Prosthetic alignment is one of the most important factors, both in terms of the correct functioning of neoarticulation and the survival duration of knee arthroplasty. Significant changes in the alignment of prosthetic components affect the distribution of stress in the knee joint. These changes may also affect the distribution of stresses on the contact surface, soft knee joints, and the subjacent bone remodeling under these forces. The malposition of the components and, in particular, the tibial component in the varus, which in practice is the most common situation alongside the malrotation of the femoral component, leads to the excessive intimal tension of the internal tibial plate by the summing of the additional stresses at this level with its physiological loading from during the unipodal support phase during the walk. Although valuable, all of these studies have no capacity to assess these changes in the kinetics of in vivo knee arthroplasty. Two methods are used for this: telemetry and mathematical models. Traditionally, telemetry has been used to determine the forces acting on the hip, and more recently, on the knee. It values ​​very precisely the value of the axial rotation forces as well as the moments of bending; however, this method is little used, because the necessary equipment is very expensive. Taking this into account, the most used method is the finite element method. The objective of this study was to investigate the effect of malpositioning in the valgus and varus of the tibial component on tension developed in polyethylene as well as in the subjacent bone. Obviously, other situations have also been analyzed. In this direction a series of original numerical models of the anatomical elements (tibia, fibula, femur) of the knee were constructed to simulate the biomechanical phenomena occurring in the normal and prosthetic joint during physical activities, in order to evaluate the factors that influence the duration operation of total knee prostheses.