Wear of the ultra-high molecular weight polyethylene (UHMWPE) insert is one of the major issue related to orthopaedic implants. In this study, the tribo-mechanical properties of zirconia-coated UHMWPE deposited by means of Pulsed Plasma Deposition (PPD) technique were analyzed. Specifically, strength to local plastic deformation, indentation work portioning and creep behavior were evaluated through nanoindentation and micro-scratch tests, whereas preliminary wear data were obtained by tribology tests. A strong reduction of plastic deformation and a drop of the creep phenomenon for the zirconia-coated UHMWPE were evidenced, whereas - in spite of similar wear data - different wear mechanism was also detected. This study supported the use of hard ceramic thin films to enhance the mechanical performance of the plastic inserts used in orthopaedics

Introduction. Aseptic loosening is a major cause of revision of total joint arthroplasty (TJA). Although crosslinked Ultra-high molecular weight polyethylene (UHMWPE) have improved wear resistance, residual radicals remaining in the material have a possibility to increase bio-reactivity of particles [2]. In this study, we attempt to evaluate the effects of irradiation and residual radicals on bio-reactivity of the material with a new method called the inverse culture method [1]. Material and methods. UHMWPE particles (10µm diameter in average, Mitsui chemicals Co., LTD) along with irradiated particles (RAD, 300kGy electron irradiation) and particles annealed after the irradiation (RAD+ANN, 100°C 72 hours) are co-incubated with mouse macrophage cell line RAW264 using the inverse culture method. The amount of TNF-α was measured with ELISA. Results and discussion. The amount of TNF-α released by macrophages reacting with virgin UHMWPE, RAD and RAD+ANN is shown in Figure 1. The horizontal axis represents the total surface area of the particles. The coefficient of determination and inclination of the approximate curve are calculated to analyze the result. The coefficient of determination suggested that cytokines released from macrophage is dose-dependent to the surface area of polyethylene particles, which was consistent with the result of our former study[1]. We use the inclination of the approximation curve in Figure 1 as an index to evaluate the bio-reactivity. The values of the index of virgin, RAD and RAD+ANN were 21×10. -4. gLm. -2. , 100×10. -4. gLm. -2. and 59×10. -4. gLm. -2. The inclination of the approximation line of RAD is significantly larger than that of virgin (test for the difference of regression line angle). These suggest that the irradiation to UHMWPE particles increases their bio-reactivity possibly due to radicals. The increased reactivity cannot be eliminated by annealing (100°C 72 hours) completely. Conclusion. Although electron irradiation increases the bio-reactivity of UHMWPE particles, annealing after the irradiation can decrease it, but cannot restore to original reactivity. For any figures or tables, please contact authors directly

Recent advancements in biomaterial technology have created novel options for acetabular fixation in primary total hip arthroplasty (THA). For example, cementless acetabular fixation has become the preferred option, however, there is continued debate concerning whether long-term survivorship is comparable to that of cemented component fixation. Many doubts previously associated with early cementless designs have been addressed with newer features such as improved locking mechanisms, enhanced congruity between the acetabular liner and the shell, and the inclusion of highly cross-linked ultra-high molecular weight polyethylene (UHMWPE). Additionally, there has been increased utilization of new porous metals, titanium mesh, and hydroxyapatite (HA) coated implants. However, several retrieval studies have indicated that porous-coated cementless acetabular components can exhibit poor bony ingrowth. Many surgeons in Europe favor cemented fixation, where registry data is favorable for this interface. A surgeon's decision to use a cemented or cementless acetabular component is typically dependent on factors such as patient bone stock, surgical training, and experience. With the frequency of THAs expected to increase, it is particularly important for orthopaedic surgeons to be familiar with appropriate preoperative planning and component selection in an effort to achieve optimal outcomes. Therefore, this talk will outline and describe the options currently available for cementless and cemented acetabular fixation in primary total hip arthroplasty

The purpose of this investigation is to assess the rate of wear the effect once the “bedding in period”/ poly creep had been eliminated. Creep is the visco-elastic deformation that polyethylene exhibits in the first 6–12 weeks. We also assessed the wear pattern of four different bearing couples in total hip arthroplasty (THA): cobalt-chrome (CoCr) versus oxidized zirconium (OxZir) femoral heads with ultra-high molecular weight polyethylene (UHMWPE) versus highly-crosslinked polyethylene (XLPE) acetabular liners. This was a randomized control study involving 92 patients undergoing THA. They were randomized to one of four bearing couples: (1) CoCr/UHMWPE (n= 23), (2) OxZir/UHMWPE (n=21), (3) CoCr/XLPE (n=24), (4) OxZir/XLPE (n=24). Patients underwent a posterior approach from one of three surgeons involved in the study. All patients received a porous-coated cementless acetabular shell and a cylindrical proximally coated stem with 28 mm femoral heads. Each patient was reviewed clinically and radiographically at six weeks, three and 12 months, two, five and 10 years after surgery. Standardized anteroposterior and lateral radiographs were taken. All polyethylene wear was measured by an independent blinded reviewer. Linear and volumetric wear rates were measured on radiographs using a validated computer software (Polyware Rev. 5). Creep was defined as the wear at 6 or 12 weeks, depending on if there was a more than 10% difference between both measurements. If a greater than 10% difference occurred than the later period's wear would be defined as creep. 72 hips were included in analysis after exclusion of seven revisions, three deaths and 10 losses to follow-up. The annual linear wear rates (in mm/y) at 10 years were (1) 0.249, (2) 0.250, (3) 0.074 and (4) 0.050. After adjusting for creep these rates become were (1) 0.181, (2) 0.142, (3) 0.040 and (4) 0.023. There is statistical differences between raw and adjusted linear wear rates for all bearing couples. The percentage of the radiographically measured wear at 10 years due to creep is (1) 30% (2) 44%, (3) 58.5% and (4) 51.5% with significant differences in couples with XLPE versus those with UHMWPE. There was no significant correlation between age, gender, cup size, tilt, planar anteversion and the linear or volumetric wear rates. The linear wear rate of both UHMWPE and XLPE are even lower thxdsxzan previously described when creep is factored out. XLPE has again demonstrated far superior linear wear rates at 10 years than UHMWPE. There were no significant differences in wear rate at 10 years between CoCr and OxZir, this may be due to an underpowered study. XLPE exhibits proportionally more creep than UHMWPE within the first 6–12 weeks and accounts for more of the total wear at 10 years as measured radiographically at the end period

Polyethylene wear-debris induced inflammatory osteolysis is known as the main cause of aseptic loosening and long term revision total hip arthroplasty. Although recent reports suggest that antioxidant impregnated ultra-high molecular weight polyethylene (UHMWPE) wear-debris have reduce the osteolytic potential in vivo when compared to virgin UHMWPE, little is known about if and/or how PE rate of oxidation affects osteolysis in vivo. We hypothesized that oxidized UHMWPE particles would cause more inflammatory osteolysis in a murine calvarial bone model when compared to virgin UHMWPE. Male C57BL/6 eight weeks old received equal amount of particulate debris overlaying the calvarium of (n=12/group): sham treatment (no particles), 2mg (6,75×107 particles/mg) of endotoxin-free UHMWPE particles (PE) or of endotoxin-free highly oxidized-UHMWPE (OX) particles. In vivo osteolysis was assessed using high resolution micro-CT and inflammation with L-012 probe dependent luminescence. At day 10, calvarial bone was examined using high resolution micro-CT, histomorphometric, immunohistochemistry analyses and qRT-PCR to assess OPG, RANK, RANK-L, IL-10, IL-4, IL-1b and TRAP genes expression using the protocol defined by individual TaqManTM Gene Expression Assays Protocol (Applied Biosystems). In vivo inflammation was significantly higher in the OX (1.60E+06 ± 8.28E+05 photons/s/cm2) versus PE (8.48E+05 ± 3.67E+05) group (p=0.01). Although there was a statistically significant difference between sham (−0.27% ± 2.55%) and implanted (PE: −9.7% ± 1.97%, and OX: − 8.38% ± 1.98%) groups with regards to bone resorption (p=0.02), this difference was not significant between OX and PE (p = 0.14). There was no significant difference between groups regarding PCR analyses for OPG, RANK, RANK-L, IL-10, IL-4, IL-1b and TRAP (p = 0.6, 0.7, 0.1, 0.6, 0.3, 0.4, 0.7 respectively). Bone volume density was significantly decreased in PE (13.3%±1.2%) and OX (12.2%±1.2%) groups when compared to sham (15%±0.9%) (p < 0 .05). Histomorphometric analyses showed a significantly decreased Bone Thickness/Tissue Thickness ratio in the implanted group (0.41±0.01 mm and 0.43±0.01 mm) compared to sham group (0.69± 0.01) (p < 0 .001). However, there were no significant difference between OX and PE (p = 0.2). Our findings suggest that oxidized UHMWPE particles display increased inflammatory potential. Results were not significant regarding in vivo or ex vivo osteolysis. As antioxidant-diffused UHMWPE induce less inflammation activity in vivo, the mechanism by which they cause reduced osteolysis requires further investigation

INTRODUCTION. Shoulder joint prostheses have become the most commonly replaced after knee and hip artificial implants. Reverse shoulder arthroplasty (RSA) is the treatment option for patients with severe osteoarthritis, rotator cuff arthropathy or a massive rotator cuff tear with pseudoparalysis. Though successful, the long-term survival of such implants are limited by wear of the materials in contact [1, 2]. The aim of this study was to investigate RSA wear in vitro using a clinically relevant activities of daily living (ADLs). MATERIALS AND METHODS. Four new JRI Orthopaedics Reverse Shoulder 42 mm diameter VAIOS with cobalt-chromium (CoCr) glenospheres and ultra-high molecular weight polyethylene (UHMWPE) humeral components were tested. A five million cycles wear test was undertaken using the unique Newcastle Shoulder Wear Simulator with dilute bovine serum as a lubricant. “Mug to mouth” was performed as the ADL to the test prostheses in intervals of 100 cycles, following by 5 seconds of high load (450N) with no motion simulating an ADL such as “lifting an object”. This combined load cycle was then repeated. A fifth reverse shoulder prosthesis was subject to dynamic loading only in a soak control station. Wear was assessed gravimetrically and roughness (Sa) of the articulating surfaces was measured with a non-contacting profilometer. RESULTS AND DISCUSSION. The mean wear rate and standard deviation of the UHMWPE components was 11.4±3.7 mm. 3. /million cycles, while the CoCr components showed minimal wear over the test duration of 0.01± 0.02 mm. 3. /million cycles (Fig.1). Wear rates are comparable with Kohut et al. (14.1 mm. 3. /million cycles) [3] and Smith et al. (14.3±1.6 mm. 3. /million cycles) [4]. The CoCr glenospheres roughness was unchanged, from 32±8 nm Sa to 28±8 nm Sa over the 5 million cycles of the test (p=0.017), while the UHMWPE humeral components became smoother, from 692±123 nm Sa to 42±29 nm Sa (Fig.2), showing a statically significant change (p<0.001). CONCLUSION. The present study is the first wear test of artificial shoulder joints using a Motion-Load-Motion configuration as a clinically relevant physiological pattern of motion and load. Results are comparable with those found in the literature for in vitro testing of reverse shoulder replacements. For any figures or tables, please contact the authors directly

Introduction. Despite the positive outcomes in shoulder joint replacements in the last two decades, polyethylene wear debris in metal-on-polyethylene artificial shoulder joints is well-known as a limitation in the long-term survival of shoulder arthroplasties systems. Consequently, there is an interest in the use of novel materials as an alternative to hard bearing surfaces such as pyrolytic carbon layer (PyroCarbon). Materials and Methods. In the present study, the unique Newcastle Shoulder Wear Simulator was used (Smith et al., 2015; Smith et al., 2016) to evaluate the wear behavior of four commercially available PyroCarbon humeral heads 43 mm diameter, articulating against conventional ultra-high molecular weight polyethylene (UHMWPE) glenoid inserts with a radius of curvature of 17.5 mm to form an anatomic total shoulder arthroplasty. A physiological combined cycled “Repeat-motion-load” (RML) (Ramirez-Martinez et al., 2019) obtained from the typical activities of daily life of patients with shoulder implants was applied as a simulator input. A fifth sample of the same size and design was used as a soak control and subjected to dynamic loading without motion during the wear test. The mean volumetric wear rate of PyroCarbon-on-polyethylene was evaluated over 5 million cycles gravimetrically and calculated on the basis of linear regression, as well as the change in surface roughness (S. a. ) of the components using a non-contacting white light profilometer throughout the test. Results. The gravimetric analysis showed a mean volumetric wear rate and standard deviation of 19.3±9.5 mm. 3. /million cycles for the UHMWPE glenoid inserts, whereas PyroCarbon humeral head counterparts did not exhibit a loss in mass throughout the test. The roughness values of the UHMWPE glenoid inserts decreased (P < .001), changing from 296±28 nm to 32±8 nm at the end of the test. In contrast, the PyroCarbon humeral heads did not show a significant change (P = .855) over the 5 million cycles; remained in the same range (21±2 nm to 20±10 nm) with no evidence of wear damage on the surface. Conclusions. This is the first in-vitro shoulder simulator study of a PyroCarbon on UHMWPE articulation. Wear rates were similar to that found to well-proven metal on UHMWPE shoulder arthroplasties. While it was interesting to see that the PyroCarbon did not roughen over the test duration, the lack of an appreciable reduction in wear of the UHMWPE component when articulated with an expensive and complex to manufacture PyroCarbon component likely means there is little clinical cost-benefit in the use of a PyroCarbon on UHMWPE shoulder implant. Declaration of competing interest. Prof. Ian A. Trail received some royalties and research support from Wright Medical Group N.V. None of the other authors, their immediate families, and any research foundation with which they are affiliated did not receive any financial payments or other benefits from any commercial entity related to the subject of this article. For any figures or tables, please contact authors directly

Introduction. Orthopedic implants are subject to wear and release ultra-high molecular weight polyethylene (UHMWPE) debris. Analysis of UHMWPE wear particles is critical in determining the safety and effectiveness of novel orthopedic implants. Complete digestion of periprosthetic tissue and wear fluid is necessary to ensure accurate morphological and quantitative particle analysis. Acid digestion methods are more effective than enzymatic and base digestion approaches [Baxter+ 2009]. However, optimal digestion times, quantity, and type of acid are unclear for particle isolation. In addition, imaging and analysis techniques are critical to ensure accurate reporting of particle characteristics. Here, we 1) compared the efficacy of three acid-based digestion methods in isolating particles from a) bovine serum and b) animal/human tissue, and 2) analyzed the effects of imaging location on particle quantity/morphology results. Methods. 1a) UHMWPE (GUR 150) particles were generated by Mode I knee wear testing for 1 million cycles in bovine serum. Serum was digested in one of four solutions: 12.2M HCl, 15.8M HNO. 3. , a 1:1 volume ratio of HNO. 3. :HCl (aqua regia), or filtered H. 2. O (control). The serum:solution volume ratio was 1:5 [Niedzwiecki+ 2001, ISO 17853:2011]. Digestion occurred for 60min on a stir plate at 60°C. Each digest was combined with MeOH at a 1:5 digest:MeOH volume ratio and filtered using a 100 nm polycarbonate membrane. The particle-containing membranes were imaged (12 images/membrane) using scanning electron microscopy (SEM) to determine particle characteristics, including quantity, equivalent circular diameter (ECD) and aspect ratio (AR). 1b) Based on 1a, HNO. 3. was used to digest porcine and human tissue at concentrations of 1:40, 1:60, or 1:80 tissue:HNO. 3. volume ratios for either 1, 12, or 24 hours, followed by SEM analysis. 2) Particle characteristics were compared at nine locations (20 images/location) across a particle-containing membrane to determine the effects of imaging location. Results. 1a) HNO. 3. and aqua regia methods successfully digested the bovine serum, whereas the HCl and H. 2. O methods were unsuccessful (Fig.1A). Comparing HNO. 3. and aqua regia groups, particle characteristics and ECD frequency distribution were nearly identical (Fig.1B). 1b) Nitric acid did not fully digest porcine or human tissues. 2) Similar particle characteristics were observed in all nine locations analyzed across the polycarbonate membrane. The particle quantity, ECD, and AR for a representative center vs. intermediate location were 808 vs. 780 particles, 0.33±0.28 vs. 0.35±0.29 µm, and 1.57±0.56 vs. 1.51±0.4, respectively (Fig.2). Conclusions. Nitric acid and aqua regia are capable of digesting bovine serum using low quantities of acid for short duration, allowing precise analysis of UHMWPE particle debris from orthopedic implants. However, further optimization of digestion techniques for animal/human tissue is warranted. In addition, an accurate representation of particle distribution can be achieved without analyzing hundreds of images, because membrane location does not strongly influence particle results. Finally, ASTM F1877-16 – Standard Practice for Characterization of Particles – could benefit from adding software-based automated particle characterization as an optional method. An automated approach that uses k-means clustering image segmentation to identify particles and computer vision tools to extract relevant morphological features is under development and validation

Introduction. Total hip replacement with metal-on-polymer (MoP) hip prostheses is a successful treatment for late-stage osteoarthritis. However, the wear debris generated from the polymer acetabular liners remains a problem as it can be associated with osteolysis and aseptic loosening of the implant. This has led to the investigation of more wear resistant polymers in orthopaedics. Cross-linked polyethylene (XLPE) is now the gold-standard acetabular liner material. However, we asked if carbon fibre reinforced polyether ether ketone (CFR-PEEK) might be a lower wear material. In addition, we sought to understand the influence of contact stress on the wear of both XLPE and CFR-PEEK as this has not previously been reported. Materials and Methods. A 50-station circularly translating pin-on-disc (SuperCTPOD) machine was used to wear test both XLPE and CFR-PEEK pins against cobalt chromium (CoCr) discs to investigate the influence of contact stress on their wear rates. Fifty XLPE and 50 CFR-PEEK pins were articulated against CoCr discs. The pins, 9 mm in outer diameter and 12 mm in height, were drilled with different diameter holes to generate different sized annuli and thus, different contact areas. The pins were tested at 1.10, 1.38, 1.61, 2.00 and 5.30 MPa, which are typical contact stresses observed in the natural hip joint. An additional pin for every test group was used as a control to track the lubricant uptake. The discs were polished to 0.015 μm Sa prior to testing. The test stations contained 16 ml of diluted newborn calf serum (protein concentration: 22 g/L). Wear was measured gravimetrically with a balance (resolution: 10 μm) every 500,000 cycles. A standardised cleaning and weighing protocol was followed. Results and Discussion. The wear rates for the XLPE pins were calculated as 1.05, 0.90, 0.77, 0.48 and 0.28 mg/million cycles for the different pin stress groups respectively. The wear rates decreased with increasing contact stress, which was similar to what was observed for ultra-high molecular weight polyethylene (UHMWPE). The change in weight of the discs was insignificant (p-value:0.85). For the CFR-PEEK pin groups, the wear rates were calculated as 0.56, 0.65, 0.61, 0.58 and 0.65 mg/million cycles respectively. The difference between the wear rates was insignificant (p-value: 0.92). However, the weight of the discs decreased significantly (p-value: 0.00). At 1.11 MPa and taking data for UHMWPE tested in the same way, comparison of the three polymers showed that CFR-PEEK produced the lowest wear against CoCr. Although the wear rates for CFR-PEEK were found to be the lowest, the decrease in weight of the CoCr discs articulated against CFR-PEEK was indicative of metallic wear. Conclusion. CFR-PEEK should not be used against orthopaedic metals. XLPE articulating against CoCr was found to be the optimum combination, producing low wear without causing weight change from the counterface, under varying contact stresses

Introduction. Wear phenomenon of ultra-high molecular weight polyethylene (UHMWPE) in hip and knee prostheses is one of the major restriction factors on the longevity of these implants. In retrieved hip prostheses with screw holes in the metal acetabular cup for fixation to the pelvis, the generation of cold flow into the screw holes is frequently observed on the backside of the UHMWPE acetabular cup liner. In most retrieved cases, the protruded areas of cold flow on the backside were located on the reverse side of the severely worn and deformed surface of the polyethylene liner. It would appear that the cold flow into screw holes contributes to increase of wear and damages of the polyethylene liner in hip prosthesis. Methods. In a previous study (Cho et al., 2016), we pointed out the generation of cold flow into the screw holes on the backside of the retrieved UHMWPE acetabular cup liner as shown in Figure 1. The primary purpose of this study was to investigate the influence of the cold flow into the screw holes on the wear of the polyethylene liner in hip prosthesis. In this study, computer simulations of the generation of cold flow were performed using the finite element method (FEM) in order to propose the design criteria about the cold flow of the hip prosthesis for improving the wear resistance of the polyethylene liner. We especially focused on the influence of polyethylene thickness and contact surface conformity on the generation of cold flow into the screw hole. Results. An example of the results of a series of the FEM simulations performed in this study is shown in Figure 2. This figure shows the distributions of the contact stress in the polyethylene liners. The graphs shown in Figure 3 are the summary of results of a series of the FEM simulations performed in this study. The graph in Figure 3(a) shows the changes in the maximum contact stress in the polyethylene liner with the thickness of polyethylene liner. The graph in Figure 3(b) shows the changes in the maximum contact stress in the polyethylene liner with the radial clearance between the femoral head and the polyethylene liner. Discussion and Conclusions. It was found that the magnitudes of cold flow and maximum contact stress in the polyethylene liner had a tendency to increase with decreasing the thickness of polyethylene liner. It was also found that the magnitude of cold flow and maximum contact stress in the polyethylene liner had a tendency to increase with increasing the radial clearance between the femoral head and the polyethylene liner. The results of this study suggest that polyethylene thickness and contact surface conformity have a significant influence on the generation of cold flow into the screw holes and wear of the polyethylene liner. For any figures or tables, please contact authors directly

This study presents the use of precision surface machining on artificial joint bearing surfaces in order to inhibit macrophage activation. Ultra-high molecular weight polyethylene (UHMWPE) is widely used as a bearing material in polymer-on-hard joint prostheses. However, UHMWPE wear particles are considered to be a major factor in long-term osteolysis and implant loosening. Several studies report that wear particle size is a critical factor in macrophage activation, with particles in the size range of 0.1 – 1.0 μm being the most biological active. The surface for a conventional Co-Cr-Mo alloy joint implant generally has a 10.0 – 20.0 nm roughness. After precision machining, the Co-Cr-Mo alloy surface had a 1.0 – 2.0 nm roughness with scattered concave shapes up to 50 nm in depth. This precision surface machining method used a typical lapping method, but the relationship between the slurry and the machining surface was strictly controlled in order to emphasize the micro-erosion mechanism. A pin-on-disc wear tester capable of multidirectional motion was used to verify that the new surface was the most appropriate for joints. Tests were carried out in 25% (v/v) fetal calf serum with sodium azide to retard bacterial growth. UHMWPE pins, 12.0 mm in diameter with a mean molecular weight of 6.0 million, were placed on the Co-Cr-Mo alloy disc at a contact pressure of 6.0 MPa. A sliding speed of 12.1 mm/s, and a total sliding distance of 15.0 km were applied. The new surface reduced the amount of UHMWPE wear, which would ensure the long-term durability of joints. The new surface also enlarged the size of UHMWPE particles, but did not change their morphological aspect. Primary human peripheral blood mononuclear phagocytes were cultured with the particles. The wear particles generated on the new surface inhibited the production of IL-6, which indicates a reduction of induced tissue reaction and joint loosening

Introduction. Ultra-high molecular weight polyethylene (UHMWPE) is the sole polymeric material currently used for weight- bearing surfaces in total joint replacement. However, the wear of UHMWPE in knee and hip prostheses after total joint replacement is one of the major restriction factors on the longevity of these implants. In order to minimize the wear of UHMWPE and to improve the longevity of artificial joints, it is necessary to clarify the factors influencing the wear of UHMWPE. A number of studies have investigated the factors influencing the wear of UHMWPE acetabular cup liner in hip prosthesis. Most of these studies, however, have focused on the main articulating surfaces between the femoral head and the polyethylene liner. Materials and Methods. In a previous study (Cho et al., 2016), the generations of cold flow into the screw holes in the metal acetabular cup were observed on the backside of the retrieved UHMWPE acetabular cup liners as shown in Figure 1. We focused on the screw holes in the metal acetabular cup (Figure 2) as a factor influencing the wear behavior of polyethylene liner in hip prosthesis. In this study, computer simulations of the generation of cold flow into the screw holes were performed using the finite element method (FEM) in order to investigate the influence of the screw holes in the metal acetabular cup on the mechanical state and wear behavior of polyethylene liner in hip prosthesis. Results. An example of the results of the FEM simulations performed in this study is shown in Figure 3. In the region which the cold flow into the screw holes occurred, it was found that locally high contact stresses which exceed the yield stress of UHMWPE and considerable plastic strains were generated throughout the overall thickness between the backside and top surface of the polyethylene liners. On the contrary, in the case of the polyethylene liner combined with the metal acetabular cup without screw hole, although the regions of high contact stress and high plastic strain had a tendency to be limited around contact surface compared with those of the combination with screw holes, the values of contact stress and plastic strain were lower than the combination with screw holes. Discussion and Conclusions. The results of this study suggest that the cold flow generated by the existence of the screw holes in the metal acetabular cup of hip prosthesis reduces the wear resistance of the UHMWPE acetabular cup liner. It would appear that the cold flow into the screw holes contributes to structural weakening of the UHMWPE and reduction of the polyethylene thickness, thus increase of internal stresses and plastic strains in and around the regions of cold flow. Therefore, it is required that improvement of the screw holes in the metal acetabular cup and/or improvement of fixation method of the metal acetabular cup to a pelvis in order to enhance the wear resistance of the polyethylene liner. For any figures or tables, please contact authors directly

Introduction. Ultra-high molecular weight polyethylene (UHMWPE) is the sole polymeric material currently used for weight- bearing surfaces in total joint replacement. However, the wear of UHMWPE in the human body after total joint replacement causes serious clinical and biomechanical reactions. Therefore, the wear phenomenon of UHMWPE is now recognized as one of the major factors restricting the longevity of artificial joints. In order to minimize the wear of UHMWPE and to improve the longevity of artificial joints, it is necessary to clarify the factors influencing the wear mechanism of UHMWPE. Materials and Methods. In a previous study (Cho et al., 2016), it was found that roundness (out-of-roundness) of the retrieved UHMWPE acetabular cup liner [Figure 1(a)] had a tendency to increase with increasing roundness of the retrieved metal femoral head [Figure 1(b)]. It appears that roundness of the femoral head contributes to increase of wear of the polyethylene liners. We focused on the roundness of femoral head as a factor influencing the wear of polyethylene liner in hip prosthesis. In this study, further roundness measurements for 5 retrieved metal femoral heads were performed by using a coordinate measuring machine. The elasto-plastic contact analyses between femoral head and polyethylene liner using the finite element method (FEM) were also performed in order to investigate the influence of femoral head roundness on the mechanical state and wear of polyethylene liner in hip prosthesis. Results. The range of roundness of the 5 retrieved metal femoral heads measured in this study was 14.50∼44.70 µm. Two examples of the results of FEM contact analyses are shown in Figure 2. Figure 2(a) is the results of the repeated contact analysis between femoral head and polyethylene liner under constant axial loading of 1000 N. Figure 2(b) is the results of the repeated contact analysis between femoral head and polyethylene liner under hip joint loading during normal gait. These figures show the distribution of the contact stress (von Mises equivalent stress) in the polyethylene liner. The graph in Figure 3 shows the changes in the maximum contact stress in the polyethylene liner with the flexion/extension angle of femoral head. Discussion and Conclusions. As the results of a series of the FEM contact analyses, it was found that repeated high contact stresses which exceed the yield stress of UHMWPE caused by roundness of the metal femoral head occurred in the polyethylene liner as shown in Figures 2 and 3. It was also found that the magnitude and amplitude of the repeated contact stresses had a tendency to increase with increasing roundness of the femoral head and axial loading applied to the femoral head. The results of this analytical study suggest that the roundness (out-of- roundness) of the femoral head is associated with accelerating and/or increasing wear of the UHMWPE acetabular cup liner in a hip prosthesis after total hip replacement. For any figures or tables, please contact authors directly

Introduction. Ultra-high molecular weight polyethylene (UHMWPE) is the sole polymeric material currently used for weight- bearing surfaces in total joint replacement. However, the wear of UHMWPE and the polyethylene wear debris generated in the human body after total joint replacement cause serious clinical and biomechanical reactions. Therefore, the wear phenomenon of UHMWPE in total joint replacement is now recognized as one of the major factors restricting the longevity of these implants. In order to minimize the wear of UHMWPE and to improve the longevity of artificial joints, it is necessary to clarify the factors influencing the wear mechanism of UHMWPE. Materials and Methods. The wear and/or failure characteristics of 33 retrieved UHMWPE acetabular cup liners of hip prostheses were examined in this study. The retrieved liners had an average in vivo duration of 193.8 months (75 to 290 months). Several examples of the retrieved liners are shown in Figure 1. The elasto-plastic contact analyses between metal femoral neck and polyethylene liner and between metal femoral head and polyethylene liner using the finite element method (FEM) were also performed in order to investigate the factors influencing the wear and/or failure mechanism of the polyethylene liner in hip prosthesis. Results. In the examination of the retrieved polyethylene liners, the generation of component impingement was observed in 24 cases of the 33 retrieved liners (72.7%) as shown in Figures 1(a) and (b). In addition, the generation of cold flow into the screw holes in the metal acetabular cup was observed in 27 cases of the 33 retrieved liners (81.8%) as shown in Figures 1(c) and (d). Several examples of the results of the FEM contact analyses are shown in Figure 2. In the simulation of the component impingement, it was found that high contact stresses which exceed the yield stress of UHMWPE and considerable plastic strains occurred in the rim of the polyethylene liner as shown in Figures 2(a) and (b). In the simulation of the cold flow, it was found that the stress concentration near the edge of screw hole has significant influence on the states of contact stresses and plastic strains in the surface and undersurface (backside) of the polyethylene liner as shown in Figures 2(c) and (d). Discussion and Conclusions. In this study, we focused on the impingement between the metal femoral neck and the polyethylene liner and the cold flow into the screw holes on the backside of the polyethylene liner as the factors influencing the wear and/or failure of the UHMWPE acetabular cup liner in hip prosthesis. The results of these retrieval and analytical studies confirmed that the component impingement and the cold flow into the screw holes contribute to increase of wear and/or failure of the polyethylene liner. Therefore, it is necessary to improve resistance to the component impingement and the cold flow in order to decrease the wear and/or failure of the UHMWPE acetabular cup liner and to increase the longevity of hip prosthesis. For any figures or tables, please contact authors directly

INTRODUCTION. Studies of retrieved TKR components demonstrate that in vivo wear on the articular surface of polyethylene liners exhibits a much higher variability on their in vitro counterparts. Only one study has attempted to validate a patient-specific model of wear with a clinically retrieved component. The purpose of this study is to investigate the relationship between observed TKR contact conditions during gait and measured volume loss on retrieved tibial components. METHODS. Eleven retrieved ultra-high molecular weight polyethylene (UHMWPE) cruciate-retaining tibial liner components from ten separate patients (implantation time = 8.6±5.6 years) had matching gait trials of normal level walking for each knee. Volume loss on retrieved components was calculated using a coordinate measuring machine and autonomous reconstruction. Motion analysis of normal level walking gait had been conducted between 1986 and 2005 for various previous studies and stored in a consented Human Mechanics Repository, ranging from pre-operative to long-term post- operative testing. Contact location between the femoral component and the tibial component on the medial and lateral plateaus were calculated throughout stance. A previously validated and fine-tuned parametric numerical model was used to calculate TKR contact forces for each gait trial. Vertical contact forces and contact paths on the medial and lateral plateaus were input as normal force and sliding distance to a simplified Archard equation for wear with material wear constant averaged from literature (2.42 × 10. −7. mm. 3. /Nm) to compute average wear per gait cycle. Wear rates were calculated using linear regression, and Pearson correlation examined correlations between modeled and measured wear. RESULTS. Secondary motions at the knee from gait testing showed distinct grouping between trials of each patient. Three components demonstrated severe polyethylene delamination and were excluded from wear rate analyses. Calculated wear rates for measured and modeled volume loss showed excellent agreement on total surface (15.9 vs. 16.4 mm. 3. /year), medial sides (11.4 vs. 11.7 mm. 3. /year) and lateral sides (4.4 vs. 4.7 mm. 3. /year) and were not significantly different. Volumes were significantly correlated between measured and modeled wear for the total part (r=0.758, p=0.017) and on the medial side (r=0.780, p=0.012), but not for the lateral side (r=0.482, p=0.154). DISCUSSION. Measured wear rates were comparable to a previous study of a large population of retrieved MGII components. Medial wear volumes for six of eight mild wearing components were closely tracked by their modeled counterparts. Because the Archard equation produces wear volumes that are linearly related to time in situ, deviations from linear predictions arise from patient-specific variations in contact forces and tibiofemoral pathways during normal walking gait. As suggested by the results of the current study, these variations in gait between patients result in meaningful differences to the wear of the UHMWPE component. Despite many assumptions, this study demonstrates the feasibility of a patient-specific model of wear using a rare population of gait-matched retrievals

Ultra-high molecular weight polyethylene (UHMWPE) is the sole polymeric material currently used for weight-bearing surfaces in total joint arthroplasty. However, the wear phenomenon of UHMWPE components in knee and hip prostheses after total joint arthroplasty is one of the major restriction factors on the longevity of these implants. In order to minimize the wear of UHMWPE and to improve the longevity of artificial joints, it is necessary to clarify the factors influencing the wear mechanism of UHMWPE. In the microscopic surface observation of the virgin knee prosthesis with anatomical design, various grades of microscopic surface scratches and defects caused by machining and surface finishing processes during manufacture of the component were observed on the surface of the metallic femoral component [Fig. 1] (C. Cho et al, 2009), although the overall surface were finished at smoother level. It is thought that certain levels of the microscopic surface asperities caused by these surface damages in the metallic femoral component might contribute to increasing and/or accelerating wear of the UHMWPE tibial insert. Therefore, it is necessary to clarify quantitatively the influence of the microscopic surface asperities of the metallic components in virgin artificial joints on the wear of UHMWPE components. The primary purpose of this study was to investigate the influence of the microscopic surface asperities of the virgin metallic femoral component on the wear of the UHMWPE tibial insert in the virgin knee prosthesis. In this study, the authors focused on the three-dimensional shape of the microscopic surface asperities as a factor influencing the wear mechanism of the UHMWPE tibial insert. The 3D microscopic surface profile measurement of the virgin metallic femoral component using a laser microscope and reproduction of the femoral component surface using 3D CAD software were performed [Fig. 2] in order to produce idealized 3D finite element models of the microscopic surface asperity of the femoral component based on actual measurement data. Elasto-plastic finite element contact analyses between idealized microscopic surface asperities and UHMWPE were also performed in order to investigate the influence of the three-dimensional shape of the microscopic surface asperities of the virgin metallic femoral component on the wear of the UHMWPE tibial insert. The analytical findings of this study suggest that the aspect ratio and shape ratio [Fig. 3] of the microscopic surface asperity of the virgin metallic femoral component have an important influence on increasing and/or accelerating wear of the UHMWPE tibial insert

Today's aging society is seeing an increase of patients with rheumatoid arthritis and osteoarthritis, as well as an increase in joint replacement surgery. The artificial joints used in this surgery frequently uses ultra-high molecular weight polyethylene (UHMWPE) as a bearing material. However, UHMWPE wear particles are considered to be a major factor in long-term osteolysis, and implant loosening. Many researchers have reported that the volume and size of particles are critical factors in macrophage activation, with particles in the size range of 0.1 – 1.0 μm being the most biologically active. The micro slurry-jet erosion (MSE) apparatus was introduced to minimize the amount of wear, and increase the size of UHMWPE wear particles by texturing the surfaces of Co-Cr-Mo alloy implants. The MSE apparatus uses a slurry of alumina particles (WA#8000: average diameter 1.2 μm) mixed with water. The slurry and compressed air are mixed within an injection nozzle, which is then applied to the Co-Cr-Mo alloy at high speed to achieve a desired nano-textured surface. In this study, four Co-Cr-Mo alloy surface profiles were prepared. The MSE injection nozzle was fed 40.0 mm in alternating directions across each surface with an orthogonal step of 0.5 mm. The surface M-1 was processed with an injection nozzle feed rate of 1.0 mm/s, and obtained a surface roughness of 5.7 nm. M-2 was processed with a feed rate of 2.0 mm/s, and had a surface roughness of 2.3 nm. The M-4 surface used a 40.0 mm alternating directions surface feed, but with a 1.0 mm orthogonal step, and an injection nozzle feed rate of 0.5 mm/s. It obtained a surface roughness of 4.0 nm. The G-1 surface, with a roughness of 10.0 nm, was processed with the typical lapping method, which is used in conventional artificial joints [Fig. 1]. A pin-on-disk wear tester, capable of multidirectional motion, was used to assess which surface was the most appropriate for artificial joints. The UHMWPE pins were flat ended cylinders, 12.0 mm in diameter, and were placed on the disk with a contact pressure of 6.0 MPa. Tests were carried out in 25% (v/v) fetal calf serum with sodium azide to retard bacterial growth. A sliding speed of 12.1 mm/s, and a total sliding distance of 15.0 km were applied. The wear weight of the MSE textured surface M-1 was significantly lower than the wear weight of the conventional surface. Moreover, the percentages of various wear particle sizes obtained from MSE surface texturing was significantly different from those obtained from the traditional surface

Introduction. Ultra-high molecular weight polyethylene (UHMWPE) tape, which comprised threads of UHMWPE fibers with the thickness less than 0.5 mm, was developed as a flexible fixation device. We describe new techniques using UHMWPE tape for the reattachment of the osteotomised fragment and the repair of intraoperative calcar fractures in total hip arthroplasty (THA). Patients & Methods. We reviewed the medical records and radiographs of the studied subjects after approval of this study by the institutional review board committee. Experiment 1: Between October 2011 and May 2012, 60 consecutive primary THAs were performed with the mini-trochanteric approach, which involved reattaching the osteotomised fragment using UHMWPE tape (Nesplon; Alfresa Pharma, Osaka, Japan). [Fig.1] By splitting the anterior one-fourth of the gluteus medius, the minitrochanteric osteotomy, a half-ellipsoid body about 15 mm long, 10 mm wide, and 5 mm deep, is performed using a curved chisel. After implanting of the prosthesis, the osteotomised fragment is reattached by using two 3-mm wide Nesplon tapes. Using 2.4 mm Kirshner wire, two sets of drill holes are created below the trochanteric bed of the femur. Nesplon tapes are passed through each drill hole and penetrated over the trochanteric fragment. Nesplon tape is tied using a double-loop sliding knot in conjunction with a special tightening gun tensioner up to 20 kgf. [Fig.2] The radiographic results were retrospectively analyzed to determine the incidence of nonunion and complications related to trochanteric site. Hip functional results were rated according to the Japanese Orthopedic Association (JOA) hip score. Experiment 2: Between July 2011 and May 2012, 5-mm wide Nesplon tapes were used for restoration of intraoperative femoral fractures in 4 primary THAs. For the repair of intraoperative proximal femoral fractures, 5-mm wide Nesplon tape is tightened with cerclage wiring technique using the gun tensioner up to 30 kgf. [Fig.3] The postoperative radiographic changes were analyzed. Results. Experiment 1: Nonunions occurred in no (0%) patient. Bone union with minimally displaced was present in three (5.0%) patients. The mean JOA scores improved 47.1 to 84.6 at 1 year postoperatively. Experiment 2: There were no migrations of the femoral prosthesis in the postoperative period. Discussion. These techniques using UHMWPE tapes are simple and more advantageous to prevent the complications resulting from metal wires. UHMWPE tape, which has flat configuration with high flexibility, can provide a greater contact area avoiding the risk of bone cutout. Using a special tightening gun can easy reattachment with precise tension even in the setting of poor bone quality

Purpose:. Although short term outcomes of reverse total shoulder arthroplasty (rTSA) have been promising, long-term success may be limited due to complications, including scapular notching. Scapular notching has been explained primarily as a mechanical erosion, however, generation of wear debris may lead to further biologic changes contributing to the severity of scapular notching. Highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) has been used routinely in constrained joint applications such as total hip arthroplasty for reduction of wear debris particles. Although rTSA shares similarity in design conformity, conventional UHMWPE remains the gold standard. Methods:. A commercially available hip simulator was converted to a 12-station rTSA wear simulator. Conventional and highly cross-linked UHMWPE humeral liners were subjected to 5,000,000 cycles of alternating abduction-adduction and flexion-extension loading profiles. Every 250,000 cycles, liners were evaluated with gravimetric wear measurements and test serum was collected for morphological characterization of wear particles. Results:. Highly cross-linked UHMWPE liners (36.5 ± 10.0 mm. 3. /million cycle) exhibited significantly lower volumetric wear rates compared to conventional UHMWPE liners (83.6 ± 20.6 mm3/million cycle) (p < 0.001) (Figure 1). The flexion-extension loading profile exhibited significantly higher wear rates for both conventional (p < 0.001) and highly cross-linked UHMWPE (p < 0.001) compared to the abduction-adduction loading profile. Highly cross-linked wear particles had an equivalent circle diameter significantly smaller than wear particles from conventional UHMWPE (p < 0.001) (Figure 2). Highly cross-linked wear particles were also significantly less fibrillar than conventional UHMWPE particles with respect to particle aspect ratio (p < 0.001) and particle roundness (p < 0.001). Conclusion:. This is the first study to examine the effect of cross-linked PE in a rTSA wear simulation. Highly cross-linked UHMWPE liners significantly reduced UHWMPE wear and subsequent particle generation. More favorable wear properties with the use of highly cross-linked UHMWPE may lead to increased rTSA device longevity and fewer complications but must be weighed against the impact of reduced mechanical properties

INTRODUCTION. Ultra-High Molecular Weight Polyethylene (UHMWPE) wear debris is thought to be a main factor in the development of osteolysis (1). However, the method for the evaluation of the biological response to UHMWPE particles has not yet been standardized. In this study, four different types of UHMWPE particles were generated using a mechanized pulverizing method and the biological responses of macrophages to the particles were investigated using an inverted cell culturing process (2). MATERIALS & METHODS. Virgin samples were manufactured via Direct Compression Molding (DCM) technique from UHMWPE GUR1050 resin powder (Ticona, USA). For vitamin E (VE)-blended sample, the resin was mixed with VE at 0.3 wt% and the mixture was then molded using DCM. The crosslinked virgin samples were made by gamma ray irradiation to UHMWPE GUR1020 resin sheet (Meditech, USA) with doses of 95kGy ±10% and annealed. The VE-blended crosslinked samples were made by electron beam irradiation to VE-blended samples with doses of 300kGy and annealed. The material conditions were summarized in Figure 1. To pulverize the samples, the Multi-Beads Shocker (Yasui Kikai, Japan) was used. After pulverization, samples were dispersed in an ethanol solution and sequentially filtered through polycarbonate filters. Over 100 sections of the filter were selected randomly and images of the particles were analyzed using scanning electron microscope (SEM). To analyze the macrophage biological response, an inverted cell culturing process was used (2). The mouse macrophage-like cells were seeded at densities of 4×105cells per well in a 96-well culture plate and incubated for 1h. UHMWPE particles suspended in the culture medium were then added to each well in the appropriate amount. After that, fresh medium was added to fill the wells, and a sealing film was used to cover the culture plate. The culture plate was then inverted to cause the UHMWPE particles interact with the adhered macrophages. The inverted culture plate was incubated for 8h. The amount of TNF-α was measured by enzyme-linked immunosorbent assay (ELISA). RESULTS & DISCUSSION. Geometric measurements showed no significant difference in the UHMWPE particles (Figure 2). The amount of TNF-α released stimulated by the crosslinked virgin particles showed significantly higher relative to the other UHMWPE particles (Figure 3). During crosslinking irradiation, the carbon free radicals are generated in the main chain (3). In the presence of oxygen, these radicals can react to form peroxy radicals and when the peroxy free radicals react with hydrogen they form hydroperoxides, which can further degrade into other oxidation products (4). It has been reported that VE hinders this cascading in UHMWPE (5). Therefore, it is possible that oxidation of the crosslinked virgin UHMWPE was involved in the cytokine response observed in this study. However resin material, molding technique and the irradiation method were different between crosslinked virgin and VE-blended crosslinked samples. Further consideration will be needed to examine the relationship between residual radicals, hydroperoxides and biological response