Metal-on-metal vs. metal-on-polyethylene total hip arthroplasty tribological evaluation of retrieved components and periprosthetic tissue.

Abstract

Metal-on-metal (MoM) bearings were introduced as an alternative to conventional metal-on-polyethylene (MoP) bearings to reduce the wear and to increase the survival of hip prostheses. The goal of the present study was to compare tribological properties and to evaluate periprosthetic tissue reaction in two identical groups of prostheses differing only in the type of bearings. At revision operations 26 MoM and 12 MoP bearing components and perisprosthetic tissue samples were collected. Prosthetic components were used to assess wear damage, linear and volumetric wear and roughness. Periprosthetic tissue samples were used for histological as well as immunohistochemical analysis and isolation and characterization of wear particles. The mean linear wear rate in the MoM group was 2.34 (SD 1.93)μm/year, significantly lower than the value in the MoP group, 11.52 (SD 7.82)μm/year. Significantly lower was also the volumetric wear, 0.19 (SD 0.32)mm(3)/year for MoM compared to 0.98 (SD 0.78)mm(3)/year for MoP. In both groups the main wear mode was abrasive wear. Histological results for MoM group indicate more lymphocyte dominated periprosthetic tissue reaction compared to MoP group. The mean size of polyethylene particles in the MoP group was 0.21 (SD 0.44)µm. In the MoM nanosized CoCrMo particles were identified. The characterization of metal particles was complex and required special attention in terms of instrumentation (field emission scanning electron microscopy in back-scattered mode); otherwise it was difficult to distinguish metal particles from other particles in the tissue. Despite a significantly lower wear and, consequently, smaller load of periprosthetic tissue with wear particles in the MoM group, the tissue reaction was similar, if not more intense than in the MoP group.