Effect of polyethylene quality on wear in total knee arthroplasty

During evaluation of 29 Ortholoc II tibial polyethylene components retrieved at revision surgery, the authors noticed that components with a lot number prefix of CP (Custom Product) consistently had minimal wear and those with a standard lot number had severe wear, regardless of patient age, weight, gender, and activity level. Non-CP components had earlier and more severe wear than CP components in service for the same amount of time. Microscopic evaluation of the polyethylene revealed major differences in the material. Large subsurface cracks, fusion defects, and intergranular cracks were present in the non-CP components, but these defects were minimal or nonexistent in the CP components. The components with defects had a significantly greater delamination rate than those without defects. Gamma irradiation did not seem to accelerate wear or delamination, because irradiated components that had minimal microscopic signs of fusion defects performed as well as nonirradiated components with a similar microscopic appearance. The manufacturing details disclosed that different materials and processing methods were used for the 2 groups. The results from this study suggest that improved quality control of polyethylene material would greatly decrease wear and delamination of total knee arthroplasty components.