A system to integrate electrical stimulation with robotically controlled treadmill training to rehabilitate stepping after spinal cord injury

The effects of walking training onset on motor evoked potentials after acute spinal cord injury

AIM

The purposes of this study were to explore the optimal time for starting walking training in the first month after spinal cord injury (SCI) in rats and to discuss the relationship between changes in motor function and transcranial electrical motor evoked potentials (tceMEPs).

METHODS

Four groups of rats with SCI (BSWTT-3, 7, 14, 12) performed body-weight-supported treadmill training (BWSTT) for three weeks beginning at 3, 7, 14, and 21 days after SCI, respectively. The Basso, Beattie, and Bresnahan (BBB) score and tceMEPs were assessed weekly. Weekly repeated measures and multiple comparisons between groups were performed to identify differences in motor function and tceMEPs. Correlation analysis was performed to clarify the relationship between BBB scores and tceMEPs over time.

RESULTS

Although there was no significant difference between the BWSTT-14 group and the other three BWSTT groups at the end of the experiment in terms of BBB scores and the latency of tceMEPs, the BWSTT-14 group obtained the best trends in improvement of BBB scores and the latencies and amplitudes of tceMEPs over time. The BBB scores of rats with SCI were strongly negatively correlated with tceMEPs latency. The BBB scores of rats with SCI, except for the rats in the BWSTT-3 group, were strongly positively correlated with the tceMEPs amplitude.

CONCLUSIONS

The preliminary conclusion was that based on a rat model, 14 days after SCI was the optimal time for starting BWSTT. tceMEPs were an objective indicator of spinal cord nerve function, which was strongly correlated with motor function recovery. However, one limitation of this study was that the rats in the Sham group did not undergo BWSTT, which made the training itself a confounding factor for the results.

Exercise Training Promotes Functional Recovery after Spinal Cord Injury

The exercise training is an effective therapy for spinal cord injury which has been applied to clinic. Traditionally, the exercise training has been considered to improve spinal cord function only through enhancement, compensation, and replacement of the remaining function of nerve and muscle. Recently, accumulating evidences indicated that exercise training can improve the function in different levels from end-effector organ such as skeletal muscle to cerebral cortex through reshaping skeletal muscle structure and muscle fiber type, regulating physiological and metabolic function of motor neurons in the spinal cord and remodeling function of the cerebral cortex. We compiled published data collected in different animal models and clinical studies into a succinct review of the current state of knowledge.

Multivariate assessment of differences between a neuromuscular electrical stimulation therapy and robotic treadmill training in the rehabilitation of spinal cord injured rats

A study was conducted to evaluate and compare the effects of two different rehabilitation therapies on spinal cord injured (SCI) rats: neuromuscular electrical stimulation which is timed to robotic treadmill training (NMES+RTT) and RTT alone. Several electromyography (EMG) based variables were measured, but most did not change significantly after treatment, contrary to observations of overall qualitative stepping ability. However, when the variables are viewed in multi-dimensional space, there are visible differences between changes after NMES+RTT vs. those after RTT only. Principal component analysis (PCA) and k-means clustering were applied to the multivariate data. The data in principal component space was significantly separated, according to the Euclidean distance. PCA also provided a straightforward tool for selecting which combination of measures to compare. The measures which best separated out the differences between NMES+RTT and RTT were percentage of steps associated with bursts, burst-to-step latency, and the standard deviation of this latency, even though these measures did not always show the greatest statistical significance individually. Thus, the rehabilitative effects of NMES+RTT are not necessarily reflected in individual EMG measures, but rather in a combination of the measures representing a multi-dimensional space.

Step trajectory analysis of spinal cord injured rats trained with neuromuscular electrical stimulation coordinated with robotic treadmill training

Applying neuromuscular electrical stimulation (NMES) during treadmill training (TT) has been shown to improve functional outcomes, such as gait speed and walking distance, in spinal cord injury (SCI) patients. However, ways to improve this combined NMES+TT therapy have not been investigated. We have developed NMES system for a rodent model of SCI to investigate whether and how more precisely timing the stimulation to robotically assisted hindlimb position might achieve rehabilitation of independent stepping after SCI. In our therapy (NMES+RTT), rodent ankle flexor muscles are stimulated while the hindlimbs are robotically driven through pre-programmed trajectories during treadmill training. The objectives of the work presented here were to quantify changes in step trajectory resulting from our combined NMES+RTT therapy and compare those effects with those induced by robotic treadmill training (RTT) alone. Animals were spinally contused to model severe SCI, and either received 2 weeks of NMES+RTT followed by 2 weeks of RTT (n=6) or 2 weeks of RTT followed by 2 weeks of NMES+RTT (n=7). Changes in step trajectories after training were analyzed. According to a deviation measure we developed, the step trajectories improved after either NMES+RTT or RTT training but more closely matched the desired pre-programmed trajectories after NMES+RTT than after RTT only. The step trajectories are also more consistent, as indicated by a coefficient of variation measure, after training and more so after NMES+RTT than after RTT only. These preliminary results from our NMES+RTT vs. RTT study are consistent with the hypothesis that appropriately timing NMES with hindlimb movements during stepping is an effective therapy for restoring the ability to step after spinal cord injury.

Modulation of ankle EMG in spinally contused rats through application of neuromuscular electrical stimulation timed to robotic treadmill training

While neuromuscular electrical stimulation (NMES) has enabled patients of neuromotor dysfunction to effectively regain some functions, analysis of neuromuscular changes underlying these functional improvements is lacking. We have developed an NMES system for a rodent model of SCI with the long term goal of creating a therapy which restores control over stepping back to the spinal circuitry. NMES was applied to the tibialis anterior (TA) and timed to the afferent feedback generated during robotic treadmill training (RTT). The effect of NMES+RTT on modifications in EMG was compared with that of RTT alone. A longitudinal study with a crossover design was conducted in which group 1 (n=7) received 2 weeks of RTT only followed by 2 weeks of NMES+RTT; group 2 (n=7) received 2 weeks of NMES+RTT followed by RTT only. On average, both types of training helped to modulate TA EMG activity over a gait cycle, resulting in EMG profiles across steps with peaks occurring just before or at the beginning of the swing phase, when ankle flexion is most needed. However, NMES+RTT resulted in concentration of EMG activation during the initial swing phase more than RTT only. In conjunction with these improvements in EMG activation presented here, a more complete analyses comparing changes after NMES+RTT vs. RTT is expected to further support the notion that NMES timed appropriately to hindlimb stepping could help to reinforce the motor learning that is induced by afferent activity generated by treadmill training.