Aim. Arthroscopic interventions have revolutionized the treatment of joint pathologies. The appropriate diagnostics and treatment are required for infections after ligament reconstructions using non-resorbable material such as tendon grafts, anchors, and sutures, prone to biofilm formation. The infection rate is around 1% for knee and shoulder, while up to 4% for Achilles tendon reconstructions. Despite high number of these procedures worldwide, there is limited evidence about the best treatment protocol. Our study aimed to provide a general protocol for the treatment of small implants for soft tissue reconstruction. Method. Between 2019 and 2023, we treated 48 infections of ligament, meniscus, and tendon reconstructions out of 7291 related procedures performed in the same time period. Early infection (<30 days) were treated with an arthroscopic debridement and implant retention (DAIR), except Achilles tendons had open DAIR, while those with delayed or chronic infection (>30 days) were treated with extensive debridement and lavage combined with one-stage exchange (OSE) or implant removal. During surgery, at least 5 microbiological s and samples for histopathology were obtained. The removed material was sonicated. After surgery, all patients were one week on iv. antibiotics, followed by oral antibiofilm antibiotics for 6 weeks including rifampicin and/or a quinolone. All patients were followed for at least 1 year. Failure was defined as the need for additional revision surgery after finished iv. antibiotic treatment. Results. Among 48 patients, 38 were early and 10 were late acute or chronic infections. The incidence of infection for our cohort was 0.7%. We observed 27 infections after ligament reconstruction of the knee, 15 of the shoulder, 5 of the ankle, and 1 infection of the elbow joint. 40 patients were treated with DAIR, 5 with OSE, and 3 with implant removal. We had 11 C. acnes, 10 S. aureus, 6 S. epidermidis, 2 P. aeruginosa, 2 S. lugdunensis, 10 mixed flora, and 3 culture-negative infections. 12 patients received antibiotics before surgery, and all culture-negative infections were related to this subgroup. We observed 2 failures, both in a combination of proximal tibial osteotomy and ligament reconstruction of the knee joint. The success rate of our protocol was 96%. Conclusions. Prompt surgical treatment followed by 6 weeks of antibiotic treatment cured 96% of infections of small implants after reconstruction procedures of knee, shoulder, and ankle joints. Our study is the first to provide a treatment protocol for infections of small implants after ligament reconstruction procedures

Introduction. It is well accepted that larger heads provide more stability in total hip arthroplasty. This is due to an increase in jump height providing increased resistance to subluxation. However, other implant parameters also contribute to the bearing's stability. Specifically, the liner's rim design and the centre of rotation relative to the liner's face. Both these features contribute to define the Cup Articular Arc Angle (CAAA). The CAAA describes the degree of dysplasia of the acetabular liner, and plays an important role in defining the jump height. The aim of this study was to determine the difference in jump height between bearing materials with a commonly used acetabular implant system. Methods. From 3D models of the Trinity acetabular implant system (Corin, UK), the CAAA was measured in CAD software (SolidWorks, Dassault Systems, France) for the ceramic, poly and modular dual mobility (DM) liners, for cup sizes 46mm to 64mm. The most commonly used bearing size was used in the analysis of each cup size. For the ceramic and poly liners, a 36mm bearing was used for cups 50mm and above. For the 46mm and 48mm cups, a 32mm bearing was used. The DM liners were modelled with the largest head size possible. Using a published equation, the jump height was calculated for each of the three bearing materials and each cup size. Cup inclination and anteversion were kept constant. Results. CAAA varied substantially between cup sizes and bearing materials. The mean CAAA for the ceramic, poly and DM bearings were 166°, 175° and 186°, respectively. Consequently, over the entire size range, the ceramic liners had the lowest mean jump height of 12.9mm. In comparison to the ceramic liner, there was a mean 10% increase in jump height when transitioning to a poly (14.2mm), and a further 30% increase when transitioning from a poly to the dual mobility bearing (18.5mm) [Fig.1]. However, the difference in jump heights between bearings was variable, and dependent on cup size. Discussion. It is well understood that increasing head size increases stability in THA. However, other implant design parameters contribute to stability. With this particular implant system, the poly bearing had a greater jump height than the ceramic for cup sizes 50mm and above. The DM bearing improved jump height over the ceramic and poly by a mean of 41% and 30%, respectively. In conclusion, different liners have different design features that affect jump height. Consequently, not all bearings of identical head size are the same. We encourage a dialogue with your implant provider to understand the differences in CAAA between cup sizes and bearing materials. For any figures or tables, please contact the authors directly

INTRODUCTION. Precise determination of material loss is essential for failure analysis of retrieved hip cups. To determine wear, the measured geometry of the retrieval hast to be compared to its pristine geometry, which usually is not available. There are different approaches to generate reference geometries to approximate the pristine geometry that is commonly assumed as sphere. However, the geometry of press fit cup retrievals might not be spherical due to deformation caused by excessive press-fitting. The effect of three different reference geometries on the determined wear patterns and material loss of pristine and worn uncemented metal-on-metal hip cups was determined. METHODS. The surfaces of two cups (ASR, DePuy, Leeds; one pristine, one a worn retrieval) were digitized using a coordinate measurement machine (CRYSTA-Apex S574, Mitutoyo; 3 µm accuracy). Both cups were measured undeformed and while being deformed between a clamp. Three different methods for generating reference geometries were investigated (PolyWorks|Inspector 2018, InnovMetric). Method 1: A sphere with the nominal internal cup dimensions was generated. Method 2: A sphere was fitted to the measured data points after removing those from worn areas (deviation > 3 µm is defined as wear) to eliminate the influence of manufacturing tolerances on the nominal diameter. Method 3: Measurements, which displayed visual deformation in the computed wear pattern based on the best fit sphere, were fitted with an ellipsoid. The direction of the deformation axes and the amount of deformation were used to scale the best fit ellipsoid. Linear wear was calculated from the distance of the respective reference geometry to the measured point cloud. Finally, material loss is defined as the difference in volume of the reference geometry and the measured geometry. RESULTS. The method used for generating the reference geometry affected the determined wear greatly. Using the nominal manufacturing radius (larger than the best fit radius) for the worn cup falsely indicates deposit. This leads to approx. 39 % less wear volume compared to the best fit sphere analysis. Using an ellipsoid as reference geometry for both deformed cups improves the determination of the wear pattern and indicates areas of material loss better than a reference sphere. Additionally, the mistake in material loss determination is decreased, especially for the worn cup almost exactly to the wear volume analyzed with the best fit sphere before deformation. DISCUSSION. For correct determination of material loss best fit geometries instead of nominal sizes have to be used to compensate the differences due to manufacturing tolerances. Furthermore, deformation always has to be eliminated to generate correct wear patterns and volumes. Using an ellipsoid as reference geometry improves the outcome. For generating an even more accurate reference geometry, the exact behavior of the cup during deformation must be understood. Limitations to this method are cups that do not provide pristine areas in order to generate an appropriate best fit geometry. For any figures or tables, please contact authors directly

Introduction. In revision TKA, the management of bone loss depends on location, type, and extent of bony deficiency. Treatment strategies involve cement filling, bone grafting and augments. On the market several solutions are currently available, differing for their shape, thickness and material. While the choice of the shape and the thickness is mainly dictated by the bone defect, no explicit guideline is currently available to describe the best choice of material to be selected for a specific clinical situation. However, the use of different materials could induce different response in term of bone stress and thus changes in implant stability that could worsen long-term implant performance. For these reasons, an investigation about the changes in bone stress in the femur and in the tibia when augments, with different materials and thicknesses was performed. Methods. Different configurations have been separately considered including proximal tibial, distal or/and posterior femoral augments with a thickness of 5, 10 and 15 mm. Apart the control, in which no augments were used, but only the TKA is considered, the augment in all the other configurations were considered made by three different materials: bone cement, to simulate cement filling, tantalum trabecular metal and conventional metal (titanium for the tibia and CoCr for the femoral augments). Each configuration was inserted on a lower leg model including a cruciate-retaining total knee arthroplasty and analyzed by means of finite element analysis applying the max force achieved during walking. The bone stress was investigated in the medial and lateral region of interest close to the augment (with a bone thickness of 10 mm) and in an additional bone region of interest of 50 mm thickness. The bone stress have been compared among the different models and also with respect to the control model. Results. In general, the use of an augment induces a change in bone stress, especially in the region close to the bone cuts. The stiffness of the augment must be as close as possible to the one of the bone. Cement has the best results in terms of bone stress, however, it is only suitable for extremely small defects. Tantalum trabecular metal has results very close to cement and it could be consider a good alternative to cement for any size of defect. Metal (both titanium and CoCr) has the least satisfying results inducing the highest change in bone stress with respect the control. Conclusions. Tibial and femoral bone augments are adopted in case of bone defects that could be present during a revision knee replacement. Several solutions are available on the market in different shapes and materials. However, very few studies are reported to provide possible guidelines. The results of this study demonstrate that material stiffness of the augment must be as close as possible to the one of the bone to achieve the best results

Introduction. Total hip arthroplasty (THA) is a commonly performed procedure to relieve arthritis or traumatic injury. However, implant failure can occur from implant loosening or crevice corrosion as a result of inadequate seating of the femoral head onto the stem during implantation. There is no consensus—either by manufacturers or by the surgical community—on what head/stem assembly procedure should be used to maximize modular junction stability. Furthermore, the role of “off-axis” loads—loads not aligned with the stem taper axis—during assembly may significantly affect modular junction stability, but has not been sufficiently evaluated. Objective. The objective of this study was to measure the three-dimensional (3D) head/stem assembly loads considering material choice—metal or ceramic—and the surgeon experience level. Methods. A total of 29 surgeons of varying levels (Attending, Fellow, Resident) were recruited and asked to perform a benchtop, head/stem assembly using an instrumented apparatus simulating a procedure in the operating room (Figure 1). The apparatus comprised of a 12/14 stem taper attached to a 3D load sensor (9347C, Kistler® USA, Amherst, NY). Surgeons were randomly assigned a metal or ceramic femoral head and instructed to assemble the taper using their preferred surgical technique. This procedure was repeated five times. Surgeons were brought back to test the opposite material after four weeks. Output 3D load data was analyzed for differences in peak vertical load applied, angle of deviation from the stem axis—termed off-axis angle, variability between trials, and impaction location. Results. Preliminary results suggest no significant differences between the loads applied to the metal heads and the ceramic heads. Across the two materials tested, both attendings and residents applied greater loads than fellows (p=0.33; Residents=9.0 kN vs Fellow=7.2 kN: p=0.27; Attendings=8.9 kN vs 7.2 kN) with significantly less variability (Attendings: σ= 1.58; Fellows: σ= 3.26; Residents: σ= 2.86). Attending surgeons also exhibited applied loads at significantly lower off-axis angles compared to fellows (p=0.01; 4.6° vs Fellow=7.2°) (Figure 2). However, all of our clinicians assembled ceramic head tapers with a greater off-axis angle as compared to assembling metal heads. In addition, metal heads were impacted more on-axis for all surgeon experience levels (Figure 3). While the impaction load plots suggest that the first impact strike is the most crucial for head stability, it was determined that the number of strikes is not as important as the maximum impaction load applied. Conclusion. Differences in impaction load when assembling metal and ceramic femoral heads were not apparent; however, variability of technique and load was observed across the different surgical experience levels as well as within surgeons of the same level. Understanding assembly mechanics and surgical habits for THA will provide insight to the best assembly procedures for these implants. For any figures or tables, please contact authors directly

Introduction. Subject-specific finite element models (FEMs) allow for a variety of biomechanical conditions to be tested in a highly repeatable manner. Accuracy of FEMs is improved by mapping density using quantitative computed tomography (QCT) and choosing a constitutive relationship relating density and mechanical properties of bone. Although QCT-derived FEMs have become common practice in contemporary computational studies of whole bones, many density-modulus relationships used at the whole bone level were derived using mechanical loading of small trabecular or cortical bone cores. These cores were mechanically loaded to derive an apparent modulus, which is related to each core's mean apparent or ash density. This study used these relationships and either elemental or nodal material mapping strategies to elucidate optimal methods for scapular QCT-FEMs. Methods. Six cadaveric scapulae (3 male; 3 female; mean age: 68±10 years) were loaded within a micro-CT in a custom CT-compatible hexapod robot Pre- and post-loaded scans were acquired (spatial resolution = 33.5 µm) and DVC was used to quantify experimental full-field displacements (BoneDVC, Insigneo) (Figure 1).. Experimental reaction forces applied to the scapulae were measured using a 6-DOF load cell. FEMs were derived from corresponding QCT scans of each cadaver bone. These models were mapped with one of fifteen density-modulus relationships and elemental or nodal material mapping strategies. DVC-derived BCs were imposed on the QCT-FEMs using local displacement measurements obtained from the DVC algorithm. Comparisons between the empirical and computational models were performed using resultant reaction loads and full-field displacements (Figure 2). Results and Discussion. Reaction forces predicted by the QCT-FEMs showed large percentage error variations across all specimens and density-modulus relationships with elemental material mapping. The percentage errors were as large as 899%, but as low as 3=57% for the different specimens. Similarly, when using a nodal material mapping strategy, percentage errors were as large as 965%, but as low as 4=59% for the different specimens (Figure 3). For all specimens, minimal variation only occurred in the slope between the QCT-FEM and DVC displacements in the x and y directions for either elemental or nodal material mapping strategies. Slopes ranged from 0.86 to 1.06. This held true for 3 specimens in the z direction; however, for the remaining 3 specimens more pronounced variations occurred between the QCT-FEM and DVC displacements, dependent on density-modulus relationship. The r. 2. values were consistently between 0.82 and 1.00 for both material mapping strategies and density-modulus relationships for all three Cartesian components of displacement and all specimens. Conclusions. The results suggest that QCT-FEMs using DVC derived boundary conditions can replicate experimental loading of cadaveric specimens. It was also shown that only slight variations exist when either elemental or nodal material mapping strategies are adopted. Given the recent advancements provided by DVC-derived BCs, this study provides a basis for a common methodology that can be implemented in future studies comparing similar outcomes in all anatomic locations. Expanding the current sample size has the potential to determine if a single density-modulus relationship can exist or if specimen or anatomic location-specific relationships should be utilized. For any figures or tables, please contact the authors directly

Background. Fretting corrosion at the junction of the modular head neck interface in total hip arthroplasty is an area of substantial clinical interest. This fretting corrosion has been associated with adverse patient outcomes, including soft tissue damage around the hip joint. A number of implant characteristics have been identified as risk factors. However, much of the literature has been based on metal on metal total hip arthroplasty or subjective scoring of retrieved implants. The purpose of this study was to isolate specific implant variables and assess for material loss in retrieved implants with a metal on polyethylene bearing surface. Methods. All 28mm and 32 mm femoral heads from a 12/14 mm taper for a single implant design implanted for greater than 2 years were obtained from our institutional implant retrieval laboratory. This included n = 56 of the 28 mm heads (−3: n = 10, +0: n = 24, +4: n = 13, and +8: n = 9), and n = 23 of the 32 mm heads (−3: n = 2, +0: n = 8, +4: n = 1, and +8: n = 6). There were no differences between groups for age, gender, BMI, or implantation time. A coordinate measuring machine was used to acquire axial scans within each head, and the resulting point clouds were analyzed with a custom Matlab program. Maximum linear wear depth (MLWD) was calculated as the maximum difference between the material loss and as-machined surface. Differences in MLWD for head length, head diameter, stem material, and stem offset were determined. Results. Within the 28 mm head diameter group, there was no difference (p = 0.65) in MLWD between head lengths (−3: 4.0 ± 1.7 µm, +0: 10.4 ± 15.2 µm, +4: 4.4 ± 1.7 µm, +8: 4.3 ± 1.8 µm). There was no difference (p = 0.12) between the 28 mm (6.7 ± 10.9 µm) and 32 mm (5.5 ± 6.2 µm) head diameters. There was also no difference (p = 0.97) between titanium (7.3 ± 11.4 µm) or cobalt-chromium (5.9 ± 5.6 µm) stems, and no difference (p = 0.20) between regular (7.0 ± 10.0 µm) or high-offset (5.7 ± 8.0 µm) stems. Discussion. The development of fretting corrosion at the head neck junction of metal on polyethylene total hip replacements is of substantial clinical importance. In a single taper design, head diameter, head length, stem material and stem offset were all not found to be contributory to magnitude of wear depth. This is in contrast to current literature, which is controversial regarding the role of head diameter, but head length is thought to be contributory. However, as this study using precise tools does not illustrate these proposed biomechanic factors of fretting corrosion, other factors influencing tribocorrosion such as trunnion surface finish, flexural rigidity, interface geometry and biochemical factors may need to be considered

INTRODUCTION. Mechanical properties mapping based on CT-attenuation is the basis of finite element (FE) modeling with heterogeneous materials and bone geometry defined from clinical-resolution CT scans. Accuracy between empirical and computational models that use constitutive equations relating CT-attenuation to bone density are well described, but material mapping strategy has not gained similar attention. As such, the objective of this study was to determine variations in the apparent modulus of trabecular bone cores mapped with various material mapping strategies, using a validated density-modulus relationship and co-registered µFEMs as the gold standard. METHODS. Micro-CT images (isotropic 32 µm) were used to create µFEMs from glenoid trabecular bone cores of 14 cadaveric scapula. Each µFEM was loaded in unconstrained compression to determine the trabecular core apparent modulus (E. app. ). Quantitative CT (QCT) images (isotropic 0.625 mm) were subsequently acquired and co-registered QCT-FEMs created for each of the 14 cores. The QCT-FEMs were meshed with either linear hexahedral (HEX8), linear tetrahedral (TET4), or quadratic tetrahedral (TET10) elements at 3 mesh densities (0.3125 mm, 0.46875 mm, 0.625 mm). Three material mapping strategies were used to apply heterogeneous element-wise (element-averaging of the native HU field (Mimics V.20, Materialise, Leuven BE)) or nodal (tri-linear interpolation of HU Field or E Field (Matlab V. R2017a, Natick, RI, USA)) material properties to the QCT FEMs. Identical boundary conditions were used and E. app. between the µFEMs and QCT-FEMs was compared (Figure 1). The QCT density of each hexahedral mesh with element size equal to voxel dimensions was used to compare the QCT density mapping between tetrahedral meshes and material mapping strategy. RESULTS. For tetrahedral meshes the mean QCT density error was 2.4±2.7%, 4.3±4.4%, and 1.6±2.5%, for tetrahedral mesh densities of 0.3125, 0.46875, and 0.625 mm, respectively. Nodal material mapping differs by TET4 and TET10 and therefore for tri-linear interpolation the QCT density error was 0.4±1.6%, 3.5±3.3%, and 2.0±2.2%, for TET4 mesh densities of 0.3125, 0.46875, and 0.625 mm, respectively. The errors were −0.6±1.4%, 2.0±1.4%, 0.2±1.9% for TET10 mesh densities of 0.3125, 0.46875, and 0.625 mm, respectively. Percentage errors in E. app. as a function of bone volume fraction (BV/TV) by material mapping strategy were lowest for HEX8 QCT-FEMs mapped with element-based HU (MIMICS). This was also the best mapping strategy for both TET4 and TET10 QCT-FEMs. The node-based material mapping using the HU field was best for TET4 QCT-FEMs with 0.625 mm elements. The node-based E field mapping had the lowest errors for TET10 QCT-FEMs but had greater errors than the other two mapping strategies for all element types (Figure 2). DISCUSSION. This study compared material mapping strategy, element type, and element density in QCT-FEMs compared to co-registered µFEMs. It was found that QCT-FEMs with hexahedral elements most closely match µFEMs when element averaging of the native HU field is used. This mapping strategy also showed relatively lower errors with linear and quadratic tetrahedral elements compared to node-based material mapping strategies. If modeling parameters are carefully considered when developing QCT-FEMs, models have the potential to accurately replicate micro-level trabecular bone apparent properties. For any figures or tables, please contact the authors directly

Graphene is a two-dimensional structure that is made of a single-atom-thick sheet of carbon atoms organised in hexagonal shapes. It is considered to be the mother of all graphite or carbon-based structures. It has shown exceptional physical and chemical properties which possess potential future applications. Graphene has an elasticity index similar to rubber and a hundred times tensile strength of steel and is even sturdier than diamonds. It is a very efficient biosensor with its exceptional electronic conductivity far greater than even copper. It is a potential future low cost material and its scalable production ability makes it even more attractive. The rediscovery of Graphene in 2008 saw few potential medical applications, specifically in the field of drug delivery, gene and cancer therapy. Nao graphene has extensive thermal conductivity and reflexivity, which can conceivably change imaging especially muskeloskeletal imaging and notably as a contrast material. It has been found to be a safe and a cheaper IV contrast agent in USA in 2012. Being an efficient biosensor especially in conducting electricity, it could assist in prosthetic and bionic limbs or prosthesis. Its durable stubborn properties, a composition which exceeds the strength of steel and light weight structure may create a potential material to develop into a new generation of a low profile internal fixing devices like plats. Most importantly, its scaffolding cell culturing assets could change the whole concept of prosthesis from mechanical press fit fixation to more dependence on bio adhesiveness

Introduction. In total joint replacement devices, material loss from the taper junctions is a clinical concern. Previous studies of explanted orthopedic devices have relied on visual scoring methods to quantify the fretting-corrosion damage on the component interfaces. Previous research has shown that visual fretting-corrosion evaluation is correlated to the volume of material loss [1], but scoring is semi-qualitative and does not provide a quantitative measure of the amount of material removed from the surface. The purpose of this study was to develop and validate a quantitative method for measuring the volume of material lost from the surfaces of explanted devices at the taper-trunnion junction. Methods. 10 new exemplar taper adapter sleeves (Ceramtec, Plochingen, Germany) were used for method validation. By using exemplar devices we were able to create clinically realistic taper damage in a controlled and repeatable manner using machining tools. Taper surfaces were measured before and after in vitro material removal using a roundness machine (Talyrond 585, Taylor Hobson, UK). Axial traces were measured on each taper surface using a diamond stylus. The mass of artificially removed material was also measured gravimetrically using a microgram balance (Sartorius, CPA225D, accuracy = ± 0.00003g). Surface profiles were analyzed using a custom MatLab script and Talymap software was used to provide 3D visualizations of the pattern of material loss. Calculated volumetric material loss was compared to the gravimetric value. A sensitivity analysis was conducted to determine the optimum number of traces to characterize the material loss from taper junctions. Results. Our calculations of material loss predicted over 99% of the variation in gravimetric material loss (Figure 1, r2 = 0.9962). Examples of the pattern of material removal from explanted components resembled the patterns reported in explants (Figure 2). The sensitivity analysis showed that a minimum of 24 axial profiles are required for measurements to stay within 2% of the volume calculated with 144 traces for cases with an axisymmetric wear pattern. Discussion. We have developed and validated a quantitative method for the material loss from taper junctions in orthopedic devices. Our sensitivity analysis showed that a minimum of 24 profiles are required to calculate volumetric material loss accurately, however a further sensitivity analysis is required to establish the minimum number of profiles required to accurately characterize “asymmetric” wear patterns. The measurement of 24 profiles takes approximately 20 minutes. The validation thus far has comprised material loss in an axisymmetric pattern. Work is underway to validate the evaluation of tapers with an asymmetric wear pattern. The axisymmetric and asymmetric patterns are realistic representations of wear patterns seen in explanted taper surfaces. This validated method of estimating material loss from taper junctions will be used in our ongoing research program to understand the mechanisms of fretting-corrosion in retrieved orthopaedic tapers

Introduction. The in vivo evolution of surface material properties is important in determining the longevity of bioceramics. Fracture toughness is particularly relevant because of its role in wear resistance. Some bioceramics, such as zirconia (ZrO2) undergo in vivo phase transformation, resulting in a marked reduction in toughness and commensurate increased wear. Here, we investigated the effect of accelerated aging on the surface toughness of alumina (Al2O3), zirconia-toughened alumina (ZTA), and silicon nitride (Si3N4) femoral heads, in order to identify the optimal ceramic material for in vivo implantation and long-term durability. Materials. A newly developed Raman microprobe-assisted indentation method was applied to evaluate and compare surface fracture toughness mechanisms operative in Si3N4 (Amedica Corporation, Salt Lake City, UT, USA), Al2O3 and ZTA (BIOLOX® forte, and delta, respectively, CeramTec, GmbH, Plochingen, Germany) bioceramics. The Al2O3 and ZTA materials have long established histories in total hip arthroplasty; whereas Si3N4 has been newly developed for this purpose. The improved method proposed here consisted in coupling the “traditional” indentation technique with quantitative assessments of microscopic stress fields by confocal Raman microprobe piezo-spectroscopy. Concurrently, crack opening displacement (COD) profiles were also monitored by Raman spectroscopy. Toughness measurements were determined using both as-received and hydrothermally exposed (100–121°C for up to 300 hours) femoral heads. Results. The Raman microprobe visualized two main toughening mechanisms operative in Si3N4 and ZTA bioceramics, namely crack-face bridging by acicular Si3N4 grains and polymorphic transformation of ZrO2 dispersoids. Both mechanisms elevated the resistance to crack propagation above the brittle behavior of Al2O3, which experienced a low crack resistance of ∼1.5 MPaâ��m1/2 independent of crack length. The as-received Si3N4 showed a sharply rising R-curve, up to ∼7 MPaâ��m1/2 within a propagation distance of ∼110 µm. A rising R-curve was also observed in the as-received ZTA, although its increase was less pronounced, ∼4 MPaâ��m1/2 within ∼120 µm. After hydrothermal exposure, surface toughness values decreased by ∼5%, ∼10%, and ∼42% for Si3N4, Al2O3, and ZTA, respectively. Substantial embrittlement was particularly noted at the surface of the ZTA material, with its toughness value reduced to the level of Al2O3. At the micromechanical scale, such embrittlement is obviously related to decreased availability of transformable (metastable) tetragonal ZrO2dispersoids at the surface. In ZTA, the hydrothermal attack annihilated any rising R-curve effect; whereas this degradation mechanism was not present in either Al2O3 or Si3N4 (Fig. 1). Discussion. Empowered by the Raman microprobe, the indentation micro-fracture method was shown capable of providing reliable surface toughness measurements in dissimilar biomaterials. Different from bulk toughness, surface toughness is the most relevant parameter in designing bioceramic microstructures for use as hip arthroplasty bearing couples for improved tribological performance. It was demonstrated that the environmentally driven phase transformation in ZTA is detrimental to surface toughness. On the other hand, Si3N4 experienced surface toughness values conspicuously independent of hydrothermal attack. Conclusions. Unlike transformation toughening (which is operative in ZTA), crack-face bridging (which is the toughening mechanism in Si3N4) proved to be the most durable surface toughening effect for a biomaterial to be employed in joint arthroplasty

Introduction. Corrosion products from modular taper junctions are a potent source of adverse tissue reactions after THR. In an attempt to increase the area of contact and resistance to interface motion in the face of taper mismatches, neck trunnions are often fabricated with threaded surfaces designed to deform upon assembly. However, this may lead to incomplete contact and misalignment of the head on the trunnion, depending upon the geometry and composition of the mating components. In this study we characterized the effect of different femoral head materials on the strength and area of contact of modular taper constructs formed with TiAlV trunnions. Materials and Methods. Three groups of 36mm femoral heads (CoCr, Biolox ceramic; Oxinium) and matching Ti-6Al-4V rods with 12/14 trunnions were selected for use in this study. The surface of each trunnion was coated with a 20nm layer of gold applied by sputter-coating in vacuo. Each head/trunnion pair was placed in an alignment jig and assembled with a peak axial impaction force of 2000N using a drop tower apparatus. After assembly, each taper was disassembled in a custom apparatus mounted in a mechanical testing machine (Bionix. MTS. After separation of the components, the surface of each trunnion was examined with backscattered electron microscopy to reveal the area of disruption of the original gold-coated surface. Images encompassing the entire surface of the trunnion were collected and quantified by image processing. Results. The force required to disassemble the Oxinium and Biolox heads from their mating tapers were 2153±104N and 2200±145N, respectively (p-=0.5359). In contrast, the average disassembly force of the CoCr-TiAlV couples was 47% less (1165±156N, p<0.0001). Direct contact between the trunnion and the femoral head was only present over 3.7±0.3% of the nominal surface area of the modular junctions and was limited to the crests of the threads. Contact area did not vary as a function of head composition (p>0.4). However, there were noticeable differences in terms of the distribution of contact between the head and the trunnion. CoCr heads typically had large spans of noncontact immediately below the apex of the taper and opposite each other at the trunnion base. Biolox heads tended to have complete contact at the apex but only extended down 30% of the taper and intermittently at the base. Oxinium heads had comparable complete contact areas to Biolox at the apex but unlike Biolox and CoCr, a uniform band of contact existed at the base. Conclusions. CoCr heads provided only half the resistance to disassembly of Biolox and Oxinium heads. The total area of direct head-trunnion contact is minimal and is not affected by head composition. The heads studied had characteristic patterns of interface contact. This may be due to variations in the geometry of the bores within each head combined with cocking of the femoral head during seating as the thread peaks are being deformed. For any figures or tables, please contact authors directly

INTRODUCTION. Many studies have looked at the effect of titanium versus cobalt chrome baseplates on backside wear. However, the surface finish of the materials is usually different [1,2]. There may also be subtle locking mechanism design changes [2]. The purpose of this study was to evaluate the wear performance of polyethylene inserts when mated with titanium baseplates to cobalt chrome baseplates, where both have non-polished topside surfaces and an identical locking mechanism. MATERIALS AND METHODS:. A total of three trays per material were used. The titanium trays are intended for cementless application and include a porous titanium surface on the underside, while the cobalt chrome trays are intended for cemented applications. All trays were Triathlon design (Stryker Orthopaedics, Mahwah, NJ). Tibial inserts were manufactured from GUR 1020 polyethylene then vacuum/flush packaged and sterilized in nitrogen (30 kGy). Cobalt chrome femoral components were articulated against the tibial inserts. Surface roughness of the baseplates was measured prior to testing using white light interferometry (Zygo, Middlefield, CT). A 6-station knee simulator (MTS, Eden Prairie, MN) was used for testing. A normal walking profile was applied [3]. Testing was conducted for 1 million cycles. A lubricant of Alpha Calf Fraction serum (Hyclone Labs, Logan, UT) diluted to 50% with a pH-balanced 20-mMole solution of deionized water and EDTA was used [4]. The serum solution was replaced and inserts were weighed for wear every 0.5 million cycles. Standard test protocols were used for cleaning, weighing, and assessing the wear loss [5]. Soak control specimens were used to correct for fluid absorption. Statistical analysis was performed using the Student's t-test (p < 0.05). RESULTS:. White light interferometry measurements (Figure 1) showed a significant difference in surface roughness between the tray materials (p < 0.01). Figure 2 displays the results of wear testing after 1 million cycles, which show no significant difference. Visually, the backside of all inserts showed mild “stenciling” which corresponded to the location of the femoral condyle during the loading cycle. This surface feature transfer phenomenon was less pronounced with the titanium trays. DISCUSSION:. Although criticized as a bearing material, the results of testing show no deleterious effect on wear performance when using titanium baseplates in comparison to cobalt chrome. In fact, the inserts mated with titanium baseplates show a slight improvement in wear performance, although the difference is not statistically significant. Visually, the backside surfaces of the polyethylene mated with titanium baseplates showed less stenciling effect, which may be due to the difference in material properties as well as the difference in surface roughness. In conclusion, the results of our wear simulation show that wear performance was not adversely affected when titanium baseplates were substituted for cobalt chrome baseplates under normal walking kinematics

Introduction. Trabecular bone transmits loads to the cortical shell and is therefore most active in bone remodeling. This remodeling alters trabecular material strength thereby changing the bending stiffness. Accounting for trabecular material heterogeneity has been shown to improve empirical-µFEM correlations by allowing for more realistic trabecular bending stiffness. In µFEMs to reduce computation time, region averaging is often used to scale image resolution. However, region averaging not only alters trabecular architecture, but inherently alters the CT-intensity of each trabeculae. The effect of CT-intensity variations on computationally derived apparent modulus (E. app. ) in heterogenous µFEMs has not been discussed. The objectives of this study were to compare trabecular E. app. among i) hexahedral and tetrahedral µFEMs, ii) µFEMs generated from 32 µm, 64 µm, and 64 µm down-sampled from 32 µm µ-CT scans, and iii) µFEMs with homogeneous and heterogeneous tissue moduli. Methods. Fourteen cadaveric scapulae (7 male; 7 female) were micro-CT scanned at two spatial resolutions (32 µm & 64 µm). Virtual bone cores were extracted from the glenoid vault, maintaining a 2:1 aspect ratio, to create µFEMs from the 32 µm, 64 µm, and down-sampled 64 µm scans. Custom code was used to generate µFEMs with 8-node hexahedral elements (HEX8), while maintaining the bone volume fraction (BV/TV) of each HEX8 32 µm model (BV/TV=0.24±0.10). Each virtual core was also generated as a 10-node tetrahedral (TET10) µFEM. All µFEMs were given either a homogeneous tissue modulus of 20 GPa, or a heterogeneous tissue modulus scaled by CT-intensity. All FEMs were constrained with identical boundary conditions and compressed to 0.5% apparent strain. The apparent modulus of each model was compared. Results. Comparing error in mean E. app. , TET10 32 µm µFEMs with a homogeneous tissue modulus had an error of 7%, and a heterogeneous tissue modulus an error of 1%. Larger errors occurred for both down-sampled and scanned 64 µm µFEMs with both homogeneous and heterogeneous tissue moduli. The error in E. app. as a function of trabecular thickness (Tb.Th*) was larger for µFEMs generated from 64 µm scans, than the down-sampled 64 µm µFEMs. The errors were lowest for Tb.Th* greater than 0.225 mm and for µFEMs generated with heterogeneous tissue moduli. The error in E. app. as a function of volume fraction (BV/TV) was lowest above 0.225 for µFEMs with both homogeneous and heterogeneous tissue moduli and hexahedral and tetrahedral elements. Error was lower for the down-sampled 64 µm µFEMs versus scanned 64 µm µFEMs. DISCUSSION. This study compared the E. app. of linear isotropic µFEMs generated with hexahedral or tetrahedral elements from 32 µm, 64 µm, or down-sampled 64 µm µ-CT scans, with a homogeneous or heterogeneous tissue modulus. It was found that except at the highest spatial resolution, tetrahedral elements underestimate E. app. Down-sampling to half the original scan spatial resolution is not equivalent in E. app. to FEMs generated from scans at that spatial resolution, and both models underestimate the E. app. of the highest spatial resolution models. In general, accounting for trabecular material heterogeneity decreased errors in E. app.

Introduction. Porous scaffolds for bone ingrowth have numerous applications, including correcting deformities in the foot and ankle. Various materials and shapes may be selected for bridging an osteotomy in a corrective procedure. This research explores the performance of commercially pure Titanium (CPTi) and Tantalum (Ta) porous scaffold materials for use in foot and ankle applications under simplified compression loading. Methods. Finite element analysis was performed to evaluate von Mises stress in 3 porous implant designs: 1) a CPTi foot and ankle implant (Fig 1) 2) a similar Ta implant (wedge angle = 5°) and 3) a similar Ta implant with an increased wedge angle of 20°. Properties were assigned per reported material and density specifications. Clinically relevant axial compressive load of 2.5X BW (2154 N) was applied through fixtures which conform to ASTM F2077–11. Compressive yield and fatigue strength was evaluated per ASTM F2077–11 to compare CPTi performance in design 1 to the Ta performance of design 3. Results. FEA results indicate peak stresses at fixture contact locations. Similar designs (CPTi design 1 and Ta design 2) resulted in similar von Mises stresses (Fig 1). Increasing the wedge angle (Ta design 3) increased stress by 15%. The static compressive yield strength of CPTi design 1 (20,560 N) was similar to the Ta design 3 (20,902 N), with yield manifesting as barreling and crushing of the components (Fig 2a). However, the fatigue strength of CPTi (6,000 N) was 40% lower than the Ta design 3 (9,500 N) (Fig 3). In both cases fracture initiated from regions of highest stress predicted in FEA. Fracture progression was not instantaneous and was characterized by an accumulation of damage (Fig 2b–c) leading to gross component fracture and loss of implant integrity. Discussion. FEA is a useful tool to determine stress variations and can be used to identify worst case within a material: in this case, a larger implant wedge angle leads to higher stresses. Additionally, FEA accurately predicted fracture initiation location. However, material selection plays a large role in porous implant performance: although FEA predicted higher stresses in a Ta component with a greater wedge angle than a similar sized CPTi component, static compressive strengths were nearly identical, and the Ta component had 58% higher fatigue strength. When selecting a material or geometry for an implant application, both FEA and static testing allow for rapid evaluation of designs. However, caution should be used in interpreting the results: the ultimate performance of an implant in-vivo will depend on its ability to maintain integrity over a long period of time, and should be characterized by dynamic testing

Introduction. There is a demand for longer lasting arthroplasty implants driving the investigation of novel material combinations. PEEK has shown promise as an arthroplasty bearing material, with potentially relatively bio inert wear debris [1]. When coupled with an all-polyethylene tibial component this combination shows potential as a metal-free knee. In this study, the suitability of PEEK Optima® as an alternative to cobalt chrome for the femoral component of total knee replacements was assessed using experimental knee wear simulation under two kinematic conditions. Methods. Three cobalt chrome and three injection moulded PEEK Optima® (Invibio Biomaterial Solutions, UK) femoral components of similar geometry and surface roughness (mean surface roughness (Ra) ∼0.02µm) were coupled with all-polyethylene GUR1020 (conventional, unsterilised) tibial components in a 6 station ProSim knee simulator (Simulation Solutions, UK). 3 million cycles (MC) of wear simulation were carried out under intermediate kinematics (maximum anterior-posterior (AP) displacement 5mm) followed by 3MC under high kinematics (AP 10mm) [2] with 25% serum as the lubricant. The wear of the tibial component was assessed gravimetrically. At each measurement point, the surface roughness of the femoral components was determined using contacting profilometry and throughout testing, the bulk lubricant temperature was monitored close to the articulating surfaces. Statistical analysis was carried out using ANOVA, with significance at p<0.05. Results. Figure 1 shows the wear rate of the all-polyethylene tibial components. After 3MC of intermediate kinematics, the mean wear rate of UHMWPE articulating against cobalt chrome was 1.0±2.3mm3/MC and against PEEK was similar (p=0.06) 2.5±0.8mm3/MC. Scratches were apparent on the surface of the PEEK implant in the AP direction significantly (p<0.05) increasing mean surface roughness of the PEEK components (Table 1) compared to pre-test values. The surface topography of the cobalt chrome components (Table 2) was similar to pre-test measurements. Increasing AP displacement caused no significant increase in the wear of the tibial inserts against either material. Under intermediate kinematics, the mean bulk lubricant temperature was 28.0±0.7°C for cobalt chrome and significantly higher (p<0.001) for PEEK, 29.5±0.1°C; kinematic conditions had no effect on the lubricant temperature. Conclusions. This study showed a similar wear rate of all-polyethylene tibial components against PEEK and cobalt chrome femoral components of similar initial surface topography and geometry. Wear simulation with a higher AP displacement did not increase the wear of the polyethylene, in contrast to other designs of knee replacements, potentially due to the low conforming geometry of the implant [3]. The linear scratching on the surface of the PEEK implants did not increase the wear rate of the tibial components and the surface did not deteriorate further between 3 and 6 MC. A higher mean lubricant temperature was measured with PEEK femoral components, which was attributed to the higher friction of the PEEK-PE bearing couple. However it is not known whether this is clinically relevant or an artefact of the continuous running of the simulator. PEEK Optima® shows promise as the femoral component in a metal-free knee

Introduction. Stress shielding is one of the major concerns of load bearing implants (e.g. hip prostheses). Stiff implants cause stress shielding, which is thought to contribute to bone resorption1. On the contrary, low-stiffness implants generate high interfacial stresses that have been related to pain and interfacial micro-movements². Different attempts have been made to reduce these problems by optimizing either the stem design3 or using functionally graded implants (FGI) where the stem's mechanical properties are optimized4. In this way, new additive manufacturing technologies allow fabricating porous materials with well-controlled mesostructure, which allows tailoring their mechanical properties. In this work, Finite Element (FE) simulations are used to develop an optimization methodology for the shape and material properties of a FGI hip stem. The resorbed bone mass fraction and the stem head displacement are used as objective functions. Methodology. The 2D-geometry of a femur model (Sawbones®) with an implanted Profemur-TL stem (Wright Medical Technology Inc.) was used for FE simulations. The stem geometry was parameterized using a set of 8 variables (Figure 1-a). To optimize the stem's material properties, a grid was generated with equally spaced points for a total of 96 points (Figure 1-b). Purely elastic materials were used for the stem and the bone. Two bone qualities were considered: good (Ecortical=20 GPa, Etrabecular=1.5 GPa) and medium (Ecortical=15 GPa, Etrabecular=1 GPa). Poisson ratio was fixed to v=0.3. Loading corresponded to stair climbing. Hip contact force along with abductors, vastus lateralis and vastus medialis muscles were considered5 for a bodyweight of 847 N. The resorbed bone mass fraction was evaluated from the differences in strain energy densities between the intact bone and the implanted bone2. The displacement of the load point on the femoral head was computed. The optimization problem was formulated as the minimization of the resorbed bone mass fraction and the head displacement. It was solved using a genetic algorithm. Results. For the Profemur-TL design, bone resorption was around 36% and 56% for good and medium bone qualities, respectively (Fig. 2). The corresponding head displacements were 11.75 mm and 21.19 mm. Optimized solutions showed bone resorption from 15% to 26% and from 44% to 65% for good and medium bone qualities, respectively. Corresponding head displacements ranged from 11.85 mm to 12.25 mm and from 16.9 mm to 22.6 mm. Conclusion. The obtained set of solutions constitutes an improvement of the implant performance for this functionally graded implant (FGI) compared to the original implant for both bone qualities. From these simulations, the final solution for the FGI could be chosen based on manufacturing restrictions or another performance indicator

Unicompartmental knee replacements (unis) offer an early option for the treatment of osteoarthritis. However there is no standard method for measuring the wear of unis in the laboratory. Most knee simulators are designed for TKA, for which there is an ISO standard. This study is about a wear method for unis, applied to a novel unicompartmental knee replacement (design by PSW). It has a metal-backed UHMWPE femoral component to articulate against a monoblock metallic tibial component. The advantage is reduced resection of strong bone from the proximal tibia for more durable fixation. The femoral component resurfaces the distal end of the femur to a flexion arc of only 42°, the area of cartilage loss in early OA (Fig. 1). We compared this novel bearing couple to the same design but with the usual arrangement of femoral metal and tibial plastic. Our hypothesis was that the wear of the reversed materials would be comparable to conventional and within the range of TKR bearings. The test was conducted on a 4-station Instron-Stanmore force-controlled knee simulator. Both specimen groups (n=4 each) were highly crosslinked UHWMPE stabilized with vitamin E. On each of the four stations, one uni system was mounted on the medial side and one on the lateral, as if a standard TKR was being tested. The ISO-14243-1 walking cycle force-control waveforms were applied for 5 million cycles (Mc) at 1Hz, but with the maximum flexion during the swing phase (usually 58°) curtailed to 35° to maintain the contact within the arc of the femoral component. In-vivo this implant would be inlaid into the distal medial femoral condyle and the articulating surface immediately transitions into native cartilage. In our test set-up there was no secondary surface as such. The reduced flexion occurred during the swing phase where compressive load was low and the effect on the wear would be negligible. Wear was measured gravimetrically at many intervals and corrected by the weight gain of extra two active soak controls per group. After 5 Mc, the average rates of gravimetric weight loss from the UHMWPE femoral and tibial bearings were 4.73±0.266 mg/Mc and 3.07±0.388 mg/Mc, respectively (statistically significantly different, p=0.0007) (Fig. 2). No significant difference was found in wear between medial and lateral placement for specimens of the same type, although the medial side generally wore more. Although the plastic femorals of the reverse design wore more than the plastic tibials, the wear was still low at <5 mg/Mc. The range for typical TKRs using ultra-high molecular weight polyethylene, tested under the same conditions in our laboratory has been 2.85–24.1 mg/Mc. In summary, we adapted the ISO standard TKA wear test for the evaluation of unis, and in this case, a uni with reversed materials. Based on the wear results, this type of ‘early intervention’ design could therefore be a viable option, offering simplicity with less modular parts as well as load sharing with the native articular cartilage

Introduction. After arthroplasty, stress shielding and high shear stresses at the bone-implant interface are common problems of load bearing implants (e.g. hip prostheses). Stiff implants cause stress shielding, which is thought to contribute to bone resorption. 1. High shear stresses, originated by low-stiffness implants, have been related to pain and interfacial micro-movements², prohibiting adequate implant initial fixation. A non-homogeneous distribution of mechanical properties within the implant could reduce the stress shielding and interfacial shear stresses. 3. Such an implant is called “functionally graded implant” (FGI). FGI require porous materials with well-controlled micro-architecture, which can now be obtained with new additive manufacturing technologies (e.g. Electron Beam Melting). Finite element (FE) simulations in ANSYS-v14.5 are used to develop an optimization methodology to design a hip FGI. Methodology. A coronal cut was performed on a femur model (Sawbones®) with an implanted Profemur®TL (Wright Medical Inc.) stem to obtain the 2D-geometry for FE simulations. The central part of the FGI stem was made porous, the neck and inferior tip were solid. Ti6Al4V elastic material was assumed (E=120 GPa, v=0.3). Three bone qualities were considered for the optimization: poor (E=6GPa; v=0.3); good (E=12GPa; v=0.3); excellent (E=30GPa; v=0.3). The structure of bone evolves to maintain a reasonable level of the strains. Similarly in the proposed algorithm, the strut sections of the porous material evolve to keep stresses (proportional to strains) at a reasonable level. Starting with a very small strut section, resulting in an almost zero-rigidity stem, strut sections are increased or decreased as a function of the stresses they support. This is done incrementally, until force values corresponding to normal walking of an 80 kg person (1867 N). 4. are reached. Force direction was vertical and no action of the abductors was considered, to analyze the worst case scenario. The optimized FGI microstructure is defined by the strut diameter distributions. Since the distance between struts remain constant, variations in strut diameters result in variations in density. Optimized FGI porous structure was compared for the three bone qualities considered and with a solid stem in terms of bone stresses. Results. Different bone qualities result in slightly different strut diameter distribution (Fig.1). An excellent bone quality (E=30 GPa) results in a less dense porous structure, where some dense zones are substituted by a thick strut surrounded by a low density area. As can be expected, a poor bone quality (E=6 GPa) results in a denser porous structure. Compared with the solid stem, in general the FGI stem produced higher bone stresses. Locally, the stresses augmented proximally, while diminished distally (Fig.2). This is expected to result in a smaller influence of stress shielding, and better load transfer. Conclusion. The presented algorithm succeeded obtaining an optimal strut diameter distribution from low rigidity struts, using a strategy similar to bone remodelling (i.e. maintaining certain stress level within the struts). Optimized diameter distribution was obtained with little computational cost

Ultra-high molecular weight polyethylene (UHMWPE) has been the gold standard material of choice for the load-bearing articulating surface in knee joint prostheses. However, the application of joint replacements to younger (aged < 64 years) and more active people plus the general increase in life expectancy results in an urgent need for a longer lasting material with better in-use performance. There are three major material related causes that can lead to joint failure in UHMWPE knee joint replacements: free radical induced chemical degradation; mechanical degradation through wear and delamination; and UHMWPE micron and submicron wear debris induced osteolysis. As a potential solution to these problems, highly crosslinked UHMWPE stabilised with infused antioxidant vitamin E (α-Tocopherol), which is abbreviated as E-Poly, has been of great interest. In the current work, the wear performance and mechanical properties of Vanguard cruciate retaining (CR) E-Poly tibial inserts were assessed and compared with Vanguard CR Arcom tibial inserts. Also E-Poly plates were compared with direct compression moulded UHMWPE wear plates. Both a multi-directional pin-on-plate tester and a six-station Prosim (Manchester, UK) knee wear simulator were used to assess wear properties of E-Poly plates and E-Poly tibial inserts respectively. All E-Poly plates and tibial inserts were sterilised and vacuum packed in the same way as Vanguard implants before wear testing. The wear knee simulator test was conducted in accordance with ISO 14243-3:2004 with the exception that a more aggressive Tibial Rotation and Anterior/Posterior displacement profiles, based on the kinematics of the natural knee were incorporated. Under the same aggressive pre-clinical wear testing condition, compared with Vanguard Arcom CR tibial inserts, Vanguard E-Poly CR tibial inserts experienced an 85% reduction in the mean wear rate. The former had a mean wear rate of 6.51±1.75 mm. 3. per million cycles (MC) and the latter had a mean wear rate of 0.96±0.11 mm. 3. /MC over the 7 million cycle testing period. A similar reduction (80%±8.5) in the mean wear factor was also observed on E-Poly plates compared with a series of direct compression moulded GUR1050 UHMWPE plates processed under a range of manufacturing processing conditions. Wear testing was conducted with a configuration of flat-ended stainless steel indenters multi-directionally sliding against the UHMWPE plates. Mechanical properties on Vanguard Arcom UHMWPE and E-Polys were evaluated using the small punch test. All tests were carried out using an Instron 5565 Universal Testing System at a constant crosshead speed of 0.5mm/min. With regard to work-to-failure, no statistical difference was observed, with the former being 254.2±4.1 mJ and the latter 255.6±28.2 mJ. However, all E-Polys exhibited strain stiffening due to the stretch of crosslinks. This resulted in a ca 12% reduction in elongation to break observed for E-Polys compared with that of Arcom UHMWPE. The former had an elongation to break of 4.1±0.2 mm and the latter of 4.7±0.3 mm. In conclusion, we have found that Vitamin E Stabilised UHMWPE tibial inserts are promising for knee joint prostheses. However, further investigations are needed to address potential issues such as the particle size and size distribution of E-Poly wear debris and the associated reactivity