Transcutaneous Spinal Cord Stimulation Restores Hand and Arm Function After Spinal Cord Injury

Spinal Cord Injury (SCI) resulting in upper limb paralysis significantly impacts patients’ independence and quality of life. Among the SCI patient population, regaining control over hand and arm movements is considered the highest priority treatment goal, surpassing even the restoration of walking ability. However, current clinical methods to improve upper limb function have not achieved the goal of restoring independent living. Traditional motor therapy, Functional Electrical Stimulation (FES), Somatosensory Stimulation, and Transcranial Magnetic Stimulation (TMS) have shown limited effects in enhancing motor function.

Recent studies have indicated that electrical stimulation techniques can activate spinal cord circuits below the injury site, thereby restoring voluntary motor function. Notably, Spinal Cord Stimulation (SCS) via implanted electrodes has shown significant improvements in voluntary control of standing and walking. However, the complexity and risks associated with this invasive method limit its application among upper limb paralysis patients. Therefore, scientists have begun exploring a non-invasive approach—Transcutaneous Spinal Cord Stimulation (tSCS)—with the aim of achieving breakthroughs in improving upper limb function.

Research and Publication Background

This paper, co-authored by Fatma Inanici, Lorie N. Brighton, Soshi Samejima, Christoph P. Hofstetter, and Chet T. Moritz, involves researchers from the departments of Electrical and Computer Engineering, Rehabilitation Medicine, and Neurosurgery at the University of Washington. It was published in the 2021 IEEE Transactions on Neural Systems and Rehabilitation Engineering journal. The research received partial funding from the Center for Neurotechnology and the Washington State Spinal Cord Injury Consortium and was registered at ClinicalTrials.gov (ID: NCT03184792).

Study Design and Methods

1. Study Design

The study was a prospective, open-label, crossover design trial. Baseline measurements were conducted weekly for four weeks prior to intervention. During the first month of the intervention phase, all participants underwent intensive functional task training only. In the second month, transcutaneous electrical stimulation was combined with training.

Two participants with complete motor injury (American Spinal Injury Impairment Scale, AIS B) and one participant with AIS D type central cord syndrome continued with electrical stimulation treatment in the second month, while the remaining three participants with incomplete injuries (AIS C-D) underwent training only. Throughout the study, a repeated arm crossover design was used to verify whether electrical stimulation truly contributed to functional improvements, with each participant serving as their own control.

2. Participants

Six volunteers with chronic cervical spinal cord injuries were recruited, with an average age of 42 years and an average injury duration of 4.6 years. These participants underwent tests, including video recording and imaging, after consenting to all trial procedures.

3. Intensive Functional Task Training

Upper limb training was conducted three times a week, each session lasting two hours. Activities included single-hand and two-hand tasks, fingertip movements, grasping, and pinching, with difficulty levels gradually increasing according to participants’ conditions.

4. Transcutaneous Spinal Cord Stimulation

The transcutaneous electrical stimulation equipment used in the experiment was developed by NeuroRecovery Technologies Inc. (now Onward Medical BV). The stimulation method employed two independent channels, targeting two locations in the cervical region and the pelvic area. The stimulation frequency was 30 pulses per second, overlaid with a 10 kHz current to ensure high-intensity stimulation could penetrate the skin without causing discomfort.

5. Outcome Measures

Primary outcome measures included the Graded Redefined Assessment of Strength Sensibility and Prehension (GRASSP) for hand strength, sensory perception, and grasping ability. Secondary measures included the International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI) exam, lateral pinch strength measurement, and clinical assessment of spasticity.

6. Data Analysis

Experimental data were analyzed using one-way repeated measures ANOVA and Tukey LSD tests, while functional change data were validated through paired sample t-tests.

Study Results

The study demonstrated that combining transcutaneous cervical spinal cord stimulation with intensive training significantly restored upper limb function in patients with complete and incomplete cervical spinal cord injuries. This restoration lasted for several months. Results indicated that all participants showed far greater functional improvements with electrical stimulation treatment than with training alone.

1. Improvements in Completely Paralyzed Patients

The first completely paralyzed patient had no finger or thumb movement upon joining the study and did not recover after four weeks of intensive training alone. However, after four weeks of combined electrical stimulation and training, the patient began to show movement and was able to generate measurable pinch strength. This functional improvement persisted for six months after ceasing treatment.

The second completely paralyzed patient exhibited similar improvements, with substantial increases in hand pinch strength that were maintained for three months after the treatment ended.

2. Improvements in Partially Paralyzed Patients

The remaining four participants already had some movement capability in their fingers and thumbs when joining the study. One participant, injured for over 12 years, regained grasping ability on the first day of electrical stimulation, and this improvement was maintained for six months after the stimulation and training ended. All participants showed significant statistical improvement (p < 0.025) in strength and grasping ability during the training with electrical stimulation.

3. Improvements in Other Functions

In addition to motor function recovery, transcutaneous spinal cord stimulation significantly improved autonomic functions. For instance, one patient, whose heart rate had been low (40-45 bpm) for 12 years post-injury, was restored to normal levels (60-65 bpm) during the stimulation period and maintained that rate in follow-up. Other participants reported improvements in thermoregulation and bladder function.

4. Emphasis on Long-term Maintenance of Functional Recovery

All functional improvements in this study were maintained for three to six months after the last intervention, indicating that this treatment promotes neuroplasticity in the central nervous system. The combined stimulation technique and intensive training may achieve immediate and long-term recovery through mechanisms involving sub-threshold excitation of spinal networks via dorsal root afferents, making residual but dormant descending pathways more readily activated, thereby restoring voluntary motor control.

Discussion and Future Directions

The findings of this study demonstrate the significant efficacy of combining transcutaneous spinal cord stimulation with intensive training in restoring function in upper limb paralysis patients. This method is non-invasive and has high clinical translation potential. However, the study also has limitations, including difficulty in achieving blinding and sham stimulation controls, as well as variability in baseline functionalities among participants. Future research requires larger sample sizes and blinded evaluator tests to rigorously evaluate the effectiveness of transcutaneous spinal cord stimulation.

This research provides important evidence for exploring new methods of treating spinal cord injuries and points towards future clinical applications of transcutaneous spinal cord stimulation methods.