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2011 Design of Medical Devices Conference Abstracts

Intelligent Motor Powered Prosthetic Knee Joint OPEN ACCESS

[+] Author and Article Information
Hildur Einarsdottir

Ossur

J. Med. Devices 5(2), 027528 (Jun 14, 2011) (1 page) doi:10.1115/1.3590866 History: Published June 14, 2011; Online June 14, 2011
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POWER KNEE is the world’s first intelligent motor powered prosthetic knee. The knee replaces lost muscle functions and is designed to increase gait symmetry and to reduce unwanted load in level ground walking, stair and ramp descent/ascent, sitting down and standing up. During the first part of swing phase, in general, the knee joint flexes, lifting the foot off the ground. This is an important part of the swing phase as insufficient ground clearance at initial swing has a rippling effect throughout the whole phase and can cause toe stubbing, insecurity of the user, and as a result some types of gait deviations. User of a passive prosthesis knee joint uses his hip to force the foot off the ground whereas a powered knee joint can actively flex the knee at the right moment, ensuring enough ground clearance throughout the swing phase. Every prosthetic knee joint has some internal resistance, which needs to be overcome in order to transfer from knee flexion to extension in swing. In order to overcome this internal resistance, users of passive knee joints use excessive hip power to force the joint into extension. This can cause gait deviations and insecurity for the user as the center of mass is shifted back. An intelligent motor powered knee joint has the ability to remove this unwanted action by actively extending the knee at the right moment. Another benefit of a motor powered prosthesis is that the motor can be actively locked in any flexed position without the risk of the joint buckling. This means that the joint does not have to be fully extended at heel strike and the extension at terminal swing can be fine tuned to leave the joint in approximately 5 deg flexion, imitating the position of a healthy knee. While the motor is blocked at heel strike, avoiding buckling, a mechanical spring controls a stance flexion angle. The stance flexion works as a shock absorption and ensures more symmetry during walking. In addition to controlling the speed and amount of flexion and extension of the knee joint in every gait cycle, a powered knee prosthesis provides the user with enough lifting power to ascend stairs step over step and stand up from a chair with equal weight on the sound side and the prosthesis side. This important feature reduces the unsymmetrical load put on the sound side, arms, and shoulders in those activities.

Copyright © 2011 by American Society of Mechanical Engineers
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