The menisci are believed to play a stabilizing role in the anterior cruciate ligament (ACL) deficient knee, and are known to be at risk for degradation in the chronically unstable knee. Much of our understanding of this behavior is based on ex vivo experiments or clinical studies in which we must infer the function of the menisci from external measures of knee motion. The objective of this study is to provide an improved understanding of the meniscal function in the ACL deficient knee, including the motion and deformation, stress and strain distributions and material properties of the medial meniscus.

We used magnetic resonance imaging (MRI) to obtain a more clear visualization of the motion and deformation of the menisci within the tibio-femoral articulation, and generate a finite element model (FEM) of the medial compartment of an ACL deficient knee. A design of experiments approach was developed to investigate the role of the soft tissue material properties on the fit of the FEM to experimental measurements of meniscal position due to an anterior tibial loading of 45 N. The peripheral and horn attachments were identified as the most important factors in this loading condition, but further experiments are needed to improve predictions of meniscal translation and deformation.

The FEM with the optimum material parameters was also used to predict the meniscal position under anterior loads of 45, 76 and 107N. General agreement was obtained between model predictions and the experimentally observed meniscal position. In addition, high stresses and strains were predicted in the posterior region where meniscal degeneration is frequently observed clinically. However the changes in curvature of the meniscus in the posterior region were not captured by the model, and the refinement of meniscal material properties as inhomogeneous and nonlinear didn’t improve the capability of the FEM to capture this dramatic deformation, suggesting the requirement of more accurate knee kinematics, and better definitions of the anatomy and material property of the meniscus and its attachments in the posterior region. Thus, the methodology developed in this study provides a valuable platform to study the biomechanical functions and injury mechanisms of the menisci.