Validation of the next generation knee simulator
Abstract
The main objective of this research was to validate the Next Generation Knee Simulator (NGKS) as an effective tool to study the knee joint under dynamic loading conditions. The validation of the knee simulator demonstrated that the tibiofemoral loads produced by the NGKS were similar to desired loads and patellofemoral loads were controlled to a limited degree. The kinematics were also shown to be similar to kinematics in the literature. The five axis electro-hydraulic NGKS was designed and built at Purdue University. A controlled moment about the flexion axis of the ankle was included, which was used to better control the loading of the patella. A dynamic model of the NGKS was developed to predict the joint loading and determine the required input loads to duplicate the desired joint loading. Joint loads were experimentally measured with fabricated load cells. The average difference between predicted quadriceps loads from the model and experimental data was 4.4% of the maximum predicted loads. The average difference in tibiofemoral loads was 8.8%. Both results validate the model's predicted loading. The average difference in patellofemoral loads was 23.1% which does not conclusively validate the model's predicted patellofemoral load prediction. While the model included a single, resultant force on the patella, the load cell was only measuring the forces in one direction, causing some of the loading discrepancies. Analysis showed qualitatively that the ankle flexion moment could reduce the quadriceps and compressive patellar forces during loading by as much as 0.23 lbf and 0.10 lbf respectively for every 1 in*lbf of applied ankle flexion moment. Similar results were predicted from the dynamic model for the quadriceps and higher reductions for the patella. Three different predicted tibiofemoral loading profiles for walking were successfully reproduced. The patellofemoral loading was shown to be improved by the ankle flexion moment. Limitations to the use of this moment were abnormal posterior motion of the tibia when the ratio of predicted tangential to normal tibiofemoral loads grew too high (above 0.4) and when the magnitude of ankle flexion moment grew above 900 in·lbf and caused the assembly to buckle.
Degree
Ph.D.
Advisors
Hillberry, Purdue University.
Subject Area
Mechanical engineering|Biomedical research
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