Spinal cord transcutaneous stimulation in cervical spinal cord injury: A review examining upper extremity neuromotor control, recovery mechanisms, and future directions.

Cervical spinal cord injury (SCI) results in significant sensorimotor impairments below the injury level, notably in the upper extremities (UE), impacting daily activities and quality of life. Regaining UE function remains the top priority for individuals post cervical SCI. Recent advances in understanding adaptive plasticity within the sensorimotor system have led to the development of novel non-invasive neurostimulation strategies, such as spinal cord transcutaneous stimulation (scTS), to facilitate UE motor recovery after SCI. This comprehensive review investigates the neuromotor control of UE, the typical recovery trajectories following SCI, and the therapeutic potential of scTS to enhance UE motor function in individuals with cervical SCI. Although limited in number with smaller sample sizes, the included research articles consistently suggest that scTS, when combined with task-specific training, improves voluntary control of arm and hand function and sensation. Furthermore, the reported improvements translate to recovery of various UE functional tasks and positively impact the quality of life in individuals with cervical SCI. Several methodological limitations, including stimulation site selection and parameters, training strategies and sensitive outcome measures, require further advancements to allow successful translation of scTS from research to clinical settings. This review also summarizes the current literature and proposes future directions to support establishing approaches for scTS as a viable neuro-rehabilitative tool.

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.

Transcutaneous Spinal Stimulation From Adults to Children: A Review.

Neuromodulation via spinal stimulation is a promising therapy that can augment the neuromuscular capacity for voluntary movements, standing, stepping, and posture in individuals with spinal cord injury (SCI). The spinal locomotor-related neuronal network known as a central pattern generator (CPG) can generate a stepping-like motor output in the absence of movement-related afferent signals from the limbs. Using epidural stimulation (EP) in conjunction with activity-based locomotor training (ABLT), the neural circuits can be neuromodulated to facilitate the recovery of locomotor functions in persons with SCI. Recently, transcutaneous spinal stimulation (scTS) has been developed as a noninvasive alternative to EP. Early studies of scTS at thoracolumbar, coccygeal, and cervical regions have demonstrated its effectiveness in producing voluntary leg movements, posture control, and independent standing and improving upper extremity function in adults with chronic SCI. In pediatric studies, the technology of spinal neuromodulation is not yet widespread. There are a limited number of publications reporting on the use of scTS in children and adolescents with either cerebral palsy, spina bifida, or SCI.

Spinal Cord Injury at Birth, Expected Medical and Health Complexity in Chronic Injury Guided Anew by Activity-Based Restorative Therapy: Case Report.

As infancy is characterized by rapid physical growth and critical periods of development, disruptions due to illness or disease reveal vulnerability associated with this period. Spinal cord injury (SCI) has devastating consequences at any age, but its onset neonatally, at birth, or within the first year of life multiplies its impact. The immediate physical and physiological consequences are obvious and immense, but the effects on the typical trajectory of development are profound. Activity-based restorative therapies (ABRT) capitalize on activity-dependent plasticity of the neuromuscular system below the lesion and when provided to children with SCI aim to improve the child's neuromuscular capacity, health and quality of life. This is a report of an infant with a cervical SCI at birth resulting in paralysis of leg and trunk muscles and paresis of arm and hands who was enrolled in an ABRT program at 3 years of age. After 59 sessions of ABRT, the child demonstrated significant improvements in trunk control and arm function, as well as social and emotional development. Despite the chronicity of injury and low expectations for improvement with therapeutic interventions, ABRT had a positive impact on the child's physical capacity and provided benefits across multiple developmental domains.

Noninvasive spinal stimulation safely enables upright posture in children with spinal cord injury.

In children with spinal cord injury (SCI), scoliosis due to trunk muscle paralysis frequently requires surgical treatment. Transcutaneous spinal stimulation enables trunk stability in adults with SCI and may pose a non-invasive preventative therapeutic alternative. This non-randomized, non-blinded pilot clinical trial (NCT03975634) determined the safety and efficacy of transcutaneous spinal stimulation to enable upright sitting posture in 8 children with trunk control impairment due to acquired SCI using within-subject repeated measures study design. Primary safety and efficacy outcomes (pain, hemodynamics stability, skin irritation, trunk kinematics) and secondary outcomes (center of pressure displacement, compliance rate) were assessed within the pre-specified endpoints. One participant did not complete the study due to pain with stimulation on the first day. One episode of autonomic dysreflexia during stimulation was recorded. Following hemodynamic normalization, the participant completed the study. Overall, spinal stimulation was well-tolerated and enabled upright sitting posture in 7 out of the 8 participants.

Single and sequential voluntary cough in children with chronic spinal cord injury.

We investigated the impact of spinal cord injury (SCI) on cough capacity in 10 children (Mean ± SD, age 8 ± 4 years) and compared it to 15 typically developing children (age 8 ± 3 years). Participants underwent spirometry, single and sequential cough assessment with surface-electromyography from respiratory muscles. Inspiratory phase duration, inspiratory phase peak flow, inspiratory phase rise time, compression phase duration, expiratory phase rise time, expiratory phase peak airflow (EPPF) and cough volume acceleration (CVA) parameters of single and sequential cough were measured. Root mean square (RMS) values of right pectoralis-major, intercostal, rectus-abdominus (RA), and oblique (OB) muscles were calculated and mean of three trials were compared. The significance criterion was set at P < 0.05. The SCI group produced significantly lower lung volumes, EPPF, CVA, and RMS values of RA and OB during expiratory phases of single and sequential coughs. The decrease in activation in expiratory muscles in the SCI group accounts for the impaired expiratory flow and may contribute to risk of respiratory complications.

Contribution of Trunk Muscles to Upright Sitting with Segmental Support in Children with Spinal Cord Injury.

To investigate and compare trunk control and muscle activation during uncompensated sitting in children with and without spinal cord injury (SCI). Static sitting trunk control in ten typically developing (TD) children (5 females, 5 males, mean (SD) age of 6 (2)y) and 26 children with SCI (9 females, 17 males, 5(2)y) was assessed and compared using the Segmental Assessment of Trunk Control (SATCo) test while recording surface electromyography (EMG) from trunk muscles. The SCI group scored significantly lower on the SATCo compared to the TD group. The SCI group produced significantly higher thoracic-paraspinal activation at the lower-ribs, and, below-ribs support levels, and rectus-abdominus activation at below-ribs, pelvis, and no-support levels than the TD group. The SCI group produced significantly higher lumbar-paraspinal activation at inferior-scapula and no-support levels. Children with SCI demonstrated impaired trunk control with the ability to activate trunk muscles above and below the injury level.

Spinal cord injury in infancy: activity-based therapy impact on health, function, and quality of life in chronic injury.

INTRODUCTION: Spinal cord injury (SCI) in infancy magnifies the complexity of a devastating diagnosis. Children injured so young have high incidences of scoliosis, hip dysplasia, and respiratory complications leading to poor health and outcomes. We report the medical history, progression of rehabilitation, usual care and activity-based therapy, and outcomes for a child injured in infancy. Activity-based therapy (ABT) aims to activate the neuromuscular system above and below the lesion through daily, task-specific training to improve the neuromuscular capacity, and outcomes for children with acquired SCI. CASE PRESENTATION: A 3-month-old infant suffered a cervical SCI from a surgical complication with resultant tetraplegia. Until age 3, her medical complications included scoliosis, kyphosis, and pneumonia. Even with extensive physical and occupational therapy, she was fully dependent on caregivers for mobility and unable to roll, come to sit, sit, stand or walk. She initiated ABT at ~3 years old, participating for 8 months. The child's overall neuromuscular capacity improved significantly, especially for head and trunk control, contributing to major advances in respiratory health, novel engagement with her environment, and improved physical abilities. DISCUSSION: From injury during infancy until 3 years old, this child's health, abilities, and complications were consistent with the predicted path of early-onset SCI. Due to her age at injury, severity and chronicity of injury, she demonstrated unexpected, meaningful changes in her neuromuscular capacity during and post-ABT associated with improved health, function and quality of life for herself and her caregivers.

Respiratory muscle activation patterns during maximum airway pressure efforts are different in women and men.

Maximum inspiratory and expiratory pressure values (PImax and PEmax) are indirect measures of respiratory muscle strength that, in healthy adults, are known to be significantly lower in women compared to men. In part, sex differences in breathing kinematics, lung size, body composition, muscle mass, and muscle fiber composition are thought to be responsible for these effects. However, it is not known whether respiratory muscle activation during maximum respiratory efforts is also sex-specific. In this study, we addressed whether respiratory multi-muscle activation patterns during PImax and PEmax efforts are different between healthy women and men. Forced vital capacity (FVC), forced expiratory volume in one second (FEV1), PImax, PEmax, and surface electromyographic (sEMG) activity recorded from respiratory muscles during these maximum airway pressure efforts were obtained in 13 women and 11 men. Percent predicted values of FVC and FEV1 were not significantly different in these two groups (women vs. men: 112 ± 14 vs. 105 ± 15%, p = 0.29; and 92 ± 12 vs. 93 ± 13, p = 0.82, Mean ± SD, respectively), while PImax and PEmax measures were significantly lower in women compared to men (68 ± 16 vs. 88 ± 19 cmH2O, p = 0.011; and 69 ± 13 vs. 94 ± 17, p = 0.0004, respectively). Using vector-based methodology, by calculating the Similarity Index (SI) as measure of the resemblance between two sEMG patterns and the Magnitude (Mag) representing the overall amount sEMG during motor task, we have found that although the Mag values for both PImax and PEmax tasks were not significantly different in two groups, the SIs revealed significant sex-dependent differences in muscle activation patterns (0.89 ± 0.08 vs. 0.97 ± 0.02, p = 0.016; and 0.77 ± 0.11 vs. 0.92 ± 0.04, p = 0.0006, respectively). During the PImax effort, presented as the percentage of total sEMG amplitude, activity of upper trapezius muscle was significantly larger (p = 0.001) while activation of rectus abdominus, oblique, and lower paraspinal muscles were significantly smaller (p = 0.002, p = 0.040, p = 0.005, respectively) in women when compared to the men (50 ± 21 vs. 22 ± 11%; 2 ± 2 vs. 8 ± 7; 4 ± 3 vs. 9 ± 7, 2 ± 3 vs. 7 ± 6, respectively). During PEmax effort, the percentage of sEMG activity were significantly larger in upper and lower trapezius, and intercostal muscles (p = 0.038, p = 0.049, p = 0.037, respectively) and were significantly smaller in pectoralis, rectus abdominus, and oblique muscles (p = 0.021, p < 0.0001, p = 0.048, respectively) in women compared to men (16 ± 10 vs. 9 ± 4%; 16 ± 9 vs. 8 ± 5; 36 ± 12 vs. 25 ± 9; 6 ± 3 vs. 15 ± 5; 14 ± 5 vs. 20 ± 7, respectively). These findings indicate that respiratory muscle activation patterns during maximum airway pressure efforts in healthy individuals are sex-specific. This information should be considered during respiratory motor control evaluation and treatment planning for people with compromised respiratory motor function.

Respiratory functional and motor control deficits in children with spinal cord injury.

Children with spinal cord injury (SCI) are at high risk for developing complications due to respiratory motor control deficits. However, underlying mechanisms of these abnormalities with respect to age, development, and injury characteristics are unclear. To evaluate the effect of SCI and age on respiratory motor control in children with SCI, we compared pulmonary function and respiratory motor control outcome measures in healthy typically developing (TD) children to age-matched children with chronic SCI. We hypothesized that the deficits in respiratory functional performance in children with SCI are due to the abnormal and age-dependent respiratory muscle activation patterns. Fourteen TD (age 7±2 yrs., Mean±SD) and twelve children with SCI (age 6±1 yrs.) were evaluated by assessing Forced Vital Capacity (FVC); Forced Expiratory Volume in 1sec (FEV1); and respiratory electromyographic activity during maximum inspiratory and maximum expiratory airway pressure measurements (PImax and PEmax). The results indicate a significant reduction (p<.01) of FVC, FEV1 and PEmax values in children with SCI compared to TD controls. During PEmax assessment, children with SCI produced significantly decreased (p<.01) activation of respiratory muscles below the neurological level of injury (rectus abdominous and external oblique muscles). In addition, children with SCI had significantly increased (p<.05) compensatory muscle activation above the level of injury (upper trapezius muscle). In the TD group, age, height, and weight significantly (p<.05) contributed towards increase in FVC and FEV1. In children with SCI, only age was significantly (p<.05) correlated with FVC and FEV1 values. These findings indicate the degree of SCI-induced respiratory functional and motor control deficits in children are age-dependent.