A new sensor system is proposed for real time, in vivo monitoring of tibiofemoral contact pressures at knee arthroplasty implants for prediction of implant failure and understanding the real time dynamic of the implants when the user carries out his/her daily activities. The proposed sensor system will consist of a pressure-sensitive magnetic layer embedded under the top surface of the polyethylene insert of a knee arthroplasty implant for mapping the contact pressures between the polyethylene insert and femoral components. The pressure-sensing layer will consist of a grid of pressure/stress-sensitive magnetoelastic thin strips that change their magnetic properties with applied forces. Pressures will be measured at the pressure points, which are at the crossings of the grid. The magnetization of each sensing strip will be remotely measured by monitoring its magnetic higher-order harmonic fields. The responses of these sensing strips will be fed into an algorithm to determine the pressure loading at all pressure points, which allows real-time, in vivo determination of pressure profiles across the top surface of the polyethylene insert. Preliminary studies have demonstrated the remote detection of pressure across a surface with an array of magnetoelastic sensing strips. Prior to applying this technology to animal models or human trials, however, several issues will be addressed including the fabrication of reproducible and biocompatible sensing layer, development of a reliable detection system and data processing algorithm, and characterizing the response of the sensing layer ensuring its effectiveness.
There is a need to measure contact pressures at the femoral component of a knee arthroplasty implant to determine the wear and tear of the polyethylene insert of the implant. Today, most pressure monitoring systems for knee arthroplasty implants are either limited for in vitro or intraoperative uses, or cannot measure contact pressures across the surfaces of the femoral component and tibia plate. Development of a new technique for continuous, ambulatory monitoring of tibiofemoral contact pressures would be an enormous advance both in the detection of the implant failure and understanding the causes of the failure. While there are sensor systems that can either map the tibiofemoral contact pressures or provide continuous monitoring of the total pressure at the knee joint, to the PIs'knowledge there is no sensor system that can provide ambulatory mapping of tibiofemoral contact pressures. Therefore, the proposed sensor system, when successfully developed, will have a significant impact on the long term care of patients who receive knee arthroplasty implantation.
