Hearing the unheard: Fundamentals of acoustic emission signals as predictors of total hip arthroplasty implant loosening.

Implant loosening remains a primary cause of failure of total hip arthroplasty (THA) and is often detected late, when pain occurs. Acoustic emission (AE) analysis is a promising method for early loosening detection, on the supposition that relative movements at the bone-implant interface induce detectable AE signals. To distinguish loosening-induced AE signals from those of stable THA components in vitro investigations are necessary. Substituting human with animal bone for such testing could enable simplified and cost-effective sample preparation. The aim of this study was to investigate whether AE signals differ between bone tissues of different species. AE signals generated by relative movements between TiAlV and human, bovine, and porcine cortical bone were investigated. Per species, 125 movements were analyzed, with 26 AE features identified for each movement. The most important time and frequency features of AE signals from human bone differed significantly from those of both animal species. Signals of human origin were longer and exhibited higher rise time. The main frequency components of human AE signals were in a lower frequency range, with a centroid frequency of 113.7 kHz. Based on these differences, it is not advisable to replace human cortical bone with animal bone for AE-related in vitro studies.