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

Abstract. Objectives. Ultra-High Molecular Weight Polyethylene (UHMWPE) can be made radiopaque through the diffusion of an oil-based contrast agent (Lipiodol Ultra-fluid). A similar process is used for Vitamin E incorporated polyethylene, which has a well-established clinical history. This study aimed to quantify the leaching of Lipiodol and compare to vitamin E polyethylene. Method. GUR 1050 polyethylene (4 mm thickness) was cut into squares, 10 mm. 2. Samples (n=5) were immersed in 25 ml Lipiodol (Guerbet, France), or 15 ml Vitamin E (L-atocopherol, Sigma-Aldrich, UK). To facilitate diffusion, samples were held at 105°C for 18 hours. After treatment, all samples were immersed in DMEM (Sigma-Aldrich, UK) with Penicillin Streptomycin (Sigma-Aldrich, Kent, UK) at 4%v/v and held at 37°C in an incubator. Untreated polyethylene samples were included as controls. Leaching was quantified gravimetrically at weeks 2, 4 and 8. The radiopacity of the Lipiodol-diffused samples was investigated from µCT images (162kV, resolution 0.2 mm, X Tec, XT H 225 ST, Nikon Metrology, UK). Results. The leaching of Lipiodol and Vitamin E followed the same trend and reached a steady state after week 2. At this point there was a 20% decrease in the Hounsfield Unit and droplets of radiopaque oil were visible in the DMEM solution; these were not evident in subsequent scans. Over 8 weeks of 20% Lipiodol leached out of the polyethylene, which was greater than of 10% Vitamin E. Conclusion. After 8 weeks the radiopaque polyethylene was still identifiable in CT scan images, even though 20% of leaching occurred. The leaching of Lipiodol may be mitigated through cross-linking, which has been shown to reduce leaching of Vitamin E; this will be investigated as future work. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Dual mobility (DM) total hip replacements (THRs) were introduced to reduce dislocation risk, which is the most common cause of early revision. Although DM THRs have shown good overall survivorship and low dislocation rates, the mechanisms which describe how these bearings function in-vivo are not fully understood. Therefore, the study aim was to comprehensively assess retrieved DM polyethylene liners for signs of damage using visual inspection and semi-quantitative geometric assessment methods. Retrieved DM liners (n=18) were visually inspected for the presence of surface damage, whereby the internal and external surfaces were independently assigned a score of one (present) or zero (not present) for seven damage modes. The severity of damage was not assessed. The material composition of embedded debris was characterised using energy-dispersive x-ray analysis (EDX). Additionally, each liner was geometrically assessed for signs of wear/deformation [1]. Scratching and pitting were the most common damage modes on either surface. Additionally, burnishing was observed on 50% of the internal surfaces and embedded debris was identified on 67% of the external surfaces. EDX analysis of the debris identified several materials including titanium, cobalt-chrome, iron, and tantalum. Geometric analysis demonstrated highly variable damage patterns across the liners. The incidence of burnishing was three times greater for the internal surfaces, suggesting that this acts as the primary articulation site. The external surfaces sustained more observable damage as evidenced by a higher incidence of embedded debris, abrasion, delamination, and deformation. In conjunction with the highly variable damage patterns observed, these results suggest that DM kinematics are complex and may be influenced by several factors (e.g., soft tissue fibrosis, patient activities) and thus further investigation is warranted

Dual mobility hip arthroplasty utilizes a freely rotating polyethylene liner to protect against dislocation. As liner motion has not been confirmed in vivo, we investigated the liner kinematics in vivo using dynamic radiostereometry. 16 patients with Anatomical Dual Mobility acetabular components were included. Markers were implanted in the liners using a drill guide. Static RSA recordings and patient reported outcome measures were obtained at post-op and 1-year follow-up. Dynamic RSA recordings were obtained at 1-year follow-up during a passive hip movement: abduction/external rotation, adduction/internal rotation (modified FABER-FADIR), to end-range and at 45° hip flexion. Liner- and neck movements were described as anteversion, inclination and rotation. Liner movement during modified FABER-FADIR was detected in 12 of 16 patients. Median (range) absolute liner movements were: anteversion 10° (5–20), inclination 6° (2–12), and rotation 11° (5–48) relative to the cup. Median absolute changes in the resulting liner/neck angle (small articulation) was 28° (12–46) and liner/cup angle (larger articulation) was 6° (4–21). Static RSA showed changes in median (range) liner anteversion from 7° (-12–23) postoperatively to 10° (-3–16) at 1-year follow-up and inclination from 42 (35–66) postoperatively to 59 (46–80) at 1-year follow-up. Liner/neck contact was associated with high initial liner anteversion (p=0.01). The polyethylene liner moves over time. One year after surgery the liner can move with or without liner/neck contact. The majority of movement is in the smaller articulation between head and liner

Abstract. Objectives. Oil-based fluids can be used to enhance the properties of polyethylene materials. For example, vitamin E infused polyethylene has a superior oxidation resistance and Lipiodol infused polyethylene has an enhanced X-ray attenuation. The aim of this study was to evaluate the long-term influence of oily fluid on the chemical, physical and tensile properties of polyethylene. Methods. An accelerated ageing procedure (an elevated temperature (80. °. C) for four weeks in air. 1. ) was used to investigate the oxidative stability (ASTM F2012-17). 2. , tensile (ISO 527). 3. and thermal properties. 4. of oil treated polyethylene (n=5, GUR 1050, Celanese, Germany)and compared with clinically used polyethylene controls (oil-free standard and thermally treated polyethylene). All the experiments were performed on aged and unaged specimens in accordance to international standards and compared to currently available literature. A Kruskal-Wallis test was performed using a custom MATLAB code (R2017a, USA); with p < 0.05 considered statistically significant. Results. Samples treated with an oil (Vitamin E or Lipiodol) had a higher oxidation stability than currently used medical grade polyethylene, indicated by a smaller increase in oxidation index after ageing (Vitamin E 36%, Lipiodol 40%, untreated 136 %, thermally treated 164%). The mechanical degradation of oil treated polyethylene was also less significant than the untreated controls, as all the tensile properties of oil treated polyethylene after ageing were significantly higher than the standard controls (p>0.05). There was also no alteration in the percentage crystallinity of oil treated samples after ageing. Conclusion. The result of this study indicate that the presence of an oily fluid in polyethylene does not reduce its oxidative stability or tensile properties, providing improved material properties for long term implant applications. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Background. Wear simulation in total knee arthroplasty (TKA) is currently based on the most frequent activity – level walking. A decade ago multi-station knee wear simulators were introduced leading to optimisations of TKA designs, component surface finish and bearing materials. One major limitation is that current wear testing is mainly focused on abrasive-adhesive wear and in vitro testing does not reflect “delamination” as an essential clinical failure mode. The objective of our study was to use a highly demanding daily activities wear simulation to evaluate the delamination risk of polyethylene materials with and without vitamin E stabilisation. Methods. A cruciate retaining fixed bearing TKA design (Columbus CR) with artificially aged polyethylene knee bearings (irradiation 30±2 kGy) blended with and without 0.1% vitamin E was used under medio-lateral load distribution and soft tissue restrain simulation. Daily patient activities with high flexion (2×40% stairs up and down, 10% level walking, 8% chair raising, 2% deep squatting) were applied for 5 million cycles. The specimens were evaluated for gravimetric wear and analysed for abrasive-adhesive and delamination wear modes. Results. The total amount of gliding surface wear was 28.7±1.9 mg for the vitamin E stabilised polyethylene compared to 355.9±119.8 mg for the standard material. The combination of artificial ageing and high demanding knee wear simulation leads to visible signs of delamination in the articulating bearing areas in vitro. Conclusion. To evaluate Vitamin E stabilised polyethylenes in regard to ageing and wear behaviour in vitro, conditions are simulated to create clinical relevant failure modes in the reference material

Wear of polyethylene is associated with aseptic loosening of orthopaedic implants and has been observed in hip and knee prostheses and anatomical implants for the shoulder. The reversed shoulder prostheses have not been assessed as yet. We investigated the volumetric polyethylene wear of the reversed and anatomical Aequalis shoulder prostheses using a mathematical musculoskeletal model. Movement and joint stability were achieved by EMG-controlled activation of the muscles. A non-constant wear factor was considered. Simulated activities of daily living were estimated from in vivo recorded data. After one year of use, the volumetric wear was 8.4 mm. 3. for the anatomical prosthesis, but 44.6 mm. 3. for the reversed version. For the anatomical prosthesis the predictions for contact pressure and wear were consistent with biomechanical and clinical data. The abrasive wear of the polyethylene in reversed prostheses should not be underestimated, and further analysis, both experimental and clinical, is required

Polyethylene wear of joint replacements can cause severe clinical complications, including; osteolysis, implant loosening, inflammation and pain. Wear simulator testing is often used to assess new designs, but it is expensive and time consuming. It is possible to predict the volume of polyethylene implant wear from finite element models using a modification of Archard's classic wear law [1–2]. Typically, linear elastic isotropic, or elasto-plastic material models are used to represent the polyethylene. The purpose of this study was to investigate whether use of a viscoelastic material model would significantly alter the predicted volumetric wear of a mobile-bearing unicompartmental knee replacement. Tensile creep-recovery experiments were performed to characterise the creep and relaxation behaviour of the polyethylene (moulded GUR 4150 samples machined to 180×20×1 mm). Samples were loaded to 3 MPa stress in 4 minutes, and then held for 6 hours, the tensile stress was removed and samples were left to relax for 6 hours. The mechanical test data was used fit to a validated three–dimensional fractional Maxwell viscoelastic constitutive material model [3]. An explicit finite element model of a mobile–bearing unicompartmental knee replacement was created, which has been described previously [4]. The medial knee replacement was loaded to 1200 N over a period of 0.2 s. The bearing was meshed using quadratic tetrahedral elements (1.5 mm seeding size based on results of a mesh convergence study), and the femoral component was represented as an analytical rigid body. Wear predictions were made from the contact stress and sliding distance using Archard's law, as has been described in the literature [1–2]. A wear factor of 5.24×10. −11. was used based upon the work by Netter et al. [2]. All models were created and solved using ABAQUS finite element software (version 6.14, Simulia, Dassault Systemes). The fractional viscoelastic material model predicted almost twice as much wear (0.119 mm. 3. /million cycles) compared to the elasto-plastic model (0.069 mm. 3. /million cycles). The higher wear prediction was due to both an increased sliding distance and higher contact pressures in the viscoelastic model. These preliminary findings indicate the simplified elasto-plastic polyethylene material representation can underestimate wear predictions from numerical simulations. Polyethylene is known to be a viscoelastic material which undergoes creep clinically, and it is not surprising that it is necessary to represent that viscoelastic behaviour to accurately predict implant wear. However, it does increase the complexity and run time of such computational studies, which may be prohibitive

There are many methods for analysing wear volume in failed polyethylene acetabular components. We compared a radiological technique with three recognised ex vivo methods of measurement. We tested 18 ultra-high-molecular-weight polyethylene acetabular components revised for wear and aseptic loosening, of which 13 had pre-revision radiographs, from which the wear volume was calculated based upon the linear wear. We used a shadowgraph technique on silicone casts of all of the retrievals and a coordinate measuring method on the components directly. For these techniques, the wear vector was calculated for each component and the wear volume extrapolated using mathematical equations. The volumetric wear was also measured directly using a fluid-displacement method. The results of each technique were compared. The series had high wear volumes (mean 1385 mm. 3. ; 730 to 1850) and high wear rates (mean 205 mm. 3. /year; 92 to 363). There were wide variations in the measurements of wear volume between the radiological and the other techniques. Radiograph-derived wear volume correlated poorly with that of the fluid-displacement method, co-ordinate measuring method and shadowgraph methods, becoming less accurate as the wear increased. The mean overestimation in radiological wear volume was 47.7% of the fluid-displacement method wear volume. Fluid-displacement method, coordinate measuring method and shadowgraph determinations of wear volume were all better than that of the radiograph-derived linear measurements since they took into account the direction of wear. However, only radiological techniques can be used in vivo and remain useful for monitoring linear wear in the clinical setting. Interpretation of radiological measurements of acetabular wear must be done judiciously in the clinical setting. In vitro laboratory techniques, in particular the fluid-displacement method, remain the most accurate and reliable methods of assessing the wear of acetabular polyethylene

Non-optimal clinical alignment of components in total hip replacements (THRs) may lead to edge loading of the acetabular cup liner. This has the potential to cause changes to the liner rim not accounted for in standard wear models. A greater understanding of the material behaviours could be beneficial to design and surgical guidance for THR devices. The aim of this research was to combine finite element (FE) modelling and experimental simulation with microstructural assessment to examine material behaviour changes during edge loading.

A dynamic deformable FE model, matching the experimental conditions, was created to simulate the stress strain environment within liners. Five liners were tested for 4Mc (million cycles) of standard loading (ISO14242:1) followed by 3Mc of edge loading with dynamic separation (ISO14242:4) in a hip simulator. Microstructural measurements by Raman spectroscopy were taken at unloaded and highly loaded rim locations informed by FE results. Gravimetric and geometric measurements were taken every 1Mc cycles.

Under edge loading, peak Mises stress and plastic deformation occur below the surface of the rim during heel strike. After 7Mc, microstructural analysis determined edge loaded regions had an increased crystalline mass fraction compared to unloaded regions (p<0.05). Gravimetric wear rates of 12.5mm³/Mc and 22.3mm³/Mc were measured for standard and edge loading respectively. A liner penetration of 0.37mm was measured after 7Mc.

Edge loading led to an increase in gravimetric wear rate indicating a different wear mechanism is occurring. FE and Raman results suggest that changes to material behaviour at the rim could be possible. These methods will now be used to assess more liners and over a larger number of cycles. They have potential to explore the impact of edge loading on different surgical and patient variables.

Nanometre-sized particles of ultra-high molecular weight polyethylene have been identified in the lubricants retrieved from hip simulators. Tissue samples were taken from seven failed Charnley total hip replacements, digested using strong alkali and analysed using high-resolution field emission gun-scanning electron microscopy to determine whether nanometre-sized particles of polyethylene debris were generated in vivo. A randomised method of analysis was used to quantify and characterise all the polyethylene particles isolated. We isolated nanometre-sized particles from the retrieved tissue samples. The smallest identified was 30 nm and the majority were in the 0.1 μm to 0.99 μm size range. Particles in the 1.0 μm to 9.99 μm size range represented the highest proportion of the wear volume of the tissue samples, with 35% to 98% of the total wear volume comprised of particles of this size. The number of nanometre-sized particles isolated from the tissues accounted for only a small proportion of the total wear volume. Further work is required to assess the biological response to nanometre-sized polyethylene particles

INTRODUCTION. Highly cross linked polyethylenes (HXPE) have to be treated thermally after irradiation to eliminate residual free radicals. By adding vitamin E in the polyethylene powder a post-irradiation thermal treatment is not necessary. In this review the correlation between the intrinsic properties and the long-term stability of Vitelene® as a high performance material for artificial hip articulation will be displayed. MATERIALS & METHODS. Three different types of polyethylene (UHMWPE; GUR1020) were analyzed to compare mechanical properties as well as oxidative stability: PE. STD. (γ, 30 kGy, N. 2. ), HXPE. REM. (γ, 75 kGy, remelted, EO), Vitelene® (β, 80 kGy, 0.1% Vitamin E, EO). Artificial aging (ASTM F2003 − 70 °C, O. 2. at 5 bar) was used to simulate environmental damage. To evaluate the oxidation stability the Oxidation-Induction-Time (OIT) was measured by Differential Scanning Calorimetry (DSC - ASTM D3895) and the Oxidation Index (OI) was determined by Fourier-Transformation-Infrared-Spectroscopy (FTIR - ASTM F2102). The mechanical properties were analyzed by tensile- and impact investigations (ASTM D638 and ISO 11542-2) as well as by Small Punch Testing (SPT - ASTM F2183). The amount of wear was measured gravimetrically (ISO 14242-2). RESULTS. OIT [minutes], after 0, 14, 28, 42, 56 and 70 days aging, respectively 0.47, 0.41, 0.45, 0.42, 0.42 and not determined (nd) for PE. STD,. 0.46, 0.46, 0.47, 0.41, 0.41 and nd for HXPE. REM,. 12.09±0.50, 11.67±0.54, 10.78±0.25, 10.42±0.36, nd and 9.25±0.19 for Vitelene®. Cristallinity [%], after 0, 14, 28 and 42 days aging, respectively 55±2, 63±2, 79±4, 88±3 for PE. STD. , 47±2, 48±0, 50±1, 57±1 for HXPE. REM. , 52±1, 51±1, 53±14, 53±2 for Vitelene®. OI, after 0, 14, 28, 35 and 42 days aging, respectively 0.11±0.03, 0.67±0.15, 4.48±1.17 for PE. STD. , 0.07±0.05, 0.06±0.02, 0.09±0.02, 0.24±0.05, 0.69±0.36 for HXPE. REM. , 0.06±0.01, 0.08±0.01, 0.08±0.01, 0.09±0.01, 0.09±0.01 for Vitelene®. Tensile Strength [MPa], after 0 and 42 days aging, respectively 47.9±10, 0.7±0 for PE. STD. , 56.0±4.0, 25.0±2.0 for HXPE. REM. , 53.1±1.0, 52.0±4.3 for Vitelene®. Elongation [%], after 0 and 42 days aging, respectively 469±69 and 0 for PE. STD. , 343±14, 7±3 for HXPE. REM. , 372±11, 380±15 for Vitelene®. Impact Strength [kJ/m²], after 0 and 42 days aging, respectively 149±6, 4±1 for PE. STD. , 95±1, 5±1 for HXPE. REM. , 86±10, 91±7 for Vitelene®. SPT - Average Ultimate Load [N], after 0, 14 and 28 days aging, respectively 61.5±4.0, 56.3±5.3, 8.2±0.2 for PE. STD. , 71.4±2.2, 68.0±9.9, 64.4±8.2 for Vitelene®. Wear [mg/Mio cycles] (Ø36 mm Biolox® delta), after 0, 14 and 42 days aging, respectively 19.0±0.6, 30.3±3.1 and 365.8±37,2 for PE. STD. , 2.0±0.3, nd and 52.0±16.4 for HXPE. REM. , 2.5±0.5, nd and 2.3±0.7 for Vitelene®. CONCLUSION. The mechanical properties of Vitelene® are unchanged even after 42 days of artificial aging which is correlated to low wear in total hip arthroplasty. Vitamin E stabilization is effective in preventing oxidation and aging of the polyethylene after irradiation cross linking

Highly cross-linked polyethylene (HXLPE) is now a common used bearing surface in total hip arthroplasty. Current studies report superior wear rates with the use of HXLPE in total hip arthroplasty. However, there are few studies to support its long term use. The aim of this study is to measure the long term wear of HXLPE and evaluate patient satisfaction at more than 10 years follow up. 44 total hip arthroplasties were performed through a direct lateral approach by a single surgeon. All patients received the same uncemented acetabular component, mean liner thickness was 6.91mm (SD= 0.68). 16 of the femur components were cemented. Outcomes analysed include wear rates, osteolysis, revision rates, SF12 and Oxford hip scores. Wear rate was calculated using computer software (Polyware®) using edge detection software. Mean age at surgery was 58.9 years (SD= 11.67). The mean follow up was 11.3 years (SD= 1.19). There was no evidence of osteolysis and none had undergone revision surgery. Mean two dimensional wear was 0.38mm (SD= 0.25) and mean wear rate per year was 0.03mm (SD= 0.02, range 0.009 to 0.078). Oxford hip score at last follow up indicated satisfactory joint function (mean= 42 SD= 6.2). Our results support the use of highly cross-linked polyethylene in primary total hip replacements. The absence of osteolysis and need for revision surgery over a mean of 11.3 years is very encouraging

Introduction. Durable bone fixation of uncemented porous-coated acetabular cups can be observed at a long-term, however, polyethylene (PE) wear and osteolysis may affect survivorship. Accurate wear measurements correlated with clinical data may offer unique research information of clinical interest about this highly debated issue. Objetive. We assessed the clinical and radiological outcome of a single uncemented total hip replacement (THR) system after twenty years analysing polyethylene wear and the appearance of osteolysis. Materials and Methods. 82 hips implanted between 1992 and 1995 were prospectively evaluated. The mean follow-up was 20.6 years (range, 18 to 23). A hemispherical porous-coated acetabular cup matched to a proximally hydroxyapatite-coated anatomic stem and a 28 mm standard PE liner, sterilised by gamma irradiation in air, was used in all hips. Radiological position and the possible appearance of loosening and osteolysis were recorded over time. Penetration of the prosthetic head into the liner was measured by the Roentgen Monographic Analysis (ROMAN) Tool at 6 weeks, 6 months, one year and yearly thereafter. Results. Six cups were revised due to wear and four due to late dislocation. All cups were radiographically well-fixed and all stems showed radiographic ingrowth. Six un-revised hips showed osteolysis on the acetabular side and two on the proximal femoral side. Creep at one year was 0.30 (±0.23) mm. Mean total femoral head penetration was 1.23 mm at 10 years, 1.52 mm at 15 years and 1.92 mm at 23 years. Overall mean wear was 0.12 (± 0.1) mm/year and 0.09 (±0.06) mm/year after the creep period. Mean wear was 0.08 (± 0.06) mm/year in hips without osteolysis and 0.14 (±0.03) mm/year in revised hips or with osteolysis (p<0.001). Conclusions. Although continued durable fixation can be observed with a porous-coated cups and a proximally hydroxyapatite-coated anatomic stem, true wear continues to increase at a constant rate over time. PE wear remains as the main reason for revision surgery and osteolysis in uncemented THR and does not stop after twenty years

Crosslinking has been already used for about 80 years to enhance the longevity of polyethylene cables. The polymer alteration has been achieved with peroxide, silane or irradiation. The medical devices industry discovered the benefit of this technology for its tribological applications like hip or knee bearings in the 2000s as crosslinking improves considerably the abrasion resistance of the material. The more current methods used are Gamma and Beta irradiation. On the basis of economical (rising prices of Cobalt), environmental (the radioactive source can not be turned off), technological (low dose rate) drawbacks for Gamma respectively low penetration for Beta irradiation we decided to investigate an alternative technology: the X-Ray irradiation, which provides a homogeneous crosslinking in a relatively short time. We analyzed the wear, mechanical, thermal, oxidative and network properties of two vitamin E doped UHMWPE: first crosslinked with E-Beam, second with X-Ray. There wasn't any significant difference between the X-Ray and the E-Beam crosslinked material

Our aim was to analyse the influence of the size, shape and number of particles on the pathogenesis of osteolysis. We obtained peri-implant tissues from 18 patients having revision surgery for aseptically loosened Freeman total knee replacements (10), Charnley total hip replacements (3) and Imperial College/London Hospital double-cup surface hip replacements (5). The size and shape of the polyethylene particles were characterised using SEM and their concentration was calculated. The results were analysed with reference to the presence of radiological osteolysis. The concentration of polyethylene particles in 6 areas with osteolysis was significantly higher than that in 12 areas without osteolysis. There were no significant differences between the size and shape of the particles in these two groups. We conclude that the most critical factor in the pathogenesis of osteolysis is the concentration of polyethylene particles accumulated in the tissue

Total Hip Arthroplasty (THA) is a well-established, cost-effective treatment for improving function and alleviating pain in patients who have disabling hip disease with excellent long-term results. Based on the excellent results, there is an ongoing trend for THA to be performed in younger and more active patients, having higher physical demands on their new total joints. Polyethylene (PE) wear and its biological consequences are one of the main causes of implant failure in THA. Macrophages phagocytise PE wear particles and this will result in osteolysis and loss of periprosthetic bone. The risk of these complications can be estimated in relation to the amount of volumetric wear based on two assumptions: that the number of PE particles dispersed in the peri-prosthetic tissues is controlled by the amount of PE wear; and that the development of osteolysis and the resulting aseptic loosening is triggered by these PE particles. Based on these assumptions, a model was developed to estimate the osteolysis-free life of a THA, depending on the Linear Wear Rate (LWR) and femoral head size of the PE bearing. A review of the literature was conducted to provide an estimate of the radiologic osteolysis threshold based on the volumetric wear of the PE bearing. This review demonstrates that this radiologic osteolysis threshold is approximated 670 mm3 for conventional PE. The osteolysis-free life of the THA was estimated by simply dividing this threshold volume by the annual Volumetric Wear Rate (VWR) of the bearing. The annual VWR is basically controlled by two parameters: (1) annual LWR and (2) head size, and was calculated by using published formulae. For 28 mm heads, following osteolysis-free life was determined in function of the annual LWR. LWR: 10 µm/y => 116.6 years / LWR: 25 µm/y => 46.6 years / LWR: 50 µm/y => 23.3 years / LWR: 100 µm/y => 11.6 years. For 40 mm heads, following osteolysis-free life was determined in function of the annual LWR. LWR: 10 µm/y => 57.1 years / LWR: 25 µm/y => 22.9 years / LWR: 50 µm/y => 11.4 years / LWR: 100 µm/y => 5.7 years. The osteolysis-free life determined by this model is in good agreement with the clinical results of PE bearings having a 28 mm head size and demonstrates that extreme low LWRs are mandatory to assure a descent osteolysis-free life for THA (PE bearings) using large heads, such as 40 mm. For such head sizes, small variations of the LWR may have large impacts on the osteolysis-free life of the THA

We have reviewed 70 patients with bilateral simultaneous total hip arthroplasties to determine the rate of failure and to compare polyethylene wear and osteolysis between an implant with a cobalt-chrome head and Hylamer liner with that of a zirconia head and Hylamer liner. The mean thickness of the polyethylene liner was 11.0 mm (8.8 to 12.2) in the hip with a zirconia head and 10.7 mm (8.8 to 12.2) in that with a cobalt-chrome head. At follow-up at 6.4 years no acetabular or femoral component had been revised for aseptic loosening and no acetabular or femoral component was loose according to radiological criteria in both the cemented and cementless groups. The mean rate of linear wear and annual wear rate were highest in the 22 mm zirconia femoral head (1.25 mm (SD 1.05) and 0.21 mm (SD 0.18), respectively) and lowest in the 22 mm cobalt-chrome femoral head (0.70 mm (SD 0.39) and 0.12 mm (SD 0.07), respectively). The mean volumetric wear was highest in the 28 mm zirconia femoral head (730.79 mm. 3. ) and lowest in the 22 mm cobalt-chrome femoral head (264.67 mm. 3. ), but if the results were compared by size of the femoral head and type of material there was no statistical difference (p > 0.05). Sequential measurements of annual wear showed that the zirconia femoral head had a relatively higher rate of penetration than the cobalt-chrome head over the first three years; thereafter the rate of wear was reduced and compared favourably with that of cobalt-chrome heads. There was a statistically significant relationship between the wear of the polyethylene liner and the age of the patient, male gender and the degree of abduction angle of the cup, but not diagnosis, weight, hip score, range of movement, or amount of anteversion. Osteolysis was identified on both sides of the acetabulum in six patients (9%). Of 12 hips with acetabular osteolysis, six had a 28 mm cobalt-chrome femoral head and the remaining six a 28 mm zirconia head. Osteolysis was observed in zones 1A and 7A of the femur in two hips (3%) with a 28 mm zirconia head (cemented hip) and in four (6%) with a 28 mm cobalt-chrome femoral head (cementless hip). Our findings suggest that although the performance of a zirconia femoral head with a Hylamer liner was not statistically different from that of a cobalt-chrome femoral head and Hylamer liner, there was a trend for the zirconia head to be worse than the cobalt-chrome femoral head

In ten male rats we inserted ceramic ‘drawing-pin’ implants in weight-bearing positions within the right proximal tibia. Two animals were killed 6 weeks after surgery and two more 14 weeks after surgery. The remaining six received intra-articular injections of either high-density polyethylene (4 rats) or saline (2 rats) at 8, 10 and 12 weeks after surgery. These animals were killed two weeks after the last injection. Histological examination of the bone-implant interface in the control animals showed appositional bone growth around the implant at both 6 and 14 weeks. Polyethylene, but not saline, caused a chronic inflammatory response with numerous foreign-body giant cells in periprosthetic tissues. Our model of a stable, weight-bearing bone-implant interface provides a simple and reliable system in which to study in vivo the effects of particulate materials used in orthopaedic surgery

We used a rat model in vivo to study the effects of the concentration of polyethylene particles on the bone-implant interface around stable implants in the proximal tibia. Intra-articular injections of 10. 4. , 10. 6. or 10. 8. high-density polyethylene (HDPE) particles per joint were given 8, 10 and 12 weeks after surgery. The animals were killed after 14 and 26 weeks and the response at the interface determined. Fibrous tissue was seen at the bone-implant interface when the head of the implant was flush with the top of the tibia but not when it was sunk below the tibial plateau. In the latter case the implant was completely surrounded by a shell of bone. The area of fibrous tissue and that of the gap between the implant and bone was related to the concentration of particles in the 14-week group (p < 0.05). Foreign-body granulomas containing HDPE particles were seen at the bone-implant interface in animals given 10. 8. particles. The pathology resembles that seen around prostheses with aseptic loosening and we suggest that this is a useful model by which to study this process