Introduction. Large-scale retrieval studies have shown backside wear in tibial inserts is dependent on the surface roughness of the tibial tray. Manufacturers acknowledge this design factor and have responded with the marketing of mirror-finished trays, which are clinically proven to have lower wear rates in comparison to historically “rough” (e.g. grit blasted) trays. While the relationship between wear and surface roughness has been explored in other polymer applications, the quantitative dependence of backside wear rate on quantitative surface finish has not yet been established for modern devices. The present study evaluates small-excursion polyethylene wear on pucks of a variety of surface roughnesses. The objective of this study is to determine where inflection points exist in the relationship between surface roughness and wear rate. Materials and Methods. An AMTI Orthopod, 6-station pin on disk tribotest was designed to mimic worst-case in vivo backside wear conditions based on published retrieval analyses. Titanium (Ti6Al4V) pucks with six different surface roughness preparations (Sa ranges from 0.06 um to 1.06 um) were characterized with white light profilometry. Never implanted polyethylene tibial inserts (never irradiated, EtO sterilized) were machined into 6 mm diameter cylindrical pins. Fretting-type motion was conducted in a 2mm square pattern at 2Hz under 100 N constant force in 25% bovine serum lubricant for 1.35 million cycles in triplicate. Mass measurements were taken every 225 thousand cycles. Results. Over the range of surface roughness studied (Sa = 0.06 – 1.06 µm), wear rate grew logistically. The wear rate for highly polished titanium (Sa = 0.06 µm) was not statistically different from less-polished titanium with Sa of 0.14 µm (p > 0.1). Titanium pucks having the highest surface roughness (Sa > 0.5µm), removed material significantly faster than those with roughness less than 0.3µm. The results of these tests suggest that Ti trays with Sa less than 0.15µm may yield equivalent clinical backside wear results, while pucks with Sa greater than 0.15µm begin to have increased wear rates that may be clinically significant. The two pucks with Sa greater than 0.5 µm yielded wear rates failing to be statistically differentiable (p = 0.059), corresponding with the flattening of the logistic curve. Discussion. These results suggest that baseplates with Sa less than 0.15 µm may ultimately yield clinically equivalent outcomes. The wear rate curve changes slope between Sa 0.14 and 0.22 µm and continues to increase across the range of surface roughnesses studied. The wear rates on rough pucks (Sa > 0.5 µm) showed high variation, reducing the ability to distinguish the two statistically (p = 0.059). Further study will better distinguish wear properties at higher surface roughnesses. Conclusion. These findings demonstrate that there may be a range of finishes between a mirror polish and grit blast that may produce clinically equivalent wear rates. This work provides justification for further study into the relationship between backside wear, baseplate tray roughness, and material choices. For any figures or tables, please contact authors directly

Introduction: Although acetabular cup wear is usually reported in terms of penetration (measured from radiographs), true wear – wear volume – depends on several variables. This study examined how these variables affect the calculation of the theoretical wear volume at the low wear penetrations found with highly cross-linked polyethylene (XLPE) cups. Method: A computerised numerical analysis technique was used to calculate the “exact” theoretical wear volume of an acetabular cup under a variety of circumstances, including: variations in wear direction, head size, and initial radial discrepancy (i.e. initial difference between socket and head sizes). The validity of published wear volume formulae was assessed. The effects of creep and wear measurement error were also assessed. Results: For a given wear penetration, as the wear direction (relative to the cup base) increased, the wear volume increased – almost doubling as the direction reached 60°. The initial radial discrepancy made a substantial difference to the calculated wear volume at penetrations less than 1 mm. At low penetrations, its neglect caused an overestimation of wear volume of well over 100%. Creep volume was substantially overestimated because of this. An analysis of wear measurement error showed that the calculation of wear direction (an important variable in the calculation of wear volume) was severely affected at low penetrations by the precision of penetration measurements. For a penetration precision of ±0.25 mm (as reported for the Martell Hip Analysis Suite), the maximum wear direction error was ±39° at a penetration of 0.4 mm. When the precision was ±0.1 mm (as with RSA), this reduced to ±14°. Discussion: Many studies have shown the superior wear performance XLPE acetabular cups compared with standard PE cups. In those studies, comparison in terms of wear penetration was possible because of the large difference in penetrations between the two groups. This study has shown that true wear (wear volume) is significantly affected by wear direction (relative to the cup), the initial radial discrepancy, and the femoral head size. The differences in penetrations when comparing two types of XLPE cups would not be so large and it is therefore necessary to compare the two groups in terms of wear volume. Published formulae for estimating the wear volume of acetabular cups do not take the initial radial discrepancy into account, and they can substantially overestimate the wear volume in the penetration range encountered with XLPE cups. Creep volume is also greatly overestimated. Since wear volume varies with wear direction, the wear measurement technique must be capable of accurately determining the wear direction. This analysis has shown that only RSA might have sufficient precision to determine the wear direction at the medium-term penetrations encountered with XLPE cups

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

Abstract. Introduction. The Oxford Unicompartmental Knee Replacement's (OUKR's) fully-congruent design minimises polyethylene wear. Consequently, wear is a rare failure mechanism. Phase-3 OUKR linear wear at 5 years was higher than previous OUKR phases, but very low compared to fixed-bearing UKRs. This study aimed to measure OUKR bearing wear at 10 years and investigate factors that may affect wear. Methodology. Bearing thickness for 39 OUKRs from a randomised study was calculated using radiostereometric analysis at regular intervals up to 10 years. Data for 39 and 29 OUKRs was available at 5 and 10 years, respectively. As creep occurs early, wear rate was calculated using linear regression between 6 months and 10 years. Relationships between wear and patient factors, fixation method, Oxford Knee Score (OKS), bearing position, and component position were analysed. Results. The mean wear rate was 0.06mm/year. Fixation method, age, OKS, component size, and bearing size had no correlation with wear. A higher BMI was associated with lower wear (p=0.01). Bearings more than 4mm from the wall had significantly more wear (p=0.04) than those less than 4mm from the wall. There was a linear correlation between the femoral component contact area on the bearing and wear (p=0.04). Conclusions. Phase-3 bearing wear rate is constant, significantly higher than previous OUKR phases at 10 years, and may increase the risk of long-term bearing failure. To minimise complications associated with wear, size 4 bearings should be used in young patients and manufacturing bearings from more durable, highly crosslinked polyethylene should be studied

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. Unicompartment knee replacement (UKR) has been an effective treatment of isolated medial compartment osteoarthritis (OA). There has been several studies which suggest that patellofemoral (PFJ) wear may not be a relative contraindication for UKR with no statistical difference in failure rates. There is currently conflicting evidence on the role of BMI. We will review if BMI and PFJ wear impacts on the post operative functional scores following UKR. A retrospective review of a prospectively collected database was performed. Data was collected between 26/6/2014 and 25/8/2022. 159 UKR procedures were identified. BMI and PFJ cartilage wear were collected. Oxford knee scores (OKS) were collected at > 2 years. PFJ wear was split into International Cartilage Research Society (ICRS) grades I&II and III&IV. 159 UKR procedures were identified, of these 115 had 2 year follow up. There were 77 who had OKS recorded at 2 years. For PFJ wear there was no statistical difference in the median OKS at 2 years 45 vs 43.5 (p=0.408). Assessing the BMI the median was 29kg/m. 2. , range 20–43kg/m. 2. Spearman's rank was performed to assess the correlation between BMI and >2 year OKS, this demonstrated a moderately negative correlation p(df)=−0.339 (CI 95% −0.538, −0.104) p=0.004. There is no statistically significant difference in >2 year OKS following UKR regardless of PFJ wear. There is a moderately negative correlation between BMI and >2 year OKS which was significant p=0.004. Therefore BMI is a more important consideration when counselling patients for UKR

Introduction. Previous studies have shown that third body damage to the femoral head in metal-on-polyethylene hip replacement bearings can lead to accelerated wear of the polyethylene liners. The resulting damage patterns observed on retrieved metal heads are typically scratches and scrapes. The damage created in vitro must represent the third body damage that occurs clinically. A computational model was developed to predict the acceleration of wear of polyethylene articulating against in vitro damaged femoral heads. This involved using a damage registry from retrieval femoral heads to develop standardized templates of femoral head scratches statistically representative of retrieval damage. The aim of this study was to determine the wear rates of polyethylene liners articulating against retrievals and artificially damaged metal heads for the purpose of validating a computational wear prediction model; and to develop and validate an in vitro standardised femoral head damage protocol for pre-clinical testing of hip replacements. Materials and Methods. Twenty nine, 32mm diameter, metal-on-moderately cross-linked polyethylene bearings (Marathon. TM. ) inserted into Ti-6Al-4V shells (Pinnacle. ®). were tested in this study. All products were manufactured by DePuy Synthes, Warsaw, Indiana, USA. Following a retrieval study seven different damage patterns were defined, and these were applied to the femoral heads using a four-degree-of-freedom CNC milling machine (Figure 1). The ProSim 10-station pneumatic hip joint simulator (Simulation Solutions, UK) was used for experimental wear simulation using standard gait cycles and testing each experimental group for 3 million cycles. The acetabular cups were inclined at 35° on the simulator (equivalent to 45° in vivo). The wear volumes were determined using a microbalance (Mettler-Toledo XP205, Switzerland) at one million cycle intervals. Statistical analysis used was one way ANOVA followed by a post hoc analysis with significance taken at p<0.05. Results. Different damage patterns accelerated the wear of polyethylene at different rates (Figure 2). The moderately scratched and severely scratched heads caused a 2 fold (p<0.01) and 5.5 fold (p<0.01) increase when compared to the wear rate of the undamaged head group. However, the scraped damage caused a lower increase than the scratched heads, with a 1.4 fold (p=0.2) increase for the moderately scraped heads and 2.6 fold (p<0.01) increase for the severely scraped heads. The moderate hybrid and severe hybrid groups resulted in a similar increase to the scraped heads with 1.8 fold (p<0.01) increase with the moderate hybrid and 3 fold (p<0.01) increase with the severe hybrid. The wear of polyethylene against the mild hybrid and retrieved heads was not significantly different (p= 0.9) to the wear against undamaged heads. Discussion. A standardised protocol for generating in vitro damage representative of clinically occurring damage on femoral heads for preclinical testing purposes is needed. The wear rates of polyethylene liners articulating against the retrieval heads were similar to those articulating against the undamaged femoral heads. This study has shown the variations in wear rate of polyethylene bearing under different damage patterns generated in vitro. The wear prediction computational model predict similar trends of the wear acceleration reported in the experimental study

Introduction:. Backside wear has been previously reported through in-vitro and in-vivo to have a significant contribution to the total wear in rotating bearing TKRs. The present study investigated the contribution of backside wear to the total wear in the PFC Sigma rotating platform mobile bearing TKR. In addition, the wear results were compared to the computed wear rates of the PFC Sigma fixed bearing TKR, with two different bearing materials. Materials and Methods:. The commercially available PFC Sigma rotating platform mobile bearing and PFC Sigma fixed bearing total knee replacements, size 3 (DePuy, UK) were tested, with either conventional or moderately cross-linked (5 MRad) GUR1020 UHMWPE bearing materials. The computational wear model for the knee implants was based on the contact area and an independent experimentally determined non-dimensional wear coefficient [1,2,3]. The experimental wear test for the mobile bearing was force controlled using the ISO anterior-posterior force (ISO14243-1-2009). However, due to time limitation of the explicit simulation required to run the force controlled model, the simulation was run using the AP displacements taken from the experimental knee simulator which was run under the ISO AP force. The Sigma fixed bearing TKR was run under high level of anterior-posterior displacements (maximum of 10 mm). Results and Discussion:. The rotating platform bearing showed lower wear rates, compared to that of the PFC Sigma fixed bearing, for both conventional and moderately cross-linked UHMWPE bearing materials (Fig. 1). Moreover, the results showed a high contribution of backside wear to the total wear, approximately 1 mm. 3. /million cycles (∼30% of the total wear). The computational wear predictions were in good agreements with the clinical and experimental measurements [4,5]. Contrasting the effect of bearing material on wear prediction, introducing the moderately cross-linked UHMWPE as a bearing material reduced the predicted wear rates by approximately 1 mm. 3. /million cycles in rotating platform bearing, compared to more than 5 mm. 3. /million cycles in PFC fixed bearing TKR. This reduced effect of cross-linking on wear in mobile bearing was mainly attributed to the lower cross-shear ratios in these bearings, compared to fixed bearings, and the less dependency of wear in moderately cross-linked UHMWPE on the degree of cross-shear, compared to conventional UHMWPE. Decreasing the degree of cross-shear from higher values (Sigma curved insert, high kinematic) to lower ones (rotating platform bearing) changed the predicted wear rates from 8.7 to 3.3 and from 3.4 to 2.4 (mm. 3. /million cycles), for conventional and moderately cross-linked UHMWPE materials respectively (Fig. 2). Conclusion:. The modelling confirmed the previous experimental observations of very low wear with the rotating platform knee. The models also determined the level of wear from the backside of the rotating platform knee which was approximately 1 mm. 3. /million cycles. The fixed bearing knee with moderately cross linked polyethylene also showed low wear at approximately 3 mm. 3. /million cycles. These low wear rates were determined under high kinematic walking cycles conditions. Future work will consider additional conditions

In the retrieval analysis of explanted hip joints, the estimation of wear volume and visualization of wear pattern are commonly used to evaluate in-vivo performance. While many studies report wear volumes from explanted hips, it is important to understand the limitations of these estimates including the sources and magnitude of uncertainty of the reported results. This study builds on a previous uncertainty analysis by Carmignato et al. to quantify the magnitude of uncertainty caused by the assumption that the as-manufactured shape of an explanted hip component is a perfect sphere. Synthetic data sets representing idealized measurements of spheroidal explants (prolate, oblate and pinched) with a nominal diameter of 50 mm were generated. These data sets represent the shape and magnitude of form deviations observed for explanted hip components (Figure 1). Data were simulated for either unworn components or those with a known volume and magnitude of wear simulated to represent 5 µm penetration of a 49.90 mm femoral head into an acetabular cup (Table 1). The volume of wear and wear pattern were estimated using a custom Matlab script developed for analysis of metrology data from explanted hip joints. This script fits a least squares sphere to data points in unworn, as manufactured regions of the surface to estimate the as-manufactured shape of the component. The diameter of the best fit sphere, and wear volume were compared to the known wear depths and volumes from the synthetic datasets. The results showed that the Matlab script estimated a wear volume of up to 1.4 mm. 3. for an unworn cup with a radial deviation of 10 µm. The maximum error of 13.3 mm. 3. was for a pinched cup with wear at the pole. The complete results are shown in Table 2. In some cases with aspherical form deviations, the least squares sphere fitted to the synthetic data was displaced in the Z direction with respect to the origin of the spheroid and the radius of the least squares sphere was outside the range of the principal radii of the spheroid. For instance, in case 5, the center was shifted 22 µm vertically from the mathematical center. The results from this study show that the magnitude of uncertainty due to form deviations on wear volume varies depending on the shape and magnitude of the form deviations and in some cases was greater than 10 mm. 3. A further important finding is that in some instances, the diameter and center of the least squares sphere fitted to the unworn regions may not be consistent with the mathematical radius and center of the synthetic data. This may have important implications for the “reverse engineering” of the as-manufactured dimensions from worn explanted hip joints. Please contact authors directly for the figure:. Figure 1 Graphical depiction of a) synthetic data set, b) deviation map of a hemispherical acetabular cup with simulated wear, c) deviation map of a prolate spheroid with simulated wear at rim with color bar set to ±5 microns, d) deviation map of pinched ellipsoid with simulated wear at 45 degrees from pole

Polyethylene wear in total knee arthroplasty (TKA) is a complex and mutifactorial process. It is generally recognized that wear is directly related to a material wear factor, contact stress, and sliding distance. Conventional methods of predicting polyethylene wear in TKA mainly focus on peak contact stress or subsurface shear stress using finite element method analysis. By incorporating kinematics and contact stress, a new predictor for polyethylene wear in TKA (“Wear Index”) has been developed. The Wear Index was defined by multiplying deformation by femoro-tibial sliding velocity. The purpose of this study was to determine the predictive value of the Wear Index for polyethylene wear in TKA using both a numeric and an in vitro model. Four commercially available total knee prostheses were modeled for this study. Deformation and sliding velocity were calculated based on the three-dimensional geometry of the components and the gait kinematic inputs using Hertz’s formula. One specimen of each of the four types of total knee prostheses was mounted on a custom-designed knee simulator. Vertical loads and flexion-extension uni-axial motion were simulated using computer controlled servohydraulic actuators. The same gait kinematic inputs used in the theoretical study were used in the simulation test. After the simulations, the surface of the tibial insert was examined microscopically and macroscopically and compared with the theoretically generated Wear Index. This study showed a high correlation between the numeric model and the simulation. The depth of wear on the tibial insert correlated significantly with the Wear Index. Microscopic findings also demonstrated a good correlation between the Wear Index and observed wear patterns. Sliding velocity is an important factor for understanding wear in TKA. In conclusion, this study suggests that the Wear Index is a reliable predictor of polyethylene wear in TKA, as it incorporates both contact stress and kinematics in its calculation

Arthroscopic hip surgery is increasingly common in Australia. Hip arthroscopy is indicated for a range of diagnostic and therapeutic purposes, including labral tears, capsular laxity and femoral-acetabular impingement (FAI). Despite this, previous cohort studies aiming to characterise hip pathology seen on arthroscopic examination are mostly limited to patients with known diagnoses of FAI. Therefore, little is known of the native articular wear patterns encountered in other disease states. Therefore, we aimed to define common osteochondral wear patterns for a cohort of patients managed via hip arthroscopy. We retrospectively analysed intraoperative data for 1127 patients managed via hip arthroscopy between 2008 and 2013, for either therapeutic or diagnostic purposes. Intraoperative data was categorized by location (A-E as defined by Fontana et al. 2016) and chondral damage (0-4 scale as defined by Beck et al. 2005) with respect to both acetabulum and femoral head. Data for 1127 patients were included. Location of acetabular chondral pathology was variable with locations C. 1. and D. 1. representing the most common regions of damage. Labral tears predominated in locations C and D. Femoral chondral pathology was evenly distributed. The degree of femoral chondral injury was predominantly grade 1, whilst acetabular wear was evenly distributed. Large proportions of wear were observed at the peripheral superior and anterior regions of the lunate surface of the acetabulum in keeping with prior works. However, we observed higher rates of central wear and lower rates of grade 4 acetabular damage extending into superior/posterior zones, in our cohort. Our work characterises common articular wear patterns encountered at the time of hip arthroscopy. Further inquiry into the natural history of osteochondral lesions is needed to better understand and manage these conditions

We sought to determine what dimensional changes occurred from wear testing of a total knee implant, as well as whether any changes developed within the polyethylene subsurface. Three fixed bearing implants underwent wear simulator testing to 6.1 million cycles. Gravimetric analysis and micro-CT scans were performed pre-test, mid-test, and post-test. Wear volume and surface deviations were greater during 0–3.2 million cycles (91±12 mm. 3. ) than from 3.2–6.1 million cycles (52±18 mm. 3. ). Deviations (wear and creep) occurred across all surfaces of the tibial inserts, including the articular surface, backside surface, sides, and locking mechanism. No subsurface changes were found. The micro-CT results were a useful adjunct to gravimetric analysis, better defining the dimensional changes that occurred with testing and ruling out subsurface fatigue

Oxidized zirconium (Oxinium) and highly cross-linked polyethylene (HXLPE) were developed with the purpose of minimizing wear, and subsequent osteolysis, in Total Hip Arthroplasty (THA). However, few articles have been published on long-term results of Oxinium on highly cross-linked polyethylene. The purpose of this investigation is to report minimum 10-year HXLPE wear rates and the clinical outcome of patients in this group and compare this population to a control group of cobalt chrome and ceramic. One hundred forty THAs were performed for 123 patients using an Oxinium head with an HXLPE liner. Ninety-seven had 10 years of clinical follow-up (avg. 14.5). Harris Hip Scores (HHS) were collected preoperatively and at the most recent follow-up. Radiographs of 85 hips were available for a minimum 10-year follow-up (avg. 14.5) and used to calculate wear using PolyWare software. Control groups of cobalt chrome and ceramic articulation on HXLPE with a minimum 10-year follow-up were studied. Clinical follow-up of the Oxinium group showed a statistical improvement compared to preoperative and was similar to the control group of patients. Radiographic evaluation found the linear and volumetric wear rates for the Oxinium group of 0.03 mm/year (range 0.00–0.08) and 3.46 mm. 3. /year (range 1.0 to 15.0) respectively. There was no statistically significant difference in linear or volumetric wear rate between the groups (P-value 0.92 and 0.55 respectively). None of these patients underwent revision of their hip for any reason. Oxinium on highly cross-linked polyethylene has performed exceptionally with wear rates comparable to those of cobalt chrome or ceramic on HXLPE

Introduction:. Failure of the polyethylene glenoid component is the most common complication of Total Shoulder Arthroplasty (TSA) and accounts for a majority of the unsatisfactory results after this procedure. Nowadays, most of the shoulder prostheses consist of metal on polyethylene bearing components. Repetitive contact between the metal ball and the polyethylene socket produces progressive abrasion of the implant if the moving part is made of polyethylene. Its debris may then lead to an active osteolysis and implant loosening. Failure of the glenoid component is often manifested clinically by pain, loss of function, and the presence of a clunking noise and leads to revision surgery. The use of ceramic balls aims at the reduction of this phenomenon. In many studies regarding knee and hip replacement it has been shown that the use of ceramic on polyethylene is more beneficial in terms of polyethylene wear and failure, when compared to metal on polyethylene. This is to our knowledge the first study to address in direct comparison wear in both TSA and RTSA. Materials and methods:. Two different wear tests were conducted in order to address both TSA and RTSA kinematics. Since up to day, there is no test standard for wear testing neither for TSA nor for RTSA a customised joint simulators were used to create worst-case scenarios motions in both cases. In the TSA testing setup, the orientation of the glenoid component and humeral component was chosen according to M. A. Wirth (2009) study but with the humeral component assembled inferiorly. For the RTSA the applied kinematics was based on a study of G. Kohut (2012) and ISO 14242-1 (2012) standard. Three articulating couples for each material were tested for both TSA and RTSA for total of 5 million cycles. Standard midterm gravimetric measurements were conducted at each 1 million cycles. Results:. The tests are currently ongoing and all results will be presented during next ISTA meeting

Introduction: Reduction of ultra high molecular weight polyethylene (UHMWPE) wear in total knee replacement (TKR) bearings may delay the onset of osteolysis and subsequent loosening of components. This study used finite element (FE) modelling and in vitro simulator testing to investigate the effect of wear path geometry on UHMWPE surface wear. Methods: The wear of PFC Sigma fixed bearing TKRs (DePuy) was investigated using a six-station force/ displacement controlled knee simulator (frequency 1 Hz) using previously developed methods [. 1. ]. High, intermediate and low kinematic inputs were simulated for up to five million cycles (Table 1) with identical flexion-extension and axial loading for all components. This kinematic data was also applied to a FE model of the PFC Sigma TKR and run using PAM-CRASH-SAFE software. The anterior-posterior (AP), medial-lateral (ML) and inferior-superior data were recorded and the resulting wear paths generated by selecting nodes from the contacting surface of the polyethylene relative to the femoral. Results and Discussion: The mean wear rates with 95% confidence limits on the simulator when subjected to high, intermediate and low kinematics were 22.75 ± 5.95, 9.85 ± 3.7 and 5.2 ± 3.77 mm3 per million cycles, respectively. All FE models exhibited looped wear paths. An example wear path for the first 60% of the gait cycle for a lateral node is displayed in Figure I. The high kinematics model generated the greatest ML displacement and similar AP displacement to the intermediate kinematics model. The low kinematics model showed least ML and AP displacements. The AP displacements for medial wear paths differed little when subjected to the different kinematics. A looped wear path on the surface of UHMWPE results in greater cross shear transverse to the principal direction of motion, which is parallel to AP displacement in TKR and is the axis along which strain hardening occurs. This study revealed that increased AP displacement and tibial rotation kinematics generate more looped wear paths, increase ML and AP displacements on the surface of fixed bearing TKR and result in greater cross shear which ultimately increases UHMWPE surface wear

Introduction. Failure of the polyethylene glenoid component is the most common complication of Total Shoulder Arthroplasty (TSA) and accounts for a majority of the unsatisfactory results after this procedure. Nowadays, most of the shoulder prostheses consist of metal on polyethylene bearing components. Repetitive contact between the metal ball and the polyethylene socket produces progressive abrasion of the implant if the moving part is made of polyethylene. Its debris may then lead to an active osteolysis and implant loosening. Failure of the glenoid component is often manifested clinically by pain, loss of function, and the presence of a clunking noise and leads to revision surgery. The use of ceramic balls aims at the reduction of this phenomenon. In many studies regarding knee and hip replacement it has been shown that the use of ceramic on polyethylene (CoP) is more beneficial in terms of polyethylene wear and failure, when compared to metal on polyethylene (MoP). Since a human shoulder is very different from a hip and a knee, it is not a self-centering, neither congruent joint. And its stability is provided by healthy muscles of the rotator cuff. We decided to compare CoP against MoP in semi- force controlled test setup. Where, for a given governing angular motion the translational motion was a function of contact (frictional) forces between the tested couple (humeral head and PE). This is to our knowledge the first study to address in direct comparison wear in TSA in semi force controlled test setup. Materials and methods. Up today, there is no test standard for wear testing of TSA. A customised joint simulator was used to create worst-case scenario motion allowing for simulation of the muscles in two perpendicular axes: inferior – superior (I-S) and anterior – posterior (A-P). Were a governing angular motion (GAM) was the abduction – adduction (±30°) in I-S. A system of springs was created so that the I-S translation and the A-P rotation were a result of the GAM. The stiffens of the springs was tuned based on the MoP pair initial kinematic (1000 cycles) to result in: about 2mm I-S translation, and about ±10° A-P rotation. All samples were tested at the same test station in order to obtain maximal repeatability. Axial load was in range of 100N to 750 N. Three articulating couples for each material were tested for total of 2M cycles. Standard midterm gravimetric measurements were conducted at each 0.5 M cycles. Results. Wear rates after 2Mc were: MoP-30.48 ± 4.86 mg/M cycles; against CoP-16.33 ± 1.95 mg/M cycles

Introduction. Hip replacements are falling short of matching the life expectancy of coxarthritis patients, due to implanting THR in younger patients and due to increasingly active patients. The most frequently implanted hip prostheses use cross linked (XL) polyethylene (PE) on metal bearings in the USA and most of the Western world. Concerns remain in the long term around the potential of wear debris-induced aseptic loosening. Thus exploring lower-wearing alternative bearings remains a major research goal. PEEK (poly-ether-ether-ketone) is a thermoplastic polymer with enhanced mechanical properties. This study compared the wear of PEEK to the wear of cross linked polyethylene, when sliding against cobalt chrome (CoCr) metallic counterfaces, and compared the wear of carbon-fibre reinforced (CFR)-PEEK to cross linked polyethylene when sliding against metallic and ceramic counterfaces under different contact stresses within the hip joint. Methods. The following materials were studied: unfilled PEEK (OPTIMA, Invibio) and CFR-PEEK (MOTIS, Invibio) against either high carbon (HC) CoCr or Biolox Delta ceramic plates. The comparative control material was a moderately cross-linked PE (Marathon, DePuy Synthes). A simple geometry wear study was undertaken. A rotational motion of ±30° across a sliding distance of ±28 mm (cross shear of 0.087), and contact pressures of 1.6 or 4 MPa were applied. The lubricant was 25% (v/v) bovine serum and the wear test was conducted for 1 million cycles at 1 Hz. Wear was assessed gravimetrically. A validated soak control method was used to adjust for serum absorption-induced mass changes during the wear test. Surface profilometry was assessed pre and post wear test. Results. Unfilled PEEK produced a six-fold higher wear factor than XL PE against HC Co Cr (p value <0.0001). CFR-PEEK vs. Biolox Delta produced a two-fold lower wear factor than XL PEvs. HC Co Cr (p value = 0.003). CFR-PEEK vs. Biolox Delta had the lowest wear factor among all studied combinations. The wear of CFR-PEEK vs. HC CoCr was higher than XL PEvs. HC CoCr (Figure 1). The counterface surfaces were scratched when articulating against CFR-PEEK. This was more evident on CoCr plates, with the average surface roughness increasing from 0.005 µm to 0.32 µm (p value = 0.0048). This might explain the accelerated wear in the CFR-PEEK vs. HC CoCr combinations. Higher contact pressures led to a 30 % reduction in the wear factor of CFR-PEEK vs. Biolox Delta combination (p value = 0.048), while no significant impact was noted against HC CoCr (Figure 2). Conclusions. The injection moulded carbon fibre reinforced PEEK vs. Biolox Delta ceramic generated significantly lower wear compared with XL PE (even under higher contact pressures). CFR-PEEK vs. Biolox Delta may lead to longer lasting hip replacements, and will be the subject of further investigations

Polyethylene wear represents a significant risk factor for the long-term success of knee arthroplasty [1]. This work aimed to develop and in vivo validate an automated algorithm for accurate and precise AI based wear measurement in knee arthroplasty using clinical AP radiographs for scientifically meaningful multi-centre studies. Twenty postoperative radiographs (knee joint AP in standing position) after knee arthroplasty were analysed using the novel algorithm. A convolutional neural network-based segmentation is used to localize the implant components on the X-Ray, and a 2D-3D registration of the CAD implant models precisely calculates the three-dimensional position and orientation of the implants in the joint at the time of acquisition. From this, the minimal distance between the involved implant components is determined, and its postoperative change over time enables the determination of wear in the radiographs. The measured minimum inlay height of 335 unloaded inlays excluding the weight-induced deformation, served as ground truth for validation and was compared to the algorithmically calculated component distances from 20 radiographs. With an average weight of 94 kg in the studied TKA patient cohort, it was determined that an average inlay height of 6.160 mm is expected in the patient. Based on the radiographs, the algorithm calculated a minimum component distance of 6.158 mm (SD = 81 µm), which deviated by 2 µm in comparison to the expected inlay height. An automated method was presented that allows accurate and precise determination of the inlay height and subsequently the wear in knee arthroplasty based on a clinical radiograph and the CAD models. Precision and accuracy are comparable to the current gold standard RSA [2], but without relying on special radiographic setups. The developed method can therefore be used to objectively investigate novel implant materials with meaningful clinical cohorts, thus improving the quality of patient care

Introduction. Edge loading commonly occurs in all bearings in hip arthroplasty. Edge loading wear can occur in these bearings when the biomechanical loading axis reaches the edge and the femoral head loads the edge of the cup producing wear damage on both the head and cup edge. When the biomechanical loading axis passes through the polished articulating surface of the acetabular component and does not reach the edge, the center of the head and the center of the cup are concentric. The resulting wear known as concentric wear is low in metal-on-metal (MOM) bearings, and is negligible in ceramic-on-ceramic (COC) bearings. Edge loading is well defined in COC hip bearings. However, edge loading is difficult to identify in MOM bearings, since the metal bearing surfaces do not show wear patterns macroscopically. The aims of this study are to compare edge loading wear rates in COC and MOM bearings, and to relate edge loading to clinical complications. Materials and Methods. Twenty-nine failed large diameter metal-on-metal hip bearings (17 total hips, 12 resurfacings) were compared to 54 failed alumina-on-alumina bearings collected from 1998 to 2011. Most COC bearings were revised for aseptic loosening or periprosthetic bone fracture, while most MOM bearings were revised for pain, soft tissue reactions or impingement. The median time to revision was 3.2 years for the metal hip bearings and 3.5 years for alumina hip bearings. The surface topography of the femoral heads was measured using a RedLux AHP (Artificial Hip Profiler, RedLux Ltd, Southampton, UK). Results. Forty-five out of fifty-four bearings (83%) alumina bearings and 15 out 29 (52%) metal bearings had edge loading wear (p<0.01). There was no difference in the median volumetric wear rates, which were 0.25 mm. 3. /yr for metal femoral heads and 0.18 mm. 3. /yr for alumina heads (means 7.87 mm. 3. /yr and 0.78 mm. 3. /yr respectively). The median volumetric wear rate was 1.77 mm. 3. /yr (mean 16.51 mm. 3. /yr) for metal heads with edge loading and 0.01 mm. 3. /yr (mean 0.19 mm. 3. /yr) for metal heads without edge loading (p=0.1). Conclusions. The median wear rates for COC and MOM bearings were the same, however MOM bearings have the potential for much higher wear rates when edge loading occurs. Most of the reasons for revision of MOM bearings were related to a biological response to the wear debris. Therefore, it may be the reactivity of the wear debris, and not the wear rate that is an important determinant for the survivorship of MOM bearings

Some mobile bearing knee replacement designs have shown truly excellent long-term clinical results. The higher laxity of a mobile bearing helps reduce the shear forces and torques transmitted to the prosthesis-bone interface, and this could only help reduce the risk of loosening. Some argue that self-alignment of a mobile bearing rotationally can produce more central patellar tracking. However, the most commonly assumed benefit of mobile bearings is the reduction in contact stress, which is typically expected to reduce fatigue and wear. In a rotating platform TKR for example, wear is also expected to be less because the rolling/sliding motion is separated from the transverse rotational motion onto two separate articulating surfaces, thus less cross-paths and less wear. Such expectations may have dominated the thinking and perhaps even clouded the expectations of TKR wear test engineers. Such wear reduction however has not really been categorically proven clinically. This paper combines in-vitro wear results from two separate laboratories, one in Nebraska USA and one in Germany. These two (industrially unattached labs) possess between them a very large set of in-vitro wear testing results across the widest variety of fixed and mobile bearing TKR designs. Fortunately, the wear testing methodology using the force-control regime used in the two labs was largely similar, and was highly consistent within each lab. The fixed and the mobile bearings were subjected to the exact same force fields, allowing their Anterior-Posterior translation and internal-external rotation kinematics to vary based on the individual TKR design. Tens of implant designs have been tested, both fixed and mobile, in total (bycondylar) form and unicompartmental, of various sizes. Some mobile bearings had rotating platforms and some were rotating-translating. Some of the tests specifically compared mobile to fixed bearing tibial components using identical femoral components. Between both labs, and across all tests, no statistically significant difference resulted in wear between fixed and mobile bearings. Yet, such differences did clearly feature with known superior bearing materials (for wear) and other favored design features. Also, generally, the force-control test methodology has proven highly discriminatory in its simulation and measurement of wear as a potential clinical failure mode. The take home message to test engineers is to expect the wear of both mobile and fixed bearings to depend more on the detailed design and materials of the TKR than on the mobility of the bearing. The results of this study re-confirm the need for wear testing to be performed prior to any clinical use on all implant designs, despite seemingly similar predicates or success of some mobile bearings