Finite element analysis of a knee joint replacement during a gait cycle

A three-dimensional (3-D) computer model was developed to predict, simultaneously, the knee joint replacement motions and the stresses occurring within the tibial insert under complex loading conditions. Friction contacts, polyethylene elastic- plastic behavior and soft tissue restraints were considered. Finite element analysis of the entire gait cycle was performed applying the displacement and loading conditions reported in the draft ISO 14243-1. The 3-D model was used to predict contact stresses and areas occurring within the polyethylene insert, when static loads of single instants on the gait cycle were applied. Results at 13% and 46% of the gait cycle were calculated with both entire cycle sim-ulation and single instant simulations. The predicted peak contact stress and contact area values were greater for single in-stant analyzes (respectively, 21% and 9%) if compared with those of the entire cycle simulation. In addition, single instant simulations were unable to predict accurately the contact region location, which was displaced in the anterior direction. Two different configurations of soft tissue restraints were compared; the first adopted from the draft ISO 14243-1 and the second from literature data. There were no significant differences observed between the two configurations. In particular, peak contact stresses followed the same trend, although the restraints of the literature data provided lower values in the last phase of the gait cycle. A preliminary verification of model reliability was performed comparing the tibial insert motions with data reported in the literature, under simplified loading conditions applied to the femoral component. (Journal of Applied Biomaterials & Biomechanics 2004; 2: 45-54).