Ultra-low wear rates for rigid-on-rigid bearings in total hip replacements

Abstract

With the increased clinical interest in metal-on-metal and ceramic-on-ceramic total-hip replacements (THRs), the objective of this hip simulator study was to identify the relative wear ranking of three bearing systems, namely CoCr-polyethylene (M-PE), CoCr-CoCr (M-M) and ceramic-on-ceramic (C-C). Volumetric wear rates were used as the method of comparison. The seven THR groupings included one M-PE study, two M-M studies and four C-C studies. Special emphasis was given to defining the 'run-in' phase of accelerated wear that rigid-on-rigid bearings generally exhibit. The hypothesis was that characterization of the run-in and steady state wear phases would clarify not only the tribological performance in vitro but also help correlate these in vitro wear rates with the 'average' wear rates measured on retrieved implants. The implant systems were studied on multichannel hip simulators using the Paul gait cycle and bovine serum as the lubricant. With 28 mm CoCr heads, the PE (2.5 Mrad/N2) wear rates averaged 13 mm3/10(6) cycles duration. This was considered a low value compared with the clinical model of 74 mm3/year (for 28 mm heads). Our later studies established that this low laboratory value was a consequence of the serum parameters then in use. The mating CoCr heads (with PE cups) wore at the steady state rate of 0.028 mm3/10(6) cycles. The concurrently run Metasul M-M THRs wore at the steady state rate of 0.119 mm3/10(6) cycles with high-protein serum. In the second Metasul M-M study with low-protein serum, the THR run-in rate was 2.681 mm3/10(6) cycles and steady state was 0.977 mm3/10(6) cycles. At 10 years, these data would predict a 70-fold reduction in M-M wear debris compared with the clinical PE wear model. All M-M implants exhibited biphasic wear trends, with the transition point at 0.5 x 10(6) cycles between run-in and steady state phases, the latter averaging a 3-fold decrease in wear rate. White surface coatings on implants (coming from the serum solution) were a confounding factor but did not obscure the two orders of magnitude wear performance improvement for CoCr over PE cups. The liners in the alumina head-alumina cup combination wore at the steady state rate of 0.004 mm3/10(6) cycles over 14 x 10(6) cycles duration (high-protein serum). The zirconia head-alumina cup THR combination wore at 0.174 and 0.014 mm3/10(6) cycles for run-in and steady state rates respectively (low-protein serum). The zirconia head and cup THR combination wore slightly higher initially with 0.342 and 0.013 mm3/10(6) cycles for run-in and steady state rates respectively. Other wear studies have generally predicted catastrophic wear for such zirconia-ceramic combinations. It was noted that the zirconia wear trends were frequently masked by the effects of tenacious white surface coatings. It was possible that these coatings protected the zirconia surfaces somewhat in this simulator study. The experimental ceramic Crystaloy THR had the highest ceramic run-in wear at 0.681 mm3/10(6) cycles and typical 0.016 mm3/10(6) cycles for ...

In vivo and in vitro outcomes of alumina, zirconia and their composited ceramic-on-ceramic hip joints

“…46) In an in vivo study, Clark et al had found that Alumina liners wore at steady-state phase of 0.004 mm 3 per million cycles; 5000 times less wear rate compared to metal-on-polyethylene bearing couple. 49) This results were comparable after Cohn et al 50) run in vitro experiment. They found that Alumina CoC bearings produce 0.2 billion wear particles/year, which was 3000 times (0.6 trillion wear particles/ year) lesser wear rate than metal-on-polyethylene bearings, and the wear debris of the ceramics were small.…”

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

“…The weight-loss curve for the GUR 1020 polyethylene is nearly identical to that published by McKellop in 1997 for the same material, 27 confirming that the data being generated is consistent with that being produced in other laboratories. Other published studies of hipsimulator wear of metal-on-metal bearings have reported wear rates two times, 28 four times, 29 and up to nine or ten times 30,31 with the use of metal-on-metal bearing combinations with similar radial clearances but using serum that had been diluted to 25% as a lubricant. One of these studies 30 also involved the use of nearly undiluted (90%) serum with wear rates similar to those of the current research.…”

Causes of Failure of Ceramic-on-Ceramic and Metal-on-Metal Hip Arthroplasties

“…One presumed advantage is lower wear rate and debris generation from the articulating surface. Wear rates of MOM and COC hip prostheses reportedly have two to three times less volumetric wear than metal-on-polyethylene (MOP) when tested in laboratory settings [5]. MOM articulations allow for larger head-neck ratios than current options for MOP, which allows for a larger ROM before impingement and stability [31].…”