MEASUREMENT AND ANALYSIS ON ELONGATION,DEFORMATION AND TENSILE CHARACTERISTIC OF THE CRUCIATELIGAMENT 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.To determine stress distribution over the entire region in the ACL,experiments were carried out to measure the change in shape and strain distribution over the entire surface of a pseudo ligament (a special rubber plate with an extremely large stretch : 600%_<max>) when the attachment sites were moved in threedimensions. An elaborate instrument (knee motion simulator) was developed, to which the pseudo ligament was attached. Both of the attachments could be moved in several directions and could be rotated on several axs, resulting in six-degrees of motion to simulate knee motion. The three-dimensional positions of 272 markers on the ligament were measured by the Stereo-Photogramtric Method to compute the components of the Lagrangian st … More rain tensor for each element.Next, the stress analysis were carried out using the finite element method for a noncompressive hyper-elastic material to verify the above-mentioned experimental results for a pseudo ligament (rubber material). The non-linear stiffness relation between the node force and the node displacement for a special triangular element, was introduced. 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 of flexion. The region near the tibial bone attachment stretched 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. ln 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