An Embedded Wireless Temperature Sensor for Orthopedic Implants

A wireless and passive (battery free) temperature sensor that can be embedded inside an orthopedic implant, such as an interference screw, was developed. The sensor is based on an inductive-capacitive-resistive resonant circuit that is inductively powered so the temperature at the implant can be measured wirelessly. A potential application of this sensor is to monitor internal wound temperature for the diagnosis of local infection at the implant site. Infections pose a significant risk to patients, who receive orthopedic implants, often lead to adverse conditions including implant failure, tissue necrosis, and amputation. Current approaches for diagnosing orthopedic implant-associated infections, such as blood tests, radiographic imaging, and histological study are slow, tedious, and nonspecific. In recent years, thermographic imaging has been used to monitor local temperature at the external surgical site as a means to detect infection, but its applications are limited to surface or near-surface wounds. The described sensor will serve as an useful research tool to investigate using temperature as an indication of deep-tissue orthopedic implant infection. When fully developed, this sensor may also improve orthopedic care by allowing simple, early detection of infection at an implant site. This paper describes the design and fabrication of the sensor, as well as characterizes its performance. Experimental results indicate the temperature response of the sensor is reproducible within the tested range of 30-42 degrees C.