Cervical Transcutaneous Spinal Cord Stimulation for Upper Limb Motor Function in Participants With and Without Neurologic Disorders: A Systematic Review of Parameters, Methods, and Safety

Transcutaneous spinal cord stimulation (tSCS) is a noninvasive intervention aimed at enhancing motor recovery in neurologic populations; however, its efficacy for upper limb function remains unclear, with substantial variability in stimulation protocols.

To identify commonly used stimulation parameters for cervical tSCS targeting upper limb function in healthy and neurologic populations and to evaluate its effectiveness and safety.

A systematic review was conducted according to a protocol previously registered in International Prospective Register of Systematic Reviews (registration number: CRD42025633565) by searching Cochrane Central Register of Controlled Trials, MEDLINE, Physiotherapy Evidence Database, Cumulative Index to Nursing and Allied Health Literature, and Web of Science. Included studies involved adults, either healthy or neurologically impaired, who received tonic cervical tSCS, with or without control conditions, and reported upper limb motor outcomes. Experimental, quasi-experimental, and uncontrolled designs were included, and the risk of bias was assessed.

Fifteen studies met the criteria, including 144 participants with spinal cord injuries, 48 noninjured participants, and two participants with stroke. The cathode was consistently placed over the cervical spinous processes. Biphasic and monophasic currents were delivered with a 0.5 to 1 ms pulse width, modulated at 30 to 50 Hz using a 10-kHz carrier frequency. Most studies combined tSCS with active interventions. tSCS was safe and improved strength and function, although the risk of bias ranged from moderate to high.

Cervical tSCS with cathodes at C3-C4 and C6-C7 and anodes over the iliac crests, using a multisession protocol (1 ms pulse width, 30 Hz with 10-kHz carrier frequency, subthreshold intensity, 20 minutes per session) combined with task-specific training, appears to be feasible and safe for improving motor outcomes. However, given the low to very low certainty of the evidence in neurologic populations, further adequately powered, high-quality randomized controlled trials are needed to establish the effectiveness of this protocol for improving motor outcomes.

PROSPERO (CRD42025633565); https://www.crd.york.ac.uk/PROSPERO/view/CRD42025633565.