Knee contact force estimation using dynamics simulation

Abstract

Body weight is supported by ground reaction force at the contact surface between the foot and ground. The pressure mat can measure the distribution of the ground reaction force on the contact surface as force per unit area, or pressure. Pressure information on the contact surface would help investigate pathomechanics of tissue degeneration in local regions. The ground reaction force, concentrated at a point, can be estimated with relatively high accuracy by solving dynamics equations, but it is almost impossible to estimate pressure distribution, which is similar to a two-dimensional array of forces. The weight of the body above the knee is supported in the knee. Contractions of muscles around the joint during activities make the knee contact force even higher than the body weight. The knee contact force is as high as three times of body weight during walking and seven times during stair descending. Though it is impossible to estimate pressure distribution in the articular surface of the knee, there have been a number of studies to estimate concentrated forces in each of the medial and lateral compartments of the knee during daily activities. It is still a difficult dynamics problem because of multiple force elements around the knee such as ligaments and muscles. It requires a number of assumptions such as ligament strengths, ratios of forces in muscles and simplified contact geometry in the knee. There was a world competition to predict in vivo knee load which was hosted by ASME Bioengineering and was sponsored by the NIH in USA from 2010 to 2015, six years. My team developed a dynamics knee model which can predict knee contact force using an inverse dynamics-based optimization method. We joined the fifth and sixth competition won in the sixth. I will briefly explain our knee model to predict in vivo knee load during walking in the presentation.