A novel low wearing differential hardness, ceramic-on-metal hip joint prosthesis

Osteolysis and loosening of artificial joints caused by polyethylene wear d ebris has prompted renewed interest in alternative bearing materials for hi p prosthesis designs. Lower wearing metal-on-metal (MOM) and ceramic-on-cer amic prostheses are being used more extensively. and there is considerable interest in further improving on their performance. This study investigated the wear properties and debris morphology of a novel differential hardness ceramic-on-metal (COM) prosthesis, in comparison with MOM articulations in a physiological anatomical hip joint simulator. The COM pairings were found to have wear rates approximately 100-fold lower than the MOM pairings. The MOM pairings showed a higher "bedding in" wear rate (3.09 +/- 0.46 mm(3)/10(6), cycles) in the first million cycles, which then reduced to a steady state wear rate of 1.23 +/- 0.5 mm(3)/10(6) cycle s. The wear rate of the COM pairings over the duration of the test was appr oximately 0.01 mm(3)/10(6) cycles with very little wear detected on the sur face of the prosthesis components. The wear particles from both articulations were oval to round in shape and in the nanometer size range. After one million cycles the mean maximum diam eter of the MOM and COM wear particles were 30 +/- 2.25 and 17.57 +/- 1.37 nm, respectively. After five million cycles the wear particles were statist ically significantly smaller than at one million cycles, 13.9 +/- 0.72 nm f or the MOM pairings and 6.11 +/- 0.40 nm for the COM pairings. The wear rates of the MOM prostheses were representative of clinical values . The use of differential hardness COM pairings dramatically reduced the we ar rate compared to MOM hip prostheses. The wear particles from the MOM art iculation were similar to particles found in retrieved tissues from around MOM prostheses. The extremely low wearing differential hardness COM bearing s presented in this study produced far smaller volumetric particle loads co mpared to MOM prostheses currently used clinically. (C) 2001 Elsevier Scien ce Ltd. All rights reserved.