Wear Of Ultra-high Molecular Weight Polyethylene Research Articles

Characteristic modeling of the wear particle formation process from a tribological testing of polyethylene with controlled surface asperities

To study the ultra-high molecular weight polyethylene (UHMWPE) wear particles-induced osteolysis which leads to the failure of artificial joints, microfabricated surfaces with controlled asperities have been applied to generate narrowly distributed UHMWPE wear particles with various sizes and shapes. Our previous study further facilitated single wedge sliding tests to investigate the mechanism of the UHMWPE particle generation. In this study, the attempt was made to characterize the particle generation process into a mathematical model to predict particle volume with a given surface-texture dimensions and mechanical loading conditions. The particle-generation process is decomposed into two steps: (1) penetration of the cutting edge, and (2) lateral sliding of the cutting edge. By combining the indentation experimental data, the viscoelastic responses of UHMWPE was incorporated in the model. The effects of normal load, feature height, and cutting edge angle on the wear particle volume were illustrated from model predictions. Both experimental results and model predictions indicate the same trend of effects of surface-texture geometry and mechanical conditions on the volume of particles. The results of the model predictions are close to the experimental results of the particle generation. However, the particle volume predicted by the model is larger than the experimental results. It is believed that the reprocessing of the generated particles and viscoelastic recovery of UHMWPE in the experiments account for this difference. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 587–594, 2007

Bio-Ferrography to Capture and Separate Polyethylene Wear Debris from Hip Simulator Fluid and Compared with Conventional Filter Method

This paper describes an experimental method, bio-ferrography, to separate ultrahigh molecular weight polyethylene (UHMWPE) wear debris, generated in hip simulators, from bovine serum lubricating fluid. A total of 54 experiments were performed in which an enzyme digestion “cocktail” was developed and used to clean the bovine serum samples of extraneous sugars, proteins, and lipids that interfere with the UHMWPE particle separation. Erbium chloride was used to marginally magnetize particles in the fluid prior to passing through the ferrographic device. The particles were captured and separated from the fluid by traversing the treated serum across a magnetic gap of a bio-ferrograph. Morphology of the captured and separated wear debris was compared with particles from samples of fluid filtered through a paper sieve arrangement with pores of 0.05micrometers in diameter. The UHMWPE wear debris collected using the described experimental method, were found to be between 0.1 and 20micrometers in diameter with spherical and pill-shaped particles. The filtered UHMWPE particles were in the same size range as the debris separated using bio-ferrography. To show that the experimental method captured UHMWPE particles, the spectra of the chemical composition of UHMWPE from an acetabular cup insert of a hip implant and of UHMWPE particles separated using bio-ferrography were compared and found to be the same. To further demonstrate that polyethylene could be captured and separated through the experimental method, manufactured polyethylene microspheres in the diameter range of 3-45micrometers, were captured and separated using the bio-ferrographic process.

Wear of UHMWPE against Zirconia/Alumina Composite

The sliding wear behavior of ultra high molecular weight polyethylene (UHMWPE) was examined on a novel low temperature degradation-free zirconia/alumina composite material and on the conventional ceramics (alumina and zirconia) used for a femoral head in total hip joint replacement. The wear of UHMWPE pins against these ceramic disks was evaluated by performing linear reciprocal sliding and repeat pass rotational sliding tests for one million cycles in a bovine serum. The weight loss of polyethylene against the novel low temperature degradation-free zirconia/alumina composite disks was much less than conventional ceramics for all tests. The mean weight loss of the polyethylene pins was more in the linear reciprocal sliding test than in the repeat pass rotational sliding test for all kinds of disk materials. Neither the coherent transfer film nor the surface damage was observed on the surface of the novel zirconia/alumina composite disks during the test. In conclusion, the novel zirconia/alumina composite leads the least wear of polyethylene among the tested ceramics and demonstrates the potential as the alternative materials for femoral head in total hip joint replacement.

Wear of ultrahigh-molecular-weight polyethylene against titanium-nitride-coated counterfaces

Simple configuration pin-on-plate tests were conducted in order to compare the wear of ultrahigh-molecular-weight polyethylene (UHMWPE) when sliding against titanium-nitride (TiN)-coated wrought cobalt-chromium (Co-Cr) plates obtained by arc evaporative physical vapour deposition (AEPVD) with that which occurs when sliding against uncoated wrought and cast Co-Cr plates. UHMWPE wear was determined for plates in their undamaged form and following simulated third-body damage to produce scratches similar to those observed on retrieved implants. In their undamaged form, the coatings produced a similar wear rate of UHMWPE to that with the uncoated Co-Cr plates. However, in their damaged form, TiN-coated plates showed significantly lower polyethylene wear than uncoated wrought Co-Cr plates (analysis of variance; α = 0.05). The TiN-coated plates prevented the generation of high scratch lips due to their higher hardness, producing much smaller Rp values (0.19 μ) than the scratched uncoated Co-Cr plates (0.92-1.15 μ). This is a probable explanation for the lower wear rate on the scratched TiN-coated plates than on the scratched uncoated wrought plates. The results of this study have illustrated the possibility of using AEPVD TiN coatings in total knee joint replacements in order to reduce polyethylene wear.

Zytokinprofil einer humanen Knochenmarkzellkultur unter dem Einfluss von UHMW-PE Abriebpartikeln / Cytokine profile of a human bone marrow cell culture under the influence of UHMW-PE wear particles

There is considerable evidence that orthopaedic wear debris plays a crucial role in the pathology of aseptic loosening of joint prostheses. The purpose of the present study was to evaluate the influence of ultra-high-molecular-weight polyethylene (UHMW-PE) on the cytokine response in a modified in vitro model. UHMW-PE particles (psi < 7.5 microm) were suspended in soluble collagen type I and subsequently solidified in different concentrations (105,106 and 107 particles per well) on the bottom of the wells. Human bone marrow cells in a concentration of 3 x 106 cells per well were seeded on the collagen-particle substrata and maintained for up to 12 days. The cytokine response (IL-1_, IL-6 and TNF-_) of the cells to the particles were examined by ELISA compared to cells on control collagen surfaces without any particles. Assays for viability using LDH activity were done immediately. Light and scanning microscopic evaluation revealed that the UHMWPE particles, which have built large conglomerates (psi7.5_m), were mainly surrounded by the cells and less phagocytosed. The results of the cytokine release revealed significant differences in interleukin (IL)6, tumor necrosis factor (TNF)- _ and IL-1beta. The cell viability was not affected by the UHMW-PE particles. The results demonstrate that the particle induced cytokine response by UHMW-PE is mainly by the release of Interleukin 6 and TNF- _. Moreover the results confirm that the present method is useful to evaluate the in vitro effects of UHMW-PE wear particles with direct particle cell contact.

New fast method for determination of number of UHMWPE wear particles

Ultra-high molecular weight polyethylene (UHMWPE) wear particles are the major cause of total joint replacement (TJR) failures because the wear particles, released from TJR's, cause bone loosening. To simplify the study of the relationship between numbers of particles at various locations around TJR's and extent of bone loosening at these locations, the authors of this work tried to develop a new method for easy and fast determination of number of wear particles. The method, called LSC (Light Scattering with Calibration spheres), is based on light scattering of a suspension of wear particles and calibration spheres, and yields relative numbers of particles. A modified LSC method, called LSCm, requires one additional experiment, a gravimetric analysis of a mixture of all studied samples, to determine absolute numbers of wear particles. LSC and LSCm methods are easy and fast, which make them suitable for processing and comparing high number of samples.

Tribological and Nanomechanical Properties of Unmodified and Crosslinked Ultra-High Molecular Weight Polyethylene for Total Joint Replacements

Wear of ultra-high molecular weight polyethylene (UHMWPE) continues to be a major obstacle limiting the longevity of total joint replacements. Efforts to solve the wear problem in UHMWPE have resulted in numerous studies dealing with the microstructure, morphology, and mechanical properties of this polymer. However, the fundamental wear mechanisms at different material length scales in total joint replacements remain elusive. Consequently, a systematic investigation of the initial stage of the wear process was performed in this study in order to obtain insight into the origins of wear in UHMWPE at submicrometer scales. Sliding experiments were performed with both unmodified and crosslinked (by gamma radiation treatment) UHMWPE subjected to reciprocating sliding against Co-Cr alloy in a bath of bovine serum under ranges of mean contact pressure and sliding speed typical of knee joints. Nanoindentation and optical, scanning electron, and transmission electron microscopy were used to examine the effect of crosslinking on the nanomechanical properties, dominant wear mechanisms, and microstructure of UHMWPE. The fundamental wear micromechanisms of unmodified and crosslinked UHMWPE are interpreted in the context of coefficient of friction, wear factor, creep, adhesion force, and microstructure results.

Wear of retrieved UHMWPE hip liners.

After the gamma-irradiation sterilization, the most widely used orthopaedic grade polymer bearing liner material for the total joint replacement, ultra-high molecular weight polyethylene (UHMWPE), degrades through the progressive in vivo oxidation. The oxidative degradation makes UHMWPE brittle and leads to reduction of its mechanical properties. In this study, the effect of the in vivo post-irradiation ageing time on the wear of UHMWPE was investigated. Twelve retrieved polyethylene hip liners implanted for 3-16 years and then stored in the air for 1.5-8 years were used. Two types of the pin-on-disk wear testing were conducted. The uni-directional repeat pass rotating and the linear reciprocating wear testing were done with stainless steel disks against stationary polyethylene pins under 4MPa at 1Hz with bovine serum lubrication. Wear of the retrieved polyethylene hip liners does not have significant correlation with the in vivo or total ageing time. The linear reciprocal sliding motion generated a more pronounced wear than the uni-directional repeat pass sliding motion. This indicates that the kinematic motion significantly affects the wear of aged UHMWPE, having a brittle, white band region.

Carbon-carbon composite bearing materials in hip arthroplasty: analysis of wear and biological response to wear debris.

Ultra-high molecular weight polyethylene wear particles have been implicated as the major cause of osteolysis, implant loosening and late aseptic failure in total hip arthroplasties in vivo. This study initially screened 22 carbon-carbon composite materials as alternatives for UHMWPE in joint bearings. New bearing materials should satisfy certain criteria--they should have good wear properties that at least match UHMWPE, and produce wear particles with low levels of cytotoxic and osteolytic activity. Initial screening was based on wear resistance determined in short-term tribological pin-on-plate tests. Three materials (HMU-PP(s), HMU-RC-P(s), and SMS-RC-P(s)) which had superior wear resistance were selected for long-term testing. All materials had very low wear factors and SMS-RC-P(s), which had a wear factor of 0.08 +/- 0.56 x 10(-7) mm3/Nm, was selected for the subsequent biological testing and particle size analysis. SMS-RC-P(s) showed good biocompatibility in bulk material form and also the wear particles had low cytotoxicity for L929 fibroblasts in culture compared to metal wear particles. Wear debris size analysis by transmission electron microscopy showed that the particles were very small, with the vast majority being under 100 nm in size, similar to metal wear particles. The potential osteolytic effect of SMS-RC-P(s) wear particles was investigated by culturing particles with human peripheral blood mononuclear cells and measuring TNFalpha production. SMS-RC-P(s) did not significantly stimulate TNFalpha production at a particle volume to cell number ratio of 80:1, indicating that the debris had a low osteolytic potential. The results of this study suggest that carbon-carbon composites, particularly those composed of PAN-based fibers may be important biomaterials in the development of next generation bearing surfaces for use in total joint replacements that have very low wear rates and reduced osteolytic and cytotoxic potential.

An augmented hybrid constitutive model for simulation of unloading and cyclic loading behavior of conventional and highly crosslinked UHMWPE

Ultra-high molecular weight polyethylene (UHMWPE) is extensively used in total joint replacements. Wear, fatigue, and fracture have limited the longevity of UHMWPE components. For this reason, significant effort has been directed towards understanding the failure and wear mechanisms of UHMWPE, both at a micro-scale and a macro-scale, within the context of joint replacements. We have previously developed, calibrated, and validated a constitutive model for predicting the loading response of conventional and highly crosslinked UHMWPE under multiaxial loading conditions (Biomaterials 24 (2003) 1365). However, to simulate in vivo changes to orthopedic components, accurate simulation of unloading behavior is of equal importance to the loading phase of the duty cycle. Consequently, in this study we have focused on understanding and predicting the mechanical response of UHMWPE during uniaxial unloading. Specifically, we have augmented our previously developed constitutive model to also allow for accurate predictions of the unloading behavior of conventional and highly crosslinked UHMWPE during cyclic loading. It is shown that our augmented hybrid model accurately captures the experimentally observed characteristics, including uniaxial cyclic loading, large strain tension, rate-effects, and multiaxial deformation histories. The augmented hybrid constitutive model will be used as a critical building block in future studies of fatigue, failure, and wear of UHMWPE.

Morphological characteristics of total joint arthroplasty-derived ultra-high molecular weight polyethylene (UHMWPE) wear debris that provoke inflammation in a murine model of inflammation.

It is recognized that the chronic inflammation in peri-prosthetic tissue that contributes to implant failure frequently is provoked by the presence of wear debris. Some wear debris is inevitable because of the nature of the prosthesis, but not all patients develop severe inflammatory responses. The precise factors that mediate the severity of tissue inflammation to wear debris has yet to be fully defined. Because wear debris retrieved from peri-prosthetic tissue consists of a heterogeneous mixture of materials with various sizes and shapes, this study evaluated the influence of two major physical aspects of ultra-high molecular weight polyethylene (UHMWPE) wear debris (shape and surface texture) using a model of tissue inflammation. UHMWPE debris particulates recovered from 50 peri-prosthetic tissue samples were examined by scanning electron microscopy and categorized into four groups based upon aspect ratio and surface texture of the material. The four groups were defined as: 1) smooth and globular, 2) smooth and fibular, 3) rough and globular, and 4) rough and fibular. Histological analysis and ELISA assays were conducted to evaluate variations in cellular responses and cytokine production between the groups. The strongest expression of tumor necrosis factor alpha and interleukin-1 beta was found in tissues exposed to UHMWPE debris with both a rough surface texture and fibular shape, and this response was significantly elevated over debris particles with a smooth surface texture and globular shape. The data suggest that both shape and texture influence the severity of specific inflammatory responses and that rough debris surface texture exerts a marked effect on adverse tissue responses when combined with particles that have a sharp, elongated shape.

Changes in macrophage morphology and prolonged cell viability following exposure to polyethylene particulate in vitro.

The interaction of macrophages and ultra-high molecular weight polyethylene (PE) wear plays an important role in perpetuating chronic inflammation at the bone implant interface, leading to peri-implant osteolysis and mechanical failure of the implant. A model to study the interaction of human mature macrophages with orthopaedic biomaterial wear has been previously developed. With the use of the model, in this study, the mature human monocyte-derived macrophages (MDMs) were observed with light, fluorescent, and scanning electron microscopy (SEM), as well as transmission electron microscopy (TEM). The cell viability was investigated using calcein and ethidium staining. Following exposure to PE particulate, the morphology of the human MDMs was heterogeneous: rounded, flattened, and elongated. There was no morphological evidence of cytotoxicity or apoptosis. The MDM viability was not influenced by phagocytosis of PE particulate in a negative fashion. In fact, more prolonged cell viability was observed in the human MDMs exposed to PE particulate when compared to controls.

Particle size and morphology of UHMWPE wear debris in failed total knee arthroplasties––a comparison between mobile bearing and fixed bearing knees

Osteolysis induced by ultrahigh molecular weight polyethylene wear debris has been recognized as the major cause of long-term failure in total joint arthroplasties. In a previous study, the prevalence of intraoperatively identified osteolysis during primary revision surgery was much higher in mobile bearing knee replacements (47%) than in fixed bearing knee replacements (13%). We postulated that mobile bearing knee implants tend to produce smaller sized particles. In our current study, we compared the particle size and morphology of polyethylene wear debris between failed mobile bearing and fixed bearing knees. Tissue specimens from interfacial and lytic regions were extracted during revision surgery of 10 mobile bearing knees (all of the low contact stress (LCS) design) and 17 fixed bearing knees (10 of the porous-coated anatomic (PCA) and 7 of the Miller/Galante design). Polyethylene particles were isolated from the tissue specimens and examined using both scanning electron microscopy and light-scattering analyses. The LCS mobile bearing knees produced smaller particulate debris (mean equivalent spherical diameter: 0.58 μm in LCS, 1.17 μm in PCA and 5.23 μm in M/G) and more granular debris (mean value: 93% in LCS, 77% in PCA and 15% in M/G).

Do current wear particle isolation procedures underestimate the number of particles generated by prosthetic bearing components?

Hip simulator serum samples containing ultra-high molecular weight polyethylene (UHMWPE) wear debris were digested in acid, and replicate digests were filtered through either a 0.2 or a 0.05 μm pore size membrane. The recovered particles were characterized using Fourier transform-infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). Debris deposited on both the 0.2 and 0.05 μm membranes were identified as UHMWPE by FT-IR and were predominantly submicron and round, with occasional elongated fibrils. The mean and median diameters of the particles on the 0.05 μm membranes were significantly lower than those of the particles on the 0.2 μm membranes. Over half of the particles on the 0.2 μm membranes had diameters which were below the specified pore size, whereas only a small percentage (2.8%) of particles on the 0.05 μm membranes were smaller than the specified pore size. More than twice as many particles were recovered on the 0.05 μm membranes than the 0.2 μm membranes. These findings indicate that a substantial number of wear particles passed freely through the pores of the 0.2 μm membranes, which resulted in an underestimation of particle number and an overestimation of particle size. Because the cellular response to wear debris has been found to be dependent upon particle number and size, among other factors, the introduction of a new orthopaedic bearing material should be supported by an accurate description of wear particle parameters. To ensure an accurate description of particle characteristics, it is recommended that filter membranes with very fine pore sizes (at most 0.05 μm) be used to isolate UHMWPE wear debris from joint simulator serum and periprosthetic tissue.

Effect of polymer molecular weight and addition of calcium stearate on response of MG63 osteoblast-like cells to UHMWPE particles

Periprosthetic osteolysis and implant loosening is associated with the presence of ultrahigh molecular weight polyethylene (UHMWPE) wear debris particles. Osteoblast phenotypic expression in vitro is affected by UHMWPE particles, suggesting that bone formation may also be affected by wear debris. Here we tested the hypothesis that the response of osteoblasts to UHMWPE can be modified by changes in UHMWPE particle chemistry. We used four different commercially available preparations of GUR UHMWPE particles to determine if chemical composition (±Ca-stearate) or polymer molecular weight (3.1–4.2 million or 5.4–6.5 million g/mol) modulates osteoblast response. Particles were characterized by size distribution, morphology, and number of particles added to the culture medium. They had an average equivalent circle diameter ranging from 0.46–1.26 μm. MG63 cell response was assessed by measuring cell number, cellular and cell layer alkaline phosphatase, and prostaglandin E 2 ( PGE 2) production. There were dose-dependent effects of the particles on cell response. Cell number and PGE 2 production were increased, while alkaline phosphatase specific activity was decreased. In addition, there was a marked difference between cultures treated with particles containing Ca-stearate and as a function of polymer molecular weight. Particles of higher molecular weight caused a greater stimulation of proliferation and inhibition of alkaline phosphatase than particles of lower molecular weight. The presence of Ca-stearate exerted a more pronounced depression of osteoblast phenotype as well as a significantly greater increase in PGE 2 release by the cells. The present study shows that chemical composition and polymer molecular weight of UHMWPE are capable of modulating osteoblast response to particles. The results suggest that osteoblast differentiation is inhibited by UHMWPE particles, whereas cell proliferation and PGE 2 production are stimulated. This may have direct effects on osteoblasts and bone formation, but also paracrine effects on cells of the monocytic lineage inducing bone resorption and promoting inflammation which may lead to aseptic loosening. The present results suggest that the cellular events in aseptic loosening may be modulated or even accelerated by changes in the composition of the UHMWPE used to fabricate implants.

The effect of molecular orientation and acetylene-enhanced crosslinking on the wear of UHMWPE in total artificial joints.

This paper investigates the benefits of combining roll-drawing and acetylene-enhanced crosslinking to alter the mechanical properties of the ultra high molecular weight polyethylene (UHMWPE) used in total hip and knee replacements, with the aim of improving its resistance to wear. UHMWPE was processed via crosslinking, roll-drawing and a combination of crosslinking and roll-drawing and subjected to gel content analysis, tensile tests, X-ray diffraction and wear tests using different types of motion and smooth and rough counterfaces. Purely roll-drawn materials with length and width draw ratios of lambda l x lambda w = 1.3 x 1.0 and lambda1 x lambdaw = 1.6 x 0.9 respectively, were found to have lower wear factors in a unidirectional motion test with a rough counterface when compared to the virgin material. The crosslinked roll-drawn material, with length and width draw ratios of lambda1 x lambdaw = 1.6 x 0.9, was seen to possess five crosslinks per initial number average molecule. This crosslinked and roll-drawn material showed 5.5 times less wear than the virgin material in a multidirectional motion test with a smooth counterface and 1.4 times more wear than the virgin material in a unidirectional motion test with a rough counterface. Hence this study supports previous work by the authors that acetylene-enhanced crosslinked materials may show benefits for a total hip replacement, but only where the femoral head remains smooth. The improvements in wear with the roll-drawn material in unidirectional tests were smaller, but may prove to have some benefits in the knee.

Clinical results of the Harris-Galante cup implanted from 1986 to 1991

In the period 1986–1991, we performed 370 consecutive total hip arthroplasties (THA) using the Harris-Galante porus coated prosthesis. The characteristics of this component are: a fiber-mesh coating in pure Ti alloy that stimulates osteoinduction, a process of fusion of fiber-mesh to the metal back that reduces potential damage to the microstructure of the fibers with consequently less resistance to fatigue and a better primary stability guaranteed by fixation screws that stimulate osteoconduction. The average follow-up was 11.5 years. The follow-up was performed through a roentgenographic control at 3, 6 and 12 months and then once a year. Mineralometric evaluation with a Hoxologic QDR apparatus [1,2] permitted quantitative examination of the periprosthetic bonestock. A questionnaire was administered to examine the characteristics of pain and the ability to perform daily activities, to go upstairs, to walk distances, to sit the down and to put on socks and shoes. We found no vascular complications because of the use of Ti screws; the cup, after a primary fixation, ran into osteointegration in most cases. We did not find any aseptic loosening due to the inadequate primary press-fit or to screw breaking. We did not find any periprosthetic bone loss due to the migration of Ultra High Molecular Weight Polyethylene (UHMWPE) wear particles from holes of the shell. When aseptic loosening of the femoral stem and UHMWPE wear particle formation did occur, the metal back was perfectiyl osteointegrated and we only had to substitute the insert. The results are clinically interesting considering the long-term follow-up, the large number of patients and, technically, the type of fixation (line-to-line without press-fit), the semplicity of assembly of UHMWPE without any bone loss around the cup, the good fixation of cups even if badly implanted because of other difficulties in impanting them or for a wrong technique. In our opinion, our choice of implanting HG1 cups line-to-line was successful 10–15 years later.

Evaluation of the response of primary human peripheral blood mononuclear phagocytes to challenge with in vitro generated clinically relevant UHMWPE particles of known size and dose.

The response of primary human peripheral blood mononuclear phagocytes to challenge with clinically relevant ultra-high molecular weight polyethylene (UHMWPE) wear debris of known particle size and dose was evaluated. Particles with a mean size of 0.24, 0. 45, 1.7, 7.6, and 88 microm were cocultured with cells for 24 h before assessment of cell viability and production of the osteolytic cytokines interleukin (IL)-1 beta, IL-6, tumor necrosis factor-alpha, and granulocyte macrophage colony-stimulating factor, and prostaglandin E(2). All particle fractions were evaluated at particle volume (microm(3)) to cell number ratios of 10:1 and 100:1, which had been previously identified as being the most stimulatory and clinically relevant. None of the test fractions had an effect on cell viability. Whereas the heterogeneity of human individuals was clearly evident in the responses of the donors evaluated in this study (the response of donor 3 was between 5 and 20 times greater than the other donors), the most biologically active particles were found to be submicrometer in size. Stimulation with phagocytosable particles (0.24, 0.45, and 1.7 microm) resulted in enhanced levels of cytokine secretion. Macrophages stimulated with particles outside this size range produced considerably less cytokines at the volumes tested. These results confirm earlier findings and suggest that the size and volume of UHMWPE particles are critical factors in macrophage activation. Furthermore, they suggest that the heterogeneity of human individuals may be another important factor in determining implant life.

Quantitative analysis of ultrahigh molecular weight polyethylene (UHMWPE) wear debris associated with total knee replacements.

The size and morphology of particulate wear debris retrieved from tissues around 18 failed total knee replacements (TKR) were characterized. Interfacial membranes from nine cemented and nine uncemented TKR were harvested from below the tibial components during revision surgery. Wear debris were extracted using papain and potassium hydroxide digestion. Ultrahigh molecular weight polyethylene (UHMWPE) particles from around cemented or uncemented TKR were similar in size and morphology. The mean size was 1.7 +/- 0. 7 microm with a range of 0.1-18 microm. Thirty-six percent of the particles were less than 1 microm and 90% were less than 3 microm. Morphologically the particles were predominantly spherical with occasional fibrillar attachments and flakes. Particles from TKR were greater than threefold larger than previously characterized particles from total hip replacements, which were 0.5 microm in mean size. Differences in joint conformity and wear patterns between the hip and knee articulations may explain the disparity in size of the wear debris. Since particle size represents an important variable influencing the magnitude of the biological response, it is possible that in vivo the larger TKR debris results in a diminished mediator release, which in turn may account for the lower incidence of osteolysis and aseptic loosening in some designs of TKR.

Quantitative analysis of polyethylene wear debris, wear rate and head damage in retrieved Charnley hip prostheses.

Submicrometer- and micrometer-sized ultra-high molecular weight polyethylene (UHMWPE) wear particles have been associated with osteolysis and failure of total artificial joints. Previous studies have isolated predominantly submicrometer-sized particles at the expense of larger particles (>10 microm). This study aimed to isolate and characterize quantitatively all sizes of UHMWPE wear particles generated in 18 Charnley hip prostheses. In addition, to analyze the wear debris with respect to the total volumetric wear of the cup and damage to the femoral head. Particle size distributions ranged from 0.1 to ->1000 microm. A significant proportion (3-82%) of the mass of the wear debris isolated was>10 microm. The mode of the frequency distribution of the particles was in the range 0.1-0.5 microm for all patients. However, analysis of the mass of wear debris as a function of its size allowed differentiation of the wear debris from different patients. Femoral head damage was associated with high volumetric wear and increased numbers of biologically active submicrometer-sized particles.