When and what to stimulate? An evaluation of a custom functional electrical stimulation system and its neuroprosthetic effect on gait in children with cerebral palsy

Zahradka, Nicole
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University of Delaware
Atypical gait patterns are commonly observed in children with cerebral palsy (CP), a neuromuscular disorder affecting the development of movement and posture and impacting approximately 764,000 people in the United States. Resulting from the absence of one or more of the components that make up a typical gait cycle, gait patterns in CP have been characterized by atypical lower extremity kinematics. Surgical and non-surgical interventions are used to treat these gait deviations. Surgical interventions produce improvements in function that are modest at best and may result in iatrogenic crouch gait while more conservative interventions (non-surgical) have successfully improved spatiotemporal deviations but have not shown changes in kinematics. Walking interventions using functional electrical stimulation (FES) have demonstrated improvements in spatiotemporal, kinematic, and kinetic parameters. Current FES systems, however, are limited in flexibility and number of muscle groups capable of being targeted with FES; potentially limiting gait improvements attainable with use of FES. The overall goal of this dissertation was to develop a FES system, programmable with individualized stimulation algorithms, to assess the feasibility of using it as a neural orthosis during walking in children with CP. ☐ In Aim 1, we successfully developed a FES system and systematically quantified its system performance to validate the system as an accurate device for assisting gait before implementing it in a patient population. By combining commercially available devices and custom software, we have developed a closed-loop FES system, capable of detecting 7 phases of gait and stimulating 10 muscle groups while walking. The FES system was validated in 7 typically developing children, during treadmill walking at self-selected speed, by comparing the FES system’s gait phase detection and delivery of stimulation to the desired timing derived from the ‘gold standard’ (motion capture system). Overall root mean square errors (RMSEs) of average gait phase detection and duration were 7.23 ± 2.38% and 4.58 ± 2.68% of the gait cycle, respectively. Modifications were made to the stimulation trigger to account for system delays in gait phase detection, resulting in the actual FES output to the desired stimulation timing having an average difference of 0.67 ± 4.25% of the gait cycle. The FES system accurately delivered stimulation, and our ability to detect all 7 phases of gait number of gait phases detected provided independent control over the delivery of stimulation. This development allowed the flexibility for the physical therapist to choose the muscle groups targeted with FES when using the system as a neuroprosthetic device. ☐ In Aim 2, we effectively deployed the FES system as a wearable device during walking in subjects with CP in which immediate effects were made to joint angles when muscle groups were stimulated during FES-assisted walking. To evaluate the immediate changes created during FES-assisted walking, six children with CP donned our custom FES system and walked on a treadmill at their self-selected speeds. Kinematic data were collected for walking conditions without FES and with FES applied using individualized stimulation programs. The results demonstrated that targeting major muscle groups during FES-assisted walking changed the lower extremity kinematics; responses to FES varied between subjects. ☐ This dissertation work illustrates the importance of improving existing FES devices and contributes to the evidence supporting positive kinematic changes produced during FES-assisted interventions in CP.
Applied sciences , Health and environmental sciences , Cerebral palsy , Functional electrical stimulation , Gait phase detection , Kinematics , Walking