Transcutaneous spinal cord electrical stimulation restores hand function after spinal cord injury

Research background 01

Spinal cord injury (SCI) interrupts communication between the brain and body, causing varying degrees of permanent paralysis. Upper limb paralysis after spinal cord injury severely limits the patient's independence and quality of life. Restoring control of hand and arm movement is the highest treatment priority for severely paralyzed patients, six times higher than restoring the ability to walk.

However, in clinical practice, methods and results for restoring hand and arm function in quadriplegics are scarce, and most of them revolve around exercise therapy. Recent research shows that electrical stimulation can activate spinal cord circuits under injury, allowing consciousness to control movement and significantly improve limb function. This usually requires continuous electrical stimulation of the surface of the spinal cord through implanted epidural electrodes to enable movement of the paralyzed limb. However, the ultimate goal of rehabilitation is to promote the return of function that no longer requires continued external stimulation.

A new non-invasive spinal cord stimulation method has recently appeared in people's field of vision. An article reported that transcutaneous spinal cord electrical stimulation with an overlapping frequency of 10khz can achieve high-intensity stimulation of the spinal cord through the skin without causing discomfort. spinal cord, thereby improving hand function in patients with quadriplegia.



Research Methods 02

This was a prospective, open-label, arms-fold study. A total of 6 subjects were recruited. The average age was 42 years old (SD±14, 28-62), and the average injury time was 4.6 years (SD±3.8, 1.5-12).

①Weeks 0-4: Baseline measurements will be repeated weekly to assess functional variability over time for each participant and to control for learning outcome measures.

② 5-8 weeks: Participants will undergo intensive functional task training three times a week for 2 hours each time.

③9-12 weeks: Participants received transcutaneous cervical spinal cord electrical stimulation (1ms pulse width, 30 Hz fundamental frequency, 10 kHz overlap frequency. Each session lasted 2 hours.), and at the same time performed intensive functional task training.

④13-16 weeks: Two participants with complete motor impairment (AIS B) and one with AIS D central spinal cord syndrome underwent transcutaneous cervical spinal cord stimulation + enhanced functional task training, while the other three participants with incomplete Participants with impairment (AIS C-D) performed only intensive functional task training. Lasts 4 weeks.

⑤17-20 weeks: Three participants with incomplete injuries (AIS C-D) underwent transcutaneous cervical spinal cord stimulation + intensive functional task training, while two participants with complete motor injuries (AIS B) and one AIS D central spinal cord comprehensive Significant participants performed only intensive functional task training. Lasts 4 weeks.

⑥21-32 weeks: follow-up for 3 months.

Outcome measures were repeated weekly during baseline, every 2 weeks throughout treatment, and monthly during follow-up lasting 3 months.

The main outcome measure is the Graded Redefined Assessment of Strength, Sensibility, and Prehension (GRASSP). Secondary outcomes included International Standard Neurological Classification of Spinal Cord Injury (ISNCSCI) examination, lateral pinch force measurement, and clinical assessment of spasticity.



Research Results 03

This study found that transcutaneous cervical spinal cord stimulation combined with high-intensity exercise training had long-term and significant upper limb functional benefits in 6 participants, which were maintained for at least 3-6 months.

Similar improvements in strength and grip were observed in all participants. Performance at the end of stimulation-combination training was significantly improved compared to training alone, in terms of pinch strength, arm and hand strength, and dexterity. Pinch force increased 2.4- to 4.8-fold during stimulus-binding training compared with baseline levels. Stimulation treatment improved each subject's function, whereas training alone resulted in only minor improvements.

In addition, improvements in autonomic function were also observed in 6 subjects. One participant had persistent bradycardia (approximately 40 to 45 bmp) for 12 years. After transcutaneous cervical spinal cord stimulation combined with exercise training, the heart rate returned to normal (approximately 60 to 65 bpm) and remained normal during follow-up. . Other participants also reported improvements in sweating, thermoregulatory disturbances, and residual urine.

No major adverse events or maladaptive plasticity related to transcutaneous spinal cord stimulation were observed throughout the intervention period.


Research conclusion 04

The results of this study demonstrate that transcutaneous spinal cord stimulation leads to rapid and sustained recovery of hand and arm function in patients with motor complete and incomplete cervical spinal cord injuries. The finding that all functional improvements were maintained for months after stimulation treatment provides strong evidence that neuroplasticity can be induced in the damaged central nervous system.

We hypothesize that transcutaneous cervical spinal cord stimulation may activate previously weak or paralyzed muscles, allowing participants to participate more fully in training exercises. In addition, varying degrees of spasticity are present in approximately 80% of patients with chronic spinal cord injury, which severely interferes with residual motor function and complicates activities of daily living. Previous studies have shown that sustained epidural spinal cord stimulation has beneficial effects on spasticity. After several transcutaneous stimulations, both during and between stimulation sessions, patients with spasticity had significant attenuation of high muscle tone in their upper limbs. This reduction in spasticity contributes to substantial improvements in function.

The combination of transcutaneous spinal cord stimulation + strengthening training is most likely to achieve immediate and long-term recovery through the following mechanisms. Transcutaneous stimulation activates the spinal cord through sensory pathways in the dorsal roots, providing subthreshold stimulation to interneurons and motor neurons within the spinal cord distal to the lesion. Near-threshold motor neurons are more easily activated by intact but dormant residual brain descending pathways, thereby restoring volitional control of movement. Restored mobility during stimulation allows people to actively participate in rehabilitation training, which in turn induces the reorganization of spinal cord networks, strengthens synaptic connections, and leads to long-term recovery of function through neuroplasticity.

However, this study has limitations such as a small sample size and the inability to perform sham stimulation controls. How to translate transcutaneous spinal cord stimulation into clinical practice still requires a lot of research.