Current analysis of tibial coverage provided by total knee arthroplasty systems

A realistic 3D model of the human tibiofemoral joint including femur, tibia, cartilage layers, menisci, and joint ligaments along with a finite element package program were used to investigate the non-linear elastostatic response of the tibiofemoral joint at full extension under internal-external torques of up to 10 N-m applied to the femur. The menisci were represented as a non-homogeneous composite and the articulation of cartilage layers with each other as well as with intervening menisci and the wrapping of the medial collateral ligament with the tibia were treated as large displacement frictionless contact problems. Analyses were carried out with the tibia fixed while the femur was free to translate in the proximal-distal, medial-lateral, and anterior-posterior directions; the internal-external rotation was left free, the varus-valgus rotation was either fixed or free while flexion-extension rotation was maintained fixed throughout the study. The influences of selective sectioning of some ligaments and presence of axial compressive preload on the joint response in axial rotation were also investigated. In the varus-valgus constrained model, both collateral ligaments were the major restraints to internal rotation while the lateral collateral ligament only played a major role in resisting femoral external torque. Setting the varus-valgus free produced noticeable changes in the ligament forces only in external rotation. The compressive preload of 1000 N caused a major reduction in the rotary laxity during applied torques of ± 0.5 N-m and some decreases in all ligament forces with the exception of that in the anterior cruciate ligament. Removal of medial collateral ligament in internal torque and lateral collateral in external torque substantially increased cruciate forces. Combined or isolated removal of cruciates markedly increased collateral forces in external torque only. Large contact forces on medial plateau were computed in external torque. Predictions were in general agreement with reported measurement results.