Wear of polyethylene in total joint replacements. Observations from retrieved PCA knee implants.

Observations of wear damage were performed on 12 retrieved porous coated anatomic (PCA) tibial components, all of which were removed because of excessive polyethylene wear. Density measurements of the remaining polyethylene were obtained as a function of depth from the surface of the components. Comparison to previous results from similar studies of total condylar type knee components and total hip acetabular components revealed distinct differences between the types and severity of damage, emphasizing the influence of design factors on the corresponding wear damage. These results confirm previous conclusions that nonconforming articulating surfaces on thin polyethylene components will be at higher risk of damage than more conforming surfaces on thicker components. It also appears that the high cyclic loads to which polyethylene implants are subjected in vivo are most responsible for the degradation in properties of the material near the articulating surface, although the heat pressing of the articulating surface of the PCA components may contribute to the problem.