An analytical technique for modeling knee joint stiffness--Part II: Ligamentous geometric nonlinearities

An analytical technique previously developed to evaluate the contribution of the ligaments to the nonlinear, coupled stiffness characteristics of the human knee joint [1] is extended here to include geometric nonlinearities. In [1], we assumed that the ligaments act as tensile bands running in a straight line between tibial and femoral insertion sites. Here, two forms of geometric nonlinearities are introduced and analyzed: ligaments wrapping around bone surfaces, such as occurs with the medial collateral ligament, the posterior capsule, and the anterior cruciate in hyperextension, and wrapping of ligaments around each other, such as occurs with the cruciate ligaments as the knee is flexed and internally rotated.