Abstract
Currently, imaging methods are used to diagnose loosening of endoprosthetic implants, but fail to achieve 100% accuracy. In this study, a passive sensor array which is based on the interaction between magnetic oscillators inside the implant and an excitation coil outside the patient was investigated. The excited oscillators produce sound in the audible range, which varies according to the extent of loosening. By performing several experimental tests, the sensor array was optimized to guarantee reproducible and selective excitation of the sound emission. Variation in the distance between the oscillators demonstrated a definite influence on the quality of the generated sound signal. Furthermore, a numerical design analysis using the boundary element method was generated for consideration of the magnetic field and the selectivity of the oscillators during excitation. The numerical simulation of the coil showed the higher selectivity of a coil with a C-shape compared to a cylindrical coil. Based on these investigations, the passive sensor system reveals the potential for detection of implant loosening. Future aims include the further miniaturization of the oscillators and measurements to determine the sensitivity of the proposed sensor system.
Highlights
Implantation of a total hip replacement (THR) has become a standard procedure for the treatment of degenerated or fractured hip joints
Due to the aforementioned challenges of implementation of an integrated active system to identify implant loosening, we proposed a passive sensor concept based on magnetic induction [24]
Oscillators which exhibit a length of 4 mm were chosen for the passive sensor array in the total hip stem
Summary
Implantation of a total hip replacement (THR) has become a standard procedure for the treatment of degenerated or fractured hip joints. After resection of the femoral head, a stem is impacted or cemented into the femur. The artificial joint is realized by connecting a ball-head to the stem and a liner into the cup. The modular design of modern total hip replacements allows choice of different materials as bearing surfaces in combination with materials of high biocompatibility and enhanced bone ingrowth. Despite more than forty years of clinical experience, complications can still occur which require an exchange (revision) of the THR or some of its components. The main reason for failure is loosening of the stem or the cup [1]. Acute pain requires clarification as to whether the THR is mechanically loose and has to be revised [2]. Each revision of a THR leads to subsequent tissue defects and functional deficits
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