Abstract:
This research investigates the biomechanical effects of an anterior cruciate ligament (ACL) deficiency on the medial collateral ligament (MCL) using a combined experimental and finite element (FE) approach. The study's primary objective was to determine how ACL deficiency impacts MCL insertion site and contact forces during anterior tibial loading and valgus loading. Six cadaveric male knees were subjected to varus-valgus and anterior-posterior loading at flexion angles of 0° and 30°, both with the ACL intact and after it was transected. Subject-specific FE models of the femur-MCL-tibia complex were created for each knee using CT images, bone and ligament geometry, and recorded joint kinematics. The MCL was modeled using a transversely isotropic hyperelastic material model with average material coefficients. The FE models' predictions of MCL fiber stretch were validated against experimental measurements, showing an excellent correlation (R²=0.95). The results showed that ACL deficiency caused a significant increase in MCL insertion site and contact forces in response to anterior tibial loading. In contrast, the study found no significant increase in MCL forces due to valgus loading when the MCL was intact. This demonstrates that while the MCL is a secondary restraint to anterior tibial translation, the ACL does not serve as a restraint to valgus rotation in knees with an intact MCL. This work highlights that an increased valgus laxity in an ACL-deficient knee is an indication of a compromised MCL, providing valuable insights for clinical evaluation.
