A computer model with surface friction for the prediction of total knee kinematics.

A computer model was generated which modelled the bearing surfaces of total knees, and predicted the kinematics for a set of input forces and moments. The model included friction at the bearing surfaces and soft tissue restraint forces, including the effect of cruciate resection. Predictions from the model were compared with data from a Knee Simulating Machine. There was close agreement in the shapes of the curves and in the magnitudes of the displacements and rotations under most conditions. The model predicted major differences in kinematics when friction between metal and polyethylene was included, the differences being even greater at the friction levels associated with small embedded acrylic particles. Soft tissue restraint was shown to reduce the displacements and rotations for tibial surfaces of low constraint but for moderate to high constraint, the soft tissues affected the kinematics only slightly. When the model was used to predict the motions for different condylar geometries, widely different contact paths on the tibial surface were determined. This suggested that condylar geometries which appeared to be generally similar, could have important differences in kinematics, function and wear.