Review of Knee Models

This paper is a review of static and dynamic models of the human knee joint. Both phenomenological and anatomically based models are discussed. The phenomenological models can be classified into two groups: first, models which consider the human knee to be a simple hinge joint and, second, rheological models. The simple hinge models have generally been used in larger models developed to predict human body dynamics during gait activities. The rheological models, which describe the knee as an equivalent viscoelastic hinge, have been used to describe the response of the knee joint during dynamic loading conditions. Anatomically based models have been used to predict the kinematics and kinetics of the knee and its structural components. The majority of kinetic models have treated static and quasistatic equilibrium conditions, and only a few have addressed nonequilibrium dynamic loading. In reviewing the static and quasistatic models, we have divided them into four groups. First, models developed to determine the forces in the muscles and the ligaments at the knee joint during various activities, second, models developed to determine the forces in the ligaments as a function of joint position, third, models used to determine the contact stresses between the femur and the tibia, and, fourth, more comprehensive models developed to study the stiffness and load–displacement characteristics of the knee joint which include both ligamentous structures and the geometric constraints of the knee. In our survey, we found few models of the patello-femoral joint. A more complete model of the human knee joint describing the interactions between the tibia, femur, patella, and fibula still needs to be developed. On the other hand, the geometric and mechanical properties of a single real knee, required to validate any model are not presently available.