The aseptic loosening is one of the main reasons for revision surgery in total hip arthroplasty. During the loosening process of hip stems, tolerable relative movements of 30-100 µm between stem and bone are exceeded and induce a characteristic progressive loosening cascade that leads to a gradual loss of fixation due to a degradation of the surrounding bone. Up to date, there is no reliable diagnostic method to detect such a loosening at an early stage.
The aim of subproject A03 is to enable an early detection of an hip stem loosening and to be able to distinguish aseptic from septic loosening in order to counteract an excessive bone destruction early enough.
The acoustic emission technology is to be used as a passive, non-invasive measurement method for the detection of friction-induced sound events caused by the relative movements in the implant-bone interface. Using ion mobility spectrometry (IMS) in combination with electrospray ionization (ESI) as well as pyrolysis gas chromatography (GC), both a compact ESI-IMS and a pyrolysis GC-IMS will be developed. Both systems will be used to detect characteristic signatures of biomarkers and abrasion products in body fluids such as serum, urine or joint fluid from patients. From the results obtained, conclusions can be drawn as to whether the stem loosening is aseptic or septic. The combination of both measuring methods offers a procedure to detect the loosening at an early stage and to be able to treat it in a differentiated manner. First of all, in vitro experiments are carried out in the laboratory in which implant materials are articulated against bone tissue in order to gain basic knowledge about the sound emission signals that are generated in the loosening process. Several piezoelectric sound transducers with different properties (broadband, resonant) will be used and compared to determine their suitability. In the course of the project, the set-up of the in vitro experiments will be successively approximated to the in vivo situation. In addition, IMS spectra of abrasion particles and bacteria associated with prosthesis loosening will be characterized in isolation in order to be able to detect them later in different body media.