A NOVEL QUICK RELEASE MECHANISM FOR ANKLE FOOT ORTHOSIS STRUTS

Abstract

BACKGROUND: A posterior dynamic element ankle-foot orthosis (PDEAFO) uses a stiff carbon fibre strut to store and release energy during various mobility tasks, with the strut securely attached to the foot and shank-cuff sections. A design that allows the user to swap struts for specific activities could improve mobility by varying PDEAFO stiffness, but current approaches where bolts securely connect the strut to the orthosis make quick strut swapping time-consuming and impractical. OBJECTIVES: Design a novel quick release AFO (QRAFO) that can enable daily living strut-swapping and thereby enable better ankle biomechanics for the person’s chosen activity. METHODOLOGY: The novel QRAFO enables device stiffness changes through a quick release mechanism that includes a quick-release key, weight-bearing pin, receptacle anchor, and immobilization pin. A prototype was modelled and simulated with SolidWorks. Mechanical tests were performed with an Instron 4482 machine to evaluate quick release mechanism strength with running and 20° slope downhill walking loads. Quick release efficiency was then evaluated via two quick release functional tests, with four participants wearing a 3D printed QRAFO. FINDINGS: Simulated stress on the weight bearing pin, anchor, and surrounding carbon fibre structure under running and downhill walking loads did not exceed the yielding stress. Mechanical tests verified the simulation results. Four participants successfully swapped the strut within 25.01 ± 3.66 seconds, outperforming the 60.48 ± 10.88 seconds result for the hand-tightened bolted strut. A learning evaluation with one participant showed that, after approximately 30 swapping iterations, swap time was consistently below 10 seconds. CONCLUSION: The quick release mechanism accommodated running and slope walking loads, and allowed easy and fast strut removal and attachment, greatly reducing strut swap time compared to screw-anchor connections. Overall, the novel quick release AFO improved strut-swapping time without sacrificing device strength, thereby enabling people to use the most appropriate AFO stiffness for their current activity and hence improve mobility and quality of life. Layman's Abstract An advancement in ankle foot orthosis (AFO) design, named Posterior Dynamic Strut AFO (PDEAFO), securely attaches a strut to the foot and shank-cuff sections via bolts, to better match a user’s activity level. The PDEAFO design approach makes quick strut swapping impractical. A novel quick release PDEAFO design was created to enable AFO users to quickly switch struts when desired, therefore enabling better ankle biomechanics for the person’s chosen activity. The novel quick release AFO (QRAFO) includes a quick-release key, weight-bearing pin, receptacle anchor, and immobilization pin. To ensure appropriate QRAFO strength, simulated loads were tested before prototyping. The prototype was mechanical testing under maximum loads. To prove quick release mechanism efficiency, the author conducted controlled experiments between screw-anchor mechanism (used by PDEAFO) and quick release mechanism on 3D printed AFOs. Simulations demonstrated safe performance under walking, running, and downhill walking conditions. Mechanical testing proved component strength under maximum loads. Functional testing showed that participants can swap struts within 25.01± 3.66 seconds on the quick release AFO, outperforming the 60.48 ± 10.88 seconds result for the screw anchor mechanism. In conclusion, the quick release AFO improved strut-swapping time without sacrificing device strength, thereby enabling people to use the most appropriate AFO stiffness for their current activity and hence improve mobility and quality of life. Article PDF Link: https://jps.library.utoronto.ca/index.php/cpoj/article/view/38802/30399 How To Cite: Li W, Baddour N, Lemaire E.D. A novel quick release mechanism for ankle foot orthosis struts. Canadian Prosthetics & Orthotics Journal. 2022; Volume 5, Issue 2, No.3. https://doi.org/10.33137/cpoj.v5i2.38802 Corresponding Author: Edward D. Lemaire, PhDCentre for Rehabilitation Research and Development, Ottawa Hospital Research Institute, Ottawa, Canada.E-Mail:elemaire@ohri.ca ORCID ID: https://orcid.org/0000-0003-4693-2623