Antennifying Orthopedic Bone-Plate Fixtures for the Wireless Monitoring of Local Deep Infections

Infection is the unavoidable threat to any orthopedic implant that can also force its removal as extreme remedy. The diagnosis of infections is currently achieved by time consuming imaging (X-Rays, MRI, CT) or just by the onset of the patient's pain, when the problem is in an advanced status. Instead, by equipping the prosthesis with a local sensor (for the temperature as a first) and with a wireless communication radio, an early-time identification of the infection could be achieved. This paper proposes a method to transform an orthopedic device provided with holes (like a bone fixation plate) into an harvesting antenna integrating an RFID sensor, with no battery onboard. A miniaturized antenna adapter, fully embedded into a free hole, with tuning capability, collects the electromagnetic power intercepted by the medical device and transfers it to the RFID circuit. Simulations and experimentations with several prototypes demonstrated that the augmented implanted device can establish a stable RFID link up to 0.5 m and that it is able to correctly sample the variation (37°C - 40°C) of the local temperature of the bone as in case of typical deep infections.