UC San Diego

During knee movement, cartilage surfaces, which are lubricated with synovial fluid (SF), contact, compress, and slide relative to each other to facilitate joint motion. However, the mechanical behavior of cartilage during joint loading remains unclear. Surface degeneration, altered SF function, and focal articular defects are common following joint injury and may markedly alter the mechanical deformation of cartilage during joint motion. Changes in cartilage mechanics due to such factors may make cartilage more susceptible to further degeneration and wear, predisposing the joint to osteoarthritis. Thus, the goal of this dissertation was to further the understanding of cartilage mechanics under normal and pathologic conditions during joint loading, by elucidating the cartilage deformation during cartilage-on-cartilage articulation as well as the effects of degeneration, lubrication, and focal defects. An experimental approach was developed that allowed the in vitro compression and relative sliding of apposing cartilage surfaces while resultant tissue deformation was imaged at a microscopic level. During cartilage-on-cartilage articulation, cartilage shear deformation varied with tissue depth, elevated with tissue degeneration, and was relatively lower with normal SF lubrication than saline. Shear kinematic studies indicated SF reduced peak shear by allowing surfaces to slide sooner. During tibio-femoral cartilage articulation, axial and shear strains were markedly higher in tibial cartilage than femoral cartilage, being reflective of their respective moduli. Also during tibio-femoral cartilage articulation, acute injury impairs SF function as indicated by elevated shear deformation, while hyaluronan (HA) supplementation partially restores SF function as indicated by reducing resultant shear strains towards normal magnitudes. Finally, tests of patello-femoral cartilage articulation with and without a focal defect showed cartilage strains were drastically elevated in cartilage adjacent to, and lowered in cartilage in direct apposition of, a focal defect following lateral motion. Collectively, this work has further elucidated the contact mechanics of cartilage during joint movement in normal health and following acute injury or trauma. Such characterization may be beneficial to tissue engineering applications, such as engineering implantable cartilage constructs, as well as the development of treatments that address mechanically induced cartilage degeneration and wear.