Patient Perspectives on the Efficacy and Ergonomics of Rechargeable Spinal Cord Stimulators

Mechanisms of Action of Dorsal Root Ganglion Stimulation

The dorsal root ganglion (DRG) serves as a pivotal site for managing chronic pain through dorsal root ganglion stimulation (DRG-S). In recent years, the DRG-S has emerged as an attractive modality in the armamentarium of neuromodulation therapy due to its accessibility and efficacy in alleviating chronic pain refractory to conventional treatments. Despite its therapeutic advantages, the precise mechanisms underlying DRG-S-induced analgesia remain elusive, attributed in part to the diverse sensory neuron population within the DRG and its modulation of both peripheral and central sensory processing pathways. Emerging evidence suggests that DRG-S may alleviate pain by several mechanisms, including the reduction of nociceptive signals at the T-junction of sensory neurons, modulation of pain gating pathways within the dorsal horn, and regulation of neuronal excitability within the DRG itself. However, elucidating the full extent of DRG-S mechanisms necessitates further exploration, particularly regarding its supraspinal effects and its interactions with cognitive and affective networks. Understanding these mechanisms is crucial for optimizing neurostimulation technologies and improving clinical outcomes of DRG-S for chronic pain management. This review provides a comprehensive overview of the DRG anatomy, mechanisms of action of the DRG-S, and its significance in neuromodulation therapy for chronic pain.

Patient-Reported Satisfaction with Using a Rechargeable 10 kHz Spinal Cord Stimulation Device

Introduction

Chronic pain is a common clinical condition and is frequently treated with a variety of medications, but pharmacotherapy is oftentimes not the optimal long-term treatment option. Safe and effective long-term pain relief for trunk and limb pain is available using high-frequency spinal cord stimulation at 10 kHz (10 kHz SCS), which is delivered using a rechargeable implantable pulse generator (IPG). Although rechargeable devices have been shown to reduce patient risk and overall cost by eliminating the need for periodic surgeries to replace depleted non-rechargeable IPGs, there is little published evidence that rechargeable technology is practical and convenient for patients, especially in the context of 10 kHz SCS.

Objective

This analysis of real-world patients implanted with 10 kHz SCS devices was undertaken using patient data from an industry-maintained database to investigate whether there was a substantial burden associated with rechargeable SCS and the degree of patient satisfaction or dissatisfaction with 10 kHz SCS.

Results

This study included 10,391 men and women who were implanted with 10 kHz SCS devices to treat chronic pain of the trunk and/or limbs. They received stimulation for a median of 361 days (180-1550 days), and 65.48% had previous spine surgery. In this patient sample, most patients were satisfied with the efficacy of 10 kHz SCS, including 77% who would repeat the procedure and 71% who would recommend it to other patients with similar pain. In regards to IPG recharging, 70% were satisfied or very satisfied and 19% were neutral, and a majority of patients recharged their device daily for 30 to 60 minutes.

Conclusion

These results indicate most patients do not find IPG recharging inconvenient or burdensome. In addition, IPG recharging is not a barrier to the majority of patients benefitting from 10 kHz SCS for long-term pain relief.

Clinical Longevity of 106,462 Rechargeable and Primary Cell Spinal Cord Stimulators: Real World Study in the Medicare Population

INTRODUCTION

Spinal cord stimulators (SCS) are available with either primary cell (PC) or rechargeable cell (RC) batteries. Although RC systems are proposed to have a battery longevity upward of nine years, in comparison with four years for PC systems, there are few studies of longevity of SCS in the real world.

MATERIALS AND METHODS

This was an observational, nonrandomized, retrospective study of Medicare beneficiaries who received neurostimulator implants in the outpatient hospital. This study used Medicare fee-for-service claims data from 2013 to 2020. The clinical longevity of the implantable pulse generator (IPG), defined as the duration from implant until removal for any reason, was compared between PC and RC devices. Life distribution analysis was used to approximate device lifespan. The secondary analysis separated removals into explant or replacements. The statistics were adjusted for relevant clinical covariates.

RESULTS

A total of 25,856 PC and 79,606 RC systems were included in the study. At seven years after implant, 53.8% of PC IPGs and 55.0% of RC IPGs remained in use. The life distribution modeling analysis projected a median lifespan of 8.2 years for PC and 9.0 years for RC devices. The rate of explant was lower for PC devices (19.2%) than for RC devices (22.0%, hazard ratio (HR) = 0.96, p = 0.082), whereas the rate of replacements was higher for PC devices (33.7%) than for RC devices (29.5%, HR = 1.31, p < 0.001). An analysis of the battery type used in device replacements showed an increasing adoption of PC devices over time.

CONCLUSIONS

This large, retrospective, real-world analysis of Medicare claims data demonstrated that the clinical longevity of neurostimulator devices is similar for PC and RC batteries. In the past, clinicians may have defaulted to RC devices based on the assumption that they provided extended battery life. Considering this longevity data, clinicians should now consider the choice between PC and RC devices based on other individual factors pertinent to the patient experience and not on purported longevity claims.

A Novel Spinal Cord Stimulation System with a Battery-Free Micro Implantable Pulse Generator

Spinal cord stimulation (SCS) is effective for the treatment of chronic intractable pain of the trunk and limbs. The mechanism of action may be based, at least in part, upon the gate control theory; however, new waveforms may suggest other mechanisms. Although benefits of the SCS technology generally outweigh the complications associated with SCS, some complications such as infection and skin erosion over the implant can result in device removal. Additional reasons for device removal, such as pocket pain and battery depletion, have driven technological innovations including battery-free implants and device miniaturization. The neurostimulation system described here was specifically designed to address complications commonly associated with implantable batteries and/or larger implantable devices. The benefits of the small size are further augmented by a minimally invasive implant procedure. Usability data show that patients found this novel neurostimulation system to be easy to use and comfortable to wear. What is more, clinical data demonstrate that the use of this system provides statistically significant reduction in pain scores with responder rates (defined as ≥ 50% reduction in pain) of 78% in the low back and 83% in the leg(s). Advances in miniaturization technology arose from the considerable shrinkage of the integrated circuit, with an increase in performance, according to Moore's law (1965). However, commensurate improvements in battery technology have not maintained a similar pace. This has prompted some manufacturers to place the battery outside, against the skin, thereby allowing a massive reduction in the implant volume, with the hopes of fewer device-related complications.

Ethical Considerations in the Implantation of Neuromodulatory Devices

OBJECTIVES

Neuromodulatory devices are increasingly used by neurosurgeons to manage a variety of chronic conditions. Given their potential benefits, it is imperative to create clear ethical guidelines for the use of these devices. We present a tiered ethical framework for neurosurgeon recommendations for the use of neuromodulatory devices.

MATERIALS AND METHODS

We conducted a literature review to identify factors neurosurgeons should consider when choosing to offer a neuromodulatory device to a patient.

RESULTS

Neurosurgeons must weigh reductions in debilitating symptoms, improved functionality, and preserved quality of life against risks for intraoperative complications and adverse events due to stimulation or the device itself. Neurosurgeons must also evaluate whether patients and families will maintain responsibility for the management of neuromodulatory devices. Consideration of these factors should occur on an axis of resource allocation, ranging from provision of neuromodulatory devices to those with greatest potential benefit in resource-limited settings to provision of neuromodulatory devices to all patients with indications in contexts without resource limitations. Neurosurgeons must also take action to promote device effectiveness throughout the duration of care.

CONCLUSIONS

Weighing risks and benefits of providing neuromodulatory devices and assessing ability to remain responsible for the devices on the level of the individual patient indicate which patients are most likely to achieve benefit from these devices. Consideration of these factors on an axis of resource allocation will allow for optimal provision of neuromodulatory devices to patients in settings of varied resources. Neurosurgeons play a primary role in promoting the effectiveness of these devices.

Ethical considerations in the surgical and neuromodulatory treatment of epilepsy

Surgical resection and neuromodulation are well-established treatments for those with medically refractory epilepsy. These treatments entail important ethical considerations beyond those which extend to the treatment of epilepsy generally. In this paper, the authors explore these unique considerations through a framework that relates foundational principles of bioethics to features of resective epilepsy surgery and neuromodulation. The authors conducted a literature review to identify ethical considerations for a variety of epilepsy surgery procedures and to examine how foundational principles in bioethics may inform treatment decisions. Healthcare providers should be cognizant of how an increased prevalence of somatic and psychiatric comorbidities, the dynamic nature of symptom burden over time, the individual and systemic barriers to treatment, and variable sociocultural contexts constitute important ethical considerations regarding the use of surgery or neuromodulation for the treatment of epilepsy. Moreover, careful attention should be paid to how resective epilepsy surgery and neuromodulation relate to notions of patient autonomy, safety and privacy, and the shared responsibility for device management and maintenance. A three-tiered approach-(1) gathering information and assessing the risks and benefits of different treatment options, (2) clear communication with patient or proxy with awareness of patient values and barriers to treatment, and (3) long-term decision maintenance through continued identification of gaps in understanding and provision of information-allows for optimal treatment of the individual person with epilepsy while minimizing disparities in epilepsy care.

A Resonant Coupler for Subcutaneous Implant

A resonator coupler for subcutaneous implants has been developed with a new impedance matching pattern added to the conventional loop antenna. The tuning element of a concentric metal pad contributes distributed capacitance and inductance to the planar inductive loop and improves resonance significantly. It provides a better qualify factor for resonant coupling and a much lower reflection coefficient for the implant electronics. Practical constraints are taken into account for designs including the requirement of operation within a regulated frequency band and the limited thickness for a monolithic implant. In this work, two designs targeting to operate in the two industrial, scientific, and medical (ISM) bands at 903 MHz and 2.45 GHz are considered. The tuning metal pad improves their resonances significantly, compared to the conventional loop designs. Since it is difficult to tune the implant antenna after implantation, the effects of tissue depth variations due to the individual's surgery and the appropriate implant depths are investigated. Simulations conducted with the dielectric properties of human skin documented in the literature are compared to measurements done with hydrated ground pork as phantoms. Experiments and simulations are conducted to explain the discrepancies in frequency shifts due to the uses of pork phantoms. The design method is thus validated for uses on human skin. A noninvasive localization method to identify the implant under the skin has been examined and demonstrated by both simulations and measurements. It can efficiently locate the subcutaneous implant based on the high quality-factor resonance owing to the tuning elements in both implant and transmitter couplers. The planar resonant coupler for wireless power transfer shows good performance and promise in subcutaneous applications for implants.

Pulse Dosing of 10 kHz Paresthesia-Independent Spinal Cord Stimulation Provides Same Efficacy with Substantial Reduction of Device Recharge Time

Objective

This study was designed to assess whether using pulse dosing (PD) (regularly cycled intermittent stimulation) of high-frequency 10-kHz spinal cord stimulation (10-kHz SCS) can reduce device recharge time while maintaining efficacy in patients with chronic intractable back pain with or without leg pain.

Design

Prospective, multicenter, observational study.

Methods

Patients successfully using 10-kHz SCS at 100%ON (i.e., continuously with no PD) for >3 months were consecutively enrolled. After a 1-week baseline period of documenting their pain twice daily on a 0–10 numerical rating scale (NRS) using 100%ON of their “favorite” program, all subjects were reprogrammed to 14%PD for 10–14 days. If subjects preferred 14%PD to 100%ON, they were programmed to 3%PD; otherwise, they were programmed to 50%PD. Subjects used this next program for another 10–14 days. Subjects then entered a 3-month observational period during which they were requested to use but not limited to their most preferred %PD program. Toward the end of 3 months, subjects completed a 7-day NRS diary and indicated a final %PD program preference. Study endpoints included %PD preference, mean diary NRS by %PD, and daily minutes and patterns of charging.

Results

Of 31 subjects completing the study, 81% preferred less than 100%ON. Among the subjects, 39% preferred 3%PD, 32% preferred 14%PD, 10% preferred 50%PD, and 19% preferred 100%ON. Average daily charge durations were 8.3 ± 3.1 minutes for 3%PD, 13.9 ± 4.9 minutes for 14%PD, 26.2 ± 7.4 minutes for 50%PD, and 43.8 ± 10.9 minutes for 100%ON. Regression modeling suggested that pain relief was weighted as more than twice as influential as charging in preference for reduced %PD.

Conclusions

This prospective study suggests that 10-kHz SCS therapy with PD may be successfully used in a large majority of 10-kHz SCS responders, maintaining efficacy while reducing device charging time by nearly two thirds.

Novel Intermittent Dosing Burst Paradigm in Spinal Cord Stimulation

INTRODUCTION

Intermittent dosing (ID), in which periods of stimulation-on are alternated with periods of stimulation-off, is generally employed using 30 sec ON and 90 sec OFF intervals with burst spinal cord stimulation (SCS). The goal of this study was to evaluate the feasibility of using extended stimulation-off periods in patients with chronic intractable pain.

MATERIALS AND METHODS

This prospective, multicenter, feasibility trial evaluated the clinical efficacy of the following ID stimulation-off times: 90, 120, 150, and 360 sec with burst waveform parameters. After a successful trial (≥50% pain relief) using ID stimulation, subjects were titrated with OFF times beginning with 360 sec. Pain, quality of life, disability, and pain catastrophizing were evaluated at one, three, and six months after permanent implant.

RESULTS

Fifty subjects completed an SCS trial using ID stimulation settings of 30 sec ON and 90 sec OFF, with 38 (76%) receiving ≥50% pain relief. Pain scores were significantly reduced from baseline at all time points (p < 0.001). Improvements in quality of life, disability, and pain catastrophizing were aligned with pain relief outcomes; 45.8% of the subjects that completed the six-month follow-up visit used an OFF period of 360 seconds.

CONCLUSIONS

ID burst SCS effectively relieved pain for six months. The largest group of subjects used IDB settings of 30 sec ON and 360 sec OFF. These findings present intriguing implications for the optimal "dose" of electricity in SCS and may offer many advantages such as optimizing the therapeutic window, extending battery life, reducing recharge burden and, potentially, mitigating therapy habituation or tolerance.

Stanford Pragmatiec Effectiveness Comparison (SPEC) protocol: Comparing long-term effectiveness of high-frequency and burst spinal cord stimulation in real-world application

OBJECTIVES

High-frequency and burst stimulation are newer waveforms that have demonstrated promise compared to traditional tonic spinal cord stimulation (SCS), but more studies are needed to compare their effectiveness. We report the study methods for an ongoing, single center, pragmatic randomized clinical trial to compare the effectiveness of high-frequency and burst SCS in patients with chronic back and/or leg pain.

MATERIALS AND METHODS

Participants who are candidates for spinal cord stimulation are enrolled and screened. Participants will be randomly assigned using point-of-care randomization to receive either high-frequency or burst SCS. Data collection will be through Stanford Pain Management Center's learning healthcare system: CHOIR. CHOIR surveys include National Institutes of Health Patient Reported Outcomes Measurement Information System item banks, a body map, questions about pain intensity, pain catastrophizing scale, and questions about patients' pain experience and healthcare utilization. Participants will complete online surveys at baseline and then 1, 3, 6, 12, 18, 24 and 36 months after their device implant. All participants will use our routine process of trial and implant. Reported adverse events are monitored throughout the study. Our primary outcome is change from baseline in pain intensity at 12 months.

RESULTS

We hypothesize that high-frequency SCS is more effective than burst SCS in improving pain, physical function and pain interference in participants with chronic low back and/or leg pain.

CONCLUSIONS

The pragmatic nature of our proposed trial enables us to recruit a larger participant cohort faster and to follow up these participants longer than currently published clinical trials.

Unique Characteristics of the Dorsal Root Ganglion as a Target for Neuromodulation

Objective

The dorsal root ganglion (DRG) is a novel target for neuromodulation, and DRG stimulation is proving to be a viable option in the treatment of chronic intractable neuropathic pain. Although the overall principle of conventional spinal cord stimulation (SCS) and DRG stimulation—in which an electric field is applied to a neural target with the intent of affecting neural pathways to decrease pain perception—is similar, there are significant differences in the anatomy and physiology of the DRG that make it an ideal target for neuromodulation and may account for the superior outcomes observed in the treatment of certain chronic neuropathic pain states. This review highlights the anatomy of the DRG, its function in maintaining homeostasis and its role in neuropathic pain, and the unique value of DRG as a target in neuromodulation for pain.

Methods

A narrative literature review was performed.

Results

Overall, the DRG is a critical structure in sensory transduction and modulation, including pain transmission and the maintenance of persistent neuropathic pain states. Unique characteristics including selective somatic organization, specialized membrane characteristics, and accessible and consistent location make the DRG an ideal target for neuromodulation. Because DRG stimulation directly recruits the somata of primary sensory neurons and harnesses the filtering capacity of the pseudounipolar neural architecture, it is differentiated from SCS, peripheral nerve stimulation, and other neuromodulation options.

Conclusions

There are several advantages to targeting the DRG, including lower energy usage, more focused and posture-independent stimulation, reduced paresthesia, and improved clinical outcomes.

The Evolution of Neuromodulation in the Treatment of Chronic Pain: Forward-Looking Perspectives

Background

The field of neuromodulation is continually evolving, with the past decade showing significant advancement in the therapeutic efficacy of neuromodulation procedures. The continued evolution of neuromodulation technology brings with it the promise of addressing the needs of both patients and physicians, as current technology improves and clinical applications expand.

Design

This review highlights the current state of the art of neuromodulation for treating chronic pain, describes key areas of development including stimulation patterns and neural targets, expanding indications and applications, feedback-controlled systems, noninvasive approaches, and biomarkers for neuromodulation and technology miniaturization.

Results and Conclusions

The field of neuromodulation is undergoing a renaissance of technology development with potential for profoundly improving the care of chronic pain patients. New and emerging targets like the dorsal root ganglion, as well as high-frequency and patterned stimulation methodologies such as burst stimulation, are paving the way for better clinical outcomes. As we look forward to the future, neural sensing, novel target-specific stimulation patterns, and approaches combining neuromodulation therapies are likely to significantly impact how neuromodulation is used. Moreover, select biomarkers may influence and guide the use of neuromodulation and help objectively demonstrate efficacy and outcomes.

New Technologies and Applications in Sacral Neuromodulation: An Update

Recently rechargeable devices have been introduced for sacral neuromodulation (SNM) with conditional safety for full-body magnetic resonance imaging (MRI). Currently a recharge-free SNM device represents the standard implant; however, it is only approved for MRI head scans. As further new technologies with broader MRI capabilities are emerging, the advantages as well as disadvantages of both rechargeable versus recharge-free devices will be briefly discussed in this commentary from the perspective of patients, healthcare professionals, and providers.

Patient Experience with Rechargeable Implantable Pulse Generator Deep Brain Stimulation for Movement Disorders

BACKGROUND/AIMS

Nonrechargeable deep brain stimulation implantable pulse generators (IPGs) for movement disorders require surgical replacement every few years due to battery depletion. Rechargeable IPGs reduce frequency of replacement surgeries and inherent risks of complications but require frequent recharging. Here, we evaluate patient experience with rechargeable IPGs and define predictive characteristics for higher satisfaction.

METHODS

We contacted all patients implanted with rechargeable IPGs at a single center in a survey-based study. We analyzed patient satisfaction with respect to age, diagnosis, target, charging duration, and body mass index. We tabulated hardware-related adverse events.

RESULTS

Dystonia patients had significantly higher satisfaction than Parkinson's disease patients in recharging, display, programmer, and training domains. Common positive responses were "fewer surgeries" and "small size." Common negative responses were "difficulty finding the right position to recharge" and "need to recharge every day." Hardware-related adverse events occurred in 21 of 59 participants.

CONCLUSION

Patient experience with rechargeable IPGs was largely positive; however, frustrations with recharging and adverse events were common. Dystonia diagnosis was most predictive of high satisfaction across multiple categories, potentially related to expected long disease duration with need for numerous IPG replacements.

Programming settings and recharge interval in a prospective study of a rechargeable sacral neuromodulation system for the treatment of overactive bladder

AIMS

The RELAX-OAB study is designed to confirm the safety, efficacy, and technical performance of the Axonics r-SNM System, a miniaturized, rechargeable SNM system approved in Europe and Canada for the treatment of bladder and bowel dysfunction. The purpose of this article is to describe study subjects' ability to charge the rechargeable neurostimulator and to document their neurostimulator program settings and recharge interval over time.

METHODS

Fifty-one OAB patients were implanted in a single-stage procedure. These results represent the 3-month charging experience for 48 subjects who completed the 3-month follow-up. Recharge intervals were estimated using therapy stimulation settings and subject experience was evaluated using questionnaires.

RESULTS

Forty-seven of forty-eight (98%) subjects were able to successfully charge their device prior to follow-up within 1-month post-implant. At 3-month post-implant, 98% of subjects were able to charge prior to their follow-up visit. Average stimulation amplitude across all subjects was 1.8 mA (±1.1 mA). A total of 69% of subjects had ≥14-day recharge intervals (time between charging) and 98% of subjects had ≥7-day recharge interval. No charging related adverse events occurred.

CONCLUSIONS

Study subjects were able to charge the Axonics r-SNM System and stimulation settings provided 2 weeks of therapy between recharging for most subjects. Subject satisfaction indicates that subjects are satisfied with rechargeable SNM therapy.

Recent advances in spinal cord stimulation for pain treatment

Traditional (40–50 Hz) spinal column stimulation is an efficacious and widely accepted treatment for chronic neuropathic pain conditions. However, there are major challenges including its ineffectiveness for axial back pain, the burden of paresthesia-related discomfort and difficulties producing indisputable research. Recently, there have been the major technological innovations of high-frequency and burst stimulation. Studies have shown these to provide improved analgesia even for axial pain without the problems associated with paresthesia. Dorsal root ganglion stimulation may be useful in certain subsets of patients with dermatomal distribution of pain. Other scientific data and technological improvements such as recent research on cost–effectiveness, MRI compatibility and very recent advances in spinal column stimulation are appraised.

Novel 10-kHz High-frequency Therapy (HF10 Therapy) Is Superior to Traditional Low-frequency Spinal Cord Stimulation for the Treatment of Chronic Back and Leg Pain: The SENZA-RCT Randomized Controlled Trial

BACKGROUND

Current treatments for chronic pain have limited effectiveness and commonly known side effects. Given the prevalence and burden of intractable pain, additional therapeutic approaches are desired. Spinal cord stimulation (SCS) delivered at 10 kHz (as in HF10 therapy) may provide pain relief without the paresthesias typical of traditional low-frequency SCS. The objective of this randomized, parallel-arm, noninferiority study was to compare long-term safety and efficacy of SCS therapies in patients with back and leg pain.

METHODS

A total of 198 subjects with both back and leg pain were randomized in a 1:1 ratio to a treatment group across 10 comprehensive pain treatment centers. Of these, 171 passed a temporary trial and were implanted with an SCS system. Responders (the primary outcome) were defined as having 50% or greater back pain reduction with no stimulation-related neurological deficit.

RESULTS

At 3 months, 84.5% of implanted HF10 therapy subjects were responders for back pain and 83.1% for leg pain, and 43.8% of traditional SCS subjects were responders for back pain and 55.5% for leg pain (P < 0.001 for both back and leg pain comparisons). The relative ratio for responders was 1.9 (95% CI, 1.4 to 2.5) for back pain and 1.5 (95% CI, 1.2 to 1.9) for leg pain. The superiority of HF10 therapy over traditional SCS for leg and back pain was sustained through 12 months (P < 0.001). HF10 therapy subjects did not experience paresthesias.

CONCLUSION

HF10 therapy promises to substantially impact the management of back and leg pain with broad applicability to patients, physicians, and payers.

Patient perspectives on the efficacy of a new kind of rechargeable deep brain stimulators(1)

PURPOSE/AIM OF THE STUDY

Rechargeable deep brain stimulation (DBS) system with longer battery life has become available for treating movement disorders. However, little information exists about the safety and management after implantation. Therefore, there is an urgent need to evaluate the recharging performance through long-term observations.

MATERIALS AND METHODS

Fifty-three Parkinson's disease (PD) patients were implanted with a new rechargeable device (G102R, PINS Medical). They were observed at the baseline and 3 months, 6 months and 12 months after surgery, with measurement of the acceptance, frequency, recharging time and feeling during recharging.

RESULTS

The patients with the ages between 34 and 70 (57.64 ± 7.34) years thought the system was very easy to recharge. The favorite time interval for recharging was 1 week, and 10 days and half a month also chosen. Most of the patients spent around 1 hour recharging, with no unacceptable hot feelings reported.

CONCLUSIONS

The PD patients could easily and safely recharge this new rechargeable implantable neurostimulators. Thus, these neurostimulators might be an excellent choice for PD patients.

Design and in vivo evaluation of more efficient and selective deep brain stimulation electrodes

OBJECTIVE

Deep brain stimulation (DBS) is an effective treatment for movement disorders and a promising therapy for treating epilepsy and psychiatric disorders. Despite its clinical success, the efficiency and selectivity of DBS can be improved. Our objective was to design electrode geometries that increased the efficiency and selectivity of DBS.

APPROACH

We coupled computational models of electrodes in brain tissue with cable models of axons of passage (AOPs), terminating axons (TAs), and local neurons (LNs); we used engineering optimization to design electrodes for stimulating these neural elements; and the model predictions were tested in vivo.

MAIN RESULTS

Compared with the standard electrode used in the Medtronic Model 3387 and 3389 arrays, model-optimized electrodes consumed 45-84% less power. Similar gains in selectivity were evident with the optimized electrodes: 50% of parallel AOPs could be activated while reducing activation of perpendicular AOPs from 44 to 48% with the standard electrode to 0-14% with bipolar designs; 50% of perpendicular AOPs could be activated while reducing activation of parallel AOPs from 53 to 55% with the standard electrode to 1-5% with an array of cathodes; and, 50% of TAs could be activated while reducing activation of AOPs from 43 to 100% with the standard electrode to 2-15% with a distal anode. In vivo, both the geometry and polarity of the electrode had a profound impact on the efficiency and selectivity of stimulation.

SIGNIFICANCE

Model-based design is a powerful tool that can be used to improve the efficiency and selectivity of DBS electrodes.

Current challenges in spinal cord stimulation

OBJECTIVES

This study aims to review the current state of spinal cord stimulation for the treatment of chronic pain associated with failed back surgery syndrome (FBSS) and complex regional pain syndrome (CRPS) and to describe intraspinal targets and stimulation parameters, patient selection, therapy cost-effectiveness, and strategies to improve outcomes.

MATERIALS AND METHODS

We drew on professional literature spanning four decades, our work with national and international professional societies, and our own extensive clinical experience to summarize contemporary knowledge of the safety, efficacy, cost-efficiency, and challenges associated with spinal cord stimulation in treating chronic pain.

RESULTS

The safety, efficacy, and cost-efficiency of spinal cord stimulation in treating chronic pain associated with FBSS and CRPS are well established through randomized controlled trials and long-term observational studies. Challenges include reducing wait-times before implant, which are associated with lower success rates; increasing awareness of this therapy among referring physicians, patients, and payers; decreasing device-related complications by incorporating advanced technology, improved operative and trialing techniques, and appropriate patient selection; and capturing functional and quality-of-life outcomes. Spinal cord stimulation must be part of an overall treatment plan to manage chronic pain, and must engage physicians, patients, their families, pharmacists, nursing staff, and mental health experts in supporting a return to employment, if possible, and to a full domestic and social life.

CONCLUSIONS

Innovation in spinal cord stimulation therapy has intensified with numerous new technical capabilities, safety advances, and novel stimulation targets. This progress holds hope for the many sufferers of chronic pain.

Evaluation of high-perimeter electrode designs for deep brain stimulation

OBJECTIVE

Deep brain stimulation (DBS) is an effective treatment for movement disorders and a promising therapy for treating epilepsy and psychiatric disorders. Despite its clinical success, complications including infections and mis-programing following surgical replacement of the battery-powered implantable pulse generator adversely impact the safety profile of this therapy. We sought to decrease power consumption and extend battery life by modifying the electrode geometry to increase stimulation efficiency. The specific goal of this study was to determine whether electrode contact perimeter or area had a greater effect on increasing stimulation efficiency.

APPROACH

Finite-element method (FEM) models of eight prototype electrode designs were used to calculate the electrode access resistance, and the FEM models were coupled with cable models of passing axons to quantify stimulation efficiency. We also measured in vitro the electrical properties of the prototype electrode designs and measured in vivo the stimulation efficiency following acute implantation in anesthetized cats.

MAIN RESULTS

Area had a greater effect than perimeter on altering the electrode access resistance; electrode (access or dynamic) resistance alone did not predict stimulation efficiency because efficiency was dependent on the shape of the potential distribution in the tissue; and, quantitative assessment of stimulation efficiency required consideration of the effects of the electrode-tissue interface impedance.

SIGNIFICANCE

These results advance understanding of the features of electrode geometry that are important for designing the next generation of efficient DBS electrodes.

Spinal stimulation for pain: future applications

With continuous progress and rapid technological advancement of neuromodulation it is conceivable that within next decade or so, our approach to the electrical stimulation of the spinal cord used in treatment of chronic pain will change radically. The currently used spinal cord stimulation (SCS), with its procedural invasiveness, bulky devices, simplistic stimulation paradigms, and frustrating decline in effectiveness over time will be replaced by much more refined and individually tailored modality. Better understanding of underlying mechanism of action will allow us to use SCS in a more rational way, selecting patient-specific targets and techniques that properly fit each patient with chronic pain based on pain characteristics, distribution, and cause. Based on the information available today, this article will summarize emerging applications of SCS in the treatment of pain and theorize on further developments that may be introduced in the foreseeable future. An overview of clinical and technological innovations will serve as a basis for better understanding of SCS landscape for the next several years.