Pseudotumor and Subsequent Implant Loosening as a Complication of Revision Total Hip Arthroplasty with Ceramic-on-Metal Bearing: A Case Report.

Pseudotumors are not uncommon complications after total hip arthroplasty (THA) and may occur due to differences in bearing surfaces of the head and the liner ranging from soft to hard articulation. The most common causes of pseudotumors are foreign-body reaction, hypersensitivity and wear debris. The spectrum of pseudotumor presentation following THA varies greatly-from completely asymptomatic to clear implant failure. We report a case of pseudo-tumor formation with acetabular cup aseptic loosening after revision ceramic-on-metal hip arthroplasty. The patient described herein underwent pseudotumor excision and re-revision complex arthroplasty using a trabecular metal shell and buttress with ceramic-on-polyethylene THA. Surgeons should be aware of the possibility of a pseudotumor when dealing with revisions to help prevent rapid progression of cup loosening and implant failure, and should intervene early to avoid complex arthroplasty procedures.

Chemically driven tetragonal-to-monoclinic polymorphic transformation in retrieved ZTA femoral heads from dual mobility hip implants.

Two short-term (two and nine months) retrieved zirconia-toughened alumina (ZTA) femoral heads and nine pristine femoral heads from the same manufacturer have been investigated with respect to their surface stability by means of confocal Raman spectroscopy. Quantitative estimations of monoclinic volume fraction have been carried out in both non-wear and main wear zones of the retrieved heads, which invariantly showed high volume fractions of monoclinic polymorph. In-depth (sub-surface) profiles, non-destructively collected in the main wear zones with the Raman probe in confocal configuration, indeed confirmed that polymorphic transformation was extended down to 100µm below the bearing surface of the femoral heads. Acceleration of tetragonal-to-monoclinic transformation rate leads to unexpectedly high fractions of monoclinic phase within very short-term in-vivo exposures. Phase transformation in-vivo is much more marked than what one could actually predict according to simply simulating a hydrothermal environment in-vitro and could not be simply ascribed to the mechanical stress fields generated during normal service at the bearing surface. Instead, the chemical consequences of metal contamination on the ZTA femoral head surface are shown to play the most detrimental role in phase destabilization.

A simulator study of adverse wear with metal and cement debris contamination in metal-on-metal hip bearings.

OBJECTIVES: Third-body wear is believed to be one trigger for adverse results with metal-on-metal (MOM) bearings. Impingement and subluxation may release metal particles from MOM replacements. We therefore challenged MOM bearings with relevant debris types of cobalt-chrome alloy (CoCr), titanium alloy (Ti6Al4V) and polymethylmethacrylate bone cement (PMMA). METHODS: Cement flakes (PMMA), CoCr and Ti6Al4V particles (size range 5 µm to 400 µm) were run in a MOM wear simulation. Debris allotments (5 mg) were inserted at ten intervals during the five million cycle (5 Mc) test. RESULTS: In a clean test phase (0 Mc to 0.8 Mc), lubricants retained their yellow colour. Addition of metal particles at 0.8 Mc turned lubricants black within the first hour of the test and remained so for the duration, while PMMA particles did not change the colour of the lubricant. Rates of wear with PMMA, CoCr and Ti6Al4V debris averaged 0.3 mm(3)/Mc, 4.1 mm(3)/Mc and 6.4 mm(3)/Mc, respectively. CONCLUSIONS: Metal particles turned simulator lubricants black with rates of wear of MOM bearings an order of magnitude higher than with control PMMA particles. This appeared to model the findings of black, periarticular joint tissues and high CoCr wear in failed MOM replacements. The amount of wear debris produced during a 500 000-cycle interval of gait was 30 to 50 times greater than the weight of triggering particle allotment, indicating that MOM bearings were extremely sensitive to third-body wear. Cite this article: Bone Joint Res 2015;4:29-37.

Third-body abrasive wear challenge of 32 mm conventional and 44 mm highly crosslinked polyethylene liners in a hip simulator model.

Hip simulator studies have shown that wear in the polyethylene liners used for total hip replacements increased with the larger-diameter femoral balls and could also be exacerbated by third-body abrasion. However, they also indicated that the more highly cross-linked polyethylene (HXPE) bearings were more wear resistant than conventional polyethylene (CXPE) bearings. Unfortunately the HXPE bearings appeared to be particularly sensitive to adverse wear conditions. One simulator study in particular indicated that poly(methyl methacrylate) (PMMA) debris increased wear sixfold by means of two-body abrasive interactions rather than the supposed third-body abrasion or roughening effects of the Co-Cr surfaces. There has been no confirmation of such novel theories. Therefore the goal of this study was to investigate the sensitivity of large-diameter HXPE bearings to the third-body PMMA wear challenge in a hip simulator model. An orbital hip simulator was used in standard test mode with a physiological load profile. The 32 mm control liners were machined from moulded GUR1050 and gamma irradiated to 35 kGy under nitrogen (CXPE). The 44 mm liners were also from moulded blanks, gamma irradiated to 75 kGy, machined to shape, given a proprietary heat treatment, and sterilized by gas plasma (HXPE). As in the published simulator model, the study was conducted in three phases. In phase 1, all cups were run in standard ('clean') lubricant for 1.5 x 10(6) cycles duration. In phase 2, three CXPE cups and six HXPE cups were run for 2 x 10(6) cycles with a slurry of PMMA particles added to the lubricant. In phase 3, the implants were again run in 'clean' lubricant for 2 x 10(6) cycles duration. In addition, three HXPE cups were run as wear controls for 5.5 x 10(6) cycles duration in clean lubricant. In phase-1, the HXPE liners demonstrated twelvefold reduced wear compared with the CXPE controls. The 32 mm and 44 mm Co-Cr balls were judged of comparable roughnesses. However, the surface finish of HXPE liners was superior to that of CXPE liners. In phase-2 abrasion, wear rates increased sixfold and eighty-fold for CXPE and HXPE bearings respectively. These data confirmed that HXPE bearings were particularly sensitive to 'severe' test modes. The Co-Cr balls revealed numerous surface patches representing transferred PMMA with average transient roughness increased to 25 nm and 212 nm for the 32 mm and 44 mm balls respectively. These PMMA patches produced an aggressive two-body abrasion wear of the polyethylene. After cleaning, the ball roughness returned to near normal. Therefore the Co-Cr roughness was not an issue in this severe test mode. In phase 3, the wear decreased to near the index values of phase 1, while liner roughness dropped by more than 90 per cent. The control CXPE liners now demonstrated twice the wear of the HXPE, as would be predicted comparing the diameter and cross-linking algorithms. No previous study has correlated polyethylene roughness profiles to wear performance. In phase 2, PMMA abrasion created significant damage to the polyethylene surfaces. The average roughness Sa of CXPE liners increased to 3.6 microm, a twenty-four-fold increase with some scratches up to 40 microm deep. The HXPE roughness also increased but only to 1.5 microm, a ninefold increase. The scratch indices Sz and Sp for HXPE surfaces were also 50 per cent less severe than on CXPE surfaces. However, within 2 x 10(6) cycles duration of phase 3, all liners had recovered to virtually their original surface finish in phase 1. In all test phases, the surface finish of the HXPE liners remained superior to control liners. These experimental data confirmed many of the results from the previous simulator study with the PMMA abrasion models. Thus the 44 mm liners appeared an excellent clinical alternative to the smaller ball designs used in total hip replacements.

What is a "normal" wear pattern for metal-on-metal hip bearings?

In addition to classical run-in and steady-state wear phases, metal-on-metal (MOM) hip bearings have encountered "runaway wear" (RAW) trends in simulator studies. This puzzling behavior has resulted in 2- to 19-fold wear increases compared with other apparently "identical" bearings. MOM bearings have shown five identifiable RAW wear patterns in joint simulators; therefore, additional descriptive terms were used here to indicate various observed patterns, for example, "breakaway wear" (BAW), which was defined as a higher wear trend that recovers to steady-state wear. As these trends commonly occur for MOM, this raises the question of what can be considered "normal" behavior or "abnormal"? In an effort to identify possible causes for this behavior, the current study investigated six Co-Cr bearings, which closely matched with respect to geometrical tolerances. Despite close control of design and test variables, BAW occurred in 30% of the MOM bearings, producing a threefold wear increase above otherwise identical MOM bearings within the same group. The majority of the BAW (85%) occurred on the cup side and was validated by growth of wear scars and concentrations of metal ions. One bearing that showed continuing BAW at 5 Mc revealed a cup that was 50% smoother than other cups whereas its mating head was 50% rougher, thus signifying that highly polished areas were sites of the highest MOM wear. The two BAW bearings with high wear showed the greatest conformity at 5 Mc, in apparent contradistinction to classical lubrication theory.

"Severe" wear challenge to 36 mm mechanically enhanced highly crosslinked polyethylene hip liners.

Our purpose was to compare the wear performance of mechanically enhanced 5Mrad highly crosslinked polyethylene (MEP, ArComXL) hip liners to (control) 3Mrad UHMWPE liners (ArCom) in 36 mm head size. As a more severe synergy of clinically relevant test models, we contrasted wear with custom roughened Co-Cr surfaces (Ra 500 nm) to the standard pristine Co-Cr heads (Ra < 20 nm) using a severe microseparation test mode in our hip simulator. We adopted a previously published model to estimate potential biological activity. On new Co-Cr heads, the MEP liners showed a 47% reduction in volumetric wear a 13% reduction in wear particle size and a 27% reduction in Functional Biological Activity (FBA) compared to our control. On rough Co-Cr heads, the MEP liners showed little advantage in terms of volumetric wear compared with the control. However, the MEP liners overall showed a 38% reduction in FBA compared to the control owing to a larger volume fraction of larger particles. Thus overall the MEP liners appeared to offer advantages in terms of reduced FBA indices.

Precision and accuracy in ceramic-on-ceramic wear analyses: influence of simulator test duration.

In this, the first report of precision and accuracy in simulator studies, ceramic-ceramic implants with ultra-low wear trends represented a relevant wear model. The effect of test durations was examined in a standard simulator test mode on the quality of the linear regression trends, the average wear estimates, and the amount of noise in the data. Three sets of diametral tolerances were compared in 28 mm diameter alumina implants. The authors' hypothesis was that wear data would be significantly improved with increased test durations. The average wear rates varied little with test duration, the biggest change amounting to only 30 and 15 per cent decreases in the wear estimate by 10 and 14 million cycles respectively. The most satisfactory improvement in the study was the decrease in variance (noise) with increasing duration, +/- 200 per cent at 5 million cycles reduced to +/- 55 per cent at 14 million cycles. The quality of the linear regression coefficients improved 150 per cent by 10 million cycles and 250 per cent by 14 million cycles. Overall the ceramic implants with highest diametral tolerances showed the least wear (15 per cent less, but not statistically significant). However, given such low wear rates for alumina liners, it was unlikely that any differences owing to diametral tolerances would be clinically significant in the typical patient.

Discerning alumina ball wear from confounding metal transfer artifact.

On dismounting a ceramic femoral ball from its metal trunnion, there is usually a range of gray metallic bands transferred to the trunnion bore inside the ball. This creates an artifact that may compromise detection by weight of the exceedingly low wear rates of ceramic balls. The objective of this study was to compare the weight trending of the metal trunnions and their ceramic balls during conditioning studies. Our hypothesis was that a pretest conditioning protocol would eliminate or greatly reduce the metal transfer artifact. The balls and tapers were placed on a hip simulator under 300-600 load cycles but with no articulation. The balls were then dismounted from the trunnions, and both were cleaned and weighed. This was repeated 6-23 times. We developed a novel hydraulic method for dismounting balls from trunnions that proved to be safe and efficient. There was significant weight loss in the trunnions after the ball removal, but there was no corresponding weight gain in the alumina balls. The weight effect of the metal transfer appeared to have been removed from the balls with our standard cleaning procedures. Therefore, wear rates for alumina balls may be gravimetrically determined without compensating for the metal transfer from trunnion to ball.

Clinical and simulator wear study of alumina ceramic THR to 17 years and beyond.

Three THAs with cementless monolithic alumina ceramic sockets and cementless Co-alloy stems were retrieved because of aseptic loosening after 17 and 24 years. At revision heads and cups were marked for orientation. Maps were drawn of wear patterns with the use of light microscopy and surveyed by SEM. In a simulator experiment 28-mm-diameter alumina heads and liners were used. The cups were mounted inverted in a hip simulator and run with calf serum as the lubricant. The hip loads were 2 kN maximum and a 1-Hz frequency for 20 million cycles. Wear severity was classified into five grades. In retrieved implants, SEM analysis showed that the main wear zones (MWZ) had Grade 4 wear. The peripheral wear zones (PWZ) showed grain pull-out regions (Grade 5 wear). These corresponded to neck-socket impingement and head-acetabular cup separation. Gray was due to transferred CoCr particles from the stem. In the simulator study, the MWZ had only localized areas of grain pull out surrounded by polished surface regions (Grade 4 wear) at 20 million cycles; stripe wear was not seen. The alumina ceramic bearings proved excellent up to 22 years in simulator studies and clinical studies. However, microseparation kinematics would be necessary in the simulator to duplicate the more peripheral wear zones.

The wear pattern in metal-on-metal hip prostheses.

The accumulated data suggest that there is a strong correlation between polyethylene wear and osteolysis, which ultimately leads to prosthetic loosening. Second-generation metal-on-metal prostheses have been introduced, with an eye toward resolving this wear-induced osteolysis problem. The metal particles and ions are biologically active and can affect the cell homeostasis. Thus, defining the wear pattern and ratio of a given metal-on-metal prosthesis system is desirable. An early high-wear or run-in phase followed by a low-wear phase or steady state has been suggested for metal-on-metal hip prostheses. The aim of this study was to define the wear pattern of metal-on-metal bearings. The prosthesis systems were tested in a joint simulator. An early accelerated wear phase transformed to a slower wear phase after 700,000 cycles. The run-in and steady-state wear rates for combined head and liner averaged 2.22 mm(3)/Mc and 1.0 mm(3)/ million cycles, respectively. The metal-on-metal prosthesis featured a biphasic wear trend with the wear ratio in run in being more than twofold higher than the steady-state phase.

Study of retrieved acetabular sockets made from high-dose, cross-linked polyethylene.

Although ultra-high molecular weight polyethylene (UHMWPE) has stable chemical properties, chemical degradation, such as oxidation reaction, progresses with long-term clinical use. The purpose of this study was to investigate the change in properties of polyethylene (PE) in vivo by examining retrieved UHMWPE sockets and high-dose, cross-linked PE (100 Mrad PE) sockets. Twenty retrieved sockets (including 2 100 Mrad PE sockets), which were implanted from 1970 to 1996, were used for analysis. The oxidation index of 100 Mrad PE sockets was approximately the same as that of the normal UHMWPE sockets in worn areas. These long-term clinical results indicate that 100 Mrad PE is sufficiently stable for clinical use and that free radicals would not affect progression of oxidation significantly.

Correlation of wear debris-induced osteolysis and revision with volumetric wear-rates of polyethylene: a survey of 8 reports in the literature.

This survey focused on clinical reports of polyethylene wear and osteolysis in total hip replacements. With regard to documentation of clinical wear-rates, 57 publications were reduced to an analysis of 8 reports of THR series, including the incidence of osteolysis. A direct correlation was found among volumetric wear-rates, incidence of osteolysis and revision rates in THR concepts of the 1983-1987 era. As volumetric wear rate increased, the incidence of osteolysis and revision rates increased. With regard to our grading system for volumetric wear, with follow-up in the 4-15 year range, osteolysis was rare in group A (wear = 0-80 mm3/year), ranging from 6% to 31% in group B (wear 40-80 mm3/year) and from 21% to 100% in group C (wear > 140 mm3/year). With regard to cup design, the optimal low-wear group had mainly cemented polyethylene cups with 22 and 28 mm head sizes. The mid-wear group B had metal-backed cemented and uncemented cups, with 28 mm head size, and the high-risk group C had only uncemented, metal-backed cups, with the highest wear in the 32 mm head size. Less than 10 years of follow-up did not distinguish adequately between different designs of THR, except in a few cases which had early failures due to material or design deficiencies. Overall, the cemented all-polyethylene cup combined with the smaller ball head proved to be better.

Microwear phenomena of ultrahigh molecular weight polyethylene cups and debris morphology related to gamma radiation dose in simulator study.

Ultrahigh molecular weight polyethylene (PE) cups with 0, 2.5, 50, 100, and 150 Mrad radiation treatments were run in a hip simulator for comparison of the microwear phenomena on the cup surfaces with the corresponding debris morphology. In general, the size and frequency of the PE surface fibrils and the size of the retrieved PE debris decreased with increasing radiation dose. The fibril size and shape on the cup surfaces were well correlated with the radiation dose. The fibrillar shape and size were found to be proportional to the square root of the radiation dose. However, the trend for size and shape factors of the wear debris related to the radiation dose was weak at best. Thus, the morphology of the PE fibrils on the cup surfaces was more sensitive to variations in the radiation dose than the actual wear debris. The wear response appeared to be a three-step process, which was dependent on the formation of surface nodules or ripples, the teasing out of surface fibrils, and the toughness of the PE matrix in releasing a wear fibril to form a debris particle. The tougher PE became with increasing radiation dose, the harder it was for the PE fibrils to break out into wear particles.

Effects of A-P translation and rotation on the wear of UHMWPE in a total knee joint simulator.

We developed a three-channel total knee joint simulator and studied the effect of tibial anterior-posterior translation and internal/external rotation on the wear of polyethylene tibial inserts in total knee replacements (Anatomic Graduated Component knees). The wear rate was the lowest in experiment (Exp.) 1, without translation and rotation [1.74 mg/million (mg/Mc) cycles]. In Exp. 2, with +/-5 degrees tibial rotation added, the wear rate increased to 10.6 mg/Mc. In Exp. 3, with rotation and -12 mm tibial translation added, the wear rate was 15.1 mg/Mc, whereas in Exp. 4, with rotation and +12 mm tibial translation, the wear rate was 18.7 mg/Mc. Internal/external rotation and anterior-posterior translation added a 6- to 11-fold increase in the wear rates of tibial knee inserts. The shapes of the tibial wear tracks were rectangular and the area of the track increased when rotation and translation were added.

Clinical and hip simulator comparisons of ceramic-on-polyethylene and metal-on-polyethylene wear.

The benefit of reduced polyethylene wear with ceramic in hip replacements does not seem to have been universally appreciated. In this current study, wear predictions from laboratory and clinical studies were compared for ceramic-on-polyethylene and cobalt chrome-on-polyethylene combinations. Many laboratory studies included water-based lubrication and linear-tracking mechanisms. Now it is appreciated that these were inappropriate methods, because of a propensity for very low or virtually no polyethylene wear against ceramics in water. Thus, water-based studies predicting a 20- to 80-fold advantage for ceramic-on-polyethylene compared with metal-on-polyethylene clearly were in error. However, serum-based simulator studies with high protein-concentrations generally have shown greater wear with alumina-on-polyethylene than with metal-on-polyethylene. Controversy still remains over the use of such nonphysiologic protein levels. The simulator studies were just beginning to explore the role of serum protein concentrations and the influence on the various wear models. Polyethylene wear with zirconia systems was particularly affected by serum protein concentrations. In one simulator study, use of proteins in the physiologic range resulted in the alumina-on-polyethylene wear rate decreasing to approximately 50% of that of metal-on-polyethylene. In the literature, many hip design and polyethylene variations were reported which confounded the wear analysis. Overall, the clinical data supported the superior performance of ceramic-on-polyethylene systems by a factor of 1.5- to fourfold. However, the amount of supporting data was not large. This summary of laboratory and clinical data indicated that ceramic-on-polyethylene hip replacement systems offered on average a 50% wear reduction from metal-on-polyethylene systems.

Wear of ultra-high molecular weight polyethylene and polytetrafluoroethylene in a hip simulator: a dose-response study of protein concentration.

Charnley's laboratory wear studies of non-gamma sterilized polytetrafluoroethylene (PTFE) and polyethylene (PE) found that the PTFE to PE wear-rate ratio of 250:1 was much higher than the in-vivo wear ratio of 20:1. Tests of PTFE and PE in our laboratory showed a wear ratio of 150:1, using bovine serum as the lubricant and 190:1 with water as the lubricant. Our hypothesis was that the wear-rates of PTFE and PE cup materials were related to the concentration of protein in the serum. We studied the wear behavior of PTFE and PE cups in varied protein concentrations, using 4 femoral head sizes to validate the clinical range reported by Charnley. The PTFE wear-rates increased with increasing protein concentration and conversely, PE wear-rates decreased with increasing protein concentration. This inverse relationship made it possible to bring the wear ratio closer to the desired clinical wear ratio. We found that the clinically relevant PTFE/PE wear ratio corresponded to 3-10 mg/mL of protein in bovine serum.

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

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 steady state. Since these implants represented the first Crystaloy THR sets made, it was likely that the surface conditions of this high-strength ceramic could be improved in the future. Overall, the ceramic THRs demonstrated three orders of magnitude wear performance improvement over PE cups. With zirconia implants, while the cup wear was sometimes measurable, head wear was seldom discernible. Therefore, we have to be cautious in interpreting such zirconia wear data. Identifying the run-in and steady state wear rates was a valuable step in processing the ceramic wear data and assessing its reliability. Thus, the M-M and C-C THRs have demonstrated two to three orders of reduction in volumetric wear in the laboratory compared with the PE wear standard, which helps to explain the excellent wear performance and minimal osteolysis seen with such implants at retrieval operations.

Particles released from the Gyro C1E3 during simulated extracorporeal circulation.

Evaluation of released particles from the blood pump during extracorporeal circulation is an important aspect because the particles may cause microembolism. The Gyro C1E3 is a centrifugal blood pump that has an impeller suspended by double pivot bearings inside the housing; therefore, it is important to evaluate the released particles. The C1E3 was driven for 14 days to simulate clinical left ventricular assist device (LVAD) and percutaneous cardiopulmonary support (PCPS). Also, a roller pump was driven for 2 days as a comparison. Released particles were weighed and examined by SEM. After 14 days of pumping, the particles from the C1E3 were 238.6 microg in an LVAD condition. The particles with the roller pump were 270.2 microg after only 2 days. Average particle sizes with the roller pump and C1E3 were 3.7 and 0.6 microm, respectively. These results suggest that the Gyro C1E3 substantially reduces the risk of microembolism from released particles.

Metal-on-metal bearing in hip prosthesis generates 100-fold less wear debris than metal-on-polyethylene.

Aseptic loosening due to osteolysis in total hip replacement has been related to wear debris released from prosthetic components. Retrospective longterm observations of patients with the metal-on-metal prosthesis has shown long-term survivorship and good mechanical performance. Thus, the new and modified metal-on-metal prosthesis has been introduced on the market. Historical clinical data from the 1st generation metal-on-metal hip prosthesis may not be relevant for the 2nd generation of metal-on-metal hip prosthesis. Therefore, preclinical testing of the prosthesis must be conducted before clinical evaluation. We assessed the tribological performance of the metal-on-metal prosthesis versus the metal-on-polyethylene prosthesis introduced on the market as Metasul and Protasul, respectively. In a 12-channel joint simulator, 6 metal-on-metal bearing and 3 metal on polyethylene prostheses were tested, with the same number of corresponding soak controls. The wear was assessed gravimetrically. The "steady-state" wear-rates from the metal-on-metal prosthesis were almost 100 times less than that from the metal-on-polyethylene prosthesis. The tribological wear performance of the metal-on-metal hip prosthetic system is promising.