A pilot study examining the impact of electrode configuration in transcutaneous spinal cord stimulation in spinal cord injury

Study design Prospective trial. Objective To evaluate the impact on muscle activation of different anatomical configurations of transcutaneous spinal cord stimulation electrodes amongst SCI and control patients. Summary of background data Spinal cord stimulation has garnered increased attention as a promising treatment for spinal cord injury (SCI). However, existing studies on transcutaneous spinal cord stimulation consist of highly variable methodologies and lack standard protocols. Methods Two adult SCI participants (PS01—T12 AIS D, and PS02—T2 AIS B) and two healthy adult controls (PS03, and PS04) were prospectively enrolled after IRB approval. Electromyography was used to record activity in the bilateral tibialis anterior (TA) and biceps femoris (BF). Four electrode configurations were trialed—cathode placement only at T11-T12 (montage T11-T12) versus combined configurations with cathodes at T11-T12 and at L1-L2, L3-L4, or S1-S2; anode placement was always at the bilateral iliac crests. Motor response was defined as EMG change >20 μV, as defined in the literature. Results SCI participants exhibited overall decreased motor responses compared to controls, other than PS01 at the T11-T12 montage. The majority of motor responses from SCI participants did not meet the 20 µV threshold, and did not show the same consistent cranial to caudal pattern. PS01’s highest response was at T11-T12/L1-L2 (BF: 265.52 µV), whereas PS02 was highest at T11-T12 (TA: 39.73 µV). Overall, the motor response from the motor complete SCI (PS02—T2 AIS B) was substantially less than the motor response from the motor and sensory incomplete SCI. Conclusion When performing transcutaneous spinal cord stimulation, the magnitude of motor response appears to vary with both the exact anatomical electrode configuration and the presence/severity of SCI. SCI participants demonstrated generally decreased motor responses, and a less predictable topographic pattern. Further work is needed to determine the ideal electrode configurations for different patients and spinal cord injury types.