Properties of the surface electromyogram following traumatic spinal cord injury: a scoping review

Decoding of unimanual and bimanual reach-and-grasp actions from EMG and IMU signals in persons with cervical spinal cord injury

Objective. Chronic motor impairments of arms and hands as the consequence of a cervical spinal cord injury (SCI) have a tremendous impact on activities of daily life. A considerable number of people however retain minimal voluntary motor control in the paralyzed parts of the upper limbs that are measurable by electromyography (EMG) and inertial measurement units (IMUs). An integration into human-machine interfaces (HMIs) holds promise for reliable grasp intent detection and intuitive assistive device control.Approach. We used a multimodal HMI incorporating EMG and IMU data to decode reach-and-grasp movements of groups of persons with cervical SCI (n = 4) and without (control, n = 13). A post-hoc evaluation of control group data aimed to identify optimal parameters for online, co-adaptive closed-loop HMI sessions with persons with cervical SCI. We compared the performance of real-time, Random Forest-based movement versus rest (2 classes) and grasp type predictors (3 classes) with respect to their co-adaptation and evaluated the underlying feature importance maps.Main results. Our multimodal approach enabled grasp decoding significantly better than EMG or IMU data alone (p<0.05). We found the 0.25 s directly prior to the first touch of an object to hold the most discriminative information. Our HMIs correctly predicted 79.3 ± STD 7.4 (102.7 ± STD 2.3 control group) out of 105 trials with grand average movement vs. rest prediction accuracies above 99.64% (100% sensitivity) and grasp prediction accuracies of 75.39 ± STD 13.77% (97.66 ± STD 5.48% control group). Co-adaption led to higher prediction accuracies with time, and we could identify adaptions in feature importances unique to each participant with cervical SCI.Significance. Our findings foster the development of multimodal and adaptive HMIs to allow persons with cervical SCI the intuitive control of assistive devices to improve personal independence.

Validity and reliability study of a novel surface electromyography sensor using a well-consolidated electromyography system in individuals with cervical spinal cord injury

STUDY DESIGN

Non-interventional, cross-sectional pilot study.

OBJECTIVES

To establish the validity and reliability of the BioStamp nPoint biosensor (Medidata Solutions, New York, NY, USA [formerly MC10, Inc.]) for measuring electromyography in individuals with cervical spinal cord injury (SCI) by comparing the surface electromyography (sEMG) metrics with the Trigno wireless electromyography system (Delsys, Natick, MA, USA).

SETTING

Participants were recruited from the Shirley Ryan AbilityLab registry.

METHODS

Individuals aged 18-70 years with cervical SCI were evaluated with the two biosensors to capture activity on upper-extremity muscles during two study sessions conducted over 2 days (day 1-consent alone; day 2-two data collections in same session). Time and frequency metrics were captured, and signal-to-noise ratio was determined for each muscle group. Test-retest reliability was determined using Pearson's correlation. Validation of the BioStamp nPoint system was based on Bland-Altmann analysis.

RESULTS

Among the 11 participants, 30.8% had subacute cervical injury at C5-C6; 53.8% were injured within 1 year of the study. Results from the test-retest reliability assessment revealed that most Pearson's correlations between the two sensory measurements were strong (≥0.50). The Bland-Altman analysis found values of the signal-to-noise ratio, frequency, and peak amplitude were within the level of agreement. Signal-to-noise ratios ranged from 7.06 to 22.1.

CONCLUSIONS

In most instances, the performance of the BioStamp nPoint sensors was moderately to strongly correlated with that of the Trigno sensors in all muscle groups tested. The BioStamp nPoint system is a valid and reliable approach to assess sEMG measures in individuals with cervical SCI.

SPONSORSHIP

The present study was supported by AbbVie Inc.

The relationship between balance control and thigh muscle strength and muscle activity in persons with incomplete spinal cord injury

STUDY DESIGN

Cross-sectional study.

OBJECTIVES

A spinal cord injury (SCI) can compromise the ability to maintain sufficient balance control during activities in an upraised position. The objective of the study was to explore the relationship between balance control and muscle strength and muscle activation in the lower extremities in persons with incomplete SCI (iSCI).

SETTING

Sunnaas Rehabilitation Hospital, Norway.

METHODS

Thirteen men and two women with iSCI and 15 healthy, matched controls were included. Performance of the Berg Balance Scale (BBS) short version (7 items) was used to indicate balance control. Maximal voluntary contraction (MVC) was performed to measure isometric muscle strength in thigh muscles (knee extension/flexion), while surface electromyography (EMG) was measured from M. Vastus Lateralis and M. Biceps Femoris. The relative activation of each muscle during each of the BBS tasks was reported as the percentage of the maximal activation during the MVC (%EMGmax).

RESULTS

The iSCI participants had a significantly lower BBS sum score and up to 40% lower muscle strength in knee- flexion and extension compared to the matched healthy controls. They also exhibited a significantly higher %EMGmax, i.e. a higher muscle activation, during most of the balance tests. Univariate regression analysis revealed a significant association between balance control and mean values of %EMGmax in Biceps Femoris, averaged over the seven BBS tests.

CONCLUSIONS

The participants with iSCI had poorer balance control, reduced thigh muscle strength and a higher relative muscle activation in their thigh muscles, during balance-demanding activities.

Characterizing neurological status in individuals with tetraplegia using transcutaneous spinal stimulation

Transcutaneous spinal stimulation (TSS) is emerging as a valuable tool for electrophysiological and clinical assessment. This study had the objective of examining the recruitment patterns of upper limb (UL) motor pools through the delivery of TSS above and below a spinal lesion. It also aimed to explore the connection between the recruitment pattern of UL motor pools and the neurological and functional status following spinal cord injury (SCI). In eight participants with tetraplegia due to cervical SCI, TSS was delivered to the cervical spinal cord between the spinous processes of C3-C4 and C7-T1 vertebrae, and spinally evoked motor potentials in UL muscles were characterized. We found that responses observed in UL muscles innervated by motor pools below the level of injury demonstrated relatively reduced sensitivity to TSS compared to those above the lesion, were asymmetrical in the majority of muscles, and were dependent on the level, extent, and side of SCI. Overall, our findings indicate that electrophysiological data acquired through TSS can offer insights into the extent of UL functional asymmetry, disruptions in neural pathways, and changes in motor control following SCI. This study suggests that such electrophysiological data can supplement clinical and functional assessment and provide further insight regarding residual motor function in individuals with SCI.

A computational model of surface electromyography signal alterations after spinal cord injury

Objective. Spinal cord injury (SCI) can cause significant impairment and disability with an impact on the quality of life for individuals with SCI and their caregivers. Surface electromyography (sEMG) is a sensitive and non-invasive technique to measure muscle activity and has demonstrated great potential in capturing neuromuscular changes resulting from SCI. The mechanisms of the sEMG signal characteristic changes due to SCI are multi-faceted and difficult to studyin vivo. In this study, we utilized well-established computational models to characterize changes in sEMG signal after SCI and identify sEMG features that are sensitive and specific to different aspects of the SCI.Approach. Starting from existing models for motor neuron pool organization and motor unit action potential generation for healthy neuromuscular systems, we implemented scenarios to model damages to upper motor neurons, lower motor neurons, and the number of muscle fibers within each motor unit. After simulating sEMG signals from each scenario, we extracted time and frequency domain features and investigated the impact of SCI disruptions on sEMG features using the Kendall Rank Correlation analysis.Main results. The commonly used amplitude-based sEMG features (such as mean absolute values and root mean square) cannot differentiate between injury scenarios, but a broader set of features (including autoregression and cepstrum coefficients) provides greater specificity to the type of damage present.Significance. We introduce a novel approach to mechanistically relate sEMG features (often underused in SCI research) to different types of neuromuscular alterations that may occur after SCI. This work contributes to the further understanding and utilization of sEMG in clinical applications, which will ultimately improve patient outcomes after SCI.

Transcutaneous spinal stimulation provides characterization of neurological status in individuals with tetraplegia

Transcutaneous spinal stimulation (TSS) is emerging as a valuable tool for electrophysiological and clinical assessment. This study had the objective of examining the recruitment patterns of upper limb (UL) motor pools through the delivery of TSS above and below a spinal lesion. It also aimed to explore the connection between the recruitment pattern of UL motor pools and the neurological and functional status following spinal cord injury (SCI). In eight participants with tetraplegia due to cervical SCI, TSS was delivered to the cervical spinal cord between the spinous processes of C3-C4 and C7-T1 vertebrae, and spinally evoked motor potentials in UL muscles were characterized. We found that responses observed in UL muscles innervated by motor pools below the level of injury demonstrated relatively reduced sensitivity to TSS compared to those above the lesion, were asymmetrical in the majority of muscles, and were dependent on the level, extent, and side of SCI. Overall, our findings indicate that electrophysiological data acquired through TSS can offer insights into the extent of UL functional asymmetry, disruptions in neural pathways, and changes in motor control following SCI. This study suggests that such electrophysiological data can supplement clinical and functional assessment and provide further insight regarding residual motor function in individuals with SCI.

Functional electrical stimulation therapy for upper extremity rehabilitation following spinal cord injury: a pilot study

STUDY DESIGN

Pilot study.

OBJECTIVES

To examine if functional electrical stimulation therapy (FEST) improves neuromuscular factors underlying upper limb function in individuals with SCI.

SETTING

A tertiary spinal cord rehabilitation center specialized in spinal cord injury care in Canada.

METHODS

We examined 29 muscles from 4 individuals living with chronic, cervical, and incomplete SCI. The analysis was focused on the changes in muscle activation, as well as on how the treatment could change the ability to control a given muscle or on how multiple muscles would be coordinated during volitional efforts.

RESULTS

There was evidence of gains in muscle strength, activation, and median frequency after the FEST. Gains in muscle activation indicated the activation of a greater number of motor units and gains in muscle median frequency the involvement of higher threshold, faster motor units. In some individuals, these changes were smaller but accompanied by increased control over muscle contraction, evident in a greater ability to sustain a volitional contraction, reduce the co-contraction of antagonist muscles, and provide cortical drive.

CONCLUSIONS

FEST increases muscle strength and activation. Enhanced control of muscle contraction, reduced co-contraction of antagonist muscles, and a greater presence of cortical drive were some of the findings supporting the effects of FEST at the sensory-motor integration level.

STIMGRASP: A Home-Based Functional Electrical Stimulator for Grasp Restoration in Daily Activities

Thousands of people currently suffer from motor limitations caused by SCI and strokes, which impose personal and social challenges. These individuals may have a satisfactory recovery by applying functional electrical stimulation that enables the artificial restoration of grasping after a muscular conditioning period. This paper presents the STIMGRASP, a home-based functional electrical stimulator to be used as an assistive technology for users with tetraplegia or hemiplegia. The STIMGRASP is a microcontrolled stimulator with eight multiplexed and independent symmetric biphasic constant current output channels with USB and Bluetooth communication. The system generates pulses with frequency, width, and maximum amplitude set at 20 Hz, 300 µs/phase, and 40 mA (load of 1 kΩ), respectively. It is powered by a rechargeable lithium-ion battery of 3100 mAh, allowing more than 10 h of continuous use. The development of this system focused on portability, usability, and wearability, resulting in portable hardware with user-friendly mobile app control and an orthosis with electrodes, allowing the user to carry out muscle activation sequences for four grasp modes to use for achieving daily activities.

Surface EMG in Subacute and Chronic Care after Traumatic Spinal Cord Injuries

Background: Traumatic spinal cord injury (SCI) is a devastating condition commonly originating from motor vehicle accidents or falls. Trauma care after SCI is challenging; after decompression surgery and spine stabilization, the first step is to assess the location and severity of the traumatic lesion. For this, clinical outcome measures are used to quantify the residual sensation and volitional control of muscles below the level of injury. These clinical assessments are important for decision-making, including the prediction of the recovery potential of individuals after the SCI. In clinical care, this quantification is usually performed using sensation and motor scores, a semi-quantitative measurement, alongside the binary classification of the sacral sparing (yes/no). Objective: In this perspective article, I review the use of surface EMG (sEMG) as a quantitative outcome measurement in subacute and chronic trauma care after SCI. Methods: Here, I revisit the main findings of two comprehensive scoping reviews recently published by our team on this topic. I offer a perspective on the combined findings of these scoping reviews, which integrate the changes in sEMG with SCI and the use of sEMG in neurorehabilitation after SCI. Results: sEMG provides a complimentary assessment to quantify the residual control of muscles with great sensitivity and detail compared to the traditional clinical assessments. Our scoping reviews unveiled the ability of the sEMG assessment to detect discomplete lesions (muscles with absent motor scores but present sEMG). Moreover, sEMG is able to measure the spontaneous activity of motor units at rest, and during passive maneuvers, the evoked responses with sensory or motor stimulation, and the integrity of the spinal cord and descending tracts with motor evoked potentials. This greatly complements the diagnostics of the SCI in the subacute phase of trauma care and deepens our understanding of neurorehabilitation strategies during the chronic phase of the traumatic injury. Conclusions: sEMG offers important insights into the neurophysiological factors underlying sensorimotor impairment and recovery after SCIs. Although several qualitative or semi-quantitative outcome measures determine the level of injury and the natural recovery after SCIs, using quantitative measures such as sEMG is promising. Nonetheless, there are still several barriers limiting the use of sEMG in the clinical environment and a need to advance high-density sEMG technology.

Combined selective peripheral neurotomy in the treatment of spastic lower limbs of spinal cord injury patients

Objective

To explore the therapeutic effect of combined selective peripheral neurotomy (cSPN) on the spasm of the lower limbs after spinal cord injury.

Methods

A prospective intervention (before-after trial) with an observational design was conducted in 14 spinal cord injury patients with severe lower limbs spasticity by cSPN. Given the severe spasm of hip adductor, triceps surae, and hamstring muscles in these patients, a total of 26 obturator nerve branches, 26 tibia nerve branches, and 4 sciatic nerve branches partial neurotomy were performed. The modified Ashworth scale, composite spasticity scale, surface electromyography, gait analysis, functional ambulation category, spinal cord independence measure, and modified spinal cord injury–spasticity evaluation tool were used before and after surgery.

Results

Compared with preoperative, the spasm of the hip adductor, triceps surae, and hamstrings of the lower limbs in the postoperative patients decreased significantly. The abnormal gait of knee flexion and varus in the standing stage were significantly reduced. The grading of walking ability and activities of daily living were significantly improved.

Conclusions

Combined selective peripheral neurotomy can significantly reduce the spasm of lower limbs post spinal cord injury, improve abnormal gait, and improve motor function and activities of daily living.

Trial registration

ChiCTR1800019003 (2018–10-20).

Wavelet coherence as a measure of trunk stabilizer muscle activation in wheelchair fencers

BACKGROUND

Intermuscular synchronization constitutes one of the key aspects of effective sport performance and activities of daily living. The aim of the study was to assess the synchronization of trunk stabilizer muscles in wheelchair fencers with the use of wavelet analysis.

METHODS

Intermuscular synchronization and antagonistic EMG-EMG coherence were evaluated in the pairs of the right and the left latissimus dorsi/external oblique abdominal (LD/EOA) muscles. The study group consisted of 16 wheelchair fencers, members of the Polish Paralympic Team, divided into two categories of disability (A and B). Data analysis was carried out in three stages: (1) muscle activation recording using sEMG; (2) wavelet coherence analysis; and (3) coherence density analysis.

RESULTS

In the Paralympic wheelchair fencers, regardless of their disability category, the muscles were activated at low frequency levels: 8-20 Hz for category A fencers, and 5-15 Hz for category B fencers.

CONCLUSIONS

The results demonstrated a clear activity of the trunk muscles in the wheelchair fencers, including those with spinal cord injury, which can be explained as an outcome of their intense training. EMG signal processing application have great potential for performance improvement and diagnosis of wheelchair athletes.