Evaluating a pediatric exoskeleton to improve walking function in children with movement disorders

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Abstract

At the time this project was initiated, no pediatric exoskeleton designed specifically for children with crouch gait (or cerebral palsy) existed. The NIH research team spent several years developing new robotic technology to fill this gap. We built a prototype exoskeleton, which we called the extension assist knee ankle foot orthosis (EA-KAFO), from the ground up to implement a novel control scheme designed specifically to improve knee extension while maintaining user muscle activity during walking. We then designed an observational trial to assess the biomechanical and neuromuscular effects of the exoskeleton on gait biomechanics. The study design includes a maximum of 10 total visits with three data collection time points, one at the beginning of the study (baseline), one immediately after the participant was able to walk independently with the exoskeleton (initial assessment) and one at the final visit (final assessment). An optional data collection can be performed between the initial and final assessments. The primary outcome measure is peak knee extension during midstance during walking, with secondary outcome measures including gait speed, step length, knee extensor and flexor muscle activity, and knee joint moment in the sagittal plane. In 2019, a Cooperative Research and Development Agreement (CRADA) with Bionic Power, a company based in Vancouver, Canada, was established to bring this technology to market. This CRADA involved new (3rd) generation hardware utilizing the Bionic Power Aglik actuators combined with the NIH custom KAFO architecture, sensors, user interface, and embedded control strategy. This new device, termed the NIH-Agilik, further expanded the control capabilities by allowing bidirectional application of torque with low latency. This created a new paradigm for gait training using the robotic exoskeleton, whereby controllable resistance to knee extension (i.e., a flexion torque) could be applied during the gait cycle. The purpose of this new mode would be to provide targeted, functional resistance exercise to the user that can result in improved knee extension after removal of the applied resistance (and exoskeleton). This new strategy required submission of a second FDA risk assessment (beyond the initial risk assessment submitted with the original protocol). The FDA determined the new approach to be non-significant risk, and the protocol was amended to include this new operational mode for evaluation. Recruitment resumed after the pandemic related pause in December 2020, with a primary focus on evaluation of the immediate effects of providing knee extension assist and targeted resistance during overground walking in children with cerebral palsy, spina bifida, muscular dystrophy or incomplete spinal cord injury. The 10-visit study with the NIH-Agilik was completed in six participants (five with cerebral palsy, one with spina bifida) with one participant withdrawn after starting the study. The improvements in peak knee extension in the Assist mode have been larger, on average, than those observed with the first-generation exoskeleton. Additionally, each participant has been able to walk overground with controllable resistance applied during stance and/or swing phase, suggesting that this approach to functional resistance training is feasible in the target clinical population. A power analysis demonstrated that the primary outcome (knee extension angle) was sufficiently powered to conclude the cohort study of the NIH-Agilik. In the past year, four additional healthy volunteers were recruited to complete a single visit per the protocol design. Recruitment and enrollment are now complete, and this protocol has transitioned to the data analysis and reporting stage.