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At least 361 records · Page 20Linked to original sources
PubMed2005

Pubovaginal bone anchor fixation with polyethylene versus fascia lata slings in the treatment of female stress incontinence: sling material and processing are predominant factors in success.

OBJECTIVE: The opponents of the In-Taca bone anchor system note the risk of a high rate of wound infection and osteitis pubis. We evaluated whether there is a difference in the outcome of the use of two different sling materials--polyethylene and fascia lata--with regard to wound infection, and analyzed the incidence of osteitis pubis further in a larger series. MATERIAL AND METHODS: A total of 61 women (mean age = 65.4 years) were treated for stress urinary incontinence (SUI) type II and III using the In-Taca bone anchor system. In 15 of 61 patients, we used a synthetic sling of polyethylene, and in 46, a fascia lata sling. The subjective success rate was determined with validated questionnaires (Urinary Distress Inventory-6, Symptom Severity Index and Symptom Impact Index). The objective assessment included a pad test according to the ICS- standard and a urogynecologic evaluation. Mean follow-up was 10.2 months. RESULTS: Wound inflammation of only very mild degree occurred in 15% in the fascia lata group, whereas 33% in the polyethylene group developed serious sling infection; in three patients explantation of the sling was necessary. Accordingly, satisfaction with the procedure was low in the polyethylene group. In both groups, there were no hints of osteitis pubis. The sling material used did not affect continence rate. CONCLUSION: Using the bone anchor system, the infection rate depends primarily on the sling material used and its processing: polyethylene is well tolerated in other reconstructive procedures (such as TVT, where a netlike mesh is used), so the processing of synthetic sling material plays an extremely important role in infection rate: platelike, dense synthetic material tends to cause wound infection.

Adult↗
PubMed1992

Periprosthetic bone loss in total hip arthroplasty. Polyethylene wear debris and the concept of the effective joint space.

Thirty-four hips in which there had been prosthetic replacement were selected for study because of the presence of linear (diffuse) or lytic (localized) areas of periprosthetic bone loss. In all hips, there was careful documentation of the anatomical location of the material that had been obtained for histological analysis, and the specific purpose of the removal of the tissue was for examination to determine the cause of the resorption of bone. Specimens from twenty-three hips were retrieved during an operation and from eleven hips, at autopsy. The area of bone loss was linear only in sixteen hips, lytic only in thirteen, and both linear and lytic in five. In all thirty-four hips, intracellular particulate debris was found in the macrophages that were present in the area of bone resorption. All thirty-four had intracellular particles of polyethylene, many of which were less than one micrometer in size. Thirty-one hips had extracellular particles of polyethylene as well. Twenty-two of the thirty-four hips had intracellular metallic debris; in ten, metallic debris was found extracellularly as well. Ten of the sixteen cemented specimens had intracellular and extracellular polymethylmethacrylate debris. In the mechanically stable prostheses--cemented and uncemented--polyethylene wear debris was identified in areas of bone resorption far from the articular surfaces. The number of macrophages in a microscopic field was directly related to the amount of particulate polyethylene debris that was visible by light microscopy. Although the gross radiographic appearances of linear bone loss and lytic bone loss were different, the histological appearance of the regions in which there was active bone resorption was similar. Regardless of the radiographic appearance and anatomical origin of the specimen, bone resorption was found to occur in association with macrophages that were laden with polyethylene debris. In general, the number of macrophages present had a direct relationship to the degree of bone resorption that was seen. We believe that these findings indicate that joint fluid penetrates far more extensively than previously thought, even in a well fixed component, along the interface between the prosthesis and bone and in the periprosthetic tissues; it is often more extensive than is shown by arthrography. We therefore suggest the concept of the effective joint space to include all periprosthetic regions that are accessible to joint fluid and thus accessible to particulate debris.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed2006

[Measurement of acetabular polyethylene wear of total hip replacement, using a universal measuring microscope. Characteristics of measurements].

PURPOSE OF THE STUDY: The aim of the study was to present our own method of measuring acetabular polyethylene wear in total hip arthroplasty, including assessment of basic measurement characteristics. It is a well known fact that, in total hip replacement, polyethylene liners wear out with use. The rate of acetabular polyethylene wear can then be related to clinical or demographic data. MATERIAL AND METHODS: Our method, using a universal measuring microscope, is based on the ability of exact identification of central positions of the head of total hip replacement before implantation and after prosthesis removal. The difference between the original and final positions allows us to calculate both linear and volumetric wear of polyethylene. During one month, the same components were repeatedly measured by two independent investigators and a total of 10 ABG 1 acetabular components were checked. The results of measurements were evaluated by a series of statistical tests, including correlation and regression analyses and analysis of variance. RESULTS: High correlations were found among individual measurements made by each observer (r = 0.998; r = 0.973) as well as between the mean values obtained from the two observers (r = 0.996). The reliability of measurements was proved by a high correlation of the regression curve of each measurement with the "ideal" line. With two exceptions, the differences between paired measurements were not significant. CONCLUSIONS: Our method facilitates an in vitro measurement of polyethylene wear with considerable accuracy and high reliability.

Acetabulum↗
PubMed1991

An analysis of polyethylene thickness in modular total knee components.

Polyethylene wear has become an important consideration in total knee arthroplasty. The actual polyethylene thickness of modular tibial components is not widely known and may be critical to long-term survival of implants. The actual polyethylene thickness of eight widely used tibial components was measured and found to vary significantly among manufacturers, even though the combined thickness of metal tray and polyethylene was similar. No component met current recommendations for minimum polyethylene thickness.

Biomechanical Phenomena↗
PubMed1981

Preferential solvent interactions between proteins and polyethylene glycols.

Preferential solvent interactions between polyethylene glycols and five proteins were investigated by density measurements and analyzed by the multicomponent theory. These measurements were conducted as a function of concentration and molecular size of the synthetic polymer at different pH values. The results showed that proteins are preferentially hydrated under the experimental conditions employed, i.e. polyethylene glycol is excluded from the protein domain. The introduction of protein thermodynamically destabilizes the solvent system. The magnitude of instability increases with increasing concentration of the polymer. Furthermore, systems of polyethylene glycols of higher molecular weight are more destabilized. A linear relationship was observed between the magnitude of destabilization and average hydrophobicity of the proteins employed with the exception of tubulin. The system is more destabilized in the presence of proteins with higher content of hydrophilic residues indicating that the interaction between polyethylene glycol and ionized residues is thermodynamically unfavorable with a negative ion being more so than a positive one. After correcting for the contribution of ionic effect on the instability of the system it was found that at least for a protein of average hydrophobicity of 1000 cal/residue the mass of the protein contributes to the instability also. It may, therefore, be concluded that in a polyethylene glycol system the presence of protein leads to unfavorable thermodynamic interaction which in turn leads to phase separation. The causes of such unfavorable interaction include the charges residing on the protein.

Animals↗
PubMed1980

A study of the use of polyethylene glycol in estimating cholesterol in high-density lipoprotein.

We studied polyethylene glycol 6000 precipitation of lipoproteins other than high-density lipoproteins, before cholesterol is estimated in the supernate. Other lipoproteins in the supernatant fractions were detected by using rocket immunoelectrophoresis. A polyethylene glycol concentration of 75 g/L in the final mixture appeared to be optimal, and results agreed with those obtained by ultracentrifugation. Differences in serum pH, use of polyethylene glycol from different suppliers, or the presence of ethylenediaminetetraacetate resulted in values that differed significantly (by 40 to 60 mumol/L) from the reference values. Polyethylene glycol did not interfere in four different methods for determination of cholesterol. In combination with an enzymic cholesterol method, the polyethylene glycol method appeared to be very precise, even when lipemic sera (triglycerides up to 5.5 mmol/L) were analyzed that had diminished high-density lipoprotein cholesterol values. We consider this method a method of choice, especially when lipemic sera are tested and enzymic cholesterol analysis is used.

Cholesterol↗
PubMed1995

The Otto Aufranc Award. Impact of gamma sterilization on clinical performance of polyethylene in the hip.

Despite studies to determine their causes, significant variations in polyethylene acetabular component wear rates, radial cracking of component rims, and occasional delamination cannot be explained. A subsurface white band frequently occurs in such damaged components. These damaged components often are gamma sterilized. To date, the origin of the band and its effect on polyethylene chemical and mechanical properties, and hence, clinical performance, have not been confirmed, and correlations between radiation sterilization and clinical wear have not been made. By developing techniques for polyethylene retrieval testing and rating, chemical analysis, and mechanical analysis, this research has determined that gamma sterilization in air alters the chemical and mechanical properties of polyethylene over time, resulting in high subsurface oxidation, reduced ductility, and reduced strength. Gamma sterilization-induced oxidation is found to be most severe in the subsurface region of components, and coincides with zones of significantly reduced strength and ductility. This chemical and mechanical property degradation is time dependent and is not typically visible until after 3 years' postirradiation. The presence of the subsurface white band significantly correlates with clinical cracking and delamination observed in retrieved components. Wear of the retrieved components often is observed to have progressed into this heavily oxidized, weakened, and embrittled zone. A method for accelerated aging shows that irradiating in air causes oxidation damage in polyethylene components that is not seen with other sterilization methods. Modifications of gamma sterilization techniques to minimize this damage are discussed.

Biomechanical Phenomena↗
PubMed1995

The origin of submicron polyethylene wear debris in total hip arthroplasty.

The microscopic morphology of worn polyethylene surfaces was compared with that of the associated polyethylene particles for acetabular cups tested in a wear simulator and for cups worn in vivo, using scanning electron microscopy. In the absence of significant third-body abrasive damage, the articulation of the ball in the cup produced a visually polished surface on the polyethylene. On a micron scale, the morphology of the worn polyethylene from in vitro and in vivo wear included nodules and fibrils consistent with adhesive, abrasive, and microfatigue wear mechanisms. Larger wear features, such as deep scratches or pits measuring in 10s of microns, that were seen in the in vivo cups were attributed to third-body wear. The polyethylene particles isolated from the serum lubricants of the wear tests and from the periprosthetic tissues were primarily submicron in size, were either rounded or elongated, and were consistent with the submicron wear features seen on the cup surfaces. It is the submicron particles that are associated with inflammatory periprosthetic bone loss in total hip replacement. Although the mean dimensions of the particles generated in vitro were slightly smaller than those of the in vivo particles, the overall morphologies were very comparable, suggesting that the same lubrication and wear processes were acting in the simulator as in vivo.

Foreign Bodies↗
PubMed1995

Titanium nitride ceramic film against polyethylene. A 48 million cycle wear test.

Wear is a major late complication of total joint arthroplasty, particularly for younger, active patients. Many patients could produce > 40 million motion cycles after joint replacement. Based on current experience and testing, typical joint prostheses are likely to wear out, and need revision in such patients. One problem is degradation of the metal (counterface) surface. A harder, more abrasion resistant, counterface surface is needed. This study evaluated the long-term wear of the titanium nitride ceramic film against ultra high molecular weight polyethylene. In this test, 4 47-mm femoral cups with a polished 8-micron-thick titanium nitride coating were run against 4-mm-thick metal-backed polyethylene bearings machined from GUR415 extruded rod in water at 37 degrees C at 5 Hz and a 2200-N fluctuating load. Wear of the counterface and bearing were extremely low. The average maximum reduction in thickness of the polyethylene was < 0.02 mm, and < 2 microns in the ceramic film. The average polyethylene wear rate was only approximately 2% of that found in a similar test using 32-mm cobalt chromium femoral heads. The titanium nitride-polyethylene couple has great potential as a lifetime bearing combination.

Alloys↗
PubMed1995

Stresses in polyethylene components of contemporary total knee replacements.

Contemporary knee designs differ considerably in the conformity that exists between the articulating surfaces of the femoral and tibial components. The thickness of the polyethylene components also varies from design to design. Conformity and thickness affect the stresses associated with surface damage and the subsequent generation of harmful polyethylene debris. In this study, the stresses and strains caused by contact were calculated for 8 contemporary knee prostheses. Finite element analysis using large-strain theory was used to determine the stresses and strains for the minimum available polyethylene thickness and for the knee in flexion. The greatest differences among designs was for the von Mises strain, which reached its maximum beneath the surface. The differences in stresses were less notable because of the nonlinear material behavior of the polyethylene. This study also confirmed the advantages of designs that have more conforming articulating surfaces and thicker polyethylene components.

Humans↗
PubMed1994

Polyethylene wear in unicompartmental knee arthroplasty.

From 1983 to 1989, 147 unicompartmental knee arthroplasties (UKA) were performed. Eighteen knees (13%) have required revision: there were 11 (37%) Porous Coated Anatomic (PCA), three (8%) Microloc, and four (17%) Fibermesh UKAs. Retrieved implants were examined to determine the pattern and extent of polyethylene wear. Wear was severe in each series and was characterized by delamination, pitting, peripheral cracking, deformation, and abrasion. Polyethylene failure appeared to result from large localized stresses resulting from lack of conformity of the articular geometries of the prostheses. Progressive subluxation of the implants occurred that produced very high localized contact stresses at the periphery of the tibial component where the polyethylene was thinnest. The progression of osteoarthritis in these knees, particularly the attenuation of the anterior cruciate ligament, increased the tendency of these incongruous implants to subluxate. Although changes in the design and manufacturing of unicompartmental knee arthroplasties may increase the resistance of these implants to polyethylene wear, the progression of osteoarthritis at an unpredictable rate is likely to be associated with persistent polyethylene wear in this type of arthroplasty.

Aged↗
PubMed1997

Acute polyethylene fracture in an uncemented acetabular cup.

The smaller acetabular components used in total hip replacement may have a polyethylene liner that is too thin, resulting in higher polyethylene stress and an increased potential for wear. The authors present a case that highlights the problem of acute polyethylene fracture. To compensate for the thinness of the polyethylene, the authors recommend the use of a smaller head size to allow polyethylene thickness of at least 8 mm.

Acetabulum↗
PubMed1990

Surface properties of copolymers of alkyl methacrylates with methoxy (polyethylene oxide) methacrylates and their application as protein-resistant coatings.

New polymeric surfactants, copolymers of alkyl methacrylates with methoxy (polyethylene oxide) methacrylates, were synthesized and characterized by gel permeation chromatography. They were studied as possible means to produce polyethylene oxide-rich surfaces by a simple coating treatment on common hydrophobic medical materials. They were further studied as cleaners for the removal of proteins preadsorbed on hydrophobic surfaces. The surface properties of the copolymers such as the adsorption properties of the copolymer on a hydrophobic surface, low density polyethylene, the protein-resistant character of the prepared polyethylene oxide surfaces and the effectiveness of the copolymers for removal of proteins pre-adsorbed on the surface, were investigated by X-ray photoelectron spectroscopy and by using 125I-labelled copolymers and 125I-labelled proteins. The surface properties of the synthesized copolymers were compared with those of commercially available polyethylene oxide containing block copolymer surfactants.

Adsorption↗
PubMed2002

Metal powder substrate-assisted laser desorption/ionization mass spectrometry for polyethylene analysis.

Polyethylene is one of the most important industrial polymers and is also one of the most challenging polymers to be characterized by mass spectrometry. We have developed a substrate-assisted laser desorption/ionization (LDI) mass spectrometric method for polyethylene analysis. In this method, cobalt, copper, nickel, or iron metal powders are used as a sample substrate and silver nitrate is used as the cationization reagent. Using a conventional UV LDI time-of-flight mass spectrometer, intact oligomer ions having masses up to 5000 u can be detected. Cobalt is found to produce spectra with the highest signal-to-noise ratio and the lowest level of fragmentation. Cobalt powder size is shown to have some effect on the spectra produced. The best results are obtained with the use of cobalt powders with diameters ranging from 30 to 100 microm. Fragmentation cannot be totally eliminated, but the fragment ion peaks can be readily discerned from the intact polyethylene ions in the substrate-assisted LDI spectrum. Thus, the average molecular masses of low-mass polyethylene samples can be determined by using this method. A rapid heating model is used to account for the effectiveness of using the coarse metal powders to assist the analysis of intact polyethylene molecules by LDI.

Journal Article↗
PubMed2005

Formation of high-stress phase and extrusion of polyethylene due to nanoconfinements during Ziegler-Natta polymerization inside nanochannels.

Polyethylene nanofibers were synthesized by heterogeneous Ziegler-Natta polymerization inside nanochannels of robust anodized aluminum oxide (AAO) membranes. The polymerization catalysts were chemisorbed at the inner wall of the nanochannels and monomers were provided through diffusion from the outside. Polyethylene is produced inside the nanochannels in the 10-20 mum region from the channel entrance. Polyethylene fibers were extruded from the nanochannels up to 3-5 mum during the polymerization. X-ray diffraction, differential scanning calorimetry, and Fourier transform infrared analyses indicated formation of a highly stressed crystalline structure although the polymerization was carried out without any external pressure or mechanical work. The highly stressed phase formation inside nanochannels and some degree of polyethylene nanofiber extrusion from nanochannels were attributed to catalytic production of excess amounts of polyethylene inside nanoconfined templates.

Journal Article↗
PubMed2005

NMR relaxation and pulsed-gradient diffusion study of polyethylene nanocomposites.

We performed pulsed-gradient spin-echo nuclear-magnetic-resonance (NMR) experiments on zinc oxide filled polyethylene. The molecular weights of the polyethylene samples ranged between 808 and 33,000 gmol, and four different zinc oxide samples were used: 27-, 33-, 51-, and 2500-nm-diameter particles. The results of these experiments showed that the diffusion coefficients of the polyethylene chains did not change with nanofiller content, but a drastic change is observed in the NMR relaxation spectrum in spin-spin-relaxation experiments. At fixed zinc oxide content and polyethylene molecular weight (close to entanglement), the system with the smallest zinc oxide showed the most rigid environment. At high polyethylene molecular weights, this effect was still observable but the difference between the three investigated systems was very small, suggesting that the system was dominated by entanglements.

Journal Article↗
PubMed2003

Increase in early polyethylene wear after sterilization with ethylene oxide: radiostereometric analyses of 201 total hips.

We evaluated polyethylene wear by measuring femoral head penetration in 201 THA (median age 62 (31-81) years, 117 women) extracted from 5 randomized studies aimed to assess various fixation principles. There were 30 cemented all-polyethylene Lubinus cups sterilized by gamma irradiation in a reduced oxygen environment, 65 porous-coated Trilogy cups with liners gamma-sterilized in inert gas. Moreover, 37 cemented cups were sterilized with ethylene oxide (Reflection all-poly) and 69 porous-coated cups had liners sterilized in ethylene oxide (Reflection). 28 mm femoral heads were used in all cups. The patients were followed with repeated radiostereometric measurements (RSA) up to 2 years. The activity level of the patients was evaluated by a questionnaire. After 2 years, cups with polyethylene sterilized in EtO had almost twice the proximal and 3D penetration rates, as compared with gamma-sterilized polyethylene. The penetration did not differ between the gamma-irradiated designs. Using stepwise linear regression analysis, we found that the type of sterilization, age and weight were the most important predictors and that they determined the direction of the proximal penetration rate. Activity score, male gender and proximal migration of the cup had little effect. The accelerated wear observed with the EtO-sterilized polyethylene causes concerns about long-term problems and especially in younger patients.

Adult↗
PubMed1993

Activation of Cytosolic Pyruvate Kinase by Polyethylene Glycol.

Homogeneous cytosolic pyruvate kinase from endosperm of germinating castor oil (Ricinus communis L. cv Hale) seeds was potently activated by polyethylene glycol. The addition of 5% (w/v) polyethylene glycol to the pyruvate kinase reaction mixture caused a 2.6-fold increase in maximal velocity and 12.5- and 2-fold reductions in Km values for phosphoenolpyruvate and ADP, respectively. Glycerol, ethylene glycol, and bovine serum albumin also enhanced pyruvate kinase activity, albeit to a lesser extent than polyethylene glycol. The addition of 5% (w/v) polyethylene glycol to the elution buffer during high-performance gel filtration chromatography of purified cytosolic pyruvate kinase helped to stabilize the active heterotetrameric native structure of the enzyme. A higher degree of inhibition by MgATP, but lower sensitivity to the inhibitors 3-phosphoglycerate and fructose- 1,6-bisphosphate, was also observed in the presence of 5% (w/v) polyethylene glycol. It is concluded that (a) plant cytosolic pyruvate kinase activity and regulation, like that of other regulatory pyruvate kinases, is modified by extreme dilution in the assay medium, probably as a result of deaggregation of the native tetrameric enzyme, and (b) ATP is probably the major metabolic effector of germinating castor endosperm cytosolic pyruvate kinase in vivo.

Journal Article↗