Reflection effects during the radiation sterilization of ultra high molecular weight polyethylene for total knee replacements (original) (raw)
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Effect of radiation sterilization and aging on ultrahigh molecular weight polyethylene
Journal of Biomedical Materials Research, 1981
The mechanical properties of polyethylene components used in prosthesis are altered after fabrication by the sterilization procedure and by the environmental and mechanical aging which occurs after implantation. To assess the importance and extent of these alterations, ultrahigh molecular weight polyethylenes from two sources, Hercules 1900 and RCH 1000C, were subjected to gamma-ray irradiation and aging in serum and argon environments. Changes induced by these treatments in the structural and mechanical parameters have been determined by a variety of experimental techniques. The effect of irradiation is to introduce crosslinks and to increase the degree of crystallinity resulting in changes in the tensile properties in the direction of higher stiffness and reduced ductility. Aging for six months produced similar changes with subtle differences. The results suggest that the initially low degree of crystallinity which results from the sluggish mobility of the very long chain molecules offers the opportunity for significant changes in the properties during use in the long run.
On the morphology of some irradiated ultra high molecular weight polyethylenes
Polymer Degradation and Stability, 2009
The morphology of various grades of ultra high molecular weight polyethylene (UHMWPE), prepared for use in orthopaedic implants, has been examined using differential scanning calorimetry (DSC), wide and small angle X-ray diffraction (WAX and SAX) and Raman spectroscopy. Preparation included gamma irradiation at various dose rates and mechanical annealing, and post-irradiation changes were of particular interest. The experimental results are interpreted in terms of previous proposals that UHMWPE is best considered as a three phase material, fully amorphous, all-trans amorphous and fully crystalline. The all-trans amorphous material is thought to be interfacial. The phase analysis shows that the age related increase in crystallinity occurs through conversion of all-trans material to fully crystalline, and there is little change in the total amorphous content of the polymers. SAX patterns show a change in the sharpness of the main diffraction peak and the emergence of a second diffraction peak at a higher q value, and this is considered to arise from crystallisation of all-trans amorphous material. Increasing the irradiation dose rate has a similar effect on the crystallography as does ageing the material. Mechanically annealed polymer also shows a similar trend towards a bimodal crystal population, accompanied by a reduction in interfacial material.
Journal of Arthroplasty, 1995
Several studies have indicated that degradation of ultrahigh-molecularweight polyethylene following gamma irradiation in air adversely affects the mechanical properties of the material; however, it is not known how this subsequently affects its wear rate. Wear studies have therefore been performed on three groups of ultrahigh-molecular-weight polyethylene: unirradiated material, recently irradiated material (aged for 2 months), and aged irradiated material (aged for 5 years). The aging took place in sterile packaging on the shelf. The wear studies were carried out on a tri-pin-on-disk wear tester, with a pin from each type of material being studied in each test. In each test the wear rate of the nonirradiated material was slightly lower than the 2-month-aged, irradiated material. The 5-year-aged, irradiated material had the highest wear rate, and this was significantly greater than that of the unirradiated material (P < .05). low wear rates in vivo have been quoted, 3 in general volumetric wear rates in vivo are much higher, with average values for acetabular cups estimated to be in the range 40 to 90 mm3/y. 4 It is recognized that in the body, femoral counterfaces that are initially very smooth can become damaged by bone-cement particles, bone particles, metallic debris from stems, and hydroxyapatite partides. These roughened counterfaces can then cause large increases in the wear rate of UHMWPE. 2 The effect of deterioration of the counterface on increased wear of UHMWPE has been well documented. In contrast, the effect of degradation of UI-IMWPE on wear has received less attention. Clinical wear takes place over much longer periods compared with "accelerated" laboratory tests, and there is increasing concern about the degradation and aging of UHMWPE following gamma irradiation, 5 with oxidative degradation affecting both density and
The Journal of Arthroplasty, 2008
The effects of a sarcoma therapy dose level neutron radiation on oxidation and wear were compared between conventional (N2\Vac, Stryker Orthopedics, Mahwah, NJ) and highly cross-linked (Crossfire, Stryker Orthopedics) ultrahighmolecular-weight polyethylene acetabular liners. Liners were exposed to 15 Gy, a typical sarcoma treatment dose. Wear testing was conducted on a hip simulator. Transvinylene and oxidation indices were measured to determine if significant radiolytic reactions and oxidation occurred after the neutron beam exposure. The neutron bombardment produced further oxidation in both N2\Vac and Crossfire liners. Surprisingly, neutron radiation caused 62% increase in wear for N2\Vac but 0% change for the Crossfire acetabular liners. This study suggested that when joint implants are exposed to neutron beam radiation therapy, the conventional polyethylene liner is at risk for rapid wear.
The Journal of Arthroplasty, 1999
The mechanism for the improved wear resistance of cross-linked ultra-highmolecular-weight polyethylene (UHMWPE) remains unclear. This study investigated the effect of cross-linking achieved by gamma irradiation in nitrogen on the tribologic, mechanical, and morphologic properties of UHMWPE. The goal of this study was to relate UHMWPE properties to the wear mechanism in acetabularbearing inserts. Wear simulation of acetabular liners was followed by detailed characterization of the mechanical behavior and crystalline morphology at the articulating surface. The wear rate was determined to be directly related to the ductility, toughness, and strain-hardening behavior of the UHMWPE. The concept of a plasticity-induced damage layer is introduced to explain the near-surface orientation of the crystalline lamellae observed in the wear-tested acetabular liners. Cross-linking reduces abrasive wear of acetabular components by substantially reducing-but not eliminating-the plasticity-induced damage layer that precedes abrasive wear.
Objective: To evaluate the efficacy of sterilization of the surface and deep layers of polyethylene acetabular components used in hip arthroplasties by the exposure to low doses of gamma radiation. Material and Methods: 15 acetabular components, made of ultrahigh molecular weight polyethylene (UHMWPE) produced by domestic industry were tested in two phases: in the first phase, the surface's sterility was studied by incubation of the components in Trypticase Soy Broth (DIFCO®). In the second phase, the sterility of the deep layer of the acetabular component was evaluated by incubation of samples of this layer, collected from regions in which there is usually greater prosthetic wear. Results: On all the samples evaluated, both the superficial and deep layers of the acetabular component showed no evidence of bacterial growth. Conclusion: Low-dose gamma radiation sterilization is effective in sterilizing both the superficial and deep layers of acetabular components used in hip replacements.
Arthroplasty Today, 2021
Background: There is a paucity of data on the long-term performance of highly cross-linked polyethylene (HXLPE). Therefore, this study evaluated 10-year 1) functional, 2) radiographic, and 3) surgical outcomes in patients who underwent total hip arthroplasty with sequentially irradiated and annealed HXLPE. Methods: A retrospective, multicenter study was conducted on patients who underwent primary total hip arthroplasty and received HXLPE polymer (n ¼ 151). Two-dimensional radiographic linear and volumetric wear analyses were quantified using the Martell Hip Analysis software, while functional outcomes were assessed by analyzing postoperative Short-Form-12 (SF-12) Physical and Mental Health Surveys and Harris Hip Scores. Radiographic outcomes included yearly linear (mm/y) and volumetric (mm 3 /y) wear rates. Surgical outcomes included additional operations and survivorship. Results: SF-12 scores were within 1 standard deviation (SD) of the normal population (SF-12 Physical: 47.0; SF-12 Mental: 52.0), while the Harris Hip Scores of 89.5 was borderline between "good" and "excellent." Total and annual linear wear rates were 0.164 mm (SD: 0.199 mm) and 0.015 mm/y (SD: 0.018 mm/y), respectively. The mean total volumetric wear rate was 141.4 mm 3 (SD: 165.0) and 12.6 mm 3 /y (SD: 14.9 mm 3 /y) when broken down into a yearly rate. Eleven patients required revisions, resulting in an all-cause polyethylene survivorship of 92.7%, with a polyethylene wear survivorship of 100.0%. Conclusions: Our results demonstrate clinically undetectable linear and volumetric wear rates after 10 years in those who received the unique sequentially irradiated and annealed HXLPE. Furthermore, high rates of survivorship coupled with low all-cause revision rates illustrate the polymers' capability to potentially increase implant longevity.
Irradiation of chemically crosslinked ultrahigh molecular weight polyethylene
Journal of Polymer Science Part B: Polymer Physics, 1996
Acetabular cups for artificial hip joints were prepared by compression molding of ultrahigh molecular weight polyethylene in the presence of peroxide. Peroxide crosslinking led to a decrease in the degree of crystallinity, peak melting temperature, and recrystallization temperature, as well as decreased crystal perfection and size. Peroxide crosslinked cups were sterilized with gamma rays at room temperature in air atmosphere to a n average dose of 3.4 Mrad. Irradiation produced further crosslinking in amorphous regions plus extensive chain scission of taut tie molecules and led to increased crystallinity and crystal perfection.
The Journal of bone and joint surgery. American volume, 2002
The mechanical toughness of polyethylene that has been sterilized by gamma irradiation in air decreases after a long shelf life. The purpose of the present study is to report the high failure rate after unicondylar knee replacements performed with polyethylene bearings that had been sterilized with gamma irradiation in air and implanted after a shelf life of < or = 4.4 years. Between December 1997 and January 2000, seventy-five unicondylar knee replacements were performed in sixty-two patients. All patients were followed both clinically and radiographically. A revision operation was offered when the patient had pain, swelling, and radiographic evidence of rapid polyethylene wear. The effect of aging of the polyethylene during storage was evaluated by dividing the knees into three groups on the basis of shelf life and comparing them with regard to the rate of revision and the observed wear of the polyethylene. Four retrieved components were examined for the presence of oxidation. ...