Acoustic sensor system for loosening detection of hip implants

One of the main reasons for revision of total hip replacements (THR) is the aseptic or septic loosening. The Osseointegration of the uncemented hip stem in the femoral bone has to detect exactly in order to enable early state loosening detection. All present diagnostic methods, e.g. radiographs and arthroscopy, show insufficient sensitivities and specificities between 70% and 80%. Osseointegration can be identified in-vivo by use of acoustic methods. The acoustic waves can be generated by a mechanical hammer or by a piezoelectric transducer placed on the inside the femoral hip stem wall. Thereby the mechanical-acoustic properties of the bone interface give information about the status of the loosening process.A functional model of the measuring principle shows significant differences in varied phases of fixation. The new acoustic sensor system demonstrates its potential to detect aseptic loosening. Moreover, the proposed system could be used in experimental applications to determine the quality of osseo-integrative coatings and new implant materials as well.