Biomechanics of passive knee joint in drawer: load transmission in intact and ACL-deficient joints.

A non-linear 3D finite element model of the passive human tibiofemoral knee joint consisting of two bony structures and their articular cartilage layers, menisci, and four principal ligaments was used to investigate the detailed response of the unconstrained joint under up to 100 N posterior femoral force at different flexion angles from 0 to 90 degrees. The analysis was repeated after the transection of the anterior cruciate ligament (ACL). The boundary conditions were selected to assure a stable and unconstrained response of the joint throughout the range of motion. The results indicated the ACL as the primary structure to resist the drawer load throughout the range of flexion considered and that the joint primary and coupled laxities substantially increased in its absence. At full extension under drawer, forces in collateral ligaments increased significantly resulting in larger overall contact forces as the ACL was transected. In the ACL-deficient joint, such large forces in collateral ligaments, however, diminished as flexion angle varied from 0 to 90 degrees. At full extension or flexion angles up to approximately 30 degrees, the medial meniscus and adjacent medial tibial and femoral cartilage layers were subjected to substantially larger loads and stresses following the transection of the ACL. Adequate consideration of such couplings is important in avoiding further damage to joint structures subsequent to an injury and restoring adequate function following injuries to primary components.