An adjustable stiffness orthosis to maintain muscle engagement and push-off power in cerebral palsy.

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PROJECT SUMMARY/ABSTRACT Ankle foot orthoses (AFOs) are commonly prescribed to improve mobility for individuals with neurological disorders. AFOs are included in the standard of care for the majority of ambulatory children with cerebral palsy (CP), a pediatric-onset movement disorder caused by insult to the developing brain. Current goals of treatment for individuals with CP center around increasing activity levels, with a focus on play, stair navigation, and running for proper social and community participation. Ankle joint stiffness varies considerably across these conditions, which suggests the same for optimal AFO stiffness. Unfortunately, commonly prescribed AFOs are unable to easily or quickly vary the joint stiffness; most are not able to vary stiffness at all. The result, at best, is a single AFO stiffness that is only optimized for ambulating in a single condition at a single speed. To address the limitations in existing AFO designs for adapting to varying ambulatory activities, and the potential decline in ankle plantar flexor function with long-term AFO use in individuals with CP, this proposal seeks to develop a differential and adjustable stiffness AFO (DAS-AFO). The primary goals of this proposal are to validate the benefits of, and customer need for, the differential and adjustable stiffness features, and initiate customer discovery to design a cost-effective and manufacturable minimum viable product. Our first aim to confirm that the DAS-AFO improves plantarflexor push-off power compared to standard (physician prescribed) AFOs during walking in CP. In a block- randomized order, participants will walk on a treadmill with their normal AFOs and with the DAS-AFO tuned for each participant to provide only enough dorsiflexor stiffness to address drop foot. We hypothesize that the DAS- AFO design will result in significancy greater biological push-off power and ankle range of motion compared to normal AFOs without effecting walking economy. Our second specific aim is to confirm that the DAS-AFO improves plantarflexor muscle activity compared to standard (physician prescribed) AFOs during walking in CP. We hypothesize that the DAS-AFO design will result in a clinically-relevant increase in plantarflexor muscle activity compared to normal AFOs; hip and knee kinematics will be similar between designs. Our third specific aim is to validate the need and ability for real-time stiffness adjustment during play and school activities; obtain feedback from the children, their parents, and orthotists to design the MVP. In this Aim, we will observe if and how children with CP adjust their AFO stiffness during simulated play and school activities, design and prototype the minimum viable product based on user and orthotist feedback, and engage AFO manufacturers. Collectively, this work will result in new knowledge on how differential and adjustable stiffness AFOs can augment mobility without blocking the active engagement necessary for muscle health and development of motor skills in CP.