Eddy Current-TMR Sensor for Micro-Motion Detection of Orthopaedic Implants

Every year millions of people around the world undergo orthopaedic surgeries with partial or complete joint replacements. However, according to the various arthroplasty registers around the world, about 10 % of the implants require re-surgery at some point in their lifetime [1]. About 80–90% of implant failures occur due to mechanical reasons [1–2]. It is proposed in [2], that micromotion of the orthopaedic implants during the limb movement can provide insights on the possible implant failure in the future. For this purpose, it is necessary to monitor the motion of metallic orthopaedic implants with the resolution of the order of tens of microns when the person moves a limb. In this paper, it is proposed to use a small sensor embedded inside the bone at a distance from the orthopaedic implant. The space available for such a sensor is limited to the cylindrical hole of dimensions 3 mm × 10 mm.