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At least 451 records · Page 25Linked to original sources
PubMed2002

The quasi-integrated porous polyethylene orbital implant.

PURPOSE: To describe a new quasi-integrated porous polyethylene orbital implant that combines the advantages of host tissue incorporation and improved motility with a single-stage surgery. METHODS: Twenty-four consecutive patients undergoing primary or secondary orbital implantation received the quasi-integrated porous polyethylene implant. Approximately 6 weeks after implantation, a custom-fitted prosthesis was made by an impression technique to provide a "lock-and-key" fit with the orbital implant. Postoperative complications and motility of the prosthetic shell were evaluated. RESULTS: During the 27-month period between December 1998 and March 2001, 24 patients received the quasi-integrated porous polyethylene implant as a buried orbital implant. Thirteen patients received the implant as a primary orbital implant after either evisceration or enucleation and 11 patients received the implant as a secondary orbital implant. Follow-up ranged from 3 months to 30 months, with an average of 16.9 months. All patients were considered to have good motility of their prosthetic shell at their final follow-up visit. No cases of implant extrusion or migration were noted. Two patients required deepening of their inferior fornix to accommodate the increased motility of their prosthesis. CONCLUSIONS: The new quasi-integrated porous polyethylene orbital implant provides improved motility without the need for secondary placement of pegs or screws. It has the advantage of biocompatibility, allowing host tissue incorporation to resist implant migration and extrusion. The implant is available in three sizes: small, medium, and large, approximating the volume of a 16-, 18-, and 20-millimeter sphere, respectively.

Adolescent↗
PubMed1996

Metal versus polyethylene wear particles in total hip replacements. A review.

Research has recently been focused on the development of hip replacements with alternative bearing surfaces with cobalt chrome alloy, to avoid the production of polyethylene wear particles in hip replacements and polyethylene wear debris mediated bone lysis. Cobalt chrome on cobalt chrome bearing surfaces are being reevaluated. Characterization of wear particles and studies on the reaction of the body to these particles, have played an important role in the determination of the factors that cause aseptic loosening and will therefore play an important role in the comparison of metal on polyethylene and metal on metal hip prostheses. In this paper, a comparison between the different aspects of metal and polyethylene wear particles is made using data from the literature and the authors' experience. The authors conclude that techniques need to be optimized to isolate and characterize individual metal wear particles from periprosthetic tissues and they advocate the performance of in vitro studies with these in vivo generated wear particles or comparable particles.

Corrosion↗
PubMed1999

Polyethylene particle morphology in synovial fluid of failed knee arthroplasty.

Synovial fluid from the knees of 16 patients undergoing revision knee arthroplasty for aseptic failure was subjected to base digestion and ultrafiltration. Filtered particles were scanned using scanning electron microscopy and analyzed with an image program. Polyethylene particles were identified visually and confirmed with the use of electron diffraction spectroscopy. Averaging more than 1500 particles per patient sample, 25,148 particles were analyzed. This corresponded to a concentration of 3000 polyethylene particles per milliliter of synovial fluid. Three populations of wear debris were identified in the fluid. Small globular particles with a mean area of 75 mu 2 represented 94% of all particles observed. The particles averaged 10 mu in diameter and often were seen in clumps. Long fibrous particles with a mean area of 1164 mu 2 made up 4% of the particle population. Large rhomboidal particles with an area of 557 mu 2 were observed least commonly and comprised the remainder of the particles visualized. All three particle types were observed in each fluid sample regardless of the wear pattern of the retrieved polyethylene liner. There were no differences in absolute particle counts, particle morphologic characteristics, or particle size between patients with and without gross polyethylene wear.

Aged↗
PubMed1999

Two-dimensional versus three-dimensional radiographic measurements of polyethylene wear.

Because polyethylene wear adversely affects the outcome of total hip arthroplasty, reliable techniques for in vivo radiographic evaluation of femoral head penetration into the polyethylene liner are needed. With the recent development of software to measure three-dimensional femoral head penetration, the adequacy of two-dimensional head penetration measurements to estimate a three-dimensional process has been questioned. Thus, the purpose of the current study was to compare directly two-dimensional and three-dimensional radiographic measurements of femoral head penetration. Using two computer assisted radiographic techniques, the authors of this study measured the two-dimensional and the three-dimensional penetration of the femoral head into the polyethylene liner in 202 hips implanted with porous coated acetabular components. A comparison of two-dimensional and three-dimensional measurements showed that, on average, the mean amount of three-dimensional head penetration was larger than the mean amount of two-dimensional head penetration. However, linear regression analysis showed that the two measurements were highly correlated (r2 = 0.87, slope = 0.99, intercept = 0.08 mm). For most patients (95%), two-dimensional and three-dimensional measurements of femoral head penetration were nearly equal. However, there was a small subset of patients (5%) for whom three-dimensional radiographic penetration measurements were three times greater than corresponding two-dimensional radiographic penetration measurements. No common risk factor among this small subset of patients was identified. The current study provides practical information for the orthopaedic surgeon trying to assess polyethylene wear in hip replacement cases. It shows that for most patients head penetration can be measured sufficiently from anteroposterior radiographs alone. However, in a small percentage of patients (5% in the current study) the femoral head also moves perpendicular to the plane of the anteroposterior radiograph. For these cases, accurate analysis of head penetration requires three-dimensional analysis using anteroposterior and lateral radiographs.

Acetabulum↗
PubMed2001

Total knee arthroplasty with 4.4 mm of tibial polyethylene: 10-year followup.

A consecutive series of 387, one-piece, 8-mm tibial components were implanted in 313 patients. All tibial prostheses were manufactured with 4.4 mm of polyethylene directly molded to a 3.6 mm cobalt chrome metal baseplate. The average age of the patients at surgery was 70.6 years. From this group, a subset of 116 patients underwent bilateral total knee arthroplasties with an 8-mm tibial component on one side and at least a 10-mm thick tibial component (at least 6.4 mm of polyethylene) on the other side. The followup averaged 10.7 years. Postoperative knee and pain scores average 81.4 points and 47.2 points, respectively. No radiographic polyethylene wear or osteolytic lesions were identified. Tibial radiolucencies were observed in four knees. There were nine failures (2.3%). Three knees were revised for infection. Five knees were revised for metallosis secondary to failure of metal-backed patellas. No loose tibial components were identified. Defining failure as revision for any reason or loosening of any component, Kaplan-Meier survival rates at 5, 10, and 15 years were 98.7%, 95.4%, and 94.3%, respectively. There was no significant difference in clinical scores or survival rates between the knee components with thicker (at least 6.4 mm) or thinner (4.4 mm) polyethylene.

Adult↗
PubMed2001

Debris from failed ceramic-on-ceramic and ceramic-on-polyethylene hip prostheses.

To compare the properties of wear debris between ceramic-on-ceramic and ceramic-on-polyethylene total hip prostheses, particles were isolated and characterized from tissue biopsies obtained at revision arthroplasty or autopsy from two similar uncemented modular hip systems. Group A hips (11 patients; mean, 31 months in vivo) had titanium shells with alumina inserts, alumina femoral heads, and titanium alloy stems. Group B hips (seven patients; mean, 42 months) were the same as Group A but with polyethylene acetabular inserts. Particles were characterized using an electrical resistance particle analyzer, scanning electron microscope, and energy dispersive xray spectroscope. Most of the particles in Group A were ceramic, whereas most of the particles in Group B were polyethylene. Metal particles from the femoral stem and the acetabular shell also were present. If one Group A hip with impingement is excluded, the rate of particle production is significantly lower in the ceramic-on-ceramic group than in the ceramic-on-polyethylene group. With the number of samples available, no significant difference in average size could be detected among the different types of particles or among the groups.

Ceramics↗
PubMed2001

Metal-backed and all-polyethylene tibial components in total knee replacement.

One hundred seventy-five patients with 243 consecutive primary Press Fit Condylar cruciate-substituting total knee replacements were evaluated at a mean of 5.5 years. One hundred thirteen knees had modular metal-backed tibial components and 130 had all-polyethylene tibial components. The mean knee score and functional score for the patients with unrevised components was not significantly different. The incidence of osteolysis and synovitis was higher in patients in the modular metal-backed tibia group (5%; five patients, six knees). No patients in the all-polyethylene tibia group had osteolysis or synovitis. Five revision operations were necessary: four for osteolytic defects and one for synovitis, all in patients in the modular metal-backed tibia group. All of the retrieved polyethylene inserts had evident backside wear. The best case rate of survival of the all-polyethylene tibial components was 96%+/-0.8% at 7 years and for the modular metal-backed components it was 75%+/-10% at 7 years. Metal backing and modularity were added to the Press Fit Condylar total knee replacement design to improve fixation durability. However, the superiority of the modular metal-backed implants remains in question.

Adolescent↗
PubMed2001

Polyethylene damage and knee kinematics after total knee arthroplasty.

This study characterizes the relationship between in vivo knee kinematics and polyethylene damage by combining fluoroscopic analysis of tibiofemoral contact during dynamic activities and implant retrieval analysis in the same patients. Six patients (eight knees) underwent posterior cruciate ligament-retaining total knee arthroplasty. All patients participated in fluoroscopic analysis during a stair-rise and descent activity and treadmill gait an average of 18 months after arthroplasty, and articular contact was measured. Subsequently, all polyethylene tibial inserts were retrieved after an average of 26 months in vivo function: three at autopsy and five at revision. There was a statistically significant correlation between the damage location on the retrieved inserts and the articular contact location measured fluoroscopically during the activities. The femoral contact and polyethylene damage occurred predominantly on the posterior half of the tibial articular surface, and the damage pattern was largest in the compartment with the greatest range of in vivo femoral contact for each patient. This study showed that in vivo fluoroscopic analysis can predict the damage location on the polyethylene articular surface.

Aged↗
PubMed2001

Direct compression molded polyethylene for total hip and knee replacements.

Direct compression molded polyethylene is a process of creating a net-shaped component with finished articular surfaces from ultrahigh molecular weight polyethylene by applying heat and pressure to the raw resin (usually Hi-fax 1900) with the use of fixed geometry metallic tools. The final product has no machining or finishing. Sterilization was by gamma radiation in air. Between 1974 and 1978, there were 378 cemented T-28 stems (321 patients) and 171 cemented TR-28 stems (158 patients) articulating with a cemented direct compression molded acetabular component. Radiographically, linear wear was 0.06 mm per year for the T-28 stem and 0.05 mm for the TR-28 stems. The revision rates for the acetabulum were 9.5% and 7.9%, respectively with only two acetabula having osteolysis. On the femoral side, the revision rates were 11.1% and 12.8%, with 11 cases and one case of osteolysis, respectively. Between 1983 and 1996, 4583 AGC cemented total knee replacements were done with direct compression molded nonmodular tibial components. There was no osteolysis seen in these nonmodular compression molded total knee replacements even with 0.1% failure of the femoral components and 0.4% failure of the tibial components. Failure of all of the hip and knee implants was because of poor cement technique, instability, or both. Wear and osteolysis were minimal. Direct compression molded polyethylene has stood the test of time and is a good choice among the currently available polyethylenes.

Adult↗
PubMed1994

Neutron attenuation characteristics of polyethylene, polyvinyl chloride, and heavy aggregate concrete and mortars.

Polyethylene and polyvinyl chloride pellets were introduced into concrete to improve its neutron attenuation characteristics while several types of heavy coarse aggregates were used to improve its gamma ray attenuation properties. Neutron and gamma ray attenuation were studied in concrete samples containing coarse aggregates of barite, pyrite, basalt, hematite, and marble as well as polyethylene and polyvinyl chloride pellets in narrow-beam geometry. The highest neutron attenuation was shown by polyethylene mortar, followed by polyvinyl chloride mortar; barite and pyrite concrete showed higher gamma ray attenuation than ordinary concrete. Broad-beam and continuous (infinite) medium geometries were used to study the neutron attenuation of samples containing polymers at different concentrations with and without heavy aggregates, the fitting equations were established, and from these the neutron removal coefficients were deduced. In a radiation field of neutrons and gamma rays, the appropriate concentration of polymer and heavy aggregate can be selected to give the optimum total dose attenuation depending on the relative intensities of each type of radiation. This would give much better design flexibility over ordinary concrete. The compressive strength tests performed on mortar and concrete samples showed that their value, in general, decreases as polymer concentration increases and that the polyvinyl chloride mortar showed higher values than the polyethylene mortar. For general construction purposes, the compression strength was considered acceptable in these samples.

Construction Materials↗
PubMed1989

Comparison of the D-xylose and polyethylene glycol absorption tests as indicators of mucosal damage in infants with chronic diarrhea.

The determination of serum levels of D-xylose and the urinary excretion of an orally administered mixture of low-molecular-weight polyethylene glycol were compared to assess their sensitivity to predict small-bowel mucosal damage. Eighteen infants with severe diarrhea and villus atrophy were observed. Results of the D-xylose and polyethylene glycol tests were compared with the villus-to-crypt ratios that were determined from biopsy specimens. The D-xylose test predicted accurately 12 (67%) of the 18 small-bowel biopsy results, while the polyethylene glycol test predicted 14 (78%). However, the McNemar test indicated that the two tests did not differ significantly in their ability to predict an abnormal small-bowel biopsy. We conclude that neither the D-xylose nor the polyethylene glycol test is a reliable indicator of small intestinal mucosal damage in infants with chronic diarrhea.

Atrophy↗
PubMed2003

Metal-on-metal versus polyethylene in hip arthroplasty: a randomized clinical trial.

A prospective, randomized, blinded clinical trial was done to evaluate polyethylene versus metal bearing surfaces in total hip replacement. Forty-one patients were randomized to receive either a metal (23 patients) or a polyethylene (18 patients) insert. The femoral and acetabular components were identical with the acetabular insert the only variable. Patients were assessed preoperatively and postoperatively using radiographs, multiple outcome measures (Western Ontario MacMaster University Score, Harris hip score, Short Form-12), erythrocyte metal ion analysis (cobalt, chromium, titanium), and urine metal ion analysis (cobalt, chromium, titanium). Patients were followed up for a minimum of 2 years (mean 3.2 years; range, 2.2-3.9 years). There were no differences in radiographic outcomes or outcome measurement tools between patients. Patients receiving a metal-on-metal articulation had significantly elevated erythrocyte and urine metal ions compared with patients receiving a polyethylene insert. Patients who had metal-on-metal inserts had on average a 7.9-fold increase in erythrocyte cobalt, a 2.3-fold increase in erythrocyte chromium, a 1.7-fold increase in erythrocyte titanium, a 35.1-fold increase in urine cobalt, a 17.4-fold increase in urine chromium, and a 2.6-fold increase in urine titanium at 2 years followup. Patients receiving a polyethylene insert had no change in erythrocyte titanium, urine cobalt, or urine chromium and a 1.5-fold increase in erythrocyte cobalt, a 2.2-fold increase in erythrocyte chromium, and a 4.2-fold increase in urine titanium. Forty-one percent of patients receiving metal-on-metal articulations had increasing metal ion levels at the latest followup.

Arthroplasty, Replacement, Hip↗
PubMed2003

Polyethylene damage on the nonarticular surface of modular total knee prostheses.

Modular tibial implants submitted for retrieval analysis were examined for evidence of cold flow, wear, or polyethylene failure. All retrieved components showed areas of cold flow and wear. Significant damage, defined as pitting, gouging, or delamination was observed in 77% of the retrieved implants. Cold flow deformation commonly was observed at the junction of the polyethylene and locking mechanisms or junction of the polyethylene and the edge of the tibial tray. Control implants did not show such areas of damage. Clinical factors such as age, activity status, length of implantation, limb alignment before revision, and thickness of the tibial insert did not correlate with backside wear. No association was found between polyethylene thickness, time of implantation, limb or prosthesis alignment, or activity status or weight of the patient.

Adult↗
PubMed2005

Ex vivo wear of conventional and cross-linked polyethylene acetabular liners.

Explanted highly cross-linked polyethylene acetabular liners show third-body scratching. It was suggested that this surface damage could increase the wear rate of highly cross-linked polyethylene. We investigated the wear behavior of surgically explanted highly cross-linked and conventional acetabular liners using a hip simulator. Highly cross-linked explants showed no weight loss. The scratches and original machine marks of the highly cross-linked liners present at explantation remained during testing; the wear rates of these liners were 1.1 +/- 2.3 mg/million cycles, representing weight gain. In contrast, conventional liners showed wear rates of -12.9 +/- 1.4 mg/million cycles, representing weight loss. Wear was associated with rapid surface polishing and scratch elimination. After testing, the liners were melted to trigger shape memory and recover plastic deformation-induced surface changes. Highly cross-linked liners showed substantial recovery of original machining marks after melting, indicating that the scratches were a result of plastic deformation and not wear. None of the conventional polyethylenes showed any recovery after melting. The wear resistance of the highly cross-linked polyethylene studied was not compromised by surface changes that occurred during the first year of in vivo service.

Acetabulum↗
PubMed2005

Arthroplasty options for the young patient: Oxinium on cross-linked polyethylene.

Our purpose was to determine whether metal femoral heads scratch with in vivo use, to characterize the scratching that occurs, and to determine whether this scratching affected polyethylene wear. Assessment of 133 consecutive retrieved femoral heads showed that metal femoral heads do scratch with in vivo use, that cobalt-chromium femoral heads are more scratch resistant than titanium alloy heads, and that scratching seems to be time dependent. Profilmetry studies showed that all roughness parameters (average roughness, maximum peak to lowest valley distance, mean peak height above the mean surface line, estimate of small peaks above the main plateau of the surface, and estimate of the depth of the valleys below the mean plateau of the surface with the exception of the symmetry of the profile about its mean line) showed increased roughness with time of use. Cobalt-chromium and Oxinium femoral heads were damaged in a dislocation model. Assessment of these femoral heads in a wear simulator revealed that against conventional polyethylene, a damaged Oxinium femoral head had no more wear than a new cobalt-chromium articulation on the same polyethylene (36.5/million cycles versus 38.4 mm/million). Against cross-linked polyethylene, a damaged Oxinium femoral head had minimal wear (1.5 mm cubed per Mc).

Adult↗
PubMed2003

Comparison of synthetic hydroxyapatite and porous polyethylene implants in eviscerated rabbit eyes.

PURPOSE: Synthetic hydroxyapatite and porous polyethylene (Polipore) spheres were placed in rabbits' eviscerated cavities to evaluate tissue reaction and volume maintenance. METHODS: Fifty-six Norfolk albino rabbits underwent unilateral evisceration and implantation of synthetic hydroxyapatite (H group, 28 animals) or porous polyethylene spheres (P group, 28 animals). Postoperative reactions, animal behavior, and socket conditions were monitored. Light microscopy and morphometric evaluation with statistical analysis of the exenterated orbits were performed at 7, 15, 30, 60, 90, 120, and 180 days. Scanning electron microscopy was appraised 7, 60, and 180 days after surgery. RESULTS: Two animals from the H group and 1 from the P group had extrusion 7 days after surgery. Throughout the experimental period, the synthetic hydroxyapatite caused more inflammation than the porous polyethylene material. Ingrowth in the sphere occurred 7 to 15 days after the surgery in both groups, and the tissue reaction became denser at approximately 60 to 90 days, when bony metaplasia began in the H group. Volume maintenance was better in the P group and with a smaller pseudocapsule surrounding the implanted sphere than in the H group. CONCLUSIONS: Clinical findings demonstrated mild inflammation inside the sphere and in the pseudocapsule surrounding it and better cavity volume maintenance in the P group animals. The authors consider porous polyethylene a more suitable material than synthetic hydroxyapatite for use in anophthalmic cavity reconstruction.

Animals↗
PubMed1982

Material thrombogenicity in central venous catheterization. I. A comparison between uncoated and heparin-coated, long antebrachial, polyethylene catheters.

In order to evaluate a new method of heparinization, uncoated (22) and heparin-coated (27) central venous polyethylene catheters were inserted in 49 patients via basilic and cephalic veins punctured at the fossa cubiti. The means duration of catheterization was 5.7 (1-11) days. One-third of the patients with heparin-coated catheters, and one sixth with uncoated catheters developed clinical thrombophlebitis, with a maximum incidence between 4 and 8 days after catheterization. A higher risk of developing thrombophlebitis in the first 4 days after catheterization was found in the patients with heparin-coated polyethylene catheters. After 8 days of catheterization, it seems that there is a lower risk of new cases of thrombophlebitis appearing both in patients with uncoated and those with heparin-coated polyethylene catheters. Radiological thrombosis, regardless of duration of catheterization and heparin-coating, was demonstrated in all 22 patients investigated by "pull-out" phlebography. The heparin-coating did not decrease the rate of thrombotic complications. Location of the catheter tip in subclavian veins was associated with a significantly higher incidence of large, parietal thrombi and catheter occlusion than when the tip was situated in anonymous veins, the superior vena cava, or the right atrium. Cannulation by heparin-coated, polyethylene tubing did not reduce the rate of catheter occlusion.

Adolescent↗
PubMed2005

Photoelectric dye-coupled polyethylene film as a prototype of retinal prostheses.

Photoelectric dyes, which absorb light and convert photon energy to electric potentials, have been previously shown to stimulate retinal neurons in culture. In this study, a photoelectric dye was coupled to a polyethylene film surface and tested in vitro using retinal tissues from chick embryos at the 12-day embryonic stage, at which time outer segments of retinal photoreceptor cells have not yet developed. Carboxyl moieties were introduced to a polyethylene film surface by fuming nitric acid, and then a photoelectric dye, 2-[2-[4-(dibutylamino)phenyl]ethenyl]-3-carboxymethylbenzothiazolium bromide, was coupled to the film through amide linkage. Intracellular calcium elevation was observed with Fluo-4 in retinal tissues placed on the dye-coupled polyethylene film, in contrast to retinal tissues which had no contact with the film. The response was inhibited by calcicludine, a voltage-gated calcium channel blocker, and also by extracellular calcium depletion. The photoelectric dye, coupled to the polyethylene film surface, absorbed light under a dissecting microscope and stimulated neurons in retinal tissues, showing that the dye-coupled film could be used as a prototype of retinal prostheses.

Aniline Compounds↗