Acoustic Properties of Femoral Components of Hip Endoprostheses Analysis Using Frequency-Resonance-Measurement in a Soft Tissue Simulation Model

Objective of this study is if the technique of Frequency-Resonance Measurement (FRM) can be used to reliably and non-invasively detect the loosening of the femoral component of a metal hip endoprosthesis. As a first step to determine the feasibility of FRM we investigated the own sound property of a full metal body hip endoprosthesis. Four different types of endoprostheses were tested to establish their acoustic properties regarding own frequency and resonance. In the first step the acoustic properties of the implants were determined. In the second step the acoustic properties of these metal specimens under the influence of a soft tissue simulation were investigated. The test results for the investigated prostheses showed typical similarities regarding the pattern of the spectral lines as well as the duration of the oscillations. All spectral lines where sharply marked and were situated between 1-20 kHz. The duration of oscillation was up to 700 ms. In all tested series the correlation in the 6 measurements of each prosthesis model in each mode were >0.95. In a soft tissue simulation model there still was a detectable specific acoustic pattern for each prosthesis model. FRM might be used as a remote and non-invasive tool for monitoring in-growth or loosening of hip endoprostheses. Mutations in this dimension can be easily automated for a computerized evaluation. The soft tissue dampening is a factor of less importance. We have now begun in vivo studies of different interface situations, cadaver studies are planned after that.