Simulation of a knee joint replacement during a gait cycle using explicit finite element analysis.

The stress distribution within the polyethylene insert of a total knee joint replacement is dependent on the kinematics, which in turn are dependent on the design of the articulating surfaces, the relative position of the components and the tension of the surrounding soft tissues. Implicit finite element analysis techniques have been used previously to examine the polyethylene stresses. However, these have essentially been static analyses and hence ignored the influence of the kinematics. The aim of this work was to use an explicit finite element approach to simulate both the kinematics and the internal stresses within a single analysis. A simulation of a total knee joint replacement subjected to a single gait cycle within a knee wear simulator was performed and the results were compared with experimental data.The predicted kinematics were in close agreement with the experimental data. Various solution-dependent parameters were found to have little influence on the predicted kinematics. The predicted stresses were found to be dependent on the mesh density. This study has shown that an explicit finite element approach is capable of predicting the kinematics and the stresses within a single analysis at relatively low computational cost.

A computational model for the prediction of total knee replacement kinematics in the sagittal plane.

A computational model has been developed using a current generation computer-aided engineering (CAE) package to predict total knee replacement (TKR) kinematic in the sagittal plane. The model includes friction and soft tissue restraint varying according to the flexion angle. The model was validated by comparing the outcomes of anterior-posterior (A-P) laxity tests of two contemporary knee replacements against data obtained from a knee simulating machine. It was also validated against predictions from a computer model reported in the literature. Results show good agreement in terms of A-P displacements. Further tests were performed to determined the influence of the soft tissue restraints varying with flexion angle. This work represents the first attempt to use a sophisticated commercial CAE package to predict TKR motions and the advantages of the modelling procedure chosen are discussed.