A Non-smooth Approach for Multiphysics Modeling of Tibiofemoral Joint Contact Forces under Impact Loading

Walking and running are not as mechanically benign as might be commonly assumed. When a heel hits the ground, the body undergoes high-frequency impulse loads, which means it experiences large and abrupt contact forces distributed over the surfaces of the tibiofemoral joints. Studying these contact forces could reveal new insights related to the diagnosis and prognosis of osteoarthritis. In vivo measurement of joint forces is impossible, making computational models essential for their study. To do this, the model must include rigid bodies, such as bones, flexible bodies, and fluids, such as synovial fluid, making this a multi-physics model. During impact, the interaction between the fluid and bone surfaces resembles a rigid body collision due to the abrupt nature of the event, causing negligible deformation or positional change. This behavior motivates the application of rigid body impact principles within a multi-physics model of the tibiofemoral joint. Instead of simulating a complex anatomical system, a simplified knee joint is represented using two blocks connected with flexible and fluid elements. Two cases are examined, which represent knee joints with chronic arthritis and healthy joint tissue. This paper discusses the effect of flexible elements on the dynamic behavior of impacting bodies and the energy transfers that occur in the system predicted by the rigid body impact analysis.