Biomechanical response of the passive human knee joint under anterior-posterior forces

Objective. To investigate the detailed biomechanics of the passive tibiofemoral knee joints in full extension under anterior/ posterior drawer forces of up to 400 N. Design. A nonlinear three-dimensional finite element model of the entire human tibiofemoral joint consisting of bony structures, their articular cartilage layers, menisci, and four principal ligaments was utilized. Background. The mechanics of the knee joint, specially under drawer forces, have extensively been investigated. Despite all these works, the detailed joint biomechanics, specially the role of boundary conditions, load transmission through menisci/ articular cartilage layers, and coupling between menisci and cruciate ligaments are not yet quantified. Method. Nonlinear elastostatic analyses were carried out considering the tibiofemoral joint at full extension under anterior and posterior loads of up to 400 N applied either to the tibial or the femoral shaft. Cases with various boundary conditions, cruciate ligament deficiency (anterior or posterior), and total unilateral meniscectomy (medial or lateral) were analysed. Results. In addition to the total primary anterior-posterior motion of about 9 mm at ± 400 N, significant coupled external tibial rotations of about 9 ° and 10 ° were computed under 400 N femoral posterior and anterior forces, respectively. The response was influenced by the manner of loading and boundary conditions. The anterior cruciate ligament and posterior cruciate ligament were the primary restraints to femoral posterior and anterior drawer forces, respectively. Section of either of these ligaments drastically increased the joint anterior-posterior motion. In the absence of cruciates, the collaterals became the primary restraints in both anterior-posterior forces. In this case, the tibial plateaus, specially the medial one in the anterior cruciate ligament-deficient joint, experienced much larger compressive forces. In addition to causing an increase in joint primary anterior-posterior laxity and anterior cruciate ligament forces, medial meniscectomy substantially increased coupled tibial external rotation, forces on the lateral plateau, and stresses in the articular cartilage of the lateral plateau.