT02837458. Registered on 12 April 2017.

Measurement of block thresholds in kiloHertz frequency alternating current peripheral nerve block

BACKGROUND

Kilohertz frequency alternating currents (KHFAC) produce rapid nerve conduction block of mammalian peripheral nerve and have potential clinical applications in reducing peripheral nerve hyperactivity. The experimental investigation of KHFAC nerve block requires a robust output measure and this has proven to be the block threshold (BT), the lowest current or voltage at which the axons of interest are completely blocked. All significant literature in KHFAC nerve block, both simulations and experimental, were reviewed to determine the block threshold method that was used. The two common methods used are the High-Low method experimentally and the Binary search method for simulations.

NEW METHOD

Four methods to measure the block threshold (High-Low, High-Low-High, Binary and Random) at three frequencies (10, 20 and 30 kHz) were compared through randomized repeated experiments in the in-vivo rodent sciatic nerve-gastrocnemius model.

RESULTS

The literature review showed that more than 50% of publications did not measure the block threshold. The experimental results showed no statistical difference in the BT value between the four methods.

COMPARISON WITH EXISTING METHOD(S)

However, there were differences in the number of significant onset responses, depending on the method. The run time for the BT determination was the shortest for the High-Low method.

CONCLUSIONS

It is recommended that all research in electrical nerve block, including KHFAC, should include measurement of the BT. The High-Low method is recommended for most experimental situations but the Binary method could also be a viable option, especially where onset responses are minimal.

Direct current contamination of kilohertz frequency alternating current waveforms

Kilohertz frequency alternating current (KHFAC) waveforms are being evaluated in a variety of physiological settings because of their potential to modulate neural activity uniquely when compared to frequencies in the sub-kilohertz range. However, the use of waveforms in this frequency range presents some unique challenges regarding the generator output. In this study we explored the possibility of undesirable contamination of the KHFAC waveforms by direct current (DC). We evaluated current- and voltage-controlled KHFAC waveform generators in configurations that included a capacitive coupling between generator and electrode, a resistive coupling and combinations of capacitive with inductive coupling. Our results demonstrate that both voltage- and current-controlled signal generators can unintentionally add DC-contamination to a KHFAC signal, and that capacitive coupling is not always sufficient to eliminate this contamination. We furthermore demonstrated that high value inductors, placed in parallel with the electrode, can be effective in eliminating DC-contamination irrespective of the type of stimulator, reducing the DC contamination to less than 1 μA. This study highlights the importance of carefully designing the electronic setup used in KHFAC studies and suggests specific testing that should be performed and reported in all studies that assess the neural response to KHFAC waveforms.

Different clinical electrodes achieve similar electrical nerve conduction block

OBJECTIVE

We aim to evaluate the suitability of four electrodes previously used in clinical experiments for peripheral nerve electrical block applications.

APPROACH

We evaluated peripheral nerve electrical block using three such clinical nerve cuff electrodes (the Huntington helix, the Case self-sizing Spiral and the flat interface nerve electrode) and one clinical intramuscular electrode (the Memberg electrode) in five cats. Amplitude thresholds for the block using 12 or 25 kHz voltage-controlled stimulation, onset response, and stimulation thresholds before and after block testing were determined.

MAIN RESULTS

Complete nerve block was achieved reliably and the onset response to blocking stimulation was similar for all electrodes. Amplitude thresholds for the block were lowest for the Case Spiral electrode (4 ± 1 Vpp) and lower for the nerve cuff electrodes (7 ± 3 Vpp) than for the intramuscular electrode (26 ± 10 Vpp). A minor elevation in stimulation threshold and reduction in stimulus-evoked urethral pressure was observed during testing, but the effect was temporary and did not vary between electrodes.

SIGNIFICANCE

Multiple clinical electrodes appear suitable for neuroprostheses using peripheral nerve electrical block. The freedom to choose electrodes based on secondary criteria such as ease of implantation or cost should ease translation of electrical nerve block to clinical practice.

Reversible nerve conduction block using kilohertz frequency alternating current

OBJECTIVES

The features and clinical applications of balanced-charge kilohertz frequency alternating currents (KHFAC) are reviewed. Preclinical studies of KHFAC block have demonstrated that it can produce an extremely rapid and reversible block of nerve conduction. Recent systematic analysis and experimentation utilizing KHFAC block have resulted in a significant increase in interest in KHFAC block, both scientifically and clinically.

MATERIALS AND METHODS

We review the history and characteristics of KHFAC block, the methods used to investigate this type of block, the experimental evaluation of block, and the electrical parameters and electrode designs needed to achieve successful block. We then analyze the existing clinical applications of high-frequency currents, comparing the early results with the known features of KHFAC block.

RESULTS

Although many features of KHFAC block have been characterized, there is still much that is unknown regarding the response of neural structures to rapidly fluctuating electrical fields. The clinical reports to date do not provide sufficient information to properly evaluate the mechanisms that result in successful or unsuccessful treatment.

CONCLUSIONS

KHFAC nerve block has significant potential as a means of controlling nerve activity for the purpose of treating disease. However, early clinical studies in the use of high-frequency currents for the treatment of pain have not been designed to elucidate mechanisms or allow direct comparisons to preclinical data. We strongly encourage the careful reporting of the parameters utilized in these clinical studies, as well as the development of outcome measures that could illuminate the mechanisms of this modality.

A new high-density (25 electrodes/mm²) penetrating microelectrode array for recording and stimulating sub-millimeter neuroanatomical structures

OBJECTIVE

Among the currently available neural interface devices, there has been a need for a penetrating electrode array with a high electrode-count and high electrode-density (the number of electrodes/mm(2)) that can be used for electrophysiological studies of sub-millimeter neuroanatomical structures. We have developed such a penetrating microelectrode array with both a high electrode-density (25 electrodes/mm(2)) and high electrode-count (up to 96 electrodes) for small nervous system structures, based on the existing Utah Slanted Electrode Array (USEA). Such high electrode-density arrays are expected to provide greater access to nerve fibers than the conventionally spaced USEA especially in small diameter nerves.

APPROACH

One concern for such high density microelectrode arrays is that they may cause a nerve crush-type injury upon implantation. We evaluated this possibility during acute (<10 h) in vivo experiments with electrode arrays implanted into small diameter peripheral nerves of anesthetized rats (sciatic nerve) and cats (pudendal nerve).

MAIN RESULTS

Successful intrafascicular implantation and viable nerve function was demonstrated via microstimulation, single-unit recordings and histological analysis. Measurements of the electrode impedances and quantified electrode dimensions demonstrated fabrication quality. The results of these experiments show that such high density neural interfaces can be implanted acutely into neural tissue without causing a complete nerve crush injury, while mediating intrafascicular access to fibers in small diameter peripheral nerves.

SIGNIFICANCE

This new penetrating microelectrode array has characteristics un-matched by other neural interface devices currently available for peripheral nervous system neurophysiological research.

Selective neural activation in a histologically derived model of peripheral nerve

Functional electrical stimulation (FES) is a general term for therapeutic methods that use electrical stimulation to aid or replace lost ability. For FES systems that communicate with the nervous system, one critical component is the electrode interface through which the machine-body information transfer must occur. In this paper, we examine the influence of inhomogeneous tissue conductivities and positions of nodes of Ranvier on activation of myelinated axons for neuromuscular control as a function of electrode configuration. To evaluate these effects, we developed a high-resolution bioelectric model of a fascicle from a stained cross-section of cat sciatic nerve. The model was constructed by digitizing a fixed specimen of peripheral nerve, extruding the image along the axis of the nerve, and assigning each anatomical component to one of several different tissue types. Electrodes were represented by current sources in monopolar, transverse bipolar, and longitudinal bipolar configurations; neural activation was determined using coupled field-neuron simulations with myelinated axon cable models. We found that the use of an isotropic tissue medium overestimated neural activation thresholds compared with the use of physiologically based, inhomogeneous tissue medium, even after controlling for mean impedance levels. Additionally, the positions of the cathodic sources relative to the nodes of Ranvier had substantial effects on activation, and these effects were modulated by the electrode configuration. Our results indicate that physiologically based tissue properties cause considerable variability in the neural response, and the inclusion of these properties is an important component in accurately predicting activation. The results are used to suggest new electrode designs to enable selective stimulation of small diameter fibers.