MEASUREMENT AND ANALYSIS ON THREE-DIMENSIONAL DEFORMATION AND STRESS DISTRIBUTION CHARACTERISTIC OF THE CRUCIATE LIGAMENT IN THE KNEE

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The objectives of this study are to experimentally measure and to theoretically analyze the change in shape and stress distribution over the entire surface of the ACL when its attachment sites are moved in the threedimensions associated with knee flexion.A study was done using a unique model of a knee joint. The femoral and tibial condyles were modeled from transparent epoxy resin, and the ligament (ACL) was formed from silicone rubber. The model was manipulated in a way that simulated actual knee motion, and the deformation and strain the model ligament underwent were observed directly. Furthermore, the problems of film adhesion to living tissue and the film's ability to display deformation of living tissue were fully resolved using human fascia and rabbits' medio-collateral ligaments. Then the application of the photoelastic method to measuring strains on an actual ligament in vivo was also carried out and stress distribution over the entire region in the ACL was determined.Next, the … More stress analysis were carried out using the finite element method for a non compressive hyper-elastic material to verify the above-mentioned experimental results for a fiber-reinforced hyper-elastic composite. The nonlinear stiffness relation between the node force and the node displacement for a special triangular element, was introcuced. The Newton-Raphson method was used to solve the nonlinear equations associated with finite element representations of the pseudo ligament.Both the measurement and theoretical results were in good agreement. Special attention was paid for the distribution of longitudinal strain as a function of the knee flexion angle and the following results were obtained ; On the anterior side of the ACL,the region near the tibial bone attachment stretched noticeably at 60ﾟ of flexion, and almost the entire region along the fiber direction stretched at 90ﾟC of flexion. The region near the tibial bone attachment streched noticeably at 120ﾟ of flexion. On the posterior side, the strain in the region near the femoral bone attachment was noticeable but not near the tibial bone attachment. In this study, clinically significant results are obtained as strain distribution varied, even along the fiber direction, and large strain gradients were observed in the regions near the bone attachments. Less