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Bioengineering 2017, 4(4), 95;

Application of the Superelastic NiTi Spring in Ankle Foot Orthosis (AFO) to Create Normal Ankle Joint Behavior

Dynamics and Smart Systems Laboratory, Mechanical, Industrial and Manufacturing Engineering Department, The University of Toledo, Toledo, OH 43606, USA
Author to whom correspondence should be addressed.
Academic Editors: Gou-Jen Wang and Liang Luo
Received: 23 September 2017 / Revised: 16 November 2017 / Accepted: 28 November 2017 / Published: 7 December 2017
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Hinge-based Ankle Foot Orthosis (HAFO) is one of the most common non-surgical solutions for the foot drop. In conventional HAFOs, the ankle joint is almost locked, and plantar flexion is restricted due to the high stiffness of the hinge mechanism. This often leads to a rigid walking gate cycle, poor muscle activity, and muscle atrophy. Since the ankle torque-angle loop has a non-linear profile, the use of a superelastic NiTi spring within the hinge, due to its nonlinear behavior, could recreate a close-to-normal stiffness of the normal ankle joint, which, in turn, could create a more natural walk. The focus of this study is to evaluate the performance of a superelastic NiTi spring versus a conventional Stainless Steel spring in a hinge mechanism of a custom-fit HAFO. To this aim, a custom-fit HAFO was fabricated via the fast casting technique. Then, motion analysis was performed for two healthy subjects (Case I and Case II): (i) subjects with bare foot; (ii) subjects wearing a conventional HAFO with no spring; (iii) subjects wearing a conventional Stainless Steel-based HAFO; and (iv) subjects wearing a NiTi spring-based HAFO. The data related to the ankle angle and the amount of moment applied to the ankle during walking were recorded using Cortex software and used for the evaluations. Finally, Finite Element Analysis (FEA) was performed to evaluate the safety of the designed HAFO. The NiTi spring offers a higher range of motion (7.9 versus 4.14 degree) and an increased level of moment (0.55 versus 0.36 N·m/kg). Furthermore, a NiTi spring offers an ankle torque-angle loop closer to that of the healthy subjects. View Full-Text
Keywords: superelastic NiTi spring; Ankle Foot Orthosis (AFO); normal ankle joint behavior superelastic NiTi spring; Ankle Foot Orthosis (AFO); normal ankle joint behavior

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Amerinatanzi, A.; Zamanian, H.; Shayesteh Moghaddam, N.; Jahadakbar, A.; Elahinia, M. Application of the Superelastic NiTi Spring in Ankle Foot Orthosis (AFO) to Create Normal Ankle Joint Behavior. Bioengineering 2017, 4, 95.

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