Development of an Artificial Meniscus Implant

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Callcott, Trent
Ku, David N.
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The menisci protect the knee by distributing the compressive loads experienced across the joint. They are able to accomplish this because of their wedge shape that conforms to the femur and tibia and their strong yet compliant structure. Meniscus lesions are among the most common orthopedic injuries, but all current treatments are only applicable to a limited number of tears or have poor clinical outcomes. The majority of the meniscus is avascular and has limited healing capacity. As a result, removal of the meniscus after a tear is the most common treatment but has shown development of osteoarthritis, increase in pain, and mechanical impairment of the joint. Accordingly, there is a need to develop a meniscus replacement. The work of this thesis developed an artificial meniscus implant with a similar shape, strength, compliance, and contact mechanics as the natural meniscus. Previous work on this implant showed that PVA gave the desired compressive properties and reinforcing Kevlar fibers had the desired strength. These materials needed to be designed into a composite implant and then tested for its durability and functionality. In order to design the implant, design specifications were established from mechanical properties of the natural menisci and loads experienced in the knee joint. One design aspect of interest was the spacing of the fibers within the hydrogel. FEA was performed to observe trends between fiber spacing on implant deformation and stresses. The remaining design variables were chosen to either resemble the structure of the natural meniscus or ease manufacturing. The easier to manufacture variables represented design choices made by previous implants in order to see if they could be improved. The best implant design was chosen based on compression and delamination durability as well as contact stress functionality tests. Once the best design was chosen, it underwent further durability and functionality testing. Tests focused on the strength and compliance of the overall implant and durability of the implant over prolonged use. Accordingly, compressive modulus and fiber tear out strength testing was performed where the design passed if it was at least as strong and compliant as the natural meniscus. High impact and cyclic compression and shear tests were performed to simulate the higher loads experienced in the knee across a year of use. After these tests, tibial contact pressure and radial extrusion testing was performed to evaluate the prolonged functionality of the implant. All design specifications were met by the chosen implant design. The tests showed that the implant can provide the mechanical properties and functionality needed to serve as a meniscus replacement. To validate this, an animal study was designed to access durability as well as the biocompatibility and chondroprotection of the implant. A sheep shaped implant was designed for this test and cadaveric work was performed to provide a final design with proper fit and fixation within the knee. This animal study was not finished before this work was concluded so the results are not reported, but they should give insight into the effectiveness the implant and which future steps should be taken.
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