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Total knee arthroplasty, as one of the most common surgeries in the United States, has been widely used to help restore the functionality of damaged knee joints. Alignment of the knee joint during surgery is an extremely important factor to achieve a successful operation. Several methods have been used to quantify the alignment and to provide surgeons with a repeatable method of surgery. However, lack of in vivo information has hindered establishment of correlation between intra- and postoperative knee conditions. In this work, the application of multiple piezoelectric transducers encapsulated inside the ultra high molecular weight polyethylene knee bearing for collecting in vivo data is suggested. The piezoelectric elements display the ability to sense and harvest energy from the joint during daily activity. As a sensor, piezoelectric transducers are designed to measure the compartmental forces as well as the location of the contact points between the femoral and tibial components of the knee implant. Initially, finite element analysis is performed to investigate the sensing performance of the system. In addition, a prototype instrumented bearing is fabricated and the performance of the system in measuring the forces and locations is investigated experimentally. In the experiments, the voltage signals generated by the piezoelectrics are obtained and processed to measure two components of force as well as two different contact points, one each on the medial and lateral compartments of the knee bearing. On the other hand, the actual force profile and the location of contact areas are recorded using the load frame’s built in load cell, and pressure-sensitive films, respectively, and compared to the measured data from the piezoelectrics. The result of FE simulation showed a maximum error of about 1.5% in force sensing and a maximum deviation of about 0.5 mm in the measured location of the contact points. The experimental results also showed that the measured force and location by the piezoelectric sensors match the actual quantities measured from load frame and pressure film fairly well.
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