The knee meniscus is a complex structure that has been the focus of important and extensive research for many years. The most common areas of study include meniscal structure, meniscal tears, regeneration, and the biomechanical and anatomical forces endured by the meniscus. Although much research has been done regarding these tissues, more is needed in order to fully understand the role that menisci plays in the function and pathophysiology of the human knee. The fibrocartilaginous meniscus plays an essential role in distributing the majority of the load and maintaining not only congruency, but also lubrication in the knee joint. Degeneration of the knee meniscus is commonplace, yet its pathophysiology has not been fully explained.
Because the meniscus is a nearly avascular tissue which lacks blood vessels for the delivery of nutrients, one area of study needing further research is the transport of fluids and solutes through meniscal tissues. In this dissertation, custom experimental methods are used to characterize the transport of solutes and fluids in meniscus fibrocartilage. For each study, we investigated the effects of mechanical strain, tissue anisotropy, and tissue region on the transport behavior in porcine meniscus tissue.
Using a direct permeation experiment, hydraulic permeability was investigated to determine its strain- and/or direction-dependent behavior in porcine meniscus fibrocartilage. Our measured permeability values (1.53-1.87×10-15 m4/Ns) are similar to those in the literature for meniscus tissues. Results indicate that hydraulic permeability is anisotropic, being significantly greater in the circumferential direction than in the axial. Additionally, it was found that with increased compressive strain, there was a significant decrease in hydraulic permeability for all groups studied.
Strain-dependent and anisotropic (i.e., direction-dependent) transport of glucose in porcine meniscus fibrocartilage was investigated using customized chambers to measure the diffusion and partition coefficients. Results indicate that both diffusivity and partitioning of glucose in porcine menisci significantly decrease with increasing compressive strain. Furthermore, diffusivity of glucose was found to be anisotropic, being significantly greater in the circumferential direction than the axial at all strain levels. Using the results from the partitioning and diffusion of glucose, we were able to calculate the effective diffusivity of porcine meniscus fibrocartilage.
Finally, the strain-dependent and anisotropic electrical conductivity and relative ion diffusion was investigated in porcine meniscus fibrocartilage using a four-wire method. Results indicate that the conductivity and diffusion of ions in the meniscus significantly decreases with increasing compressive strain. Additionally, the conductivity and diffusion of ions was found to be significantly anisotropic, being greater in the circumferential directions than the axial direction at all strain levels.
To our knowledge, this is the first study to quantitatively characterize the effects of strain, anisotropy, and region on transport properties in meniscus tissues. In particular, this is first study to measure glucose or ion diffusivity, glucose partitioning, or electrical conductivity in meniscus. The findings of this dissertation greatly enhance the knowledge of fluid and solute transport in the knee meniscus. Given that nutrient transport is critical for meniscus survival, this information can provide important insight into the functions and mechanisms of meniscus disease and even help identify effective treatment solutions for osteoarthritis.
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