Polyethylene Wear Particles Research Articles

Back-side wear in HexLoc cups clinico-radiological, immunohistopathological, finite element, and retrieval analysis studies.

The HexLoc locking system was designed to prevent back-side wear of the polyethylene liner in the modular cementless metal-backed acetabular cup, but failed. Back-side wear was analyzed using clinico-radiological data, immunohistopathology, finite element modeling (FEM, and retrieval analysis. Screw holes allowed entry of titanium oxide and exit of polyethylene particles. Birefringent polyethylene wear particles were found behind the metal cup in macrophages containing pro-inflammatory tumor necrosis factor-α and interleukin-1β, whereas fibroblast-like cells stained for osteoclastogenic receptor activator of nuclear factor kappa B ligand (RANKL). Computerized tomography revealed granulomas (83% versus 17 %) and cortical destruction (50% versus 5%) better than radiographs. In FEM, a change of the abduction angle from 45 to 60 deg, and liner thickness from 4.8 mm to 2.5 mm, increased the back-side wear by 90% and 120%, respectively. Screw holes were stress concentration areas; their removal decreased wear by 40%. Modeling results were validated in retrieved implants, which demonstrated extensive back-side wear damage of liners with a high abduction angle. Combined clinico-radiological, immunohistopathological, FEM, and retrieval analysis disclosed that back-side wear in the HexLoc design is sensitive to the abduction angle, liner thickness, and presence of screw holes.

Polyethylene wear particles induce TLR 2 upregulation in the synovial layer of mice

A cellular and receptor mediated response to ultra-high-molecular-weight-polyethylene (UHMWPE) wear particles results in a release of proinflammatory cytokines and induces an inflammatory reaction causing osteolysis in total joint replacement. This investigation offers insight into the toll-like receptor (TLR) mediated activation by polyethylene wear particles in the synovial layer of mice. We hypothesized that, similar to recent in vitro results, UHMWPE particles lead to an upregulation of TLR 1 and 2 and TLR 4 in vivo in the synovial tissue of mice as well. Therefore, UHMWPE particles were generated in a common knee simulator according to the ISO standard, separated by acid digestion and determined by scanning electron microscopy. Endotoxin was removed using a method based on ultracentrifugation. A particle suspension (50μl; 0.1vol./vol.%) was injected into the left knee joint of female Balb/c mice (n=8). In a control group, phosphate-buffered saline was injected into the left knee of Balb/c mice (n=8). The mice were sacrificed after 7days. Immunohistochemical staining was performed with TLR 1, 2 and 4 polyclonal antibodies for Balb/c mice and evaluated by light microscopy. The particle-stimulated group showed a thickened synovial layer, an increased cellular infiltration and a TLR 2-upregulation in the synovial layer compared to the control group. An increased expression of TLR 1 and TLR 4 could not be demonstrated. These results indicate a mainly TLR 2-induced inflammation to polyethylene wear debris in the synovial layer of mice.

Polyethylene wear particles play a role in development of osteoarthritis via detrimental effects on cartilage, meniscus, and synovium

While ultra-high molecular weight polyethylene (UHMWPE) wear particles are known to cause periprosthetic osteolysis, its interaction with other intra-articular tissues in the case of partial joint arthroplasties is not well understood. We hypothesized that UHMWPE particles per se would interact with intra-articular tissue, which by acting as inflammatory reservoirs, would subsequently induce osteoarthritic (OA) changes. Our goal was to assess the inflammatory response, phagocytic activity, as well as apoptosis of intra-articular cells in the presence of UHMWPE particles in vitro, and the in vivo response of those tissues after intra-articular injection of particles in a murine model. Three cell types were used for the in vitro study; chondrocytes, meniscal fibrochondrocytes, and synoviocytes. Each cell type was cultured with two different concentrations of UHMWPE particles. Pro-inflammatory cytokine production, phagocytosis, and apoptosis were analyzed. In vivo experiments were done by injecting two concentrations of UHMWPE particles into normal and murine OA model knee joints. In vitro experiments showed that UHMWPE particles increase pro-inflammatory cytokine and mediator (IL-1β, IL-6, TNF-α, Nitric Oxide, and Prostaglandin E2) production, phagocytosis of particles, and apoptosis in all cell types. In vivo experiment showed degeneration of cartilage and meniscus, as well as synovitis after particle injection. UHMWPE wear particles per se exert detrimental effects in cartilage, synovium, and meniscus of the knee joint resulting in pro-inflammatory cytokine release, phagocytosis of particles and apoptosis. Particles induced and exacerbated OA changes in a murine model.

No difference in in vivo polyethylene wear particles between oxidized zirconium and cobalt–chromium femoral component in total knee arthroplasty

Polyethylene wear particle generation is one of the most important factors affecting mid- to long-term results of total knee arthroplasties. Oxidized zirconium was introduced as a material for femoral components to reduce polyethylene wear generation. However, an in vivo advantage of oxidized zirconium on polyethylene wear particle generation is still controversial. The purpose of this study was to compare in vivo polyethylene wear particles between oxidized zirconium total knee prosthesis and conventional cobalt-chromium (Co-Cr) total knee prosthesis. Synovial fluid was obtained from the knees of 6 patients with oxidized zirconium total knee prosthesis and from 6 patients with conventional cobalt-chromium (Co-Cr) total knee prosthesis 12months after the operation. Polyethylene particles were isolated and examined using a scanning electron microscope and image analyser. Total number of particles in each knee was 3.3±1.3×10(7) in the case of oxidized zirconium (mean±SD) and 3.4±1.2×10(7) in that of Co-Cr (n.s.). The particle size (equivalent circle diameter) was 0.8±0.3μm in the case of oxidized zirconium and 0.6±0.1μm in that of Co-Cr (n.s.). The particle shape (aspect ratio) was 1.4±0.0 in the case of oxidized zirconium and 1.4±0.0 in that of metal Co-Cr (n.s). Although newly introduced oxidized zirconium femoral component did not reduce the in vivo polyethylene wear particles in early clinical stage, there was no adverse effect of newly introduced material. At this moment, there is no need to abandon oxidized zirconium femoral component. However, further follow-up of polyethylene wear particle generation should be performed to confirm the advantage of the oxidized zirconium femoral component. Therapeutic study, Level III.

Mechanical Properties and Three-Dimensional Topological Characterisation of Micron, Submicron and Nanoparticles from Artificial Joints

Study of the geometry, nanomechanical properties and three-dimensional topographic characteristics of ultra-high-molecular-weight polyethylene (UHMWPE) wear particles provides an insight into understanding the wear mechanisms in artificial joints, which have not been fully explored. In this study, UHMWPE particles were generated, collected and then separated into three groups based on their size: micrometre, submicrometre and nanometre. Particle size distribution and shape features were investigated using scanning electron microscopy. Atomic force microscopy was used to quantify wear particle topographic features and nanomechanical properties. From the wear particle geometry analysis, it was found that nano- and submicron-sized particles had a granular shape while micrometre-sized particles had a flake-like morphology. Moreover, the mechanical properties and topographic characterisation of the UHMWPE material indicated that the nano- and submicron-sized particles had a much greater modulus and smoother surface than that of the micron-sized particles and bulk polymer sample. These differences in the geometric, topographic and mechanical properties between the nanoparticles, submicron particles and the micron particles revealed that the micron particles were most likely to be produced under macroscopic polymer asperity wear, while the nano- and submicron-sized particles were generated under microscopic polymer asperity wear. These findings provide a deeper understanding of the wear mechanism and processes of wear particle generation. Furthermore, the information may be useful to develop strategies for controlling and minimising the production of wear particles with particular features.

Characterization of polyethylene wear particle: The impact of methodology

Due to the prevalence of problems caused by wear particles, the reduced durability of total joint replacements is well documented. The characterization of wear debris enables the size and morphology of these wear particles to be measured and provides an assessment of the biological response in vivo. However, the impact of different methodologies of particle analysis is not yet clear. Hence, the aim of this investigation was to analyze the influence of different particle characterization methods performed by three research centers within the scope of a “round robin test”. To obtain knowledge about possible pitfalls, single steps of the particle characterization process (storage, pore size of the filter, coating durations by gold sputtering and scanning electron microscopy (SEM) magnification) were analyzed. The round robin test showed significant differences between the research groups, especially for the morphology of the particles. The SEM magnification was identified as having the greatest influence on the size and shape of the particles, followed by the storage conditions of the wear particle containing lubricant. Gold sputter coating and filter pore size also exhibit significant effects. However, even though they are statistically significant, it should be emphasized that the differences are small. In conclusion, particle characterization is a complex analytical method with a multiplicity of influencing factors. It becomes apparent that a comparison of wear particle results between different research groups is challenging.

The evaluation and management of peri-acetabular osteolysis

Total hip arthroplasty is one of the most successful and cost-effective surgical procedures in medicine and continues to be the most effective treatment for advanced osteoarthritis of the hip. The bearing surface remains one of the most critical factors limiting long-term survival of this procedure. This is partly due to the ceramic, metal, and polyethylene wear particles that can spur an inflammatory response within the body that induces periprosthetic bone resorption. In the case of wear of the bearing surface and resorption of acetabular bone, this can result in a confusing diagnostic scenario and an appropriate algorithm must be followed to diagnose, observe, and surgically manage these complex patients.

Investigation of the geometries and surface topographies of UHMWPE wear particles

Investigation of the topographical features on the surface of wear particles is important as the surface textures of ultrahigh molecular weight polyethylene (UHMWPE) wear particles potentially impact the biocompatibility of an implanted prosthesis. In this study, atomic force microscopy (AFM) was used to examine the geometry and surface topographies of UHMWPE wear particles at a nanometre-scale. The wear particles were categorised into four distinct groups based on their geometrical features and via the use of objective mathematical algorithms. The four groups were defined as granular, fibrous, platelet and flake-like particles. The particles in each category also had distinct topographical properties. Granular particles were comprised of a large number of valley structures and had a smooth surface. The Sa value of most granule particles fell into a range of 10–20nm. Fibrous particles had a surface dominated by a peak structure, while the surface of platelet particles had a valley structure. Despite this difference, approximately half of both the fibrous and platelet particles had a similar Sa value, in a range of 20–40nm. Flake-like particles had a rough surface and Sa value of 80% of them were larger than 70nm. The results of this study have clearly shown that there were differences in the geometrical and topographical properties of granule, fibrous, platelet and flake-like particles. This quantitative study of the surface topographies of the UHMWPE particles has laid a foundation for quantitatively assessing the influence of particle surface textures on the pathophysiological responses of the particles at the nanometre scale. This information can be used to determine the optimal surface texture of wear particles for an improved control of wear and the adverse particle-tissue reaction process in the future.

Characteristics of highly cross-linked polyethylene wear debris in vivo.

Despite the widespread implementation of highly cross-linked polyethylene (HXLPE) liners to reduce the clinical incidence of osteolysis, it is not known if the improved wear resistance will outweigh the inflammatory potential of HXLPE wear debris generated in vivo. Thus, we asked: What are the differences in size, shape, number, and biological activity of polyethylene wear particles obtained from primary total hip arthroplasty revision surgery of conventional polyethylene (CPE) versus remelted or annealed HXLPE liners? Pseudocapsular tissue samples were collected from revision surgery of CPE and HXLPE (annealed and remelted) liners, and digested using nitric acid. The isolated polyethylene wear particles were evaluated using scanning electron microscopy. Tissues from both HXLPE cohorts contained an increased percentage of submicron particles compared to the CPE cohort. However, the total number of particles was lower for both HXLPE cohorts, as a result there was no significant difference in the volume fraction distribution and specific biological activity (SBA; the relative biological activity per unit volume) between cohorts. In contrast, based on the decreased size and number of HXLPE wear debris there was a significant decrease in total particle volume (mm(3)/g of tissue). Accordingly, when the SBA was normalized by total particle volume (mm(3)/gm tissue) or by component wear volume rate (mm(3)/year), functional biological activity of the HXLPE wear debris was significantly decreased compared to the CPE cohort. Indications for this study are that the osteolytic potential of wear debris generated by HXLPE liners in vivo is significantly reduced by improvements in polyethylene wear resistance.

Investigation of three-dimensional surface topographies and mechanical properties of hypothesized biological active wear particles from artificial joints

Numerical characterization of geometry, topographies and mechanical properties of ultra-high molecular weight polyethylene (UHMWPE) wear particles from artificial hip joints provides an insight into the wear mechanisms of the artificial joints. In this study, two types of UHMWPE wear particles, namely, hypothesized bio-active and less active particles, were produced on a six-station pin-on-plate multi-directional wear simulator. Atomic force microscopy (AFM) was used to quantify wear particle features in three dimensions. In addition to the geometric features of the wear particles, comprehensive surface topography investigations were carried out on AFM using numerical image analysis techniques. Furthermore, the nano-mechanical properties of the wear particles were investigated. The results revealed that the hypothesized bio-active particles had a larger aspect ratio and thickness, a rougher surface and a smaller modulus in comparison to the hypothesized less bio-active or bio-inactive particles. The investigations in this study have provided further knowledge to the specific geometries, surface morphologies and mechanical characteristics of the hypothesized bio-active and less bio-active particles, as well as an insight into the particle generation mechanisms. This knowledge can be utilized to minimize particle-related tissue reactions through developing effective methods to control the generation of biologically active particles or to assist in inventing new artificial joint materials.

Microscratching Characterization of the Wear-in of UHMW Polyethylene in Prostheses

A new measurement technique of prosthesis wear by microscratching has been demonstrated. The technique has been applied in a study of the backside wear of a UHMW polyethylene tibial insert of a rotating platform knee prosthesis. Four disc-shaped UHMW polyethylene plugs, prepared with 5-μm deep microscratches, were carefully recessed into the backside of the tibial insert. It was demonstrated that the scratches are not affected by creep under static load. A realistic in vitro wear simulation experiment was performed over 0.8 × 106 flexion cycles. SEM and AFM show that following the experiment the initial microscratches are effectively absent in all four locations with only residual depressions observed. This implies that typically at least 5 μm of polyethylene material was worn over the first 0.8 × 106 cycles by processes other than creep. Evidence from AFM and SEM indicates the in-fill and reintegration of polyethylene wear particles into residual scratch depressions. This supports a two-phase model of the wear process that has been independently confirmed by radioisotope tracing. For an initial wear-in phase, the model implies large, but rapidly decreasing, wear, resulting from abrasive wear and a competition between the loss and the reintegration of wear particles. The in vitro wear-in of the backside may typically produce a wear debris volume of 8.5 mm3. In addition to wear-in, the model assumes a much lower, constant long-term wear rate. The model has been used to correct published backside wear rates for the effects of the wear-in phase. A best estimate of 0.7 mm3/106 cycles has been determined for the long-term in vitro backside wear rate of a tibial insert in a rotating platform design.

Revision surgery after failed ACL reconstruction with artificial ligaments: clinical, histologic and radiographic evaluation

Synthetic ligament for anterior cruciate ligament (ACL) reconstruction has been widely used in the past. Long-term follow-up has demonstrated the unreliability of many of these devices in ACL surgery, and problems may arise for the surgeon approaching a patient with failed artificial ligament reconstruction. The aim of this study is to investigate whether revision surgery may improve clinical and radiographic outcomes in patients with failed synthetic ACL reconstruction. Fourteen patients who were treated in the past with ACL reconstruction with synthetic grafts underwent two-stage revision surgery. Follow-up averaged 4.2years (range 2-6years). Mean KOOS score was 75.8 (SD 10.2); IKDC score was B in two patients, C in nine and D in three. The improvement compared to preoperative status was not statistically significant (p>0.05). Four patients were positive to Lachman and anterior drawer tests. Mean side-to-side anterior laxity averaged 4.3mm (SD 1.2). Biopsy specimens documented the presence of foreign body granulomatous reaction, giant foreign body cells and polyethylene wear particles. The level of osteoarthritis worsened at follow-up compared to preoperative status (p<0.05). ACL revision surgery with autografts in patients who underwent previous failed primary synthetic ligament reconstruction does not improve clinical outcomes and does not influence the natural history of knee osteoarthritis started from artificial ligament debris.

Wear, bone density, functional outcome and survival in vitamin E-incorporated polyethylene cups in reversed hybrid total hip arthroplasty: design of a randomized controlled trial

BackgroundAseptic loosening of total hip arthroplasties is generally caused by periprosthetic bone resorption due to tissue reactions on polyethylene wear particles. In vitro testing of polyethylene cups incorporated with vitamin E shows increased wear resistance. The objective of this study is to compare vitamin E-stabilized highly cross-linked polyethylene with conventional cross-linked polyethylene in “reversed hybrid” total hip arthroplasties (cemented all-polyethylene cups combined with uncemented femoral stems). We hypothesize that the adjunction of vitamin E leads to a decrease in polyethylene wear in the long-term. We also expect changes in bone mineral density, less osteolysis, equal functional scores and increased implant survival in polyethylene cemented cups incorporated with vitamin E in the long-term.DesignA double-blinded randomized controlled trial will be conducted. Patients to be included are aged under 70, suffer from non-inflammatory degenerative joint disease of the hip and are scheduled for a primary total hip arthroplasty. The study group will receive a reversed hybrid total hip arthroplasty with a vitamin E-stabilized highly cross-linked polyethylene cemented cup. The control group will receive a reversed hybrid total hip arthroplasty with a conventional cross-linked polyethylene cemented cup. Radiological follow-up will be assessed at 6 weeks and at 1, 3, 5, 7 and 10 years postoperatively, to determine polyethylene wear and osteolysis. Patient-reported functional status (HOOS), physician-reported functional status (Harris Hip Score) and patients’ physical activity behavior (SQUASH) will also be assessed at these intervals. Acetabular bone mineral density will be assessed by dual energy X-ray absorptiometry (DEXA) at 6 weeks and at 1 year and 2 years postoperatively. Implant survival will be determined at 10 years postoperatively.DiscussionIn vitro results of vitamin E-stabilized polyethylene are promising, showing increased wear resistance. However, controlled clinical follow-up data are not available at this moment.This randomized controlled trial has been designed to determine wear, bone mineral density, functional outcome and survival in reversed hybrid total hip arthroplasty comparing cemented vitamin E-stabilized highly cross-linked polyethylene cups with cemented conventional cross-linked polyethylene cups.Trial registrationDutch Trial Registry NTR3049

Comparison of the Genesis II total knee replacement with oxidised zirconium and cobalt-chromium femoral components in the same patients

Despite many claims of good wear properties following total knee replacement (TKR) with an oxidised zirconium (OxZr) femoral component, there are conflicting clinical results. We hypothesised that there would be no difference in either the mid-term clinical and radiological outcomes or the characteristics of the polyethylene wear particles (weight, size and shape) in patients using an OxZr or cobalt-chrome (CoCr) femoral component. In all 331patients underwent bilateral TKR, receiving an OxZr femoral component in one knee and a CoCr femoral component in the other. The mean follow-up was 7.5 years (6 to 8). Following aspiration, polyethylene wear particles were analysed using thermogravimetric methods and scanning electron microscopy. At the most recent follow-up, the mean Knee Society score, Western Ontario and McMaster Universities Osteoarthritis Index score, range of movement and satisfaction score were not significantly different in the two groups. The mean weight, size, aspect ratio and roundness of the aspirated wear particles were similar for each femoral component. Survivorship of the femoral, tibial and patellar components was 100% in both groups. In the absence of evidence of an advantage in the medium term we cannot justify the additional expense of an OxZr femoral component.

Surface modification of ultra-high-molecular-weight polyethylene by argon plasma

The generation of wear particles from the ultra-high-molecular-weight polyethylene (UHMWPE) counter-face of metal sliding pair is relatively high. These polyethylene wear particles lead to osteolysis and that result in the failure of the implant made with the sliding pair. Hence, an investigation has been carried out to enhance the wear resistance of UHMWPE by argon plasma surface modification of UHMWPE. Results show the argon plasma-treated UHMWPE gains high crosslink, which provides less adhesive force interactions between the materials. Thus, a lower value of steady state coefficient of friction can be obtained.

Study on in vitro release and cell response to alendronate sodium‐loaded ultrahigh molecular weight polyethylene loaded with alendronate sodium wear particles to treat the particles‐induced osteolysis

The aim of this study is to investigate in vitro release and cell response to wear particles of ultrahigh molecular weight polyethylene loaded with alendronate sodium (UHMWPE-ALN), a potent bone resorption inhibitor. Wear particles of UHMWPE-ALN with different ALN contents (0.5 wt % or 1.0 wt %) and size ranges (<45 μm or 45-75 μm) were cocultured with macrophages (RAW264.7) and osteoblasts (MC3T3-E1), respectively. The in vitro ALN release was divided into three stages: an initial burst release, subsequent rapid release, and final slow release. The particle size and ALN content of UHMWPE-ALN wear particles affected the in vitro release mainly during initial burst and rapid release. Compared with the control cells, UHMWPE-ALN wear particles stimulated a significant elevation of tumor necrosis factor-alpha (TNF-α) release from macrophages but had no obvious effect on interleukin-6 release. However, this stimulation of TNF-α release could be reduced by ALN released from UHMWPE-ALN wear particles. The wear particle size had stronger effect of on the macrophages compared with the ALN concentration. After coculture with UHMWPE-ALN wear particles, osteoblast proliferation and alkaline phosphatase activities increased moderately with the increase in particle sizes and ALN concentrations. These results suggest that incorporation of ALN in UHMWPE-ALN may be an effective approach to prevent or reduce particles-induced osteolysis.

Evaluation of different methods to eliminate adherent endotoxin of polyethylene wear particles

Wear particles have to be cleaned from any substances, which could eventually lead to confounding effects in studies concerning the in vitro or in vivo biological activity of wear debris. Several observations have demonstrated that lipopolysaccharide (LPS) as a component of the outer membrane of gramnegative bacteria can modulate the cell response to wear debris.There are numerous methods described in the literature for the removal of LPS. But there is an exception for polyethylene particles, they cannot be treated with radiation and heating processes.There remain four possible methods: Cleaning the particles with sodium hydroxide or with acetic acid, washing them with ethanol or via using a demanding ultracentrifugation procedure. Thus we decided to compare the different methods in consideration of the remaining LPS level and their effects on the particle numbers and morphology.During the study several problems regarding these methods appeared: Either they could not remove the LPS below the demanded detection level, or the methods had influence on amount and morphology of the particles.Due to these findings the authors developed a new method based on ultracentrifugation. With this method the LPS could be removed as required, amount and morphology of the particles were not affected.

Highly crosslinked polyethylene does not reduce aseptic loosening in cemented THA 10-year findings of a randomized study.

Polyethylene (PE) wear particles are believed to cause aseptic loosening and thereby impair function in hip arthroplasty. Highly crosslinked polyethylene (XLPE) has low short- and medium-term wear rates. However, the long-term wear characteristics are unknown and it is unclear whether reduced wear particle burden improves function and survival of cemented hip arthroplasty. We asked whether XLPE wear rates remain low up to 10 years and whether this leads to improved implant fixation, periprosthetic bone quality, and clinical function compared to conventional PE. We randomized 60 patients (61 hips) to receive either PE or XLPE cemented cups combined with a cemented stem. At 10 years postoperatively, 51 patients (52 hips) were evaluated for polyethylene wear and component migration estimation by radiostereometry, for radiolucent lines, bone densitometry, and Harris hip and pain scores. Revisions were recorded. XLPE cups had a lower mean three-dimensional wear rate between 2 and 10 years compared to conventional PE hips: 0.005 mm/year versus 0.056 mm/year. We found no differences in cup migration, bone mineral density, radiolucencies, functional scores, and revision rate. There was a trend toward improved stem fixation in the XLPE group. The overall stem failure rate was comparably high, without influencing wear rate in XLPE hips. XLPE displayed a low wear rate up to 10 years when used in cemented THA, but we found no clear benefits in any other parameters. Further research is needed to determine whether cemented THA designs with XLPE are less prone to stem loosening. Level I, therapeutic study. See the Instructions for Authors for a complete description of levels of evidence.

Polyethylene particles stimulate expression of ITAM-related molecules in peri-implant tissues and when stimulating osteoclastogenesis in vitro

Wear particle-induced orthopaedic prosthesis loosening is associated with elevated osteoclast activity. The immunoreceptor tyrosine-based activation motif (ITAM)-related molecules OSCAR, FcRγ, TREM2 and DAP12 are important for osteoclast formation. The aim of this study was to determine if these molecules are involved in peri-implant loosening by investigating their expression in peri-implant tissues obtained at revision of joint replacement components containing polyethylene (PE) wear particles, and in osteoclasts formed in vitro in the presence of PE particles. The results showed that there was a marked and statistically significant increase in protein levels of the ITAM-related molecules in the revision tissues. The levels of OSCAR, FcRγ, TREM2 and DAP12 mRNA in the revision tissues were also increased. In vitro PE particles stimulated osteoclast resorption in the presence of 50ngml−1 receptor activator NFκB (RANKL) and significantly elevated the expression of OSCAR, FcRγ, TREM2 and DAP12 during osteoclast formation. These findings suggest that the ITAM signalling molecules and their co-receptors have a role in pathogenic bone loss associated with implant PE wear.

Biological activity of polyethylene wear debris produced in the patellofemoral joint

Polyethylene wear is considered a threat to the long-term survival of total knee replacements. The aim of this study was to investigate the contribution that resurfacing the patella makes to wear debris-induced osteolysis following total knee replacement. Ultra-high molecular-weight polyethylene wear particles were isolated from simulator lubricant. Particle shape, size, and volume distributions were recorded allowing the osteolytic potential of the wear debris produced in the patellofemoral joint to be estimated using the concept of specific biological activity and functional biological activity. Values were compared with those reported for the tibiofemoral joint. Specific biological activity for the patellofemoral joint was not significantly different from the values for the tibiofemoral joint of total knee replacement devices, and therefore, has a similar potential to stimulate osteolytic cytokine release from macrophages. Functional biological activity was significantly lower for the patellofemoral joint compared with the tibiofemoral joint. Functional biological activity was significantly lower for the patellofemoral joint compared with the fixed bearing and rotating platform total knee replacement devices. However, as patellar resurfacing is commonly fitted as part of a total knee replacement system, this results in a 20% increase in overall functional biological activity for the system. Therefore, implanting a patellar resurfacing will increase the potential for osteolysis in the knee.