Aims. Highly cross-linked polyethylene (HXLPE) greatly reduces wear in total hip arthroplasty, compared to conventional polyethylene (CPE). Cross-linking is commonly achieved by irradiation. This study aimed to compare the degree of cross-linking and in vitro wear rates across a cohort of retrieved and unused polyethylene cups/liners from various brands. Methods. Polyethylene acetabular cups/liners were collected at one centre from 1 April 2021 to 30 April 2022. The trans-vinylene index (TVI) and oxidation index (OI) were determined by Fourier-transform infrared spectrometry. Wear was measured using a pin-on-disk test. Results. A total of 47 specimens from ten brands were included. The TVI was independent of time in vivo. A linear correlation (R. 2. = 0.995) was observed between the old and current TVI standards, except for vitamin E-containing polyethylene. The absorbed irradiation dose calculated from the TVI corresponded to product specifications for all but two products. For one electron beam-irradiated HXLPE, a mean dose of 241% (SD 18%) of specifications was determined. For another, gamma-irradiated HXLPE, a mean 41% (SD 13%) of specifications was determined. Lower wear was observed for higher TVI. Conclusion. The TVI is a reliable measure of the absorbed irradiation dose and does not alter over time in vivo. The products of various brands differ by manufacturing details and consequently cross-linking characteristics. Absorption and penetration of electron radiation and gamma radiation differ, potentially leading to higher degrees of cross-linking for electron radiation. There is a non-linear, inverse correlation between TVI and in vitro wear. The wear resistance of the HXLPE with low TVI was reduced and more comparable to CPE. Cite this article: Bone Joint Res 2024;13(11):682–693

Aims. Limited implant survival due to aseptic cup loosening is most commonly responsible for revision total hip arthroplasty (THA). Advances in implant designs and materials have been crucial in addressing those challenges. Vitamin E-infused highly cross-linked polyethylene (VEPE) promises strong wear resistance, high oxidative stability, and superior mechanical strength. Although VEPE monoblock cups have shown good mid-term performance and excellent wear patterns, long-term results remain unclear. This study evaluated migration and wear patterns and clinical and radiological outcomes at a minimum of ten years’ follow-up. Methods. This prospective observational study investigated 101 cases of primary THA over a mean duration of 129 months (120 to 149). At last follow-up, 57 cases with complete clinical and radiological outcomes were evaluated. In all cases, the acetabular component comprised an uncemented titanium particle-coated VEPE monoblock cup. Patients were assessed clinically and radiologically using the Harris Hip Score, visual analogue scale (pain and satisfaction), and an anteroposterior radiograph. Cup migration and polyethylene wear were measured using Einzel-Bild-Röntgen-Analyze software. All complications and associated treatments were documented until final follow-up. Results. Clinical assessment showed persistent major improvement in all scores. On radiological assessment, only one case showed a lucent line (without symptoms). At last follow-up, wear and migration were below the critical thresholds. No cup-related revisions were needed, indicating an outstanding survival rate of 100%. Conclusion. Isoelastic VEPE cups offer high success rates and may prevent osteolysis, aseptic loosening, and the need for revision surgeries in the long term. However, longer follow-up is needed to validate our findings and confirm the advantages offered by this cup. Cite this article: Bone Jt Open 2024;5(10):825–831

Aims

The aim of this study was to compare the migration of the femoral component, five years postoperatively, between patients with a highly cross-linked polyethylene (HXLPE) insert and those with a conventional polyethylene (PE) insert in an uncemented Triathlon fixed insert cruciate-retaining total knee arthroplasty (TKA). Secondary aims included clinical outcomes and patient-reported outcome measures (PROMs). We have previously reported the migration and outcome of the tibial components in these patients.

While high-performance ceramics like alumina and zirconia exhibit excellent wear resistance, they provide poor osseointegration capacity. As osseointegration is crucial for non-cemented joint prostheses, new techniques have been successfully developed for biofunctionalizing high-performance ceramic surfaces. Stable cell adhesion can be achieved by covalently bound specific peptides. In this study we investigate the effect of sterilization processes on organo-chemically functionalized surfaces. To enhance the performance of alumina-toughened zirconia ceramics (ATZ), a 3-aminopropyldiisopropylethoxysilane (APDS) monolayer was applied and coupled with cyclo-RGD peptides (cRGD) by using bifunctional crosslinker bis(sulfosuccinimidyl)suberat (BS³). The samples were sterilized using e-beam or gamma-sterilization at 25 kGy, either before or after biofunctionalization with cRGD. Functionalization stability was investigated by contact angle measurements. The functionality of cRGD after sterilization was demonstrated using proliferation tests and cytotoxicity assays. Immunofluorescence staining (pFAK, Actin, DAPI) was conducted to evaluate the adhesion potential between the samples and human mesenchymal stem cells (hMSCs). Functionalized samples before and after sterilization showed no significant difference regarding their contact angles. A proliferation test demonstrated that the cells on functionalized samples proliferate significantly more than on untreated samples before and after sterilization. hMSCs showed a significant higher proliferation on gamma sterilized samples compared to all other groups after 14 days. It was confirmed that the samples did not exhibit cytotoxic behavior before or after sterilization. Fluorescence microscopy demonstrated that both, cells on sterilized and on non-sterilized samples, expressed high levels of pFAK-Y397. The investigated functionalization enables improved adhesion and proliferation of hMSCs and is stable against the investigated sterilization processes. This is of importance as the option of having a sterile product enables the start of the translation of this biofunctional coating towards preclinical and subsequently first-in-man applications. Acknowledgments: We acknowledge the financial support of the Federal Ministry of Education and Research, BMBF (13GW0452A-C)

Aims

The primary outcome was investigating differences in wear, as measured by femoral head penetration, between cross-linked vitamin E-diffused polyethylene (vE-PE) and cross-linked polyethylene (XLPE) acetabular component liners and between 32 and 36 mm head sizes at the ten-year follow-up. Secondary outcomes included acetabular component migration and patient-reported outcome measures (PROMs) such as the EuroQol five-dimension questionnaire, 36-Item Short-Form Health Survey, Harris Hip Score, and University of California, Los Angeles Activity Scale (UCLA).

Majority of ultra-high molecular weight polyethylene (UHMWPE) medical devices used in total joint arthroplasty are crosslinked using gamma radiation to improve wear resistance. Alternative methods of crosslinking are urgently needed to replace gamma radiation due to rapid decline in its supply. Peroxide crosslinking is a candidate method with widespread industrial applications. Oxidative stability and biocompatibility, which are critical requirements for medical device applications, can be achieved using vitamin-E as an additive and by removing peroxide by-products through high temperature melting, respectively. We investigated compression molded UHMWPE/vitamin-E/di-cumyl peroxide blends followed by high-temperature melting in inert gas as a material candidate for tibial knee inserts. Wear resistance increased and mechanical properties remained largely unchanged. Oxidation induction time was higher than most of the other clinically available formulations. The material passed the local-end point biocompatibility tests per ISO 10993. Compounds found in exhaustive extraction were of no concern with margin-of-safety values well above the accepted level, indicating a desirable toxicological risk profile. Peroxide crosslinked, vitamin-E stabilized, and high temperature melted UHMWPE has recently been cleared for clinical use in tibial knee inserts. With all the salient characteristics needed in a material that can provide superior long-term performance in total joint patients, peroxide crosslinking can replace gamma radiation crosslinking of UHMWPE for use in all total joint replacement implant including acetabular liners

Aims

The primary objective of this study was to compare the five-year tibial component migration and wear between highly crosslinked polyethylene (HXLPE) inserts and conventional polyethylene (PE) inserts of the uncemented Triathlon fixed insert cruciate-retaining total knee arthroplasty (TKA). Secondary objectives included clinical outcomes and patient-reported outcome measures (PROMs).

The purpose of the study was to compare the mechanical properties, oxidation and wear resistance of a vitamin E blended and moderately crosslinked polyethylene for total knee arthroplasty (MXE) in comparison with clinically established polyethylene materials. The following polyethylene materials were tested: CPE (30 kGy e-beam sterilized), XLPE (75 kGy gamma crosslinked @ 100°C), ViXLPE (0.1 % vitamin E blended, 80 kGy e-beam crosslinked @ 100°C), and MXE (0.1 % vitamin E blended polyethylene, 30 kGy gamma sterilized). For the different tests, the polyethylene materials were either unaged or artificially aged for two or six weeks according to ASTM F2003-02. The oxidation index was measured based on ASTM F2102 at a 1 mm depth. Small punch testing was performed based on ASTM F2977. Mechanical properties were measured on unaged materials according to ASTM D638. Wear simulation was performed on a load controlled 3 + 1 station knee wear simulator (EndoLab GmbH, Thansau, Germany) capable of reproducing loads and movement of highly demanding activities (HDA) as well as ISO 14243-1 load profiles. The load profiles were applied for 5 million cycles (mc) or delamination of the polyethylene components. Medium size AS e.motion. ®. PS Pro (Aesculap AG, Tuttlingen, Germany) femoral and tibial components with a ZrN-multilayer surface, as well as Columbus. ®. CR cobalt-chrome alloy femoral and tibial components were tested. Particle analysis was performed on the serum samples of the ISO 14243-1 wear simulations based on ISO 17853:2011 and ASTM F1877. The analysis of the mechanical properties show that moderately crosslinked polyethylene (MXE) might be a superior material for total knee arthroplasty applications [Schwiesau et al. 2021]. The addition of vitamin E in a moderately crosslinked polyethylene prevented its oxidation, kept its mechanical characteristics, and maintained a low wear, even under a HDA knee wear simulation

Aims

This study reports the ten-year wear rates, incidence of osteolysis, clinical outcomes, and complications of a multicentre randomized controlled trial comparing oxidized zirconium (OxZr) versus cobalt-chrome (CoCr) femoral heads with ultra-high molecular weight polyethylene (UHMWPE) and highly cross-linked polyethylene (XLPE) liners in total hip arthroplasty (THA).

Aims. The aim of this study was to evaluate the performance of first-generation annealed highly cross-linked polyethylene (HXLPE) in cementless total hip arthroplasty (THA). Methods. We retrospectively evaluated 29 patients (35 hips) who underwent THA between December 2000 and February 2002. The survival rate was estimated using the Kaplan-Meier method. Hip joint function was evaluated using the Japanese Orthopaedic Association (JOA) score. Two-dimensional polyethylene wear was estimated using Martell’s Hip Analysis Suite. We calculated the wear rates between years 1 and 5, 5 and 10, 10 and 15, and 15 and final follow-up. Results. The mean follow-up period was 19.1 years (SD 0.6; 17.3 to 20.1). The 19-year overall survival rate with the end point of all-cause revision was 97.0% (95% confidence interval (CI) 91 to 100). The mean JOA score improved from 43.2 (SD 10.6; 30 to 76) before surgery to 90.2 (SD 6.4; 76 to 98) at the final follow-up (p < 0.001). There was no osteolysis or loosening of the acetabular or femoral components. The overall steady-state wear rate was 0.013 mm/year (SD 0.012). There was no hip with a steady-state wear rate of > 0.1 mm/year. There was no significant difference in wear rates for each period. We found no significant correlation between the wear rate and age, body weight, BMI, or cup inclination. Conclusion. First-generation annealed HXLPE shows excellent wear resistance and no acceleration of wear for approximately 20 years, with low all-cause revision rates. Cite this article: Bone Joint J 2022;104-B(2):200–205

Aims

Dual mobility implants in total hip arthroplasty are designed to increase the functional head size, thus decreasing the potential for dislocation. Modular dual mobility (MDM) implants incorporate a metal liner (e.g. cobalt-chromium alloy) in a metal shell (e.g. titanium alloy), raising concern for mechanically assisted crevice corrosion at the modular liner-shell connection. We sought to examine fretting and corrosion on MDM liners, to analyze the corrosion products, and to examine histologically the periprosthetic tissues.

Introduction. According to American Joint Replacement Registry, particle mediated osteolysis represents 13 % of the knee revision surgeries performed in the United States. The comprehension of mechanical and wear properties of materials envisioned for TJR is a key step in product development. Furthermore, the maintenance of UHMWPE mechanical properties after material modification is an important aspect of material success. Initial studies conducted by our research group demonstrated that the incorporation of ibuprofen in UHMWPE had a minor impact on UHMWPE physicochemical and mechanical properties. Drug release was also evaluated and resulted in an interesting profile as a material to be used as an anti-inflammatory system. Therefore, the present study investigated the effect of drug release on the mechanical and biological properties of ibuprofen-loaded UHMWPE. Experimental. UHMWPE resin GUR 1020 from Ticona was for sample preparation. Samples with drug concentrations of 3% and 5% wt were consolidated as well as samples without anti-inflammatory addition through compression molding at 150 °C and 5 MPa for 15 minutes. Mechanical properties were evaluated via the tensile strength experiment (ASTM D638) and dynamic mechanic tests. Wear resistance was measured using the pin on disc (POD) apparatus. Finally, cytotoxicity analysis was conducted based on ISO 10993–5. Results. Dynamic-mechanic analysis demonstrated no difference in flexion modulus and stress for all materials (Table 1). No difference was also verified during cyclical loading experiments (Table 1), which indicates that the drug concentration added to material composition did not affect these properties. POD experiments were proposed to evaluate wear resistance of ibuprofen-loaded UHMWPE samples considering the combination of materials similar to those employed in TJR. Results from POD tests are presented in Table 1. Volumetric wear was close to zero for all samples after 200 thousand cycles. Comprehension of the effect of drug release on mechanical properties is essential to estimate how the material will behave after implantation. Therefore, mechanical properties were assessed after 30 days of ibuprofen release and the results were compared with those obtained in samples as prepared (Table 2). Initial results demonstrated a decrease in elastic modulus in samples prepared with ibuprofen. However, no difference was verified between UHMWPE, UHMWPE 3% IBU and UHMWPE 5% IBU after ibuprofen release. Finally, cell viability of UHMWPE 3% IBU and UHMWPE 5% was found to be superior to 100% (Figure 1). Therefore, both materials can be considered nontoxic. Conclusions. Ibuprofen-loaded UHMWPE did not demonstrate a significant influence on the mechanical and biological behavior of UHMWPE. Dynamic-mechanical tests demonstrated constancy for all samples under analysis. Wear testing resulted in gravimetric wear close to zero, for all tested materials. Mechanical properties conducted after 30 days of ibuprofen release also had a positive outcome. Although presenting a difference in modulus prior and after release tests, modulus and tensile yield stress remained inside acceptable range indicated to UHMWPE used in orthopedic implants. Furthermore, after drug elution UHMWPE 3% IBU and UHMWPE 5% IBU recovered original UHMWPE properties. Cytotoxicity assessment was performed and both ibuprofen-based formulations were considered nontoxic according to ISO 10993–5. For any figures or tables, please contact the authors directly

Aims

The material and design of knee components can have a considerable effect on the contact characteristics of the tibial post. This study aimed to analyze the stress distribution on the tibial post when using different grades of polyethylene for the tibial inserts. In addition, the contact properties of fixed-bearing and mobile-bearing inserts were evaluated.

Aims

The most frequent indication for revision surgery in total hip arthroplasty (THA) is aseptic loosening. Aseptic loosening is associated with polyethylene liner wear, and wear may be reduced by using vitamin E-doped liners. The primary objective of this study was to compare proximal femoral head penetration into the liner between a) two cross-linked polyethylene (XLPE) liners (vitamin E-doped (vE-PE)) versus standard XLPE liners, and b) two modular femoral head diameters (32 mm and 36 mm).

Aims

We have previously demonstrated raised cobalt and chromium levels in patients with larger diameter femoral heads, following metal-on-polyethylene uncemented total hip arthroplasty. Further data have been collected, to see whether these associations have altered with time and to determine the long-term implications for these patients and our practice.

Aims

We propose a state-of-the-art temporary spacer, consisting of a cobalt-chrome (CoCr) femoral component and a gentamicin-eluting ultra-high molecular weight polyethylene (UHMWPE) tibial insert, which can provide therapeutic delivery of gentamicin, while retaining excellent mechanical properties. The proposed implant is designed to replace conventional spacers made from bone cement.

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

AM Open Cell porous Ti Structures were investigated for compressive strength, morphology (i.e. pore size, struts size and porosity), and wear resistance with the aim to improve design capability at support of implant manufacturing. Specimens were manufactured in Ti6Al4V using a SLM machine. Struts sizes had nominal diameters of 200µm or 100µm, pores had nominal diameters of 700µm, 1000µm or 1500µm. These dimensions were applied to three different open-cell geometrical configurations: one with unit-cells based on a regular cubic arrangement (Regular), one with a deformed cubic arrangement (Irregular), and one based on a fully random arrangement (Fully Random). Morphological analysis was performed by image analysis applied onto optical and SEM acquired pictures. The analyses estimated the maximum and minimum Feret pores diameter, and the latter was used as one of the key parameters to describe the interconnected network of pores intended for bone colonization. Outcome revealed the systematic oversizing of the actual struts diameter Vs designed diameter; by opposite min. Feret diameters of the pores resulted significantly smaller than nominal pore diameters, thus better fitting within the range of pores dimension acknowledged to favor the osseointegration. Consequently, the actual total porosity is also reduced. Many technologic factors are responsible for the morphologic differences design vs actual, among these the influence of melting pool dimension, the struts orientation during building and the layer thickness have a significant impact. Mechanical compression was performed on porous cylinder samples. Test revealed the Yield Strength and Stiffness are highly sensitive to the actual porosity. Deformation behavior follows densification phenomenon at lower porosity, whereas at higher porosity the Gibson-Ashby model fits for most of the structure tested. The relationship among load direction, struts alignment and the collapse behavior of the unit cell geometries are discussed. Stiffness of the porous structure is evaluated in both quasistatic and cyclic compression. Wear was investigated according to Taber test method. The abrasion resistance is measured by scratching a ceramic wheel against the different AM porous structures along a circular path. Metal debris eventually loss were quantified by gravimetric analysis at different number of cycles. Correlation among AM porous structure geometry, porosity and wear loss is discussed. All the tested structures showed a debris loss within the limit suggested by FDA for the porous coating in contact with the bone tissue. The actual AM porous Titanium unit cell geometry and features are a key design input. In combination with all the other design factors of a device they may result helpful in address the stress shielding and prevent metal debris release issues. The study underlines the importance of the research activity in AM to support Design for Additive Manufacturing (DFAM) capability. For any figures or tables, please contact authors directly

Introduction. In vivo, UHMWPE bearing surfaces are subject to wear and oxidation that can lead to bearing fatigue or fracture. A prior study in our laboratory of early antioxidant (AO) polyethylene retrievals, compared to gamma-sterilized and highly cross-linked (HXL) retrievals, showed them to be more effective at preventing in vivo oxidation. The current analysis expands that early study, addressing the effect of:. manufacturing-variables on as-manufactured UHMWPE;. in vivo time on these initial properties;. identifying important factors in selecting UHMWPE for the hip or knee. Methods. After our prior report, our IRB-approved retrieval laboratory received an additional 96 consecutive AO-retrievals (19 hips, 77 knees: in vivo time 0–6.7 years) of three currently-marketed AO-polyethylenes. These retrievals represented two different antioxidants (Vitamin E and Covernox) and two different delivery methods: blending-prior-to and diffusing-after irradiation cross-linking. Consecutive HXL acetabular and tibial inserts, received at retrieval, with in vivo time of 0–6.7 years (260 remelted, 170 annealed) were used for comparison with AO-retrievals. All retrievals were analyzed for oxidation and trans-vinylene index (TVI) using a Thermo-Scientific iN10 FTIR microscope. Mechanical properties were evaluated for 35 tibial inserts by uniaxial tensile testing using an INSTRON load frame. Cross-link density (n=289) was measured using a previously published gravimetric gel swell technique. Oxidation was reported as maximum ketone oxidation index (KOI) measured for each bearing. TVI was reported as the average of all scans for each material. Cross-link density and mechanical properties were evaluated as a function of both TVI and oxidation. Results. Minimal increase in oxidation was seen in these AO-retrievals, out to almost 7 years in vivo. In contrast, HXL-retrievals showed increasing KOI with time in vivo (annealed-HXL = 0.127/year, remelted-HXL = 0.036/year, p<0.001). HXL oxidation rate was higher in knees (0.091/year) than in hips (0.048/year), p<0.001. Cross-link density (XLD) correlated positively with TVI for both HXL (Pearson's correlation=0.591, p<0.001) and AO (Pearson's correlation=0.598, p<0.001) retrievals. AO-materials had higher TVI for the same or similar XLD than did HXL polyethylene. XLD correlated negatively with KOI for HXL retrievals (Pearson's correlation=−0.447, p<0.001). Mechanical properties varied by material across all materials evaluated, with tensile toughness correlating negatively with increasing TVI (Pearson Correlation=−0.795, p<0.001). Discussion. Irradiation cross-linking has been used effectively to improve wear resistance. Residual free radicals from irradiation are the target of AO-polyethylene, to prevent loss of UHMWPE XLD, resulting from in vivo oxidation of free radicals as seen in HXL retrievals, and toughness, resulting from oxidation or initial remelting. Despite different manufacturing variables, AO-polyethylene retrievals in this cohort had minimal oxidation and no change in XLD or toughness due to oxidation. However, toughness did vary with irradiation dose as did cross-link density. To achieve the same level of cross-linking as HXL-polyethylene required a higher irradiation dose in blended AO-polyethylene. AO-polyethylenes evaluated in this study had toughness that decreased with irradiation dose, but avoided loss of toughness due to remelting. Because AO-polyethylenes did not oxidize, they did not show the decrease of cross-link density, and potential loss of wear resistance, seen in HXL-polyethylene. For any figures or tables, please contact authors directly

Aims

A retrospective study was conducted to measure short-term in vivo linear and volumetric wear of polyethylene (PE) inserts in 101 total knee arthroplasty (TKA) patients using model-based radiostereometric analysis (MBRSA).