A novel in vivo sensor for loosening diagnostics in total hip replacement

Approximately 200,000 patients are treated with total hip replacements (THR) in the United States per annum, in European Countries over 500.000. The main reason 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 be detected 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 `active' acoustic methods. The acoustic waves can be generated, e.g. by a mechanical hammer placed on the inside of the femoral hip stem wall. The mechanical-acoustic properties of the bone-implant interface give information about the status of the loosening process. A functional in-vitro 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.