Implanted functional electrical stimulation: an alternative for standing and walking in pediatric spinal cord injury

Boosting brain-computer interfaces with functional electrical stimulation: potential applications in people with locked-in syndrome

Individuals with a locked-in state live with severe whole-body paralysis that limits their ability to communicate with family and loved ones. Recent advances in brain-computer interface (BCI) technology have presented a potential alternative for these people to communicate by detecting neural activity associated with attempted hand or speech movements and translating the decoded intended movements to a control signal for a computer. A technique that could potentially enrich the communication capacity of BCIs is functional electrical stimulation (FES) of paralyzed limbs and face to restore body and facial movements of paralyzed individuals, allowing to add body language and facial expression to communication BCI utterances. Here, we review the current state of the art of existing BCI and FES work in people with paralysis of body and face and propose that a combined BCI-FES approach, which has already proved successful in several applications in stroke and spinal cord injury, can provide a novel promising mode of communication for locked-in individuals.

The role of electrical stimulation for rehabilitation and regeneration after spinal cord injury

Electrical stimulation is used to elicit muscle contraction and can be utilized for neurorehabilitation following spinal cord injury when paired with voluntary motor training. This technology is now an important therapeutic intervention that results in improvement in motor function in patients with spinal cord injuries. The purpose of this review is to summarize the various forms of electrical stimulation technology that exist and their applications. Furthermore, this paper addresses the potential future of the technology.

A Systematic Review of the Scientific Literature for Rehabilitation/Habilitation Among Individuals With Pediatric-Onset Spinal Cord Injury

Objectives

To conduct a systematic review to examine the scientific literature for rehabilitation/habilitation among individuals with pediatric-onset spinal cord injury (SCI).

Methods

A literature search of multiple databases (i.e., PubMed/MEDLINE, CINAHL, EMBASE, PsychINFO) was conducted and was filtered to include studies involving humans, published as full-length articles up to December 2020, and in English. Included studies met the following inclusion criteria: (1) ≥50% of the study sample had experienced a traumatic, acquired, nonprogressive spinal cord injury (SCI) or a nontraumatic, acquired, noncongenital SCI; (2) SCI onset occurred at ≤21 years of age; and (3) sample was assessed for a rehabilitation/habilitation-related topic. Studies were assigned a level of evidence using an adapted Sackett scale modified down to five levels. Data extracted from each study included author(s), year of publication, country of origin, study design, subject characteristics, rehabilitation/habilitation topic area, intervention (if applicable), and outcome measures.

Results

One hundred seventy-six studies were included for review (1974-2020) with the majority originating from the United States (81.3%). Most studies were noninterventional observational studies (n = 100; 56.8%) or noninterventional case report studies (n = 5; 2.8%). Sample sizes ranged from 1 to 3172 with a median of 26 (interquartile range [IQR], 116.5). Rehabilitation/habilitation topics were categorized by the International Classification of Functioning, Disability and Health (ICF); most studies evaluated ICF Body Function. There were 69 unique clinical health outcome measures reported.

Conclusion

The evidence for rehabilitation/habilitation of pediatric-onset SCI is extremely limited; nearly all studies (98%) are level 4-5 evidence. Future studies across several domains should be conducted with novel approaches to research design to alleviate issues related to sample sizes and heterogeneity.

Interventions for Gait Training in Children With Spinal Cord Impairments: A Scoping Review

PURPOSE

This is a scoping review of the literature on interventions for gait in individuals with pediatric spinal cord impairments.

SUMMARY OF KEY POINTS

Four categories of interventions were identified: orthoses/assistive devices, electrical stimulation, treadmill training, and infant treadmill stepping.

CONCLUSIONS

Studies on orthotic intervention, electrical stimulation, and treadmill training reported benefits for various components of gait. The majority of articles (77%) were classified as levels of evidence III and IV.

CLINICAL RECOMMENDATIONS

Each intervention targeted specific outcomes; therefore, it is important to identify individual patient characteristics and goals appropriate for each intervention to guide clinical practice. Determining the appropriate orthotic support for each child, and incorporating treadmill training or electrical stimulation, is recommended.

"Long-term stability of stimulating spiral nerve cuff electrodes on human peripheral nerves"

Background

Electrical stimulation of the peripheral nerves has been shown to be effective in restoring sensory and motor functions in the lower and upper extremities. This neural stimulation can be applied via non-penetrating spiral nerve cuff electrodes, though minimal information has been published regarding their long-term performance for multiple years after implantation.

Methods

Since 2005, 14 human volunteers with cervical or thoracic spinal cord injuries, or upper limb amputation, were chronically implanted with a total of 50 spiral nerve cuff electrodes on 10 different nerves (mean time post-implant 6.7 ± 3.1 years). The primary outcome measures utilized in this study were muscle recruitment curves, charge thresholds, and percent overlap of recruited motor unit populations.

Results

In the eight recipients still actively involved in research studies, 44/45 of the spiral contacts were still functional. In four participants regularly studied over the course of 1 month to 10.4 years, the charge thresholds of the majority of individual contacts remained stable over time. The four participants with spiral cuffs on their femoral nerves were all able to generate sufficient moment to keep the knees locked during standing after 2–4.5 years. The dorsiflexion moment produced by all four fibular nerve cuffs in the active participants exceeded the value required to prevent foot drop, but no tibial nerve cuffs were able to meet the plantarflexion moment that occurs during push-off at a normal walking speed. The selectivity of two multi-contact spiral cuffs was examined and both were still highly selective for different motor unit populations for up to 6.3 years after implantation.

Conclusions

The spiral nerve cuffs examined remain functional in motor and sensory neuroprostheses for 2–11 years after implantation. They exhibit stable charge thresholds, clinically relevant recruitment properties, and functional muscle selectivity. Non-penetrating spiral nerve cuff electrodes appear to be a suitable option for long-term clinical use on human peripheral nerves in implanted neuroprostheses.

Evoked Electromyographically Controlled Electrical Stimulation

Time-variant muscle responses under electrical stimulation (ES) are often problematic for all the applications of neuroprosthetic muscle control. This situation limits the range of ES usage in relevant areas, mainly due to muscle fatigue and also to changes in stimulation electrode contact conditions, especially in transcutaneous ES. Surface electrodes are still the most widely used in noninvasive applications. Electrical field variations caused by changes in the stimulation contact condition markedly affect the resulting total muscle activation levels. Fatigue phenomena under functional electrical stimulation (FES) are also well known source of time-varying characteristics coming from muscle response under ES. Therefore, it is essential to monitor the actual muscle state and assess the expected muscle response by ES so as to improve the current ES system in favor of adaptive muscle-response-aware FES control. To deal with this issue, we have been studying a novel control technique using evoked electromyography (eEMG) signals to compensate for these muscle time-variances under ES for stable neuroprosthetic muscle control. In this perspective article, I overview the background of this topic and highlight important points to be aware of when using ES to induce the desired muscle activation regardless of the time-variance. I also demonstrate how to deal with the common critical problem of ES to move toward robust neuroprosthetic muscle control with the Evoked Electromyographically Controlled Electrical Stimulation paradigm.

A preliminary comparison of myoelectric and cyclic control of an implanted neuroprosthesis to modulate gait speed in incomplete SCI

OBJECTIVE

Explore whether electromyography (EMG) control of electrical stimulation for walking after incomplete spinal cord injury (SCI) can affect ability to modulate speed and alter gait spatial-temporal parameters compared to cyclic repetition of pre-programmed stimulation.

DESIGN

Single case study with subject acting as own concurrent control. Setting Hospital-based biomechanics laboratory.

PARTICIPANTS

Single subject with C6 AIS D SCI using an implanted neuroprosthesis for walking. Interventions Lower extremity muscle activation via an implanted system with two different control methods: (1) pre-programmed pattern of stimulation, and (2) EMG-controlled stimulation based on signals from the gastrocnemius and quadriceps.

OUTCOME MEASURES

Gait speed, distance, and subjective rating of difficulty during 2-minute walks. Range of walking speeds and associated cadences, stride lengths, stride times, and double support times during quantitative gait analysis.

RESULTS

EMG control resulted in statistically significant increases in both walking speed and distance (P < 0.001) over cyclic stimulation during 2-minute walks. Maximum walking speed with EMG control (0.48 m/second) was significantly (P < 0.001) faster than the fastest automatic pattern (0.39 m/second), with increased cadence and decreased stride and double support times (P < 0.000) but no change in stride length (z = -0.085; P = 0.932). The slowest walking with EMG control (0.25 m/second) was virtually indistinguishable from the slowest with automatic cycling (z = -0.239; P = 0.811).

CONCLUSION

EMG control can increase the ability to modulate comfortable walking speed over pre-programmed cyclic stimulation. While control methods did not differ at the lowest speed, EMG-triggered stimulation allowed significantly faster walking than cyclic stimulation. The expanded range of available walking speeds could permit users to better avoid obstacles and naturally adapt to various environments. Further research is required to definitively determine the robustness, generalizability, and functional implications of these results.

Inverted Pendulum Standing Apparatus for Investigating Closed-Loop Control of Ankle Joint Muscle Contractions during Functional Electrical Stimulation

The restoration of arm-free standing in individuals with paraplegia can be facilitated via functional electrical stimulation (FES). In developing adequate control strategies for FES systems, it remains challenging to test the performance of a particular control scheme on human subjects. In this study, we propose a testing platform for developing effective control strategies for a closed-loop FES system for standing. The Inverted Pendulum Standing Apparatus (IPSA) is a mechanical inverted pendulum, whose angular position is determined by the subject's ankle joint angle as controlled by the FES system while having the subject's body fixed in a standing frame. This approach provides a setup that is safe, prevents falling, and enables a research and design team to rigorously test various closed-loop controlled FES systems applied to the ankle joints. To demonstrate the feasibility of using the IPSA, we conducted a case series that employed the device for studying FES closed-loop controllers for regulating ankle joint kinematics during standing. The utilized FES system stimulated, in able-bodied volunteers, the plantarflexors as they prevent toppling during standing. Four different conditions were compared, and we were able to show unique performance of each condition using the IPSA. We concluded that the IPSA is a useful tool for developing and testing closed-loop controlled FES systems for regulating ankle joint position during standing.

In vivo (31)P NMR spectroscopy assessment of skeletal muscle bioenergetics after spinal cord contusion in rats

PURPOSE

Muscle paralysis after spinal cord injury leads to muscle atrophy, enhanced muscle fatigue, and increased energy demands for functional activities. Phosphorus magnetic resonance spectroscopy ((31)P-MRS) offers a unique non-invasive alternative of measuring energy metabolism in skeletal muscle and is especially suitable for longitudinal investigations. We determined the impact of spinal cord contusion on in vivo muscle bioenergetics of the rat hind limb muscle using (31)P-MRS.

METHODS

A moderate spinal cord contusion injury (cSCI) was induced at the T8-T10 thoracic spinal segments. (31)P-MRS measurements were performed weekly in the rat hind limb muscles for 3 weeks. Spectra were acquired in a Bruker 11 T/470 MHz spectrometer using a 31P surface coil. The sciatic nerve was electrically stimulated by subcutaneous needle electrodes. Spectra were acquired at rest (5 min), during stimulation (6 min), and recovery (20 min). Phosphocreatine (PCr) depletion rates and the pseudo first-order rate constant for PCr recovery (k PCr) were determined. The maximal rate of PCr resynthesis, the in vivo maximum oxidative capacity (V max) and oxidative adenosine triphosphate (ATP) synthesis rate (Q max) were subsequently calculated.

RESULTS

One week after cSCI, there was a decline in the resting total creatine of the paralyzed muscle. There was a significant reduction (~24 %) in k PCr measures of the paralyzed muscle, maximum in vivo mitochondrial capacity (V max) and the maximum oxidative ATP synthesis rate (Q max) at 1 week post-cSCI. During exercise, the PCr depletion rates in the paralyzed muscle one week after injury were rapid and to a greater extent than in a healthy muscle.

CONCLUSIONS

Using in vivo MRS assessments, we reveal an acute oxidative metabolic defect in the paralyzed hind limb muscle. These altered muscle bioenergetics might contribute to the host of motor dysfunctions seen after cSCI.

Can administrative claim file review be used to gather physical therapy, occupational therapy, and psychology payment data and functional independence measure scores? Implications for rehabilitation providers in the private health sector

PURPOSE

Rehabilitation costs for spinal-cord injury (SCI) are increasingly borne by Canada's private health system. Because of poor outcomes, payers are questioning the value of their expenditures, but there is a paucity of data informing analysis of rehabilitation costs and outcomes. This study evaluated the feasibility of using administrative claim file review to extract rehabilitation payment data and functional status for a sample of persons with work-related SCI.

METHODS

Researchers reviewed 28 administrative e-claim files for persons who sustained a work-related SCI between 1996 and 2000. Payment data were extracted for physical therapy (PT), occupational therapy (OT), and psychology services. Functional Independence Measure (FIM) scores were targeted as a surrogate measure for functional outcome. Feasibility was tested using an existing approach for evaluating health services data.

RESULTS

The process of administrative e-claim file review was not practical for extraction of the targeted data.

CONCLUSIONS

While administrative claim files contain some rehabilitation payment and outcome data, in their present form the data are not suitable to inform rehabilitation services research. A new strategy to standardize collection, recording, and sharing of data in the rehabilitation industry should be explored as a means of promoting best practices.

Spinal cord injuries in children and adolescents

This chapter provides an overview of spinal cord injuries (SCI) in children and adolescents, including epidemiology, medical and musculoskeletal complications, rehabilitation and psychosocial aspects. Males are more commonly affected than females during adolescence; however, as the age at injury decreases, the preponderance of males becomes less marked, and by 3 years of age the number of females with SCIs equals that of males. The neurologic level and degree of completeness varies with age; among children injured prior to 12 years of age approximately two-thirds are paraplegic and approximately two-thirds have complete lesions. Among adolescents, approximately 50% have paraplegia and 55% have complete lesions. Management of pediatric-onset SCI should be family centered and developmentally based, responsive to the dynamic changes that occur during growth and development. Distinctive anatomical and physiological features of children and adolescents, along with growth and development, are responsible for unique manifestations and complications of pediatric SCI. SCI without radiological abnormalities (SCIWORA), birth injuries, lap-belt injuries, upper cervical injuries, and the delayed onset of neurological deficits are relatively unique to pediatric SCI. Children who sustain their SCI before puberty experience a higher incidence of musculoskeletal complications, such as scoliosis and hip dislocation.

Effects of electrical stimulation, exercise training and motor skills training on strength of children with meningomyelocele: a systematic review

This systematic review provides a critical synthesis of research regarding the effects of electrical stimulation, exercise training, and motor skills training on muscle strength in children with meningomyelocele. Nine databases were searched using terms related to meningomyelocele and physical therapy interventions. Of 298 potentially relevant citations, six met the inclusion criteria. Each was rated using the systematic review guidelines of the American Academy for Cerebral Palsy and Developmental Medicine. Two studies examined changes in quadriceps muscle torque following electrical stimulation, three investigated upper extremity exercise training, and one evaluated quadriceps strength after motor skills training. Although the limited evidence suggests improvements in strength when using these interventions, much of the evidence is of low methodological quality and all studies were published more than 10 years ago. Further research is needed regarding various strength-training interventions for children with meningomyelocele and the relationship between increased strength and improved activity and participation.

Benefits of FES gait in a spinal cord injured population

STUDY DESIGN

Review.

OBJECTIVES

This review article investigated the objective evidence of benefits derived from functional electrical stimulation (FES)-assisted gait for people with spinal cord injury (SCI). Both FES and gait have been proposed to promote not only augmented health and fitness, but specific ambulatory outcomes for individuals with neurological disabilities. However, due to small sample sizes and the lack of functionality of the intervention, it has not been widely used in clinical practice. This review assessed whether there is sufficient evidence to encourage a more widespread deployment of FES gait within the rehabilitation community.

METHODS

Hand searches and online data collection were performed in Medline and Science Direct. Specific search terms used included SCI/paralysis/paraplegia and tetraplegia with electrical stimulation/FES, gait and walking.

RESULTS

The searches generated 532 papers. Of these papers, 496 were excluded and 36 papers were included in the review. Many reported benefits were not carefully investigated, and small sample sizes or different methodologies resulted in insufficient evidence to draw definitive conclusions.

CONCLUSIONS

FES gait can enhance gait, muscle strength and cardiorespiratory fitness for people with SCI. However, these benefits are dependent on the nature of the injury and further research is required to generalize these results to the widespread population of SCI individuals. Proof of the functionality and further evidence of the benefits of FES gait will assist in FES gait gaining clinical acceptance.

Design and evaluation of a stand-up motorized prone cart

BACKGROUND/OBJECTIVE

Prone carts are used for mobility by individuals with spinal cord injury in whom seated mobility (wheelchair) is contraindicated due to ischial or sacral pressure ulcers. Currently available prone carts are uncomfortable, subjecting the user to neck and shoulder strain, and make social interaction and performing activities of daily living difficult. A better design of prone carts is needed. In addition, standing devices have shown some medical benefits. The objective was to design and evaluate an improved prone cart that facilitates standing.

DESIGN

Engineering development project with user feedback through questionnaire. Users selected by convenience sampling.

METHODS

A marketing survey was performed of nurse managers of spinal cord injury units. Then 2 prototype carts were designed and built. These carts are able to tilt up to 45 degrees and have a joystick-controlled motor for propulsion and other design features, including a workspace storage shelf and rearview mirrors. The carts were evaluated by both patients and caregivers at 2 Veteran's Administration hospitals.

OUTCOME MEASURES

Questionnaire of subjects, both patients and caregivers, who used the cart.

FINDINGS

Both patients and caregivers liked the carts and the ability to assume a nonhorizontal body angle. The major complaint about the cart was that it seemed too long when it came to making turns.

CONCLUSION

This prone cart design is an improvement over the standard, flat variety. However, further design changes will be necessary. This study provided valuable information that will be useful in the next-generation prone cart design project.

Implantable FES system for upright mobility and bladder and bowel function for individuals with spinal cord injury

STUDY DESIGN

Postintervention.

OBJECTIVES

To determine the effectiveness of the Praxis multifunctional implantable functional electrical stimulation (FES) system (Neopraxis Pty. Ltd, Lane Cove, NSW, Australia) to provide standing and stepping ability and bladder and bowel management for individuals with motor complete thoracic level spinal cord injuries (SCI).

SETTING

Pediatric orthopedic hospital specializing in SCI.

SUBJECTS

Three males, ages 17 and 21 years, with motor-complete thoracic level SCI and intact lower motor neurons to the muscles targeted for stimulation.

METHODS

Each subject was successfully implanted with the Praxis FES system. All three subjects received electrodes for upright mobility and the first two subjects received additional electrodes for stimulated bladder and bowel management. Following training, subjects were evaluated in their ability to use FES for nine mobility activities. Acute and chronic experiments of the effect of stimulation on bowel and bladder function were also performed.

RESULTS

All three subjects could independently stand up from the wheelchair and could walk at least 6 m using a swing through gait pattern. Two subjects were able to independently perform swing through gait for 6 min and one subject was able to independently ascend and descend stairs. Suppression of reflex bladder contractions by neuromodulation (subject 1) and stimulated contractions of the rectum (subject 2) were observed in acute experiments. When stimulation was applied over the course of several weeks, a positive effect on bowel function was measured. Stimulated bladder contractions were not achieved.

CONCLUSION

The feasibility of using the Praxis FES system for upright mobility and aiding aspects of bladder and bowel function was demonstrated with three subjects with thoracic level SCI.

Patterns of lower extremity innervation in pediatric spinal cord injury

STUDY DESIGN

Retrospective review.

OBJECTIVES

To identify relationships between lower extremity innervation and level of injury, mechanism of injury, and age at injury in a pediatric population with spinal cord injury (SCI). Secondarily, relationships between innervation and completeness of injury, time since injury, race, and sex were evaluated.

SETTING

Pediatric orthopedic referral hospital, Philadelphia, Pennsylvania.

METHODS

Records of 190 subjects, ages 1-21 years, were reviewed. Data collected from the medical record included lower extremity muscle innervation, American Spinal Injury Association (ASIA) level and class, mechanism of injury, age at injury, time since injury, race, and sex. To determine innervation, lower extremity muscles had been tested using surface electrical stimulation and identified as being innervated or denervated. If a muscle responded weakly, strength duration testing was performed. For analysis via logistic regression, subjects were grouped based upon level and mechanism of injury.

RESULTS

A relationship (P<0.0001) was found between ASIA level and lower extremity innervation of all muscles and between length of time since injury and lower extremity innervation for some muscles. Following multiple logistic regression, only ASIA level remained as an independent predictor of lower extremity innervation status.

CONCLUSION

Our results show that lower extremity innervation does differ based on the level of the injury. Denervation began to be seen with injuries in the lower thoracic region and more predominantly with injuries in the lumbar region. This supports our hypothesis that the incidence of lower motor neuron injuries would increase as injuries became more caudal. Our hypotheses of a relationship between innervation status and mechanism of injury and age at injury were not supported. This information is important in determining treatment strategies, eligibility for electrical stimulation techniques, and potential regenerative strategies.

SPONSORSHIP

This study was funded by Shriners Hospitals for Children, Grant #8530.

Functional Electrical Stimulation for Neuromuscular Applications

Paralyzed or paretic muscles can be made to contract by applying electrical currents to the intact peripheral motor nerves innervating them. When electrically elicited muscle contractions are coordinated in a manner that provides function, the technique is termed functional electrical stimulation (FES). In more than 40 years of FES research, principles for safe stimulation of neuromuscular tissue have been established, and methods for modulating the strength of electrically induced muscle contractions have been discovered. FES systems have been developed for restoring function in the upper extremity, lower extremity, bladder and bowel, and respiratory system. Some of these neuroprostheses have become commercialized products, and others are available in clinical research settings. Technological developments are expected to produce new systems that have no external components, are expandable to multiple applications, are upgradable to new advances, and are controlled by a combination of signals, including biopotential signals from nerve, muscle, and the brain.

Timed motor test for wheelchair users: initial development and application in children with spinal cord injury

OBJECTIVE

The objective of this study was to describe the development and preliminary results of reliability testing of the timed motor test (TMT), a performance-based measure of functional status for children with a spinal cord injury (SCI) who use a manual wheelchair. This study will also provide pilot data using the TMT to examine the impact of thoracolumbosacral orthoses (TLSO) on function in children with a SCI.

STUDY DESIGN

Cross-sectional observational study. METHODS/PARTICIPANTS: This study enrolled 11 subjects with SCI. The TMT consisted of donning a shirt, donning pants, even transfers, uneven transfers, and propelling a wheelchair 80 feet and up a ramp of 45 feet. Nine subjects completed the TMT with and without a TLSO, and 6 subjects (4 of whom also completed the TMT with and without a TLSO) completed the reliability testing.

RESULTS

Except for donning pants, the intertester and intratester reliability of the TMT was fair-to-good with intraclass correlation coefficients (ICCs) of 0.60 or greater. When wearing a TLSO, participants were slower at donning a shirt, donning pants, performing even and uneven transfers, and hallway propulsion (P < 0.05). There was a preference for not wearing a TLSO for dressing and transfer skills.

CONCLUSION

In general, the TMT for wheelchair users had fair-to-good intertester and intratester reliability. Based on these pilot data, there was an increase in time to complete several functional tasks because of the use of a TLSO as measured by the TMT in children with a SCI.