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At least 649 records · Page 36Linked to original sources
PubMed2001

Correlation of wear debris-induced osteolysis and revision with volumetric wear-rates of polyethylene: a survey of 8 reports in the literature.

This survey focused on clinical reports of polyethylene wear and osteolysis in total hip replacements. With regard to documentation of clinical wear-rates, 57 publications were reduced to an analysis of 8 reports of THR series, including the incidence of osteolysis. A direct correlation was found among volumetric wear-rates, incidence of osteolysis and revision rates in THR concepts of the 1983-1987 era. As volumetric wear rate increased, the incidence of osteolysis and revision rates increased. With regard to our grading system for volumetric wear, with follow-up in the 4-15 year range, osteolysis was rare in group A (wear = 0-80 mm3/year), ranging from 6% to 31% in group B (wear 40-80 mm3/year) and from 21% to 100% in group C (wear > 140 mm3/year). With regard to cup design, the optimal low-wear group had mainly cemented polyethylene cups with 22 and 28 mm head sizes. The mid-wear group B had metal-backed cemented and uncemented cups, with 28 mm head size, and the high-risk group C had only uncemented, metal-backed cups, with the highest wear in the 32 mm head size. Less than 10 years of follow-up did not distinguish adequately between different designs of THR, except in a few cases which had early failures due to material or design deficiencies. Overall, the cemented all-polyethylene cup combined with the smaller ball head proved to be better.

Bone Cements↗
PubMed1977

A theory for the displacement of proteins and viruses with polyethylene glycol.

The displacement action of polyethylene glycol of different molecular weights may be linked to the ability of the polymers to form coiled particles in solution. From conclusions drawn from their sedimentating properties in centrifugal fields the polyethylene glycols of low molecular weights, as expected, are less randomly coiled than those of higher molecular weight. It is suggested that protein molecules have the ability to diffuse into the coils of the polyethylene glycol from which they are excluded when the random coiling increases with increasing polymer concentration. From considerations based on the interaction of the polymer filament with the displaced particle the distribution of the substance between the coils and the intermolecular spaces may be predicted semi-quantitatively.

Chemical Phenomena↗
PubMed2006

Effect of tocopheryl polyethylene glycol succinate on the percutaneous penetration of minoxidil from water/ethanol/polyethylene glycol 400 solutions.

We described to achieve the local retention of minoxidil which has penetrated the skin with minimization of its absorption into the general circulation and elimination of local irritation induced by propylene glycol. The effect of tocopheryl polyethylene glycol succinate (TPGS) on the penetration flux of minoxidil and its retention in the skin from topical minoxidil formulations consisting of water, alcohol, and polyethylene glycol 400 was characterized by an experimental design of ten solvent formulations in this study. Results show that the addition of TPGS was only able to improve the solubility of minoxidil in those solvent systems containing higher proportions of water and PEG 400, and the extent of improvement was also more profound with the addition of TPGS at concentrations higher than 5%. For those solvent systems containing a higher fraction of alcohol, an insignificant change in minoxidil solubility with increasing added amounts of TPGS was noted even with the tendency to decrease the solubility of minoxidil with higher amounts of TPGS. Increasing the amount of TPGS added gradually increased the flux and the corrected flux from solvent formulations with a lower solubility parameter, but decreased those from solvent systems with a higher solubility parameter. With the addition of TPGS, solvent formulation F6 (alcohol:PEG 400 of 50:50) was demonstrated to be the optimal choice by having an improved local effect and a reduced systemic effect compared to the reference of 2% Regaine((R)). Tocopheryl polyethylene glycol succinate (TPGS) was mainly retained locally in the stratum corneum, and the amount was proportional to the increase in the amount of TPGS added to these ten solvent formulations.

Administration, Cutaneous↗
PubMed2006

Use of porous polyethylene as nasal dorsal implants in Asians.

BACKGROUND: A variety of implants have been used for nasal augmentation. A new implant made of porous polyethylene has recently been available. OBJECTIVE: To evaluate the stability (non-extrusion) of MEDPOR porous polyethylene as nasal dorsal implants in Asian patients. METHODS: Nineteen patients' charts were reviewed looking for implant displacement, extrusion of porous implants, postoperative bleeding and infection of tissues surrounding the implants in the postoperative follow-ups which range from 3 months to 5 years. RESULTS: No postoperative bleeding, infection, or displacement or extrusion of porous implants was noted. Explantation was easily performed in one patient. CONCLUSION: Porous polyethylene is stable as a nasal dorsal implant in Asians. Explantation can also be performed with ease if needed.

Adolescent↗
PubMed2005

All-polyethylene vs. metal-backed tibial component in total knee arthroplasty-a randomized RSA study comparing early fixation of horizontally and completely cemented tibial components: part 1. Horizontally cemented components: AP better fixated than MB.

BACKGROUND: Controversy still exists as to whether to mount the tibial bearing on a metal baseplate or not. Furthermore, the tibial component can be either horizontally or completely cemented. We evaluated metal backing versus all-polyethylene using horizontal cementing technique. PATIENTS AND METHODS: We randomized 40 patients with knee arthrosis (40 knees) to 2 groups: cemented total knee arthroplasty (AGC, Biomet) using either all-polyethylene (AP) or metal-backed (MB) tibial components (n = 20 for each group). All tibial implants had a total thickness of 8 mm. We used proximal cement-ing, including only the horizontal part of the tibia with avoidance of the stem-bone interface. RESULTS: The positioning of the implants, as judged by the HKA angle, showed an average neutral alignment in both groups. Preoperatively and after 2 years, there was no statistically significant difference between the HSS scores in both groups (p = 0.6 and 0.4). After 2 years, the metal-backed components had rotated more around the longitudinal axis, median 0.5 degrees vs. 0.2 degrees (internal or external rotation, p = 0.002), and showed increased maximum total point motion, median 1.0 vs. 0.4 mm (maximum migration or MTPM, p = 0.003). INTERPRETATION: Our study indicates that better fixation can be obtained with the all-polyethylene design if proximally cemented thin components are used.

Aged↗
PubMed1997

Reduction of polyethylene in a congruent meniscal knee prosthesis. Experimental and clinical studies.

Polyethylene wear was assessed in the Rotaglide congruent meniscal bearing total knee prosthesis and a partial congruent total knee prosthesis with fixed bearing polyethylene tibial platform and a posterior stabilizer mechanism. A special wear test rig was used to test the 2 prostheses under compression load of 2960 N/mm2 (about 4 times the average body weight) and continuous 0 degree-70 degrees flexion-extension motion at the rate of 1 cycle per second. The most remarkable finding was the lack of measurable wear on the Rotaglide meniscal bearing up to 3.5 million cycles, while the other prosthesis began to show wear from the first million cycles and progressed to 0.38 mm at about 3.5 million cycles. At 11 million cycles (about 20 years of life), the Rotaglide showed penetration wear of 0.35 mm compared to 2.1 mm in the other prosthesis. In 7 meniscal bearings, retrieved either at postmortem (2) or at reoperation (5), no measurable penetration wear was observed after 3 years of implantation. Only 1 prosthesis obtained 5 years after implantation showed 0.23 mm penetration wear or about 0.05 mm per year. These findings strongly suggest that the use of congruent meniscal bearing prosthesis can reduce the polyethylene wear in total knee replacement.

Arthroplasty, Replacement, Knee↗
PubMed1995

The evaluation of nylon and polyethylene as build-up material in a neutron therapy beam.

In high-energy neutron beams a substantial amount of build-up material is required to irradiate biological samples under conditions of charged particle equilibrium. Ideally A-150 tissue-equivalent plastic is used for this purpose. This material is however not always readily available and hence the need for a substitute compound. The selected hydrocarbon should satisfy two requirements: the quality of the radiation on the distal side needs to be the same as that measured for A-150 plastic and the absorbed dose should remain consistent. A tissue-equivalent proportional counter operating at reduced pressure not only measures the absorbed dose accurately but provides a means for assessing the nature of a radiation field in terms of a secondary charged particle spectrum. Using build-up caps manufactured from nylon (type 6) and polyethylene, it is shown that the former is an acceptable substitute for A-150 plastic. The data further demonstrate that both the absorbed dose and the spectral character of the measured single-event distribution are altered when polyethylene is used and that these discrepancies are attributable to the higher hydrogen content of polyethylene.

Humans↗
PubMed1998

Ultrasound covers and sonographic gels are embryo-toxic and could be replaced by non-toxic polyethylene bags and paraffin oil.

The objective of this study was to test the hypothesis that ultrasound covers and sonographic gels, used during vaginal ultrasound, are toxic for mouse embryonic development in vitro. A prospective randomized design was used on pronucleate ova of F1 hybrid CBA x C57Bl female mice. The mice were superovulated with pregnant mare's serum gonadotrophin and human chorionic gonadotrophin and mated with CBA x C57Bl males. The pronucleate ova were randomly divided between culture media with the addition of commercially available ultrasound covers and sonographic gels in different concentrations. As controls and potential alternatives, plastic polyethylene bags and paraffin oil were tested simultaneously. Embryo-toxicity was assessed by documenting cleavage capacity, blastocyst formation and embryo degeneration in vitro. Exposure of culture medium to the ultrasound covers and sonographic gels tested resulted in a severely reduced cleavage capacity, a high incidence of embryo degeneration and absent or impaired blastocyst formation. This toxic effect could be reduced by high dilutions in vitro. In contrast, plastic polyethylene bags and paraffin oil had no influence on in-vitro development of mouse ova. We conclude that commercially available ultrasound latex covers and sonographic gels are toxic for mouse embryos and can potentially influence embryonic development during infertility treatment. It is safer to perform vaginal ultrasonic measurements using non-toxic paraffin oil (as contact fluid) and plastic polyethylene bags (as ultrasonic cover).

Animals↗
PubMed2004

Polyethylene barrier impregnated with lambda-cyhalothrin for exclusion of subterranean termites (Isoptera: Rhinotermitidae) from structures.

Polyethylene film impregnated with lambda-cyhalothrin was placed over a sand plot and covered with a concrete slab to allow insecticide movement into the sand for a period of 5.5 yr. Discs of polyethylene film and sand beneath them were sampled annually for 5 yr and at 5.5 yr for bioassay with the Formosan and eastern subterranean termite. Results demonstrated that sufficient quantities of lambda-cyhalothrin were released from the impregnated polyethylene film into adjacent sand to prevent termite penetration. The impregnated film has less environmental impact than conventional liquid termiticides because the insecticide is held in the polymer. Other advantages include its dual function as a construction moisture barrier and ease in verifying its proper installation.

Animals↗
PubMed2004

Craniofacial reconstruction with high-density porous polyethylene implants.

Deformities of the facial skeleton may be reconstructed using autogenic or allogenic materials. Porous polyethylene is one of the few alloplastic materials currently in use having a well-documented history of reconstruction or augmentation in the maxillofacial region. High-density porous polyethylene, which is shown to be effective as a biomaterial, has additional advantages like tissue ingrowth, no capsule formation around it, and easy fixation. In this study, 83 implants in 71 patients were evaluated. Seven patients were in need of a second intervention. Three of the seven secondary interventions were for contour alignment, and four interventions were for extraction of the implants because of extrusion or infection. Placement of porous polyethylene implants directly under the skin without coverage of periosteum or another fascial envelope has an increased risk of early and especially late exposure. In cases like nasal dorsum or microtia reconstruction, we prefer autogenic grafts instead of allogenic materials.

Biocompatible Materials↗
PubMed1994

Animal model of porous polyethylene orbital implants.

Ophthalmologists continue to search for the ideal orbital implant for the anophthalmic socket. The successful long-term clinical performance of an implantable prosthesis is highly dependent on the materials from which the device is fabricated. Among the materials issues are chemistry, surface texture, and porosity. Polyethylene, a polymer comprised of simple hydrocarbon chains, is highly resistant to biological degradation and possesses mass and fabrication properties that would be favorable in an orbital implant. In this report, our early experimental experience with porous polyethylene orbital enucleation implants is reported. Our findings are sufficiently encouraging to warrant further exploration and refinement of the polyethylene device examined.

Animals↗
PubMed1998

Extrusion of porous polyethylene orbital implant in recurrent retinoblastoma.

High-density porous polyethylene allografts are used as orbital implants in reconstruction of anophthalmic sockets. The use of this material for integrated buried implants is rather new, and studies on removed implants from humans are limited. We studied the case of a 6-year-old boy with an extruded porous polyethylene implant due to orbital recurrence of retinoblastoma. The clinical and morphological features are reported. Histopathology revealed fibrovascular downgrowth in the outer two thirds of the sphere. Scanning electron microscopy, however, documented further downgrowth of fibrous tissue into the central core. Transmission electron microscopy depicted a spectrum of collagen fiber orientations to polyethylene material, ranging from perpendicular to concentric. Immunohistochemistry studies were inconclusive.

Child↗
PubMed1998

Infection of a porous polyethylene orbital implant with Capnocytophaga.

A 68-year-old woman experienced an infection of a porous polyethylene orbital implant caused by Capnocytophaga after a dental procedure. The infection was unresponsive to both topical and oral antibiotics and required removal of the porous polyethylene orbital implant. Capnocytophaga is a capnophilic, gram-negative bacillus. Capnocytophaga is a normal commensal of the mouth and is responsible for both gingivitis and periodontal disease. Capnocytophaga is a rare cause of ocular infections. This is the first reported patient with an infection of a porous polyethylene orbital implant caused by Capnocytophaga. The authors believe infected integrated orbital implants must be removed because neither topical or systemic therapy provide effective treatment.

Aged↗
PubMed2000

Epidermal and fibroblast growth factors enhance fibrovascular integration of porous polyethylene implants.

PURPOSE: Porous implants used in functional and aesthetic reconstruction of the orbit, face, and cranium are less likely to develop complications after they become biointegrated. We investigated whether the administration of exogenous growth factors could increase the rate of implant integration. METHODS: High-density porous polyethylene cubes were placed in dorsal paraspinal muscles of rabbits, and daily transcutaneous injections of saline, epidermal growth factor, or basic fibroblast growth factor were administered directly over the cubes for 10 days. At serial time points up to 10 weeks, cubes were explanted and the fibroblasts present at the center of the cubes were counted. RESULTS: Injections of epidermal growth factor and basic fibroblast growth factor increased the rate at which fibroblasts accumulated in porous polyethylene implants and decreased the time required to achieve a maximal rate of cellular accumulation within the cubes. At 4 weeks, when all cell populations had attained a linear rate of accumulation, cubes previously injected with saline, epidermal growth factor, or basic fibroblast growth factor contained an average of 10, 40, and 80 cells per 0.0156 mm2, at their centers, respectively. CONCLUSIONS: Enhancement of the rate of biointegration of porous polyethylene cubes in rabbits is achievable by repeated, transcutaneous administration of exogenous growth factors.

Animals↗
PubMed2001

Wear-through of a modular polyethylene liner: four case reports.

Four patients in whom the S-ROM Total Hip System Polydial polyethylene liner was used illustrate the importance of, and difficulties in, detecting polyethylene wear-through before a complete acetabular revision is necessary. The patients in these cases had full thickness polyethylene wear-through 11 or more years after total hip arthroplasties. Dorr and Livermore wear measurements from radiographs of the patients underestimated the actual wear and did not indicate wear-through. Because excessive head penetration was not evident radiographically with the S-ROM components, the cases showed the necessity of using additional measures to diagnose wear-through, particularly with these components. Repeat radiographs at a higher kilovoltage were used to better visualize the outline of the femoral head, and hip aspiration was used to diagnose metallosis. These cases also showed the importance of yearly followup evaluations, especially 10 or more years after surgery for patients with the S-ROM Polydial locking mechanism.

Adult↗
PubMed2001

Effect of femoral component offset on polyethylene wear in total hip arthroplasty.

Seventeen staged, bilateral total hip arthroplasties performed in 17 patients were reviewed to compare side-to-side polyethylene wear. Implants used on both sides were similar except for implant offset: one hip in each patient was replaced using a femoral component having a standard implant offset, whereas the other side had a lateral offset implant. The mean followup was 5.70 years (range, 2-10.2 years) on the side with a standard femoral implant and 5.67 years (range, 2-9.7 years) on the side with a lateralized femoral component. The only statistically different parameter between the sides was the femoral component offset. All other parameters affecting polyethylene wear, such as period of followup, head size, head type, cup size, cup inclination, medialization of cup, and patient-related factors were similar on both sides. On the side with a standard femoral component, the mean actual prosthetic offset (determined by manufacturer's specifications) was 35.2 mm and the radiologic offset was 31.5 mm. On the side with a lateralized femoral component, the actual prosthetic offset was 42.5 mm and the radiologic offset was 40.1 mm. The difference in offsets between the sides was statistically significant. The mean preoperative offset of the femur was 38.8 mm. Regression analysis revealed that only femoral component offset and cup size correlated significantly with linear wear rate. On the side with a standard femoral component, the linear wear rate was 0.21 mm per year, whereas on the side with a lateralized femoral component, the linear wear rate was 0.10 mm per year. The differences in the linear wear rates were significant. Lateralization of the femoral component in this series more closely restored preoperative hip biomechanics and significantly decreased polyethylene wear.

Adult↗
PubMed2002

Analysis of polyethylene particles produced in different wear conditions in vitro.

The production of ultrahigh molecular weight polyethylene wear particles is a major factor limiting the life of prosthetic joints. The aim of the current study was to determine whether the morphologic features and size distribution of polyethylene particles produced in wear tests were in agreement with clinical findings. Particles from two hip simulators, a pin-on-disk hip wear device and a knee wear simulator, were studied and compared with particles found from synovial fluid of a prosthetic hip, and with published findings on clinical wear particles. Scanning electron microscopy and digital image analysis were used for characterization and sizing. The average equivalent circle diameter ranged from 0.27 microm to 0.69 microm, which corresponded well with published clinical findings. Common to all wear tests was that the lubricant contained albumin or globulin, and that the relative motion was multidirectional. In the hip wear simulation, the particle size distribution was not sensitive to the type of loading, counterface material, protein content of the lubricant, and whether the polyethylene was irradiated. In the knee wear simulation, the debris on average was larger than in the hip wear simulation. The simulators produced wear particles similar to those seen clinically, which indicates that the current test methods are relevant for assessing wear of prosthetic joints.

Hip Prosthesis↗
PubMed2002

Effects of metal-inlay thickness in polyethylene cups with metal-on-metal bearings.

A way to prevent polyethylene wear in total hip replacements is to use metal-on-metal bearings. The cup design of these bearings may be a metal inlay in a polyethylene cup. However, these metal inlays are relatively thin and may deform on loading. The purpose of the current study was to determine whether these potential problems become actual for a realistic range of metal-inlay components having a thickness greater than 1 mm. For this purpose, the effects of thickness variation of a metal inlay in an ultrahigh molecular weight polyethylene cup were determined using three-dimensional finite element techniques. The results showed no indications for jamming of the bearing assuming a realistic inlay thickness (3-5 mm), even with a small clearance (25 microm). The metal inlay acted rigidly beyond a thickness of approximately 5 mm. Metal inlays thinner than 1.5 mm led to a considerable increase in contact area and a reduction in contact peak stress, which may be beneficial for the bearing performance. Currently, these thin liners have too many unknown characteristics and therefore the current authors recommend using rigid metal liners that have a thickness greater than 5 mm.

Biomechanical Phenomena↗