The ACL model geometry is similar to the geometry used by the Open Knee Project,[8] but with different dimensions. It is an approximate model with nonuniform geometry, where the midsection cross-sectional area is smaller than that of the insertions. A typical ACL has bundles of collagen fibers, but the model used here is a solid model with anisotropic material properties.
A tetrahedral mesh of the ACL is built with SOLID187 elements. A rigid surface is modeled to represent the action of the femur. A standard contact behavior (KEYOPT(12) = 0) is defined between the femur surface and the upper part of the ACL. A pilot node is also defined for the rigid surface to give the rotations.