A flexible electrode array for determining regions of motor function activated by epidural spinal cord stimulation in rats with spinal cord injury

✓ Six patients with intractable spasms after spinal cord injury underwent implantation of an epidural spinal cord stimulation system. All the patients experienced good relief postoperatively. In three patients spinal cord stimulation consistently produced immediate inhibition of the spasms. This was evident within less than 1 minute of stimulation. Conversely, the spasms reappeared within less than 1 minute after cessation of the stimulation. The clinical observations were confirmed by polygraphic electromyographic recordings.

Spinal cord injury (SCI) commonly results in permanent loss of motor, sensory, and autonomic function. Recent clinical studies have shown that epidural spinal cord stimulation may provide a beneficial adjunct for restoring lower extremity and other neurological functions. Herein, we review the recent clinical advances of lumbosacral epidural stimulation for restoration of sensorimotor function in individuals with motor complete SCI and we discuss the putative neural pathways involved in this promising neurorehabilitative approach. We focus on three main sections: review recent clinical results for locomotor restoration in complete SCI; discuss the contemporary understanding of electrical neuromodulation and signal transduction pathways involved in spinal locomotor networks; review current challenges of motor system modulation and future directions towards integrative neurorestoration. The current understanding is that initial depolarization occurs at the level of large diameter dorsal root proprioceptive afferents that when integrated with interneuronal and latent residual supraspinal translesional connections can recruit locomotor centers and augment downstream motor units. Spinal epidural stimulation can initiate excitability changes in spinal networks and supraspinal networks. Different stimulation parameters can facilitate standing or stepping, and it may also have potential for augmenting myriad other sensorimotor and autonomic functions. More comprehensive investigation of the mechanisms that mediate the transformation of dysfunctional spinal networks to higher functional states with a greater focus on integrated systems based control system may reveal the key mechanisms underlying neurological augmentation and motor restoration after severe paralysis.

BACKGROUND: Epidural spinal cord stimulation (ESCS) emerged as a technology for eliciting motor function in the 1990’s and was subsequently employed therapeutically in the spinal cord injured (SCI) population. Despite a considerable number of ESCS studies, a comprehensive systematic review of ESCS remains unpublished. OBJECTIVE: The current review of the existing literature evaluated the efficacy of ESCS for improving motor function in individuals with SCI. METHODS: A search for ESCS studies was performed using the following databases: Medline (Ovid), Web of Science and Embase. Furthermore, to maximize results, an inverse manual search of references cited by identified articles was also performed. Studies published between January 1995 and June 2020 were included. The search was constructed around the following key terms: Spinal cord stimulation, SCI and motor response generation. RESULTS: A total of 3435 articles were initially screened, of which 18 met the inclusion criteria. The total sample comprised of 24 participants with SCI. All studies reported some measure of improvement in motor activity with ESCS, with 17 reporting altered EMG responses. Functional improvements were reported in stepping (n = 11) or muscle force (n = 4). Only 5 studies assessed ASIA scale pre- and post-intervention, documenting improved classification in 4 of 11 participants. Appraisal using the modified Downs and Black quality checklist determined that reviewed studies were of poor quality. Due to heterogeneity of outcome measures utilized in studies reviewed, a meta-analysis of data was not possible. CONCLUSION: While the basic science is encouraging, the therapeutic efficacy of ESCS remains inconclusive.