Abstract
Introduction
In total knee arthroplalsties, there are risks of revision surgeries because of aseptic loosening, polyethylene wear, and metal component breakage. The data such as model, type, size, and manufacturing companies are required at the time of revision surgeries. However, it is sometimes difficult to acquire such data due to patient's change of address and the elimination and consolidation of hospitals in the long-term. Therefore, we try to use the Radio Frequency IDentification (RFID) in the total knee joint system.
Materials and methods
The FerVID family (Fujitsu Co. Ltd., Tokyo, Japan) was prepared as the RFID tag. It was radio-resistant below the dose of 50kGy, which allowed gamma sterilization. The RFID tags were embedded into the anterior side of GUR 1050 UHMWPE inserts and 0.3wt% vitamin E blended UHMWPE. The UHMWPE inserts were manufactured by thecompression molding method at the maximum temperature of 220°C and the maximum compressive force of 245kgf/cm2. The manufactured inserts were implanted in fresh cadaveric knees. The tibial base plate was made of Ti6Al4V. The femoral components were made of Co-Cr-Mo or Ti-6Al-4V. Communication Performance was measured with the interrogator (DOTR-920 MHz-band, Tohoku Systems Support Co. Ltd., Miyagi, Japan). The transmission output was up to 1W. Received Signal Strength Indicator (RSSI) was measured 500 times at 15 mm away from the surface of skin in the extension and 90° flexion of the knee (Fig1).
Results and discussion
The figure 2 indicated the maximum communicable distance and communication sensitivity in cadaveric knees. The inserts with tags worked in cadaveric knees, though the maximum communicable distance and the communication sensitivity of the RFID tags were shortened and reduced, respectively. The possible causes were as follows. The radio wave was absorved by the skin and subcutaneous tissues containing water. In the human body, the resonance frequency of RFID tag shifted to the lower side. The reflected radio wave on the surface of femoral and tibial components interfered with the radio wave from the tag to the interrogator. The femoral component made of Ti-6Al-4V showed better communicable distance and communication sensitivity at knee flexion. The electrical conductivity of Co-Cr-Mo and Ti-6Al-4V are 1.1 – 104S/cm and 0.59 – 104S/cm, respectively. Therefore, the Co-Cr-Mo femoral component reflects radio waves more easily.
The communication performance was deteriorate in the implanted knee. However, the maximum communicable distance was more than 30 mm, which can be usable in clinical application.
