Trunk Stability Enabled by Noninvasive Spinal Electrical Stimulation after Spinal Cord Injury

Abstract

Electrical neuromodulation of spinal networks improves the control of movement of the paralyzed limbs after spinal cord injury (SCI). However, the potential of noninvasive spinal stimulation to facilitate postural trunk control during sitting in humans with SCI has not been investigated. We hypothesized that transcutaneous electrical stimulation of the lumbosacral enlargement can improve trunk posture. Eight participants with non-progressive SCI at C3-T9, American Spinal Injury Association Impairment Scale (AIS) A or C, performed different motor tasks during sitting. Electromyography of the trunk muscles, three-dimensional kinematics, and force plate data were acquired. Spinal stimulation improved trunk control during sitting in all tested individuals. Stimulation resulted in elevated activity of the erector spinae, rectus abdominis, and external obliques, contributing to improved trunk control, more natural anterior pelvic tilt and lordotic curve, and greater multi-directional seated stability. During spinal stimulation, the center of pressure (COP) displacements decreased to 1.36 ± 0.98 mm compared with 4.74 ± 5.41 mm without stimulation (p = 0.0156) in quiet sitting, and the limits of stable displacement increased by 46.92 ± 35.66% (p = 0.0156), 36.92 ± 30.48% (p = 0.0156), 54.67 ± 77.99% (p = 0.0234), and 22.70 ± 26.09% (p = 0.0391) in the forward, backward, right, and left directions, respectively. During self-initiated perturbations, the correlation between anteroposterior arm velocity and the COP displacement decreased from r = 0.5821 (p = 0.0007) without to r = 0.5115 (p = 0.0039) with stimulation, indicating improved trunk stability. These data demonstrate that the spinal networks can be modulated transcutaneously with tonic electrical spinal stimulation to physiological states sufficient to generate a more stable, erect sitting posture after chronic paralysis.

Reversing 21 years of chronic paralysis via non‐invasive spinal cord neuromodulation: a case study

“…Although recent transcutaneous spinal cord stimulation studies have shown improvement of trunk control during sitting 16 and self‐assisted standing 17 in individuals with SCI, this is the first study to show that tES can facilitate volitional movements in the completely paralyzed leg of a SCI patient after just 16 weeks of stimulation and training. This finding is comparable with previous research using invasive epidural electrical stimulation on a motor complete paraplegic patient regaining volitional movements of lower limbs after stimulation and training 4 .…”

The relationship between maximum tolerance and motor activation during transcutaneous spinal stimulation is unaffected by the carrier frequency or vibration

“…Regardless of the exact mechanism, the ratio between tolerance and spinally evoked motor potentials has to be considered when choosing a stimulation paradigm for studies that require TSS‐induced motor activation for functional outcomes (e.g., for standing such as in Sayenko et al, 2019). On the other hand, previous studies have demonstrated the TSS can be used to facilitate other functions such as rhythmic motions (Gerasimenko et al, 2015), trunk stability (Rath et al, 2018), cardiovascular function (Phillips et al, 2018), and bladder function (Gad et al, 2018) in individuals with spinal cord injury, without directly inducing motor responses. These studies used the carrier frequency stimulation paradigm in an attempt to increase stimulation intensity and engage spinal interneural networks while reducing stimulation‐related pain.…”

“…As such, mechanisms of spinal neuromodulation may also include activation of spinal interneural networks and antidromic activation of ascending fibers in the dorsal columns. TSS has been used to increase excitability at multiple levels of the spinal neuraxis to enable motor and autonomic functions in individuals with chronic spinal cord injury (SCI) (Gad et al, 2018; Hofstoetter et al, 2013, 2015; Minassian et al, 2013, 2016; Phillips et al, 2018; Rath et al, 2018; Sayenko et al, 2019). Although TSS has been examined as a possible clinical intervention for individuals with SCI, the promising findings with regard to motor recovery and the noninvasive nature of the technique could make TSS suitable for use with other neurologically‐impaired populations.…”

“…Previous studies have suggested that it may be possible to reduce discomfort during TSS by using a specific waveform to deliver electrical stimulation (Gad et al, 2018; Gerasimenko et al, 2015, 2016; Rath et al, 2018; Sayenko et al, 2019). The waveform consists of 0.1–1 ms bursts of alternating biphasic rectangular pulses with a carrier frequency of up to 10 kHz.…”

Emergence of Epidural Electrical Stimulation to Facilitate Sensorimotor Network Functionality After Spinal Cord Injury

“…In contrast to EES which requires a permanently implanted array on the spinal cord requiring a laminectomy, followed by connection to an implanted electrical pulse generator, wearable transcutaneous stimulation systems could be donned and doffed by subjects or their caretakers. Early reports have shown promising results as transcutaneous stimulation has demonstrated efficacy in enabling voluntary control of lower limb movement while side‐lying in five subjects with chronic paraplegia and increased trunk stability in eight individuals with SCI . In addition, transcutaneous stimulation increased grip force by 325% in eight subjects with cervical level injuries after just eight sessions .…”