| Summary: | Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2008. === Includes bibliographical references (p. 236-259). === Osteoarthritis is affecting over 20 million people in the United States, the etiology of which is still unclear. As abnormal stress is believed to be one of the factors causing the degeneration of cartilage, the combined dual-orthogonal fluoroscopic and magnetic resonance imaging technique was applied to investigate the in-vivo biomechanics of human ankle joint complex in this work. The in-vivo kinematic data showed that the talocrural joint contributes more in dorsi/plantarflexion, while the subtalar joint is more responsible for inversion/eversion and internal/external rotation of the joint. During the stance phase of walking there is a complicated combination of the motion of the talocrural and subtalar joints. Cartilage-to-cartilage contact area during the stance phase of walking was determined by quantifying the amount of overlap of the cartilage surfaces of the tibia and talus. The in-vivo cartilage contact data showed significant changes in cartilage contact areas at different positions during the stance phase of walking. The articular cartilage contact was only observed in less than 50% of the cartilage coverage areas in the talocrural joint at various positions of the simulated stance phase of walking. The 3D compressive contact strain distribution within the ankle joint was determined under full body weight based on the thickness distribution and the deformation of the cartilage layers. The mean of the average cartilage contact strain of the entire contact area was only 7.5% whereas the mean peak contact strain reached 34.5%. With Young's modulus as 7.5 MPa and Poisson's ratio as 0.4, the average peak pressure was 6.87 ± 1.76 MPa and the average joint contact force was 1.66 ± 0.12 body weight. The in-vivo creep test of human ankle joint was also carried out and the contact deformation occurred mostly in early 30 to 40 seconds after loading the ankle joints. The in-vivo material properties was calculated and compared with the in vitro data. More computational research was performed focusing on the finite element analysis of the in-vivo ankle cartilage with biphasic/poroelastic material properties. The variation of the cartilage surface layer permeability was shown to have significant effects on the biomechanics behavior of human ankle cartilage. === by Lu Wan. === Ph.D.
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