A development of force distribution measurement system in total knee arthroplasty and with high resolution

Recently, the number of total knee arthroplasty (TKA) has been more than 65,000 with the aging of population in Japan. Although it is well known that the soft tissue balance is important for the TKA, there is a problem that it depends much on past experiences of an examiner in clinical situation. Thus, a nonexpert doctor makes deviation of the balance due to insufficient experiences. In this study, we set a goal to develop a measurement system which can provide a useful and quantitative criterion for evaluating force concentration of the knee joint in the TKA. This study measures force distribution by using a measurement trial insert instead of an actual insert which is one of the parts constituting a total knee prosthesis. The measurement trial insert visualizes a force distribution when an electroactuator applies a loading force. There were two experiments as fundamental and practical experiments. In the fundamental experiment, a force distribution was visually confirmed by a developed force sensor during a force loading through two cubic shaped woods of 5.0 mm and 10.0 mm on sides. In the practical experiment, the developed measurement trial insert visualized a force distribution in case of valgus and flexion. Consequently, the developed system could visualize the size of applying force area in the fundamental experiment. In addition, the developed system could visualize a gravity point movement in case of valgus and flexion in the practical experiment.