Wear evaluation of cobalt–chromium alloy for use in a metal‐on‐metal hip prosthesis

Abstract

Wear of the polyethylene in total joint prostheses has been a source of morbidity and early device failure, which has been extensively reported in the last 20 years. Although research continues to attempt to reduce the wear of polyethylene joint-bearing surfaces by modifications in polymer processing, there is a renewed interest in the use of metal-on-metal bearing couples for hip prostheses. Wear testing of total hip replacement systems involving the couple of metal or ceramic heads on polymeric acetabular components has been performed and reported, but, until recently, there has been little data published for pin-on-disk or hip-simulator wear studies involving the combination of a metallic femoral head component with an acetabular cup composed of the same or a dissimilar metal. This study investigated the in vitro wear resistance of two cobalt/chromium/molybdenum alloys, which differed primarily in the carbon content, as potential alloys for use in a metal-on-metal hip-bearing couple. The results of pin-on-disk testing showed that the alloy with the higher (0.25%) carbon content was more wear resistant, and this alloy was therefore chosen for testing in a hip-simulator system, which modeled the loads and motions that might be exerted clinically. Comparison of the results of metal-on-polyethylene samples to metal-on-metal samples showed that the volumetric wear of the metal-on-polyethylene bearing couple after 5,000,000 cycles was 110 -180 times that for the metal-bearing couple. Polyethylene and metal particles retrieved from either the lubricant for pin-on-disk testing or hip simulator testing were characterized and compared with particles retrieved from periprosthetic tissues by other researchers, and found to be similar. Based upon the results of this study, metal-on-metal hip prostheses manufactured from the high carbon cobalt/chromium alloy that was investigated hold sufficient promise to justify human clinical trials.

Wear of CoCrMo alloys used in metal-on-metal hip joints: A tribocorrosion appraisal

“…The number of loading cycles varies typically from 3 up to 10 Mcycles at frequencies of 1 or 1.13 Hz. Table 2 summarizes the key features of published papers on the characterisation of metal on metal CoCrMo artificial hip joints using simulators [12,[46][47][48][49][50][51][52][53][54][55][56][57][58]. Among the authors, only Yan [49] measured the evolution of open circuit potential during a simulator test.…”

“…With approximately 40 components [63] bovine serum is a very complex liquid with a broad reactivity spectrum. It is seldom used without additions of biocides (such as sodium azide NaN 3 ) and complexing agents (such as EDTA) to avoid metal precipitation [46][47][48]51,[53][54][55][56][57]. Moreover, it can be used at different dilutions in water [51] or Ringer's solutions [52] depending on laboratory.…”

State of the art in hard-on-hard bearings: how did we get here and what have we achieved?

“…Both in vitro and in vivo studies have suggested that there may be considerable differences in material wear and implant failure rates based on whether implants are manufactured using a wrought, cast or heated-cast process, although the published results are contradictory [47,[57][58][59][60]. However, several authors have reported improved wear characteristics and survival rates of high carbon versus low carbon cobalt-chromium alloys in metal-on-metal hip resurfacing arthroplasties [54,56,61,62]. The commercial introduction of highly cross-linked polyethylene has reduced wear rates, with one in vitro study reporting volumetric wear rates of 3 mm 3 per million cycles compared with 48 mm 3 per million cycles before cross-linking [11].…”

“…After an initial run-in period over the first 1-2 years, during which time linear wear rates of 20-25 µm/year have been reported, a low steady-state linear wear rate of 2.5-10 µm/year is usually achieved [25,52,53]. This translates into a 20-180-times lower linear wear rate compared with conventional metal-onpolyethylene bearings [25,54], although because of the considerably smaller mean size of metal wear particles, the number of wear fragments is typically greater [55,56]. Even with modern metal-on-metal bearings, there is considerable heterogeneity in metallurgical properties, with variability in alloy composition and manufacturing techniques.…”

Immunologic Adverse Reaction Associated with Low-carbide Metal-on-metal Bearings in Total Hip Arthroplasty

“…The volumetric wear rates of CoCr alloys are affected by the carbide content and the material combinations used, with the wear rate decreasing (pin-on-disc experiments) from a low-carbide head/lowcarbide cup (5.6 ± 2.4 mg) to a low-carbide head/ high-carbide cup (1.4 ± 0.9 mg) to a high-carbide head/ high-carbide cup (1.3 ± 0.6 mg) [34]. The in vivo wear rate of Metasul 1 (Sulzer Medica, Winterthur, Switzerland) bearings (high-carbide head/high-carbide cup) showed a steady-state wear rate of 2 to 5 lm per year [3,30], whereas a higher wear rate of 7.6 lm per year was reported for Sikomet TM (from a low-carbide head/low-carbide cup) bearing couples [29].…”