polyethylenes

..Overall, our results suggest that PE particles directly induce a change in the phenotype of mature osteoblasts and osteocytes, consistent with the net loss of bone near orthopaedic implants...

..Obviously, other considerations will influence the minimum thickness to be recommended...

..Even for the 46-mm femoral head, wear was reduced significantly using criteria of gravimetric and geometric measurements and morphologic appearance of the machining marks out to 11 million cycles of simulated gait...

..These data compared well with the clinical data...

Polyethylene wear-induced osteolysis is a major cause of implant loosening in total hip arthroplasty. New crosslinked polyethylenes are presumed to give lower wear rates, but no long-term clinical results are available yet.

..This indicates that we should take care to ensure that our desire to reduce the wear debris to a zero amount does not result in a modified UHMWPE that lacks the necessary mechanical properties for contemporary metal-backed cup designs...

..No correlation was found between the thickness of the liner and the clinical wear factor. Within the range of thicknesses tested here, UHMWPE thickness is not an influential parameter for the hip prosthesis and this is confirmed..

..We conclude that a significant therapeutic effect may be achieved by further optimization in dose and regime of administration of antisense oligonucleotide...

....

..Taken together, these results indicate that phytantriol may not only provide an alternative lipid for preparation of liquid crystalline systems in excess water but may also provide access to properties not available when using GMO...

..These observations support the hypothesis that the early in vivo scratching of highly cross-linked polyethylene acetabular liners is primarily caused by plastic deformation...

....

..With regard to the inductive effect on the osteoclastogenesis, our results show that the Al(2)O(3) wear debris are less active...

Highly cross-linked polyethylenes (HXLPEs) have been incorporated into the hip replacement armamentarium based on their improved wear resistance...

..We conclude that HXLPE has a 40% lower wear rate as compared with UHMWPE, suggesting that it will perform better in the long term...

..There were no radiographic signs of lysis or radiolucencies at a minimum 3-year follow-up...

..Continued monitoring will be necessary to elucidate the clinical efficacy of these devices...

..In such a way a risk-to-benefit ratio for the patient could be established...

..This method leads to the absence of detectable free radicals in the polymer and, as a result, excellent resistance to oxidation of the polymer...

..This newly developed platform can assist in the further understanding of the mechanism and therapy strategies of osteolysis induced by polyethylene particles...

..Our prospective randomised study has assessed the results using two different polyethylenes associated with the same prosthetic design...

....

..1 and 0.15 mm where the average linear wear rate was 0.1mm/yr and the volumetric wear was 55 mm(3)/yr. The present work indicates the importance of avoiding too tight or too loose a diametrical clearance...

..Longer follow-up is necessary to determine if Marathon cross-linked polyethylene will continue to demonstrate the encouraging improved wear and osteolysis characteristics...

..The results of the simulations are discussed in relation to the wear distribution measured on the articular surface of 12 UHMWPE components retrieved from failed hip joint prostheses, after a period of in situ functioning...

..It is possible that the rotational system reduces the stress against acetabular and femoral components, but the 30 mm diameter head caused high friction torque and required at least 9.5 mm thickness in the acetabular component...

..The importance of contact mechanics on the clinical performance of artificial hip joint replacements has also been discussed...

..Preclinical laboratory wear testing showed a number of cross-linked polyethylenes to have dramatically less wear than the polyethylene that had been in use for several decades...

..However, the bi-directional pin-on-disc wear rate did not change with the processing temperature, indicating that adhesive and abrasive wear is independent of the extent of consolidation in the range of parameters studied here...

..However, this study did not reveal any advantage in terms of predicted FBA for moderately crosslinked UHMWPE compared with non-crosslinked UHMWPE...

..These findings may have significant implications for the choice of fixation systems to be used for different types of bearing couples...

..Additionally, it was concluded that the nanomechanical response of material with higher percentage crystallinity (67 per cent) was predominantly determined by the crystalline regions within the semi-crystalline UHMWPE nanostructure...

..Such tests allow the optimisation of the wear behaviour of the tested metacarpophalangeal prosthesis and therefore permit a minimisation of the possible risks to the patients...

....

..Proximal and, to a lesser degree, distal interface contact area footprints decreased significantly with increasing flexion angle based on the conformity of the designs, resulting in a corresponding increase in the mean and peak stresses...

..The presence of saline lubricant retards the formation of the beneficial polymer transfer thus leading to faster abrasion of the polymeric counterface which explains the relatively rapid and progressive increases in friction and wear...

..The reduced wear volumes coupled with the reduced cytotoxicity per unit volume of wear indicate the potential for the clinical application of this technology...

..Longer follow-up is necessary to confirm the benefits to patients from reduction of debris released from the articulation...

..Mechanical tests as well as computational material and structural models should be developed to evaluate the combined effect of material and geometry (structure) on fracture resistance under clinically relevant loading conditions...

..In the test model used, oxidation led to delamination, whereas increased cross-link density resulted in reduced adhesive/abrasive wear of tibial inserts...

..Furthermore, if the head diameter increases beyond 42 mm, a rapid increase in the contact pressure was predicted, owing to the decrease in the wall thickness of the cross-linked UHMWPE cup...

..Alumina MP generated fewer and rounder polyethylene wear particles than metal MP in early clinical stage, and could potentially reduce prevalence of osteolysis and aseptic loosening...

..Also, even if Type 1 defects are prevented, Type 2 defects heal extremely slowly. They must be an intrinsic feature of UHMWPE for all reasonable forming conditions, and products and forming processes should be designed accordingly...

..To evaluate the outcome of different types of polyethylene, bone cements and one design of uncemented fixation with porous and ceramic coating using radiostereometry, bone densitometry, conventional radiography and clinical parameters...

..Patient kinematics are an important factor affecting the wear and long-term biocompatibility of UHMWPE used as a bearing surface in THR...

..The mean equivalent circle diameter was 0.71 and 0.26 microm for UHMWPE and XLPE, respectively...

..In knee simulator studies, wear of TKR bearings was dependent on kinematics at the articulating surfaces and the prosthesis design, as well as the type of material...

..Total computation time for each damage prediction was less than 30 min. Continuing refinement of this approach will provide a robust tool for accurately predicting clinically relevant wear in total knee replacements...

..The worn surface whose macroscopic geometrical congruity had been improved due to wear after joint replacement showed lower contact stress at macroscopic level...

..This review examines femoral fixation, bone remodeling, and wear studies of MOM implants and provides a brief overview of the latest outcome and retrieval data and how these data integrate with the in vitro wear studies...

..In this review, we discuss the most common theories concerning aseptic loosening. It emerges from this review that aseptic loosening has a multifactorial etiology and cannot be explained by a single theory...

..Upon simulator testing, UHMWPE showed more significant changes in oxidation indexes and distribution of carbonyl compounds than XLPE, confirming a better wear behavior for XLPE under the adopted testing conditions...

..This is the first clinically relevant laboratory demonstration of the wear-reducing ability of these films. Further optimization will be needed before this novel class of materials can be used by the orthopedic community...

....

..The present investigation nevertheless confirms the potential of carefully designed and manufactured metal-on-metal total replacement joints for the treatment of diseased and damaged hips...

..A simple model, which describes and explains all supermolecular structure changes, is introduced. An effective way of eliminating residual macroradicals in UHMWPE is proposed...

..The full coupling between the thermal and the mechanical conditions used in this study appears to be necessary if accurate predictions of the polyethylene deformation are required...

....

..022 mm/year...

..2 mm was reduced from 35% to 15%. Wear measurements are less sensitive to differences in two-dimensional projection of the THA when using the correction method...

....

..The high plastic strains predicted offer an explanation for the highly elevated wear rates in scratched counterface tests and the aspect ratio of scratch lips is therefore a critical determinant of plastic strain...

..Long-term clinical experience suggests that loosening may be the primary cause while the presence of HDP wear particles is secondary. Healing of endosteal cavities can take place in the presence of HDP wear particles...

..As far as the cup-ball pairing is concerned and under the current pressure of costs, the surgeon should be able to select the optimum hip prosthesis model for every patient from these three categories...

..Many of these factors contribute to the wear encountered in clinical practice. These mechanisms are reviewed and examples identified in which they have resulted in increased wear...

..Although the wear rate decreased less rapidly with decreased counterface roughness for Ra values below 0.05 micron, there were significant advantages to be gained from improved femoral head roughness to below 0.01 micron Ra...

..No systematic differences in size and morphology were found between the groups in this study. The similarity in size and morphology of the wear particles suggested that the same basic wear mechanisms were occurring in these components...

..Experiments conducted on both gamma irradiated and unirradiated UHMWPE specimens using a linear wear machine and multi-axial joint simulators confirmed the validity of the molecular wear theory...

..Of major clinical significance in relation to osteolysis and loosening is roughening of the femoral components, which may lead to greater numbers of the sub-micron-sized particles...

..The composite osteochondral device became rapidly attached to host bone by ingrowth into the supporting mesh. The clinical implications of the possible use of this material in articular resurfacing and joint replacement are discussed...

..A greater than twofold increase in wear rate is reported for these heads when compared with smooth heads. This increased wear rate is, however, still within the limits of data from clinical wear studies...

....

....

..New locking mechanism designs directed toward better methods of securing the polyethylene insert to the tibial tray are needed to minimize the generation of particulate wear debris at the modular interface...

..These results demonstrated that at higher irradiation levels the materials became more brittle in fatigue, with less ductile folding and tearing of the fracture surfaces...

....

..Therefore, it is important to analyse the contact mechanics in artificial hip joint replacements. Practical considerations of manufacturing these bearing surfaces have also been discussed...

..5 MPa. It appears that the pressure value of 2.0 MPa should not be exceeded in pin-on-disc wear tests that are to reproduce the clinical wear of UHMWPE acetabular cups...

....

..15). The wear rates for all the joints tested were consistent with other simulator studies. The friction factors produced by each joint were found to decrease significantly after wear testing (p < 0.05)...

Cross-linked polyethylenes are being introduced widely in acetabular cups in hip prostheses as a strategy to reduce the incidence of wear debris-induced osteolysis...

....

..6%, respectively...

..This has important implications for its osteolytic potential...

..The uncertainty in the results is estimated for each cup. The repeatability of the technique is studied for a case showing very slight wear. The advantages, disadvantages and limitations of the method are presented and discussed...

....

..Low density polyethylenes as well as polypropylene and polybutadiene, containing high degrees of branching and high molar masses, have ..

..and viscometry (Visc) detection is introduced as a tool for the characterization of high molecular weight polyethylenes. The high molecular weight fraction strongly affects the rheological behaviour and processability of ..

The response of murine macrophages to clinically relevant polyethylene wear particles generated from different polyethylenes at various time points and volumetric doses in vitro was evaluated...

..As a function of the Fe-2/Cr-1/Cr-2 mixing ratio it is possible to control the weight ratio of these three polyethylenes without affecting the individual average molecular weights and narrow polydispersities of the three ..

..and had a maximal effect on the surface and subsurface regions for the gamma-air and gamma-low oxygen polyethylenes, respectively...

..accurate predictions of the in vivo wear of a broad spectrum of bearing materials, including cross-linked polyethylenes, metal-on-metal, ceramic-on-ceramic, and others in development...

..Newer "second-generation" highly cross-linked polyethylenes have been developed that are annealed below the melt temperature, but use either a pharmacologic antioxidant, ..

..the polyethylene implant influence the extent of wear, and surgeons should be cautious in considering enhanced polyethylenes pending results of further investigations...

..However, trials to improve the methylmethacrylate cement or to invent better polyethylenes have often failed...

....

..Copolymerization of ethylene with a bifunctional acrylate-methacrylate monomer yields linear polyethylenes with intact methacrylate substituents...

..Crosslinking increased the ultimate load at failure and decreased the ultimate displacement of the polyethylenes during the small punch test...

..The long-term clinical performance of first-generation highly cross-linked liners remains promising based on the midterm outcomes of the components documented in this study [corrected]...

..The goal is to improve the long-term performance of UHMWPE joint components, regardless of UHMWPE formulation, through significantly improved numerical modeling of components prior to implantation. ..

..clinically retrieved orthopedic components is critically needed to guide the development of improved polyethylenes, such as the highly crosslinked polyethylenes which have recently been introduced into clinical practice for ..

..The MDR's and our own implant retrieval experience support that mechanical failure of highly cross linked UHMWPE, albeit in a subset of retrieved cases, is nonetheless a clinically relevant phenomenon. ..

..This study will efficiently inform the Nephrology community by providing a foundation of fundamental information (ARF definitions, incidence, consequences and costs) upon which a clinical trials network can be built. ..

..We are committed to working cooperatively and constructively with the other CCC and Data Analysis Coordinating Center-regardless of the final agreed-upon protocol. ..

....

..abstract_text> ..

....

..This research will elucidate important mechanisms of particle-induced, chemokine-directed cell trafficking and suggest new treatment strategies. ..

..This research will elucidate important mechanisms of particle-induced, chemokine-directed cell trafficking and suggest new treatment strategies. ..

..Thus, successful achievement of the proposed research will provide essential information on TDR implant performance and on clinical outcomes, which are needed for informed health care decisions. ..

....

..Thisinstrumentcouldbeextendedtowardstheimplementationand evaluationofnovelvolumecontrolstrategiesandalsoappliedtootherareasof rehabilitationwheremanagementofinterstitialfluidcontrolisclinicallyrelevant. ..

..However, before they can be used for this purpose, their predictions need to be validated. This study proposes unique data and methods to perform such a validation with a focus on the knee during walking. ..

..abstract_text> ..

....

..of the wear rate improvements otherwise associated with advanced bearing materials such as highly cross-linked polyethylenes. While long recognized as a potential clinical concern, the difficulties of quantifying 3rd body challenge ..

..to developing new treatment targets beyond traditional (Framingham) CV risk factors to improve poor outcomes in these 2 patient populations and maybe in geriatric populations or those with chronic disease states and similar paradoxes ..

....

..This application represents an important step in this ongoing research initiative. ..

..to developing new treatment targets beyond traditional (Framingham) CV risk factors to improve poor outcomes in these 2 patient populations and maybe in geriatric populations or those with chronic disease states and similar paradoxes ..

..The primary comparison between these prosthesis designs will be the incidence of Outcomes Requiring Intervention (failure of prosthesis or non-failures requiring intervention) observed over three years of recall examination. ..

..This partnership proposes to bring together a critical mass of engineers and surgeons, to achieve clinically grounded advances in nonlinear numerical simulations of surgery of the hip. ..

..e. soft-tissue complications that require surgical repair through use of a biomaterial. The new materials will prevent scar tissue formation and reduce the occurrence of secondary complications. ..

....

....

..At the project's conclusion, we expect to have filled a longstanding need in the field of osteonecrosis research: an animal model suitable for systematic study of human-implementable interventions to forestall femoral head collapse. ..

....

..Finally, while highly-crosslinked polyethylenes appear to offer dramatic performance improvement under relatively favorable tribologic conditions, it remains ..