Introduction: Ankle-foot-orthoses (AFOs) are common interventions for treating foot drop in patients post stroke. Current designs for passive AFOs are either optimized for heel strike and push off with a low stiffness, or for heel off with high stiffness. The goal of this study is to create a variable stiffness ankle foot orthosis (VSAFO) which can have an adjustable stiffness profile to allow for low stiffness at heel strike and push off, as well as high stiffness at heel off. Methods: An AFO modifier was designed to be combined with a base flat blade AFO in order to meet the VSAFO design requirements. The modifier has two variations: one was made with a thermoplastic elastomer gel and the other was made with an extruded polystyrene foam. The modifiers are placed on the blade of the AFO and can be tuned to five different levels of resistance. The modifiers were tested in combination with three AFOs to determine how it affected their stiffness profiles. Results: The findings from this study showed that the modified AFOs could meet some of the design requirements, but not all: 1) all of the combinations were able to achieve the required range of motion, 2) the modifiers were able to steadily increase AFO stiffness in RD and half of the combinations were within the required range, but they could not steadily increase stiffness in DF and none of these combinations were within range, 3) none of the combinations were able to show the required increase in stiffness from RD to DF, 4) all of the combinations (except for one) did not increase stiffness in RPF and 5) both of the modifiers weighed less than 300g. Discussion: While the VSAFO designs did not meet all of the requirements, the results did show some promise. It was able to increase stiffness in RD and, to some extent, DF without increasing stiffness in RPF. This alone is promising because it means that there is the potential to have a higher stiffness for the ankle at heel off, while keeping a low stiffness for heel strike and push off.
Stoop, Ashton,
"Design of a Variable Stiffness Ankle Foot Orthosis"
(2020).
Biomedical Engineering Theses and Dissertations.
Brown Digital Repository. Brown University Library.
https://doi.org/10.26300/r2ec-j685
