Anterior and Posterior Bundles of Superficial Medial Collateral Ligament of Knee Joint: Achieving Balanced Structural Behaviors with Different Material Properties

Abstract

Background In the knee joint simulations under accidents or physiological loadings, the mechanical properties of the superficial medial collateral ligament (sMCL) are essential. The common practice for sMCL material parameters in simulations is to either assign different structural properties to the fiber bundles of the sMCL in 1D models or give homogeneous material properties in 2D or 3D models. The sMCL can be functionally divided into anterior bundle (AB) and posterior bundle (PB), which are alternatively loaded during walking. However, little data are available on the mechanical properties of the two bundles; consequently, the rationality of the material assignment method used in current computational studies is questionable. Methods Using porcine stifle joints as test subjects, we obtained the mechanical properties (i.e., threshold strain, failure strain, failure stress, and modulus) of the AB, PB, and whole ligament of the sMCL. Results The three subjects had significant differences in the modulus (p < 0.05), and the AB had higher failure strain (p < 0.01) and threshold strain (p < 0.001) than the PB. The ligament length may be the main reason for the modulus and failure strain differences. Meanwhile, the AB and PB had no significant differences in the structural properties (i.e., stiffness per unit area and failure displacement) as well as the failure stress. Based on the understanding of the balanced structural properties, we proposed a method to estimate the material properties of the AB and PB from those of the whole ligament to reduce the experimental cost for simulations. Conclusions This study suggests that, contrary to the current material assignment method, the AB and PB of the sMCL have different material properties and similar structural properties. The AB and PB should be treated separately and assigned different properties according to their geometry to realize the biomechanics of native knee joints in simulations.