John Fisher

Wear of moderately cross-linked polyethylene in fixed-bearing total knee replacements

Cross-linked polyethylene has been introduced into total joint replacement to improve wear resistance. Although the performance of highly cross-linked polyethylene is well documented clinically and experimentally for total hip replacements, the reduction in mechanical properties with increasing irradiation is of concern for application to total knee replacement. The aim of this study was to investigate the wear performance of a moderately cross-linked polyethylene material in a fixed-bearing total knee replacement. The study was conducted using two femoral geometries, a conventional cruciate-retaining femoral and a high-flexion femoral geometry. The femoral geometry appeared to have no effect on the wear of the knee replacement under standard gait conditions. A significant reduction in wear volume was measured with the moderately cross-linked polyethylene compared with the conventional polyethylene over a six-million-cycle wear study. This study indicates the use of a moderately cross-linked polyethylene in a fixed-bearing total knee replacement may provide a low wearing option for total knee replacement.

Chapter 27 – Characterization of UHMWPE Wear Particles

Although most total joint prostheses remain stable for many years, a significant proportion experience loosening, with about 10% requiring revision 10 years after primary arthroplasty. It is generally accepted that osteolysis, among other causes, is initiated by the biological response to wear particles, which are released from ultra high molecular weight polyethylene acetabular liners and tibial trays. Wear particles up to 10 μm in size are predicted to be phagocytosed by resident macrophages and cause the release of inflammatory cytokines and chemokines, including tumor necrosis factor alpha (TNF-α), interleukin-1beta (IL-1β, IL-6, and IL-8. These cytokines stimulate the release of other mediators and the ensuing inflammatory cascade results in the formation of a periprosthetic granulomatous tissue reaction. Histopathological studies have revealed that these inflammatory cytokines facilitate osteoclastagenesis, which results in resorption of bone and a painfully loose implant. Revision surgery is currently the only option for the patient and surgeon.