Finite Element Study of the Healthy and Meniscectomized Knee Joints Considering Fibril-Reinforced Poromechanical Behaviour for Cartilages and Menisci
Creators: name: Kazemi Miraki, Mojtaba
Publisher: name: Graduate Studies
Year: 2013
Subjects: subject: Applied Mechanics
subject: Engineering--Biomedical
subject: Engineering--Mechanical
subject: Finite Element
subject: Creep
subject: Stress relaxation
subject: Viscoelasticity
subject: Hyperelasticity
subject: Fluid pressure
subject: Porous Media
subject: Fibril-reinforced
subject: Knee Joint
subject: Articular cartilage
subject: Meniscectomy
subject: Menisci
subject: Large deformations

description: From an engineering standpoint, articular cartilage and meniscus are porous viscoelastic materials with water as their most prevalent component. However, fluid pressurization has been commonly ignored in the three-dimensional Finite Element (FE) models of the knee joint and the soft tissues have been usually assumed as single-phase elastic materials. These elastic models cannot capture the time-dependent behaviour of the joint and are limited to either the instantaneous or equilibrium response, depending on the modulus used. A patient-specific FE model describing the time-dependent response of the healthy and injured knee joints is still a challenge. The main objective of this research was to investigate the fluid-flow dependent creep/relaxation behaviours of the normal and meniscectomized knees using a patient-specific FE model of the knee joint. The model included distal femur, tibia, fibula, articular cartilages, menisci and four major ligaments: ACL, PCL, LCL and MCL. Cartilages and menisci were modelled as fluid-saturated solid matrices reinforced by a nonlinear collagen network. Both small and large deformations were considered in the simulations. The theory of quasi-linear viscoelasticity was used to describe the nonlinear behaviour of the collagen fibrils. Neo-Hookean hyperelasticity was considered for the non-fibrillar solid matrix of the tissues in large deformations. The constitutive models were numerically formulated in a co-rotational reference frame for large deformations and a user defined FORTRAN subroutine, UMAT, was developed to implement the material model in ABAQUS. The obtained results indicated the important role of fluid pressurization of cartilaginous tissues in the contact mechanics of the joint. Removal of the menisci not only changed the stresses in the cartilages, which was in agreement with the published studies, but also altered the distribution and the rate of dissipation of fluid pressure in the cartilages. While in the intact joint, the location of the maximum fluid pressure was dependent on the loading conditions, in the meniscectomized joint the location was predominantly determined by the site of meniscal resection. The results also indicated different load transfer mechanisms of the joint in creep and stress relaxation. In the creep loading, the stress in femoral cartilage decreased with time while the stress in the menisci increased. This resulted in a gradual transfer of the loading from the cartilage to the menisci. In stress relaxation, however, the stress level decreased with time in cartilages and menisci. Such phenomena cannot be captured using single-phase models of the joint.