Electrophysiological Guidance of Epidural Electrode Array Implantation over the Human Lumbosacral Spinal Cord to Enable Motor Function after Chronic Paralysis

JOURNAL OF NEUROTRAUMA, 2019 · DOI: 10.1089/neu.2018.5921 · Published: May 1, 2019

Simple Explanation

Epidural electrical stimulation (EES) of the spinal cord has been shown to restore function after spinal cord injury (SCI). Characterization of EES-evoked motor responses has provided a basic understanding of spinal sensorimotor network activity related to EES-enabled motor activity of the lower extremities. The 16-contact electrode array was initially positioned under ﬂuoroscopic guidance. Then, EES-evoked motor responses were recorded from select leg muscles and displayed in real time to determine electrode array proximity to spinal cord regions associated with motor activity of the lower extremities. Motor response latencies were not signiﬁcantly different between intraoperative recordings and post-operative recordings, indicating that array positioning remained stable. Additionally, EES enabled intentional control of step-like activity in both subjects within the ﬁrst 5 days of testing.

Study Duration

Not specified

Participants

2 males with motor complete paralysis

Evidence Level

Level IV; Case Series

Key Findings

1
Positioning active electrodes at the rostral region of the array resulted in significantly higher EES-evoked motor response amplitudes in proximal leg muscles.
2
Stimulation through caudal electrode conﬁgurations resulted in distal muscle EES-evoked motor response amplitudes that were signiﬁcantly higher than rostral positioning of active electrodes.
3
Lateral adjustment in array positioning resulted in both the left and right leg muscles becoming active at lower EES voltages with signiﬁcantly greater evoked motor response amplitudes.

Research Summary

Herein, we describe the surgical and intraoperative electrophysiological approach used, followed by initial EES-enabled results observed in 2 human subjects with motor complete paralysis who were enrolled in a clinical trial investigating the use of EES to enable motor functions after SCI. Acceptable array positioning was determined based on achievement of selective proximal or distal leg muscle activity, as well as bilateral muscle activation. These results suggest that the use of EES-evoked motor responses may guide intraoperative positioning of epidural electrodes to target spinal cord circuitry to enable motor functions after SCI.

Practical Implications

Surgical Foundation

The detailed surgical procedures of EES implantation can be used as a foundation for future clinical investigations.

Intraoperative Guidance

Intraoperative EES-evoked motor responses can guide electrode array positioning and can be compared to post-surgical responses.

Rehabilitative Strategy

The study shows the ability to achieve coordinated motor output to generate leg muscle activity that can be intentionally modulated to create step-like movements.

Study Limitations

1
The study does not directly demonstrate how single evoked potentials can serve as a biomarker of the most effective stimulation parameters to perform step-like behavior.
2
The responsiveness of the spinal network intraoperatively and soon after implantation is likely to change substantially as motor function improves.
3
The behavioral responses reﬂect the engagement of proprioception and a return of supraspinal connectivity.

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