Transcutaneous Spinal Stimulation From Adults to Children: A Review

Synergistic effects of transcutaneous spinal stimulation and neuromuscular electrical stimulation on lower limb force production: Time to deliver

BACKGROUND

Transcutaneous spinal stimulation (TSS) and neuromuscular electrical stimulation (NMES) can facilitate self-assisted standing in individuals with paralysis. However, individual variability in responses to each modality may limit their effectiveness in generating the necessary leg extension force for full body weight standing. To address this challenge, we proposed combining TSS and NMES to enhance leg extensor muscle activation, with optimizing timing adjustment to maximize the interaction between the two modalities.

METHODS

To assess the effects of TSS and NMES on knee extension and plantarflexion force, ten neurologically intact participants underwent three conditions: (1) TSS control, (2) NMES control, and (3) TSS + NMES. TSS was delivered between the T10 and L2 vertebrae, while NMES was delivered to the skin over the right knee extensors and plantarflexors. TSS and NMES were administered using a 15 Hz train of three 0.5 ms biphasic pulses. During the TSS + NMES condition, the timing between modalities was adjusted in increments of ¼ the interval within a 15 Hz frequency, i.e., 66, 49.5, 33, 16.5, and 1 ms.

RESULTS

NMES combined with TSS, produced synergistic effects even on non-targeted muscle groups, thereby promoting leg extension across multiple joints in the kinematic chain. The sequence of NMES or TSS trains relative to each other did not significantly impact motor output. Notably, a delay of 16.5 to 49.5 ms between interleaved TSS and NMES pulses, each delivered at 15 Hz, results in more robust and synergistic responses in knee extensors and plantarflexors.

CONCLUSIONS

By adjusting the timing between TSS and NMES, we can optimize the combined use of these modalities for functional restoration. Our findings highlight the potential of integrated TSS and NMES protocols to enhance motor function, suggesting promising avenues for therapeutic applications, particularly in the rehabilitation of individuals with SCI.

Functional outcomes and participants' perspectives during short-term application of spinal stimulation in individuals with spinal cord injury

OBJECTIVE

The primary objective of this study was to quantify changes in performance of task-specific motor activities over 12 motor rehabilitation sessions with lumbosacral spinal cord stimulation (SCS) via either transcutaneous stimulation or epidural stimulation. Both stimulation modalities have been used in recent years to restore functions lost to spinal cord injury (SCI). Secondary outcomes examine participants' perspectives captured via the User Experience Questionnaire (UEQ) upon study completion to further understand their perception of SCS.

METHODS

Six individuals with SCI completed 12 sessions with one modality of SCS during supine and/or side-lying, seated forward reaching, and standing activities. Changes in volitional lower extremity movement, the number of points of contact needed at hips and/or knees to facilitate standing, and changes in seated forward reaching distance were used to quantify performance. The UEQ was administered to gauge participants' perspectives following use of SCS to enable functions impaired due to SCI.

RESULTS

For all participants, performance of motor activities improved with SCS compared to without stimulation. Responses for the UEQ showed an overall positive perception of trialing SCS with rehabilitation to enhance motor functions impaired by SCI.

CONCLUSIONS

Regardless of injury severity, location of injury, time since SCI, or SCS modality, all participants experienced gains in motor function in the presence of SCS combined with a condensed rehabilitation program. However, no evidence of sustained motor functions was found in the absence of SCS. UEQ results highlight the positive perception of SCS with rehabilitation as well as the importance of consulting persons with lived experience of SCS during clinical trial design and protocol development.Trial registration: ClinicalTrials.gov identifier: NCT05095454.

Safety and Feasibility of Cervical and Thoracic Transcutaneous Spinal Cord Stimulation to Improve Hand Motor Function in Children With Chronic Spinal Cord Injury

OBJECTIVE

In adults with cervical spinal cord injury (SCI), transcutaneous spinal stimulation (scTS) has improved upper extremity strength and control. This novel noninvasive neurotherapeutic approach combined with training may modulate the inherent developmental plasticity of children with SCI, providing even greater improvements than training or stimulation alone. Because children with SCI represent a vulnerable population, we first must establish the safety and feasibility of any potential novel therapeutic approach. The objectives of this pilot study were to determine the safety, feasibility, and proof of principle of cervical and thoracic scTS for short-term effect on upper extremity strength in children with SCI.

MATERIALS AND METHODS

In this nonrandomized, within-subject repeated measure design, seven participants with chronic cervical SCI performed upper extremity motor tasks without and with cervical (C3-C4 and C6-C7) and thoracic (T10-T11) site scTS. Safety and feasibility of using cervical and thoracic sites scTS were determined by the frequency count of anticipated and unanticipated risks (eg, pain, numbness). Proof-of-principle concept was tested via change in force production during hand motor tasks.

RESULTS

All seven participants tolerated cervical and thoracic scTS across the three days, with a wide range of stimulation intensities (cervical sites = 20-70 mA and thoracic site = 25-190 mA). Skin redness at the stimulation sites was observed in four of 21 assessments (19%) and dissipated in a few hours. No episode of autonomic dysreflexia was observed or reported. Hemodynamic parameters (systolic blood pressure and heart rate) remained within stable limits (p > 0.05) throughout the assessment time points at baseline, with scTS, and after the experiment. Hand-grip and wrist-extension strength increased (p < 0.05) with scTS.

CONCLUSIONS

We indicated that short-term application of scTS via two cervical and one thoracic site is safe and feasible in children with SCI and resulted in immediate improvements in hand-grip and wrist-extension strength in the presence of scTS.

CLINICAL TRIAL REGISTRATION

The Clinicaltrials.gov registration number for the study is NCT04032990.

Non-Invasive Spinal Cord Stimulation for Motor Rehabilitation of Patients with Spinal Muscular Atrophy Treated with Orphan Drugs

Spinal muscular atrophy (SMA) is an orphan disease characterized by the progressive degeneration of spinal alpha motor neurons. In recent years, nusinersen and several other drugs have been approved for the treatment of this disease. Transcutaneous spinal cord stimulation (tSCS) modulates spinal neuronal networks, resulting in changes in locomotion and posture in patients with severe spinal cord injury and stroke. We hypothesize that tSCS can activate motor neurons that are intact and restored by medication, slow the decline in motor activity, and contribute to the development of motor skills in SMA patients. Thirty-seven children and adults with SMA types 2 and 3 participated in this study. The median duration of drug treatment was over 20 months. The application of tSCS was performed during physical therapy for 20-40 min per day for ~12 days. Outcome measures were specific SMA motor scales, goniometry of contractured joints, and forced vital capacity. Significant increases in motor function, improved respiratory function, and decreased contracture were observed in both type 2 and 3 SMA participants. The magnitude of functional changes was not associated with participant age. Further studies are needed to elucidate the reasons for the beneficial effects of spinal cord electrical stimulation on SMA.

Transcutaneous spinal cord stimulation on motor function in patients with spinal cord injury: A meta-analysis

BACKGROUND

It has been suggested that transcutaneous spinal cord stimulation (SCS) is effective in the rehabilitation of patients with spinal cord injury (SCI). However, the evidence is mainly based on case reports.

OBJECTIVE

To summarize the influence of transcutaneous SCS on extremity motor function of patients with SCI in a meta-analysis.

METHODS

A systematic literature search was performed in electronic databases including PubMed, Cochrane library, Embase, Web of Science, Wanfang, and CNKI to obtain relevant randomized controlled trials (RCTs). A random-effects model was used to pool the results by incorporating the impact of the potential heterogeneity. The most recent database search was conducted on December 31, 2023.

RESULTS

Six small-scale open-label or single-blind RCTs were included. Transcutaneous SCS on the basis of conventional rehabilitation could significantly improve limb strength (mean difference: 4.82, p = 0.004; I2 = 0%) and attenuate spasticity (MD: -0.40, p = 0.02; I2 = 0%). The upper-extremity motor function was not significantly affected (p = 0.75). However, transcutaneous SCS significantly improved mobility as indicated by walking speed (MD: 0.13 m/s, p = 0.009; I2 = 0%) and walking distance (standardized MD: 0.62, I2 = 0%).

CONCLUSION

Transcutaneous SCS is effective in improving limb strength, spasticity and mobility of patients with SCI.

Combining transcutaneous spinal stimulation and functional electrical stimulation increases force generated by lower limbs: When more is more

Background

Transcutaneous Spinal Stimulation (TSS) has been shown to promote activation of the lower limb and trunk muscles and is being actively explored for improving the motor outcomes of people with neurological conditions. However, individual responses to TSS vary, and often the muscle responses are insufficient to produce enough force for self-supported standing. Functional electrical stimulation (FES) can activate individual muscles and assist in closing this functional gap, but it introduces questions regarding timing between modalities.

Methods

To assess the effects of TSS and FES on force generation, ten neurologically intact participants underwent (1) TSS only, (2) FES only, and (3) TSS + FES. TSS was delivered using four electrodes placed at T10-T11 through the L1-L2 intervertebral spaces simultaneously, while FES was delivered to the skin over the right knee extensors and plantarflexors. For all conditions, TSS and FES were delivered using three 0.5 ms biphasic square-wave pulses at 15 Hz. During the TSS + FES condition, timing between the two modalities was adjusted in increments of ¼ time between pulses (16.5 ms).

Results

When TSS preceded FES, a larger force production was observed. We also determined several changes in muscle activation amplitude at different relative stimulus intervals, which help characterize our finding and indicate the facilitating and inhibitory effects of the modalities.

Conclusions

Utilizing a delay ranging from 15 to 30 ms between stimuli resulted in higher mean force generation in both the knee and ankle joints, regardless of the selected FES location (Average; knee: 112.0%, ankle: 103.1%).

Multi-Site Spinal Cord Transcutaneous Stimulation Facilitates Upper Limb Sensory and Motor Recovery in Severe Cervical Spinal Cord Injury: A Case Study

Individuals with cervical spinal cord injury (SCI) rank regaining arm and hand function as their top rehabilitation priority post-injury. Cervical spinal cord transcutaneous stimulation (scTS) combined with activity-based recovery training (ABRT) is known to effectively facilitate upper extremity sensorimotor recovery in individuals with residual arm and hand function post SCI. However, scTS effectiveness in facilitating upper extremity recovery in individuals with severe SCI with minimal to no sensory and motor preservation below injury level remains largely unknown. We herein introduced a multimodal neuro-rehabilitative approach involving scTS targeting systematically identified various spinal segments combined with ABRT. We hypothesized that multi-site scTS combined with ABRT will effectively neuromodulate the spinal networks, resulting in improved integration of ascending and descending neural information required for sensory and motor recovery in individuals with severe cervical SCI. To test the hypothesis, a 53-year-old male (C2, AIS A, 8 years post-injury) received 60 ABRT sessions combined with continuous multi-site scTS. Post-training assessments revealed improved activation of previously paralyzed upper extremity muscles and sensory improvements over the dorsal and volar aspects of the hand. Most likely, altered spinal cord excitability and improved muscle activation and sensations resulted in observed sensorimotor recovery. However, despite promising neurophysiological evidence pertaining to motor re-activation, we did not observe visually appreciable functional recovery on obtained upper extremity motor assessments.

Activity-Based Restorative Therapy Promotes Progression from Asymmetry to Symmetry in Posture and Gait in a Child with Chronic, Incomplete Spinal Cord Injury

Incomplete spinal cord injuries (ISCI) in pediatrics and adults can lead to asymmetric motor impairments exhibiting as asymmetries of posture and gait. Recently, rehabilitation guidelines for adults with neurologic injuries have focused on gaining a functional gait pattern as measured by speed and distance, even if asymmetry deficits persist. Activity-based restorative therapies (ABRT) take advantage of activity-dependent neuroplasticity to change an individual's neuromuscular capacity. This is a report of an ambulatory child with chronic ISCI presenting with significant postural and gait asymmetries who enrolled in an ABRT program. Across 79 ABRT sessions, the child gained symmetry during sitting, standing, and walking. Even though this child was a functional ambulator at enrollment, targeting symmetry of movements via improved neuromuscular capacity further enhanced her achievement of kinematically appropriate function for participation in daily activities.

Preservation of functional descending input to paralyzed upper extremity muscles in motor complete cervical spinal cord injury

OBJECTIVE

Spinal cord injury (SCI) is classified as complete or incomplete depending on the extent of sensorimotor preservation below the injury level. However, individuals with complete SCIs can voluntarily activate paralyzed lower limb muscles alone or by engaging non-paralyzed muscles during neurophysiological assessments, indicating presence of residual pathways across the injury. However, similar phenomena have not been explored for the upper extremity (UE) muscles following cervical SCIs.

METHODS

Eighteen individuals with motor complete cervical SCI (AIS A or B) and five age-matched non-injured (NI) individuals performed various UE events against manual resistance during functional neurophysiological assessment (FNPA), and electromyographic (EMG) activity was recorded from UE muscles.

RESULTS

Our findings demonstrated i) voluntary activation of clinically paralyzed muscles as evident from EMG readouts, ii) increased activity in these muscles during events engaging muscles above the injury level, iii) reduced spectral properties of paralyzed muscles in SCI compared to NI participants.

CONCLUSIONS

Functional EMG activity in clinically paralyzed muscles indicate presence of residual pathways across the injury establishing supralesional control over the sublesional neural circuitry.

SIGNIFICANCE

The findings may help explain the neurophysiological basis for UE recovery and can be exploited in designing rehabilitation techniques to facilitate UE recovery following cervical SCIs.