Results

Loosening of total hip replacements (THR) is still the main reason for revision. Approximately 36,000 revisions are necessary in Germany each year. Due to suboptimal sensitivity of current diagnostic methods, e.g. radiographs, the loosening is often identified late.

To improve the accuracy, an acoustic method was develop and tested in a simulated environment. Therefore a test rig was developed including an instrumented THR as well as external electronic devices, whereby the hip stem is situated in an ethanol fixed human femur (without soft tissue) at different states of loosening.

The implants were excited externally using a coil to produce an impingement of a magnetic balls inserted in the hip stem. The resulting structure borne sound was analyzed by an acceleration sensor. The structure borne sound for different loosening states was analyzed.

The present vibration study provided relevant data for a frequency spectrum analysis of a forced vibration in a THR. Hence, the frequency analysis can be classified into different levels of loosening.