In vitro generation of replacement knee wear by simulation

This paper describes a first stage simulation device used to generate wear of knee implants. The simulator was also used to evaluate the wear and damage of various material combinations, the effect of conformity, lubricant type, and material integrity. The level of sophistication relating to each type of simulation device is reflected in the development costs of each simulator. For merely material ranking tests the simple pin-on-disc machines represent a quick and low cost estimate of relative material performance. However, for a more accurate representation of the in vivo performance of prosthetic knee replacements it is necessary to replicate the complex kinematics by means of electro-hydraulic or electro-pneumatic simulators with superimposed variable loading patterns. The simulation device detailed in this paper offers some level of performance prediction with respect to the material combinations used for total knee replacements and the laboratory simulation results compare favourably with clinical retrievals. The paper concludes that true simulation is difficult because of the complexity of the systems involved. However, comparative results for both different designs and different biomaterials can be reasonably estimated if there is a good analogue of both the duty cycle and the predominant in vitro conditions. From the work carried out it appears that important factors for this type of simulation are the integrity of the UHMWPE, lubricant type, surface conformity, and the inclusion of superimposed twisting