Forward dynamics simulation using a natural knee with menisci in the multibody framework

Information on knee loading and the relationship between muscle force and tissue response would benefit orthopaedic medicine, the development of engineered tissues, and our understanding of degenerative joint disease. As a step toward developing subject specific musculoskeletal simulations that predict loading on knee structures, this study combines a cadaver-based validated natural multibody knee model with a muscle driven forward dynamics simulation from a subject of similar height and weight for prediction of joint contact mechanics. Geometries for the multibody model were obtained from magnetic resonance images of a cadaver knee. The ligaments were represented with non-linear spring-damper elements with insertions and zero-load lengths derived from experimental measurements. The menisci were represented as discrete elements connected by 6×6 stiffness matrices and to allow prediction of contact pressure, the medial tibia plateau cartilage was divided into discrete elements. The force-displacement relationships of the knee model were validated by placing it in a model of a dynamic knee simulator and comparing predicted kinematics to experimental kinematics of the identically loaded cadaver knee. Motion, ground reaction forces, and surface electromyography were measured during a dual-limb squat on a female subject with similar height and weight as that of the cadaver donor. The gait data were used in a forward dynamics simulation of the dual-limb squat that included the cadaver knee model. The resulting tibio-femoral contact forces and pressures were compared for versions of the model with and without representation of the menisci. Inclusion of the menisci decreased the peak contact pressure on the medial tibia plateau by 20% and the cartilage-to-cartilage contact force on the lateral side was reduced by 40% through the squat cycle.