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At least 721 records · Page 40Linked to original sources
PubMed2004

Wear and surface cracking in early retrieved highly cross-linked polyethylene acetabular liners.

BACKGROUND: A higher degree of cross-linking has been shown to improve the tribological properties of ultra-high molecular weight polyethylene in laboratory studies; however, its effect on in vivo behavior has not been well established. We investigated in vivo wear mechanisms in retrieved highly cross-linked polyethylene acetabular liners in order to determine if early in vivo wear behavior is accurately predicted by hip-simulator studies. METHODS: A total of twenty-four liners (twenty-one explanted and one unimplanted highly cross-linked liners and two explanted ethylene-oxide-sterilized non-cross-linked liners) were examined for this study. The average age of the patients was 59.9 years, and the average time in vivo was 10.1 months. Articular surface damage on the front and back sides of the liners was assessed with an optical scoring system. Surface quadrants were assigned a grade from 0 to 3 according to the observed wear mechanisms and the percentage of surface affected. The micromechanisms of liner damage were evaluated with use of scanning electron microscopy. RESULTS: The average front and back-side explant damage scores were 11 (range, 2 to 26.5) and 6.7 (range, 3.7 to 13.3), respectively. There was consistent evidence of early surface deformation and cracking. All explants exhibited some form of surface change, including surface cracking, abrasion, pitting, or scratching. The original machining marks on the liner surface were observed to be either unaltered, drastically distorted, or absent. CONCLUSIONS: Highly cross-linked ultra-high molecular weight polyethylene acetabular liners that were retrieved at an average of ten months after implantation exhibited signs of surface damage that had not been predicted by in vitro hip-simulator studies. These devices had not failed clinically as a result of wear. The discrepancy between in vitro and in vivo wear surfaces may be due to variability in terms of in vivo lubrication and cyclic loading or may represent early surface damage mechanisms that are not well demonstrated by long-term simulator studies.

Acetabulum↗
PubMed2005

Surface roughness of ceramic femoral heads after in vivo transfer of metal: correlation to polyethylene wear.

BACKGROUND: A dark metallic-appearing smear, resembling a lead pencil mark, may be seen on a ceramic femoral head component at revision total hip arthroplasty. The purpose of this study was to investigate the hypothesis that such a mark on a retrieved ceramic femoral head is associated with increased surface roughness of the head and increased polyethylene liner wear in total hip replacement. METHODS: Fifteen ceramic prosthetic femoral heads retrieved from fifteen patients at revision arthroplasty were examined in this study. Thirteen heads had been in vivo for an average of 10.8 years (range, 7.8 to 14.2 years). The remaining two heads had been in vivo for less than one month. The surface roughness characteristics of the explanted ceramic heads, the linear wear of the polyethylene liner, and the patient activity levels after the primary replacement and before the revision were determined. RESULTS: Four of the thirteen ceramic heads that had been in vivo for >/=7.8 years had severe smears (>6% of the surface area), and the remaining nine heads had slight smears (<6% of the surface area). The two heads that had been in vivo less than one month had severe smears. The mean Ra and Rpm, the values for surface roughness, were 44.95 nm and 571.15 nm, respectively, in the hips with slightly smeared regions and 180.77 nm and 1245.88 nm, respectively, in the hips with severely smeared regions (p = 0.002). The mean linear liner wear rate was 0.10 mm/yr in the hips with slightly smeared heads and 0.19 mm/yr in the hips with severely smeared heads (p = 0.002). The activity score for all patients was 5 or 6 points on a 6-point scale. CONCLUSIONS: The results of this study confirm the hypothesis that a visual dark metallic-appearing smear on a ceramic femoral head correlates with increased surface roughness of the head and increased polyethylene wear. These findings imply that contact of a ceramic femoral head with a metallic material, such as may occur with femoral head reduction or dislocation of a total hip replacement, is best avoided to prevent this metallic smear phenomenon.

Arthroplasty, Replacement, Hip↗
PubMed2005

Osteolysis after total knee arthroplasty: influence of tibial baseplate surface finish and sterilization of polyethylene insert. Findings at five to ten years postoperatively.

BACKGROUND: Debris displaced from the articular and backside surfaces of the polyethylene inserts of modular tibial components is considered a chief cause of osteolysis at the sites of total knee arthroplasties. One design of total knee replacement featured changes, over time, in the proximal surface roughness of the tibial baseplate and the method of sterilization of the polyethylene insert. We hypothesized that polishing the baseplate surface and sterilizing the insert with means other than gamma radiation in air had reduced the prevalence of osteolysis. METHODS: Three hundred and sixty-five posterior cruciate ligament-retaining Anatomic Modular Knee primary total knee arthroplasties were performed in 300 patients from 1987 to 1998. Anteroposterior and lateral radiographs of the knees were made within a five to ten-year postoperative interval. Two arthroplasty specialists independently examined the radiographs for evidence of osteolysis (defined as any nonlinear region of cancellous bone loss with delineable margins). RESULTS: Osteolysis was identified in 34% (eighty-two) of 242 knees treated with an insert that had been gamma-irradiated in air and affixed to a rough baseplate surface, and it was identified in 9% (nine) of ninety-eight knees treated with an insert that had been gamma-irradiated in an inert gas, or had not been irradiated, and joined to a polished surface. Osteolysis was associated with six factors, including one related to the patient (male gender), one related to the tibial baseplate (the proximal surface finish), three related to the polyethylene insert (the material from which it was machined, the sterilization method, and the shelf age), and one related to the technique (hyperextension of the femoral component relative to the tibial component). CONCLUSIONS: In this design of a total knee prosthesis, polishing the tibial baseplate counterface and implementing a more contemporary sterilization practice (as opposed to gamma radiation in air) noticeably diminished but did not eliminate osteolysis.

Aged↗
PubMed2003

MR imaging of the small bowel using polyethylene glycol solution as an oral contrast agent in adults and children with celiac disease: preliminary observations.

OBJECTIVE: The purpose of our report is to describe morphologic abnormalities of the small bowel in a population of patients with known celiac disease using MR imaging with polyethylene glycol solution as an oral contrast agent. CONCLUSION: Polyethylene glycol-enhanced MR imaging is a noninvasive (no ionizing radiation is used), feasible, and reproducible imaging technique in both adult and pediatric populations. Findings on polyethylene glycol-enhanced MR imaging, similar to those of conventional barium studies, may suggest a diagnosis of celiac disease because the technique can not only reveal intestinal involvement but also show extraintestinal findings.

Administration, Oral↗
PubMed1987

Inability of polyethylene-glycol substituted copper- and zinc-containing superoxide dismutase to protect mice against radiation lethality.

The superoxide radical has been implicated in the mediation of radiation damage and CuZn superoxide dismutase, given to mice immediately before or after irradiation has, in several studies, reduced radiation lethality. CuZn superoxide dismutase has a very short plasma half-life, but if the enzyme is substituted with polyethylene-glycol a markedly increased circulation time can be achieved. In the present study an 80-fold increase in plasma superoxide dismutase activity was brought about in CBA mice by intraperitoneal injection of 7.5 ml polyethylene-glycol substituted CuZn superoxide dismutase. Although the treatment was found to have a slight radioprotective effect with a dose-modifying factor of 1.02 (p = 0.027), CuZn superoxide dismutase inactivated by hydrogen peroxide-treatment was found to be equally protective. The radioprotective effect of polyethylene-glycol substituted CuZn superoxide dismutase therefore does not seem to be dependent on the enzyme activity.

Animals↗
PubMed1991

Polyethylene failure of metal-backed patellar components. 111 AGC total knees followed for 7-22 months.

In a series of 111 AGC total knee arthroplasties, eight failures of the polyethylene part of the metal-backed patellar component were seen after a period of 7-22 months. All of these patients experienced a characteristic grating sound as the knee was bent, and skyline radiographs revealed direct metal-on-metal contact. At revision, fracture and separation of the polyethylene part were found together with an extensive, black, thickened synovium and abrasive wear of the naked metal backing of the patellar component. The cemented metal backings were all solidly anchored in the patella. Based on this high failure rate, we have abandoned the metal-backed patellar component in favor of an all-polyethylene component.

Aged↗
PubMed1992

Polyethylene delamination in the PCA total knee. Material analysis in two failed cases.

Two patients had severe polyethylene-wear synovitis after total knee arthroplasty for arthrosis. Full-leg length weight-bearing radiographs were diagnostic. The polyethylene of the tibial components showed excessive delamination. The morphology and crystallinity of the polyethylene showed that surface treatment of the material could well be held responsible for the massive wear.

Aged↗
PubMed1993

Wear of polyethylene acetabular cups against alumina femoral heads. 5 prostheses compared in a hip simulator for 35 million walking cycles.

5 ultra-high molecular weight polyethylene acetabular cups articulated against alumina femoral heads for 35 million walking cycles in a hip joint simulator designed for wear tests of total hip prostheses. The specimens were from Protek, Biomet, Link, Howmedica and Thackray. In the Howmedica specimen, the wear was zero, and in Link and Thackray practically negligible. In Biomet, however, the wear was noteworthy and in Protek disastrous after 20 million cycles because in these 2 prostheses the head was attached to a titanium-alloy stem by taper-fit: titanium-alloy particles that were removed from the taper because of micromotion between the head and stem were entrapped between the head and cup, adhering to the head and making it rough, which led to severe abrasive wear of the Protek cup. It was worn through at 26 million cycles, the total wear being 3,170 mg. In Biomet, Link and Thackray, the total wear was 124, 5.3 and 17.6 mg, respectively. Polyethylene wear particles may lead to adverse tissue reactions and eventual loosening of the implant. The results indicate that by the use of alumina heads, polyethylene wear can be eliminated, but this advantage may be lost if the head is attached to a titanium-alloy taper.

Aluminum Oxide↗
PubMed1996

Hip-simulator ranking of polyethylene wear: comparisons between ceramic heads of different sizes.

We carried out simulator studies on ceramic-polyethylene total-hip combinations to determine the volumetric wear-rates of 22 mm, 26 mm and 28 mm femoral-head sizes. Bovine-serum lubrication and 2 kN peak sinusoidal load-profile were used with polyethylene (UHMWPE) cups. Wear was assessed by gravimetric technique. Precision (9%) was ensured by the use of multiple specimens, multiple wear-events, and the linear-regression method of estimating the average wear trend, thereby reducing the inherent, unpredictable nature of each wear-event. Volumetric wear-rates for polyethylene averaged 23 mm3 per 10(6) cycles for the 22 mm ceramic head and up to 32 mm3 per 10(6) cycles for the 28 mm head. The difference between 22 mm and the larger head-sizes was significant. This may well be the first laboratory confirmation of Charnley's original clinical Low-Friction Arthroplasty concept with regard to wear rate. The wear penalty increased linearly at the rate of 6% to 9% per mm of diameter increase.

Ceramics↗
PubMed1999

Metal-on-metal bearing in hip prosthesis generates 100-fold less wear debris than metal-on-polyethylene.

Aseptic loosening due to osteolysis in total hip replacement has been related to wear debris released from prosthetic components. Retrospective longterm observations of patients with the metal-on-metal prosthesis has shown long-term survivorship and good mechanical performance. Thus, the new and modified metal-on-metal prosthesis has been introduced on the market. Historical clinical data from the 1st generation metal-on-metal hip prosthesis may not be relevant for the 2nd generation of metal-on-metal hip prosthesis. Therefore, preclinical testing of the prosthesis must be conducted before clinical evaluation. We assessed the tribological performance of the metal-on-metal prosthesis versus the metal-on-polyethylene prosthesis introduced on the market as Metasul and Protasul, respectively. In a 12-channel joint simulator, 6 metal-on-metal bearing and 3 metal on polyethylene prostheses were tested, with the same number of corresponding soak controls. The wear was assessed gravimetrically. The "steady-state" wear-rates from the metal-on-metal prosthesis were almost 100 times less than that from the metal-on-polyethylene prosthesis. The tribological wear performance of the metal-on-metal hip prosthetic system is promising.

Hip Prosthesis↗
PubMed1991

Effects of prepartum diet, inert rumen bulk, and dietary polyethylene glycol on dry matter intake of lactating dairy cows.

Effects of prepartum energy intake, replacement of 25% of reticulorumen contents with water-filled bladders, and feeding of polyethylene glycol on DM intake during lactation were assessed in two trials. In trial 1, six rumen-cannulated cows were assigned to diets of either 1.50 or 1.68 Mcal NEL/kg 70 d prepartum. Animals fed the higher energy diet had greater NEL intake and tended to gain more BW prepartum. Intake from 28 to 70 d postpartum was not affected by prepartum diet but was reduced by 24.2 L of bladders placed in the rumen. Milk production tended to be increased for cows fed high energy prepartum and to be reduced by bladders. Total reticulorumen volume, digesta fractional passage rates, and acetate:propionate ratio were increased by bladders. In trial 2, eight rumen-cannulated cows, 28 d postpartum, received polyethylene glycol, 4% of diet DM, and 21.4 L of bladders in the rumen in a 2 x 2 factorial arrangement. Polyethylene glycol did not affect DM intake but reduced DM, CP, ADF, and NDF digestibilities. Bladders increased total reticulorumen volume, rumen fluid pH, and acetate:propionate ratio but decreased DM intake. Intake of DM was reduced .099 kg/L added bulk in trial 1 and .130 kg/L in trial 2. Compensation for replacement of rumen contents with inert bulk occurred by expansion of organ volume and, in trial 1, by a reduction in rumen retention time. These factors may explain why reductions in voluntary intake after addition of inert bulk to the reticulorumen often are proportionally lower than would be predicted from the volume of bulk added.

Animal Feed↗
PubMed1995

Immobilization of lipases on polyethylene and application to perilla oil hydrolysis for production of alpha-linolenic acid.

The conditions of immobilization of lipase on the polyethylene powder were examined and the immobilized lipase was used for effective production of alpha-linolenic acid from perilla oil hydrolysis. Using the polyethylene powder containing micropores in its structure enabled immobilization of lipases. Ethanol pretreatment increased the immobilization efficiency. The efficiency of immobilization of six different lipases was 67-91%. On hydrolysis of perilla oil, the activity of the immobilized lipase was nearly the same as that of free lipase. Among the enzymes used, the Candida rugosa lipase hydrolyzed perilla oil most effectively. When the immobilized C. rugosa lipase was used 10 times for perilla oil hydrolysis by the batch reaction method (1 batch, 24-h reaction at 37 degrees C), there was little decrease in its activity. These results suggest that polyethylene-immobilized lipase can be used for the effective hydrolysis of perilla oil to produce alpha-linolenic acid.

Candida↗
PubMed2000

Comparison of migration in modular sockets with ceramic and polyethylene inlays.

This study compared migration in 73 cementless total hip arthroplasties (THAs) with either alumina ceramic (n = 23) or polyethylene (n = 50) inlays; prosthesis sockets and stems were identical except for the inlays. After 7 years of follow-up, 5 sockets (4 with ceramic and 1 with polyethylene inlays) had been revised an average of 63.3 months (range: 49-81 months) after implantation, and survival analysis showed a significantly higher revision rate for sockets with ceramic inlays (89 +/- 6%) versus polyethylene inlays (98.2 +/- 1.7%) (P = .032). Migration analysis of the first three postoperative years revealed significantly higher vertical migration in sockets with ceramic inlays (P = .047), in patients aged <60 years (P = .02), and in osteoporotic type C bone (A versus C, P = .0071 and B versus C, P = .0004).

Ceramics↗
PubMed2002

The effect of abduction differences between cup and contralateral acetabular angle on polyethylene component wear.

One hundred forty-two patients who underwent cemented or uncemented hip replacement were studied radiographically to determine acetabular component wear. Mean duration of follow-up was 58 months (range: 35-92 months). Average linear wear was 0.78 mm (range: 0-1.9 mm), and average wear rate was 0.16 mm/year (range: 0-0.45 mm/year). An increased wear rate per year correlated with a discrepancy >18.3 degrees between contralateral acetabular angle and acetabular cup inclination (P<.005). Statistical analysis revealed no significant correlation between cup inclination and polyethylene wear, which was studied without considering the contralateral hip (P>.3). There was no relationship between polyethylene wear and cup design, weight, and initial polyethylene thickness.

Aged↗
PubMed1990

A radiographic and histological analysis of 17 retrieved ultrahigh-molecular-weight polyethylene porous-coated femoral stems.

Radiographic and histological and evaluation for failure of 17 retrieved implants was performed. The implants consisted of a titanium stem with a 3-mm ultrahigh-molecular-weight polyethylene coating and an outer 1.5-mm ultrahigh-molecular-weight polyethylene fiber layer. Particular attention was paid to osteolysis, subsidence, debris, and foreign body reaction. Radiographic analysis showed subsidence (14 of 17), osteolytic lesions (9 of 14), and unique posterior medial exostoses (8 of 14). Histological analysis showed no significant evidence of acrylic bone cement either as debris or reactive tissue. There was an intense foreign body reaction directly related to the amount and size of polyethylene debris.

Adult↗
PubMed1999

Polyethylene glycol as a non-absorbable prokinetic agent in the lower gastrointestinal tract.

In the rabbit isolated colon, intraluminal infusion of polyethylene glycol facilitates peristaltic activity. The primary target of polyethylene glycol appears to be the intrinsic sensory neurons, and not the excitatory motor neurons. It would appear that polyethylene glycol activates the excitatory pathways of the peristaltic reflex releasing tachykinins and acetylcholine at the level of the intrinsic sensory neurons.

Animals↗
PubMed1999

Use of polyethylene glycol solution in functional and organic constipation in children.

A brief review is made of the use of high dose polyethylene glycol solution in the treatment of functional constipation and encopresis in children. Experience with low dose polyethylene glycol for the treatment of neurogenic constipation in children with severe brain damage is also reported. Treatment with polyethylene glycol caused a significant increase in bowel frequency and a decrease in gastrointestinal transit time. Side-effects, consisting of nausea, vomiting and irritability, have limited the use of this treatment in a few children.

Cathartics↗
PubMed2000

Effect of the wettability characteristics of polyethylene glycol derivatives on the drug release of wax matrices.

The purpose of the present work was to study the relationship between the physicochemical characteristics of different polyethylene glycol aqueous solutions and the kinetics of potassium chloride release from wax matrix samples containing polyethylene glycol derivatives. Potassium chloride was embedded into thermosoftening matrix material to produce a sustained-release dosage form. Potassium chloride release was measured by the rotating paddle method of USP 23 and the dissolution process was characterized by a modified Nernst equation. Physicochemical characteristics--surface tension, dynamic contact angle, viscosity--of the polyethylene glycol aqueous solutions were also determined. The results indicate that the adhesion tension of surfactant containing aqueous solutions has a decisive impact on the prediction of the potassium chloride release rate from wax matrices.

Adhesiveness↗