Design issues in clinical studies of the in vivo volumetric wear rate of polyethylene bearing components.

Abstract

The issue of wear of ultra-high molecular weight polyethylene bearing surfaces in total hip and knee replacements is, without doubt, one of the dominant themes in contemporary orthopaedics. Thus, an array of relevant facets of this topic have been extensively and intensively researched, spawning, in the process, a very large volume of literature. The main topics that have been studied are the place of wear in the hierarchy of degradation modes of polyethylene bearing surfaces, the role of polyethylene wear particles in the in vivo longevity of the prosthesis, the methods of determining the extent of wear of polyethylene bearing components (for example, the acetabular cup, acetabular cup liner, or tibial insert), the magnitude of the volumetric wear rate, the relationship between the results of in vitro wear-testing of polyethylene specimens or components and the clinical performance of polyethylene components, and the key factors influencing the clinical wear of polyethylene components. It is widely acknowledged that wear is one of many degradation modes that affect polyethylene bearing surfaces in vivo (other modes include creep, delamination, and burnishing) and that, under certain circumstances, it is not the predominant one. For example, polyethylene creep of the liner predominates during the initial stages of penetration of the femoral head into the acetabular cup, but additional penetration after the first twelve to eighteen months in situ is due to wear24. A consensus has emerged that wear of polyethylene bearing components is implicated in the aseptic loosening of hip and knee implants, and in the development of osteolysis around those implants, through resorption of the periprosthetic bone initiated by a foreign-body-giant-cell granulomatous tissue reaction. This biological reaction arises in response to the polyethylene and other wear particles (such as acrylic cement and metal) that are released into the periprosthetic bone. Furthermore, in the …