Design and mechanical evaluation of an artificial meniscus implant

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Schwartz, Jonathan William
Ku, David N.
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The menisci are wedges of fibrocartilage in the knee joint that help to redistribute compressive loads by increasing the contact area within the joint. Meniscus tears are among the most common orthopedic injuries, but shortcomings with the current treatments leave a clinical need for a new method for repair or replacement. The meniscal tissue can only be repaired in limited cases due to its healing capacity and no artificial meniscal replacement is currently approved by the FDA. The most common treatment for meniscal tears is removal of the damaged tissue, or a meniscectomy. The contact stress in the joint increases proportionally with the amount of meniscus tissue removed due to the decrease in contact area, and the changes in contact stress leads to articular cartilage damage and the development of osteoarthritis. This work explores the use of an artificial composite material with the shape, strength, properties, and contact mechanics needed to serve as a meniscal replacement implant following injury. In this research, a proposed artificial meniscus implant design is made from an aramid fiber-reinforced composite of polyvinyl alcohol (PVA) hydrogel, which is a promising biomaterial for orthopedic applications. A set of functional requirements and design specifications are created from literature values related to the loading experienced on the menisci in the knee joint and the mechanical properties of the natural menisci. Samples of the composite material underwent a series of tests to determine if the design specifications could be met. The ultimate strength (tensile and shear), the elastic modulus (tensile and compressive), resistance to change after cyclic loading, resistance to change after high magnitude compressive loading, and fiber tear out strength were evaluated. The pressure distributing properties of various meniscus implant prototypes and conditions in a knee joint model were also assessed. All design specifications were met using the composite material and the proposed implant design restored the contact mechanics within the knee joint model to natural conditions. The results of this work show that the right combination of material, structure, and shape for an artificial meniscus implant can provide the functional and mechanical properties needed to serve as a suitable meniscus replacement following injury. The artificial implant can be a possible treatment for damaged menisci that overcomes the deficiencies associated with the current options.
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