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PubMed1996

Cancer risk after metal on metal and polyethylene on metal total hip arthroplasty.

The incidence of cancer after metal on metal total hip arthroplasty (McKee-Farrar) and polyethylene on metal total hip arthroplasty (Brunswik, Lubinus) was compared with that of the general population in Finland. The mean followup time for the patients who had metal on metal total hip arthroplasty was 15.7 (9092 person years) and for the patients who had polyethylene on metal total hip arthroplasty it was 12.5 years (19,846 person years). One hundred thirteen malignant cancers were observed in patients who had metal on metal total hip arthroplasty and 212 were observed in patients who had polyethylene on metal total hip arthroplasty. The standardized incidence ratio for all cancers of the metal on metal arthroplasty group was 0.95 (95% confidence limits 0.79-1.13) and that of the polyethylene on metal arthroplasty group was 0.76 (95% confidence limits 0.68-0.86). The risk of total cancer in the patients who had metal on metal total hip arthroplasty was 1.23-fold compared with that of the patients who had polyethylene on metal total hip arthroplasty. Both groups had significantly less lung cancer than the general population: the leukemia incidence in the patients who had metal on metal total hip arthroplasty was slightly increased (observed to experienced 7/3.03, standardized incidence ratio 0.61; 95% confidence limits 0.17-1.56). The leukemia rate of the patients who had metal on metal total hip arthroplasty was 3.77-fold compared with that of the patients who had polyethylene on metal total hip arthroplasty, but this difference was not statistically significant. No sarcomas were observed at the site of the prosthesis. The incidence of the other forms of cancers did not differ significantly from those in the general population. The observed variation in the incidence of different cancers among patients who had total hip arthroplasty compared with the general population suggests that factors other than total hip arthroplasty play a major role in the origin of cancer.

Aged↗

PubMed1999

Wear of gamma-crosslinked polyethylene acetabular cups against roughened femoral balls.

Crosslinking of ultrahigh molecular weight polyethylene has been shown to markedly improve its wear resistance in clinical studies and laboratory tests using hip joint simulators. However, because most of the laboratory studies have been done under clean conditions using prosthesis-quality, highly polished counterfaces, there is concern regarding how well an intentionally crosslinked polyethylene acetabular cup will resist abrasion by a femoral ball that has been damaged by third-body abrasion in vivo. To investigate this, conventional and radiation crosslinked-remelted acetabular cups of ultra-high molecular weight polyethylene were tested in a hip joint simulator bearing against smooth femoral balls and against balls with moderate and severe roughening. Cups were tested with and without aging to accelerate any oxidative degradation. The crosslinked cups were produced by exposing extruded GUR 4150 bar stock of ultrahigh molecular weight polyethylene to 5 Mrad gamma radiation under a partial vacuum and then the bars were remelted to extinguish residual free radicals. Artificial aging at 70 degrees C under 5 atm oxygen for 14 days induced negligible oxidation in the crosslinked and remelted material. Against smooth balls, the wear of the crosslinked cups, with or without aging, averaged approximately 15% of that of the conventional cups. Against the moderately rough balls, the wear rate of the conventional cups was unchanged, whereas the wear rate increased slightly for the nonaged and aged crosslinked cups, but was still only 26% and 20% of that of the conventional cups, respectively. Against extremely rough balls, the mean wear rates increased markedly for each material such that during the final 1 million cycle interval, the average wear rates of the nonaged and the aged crosslinked cups were 72% and 47% of that of the conventional cups, respectively. That is, the crosslinked polyethylene showed substantially better wear resistance than conventional polyethylene across the range of ball roughnesses, with or without accelerated aging.

Acetabulum↗

PubMed2000

Effect of low-friction ion-treated femoral heads on polyethylene wear rates.

Polyethylene wear is a major contributor to osteolysis and subsequent aseptic loosening of prosthetic components in total hip arthroplasty. Use of ion implantation as a surface modification to the metallic bearing component of orthopaedic implants may be an effective means of reducing wear debris at the bearing interface. In July 1991, low friction ion treated femoral heads were introduced. This study evaluates the effect of the low friction ion treated femoral head on polyethylene wear. Fifty-five total hip arthroplasties (53 patients) with low friction ion treated femoral heads followed up a minimum of 3 years were matched with 55 total hip arthroplasties (47 patients) without low friction ion treated femoral heads for the same postoperative period. Socket wear was evaluated radiographically. Case matching and strict inclusion criteria were used to control for known factors influencing polyethylene wear. These criteria included: (1) cases matched for gender and age within 2 years; (2) diagnosis limited to osteoarthritis or avascular necrosis of the femoral head only; (3) femoral head diameter limited to 26 or 28 mm only; (4) hydroxyapatite coated femoral stem of the same design and a metal backed socket of the one of two designs with the same polyethylene insert; and (5) minimum followup of 3 years. The linear wear rate of polyethylene was 0.161 +/- 0.095 mm per year in the group without the low friction ion treated heads and 0.116 +/- 0.101 mm per year in the low friction ion treated group. The volumetric wear rates were 74.5 +/- 44.3 mm3 per year for the group without the low friction ion treated heads and 57.8 +/- 51.1 mm3 per year for the low friction ion treated group. Assuming the sensitivity of these measurements can detect these small differences in wear accurately, these results suggest low friction ion treated prosthetic heads are useful in reducing polyethylene wear at 3-year minimum followup.

Adult↗

PubMed2004

Fatigue crack propagation resistance of highly crosslinked polyethylene.

A higher degree of cross-linking has been shown to improve wear properties of ultra-high molecular weight polyethylene in laboratory studies. However, cross-linking can also affect the mechanical properties of ultra-high molecular weight polyethylene. Fatigue crack propagation resistance was determined for electron beam cross-linked ultra-high molecular weight polyethylene and compared with gamma irradiation cross-linked and noncross-linked polyethylene fatigue specimens. Crosslinking was done with different dosages of irradiation followed by melting. For one irradiation dose (50 kGy) extrusion and molding processes were compared. A fracture mechanics approach was used to determine how the degree of cross-linking affects resistance to crack propagation in ultra-high molecular weight polyethylene. Fatigue crack propagation resistance was reduced in proportion to the irradiation dose. The type of irradiation (gamma or electron beam) or manufacturing method (extrusion or molding) did not affect fatigue crack propagation resistance. The reduced fatigue strength of highly cross-linked ultra-high molecular weight polyethylene could lead to mechanical failure in conditions that are associated with cyclic local tensile stresses.

Case-Control Studies↗

PubMed2005

Effect of cross-linking on the microstructure and mechanical properties of ultra-high molecular weight polyethylene.

Ultra-high molecular weight polyethylene is a semicrystalline polymer, which means that a portion of the molecules is in a solid crystalline phase and the remaining portion is in a rubbery amorphous phase. Varying the polymer chemistry in the two phases can alter the mechanical properties of the material. When highly cross-linked polyethylene is formed, the cross-links occur in the amorphous but not the crystalline region. Remelting after irradiation-induced cross-linking neutralizes the free radicals that are caused by irradiation but also decreases the amount of crystallinity. Decreased crystallinity can contribute to a decrease in mechanical properties. Annealing below the melt temperature after irradiation retains a higher level of crystallinity. However, heating below the melt temperature does not neutralize irradiation-induced free radicals that can then react with oxygen, causing oxidative degradation. Newer "second-generation" highly cross-linked polyethylenes have been developed that are annealed below the melt temperature, but use either a pharmacologic antioxidant, mechanical deformation, or sequential low-dose irradiation and annealing treatments rather than heating above the melt point to neutralize residual free radicals. High-pressure treatment at elevated temperatures also can increase crystallinity. However, increased crystallinity is associated with an increase in modulus and contact stress, which can increase wear. Although cross-linking ultra-high molecular weight polyethylene can reduce wear, currently available highly cross-linked polyethylenes also decrease mechanical properties when compared with conventional ultra-high molecular weight polyethylene, so that use of these materials in total knee arthroplasty may contribute to mechanical failure of the bearing surface.

Compressive Strength↗

PubMed2005

Polyethylene in knee arthroplasty: what is the future?

Ultra-high molecular weight polyethylene remains the gold standard as a bearing surface for total knee arthroplasty. But problems of oxidative degradation and wear have prompted new sterilization techniques and new forms of more highly cross-linked polyethylene. The value of these solutions can be shown initially from laboratory data, but in the end their usefulness will be confirmed through clinical performance. The significance of new polyethylenes cannot be established on the basis of a single type of test or even on a single goal such as improved wear resistance. Rather, a range of requirements dictated by design goals (function, fixation, and wear) must be considered. The requirements can be competing, so that matching one compromises matching another that, if not taken into account, can lead to failure in clinical use. Previous improvements to polyethylene ultimately failed because not all the requirements were met. The same concern exists with highly cross-linked polyethylenes; improvements in wear resistance are tempered by a decrease in toughness. A case can be made for and against these polyethylenes, but early clinical results in hip arthroplasty show significantly improved wear, raising the possibility of also improving wear performance in knee arthroplasties.

Arthroplasty, Replacement, Knee↗

PubMed2006

Revision hip arthroplasty for late instability secondary to polyethylene wear.

We evaluated the outcome of revision arthroplasty for polyethylene wear presenting as late dislocation. The computerized databases at two institutions were reviewed to identify all patients presenting with first time dislocation five or more years after total hip arthroplasty. Records and radiographs were then evaluated, and patients whose late dislocation occurred in the presence of greater than two millimeters of polyethylene liner wear with no other etiology for dislocation were identified. There were 22 patients with a mean age of 57.8 years at primary procedure. The average time from initial arthroplasty to dislocation was 9.0 years. Revision surgery to address polyethylene wear and instability was performed at a mean of 11.1 years (range 5.8 to 23 years). Revision surgery restored stability to eighteen patients (eighty-two percent). Polyethylene wear can and is associated with late dislocation after hip arthroplasty. Exchange of polyethylene lining of a metal backed implant or revision of the all polyethylene acetabular component can successfully address late instability in the majority of patients.

Adult↗

PubMed2007

All-polyethylene and metal-backed tibias have similar outcomes at 10 years: a randomized level I [corrected] evidence study.

The advantages of a monoblock design and lower cost have generated renewed interest in all-polyethylene tibial components for total knee arthroplasty (TKA). We hypothesized an all-polyethylene design would function equivalently to a metal-backed modular design at lower cost and at long-term followup. We report the 8- to 12-year followup of our earlier reported prospective randomized comparison of a modern congruent all-polyethylene tibial component with a modular metal-backed tibial component of the same design. The mean age of the patients was 69 years and 92% were diagnosed with osteoarthritis. Of 290 patients (316 total knee arthroplasties) enrolled, 120 patients died, 22 had revision surgery, and one was lost to followup. We followed the remaining 147 patients (167 TKAs: 97 all-polyethylene/70 metal-backed) clinically and radiographically. There were no differences in knee function (Knee Society clinical score, range of motion, stability) or radiographic parameters between the groups. Of the 22 revisions, only three were performed for tibial aseptic loosening (three metal-backed). Ten-year survivorship of the all-polyethylene tibial component was 91.6% with revision for any reason and 100% for aseptic loosening. The metal-backed tibial component survivorship was 88.9% with revision for any reason and 94.3% for aseptic loosening. The contemporary all-polyethylene tibial component functioned equivalently to its monoblock counterpart and was less costly.

Aged↗

PubMed1992

Short report: comparison of two orally administered bowel preparations for colonoscopy--polyethylene glycol and sodium picosulphate.

Fifty-nine consecutive patients admitted for colonoscopy were randomized to receive polyethylene glycol or sodium picosulphate. Patients expressed their opinion in a questionnaire and the endoscopists, blinded to the preparation, assessed the cleanliness of different segments of the colon. There was no statistically significant difference in the taste-acceptability of the preparations, frequency of nausea, abdominal pain, peri-anal soreness or sleep disturbance between the two groups. Polyethylene glycol caused vomiting in 13% of patients while this was absent in those who received sodium picosulphate (P less than 0.05). The average number of stools passed was 12.4 in the polyethylene glycol and 8.6 in the sodium picosulphate groups; mean difference 3.8 (95% C.I. 0.7-6.9) with P less than 0.02. The overall cleanliness of the colon was better in the polyethylene glycol group (P = 0.002) as judged by the blinded colonoscopist. There was less delay (P = 0.06) and more completed colonoscopies (P = 0.01) in this group. Polyethylene glycol was a better preparation in all segments of the colon except the rectum. We conclude that polyethylene glycol is the choice of the colonoscopist and should be given to all patients; sodium picosulphate would be a good alternative if patients are intolerant. If a limited colonoscopy or flexible sigmoidoscopy is intended, sodium picosulphate may be preferred because of its acceptable efficacy and slightly advantageous side-effect profile.

Abdominal Pain↗

PubMed2004

Prospective, randomized, parallel-group trial to evaluate the effects of lactulose and polyethylene glycol-4000 on colonic flora in chronic idiopathic constipation.

BACKGROUND: Although lactulose and polyethylene glycol are osmotic laxatives widely used in the treatment of chronic constipation, no study has been conducted to compare their actions on the colonic bacterial ecosystem, which has an important influence on host health. AIM: To assess the effects of lactulose and polyethylene glycol on the composition and metabolic indices of the faecal flora in patients with chronic idiopathic constipation. METHODS: Sixty-five patients with chronic idiopathic constipation were included in this controlled, multi-centre, randomized, parallel-group study. Participants received lactulose (Duphalac) or polyethylene glycol-4000 (Forlax) powders for the first week at a fixed dosage at night (20 g/day); in the second week, patients were given the option to vary the dose according to efficacy and tolerance (10-30 g/day); for the last 2 weeks, treatment was administered at a fixed dosage based on the results of the second week (10-30 g/day). Stools were recovered for bacteriological analysis at days -1, 21 and 28. RESULTS: Clinical efficacy and tolerance were similar with both treatments. In the lactulose group, an increase in faecal bifidobacteria counts (P = 0.04) and beta-galactosidase activity (P < 0.001) was observed from day -1 to day 28, whereas, in the polyethylene glycol group, there was a decrease in total short-chain fatty acids (P = 0.02), butyrate (P = 0.04), acetate (P = 0.02) and faecal bacterial mass (P = 0.001). No differences were observed in stools with regard to the following parameters: counts of Lactobacillus, clostridial spores, Bacteroides and enterobacteria, pH, biliary acids and neutral sterol concentrations. CONCLUSIONS: Both lactulose and polyethylene glycol are efficacious and well tolerated. However, although lactulose can be considered as a pre-biotic in constipated patients, polyethylene glycol produces signs of decreased colonic fermentation in the stool.

Bile Acids and Salts↗

PubMed2005

Effects of lactulose and polyethylene glycol on colonic transit.

BACKGROUND: The effects of lactulose and polyethylene glycol on colonic transit are poorly established. AIM: To assess the effects of these laxatives on colonic transit in normal subjects. METHODS: Colonic transit (mean residence time, cumulative counts in stool, counts remaining in the proximal or distal colon) was measured scintigraphically in normal subjects on the second and third day of a 3-day ingestion of 67-134 g/day lactulose, or 59 g/day polyethylene glycol. RESULTS: At similar stool weight (lactulose: 653 +/- 120 g/day; polyethylene glycol: 522 +/- 66 g/day), transit was significantly slower during 99 g/day lactulose when compared with 59 g/day polyethylene glycol; this was most pronounced in the distal colon (mean residence time: lactulose - 403 +/- 55 min; polyethylene glycol - 160 +/- 41.9 min). Short chain fatty acid concentration in 24-h stool correlated significantly with counts remaining in the distal colon at 12 h (r = 0.79, P = 0.001). Increasing lactulose doses were significantly associated with increasing stool weight (r = 0.79) and shorter mean residence time in the total (r = -0.56) and distal colon (r = -0.64). The sum of faecal carbohydrates plus short chain fatty acids was associated with stool weight (r = 0.95, P < 0.001). CONCLUSION: Lactulose accelerates colonic transit. However, compared with polyethylene glycol, transit during lactulose is prolonged.

Adult↗

PubMed2006

Results of a prospective randomised multicentre controlled trial comparing a new 2-L ascorbic acid plus polyethylene glycol and electrolyte solution vs. sodium phosphate solution in patients undergoing elective colonoscopy.

BACKGROUND: Elective colonoscopy is used increasingly to screen at risk patients for colonic malignancy. Bowel preparation quality is a critical factor for successful screening. Preparations used include high doses of potent laxatives, e.g. sodium phosphate solution or high volume polyethylene glycol. Because of constraints and limited patient acceptability, there remains a need for a more acceptable bowel preparation with at least equivalent cleansing to existing preparations. AIM: To determine if a 2-L polyethylene glycol solution with electrolytes and ascorbic acid (polyethylene glycol + ascorbic acid) produces equivalent bowel cleansing to sodium phosphate solution, and is acceptable to patients and well tolerated. METHODS: This was a single blind, parallel group, equivalence study comparing polyethylene glycol + ascorbic acid with sodium phosphate solution in 352 patients undergoing elective colonoscopy. A blinded, independent expert scored a video recording of each colonoscopy. Patients completed a questionnaire reporting acceptability of the bowel preparation process. RESULTS: Clinically successful bowel preparation was reported in 72.5% of cases prepared using polyethylene glycol + ascorbic acid and in 63.9% of cases prepared using sodium phosphate solution (treatment difference +8.6%, 95% confidence interval -2.3%, +19.4%). The new solution was well accepted and better tolerated than sodium phosphate solution. CONCLUSIONS: The new 2-L solution of polyethylene glycol + ascorbic acid was at least as efficacious as sodium phosphate solution with comparable efficacy and a better tolerability profile.

Ascorbic Acid↗

PubMed1991

Free fatty acid uptake by polyethylene: what can one learn from this?

Previous experiments have shown that fatty-acid uptake by isolated hepatocytes is inhibited by albumin, but this inhibition was less than expected from the decrease in the equilibrium concentration of fatty acid. The possible explanation of this observation by the effects of codiffusion of protein-bound and unbound fatty acid across the unstirred layer surrounding these isolated cells has recently been challenged on the basis of experiments in which uptake by monolayers of hepatocytes was compared with that by a polyethylene sheet [F.J. Burczynski et al., Am. J. Physiol. 257 (Gastrointest. Liver Physiol. 20): G584-G593, 1989]. In the present report, we reevaluate the theoretical basis for interpretation of these experiments by solving the differential equations describing diffusion into a sheet behind a linear barrier. The diffusion coefficient for palmitate in polyethylene is estimated to be approximately 10(-9) cm2/s. We conclude that when proteins are absent from the aqueous phase, diffusion across the unstirred layer is rate limiting for removal of fatty acids by cellular monolayers, and also rate limiting for net flux across the water-polyethylene interface. In contrast, if the aqueous phase contains either 5 microM albumin or 125 microM beta-lactoglobulin, diffusion within the polyethylene sheet will become rate limiting. The net flux of fatty acids into a polyethylene sheet becomes insensitive to an increase in protein concentration if the latter rises above a certain threshold. The polyethylene data provide no additional insight into the manner in which hepatocytes take up free fatty acids.

Fatty Acids, Nonesterified↗

PubMed2006

Determination of crystallinity and crystal structure of Hylamer polyethylene after in vivo wear.

Hylamer polyethylene is a crystalline form of polyethylene of 70% crystallinity whereas conventional polyethylene (PE) has 50% crystallinity. Crystallinity is the percentage by weight of the crystalline phase present in the whole polymer, which comprises both amorphous and crystalline phases. Clinical experience has shown that Hylamer components used in joint prostheses, if sterilized by gamma rays in the presence of oxygen, are easily affected by wear, which leads to osteolysis. The authors have analyzed the crystallinity of polyethylene liners removed from seven patients who had received Hylamer polyethylene implants sterilized by gamma rays in air and had suffered prosthetic loosening, using Raman spectroscopy coupled with partial least squares (PLS) analysis. The results have been compared to those of two controls who had received Hylamer polyethylene implants sterilized by gamma irradiation in a nitrogen atmosphere. The crystal structure of wear particles released into the tissues from the Hylamer liners sterilized by gamma rays in air is also studied. The materials undergoing two different types of sterilization methods show different crystallinity values (71.50 vs. 69.43), but the crystallinity do not change according to wear (worn and unworn liner region). Both monoclinic and orthorhombic phases are present in the liner, while in wear debris prevalently monoclinic crystals are found in both types of sterilized liners. Different crystallinity rates can explain different wear rates observed in vivo.

Aged↗

PubMed1997

Clinical wear behaviour of ultra-high molecular weight polyethylene cups paired with metal and ceramic ball heads in comparison to metal-on-metal pairings of hip joint replacements.

In the course of 30 years of hip endoprosthetics, a number of material combinations for the cups and balls of total hip prostheses have proven successful under clinical conditions. Favourably priced hip prostheses with polyethylene cups and metal balls are available for older patients with a moderate range of activity. Polyethylene wear of 100-300 microns/year is to be expected with these models. Ceramic balls (aluminium oxide for diameters 32 and 28 mm and zirconium oxide for 22 mm) paired with polyethylene cups are recommended for patients with a life expectancy of 10 to 20 years, because the expected polyethylene wear rate with this material combination is only 50-150 microns/year. In other words, the life cycle of the polyethylene cup is doubled, when it is paired with a ceramic ball. A similar polyethylene wear rate is also to be expected with oxygen-deep-hardened TiAlNb metal balls, which are currently the subject of a clinical field study. Last but not least, CoCrMoC metal-metal and Al2O3 ceramic ceramic pairings, which have the lowest wear rate of 2-20 microns/year, are available for highly active patients with a life expectancy of more than 20 years. As far as the cup-ball pairing is concerned and under the current pressure of costs, the surgeon should be able to select the optimum hip prosthesis model for every patient from these three categories.

Alloys↗

PubMed1993

Polyethylene wear in cemented metal-backed acetabular cups.

We examined radiographic polyethylene wear in 233 cemented total hip arthroplasties (201 patients) with either a metal-backed or a non-metal-backed acetabular cup. All patients had identical cemented one-piece titanium femoral stems with a femoral head diameter of 28 mm. The mean linear wear rate was 0.11 mm/yr in metal-backed sockets and 0.08 mm/yr in non-metal-backed sockets (p = 0.0002). The mean volumetric wear rate was 66.2 mm3/yr in the metal-backed sockets and 48.2 mm3/yr in the polyethylene sockets (p = 0.0002). The addition of metal backing to a cemented acetabular cup therefore resulted in a 37% increase in mean polyethylene wear rates which may partially explain the higher failure rate of cemented metal-backed cups. Linear regression analysis also implicated increased follow-up time (log), gross acetabular migration, metal backing and male gender in increasing polyethylene wear. We advocate the use of an all-polyethylene cup in cemented total hip arthroplasty. The increased polyethylene wear must also cause concern about the wear rate of uncemented metal-backed acetabular sockets.

Acetabulum↗

PubMed1995

Tissue ingrowth and differentiation in the bone-harvest chamber in the presence of cobalt-chromium-alloy and high-density-polyethylene particles.

Particulate wear debris from joint replacements has been implicated in the etiology of periprosthetic bone resorption. However, the effect of high-density-polyethylene or cobalt-chromium-alloy particles on osteoclastic bone resorption in vivo has not been studied previously, to our knowledge. Therefore, we examined the effect of these particles on tissue ingrowth, net bone formation (per cent trabecular bone), and osteoclastic bone resorption (osteoclasts per unit of bone surface) with use of a bone-harvest chamber that had a transverse one-millimeter channel for tissue ingrowth. After an initial six-week period for incorporation of the chamber into the proximal part of the tibia of rabbits, the contents of the channel were harvested repeatedly at three-week intervals. The carrier solution, 1 per cent sodium hyaluronate, was implanted first. In subsequent implantations, the hyaluronate was mixed with high-density-polyethylene or cobalt-chromium particles at concentrations of 10(8) particles per milliliter. The tissue harvested from the chambers that contained no particles was composed of longitudinally oriented trabecular bone in a fibrovascular stroma. Particulate high-density polyethylene evoked a moderate foreign-body reaction and a chronic inflammatory response and decreased net bone formation. When cobalt-chromium particles had been implanted, the tissue exhibited a more florid foreign-body reaction and a chronic inflammatory response, often in a nodular arrangement, in a background of dense connective tissue. Bone was sparse, and areas of cell necrosis and hyaline degeneration were noted. Histomorphometric analyses were carried out to determine the amount of net bone formation and osteoclastic bone resorption in the presence or absence of high-density-polyethylene or cobalt-chromium particles. The amount of bone was greatest in the control specimens, moderately decreased in the presence of high-density-polyethylene particles, and greatly decreased in the presence of cobalt-chromium particles. The number of osteoclasts in Howship lacunae per unit of trabecular bone surface was increased in the presence of high-density polyethylene, indicating that these particles stimulate osteoclastic bone resorption.

Animals↗

PubMed2001

Relationship between gravimetric wear and particle generation in hip simulators: conventional compared with cross-linked polyethylene.

Hip-simulator studies have shown reduced gravimetric wear rates for inert-gas gamma-irradiated ultra-high molecular weight polyethylene when compared with conventional ethylene-oxide-sterilized ultra-high molecular weight polyethylene. Analysis shows a greater number of particles generated from inert-gas gamma-irradiated ultra-high molecular weight polyethylene. This study was undertaken to examine particle-generation rates of polyethylene with different levels of cross-linking and to correlate them with gravimetric wear data. Particle-generation rates did not correlate with gravimetric wear rates. Particle analysis should be performed to predict the in vivo behavior of bearing surface materials. Cross-linked ultra-high molecular weight polyethylene subjected to 10 Mrad (100,000 Gy) of gamma irradiation generated significantly fewer particles than ethylene-oxide-sterilized ultra-high molecular weight polyethylene; it also demonstrated a 96% reduction in the volume of particles.

Hip Prosthesis↗