Basic study of artificial knee menisci (Investigation into meniscal functions and its reproduction with synthetic materials)

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We have developed a novel device with a flexible needle and a laser proximity sensor for precise measurement of displacement of a soft tissue. The displacement vector in the transverse plane in the knee joint was measured by fixing the tips of the two needles at each measuring point in the meniscus. Thus, the paradoxical functions of the menisci were investigated by use of the device.Displacement of the porcine knee minisci were measured with a joint simulator. Under longitutional joint load, as outward displacement of the meniscusis is limited, the force is transmitted between articular cartilages via the meniscus while supination arises due to anterior movement of the lateral meniscus. Rotation results from antero-posterior shear force because the lateral meniscus moves while the displacement of the medial meniscus is limited. As the menisci are scarcely moved by latero-medial force, they contribute to the knee stability by supporting latero-medial force. Thus the menisci enable the knee to move in the sufficient range of flexionextension while they improve the knee stability by restricting the other motions caused by external forces. The investigation of the paradoxical functions of the knee menisci would be impossible without the precise measuring instrument developed in this project.It was found by 3-dimensional finite element analysis that the meniscus transmits stress waves as well as a bone does under impact loading. The stress waves detected by micro stress sensors attached in the cancellous bone near the knee joint. According to the experiment, most of static stress is transmitted to the cancellous bone while impact stress is transmitted direct to the peripheral cortical bone via the menisci.