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research-article

Design and Testing of a Prosthetic Foot with Interchangeable Custom Rotational Springs for Evaluating Lower Leg Trajectory Error, an Optimization Framework for Prosthetic Feet

[+] Author and Article Information
Victor Prost

Graduate Student, GEAR Laboratory, Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
vprost@mit.edu

Kathryn M. Olesnavage

Graduate Student, GEAR Laboratory, Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
kolesnav@mit.edu

Brett Johnson

Post-doctoral Researcher, GEAR Laboratory, Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
wbj@mit.edu

Matthew Major

Professor, Department of Physical Medicine and Rehabilitation, Northwestern University, Jesse Brown VA Medical Center, Chicago, IL 60208
matthew-major@northwestern.edu

Amos G. Winter, V

Associate Professor, GEAR Laboratory, Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
awinter@mit.edu

1Corresponding author.

ASME doi:10.1115/1.4039342 History: Received September 15, 2017; Revised December 28, 2017

Abstract

An experimental prosthetic foot intended for evaluating a novel design objective is presented. This objective, called the Lower Leg Trajectory Error (LLTE), enables the optimization of passive prosthetic feet by modeling the trajectory of the shank during single support for a given prosthetic foot and selecting design variables that minimize the error between this trajectory and able-bodied kinematics. A light-weight, fully-characterized test foot with variable ankle joint stiffness was designed to evaluate the LLTE. The test foot can replicate the range of motion of a physiological ankle over a range of different ankle joint stiffnesses. The test foot consists of a rotational ankle joint machined from acetal resin, interchangeable U-shaped nylon springs that range from 1.5 Nm/deg to 24 Nm/deg, and a flexible nylon forefoot with a bending stiffness of 16 Nm^2 . The U-shaped springs were designed to support a constant moment along their length to maximize strain energy density; this feature was critical in creating a high stiffness and high-range of motion ankle. The design performed as predicted during mechanical and in vivo testing, and its modularity allowed us to rapidly vary the ankle joint stiffness. Qualitative feedback from preliminary testing showed that this design is ready for use in larger scale clinical trials to further evaluate the use of the LLTE as an optimization objective for passive prosthetic feet.

Copyright (c) 2018 by ASME
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