Mapping Spinal Cord Stimulation-Evoked Muscle Responses in Patients With Chronic Spinal Cord Injury

Area of Science:

• Neuroscience
• Biomedical Engineering
• Rehabilitation Medicine

Background:

• Epidural spinal cord stimulation (eSCS) shows promise for motor function recovery post-spinal cord injury (SCI).
• Optimizing eSCS requires precise spatial configuration of electrodes for effective muscle activation.
• The E-STAND trial investigates eSCS for chronic SCI (cSCI) recovery.

Purpose of the Study:

• To investigate the spatial specificity of stimulation-evoked responses in targeted muscle groups after chronic SCI.
• To explore how the spatial distribution of low-frequency stimulation affects muscle activation patterns.
• To determine optimal electrode configurations for restoring volitional motor control.

Main Methods:

• Evaluated 15 participants with cSCI from the E-STAND study.
• Utilized a wide range of bipolar spatial stimulation patterns (vertical, horizontal, oblique).
• Measured stimulation-evoked responses using surface electromyography across multiple bilateral muscle groups.

Main Results:

• Cathodic stimulation showed ipsilaterally biased activation across most tested muscle groups.
• Caudal cathodic stimulation significantly activated only the rectus femoris (RF) and extensor hallucis longus (EHL) muscles.
• Oblique stimulation configurations yielded greater activation in several muscle groups compared to transverse (horizontal) configurations.

Conclusions:

• Cathodic stimulation offers uniform specificity for targeting laterality.
• Limited muscle groups responded specifically to rostral/caudal stimulation variations.
• Oblique stimulation configurations enhance stimulation responses, potentially enabling tailored muscle group targeting.
• Monitoring evoked muscle responses is crucial for optimizing eSCS therapy.