Characterisation of wear debris from UHMWPE on zirconia ceramic, metal-on-metal and alumina ceramic-on-ceramic hip prostheses generated in a physiological anatomical hip joint simulator

There is currently much interest in the characterisation of wear debris fro m different types of artificial hip joints. There have been numerous studie s on the wear of UHMWPE in hip joint simulators, but relatively few studies on the wear of alternative materials such as metal-on-metal (MOM) and cera mic-on-ceramic (COC). The aim of this study was to compare the wear volumes and wear debris generated from zirconia ceramic-on-UHMWPE, MOM and COC hip joints under identical conditions in the same hip joint simulator. All prostheses showed an initial higher 'bedding in' wear rate, which was f ollowed by a lower steady state wear rate. The zirconia ceramic-on UHMWPE p rostheses showed the highest wear rates (31 +/- 4.0 mm(3)/million cycles), followed by the MOM (1.23 +/- 0.5 mm/million cycles), with the COC prosthes es showing significantly (P < 0.01) lower wear rates at 0.05 +/- 0.02 mm(3) /million cycles. The mode (+/- 95% confidence Emits) of the size distributi on of the UHMWPE wear debris was 300 +/- 200, 30 +/- 2.25 nm for the metal particles, and 9 +/- 0.5 nm for the ceramic wear particles. The UHMWPE part icles were significantly larger (P < 0.05) than the metal and ceramic wear particles, and the metal particles were significantly larger (P < 0.05) tha n the ceramic wear particles. A variety of morphologies and sizes were obse rved for the UHMWPE wear particles, including submicrometer granules and la rge flakes in excess of 50 mum. However, the wear particles generated in bo th the MOM and COC articulations were very uniform in size and oval or roun d in shape. This investigation has demonstrated substantial differences in volumetric w ear. The in vitro wear rates for the zirconia-on-UHMWPE and MOM are compara ble with clinical studies and the UHMWPE and metal wear particles were simi lar to the wear debris isolated from retrieved tissues. However, the alumin a/alumina wear rate was lower than some clinical retrieval studies, and the severe wear patterns and micrometer-sized particles described in vivo were not reproduced here. This study revealed significant differences in the wear volumes and particl e sizes from the three different prostheses. In addition, this study has sh own that the alternative bearing materials such as MOM and COC may offer a considerable advantage over the more traditional articulations which utilis e UHMWPE as a bearing material, both in terms of wear volume and osteolytic potential. (C) 2001 Elsevier Science BN. All rights reserved.