Dynamic Response Analysis of the Human Knee Joint

Objective. To perform frequency response analysis of passive intact and rneniscectomized human knee joints under body mass. The knee dynamic system parameters and their alterations with different preloads and displacement amplitudes will be determined.

Design. Using an Instron Mechanical Testing System, specially designed fixtures, and the following softwares: WaveMaker, Excel, LabView, and Matlab, the knees were dynamically tested and analyzed.

Background. Studies have been performed to analyze the dynamic behavior of the human knee. However, no experimental study has investigated the dynamic response of the knee joint under an axial compressive dynamic loading condition considering the effect of the upper body mass.

Methods. Ten human knee joints were each placed in fixtures and secured in the Instron equipment, with an added mass to simulate body weight. The dynamic testing sequence consisted of creep tests, a series of frequency sweeps at increasing amplitudes, and relaxation tests. This testing series was performed with the knee in full extension, and at a 25-degree flexion angle. A meniscectomy was performed on each specimen, and the testing trial was performed again. The data from testing was then analyzed, and the joint response was obtained.

Results. The results indicated that the resonance frequency is significantly affected by change in preload and flexion angle. Increase in preload resulted with an increase in resonant frequency, but flexing the knee resulted in a decreased resonant frequency. The stiffness also decreased significantly when the knee was flexed. The joint compliance response increased up to two fold at resonant frequency compared with that of 1 Hz frequency at different joint conditions.

Conclusion. The compliance graphs had similar shapes and had interesting trends that yielded results that can be used as reference data for future studies and rehabilitation means. The analysis indicated that there is a range in the dynamic factors depending on the testing conditions. The meniscectomy had a significant effect on the joint response as well.