Effects of Spinal Cord Stimulation on Neuromechanics of Gait for Children with Cerebral Palsy

Abstract

Cerebral palsy (CP) is one of the largest causes of motor disability in children. Due to an injury in the central nervous system around the time of birth, children with CP have altered motor control and function that affects their movement. Common interventions to support mobility in children with CP often target secondary complications such as bone deformities, muscle contracture, and spasticity. Interventions are needed that can non-invasively support mobility in children with CP while targeting the underlying nervous system injury. Expertise in engineering, biomechanics, neuroscience, and rehabilitation can help to design and evaluate novel interventions for children with CP. This dissertation investigates how three novel interventions: spinal stimulation, interval treadmill training, and exoskeletons impact movement for children with CP.Transcutaneous spinal cord stimulation (tSCS) is a novel technique for modulating neural activity. Previous research suggests that tSCS can boost sensory feedback as it enters the spinal cord and may be effective for improving motor output when applied during rehabilitation. The evidence thus far for how tSCS may impact movement for children with CP is minimal but suggests that tSCS may improve whole-body motor function and coordination of muscle activity, even after one session of use. We enrolled four children with CP in a pilot study where they received 24 sessions each of short-burst interval treadmill training (SBLTT) only and SBLTT with tSCS. We found that tSCS+SBLTT reduced spasticity while maintaining walking function and reducing self-reported fatigue more than SBLTT only. However, we are continuing to understand the underlying neural and biomechanical changes that drive these functional improvements, as well as more about how these changes translate to community mobility. Increased sensory information from tSCS+SBLTT may change how the body controls movement. Understanding the biomechanical changes with tSCS+SBLTT can elucidate the mechanisms driving functional improvements. In the same study of four children with CP, we quantified changes in muscle activity and joint kinematics. We found that participants walked in a more upright posture, with more knee and hip extension, after tSCS+SBLTT. Muscle co-contraction was also reduced, primarily in the thigh. Participants also had a reduction in motor control complexity after SBLTT only, but not after tSCS+SBLTT, despite reductions in spasticity. These results suggest that tSCS+SBLTT may improve coordination of movement and lead to more energy efficient walking patterns in children with CP. One challenge when implementing novel rehabilitation techniques is tracking individual progress. Understanding why and how someone’s walking changes with rehabilitation is important for determining the best method for reaching their movement goals. This can be challenging to quantify due to the natural variability in movement, nonlinear rehabilitation progression, and additional factors that can mask change. We developed a causal modeling and machine learning paradigm to measure the direct effect of SBLTT on step length in children with CP. Using a virtual dataset, we validated that this paradigm can accurately capture nonlinear changes in step length with simulated training data. We then applied the causal modeling and machine learning paradigm to show that three of four children with CP improved step length with SBLTT, even after controlling for changes like treadmill speed and incline. This framework can be used to track individual therapy progression and determine how an intervention is affecting an individual's movement, remaining accurate even when there is high variability in the data. Another aspect of translating novel techniques into rehabilitative care is understanding how they affect muscle fatigue during training. Overexertion of muscles that causes fatigue can limit motor learning of new tasks. Children with CP fatigue faster than peers, making fatigue an important consideration when developing rehabilitation programs. We quantified how tSCS and a resistive ankle exoskeleton, designed to increase muscle engagement, affected fatigue in nine children with CP. Each participant did 20-minutes of walking on separate days with no devices, tSCS only, bilateral resistive ankle exoskeletons (Exo), and tSCS+Exo. We found that the Exo session had the greatest rate of fatigue within the first 5-minutes of training, while there was an increase in muscle engagement with minimal signs of fatigue during the tSCS+Exo training. These findings suggest that the resistive exoskeleton may be more fatiguing on muscles, but that tSCS reduces the rate of fatigue. The use of these tools together may be beneficial for optimizing engagement in rehabilitation programs while supporting neuroplasticity. This dissertation contributes to the fields of mechanical engineering, rehabilitation engineering, and neuroscience through a detailed investigation into how novel rehabilitation strategies affect movement for children with CP. We employ methods across these fields to comprehensively deepen our understanding of human movement and evaluating individual responses to rehabilitation. This work will support future translation of novel, non-invasive rehabilitation strategies into clinical care with tools to support how we can optimize and personalize their implementation.