Finite element modeling of knee and shoulder ligaments

The medial collateral ligament (MCL) is the primary restraint to knee valgus rotation and a secondary restraint to anterior tibial translation. The anterior cruciate ligament (ACL) is a primary restraint to anterior tibial translation, but its contribution to valgus restraint was debated. To address this, a combined experimental and computational study was conducted to determine the effect of ACL injury on MCL insertion site and contact forces during valgus loading and anterior tibial loading. Six finite element (FE) models were constructed and used to simulate boundary and loading conditions from corresponding cadaveric experiments. It was shown that in the ACL-deficient knee, the MCL is indeed subjected to higher insertion site and contact forces in response to an anterior load. However, MCL forces due to a valgus torque were not significantly increased in the ACL-deficient knee. It follows that the MCL resists anterior tibial translation when the ACL is intact, but the ACL is not a restraint to valgus rotation when a healthy MCL is present.;Physical diagnostic exams are the most crucial step for diagnosis of the location of injury to the shoulder capsule, but the exams are relatively imprecise and the joint positions used for these exams are not standardized between physicians. Due to the complexity of the strains in the capsule during joint motion, a method to correlate joint positions and the capsule strains produced by these positions was needed. To address this discrepancy, a methodology for three-dimensional, subject-specific FE modeling of the inferior glenohumeral ligament (IGHL) as a continuous structure was developed. This FE model was then used to develop a method for evaluating the region of the glenohumeral capsule being tested by clinical exams for shoulder instability. Finally, for the clinical exam known as the simple translation test it was shown that regions of localized strain created by the exam indicate that the joint positions can be used to test the glenoid side of the IGHL, but are not useful for assessing the humeral side of the IGHL.