A New Load Application System for In Vitro Study of Ligamentous Injuries to the Human Knee Joint

[+] Author and Article Information
J. M. Bach

Biomedical Engineering Graduate Group, University of California, Davis, CA 95616

M. L. Hull

Department of Mechanical Engineering, University of California, Davis, CA 95616

J Biomech Eng 117(4), 373-382 (Nov 01, 1995) (10 pages) doi:10.1115/1.2794195 History: Received January 10, 1994; Revised September 26, 1994; Online October 30, 2007


This paper describes the design and accuracy evaluation of a new six degree of freedom load application system for in vitro testing of the human knee joint. External loads of both polarity in all six degrees of freedom can be applied either individually or in any combination while the knee is permitted to move unconstrained in response to applied loads. The flexion/extension degree of freedom permits the full physiological range of motion. In addition to external loads, forces of the three major muscle groups (quadriceps, hamstrings, gastrocnemius) crossing the joint can be developed. Full automation and rapid convergence of loads to programmed values are achieved through a computer which feeds command signals to servo controller/electro-pneumatic servo valves. The servo valves regulate pressure to pneumatic actuators which develop the various loads. Experiments undertaken to quantify the accuracy of both load and displacement measurements reveal that errors particularly in load measurement are effectively controlled through the apparatus design.

Copyright © 1995 by The American Society of Mechanical Engineers
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