Region Partitioning of Articular Cartilage to Approximate Tissue Inhomogeneity with Applications in Knee Joint Modeling

Articular cartilage is an inhomogeneous material due to variations in its structure and composition, and resulting from adaptation to its mechanical environment. This inhomogeneity is present both along the thickness and across the surface of the tissue . The depth- dependent inhomogeneity of cartilage, which is widely accepted and extensively studied, is characterized by three zones, namely superficial, middle, and deep zones. On the other hand, a common standard to divide the surface of articular cartilage i nto distinct regions to represent tissue inhomogeneity is yet to be established. This thesis is aimed at attempting to suggest region partitions across knee cartilages in order to approximate tissue inhomogeneity and to see how region-dependent cartilage inhomogeneity affects the contact mechanics of the knee joint. For this purpose, fresh porcine knee joints were dissected and cartilage -bone pieces, i.e. , femoral groove, lateral and medial femoral condyles, and lateral and medial tibial plateaus were harvested. The samples were tested with automated indentation, and the relaxation plus thickness data were grouped into 17 regions using machine learning. The extracted material properties for these regions demonstrated significant differences, highlighting the importance of considering region- dependent inhomogeneity in cartilage research . As a separate case study, streaming potentials of articular cartilage were confirmed to be region -dependent with machine learning, using porcine femoral condyle cartilages. In the third study, the region- dependent material properties were implemented in a porcine knee FE model and the distribution of mechanical responses including stress, strain, fluid pressures, and fluid flow, were compared with the ones determined using a homogeneous implementation of cartilage properties. Considerable differences were seen in the mechanical responses between the homogeneous and inhomogeneous implementations of cartilage properties, highlighting the necessity to consider region- dependent cartilage inhomogeneity in applications such as joint modeling.