The Roles of the Normal Mechanical Properties of Articular Cartilage in the Contact Mechanics of the Human Knee Joint: a Finite Element Approach
In spite of numerous research devoted to the study of the mechanical behaviour of cartilage, few of them considered fluid pressure in an anatomically accurate knee joint model. Including the fluid phase as a cartilage constituent, this thesis investigated the mechanics of human knee joint. The main hypothesis of this thesis was that the depth-wise integrity of the structure of cartilage has an important role in its mechanical performance especially its fluid pressurization. The roles of depth-dependent properties, local degenerations and defects on the knee joint mechanics were modeled. Moreover, the effect of individual muscle forces on the knee joint mechanics was investigated. In one of our studies, four models including healthy and degenerated cartilage with local OA progressed from the superficial, to the middle and deep zones were compared. In another study, the effects of depth-wise progression of a local cartilage defect on the knee contact mechanics were investigated. A model with individual muscle forces was compared with a model without muscle forces to examine the effects of muscle forces. The normal cartilage produced higher surface fluid pressure under a given compression. The lack of structural integrity, as happened in local cartilage degeneration, resulted in reduced fluid pressure in the degenerated zone as well as at the cartilage-bone interface. Cartilage defects, on the other hand, had more complex effects on knee joint mechanics. While a local superficial defect reduced pressure in the remaining affected cartilage, a defect advanced to the middle zone increased fluid pressure. Regarding effects of muscle forces, the knee mechanics was noticeably affected when muscles were included. Contact pressure, for instance, was significantly increased in a model with muscle forces compared to a model without muscle forces. The results were in line with previous experimental and computational studies that reported the importance of the structural integrity and depth-dependent properties of cartilage. Integrating fluid pressure, complex three-dimensional geometry, depth-dependent properties, individual muscle forces, and a more realistic treatment of free surface fluid pressure, this project aimed to better understanding of human knee joint mechanics. Results may contribute to better understanding of osteoarthritis as well as the design of artificial cartilage.
Applied Mechanics, Engineering--Biomedical, Engineering--Mechanical
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