Knee ligament injury can lead to ligamentous laxity, joint instability and degenerative joint disease. Methodologies that improve the diagnosis, treatment and prevention of ligament injuries are crucial to prevent this progression. The medial collateral ligament (MCL) is one of the most commonly injured knee ligaments, provides primary stabilization against valgus rotation, and is a secondary restraint to anterior tibial translation and external tibial rotation. The structure experiences extreme variations in strain as a function of knee flexion angle. The broad aims of this project are to develop and validate a constitutive model for the MCL, a finite element model of the superficial MCL, and to determine the stress/strain distribution within the MCL under varus-valgus (V-V) torques and anterior-posterior (A-P) tibial force in intact, ACL-deficient, and ACL-deficient+meniscus compromised knees. Following acquisition of volumetric CT data for individual knees, experimental kinematic testing will be performed under V-V and A-P loading conditions as a function of knee flexion angle. Knee kinematics and MCL surface strains will be continuously monitored during all kinematic testing. The MCL will then be isolated from the joint to measure regional in situ strain at 0 degrees knee flexion. Material testing of the MCL will be performed to determine coefficients for a three-dimensional constitutive model. Using the volumetric CT data, detailed geometric and finite element (FE) models of the MCL, distal femur and proximal tibia will be constructed. Appropriate boundary conditions, including representation of contact between the MCL and bones, will be applied to the model, using the experimentally measured joint kinematics to drive the motion of the model. The experimentally measured in situ strains will be applied to the FE model using numerical algorithms developed by the PI. Predictions of MCL stress/strain under V-V and A-P loading will be obtained from FE simulations. The regional MCL strain predictions will be statistically compared with experimental measurements to validate the model. The results for the normal and ACL-deficient knee will be compared to determine the effect of ACL deficiency on MCL stresses under V-V and A-P loading. Information obtained from this study will yield a detailed understanding of the function of the superficial MCL and its propensity for injury in the ACL-deficient and meniscus-compromised knee. The methods developed in conjunction with this research will facilitate future modeling of other ligamentous structures, and the eventual modeling of entire joints. This work will form the basis for the PI's long term research program aimed at the computational modeling of ligaments and joints.