Ultra-high Molecular Weight Polyethylene Cup Research Articles

Improving the protective properties of an artificial joint friction couple by using TiN and DLC films

Artificial joint replacement represents the most effective approach for addressing joint pathologies. However, friction and wear, the production of debris and the release of metal ions reduce the durability of artificial joints and negatively impact human health.This study focuses on a CoCrMo alloy joint femoral head and an ultra-high molecular-weight polyethylene cup, which are commonly used as standard artificial joint friction couples. Two different types of films have been deposited on the surface of the joint femoral head. Multilayer TiN/(Ti/DLC) × 3 films were deposited on the surface of the alloy ball via pulsed cathode-arc discharge, and a friction experiment was carried out by a hip friction simulation tester. As an alternative film for use in medicine, TiN films were deposited by direct current arc evaporation of the titanium cathode in a nitrogen atmosphere at a partial pressure of 1.2 × 10−1 Pa. Prior to conducting the wear test, the film structure was studied through Raman and XPS spectroscopy. The surface morphology and adhesion of the films to the joint femoral head were studied.A change in the mass of the prosthesis has been seen when comparing the presence and absence of deposited films. Inductively coupled plasma mass spectroscopy has shown the effectiveness of protecting the surface of the prosthesis with the deposited TiN/(Ti/DLC) × 3 film. This method successfully reduces the concentration of Co and Cr released during friction. The findings indicate that the TiN/(Ti/DLC) × 3 film deposited on the joint femoral head reduces the wear of the UHMWPE cup and did not degrade over five million cycles, thus significantly exceeding the operating life of the TiN film. The results show that TiN/(Ti/DLC) × 3 film demonstrates a 55 % reduction in the generation of abrasive debris in the UHMUPE cup. Furthermore, it effectively prevents the release of metal ions from the alloy femoral head.

Raman analysis of chemisorbed tribofilm for metal‐on‐polyethylene hip joint prostheses

The biochemical reaction during the formation of lubricant film the in case of a cobalt-chromium ball on an ultrahigh-molecular weight polyethylene cup was studied. Three types of model synovial fluids and hyaluronic acid (HA) at physiologic concentrations were used in the experiment. The coefficient of friction was measured using a pendulum hip simulator, and Raman spectroscopy was used to perceive chemical reactions between the synovial fluid and implant material. Raman spectra evidenced that the three model fluids and HA chemisorbed onto the cobalt-chromium surface. An α-helix structure of the model fluid components was detected on the surface of the prosthesis.

Reduced wear in vitamin E-infused highly cross-linked polyethylene cups: 5-year results of a randomized controlled trial

Background and purpose — Vitamin E-infused polyethylene is a relatively new material in joint arthroplasty; there are no long-term reports, and only few mid-term results. Using radiostereometric analysis (RSA), we primarily determined whether vitamin E-infused highly cross-linked polyethylene (HXLPE/VitE) acetabular cups show less wear than ultra-high molecular weight polyethylene (UHMWPE) acetabular cups at 5 years after total hip arthroplasty (THA). We also assessed whether wear rates correlate with increasing cup inclination angles or cup sizes. Patients and methods — This is a 5-year follow-up of our previously reported randomized controlled trial of 62 patients with 3 years’ follow-up, who received THA with either an HXLPE/VitE or a UHMWPE acetabular cup. At 5 years, 40 patients were analyzed (22 in the HXLPE/VitE and 18 in the UHMWPE group). Results — HXLPE/VitE cups continued to show less cumulative femoral head penetration than UHMWPE cups (HXLPE/VitE: 0.24 mm, UHMWPE: 0.45 mm; p < 0.001). Distribution of wear was also more even with HXLPE/VitE cups than with UHMWPE cups (p = 0.002). Moreover, the difference in PE wear between 1 and 5 years in both groups showed no statistically significant correlation with increasing cup inclination angles or cup sizes. Finally, no osteolysis and implant loosening occurred, and no revision surgeries were required. Interpretation — Wear rates continue to be lower in HXLPE/VitE cups than in UHMWPE cups at 5 years of follow-up without correlation with increasing cup inclination angles or cup sizes. Finally, HXLPE/VitE cups may have the potential to prevent osteolysis and implant loosening.

A vitamin E blended highly cross-linked polyethylene acetabular cup results in less wear: 6-year results of a randomized controlled trial in 199 patients

Background and purpose — Survivorship of total hip arthroplasty (THA) with the ultra-high molecular weight polyethylene (UHMWPE) monoblock cup has been limited due to periprosthetic osteolysis and aseptic loosening, secondary to wear of the UHMWPE. In response, a vitamin E blended highly cross-linked polyethylene (HXLPE) cup was developed. This study set out to compare the wear and clinical 6-year outcomes of vitamin E blended HXLPE with UHMWPE in an isoelastic monoblock cup in patients with hip osteoarthritis who underwent uncemented THA. The 2-year results have been reported previously. Patients and methods — For this randomized controlled trial 199 patients were included. 102 patients received the vitamin E blended HXLPE uncemented acetabular cup and 97 patients the uncemented UHMWPE monoblock cup. Clinical and radiographic parameters were obtained preoperatively, directly postoperatively, and at 3, 12, 24, and 72 months. Wear rates were compared using the femoral head penetration (FHP) rate. Results — 173 patients (87%) completed the 6-year follow-up. The mean NRS scores for rest pain, load pain, and patient satisfaction were 0.3 (SD 1), 0.6 (SD 1), and 8.6 (SD 1) respectively. The mean Harris Hip Score was 93 (SD 12). The FHP rate was lower in the vitamin E blended HXLPE cup (0.028 mm/year) compared with the UHMWPE cup (0.035 mm/year) (p = 0.002). No adverse reactions associated with the clinical application of vitamin E blended HXLPE were observed. 15 complications occurred, equally distributed between the two cups. The 6-year survival to revision rate was 98% for both cups. There was no aseptic loosening. Interpretation — This study shows the superior performance of the HXLPE blended with vitamin E acetabular cup with clinical and radiographic results similar to the UHMWPE acetabular cup.

2-year results of an RCT of 2 uncemented isoelastic monoblock acetabular components: lower wear rate with vitamin E blended highly cross-linked polyethylene compared to ultra-high molecular weight polyethylene

Background and purpose — The long-term survival of arthroplasty components may be limited by polyethylene wear-related problems such as periprosthetic osteolysis and aseptic loosening. Highly cross-linked polyethylene (HXLPE) blended with vitamin E was introduced to improve oxidative stability and to avoid long-term embrittlement. This study clinically compares the tribological behavior and clinical outcome of vitamin E blended HXLPE with ultra-high molecular weight polyethylene (UHMWPE) in an isoelastic monoblock cup for uncemented total hip arthroplasty.Patients and methods — In this randomized controlled trial (RCT), 199 patients were included: 102 patients received the vitamin E blended HXLPE cup, 97 patients the UHMWPE cup. Clinical and radiographic parameters were obtained preoperatively, directly postoperative and at 3, 12, and 24 months. Wear rates were compared using the mean linear femoral head penetration (FHP) rate.Results — 188 patients (94%) completed the 2-year follow-up. Mean patient satisfaction was higher in the vitamin E blended HXLPE group (8.9 [1]) than in in the control group (8.5 [2], p = 0.03). The Harris Hip Score (HHS) was higher in the vitamin E blended HXLPE group (95 [8]) than in the control group (92 [11], p = 0.3). The FHP rate was lower in the vitamin E blended HXLPE group: 0.046 mm/year compared with 0.056 mm/year in the control group (p = 0.05). No adverse reactions associated with the clinical application of vitamin E blended HXLPE were observed during follow-up, with an excellent 2-year survival to revision rate of 98% for both cups.Interpretation — This study shows the superior performance of the HXLPE blended with vitamin E acetabular cup with lower linear femoral head penetration rates and better clinical results compared with the UHMWPE acetabular cup after 2 years.

Does the addition of vitamin E to conventional UHMWPE improve the wear performance of hip acetabular cups? Micro-Raman characterization of differently processed polyethylene acetabular cups worn on a hip joint simulator.

In knee replacements, vitamin E-doped ultra-high molecular weight polyethylene (UHMWPE) shows a better wear behavior than standard UHMWPE. Therefore, different sets of polyethylene (PE) acetabular cups, i.e. standard UHMWPE and cross-linked polyethylene irradiated with 50 kGy and 75 kGy, were compared, at a molecular level, with vitamin E-doped UHMWPE to evaluate their wear performance after being tested on a hip joint simulator for five million cycles. Unworn control and worn acetabular cups were analyzed by micro-Raman spectroscopy to gain insight into the effects of wear on the microstructure and phase composition of PE. Macroscopic wear was evaluated through mass loss measurements. The data showed that the samples could be divided into two groups: 1) standard and vitamin E-doped cups (mass loss of about 100 mg) and 2) the cross-linked cups (mass loss of about 30-40 mg). Micro-Raman spectroscopy disclosed different wear mechanisms in the four sets of acetabular cups, which were related to surface topography data. The vitamin E-doped samples did not show a better wear behavior than the cross-linked ones in terms of either mass loss or morphology changes. However, they showed lower variation at the morphological level (lower changes in phase composition) than the UHMWPE cups, thus confirming a certain protecting role of vitamin E against microstructural changes induced by wear testing.

Creep and Wear in Vitamin E-Infused Highly Cross-Linked Polyethylene Cups for Total Hip Arthroplasty: A Prospective Randomized Controlled Trial.

Aseptic loosening, the most common indication for revision surgery in total hip arthroplasty, can result from osteolysis caused by polyethylene (PE) wear particles. PE wear is increased by age-related oxidation of PE and free radicals emerging during irradiation cross-linking. Diffusion of vitamin E into PE stabilizes free radicals to maintain the biomechanical properties of PE. The purpose of this study was to determine whether vitamin E-infused highly cross-linked PE cups could reduce wear rates. We performed a prospective randomized controlled trial, in which 62 patients were allocated to 2 groups: a study group that received a vitamin E-infused highly cross-linked PE (HXLPE/VitE) cup and a control group that received an ultra-high molecular weight PE (UHMWPE) cup. Using radiostereometric analysis, we measured the penetration of the femoral head into the cup 7 days after surgery (baseline) and then again at 6 months and at 1, 2, and 3 years later. Baseline variables did not differ significantly between the groups. At 1, 2, and 3 years after surgery, the HXLPE/VitE cup showed significantly less cumulative penetration (creep and wear) than the UHMWPE cup (p = 0.004, p < 0.0001, and p < 0.0001, respectively). The cumulative penetration after 3 years was 0.200 mm for the HXLPE/VitE cup versus 0.317 mm for the UHMWPE cup (p < 0.0001). From 1 to 3 years after surgery, after creep had stabilized and further penetration was mainly due to wear, the mean penetration increased only 0.04 mm in the HXLPE/VitE cup and 0.116 mm in the UHMWPE cup. Our results confirm that wear rates over the first 3 years following surgery were lower in HXLPE/VitE cups than in UHMWPE cups. This suggests that HXLPE/VitE cups may prevent osteolysis, implant loosening, and eventually revision surgery. Long-term follow-up data continue to be collected to confirm these findings. Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.

THE EFFECT OF ASPHERICITY OF ACETABULAR BEARING SURFACE ON CONTACT MECHANICS OF UHMWPE TOTAL HIP IMPLANTS BY FINITE ELEMENT ANALYSIS

Asphericity and out-of-roundness are generally used to evaluate the manufacturing quality of ultra-high molecular weight polyethylene (UHMWPE) cup inner surfaces, which can potentially affect initial clinical wear and contribute to osteolysis of total hip arthroplasty. This study measured the location and magnitude of asphericity and the out-of-roundness value for four UHMWPE cups in a single set, and then investigated the effects of the asphericity on the contact mechanics of UHMWPE cups. A co-ordinate measuring machine (CMM) was used for the surface measurement and finite element analysis (FEA) was adopted for contact mechanics study. The results demonstrated that the asphericity varied between cups with the maximum value as 0.088[Formula: see text][Formula: see text][Formula: see text]0.004[Formula: see text]mm. Although such a value met the ISO specification, large difference of volume appeared for the asphericity above 0.060[Formula: see text]mm. Actual surface profile accounting for the asphericity was found to affect the value of contact pressure and contact area by around 12%. The inferior asphericity resulted in a nonsmoothly distributed contact pressure, which had a negative effect on the contact mechanics of UHMWPE cups and the edge loading was predicted to occur for the sample with a large asphericity. In conclusion, the asphericity of UHMWPE cup could affect the contact mechanics of the articular bearings and may subsequently contribute to initial wear during bedding-in phase.

Do temperature variations at the bearing surface during gait affect polyethylene wear in Charnley low-friction arthroplasty of the hip? Simulator study comparing UHMWPE and highly cross-linked polyethylene

IntroductionThere are significant individual variations in the polyethylene (PE) wear of Charnley total hip arthroplasty (THA) in published studies. This could be in part related to variations in hip joint kinematics with abnormal heating at the metal/PE interface. The objectives of our hip simulator experiment were: (1) to measure PE wear as a function of hip kinematics and temperature variations at the interface; (2) to compare ultra-high molecular weight polyethylene (UHMWPE) to latest generation highly cross-linked PE (XLPE). HypothesisOur hypothesis was that PE wear is correlated with temperature increases at the interface and thereby hip joint kinematics. Material and methodsA simulator study was performed with four UHMWPE cups (Initiale™, Amplitude, Valence, France) and two XLPE cups (X3, Stryker, Kalamazoo, Michigan, USA) subjected to 5 million cycles each. The temperature at the femoral head/cup interface was measured every 500 cycles and implant dimensions were measured every 1 million cycles. ResultsThe average temperature was 42°C for 1Hz and 50°C for 1.5Hz, no matter the type of PE tested. There was a large difference between UHMWPE and XLPE in their roughness, but no temperature variations or wear effects. Femoral head penetration after the first 1 million cycles was 0.18mm for the XLPE and 0.075mm UHMWPE on average. Between 1 and 5 million cycles, the penetration was less than 0.1mm per million cycles, with XLPE being similar to UHMPWE. DiscussionOur study found a significant temperature increase at the bearing interface as a function of frequency. But there was no correlation between temperature variations and PE degradation. However, shear stresses were under-estimated because our simulator could not reproduce abduction and adduction movements. Our hypothesis was not confirmed because PE deformation was not correlated to temperature variations. XLPE was not better than UHMWPE in the particular conditions of this study. Simulator studies are limited because of the lack of standards on cycling and the simulator bath. Level of evidenceIII–prospective case-control study in vitro.

Dynamic contact analysis of total hip prosthesis during normal active walking cycle

The lifetime of the hip prosthesis is highly connected with the contact mechanism that occurs at the interface of the acetabular cup and femoral head. A three-dimensional acetabular component model is modelled to investigate the contact consequences for the different possible material combinations during the normal dynamic walking cycle. The different bearing couples considered for the analysis are metal in contact with plastic, metal on metal, metal on ceramic, ceramic on plastic, ceramic on metal and ceramic on ceramic combinations. The result reveals that the ceramic in contact with plastic i.e. alumina femoral head paired with Ultra-High Molecular Weight Polyethylene cup reduces the maximum von Mises stress and maximum contact pressure developed between the contacting interface when compared with other combinations. The finite element results are validated with the results of Jiang et al., and it is found to be high correlation of about 95% between the two results.

Femur Design Parameters and Contact Stresses at UHMWPE Hip Joint Cup

The contact stress that occurs in the ultra-high molecular weight polyethylene (UHMWPE) hip joint cup has been shown to be correlated with the implant wear rate. The wear of the hip joint is considered as one of the main factors that affect the long term performance of the implant. The contact stress that occurs in the UHMWPE hip joint cup is affected by the implant dimensions and materials. In this study, four different femur materials and geometries were used to investigate the effects of femur design parameters on the resultant contact stress on the UHMWPE cup. The results of the finite element (FE) simulation show that the contact stresses at the UHMWPE cup decreases dramatically with increasing the femur diameter. Also the results indicated that the contact stresses on the UHMWPE cup decrease significantly when using functionally graded (FG) femur with low modulus of elasticity. The presence of metal backing results in a slight reduction in the UHMWPE cup contact stresses especially for small femurs. Finally, the presence of a gap between the UHMWPE cup and the femur results in a remarkable increase in the cup stress especially for a small femur. The hip joint femur dimensions and materials are thought to play an important role in the transition of load in the implant and should be taken into consideration during the design of the hip joint.

Validation of a 3D CT method for measurement of linear wear of acetabular cups

Background We evaluated the accuracy and repeatability of a 3D method for polyethylene acetabular cup wear measurements using computed tomography (CT). We propose that the method be used for clinical in vivo assessment of wear in acetabular cups.Material and methods Ultra-high molecular weight polyethylene cups with a titanium mesh molded on the outside were subjected to wear using a hip simulator. Before and after wear, they were (1) imaged with a CT scanner using a phantom model device, (2) measured using a coordinate measurement machine (CMM), and (3) weighed. CMM was used as the reference method for measurement of femoral head penetration into the cup and for comparison with CT, and gravimetric measurements were used as a reference for both CT and CMM. Femoral head penetration and wear vector angle were studied. The head diameters were also measured with both CMM and CT. The repeatability of the method proposed was evaluated with two repeated measurements using different positions of the phantom in the CT scanner.Results The accuracy of the 3D CT method for evaluation of linear wear was 0.51 mm and the repeatability was 0.39 mm. Repeatability for wear vector angle was 17°.Interpretation This study of metal-meshed hip-simulated acetabular cups shows that CT has the capacity for reliable measurement of linear wear of acetabular cups at a clinically relevant level of accuracy.

Analysis of Contact Stress on the Ultra-High Molecular Weight Polyethylene Cup for Different Hip Implants Dimensions and Materials

The subsurface fatigue that occurs in the Ultra-High Molecular Weight Polyethylene (UHMWPE) hip joint cup has been shown to be correlated with the contact stress at that cup. This cup stress is known to be affected by the implant design, dimensions and materials. In this study, 3D finite element modeling has been used to investigate the effects on the cup contact stress when using Function Graded (FG) Material as a femur head. Also the effects on the cup contact stress due to using different sizes of femur heads, presence of metal backing shell and presence of radial clearance (gap) between cup and femur head are studied. The finite element results show that the using of FG femur head with low stiffness at the outer surface and high stiffness at the core results in significant reduction in the cup contact stress compared with Titanium (Ti), Stainless Steel (SS) and Cobalt Chromium (Co Cr Mo) femur heads. The presence of metal backing shell results in a slight reduction in the cup contact stresses especially for small femur heads. Finally, the presence of radial clearance results in remarkable increase in the cup stress especially for small femur heads. The present results suggested that rather minor changes in design and geometrical parameters of the hip joint have significant consequences (e.g. fatigue, wear, loosening) in the long term use of the joint and should be taken into consideration during the design of the hip joint.

UHMWPE wear response to apposing nitrogen S-phase coated and uncoated orthopaedic implant grade stainless steel

The use of ultra-high molecular weight polyethylene (UHMWPE) components for the articulating surfaces of total hip replacements can be problematic because of their proneness to wear which leads to osteolysis, implant loosening and failure. The ability of the metallic counterface (femoral head) to avoid damage by third body particles is crucial because it is the scratching of this surface that is responsible for the wearing of the UHMWPE (acetabular cup). In the present study the tribological appropriateness of using nitrogen S-phase coatings for the protection of Ortron 90 femoral heads and their suitability for making sliding contact with UHMWPE cups was evaluated. Three S-phase coating materials, containing ∼8, 19 and 26 at.% N, were deposited on to orthopaedic implant grade austenitic stainless steel (Ortron 90) test plates using magnetron sputter deposition and then polished. The UHMWPE wear response to the coated test plates was compared to that of uncoated Ortron 90 with a similar surface roughness ( R a ∼ 0.009 μm or better). The results demonstrated that S-phase coated Ortron 90 caused slightly greater UHMWPE wear, even though the R a for the coatings was lower than the uncoated Ortron 90. This was attributed to subtle differences in the micrometre and sub-micrometre topography between the coated and uncoated test plate countersurfaces, which resulted in a greater frequency of asperity shearing when UHMWPE was slid against the coated plates.

Effect of low protein concentration lubricants in hip simulators

BackgroundProteins play an important role as boundary lubricants in vivo and in vitro. Hip simulator studies have tested various protein concentrations of lubricants. Several groups reported that nonphysiological pits were created with low protein concentrations. Our study showed details of wear findings with low protein concentrations. This may be the first mapping of the run-in wear morphology on ultra high molecular weight polyethylene (UHMWPE) cups. MethodsThe UHMWPE cups used were holding cobalt chrome (CoCr) balls. This study was run on orbital-type hip simulators at up to 1.0 million cycles (Mc). The lubricant was bovine calf serum (0, 3, 5, 7, 10, and 15mg/ml protein concentrations). Two volumes of lubricant were used (40 and 160ml). Volumetric wear rates were calculated and the cup surfaces were observed using reflected light microscopy (RLM) and scanning electron microscopy (SEM). ResultsThe 40-ml volume showed a lower wear rate than the 160-ml volume. The RLM findings showed that the machine marks gradually disappeared up to 1.0 Mc, but there were no obvious pits on the polyethylene surface. The SEM findings showed nonphysiological wear phenomena in the 0-mg/ml protein concentration and physiological wear phenomena in the low protein concentrations. In the main bearing wear area, many nodules were observed with fibrils. In the peripheral bearing wear area, mainly ripples were observed. At the nonbearing wear area, folds were observed. ConclusionsOur study showed the microwear findings with low-protein serum: First, folds were formed, followed by ripples, and finally nodules accompanied by fibrils. During the run-in wear phase, nodules and fibrils had already appeared in the main bearing wear area. Thus, we need to investigate more details of the wear process when folds or ripples change tonodules at the main wear area in the run-in wear.

Wear behaviour of cross-linked polyethylene assessed in vitro under severe conditions

The polyethylene (PE) for hip implants presents serious clinical problems; the production of debris may induce adverse tissue reactions that may lead to extensive bone loss around the implant and consequently osteolysis and implant loosening. Several attempts have been made to improve the wear properties of ultra-high molecular weight polyethylene (UHMWPE). More recently the attention of various researchers has been focused on cross-linked polyethylene (XLPE), due to its improved wear resistance with respect to conventional UHMWPE. This study was aimed at comparing the wear performances of clinically available acetabular liners (Zimmer Inc.) made of electron beam XLPE and conventional UHMWPE. To evaluate the influence of the material properties on wear, conventional UHMWPE and XLPE acetabular cups were tested against deliberately scratched CoCrMo femoral heads ( R a=0.12–0.14 μm) in a hip joint wear simulator run for 3 million cycles with bovine calf serum as lubricant. Gravimetric measurements revealed significant differences between the wear behaviours of the two sets of acetabular cups: XLPE exhibited a wear rate about 40 times lower than conventional UHMWPE. Raman spectroscopy coupled to partial least-squares analysis was used to evaluate the possible crystallinity changes induced by mechanical stress (and thus the material wear resistance): only the UHMWPE cup which showed the highest weight loss displayed significant crystallinity changes. These results were correlated to the thickness of the plasticity-induced damage layer. The wear debris produced during the tests were isolated according to a validated protocol and imaged by scanning electron microscopy . The wear particles produced by XLPE were smaller than those produced by UHMWPE; the latter were observed as fibrillar and agglomerated particles. The mean equivalent circle diameter was 0.71 and 0.26 μm for UHMWPE and XLPE, respectively.

Elastohydrodynamic lubrication analysis of hip implants with ultra high molecular weight polyethylene cups under transient conditions

The transient variation of both the load and speed experienced during walking in an elastohydrodynamic lubrication (EHL) analysis for artificial hip joints employing an ultra high molecular weight polyethylene (UHMWPE) acetabular cup against either a metallic or ceramic femoral head was considered in this study. A general numerical procedure to solve the transient EHL problem in spherical ball-in-socket coordinates, developed in a previous study by Jalali-Vahid and Jin in 2002, was applied under three specific conditions experienced during typical gait cycles, including speed reversal, a sudden load increase and a sudden load decrease. The predicted minimum film thickness was found to stay remarkably constant and similar to that prior to the change in either the load or the angular velocity, despite a large change in these operating conditions. This was attributed to the remarkably effective squeeze-film action of preserving and maintaining the lubricating film developed before the transient variations in either the load or speed. It is therefore possible to neglect the effect of these specific transient variations of load and speed under physiological walking conditions considered in the present study on the predicted film thickness in hip implants with UHMWPE cups.

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.

Contamination of polyethylene cups with polymethyl methacrylate particles: An experimental study

The articulating surfaces of 6 ultra–high molecular weight polyethylene cups were exposed to curing polymethyl methacrylate (PMMA) bone–cement and examined with scanning electron microscopy and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). Three of the cups were exposed to blood and bone–cement, and the rest were exposed to bone–cement only. After removal of the bone–cement bulk, PMMA particles were found and identified in all 6 cups. The particles were verified by identifying zirconium with energy-dispersive x-ray fluorescence spectroscopy in 5 cups and with LA-ICPMS in 1 cup. The degree of surface contamination was estimated with LA-ICPMS. The number of zirconium-containing particles detected was on average 10 to 20/mm2. PMMA bone–cement left in polyethylene cups during polymerization can contaminate the articulating surface with adherent PMMA particles.

Microwear phenomena of ultrahigh molecular weight polyethylene cups and debris morphology related to γ radiation dose in simulator study

Microwear phenomena of ultrahigh molecular weight polyethylene cups and debris morphology related to γ radiation dose in simulator study