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Biomedical subjects

I C Clarke

Publications and source records attributed to I C Clarke.

At least 19 recordsLinked to original sources
PubMed2005

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.

Aluminum Oxide↗
PubMed2005

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.

Ceramics↗
PubMed2003

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.

Adult↗
PubMed2001

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.

Biomechanical Phenomena↗
PubMed2001

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.

Arthroplasty, Replacement, Hip↗
PubMed2001

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.

Biocompatible Materials↗
PubMed2001

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.

Acetabulum↗
PubMed2001

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.

Bone Cements↗
PubMed2000

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.

Biocompatible Materials↗
PubMed2000

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.

Animals↗
PubMed2000

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.

Ceramics↗
PubMed2000

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.

Aluminum Oxide↗
PubMed1999

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.

Hip Prosthesis↗
PubMed1998

The fallacy of evaluating biomaterial wear-rates with water as lubricant: a hip simulator study of alumina-PTFE nd CoCr-PTFE combinations.

Controversy surrounds wear data from hip-simulator studies, whether from the choice of lubricants or other parameters such as the particular biomaterial combinations used, and whether any such interactions could bias the resulting wear predictions. To investigate these phenomena, we studied the wear performance of CoCr and alumina femoral heads, in water and serum-based lubricants, using as our standard the polytetrafluoroethylene wear data derived clinically by Charnley. To model Charnley's clinical experience, PTFE acetabular cups were used in sets of three each with each size of femoral head for 22.25, 28, and 42-mm diameters in a nine-channel hip simulator. From the serum-based tests, the CoCr-PTFE wear data were consistently linear with duration of test, exhibited very large wear rates of 3,000-8,400 mm3/10(6), cycles had a precision within +/- 4% for each set of three cups, and copious amounts of small particulate were clearly seen circulating. The wear data clearly demonstrated Charnley's thesis that volume of wear increased with regard to size of femoral head. From the water-based tests, the CoCr-PTFE wear data were nonlinear with duration of test, had much reduced wear rates compared to the serum tests, lost the clinical relationship with ball size, and precision deteriorated to +/- 27% for each set. The wear debris appeared as 1-2 cm long ribbons which floated to the surface. For the alumina-PTFE combination in serum, the wear data appeared identical in performance to the CoCr-PTFE data in serum. Thus, the PTFE wear rates were not sensitive to the choice of femoral-head material. The most surprising outcome in this study was the zero-wear performance of the ceramic-PTFE combination in water. This contrasted remarkably with the large wear rates established for the same combinations run in serum. The zero-wear performance of the ceramic-PTFE combination in water was unexpected, but a similar phenomenon was noted in published simulator tests of ceramic-UHMWPE run in water. It now seems likely that such data may reflect the capricious behavior of water lubrication rather than any other variables under evaluation. The water-based experiments clearly favored the ceramic's superior tribological performance and placed metal bearings at a decided disadvantage. Therefore, for an in vitro simulation of materials wear-ranking of clinical relevance, it may be advisable to use a serum-based lubricant.

Alloys↗
PubMed1997

Charnley wear model for validation of hip simulators--ball diameter versus polytetrafluoroethylene and polyethylene wear.

Wear rates of polytetrafluoroethylene (PTFE) and polyethylene cups were compared in 9-channel and 12-channel simulators, using serum lubrication and gravimetric techniques for wear assessment. Cobalt-chromium (CoCr) and alumina ceramic femoral heads in 22-42 mm diameter range were used to validate simulator wear rates against clinical data. This was also the first study of three femoral head sizes evaluated concurrently in a simulator (with three replicate specimens) and also the first report in which any wear experiments were repeated. Fluid absorption artefacts were within +/-1 per cent of wear magnitude for PTFE and +/-8 per cent for polyethylene and were corrected for. Wear rates were linear as a function of test duration. Precision within each set of three cups was within +/-6 per cent. The wear rates from experiments repeated over 15 months were reproducible to within +/-24 per cent. However, the magnitudes of the simulator wear rates were not clinically accurate, the PTFE wear rates (2843 mm3/10(6) cycles; 22 mm diameter) were over three times higher than in vivo, the polyethylene 30 to 50 per cent on the low side (23 mm3/10(6) cycles; 22 mm diameter). Volumetric wear rate increased with respect to size of femoral head and a linearly increasing relationship of 7 8 per cent/mm was evident with respect to femoral head diameter for both PTFE and polyethylene. These data compared well with the clinical data.

Aluminum Oxide↗
PubMed1996

Water and bovine serum lubrication compared in simulator PTFE/CoCr wear model.

Controversy surrounds wear data from laboratory hip simulator studies, whether derived from water-based or serum-based studies or whether a major design parameter such as the size of the femoral head has an effect on the volume of wear particulate released. To investigate these relationships, we studied cup wear in water- and serum-based lubricants using as our standard the polytetrafluoroethylene (PTFE) data derived by Charnley. To model Charnley's clinical experience, PTFE acetabular cups were used in sets of three each of four sizes of CoCr femoral heads: 22.25-, 28-, 32-, and 42-mm diameters. Six criteria were used to evaluate the performance of the lubricants against clinical accuracy and scientific methods. The PTFE wear data from the serum-based tests was consistently linear with the duration of the test, exhibited a precision within +/-3% about the average for each set of three cups, and copious amounts of wear debris were clearly seen circulating and settling to the bottom of the wear chambers. The wear data clearly demonstrated Charnley's thesis that volume of wear increases with regard to the size of the femoral head in a linear manner. This increase was considered satisfactory at 9%/ mm. However, in terms of clinical accuracy, the simulator wear rates averaged 3 to 4 times greater than the comparable clinical data for wear magnitude. Thus, the serum-based tests satisfied three of the six criteria used. The PTFE wear data from the water-based tests was generally nonlinear, continually increasing with test duration. These wear trends were examined in three discrete phases to estimate the changing wear rates. By the end of the tests, the wear rates had increased from 1.3 to 3.9 times, with the 42-mm heads showing the greatest change. The resulting precision was never better than +/-26% and deteriorated to +/-70%. In terms of clinical accuracy, the water-based wear rates varied from 2 to 7 times less than the Charnley PTFE wear magnitudes, averaging 4 times less. The water-based data did not satisfactorily model the relationship between increased wear with increased head size. Minimal PTFE wear debris was observed, and what did emerge after thousands of wear cycles appeared as streamers up to 30 mm long and up to 5 mm wide. When these detached, they floated up to the surface where they could be separated into smaller particulates. A similar phenomenon was noted for polyethylene wear tests conducted with water lubrication. Thus the water-based tests satisfied none of the six validation criteria evaluated. These data raise serious doubts as to the validity of testing implant and material combinations in water as a predictor of clinical performance. Bovine serum was not totally satisfactory, but the wear data did model some of the important clinical characteristics of hip joint behavior.

Animals↗
PubMed1996

Hip-simulator ranking of polyethylene wear: comparisons between ceramic heads of different sizes.

We carried out simulator studies on ceramic-polyethylene total-hip combinations to determine the volumetric wear-rates of 22 mm, 26 mm and 28 mm femoral-head sizes. Bovine-serum lubrication and 2 kN peak sinusoidal load-profile were used with polyethylene (UHMWPE) cups. Wear was assessed by gravimetric technique. Precision (9%) was ensured by the use of multiple specimens, multiple wear-events, and the linear-regression method of estimating the average wear trend, thereby reducing the inherent, unpredictable nature of each wear-event. Volumetric wear-rates for polyethylene averaged 23 mm3 per 10(6) cycles for the 22 mm ceramic head and up to 32 mm3 per 10(6) cycles for the 28 mm head. The difference between 22 mm and the larger head-sizes was significant. This may well be the first laboratory confirmation of Charnley's original clinical Low-Friction Arthroplasty concept with regard to wear rate. The wear penalty increased linearly at the rate of 6% to 9% per mm of diameter increase.

Ceramics↗