Aims. Radiostereometric analysis (RSA) is the most accurate radiological method to measure in vivo wear of highly cross-linked polyethylene (XLPE) acetabular components. We have previously reported very low wear rates for a sequentially irradiated and annealed X3 XLPE liner (Stryker Orthopaedics, USA) when used in conjunction with a 32 mm femoral heads at ten-year follow-up. Only two studies have reported the long-term wear rate of X3 liners used in conjunction with larger heads using plain radiographs which have poor sensitivity. The aim of this study was to measure the ten-year wear of thin X3 XLPE liners against larger 36 or 40 mm articulations with RSA. Methods. We prospectively reviewed 19 patients who underwent primary cementless THA with the XLPE acetabular liner (X3) and a 36 or 40 mm femoral head with a resultant liner thickness of at least 5.8 mm. RSA radiographs at one week, six months, and one, two, five, and ten years postoperatively and femoral head penetration within the acetabular component were measured with UmRSA software. Of the initial 19 patients, 12 were available at the ten-year time point. Results. The median proximal, 2D, and 3D wear rates calculated between one and ten years were all less than 0.005 mm/year, with no patient recording a proximal wear rate of more than 0.021 mm/year. Importantly, there was no increase in the wear rate between five and ten years. Conclusion. The very low wear rate of X3 XLPE liners with larger articulations remains encouraging for the future clinical performance of this material. Cite this article: Bone Jt Open 2023;4(11):839–845

Objectives. Third-body wear is believed to be one trigger for adverse results with metal-on-metal (MOM) bearings. Impingement and subluxation may release metal particles from MOM replacements. We therefore challenged MOM bearings with relevant debris types of cobalt–chrome alloy (CoCr), titanium alloy (Ti6Al4V) and polymethylmethacrylate bone cement (PMMA). Methods. Cement flakes (PMMA), CoCr and Ti6Al4V particles (size range 5 µm to 400 µm) were run in a MOM wear simulation. Debris allotments (5 mg) were inserted at ten intervals during the five million cycle (5 Mc) test. . Results. In a clean test phase (0 Mc to 0.8 Mc), lubricants retained their yellow colour. Addition of metal particles at 0.8 Mc turned lubricants black within the first hour of the test and remained so for the duration, while PMMA particles did not change the colour of the lubricant. Rates of wear with PMMA, CoCr and Ti6Al4V debris averaged 0.3 mm. 3. /Mc, 4.1Â mm. 3. /Mc and 6.4 mm. 3. /Mc, respectively. . Conclusions. Metal particles turned simulator lubricants black with rates of wear of MOM bearings an order of magnitude higher than with control PMMA particles. This appeared to model the findings of black, periarticular joint tissues and high CoCr wear in failed MOM replacements. The amount of wear debris produced during a 500 000-cycle interval of gait was 30 to 50 times greater than the weight of triggering particle allotment, indicating that MOM bearings were extremely sensitive to third-body wear. Cite this article: Bone Joint Res 2015;4:29–37

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

Aims. Micromotion of the polyethylene (PE) inlay may contribute to backside PE wear in addition to articulate wear of total knee arthroplasty (TKA). Using radiostereometric analysis (RSA) with tantalum beads in the PE inlay, we evaluated PE micromotion and its relationship to PE wear. Methods. A total of 23 patients with a mean age of 83 years (77 to 91), were available from a RSA study on cemented TKA with Maxim tibial components (Zimmer Biomet). PE inlay migration, PE wear, tibial component migration, and the anatomical knee axis were evaluated on weightbearing stereoradiographs. PE inlay wear was measured as the deepest penetration of the femoral component into the PE inlay. Results. At mean six years’ follow-up, the PE wear rate was 0.08 mm/year (95% confidence interval 0.06 to 0.09 mm/year). PE inlay external rotation was below the precision limit and did not influence PE wear. Varus knee alignment did not influence PE wear (p = 0.874), but increased tibial component total translation (p = 0.041). Conclusion. The PE inlay was well fixed and there was no relationship between PE stability and PE wear. The PE wear rate was low and similar in the medial and lateral compartments. Varus knee alignment did not influence PE wear. Cite this article: Bone Joint Res 2024;13(5):226–236

Aims. Oxidized zirconium (OxZi) and highly cross-linked polyethylene (HXLPE) were developed to minimize wear and risk of osteolysis in total hip arthroplasty (THA). However, retrieval studies have shown that scratched femoral heads may lead to runaway wear, and few reports of long-term results have been published. The purpose of this investigation is to report minimum ten-year wear rates and clinical outcomes of THA with OxZi femoral heads on HXLPE, and to compare them with a retrospective control group of cobalt chrome (CoCr) or ceramic heads on HXLPE. Methods. From 2003 to 2006, 108 THAs were performed on 96 patients using an OxZi head with a HXLPE liner with minimum ten-year follow-up. Harris Hip Scores (HHS) were collected preoperatively and at the most recent follow-up (mean 13.3 years). Linear and volumetric liner wear was measured on radiographs of 85 hips with a minimum ten-year follow-up (mean 14.5 years). This was compared to a retrospective control group of 45 THAs using ceramic or CoCr heads from October 1999 to February 2005, with a minimum of ten years’ follow-up. Results. Average HHS improved from 50.8 to 91.9 and 51.0 to 89.8 in the OxZi group and control group, respectively (p = 0.644), with no osteolysis in either group. Linear and volumetric wear rates in the OxZi group averaged 0.03 mm/year and 3.46 mm. 3. /year, respectively. There was no statistically significant difference in HHS scores, nor in linear or volumetric wear rate between the groups, and no revision for any indication. Conclusion. The radiological and clinical outcomes, and survivorship of THA with OxZi femoral heads and HXLPE liners, were excellent, and comparable to CoCr or ceramic heads at minimum ten-year follow-up. Wear rates are below what would be expected for development of osteolysis. OxZi-HXLPE is a durable bearing couple with excellent long-term outcomes. Cite this article: Bone Joint J 2024;106-B(3 Supple A):38–43

Aims. Wear of the polyethylene (PE) tibial insert of total knee arthroplasty (TKA) increases the risk of revision surgery with a significant cost burden on the healthcare system. This study quantifies wear performance of tibial inserts in a large and diverse series of retrieved TKAs to evaluate the effect of factors related to the patient, knee design, and bearing material on tibial insert wear performance. Methods. An institutional review board-approved retrieval archive was surveyed for modular PE tibial inserts over a range of in vivo duration (mean 58 months (0 to 290)). Five knee designs, totalling 1,585 devices, were studied. Insert wear was estimated from measured thickness change using a previously published method. Linear regression statistical analyses were used to test association of 12 patient and implant design variables with calculated wear rate. Results. Five patient-specific variables and seven implant-specific variables were evaluated for significant association with lower insert wear rate. Six were significant when controlling for other factors: greater patient age, female sex, shorter duration in vivo, polished tray, highly cross-linked PE (HXLPE), and constrained knee design. Conclusion. This study confirmed that knee wear rate increased with duration in vivo. Older patients and females had significantly lower wear rates. Polished modular tibial tray surfaces, HXLPE, and constrained TKA designs were device design factors associated with significantly reduced wear rate. Cite this article: Bone Joint J 2021;103-B(11):1695–1701

The leading indication for revision total hip arthroplasty (THA) remains aseptic loosening owing to wear. The younger, more active patients currently undergoing THA present unprecedented demands on the bearings. Ceramic-on-ceramic (CoC) bearings have consistently shown the lowest rates of wear. The recent advances, especially involving alumina/zirconia composite ceramic, have led to substantial improvements and good results in vitro. Alumina/zirconia composite ceramics are extremely hard, scratch resistant and biocompatible. They offer a low co-efficient of friction and superior lubrication and lower rates of wear compared with other bearings. The major disadvantage is the risk of fracture of the ceramic. The new composite ceramic has reduced the risk of fracture of the femoral head to 0.002%. The risk of fracture of the liner is slightly higher (0.02%). Assuming that the components are introduced without impingement, CoC bearings have major advantages over other bearings. Owing to the superior hardness, they produce less third body wear and are less vulnerable to intra-operative damage. The improved tribology means that CoC bearings are an excellent choice for young, active patients requiring THA. Cite this article: Bone Joint J 2016;98-B(1 Suppl A):14–17

Aims. This study aimed to assess the impact of using the metal-augmented glenoid baseplate (AGB) on improving clinical and radiological outcomes, as well as reducing complications, in patients with superior glenoid wear undergoing reverse shoulder arthroplasty (RSA). Methods. From January 2016 to June 2021, out of 235 patients who underwent primary RSA, 24 received a superior-AGB after off-axis reaming (Group A). Subsequently, we conducted propensity score matching in a 1:3 ratio, considering sex, age, follow-up duration, and glenoid wear (superior-inclination and retroversion), and selected 72 well-balanced matched patients who received a standard glenoid baseplate (STB) after eccentric reaming (Group B). Superior-inclination, retroversion, and lateral humeral offset (LHO) were measured to assess preoperative glenoid wear and postoperative correction, as well as to identify any complications. Clinical outcomes were measured at each outpatient visit before and after surgery. Results. There were no significant differences in demographic data and preoperative characteristics between the two groups. Both groups showed significant improvements in patient-reported outcome measures (visual analogue scale for pain, visual analogue scale for function, American Shoulder and Elbow Surgeons, Constant, and Simple Shoulder Test scores) from preoperative to final assessment (p < 0.001). However, AGB showed no additional benefit. Notably, within range of motion, Group B showed significant postoperative decrease in both external rotation and internal rotation, unlike Group A (p = 0.028 and 0.003, respectively). Both groups demonstrated a significant correction of superior-inclination after surgery, while patients in Group B exhibited a significant decrease in LHO postoperatively (p = 0.001). Regarding complications, Group A experienced more acromial stress fractures (3 cases; 12.5%), whereas Group B had a higher occurrence of scapular notching (24 cases; 33.3%) (p = 0.008). Conclusion. Both eccentric reaming with STB and off-axis reaming with AGB are effective methods for addressing superior glenoid wear in RSA, leading to improved clinical outcomes. However, it is important to be aware of the potential risks associated with eccentric reaming, which include excessive bone loss leading to reduced rotation and scapular notching. Cite this article: Bone Joint J 2024;106-B(3):268–276

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

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

Aims. Several short- and mid-term studies have shown minimal liner wear of highly cross-linked polyethylene (HXLPE) in total hip arthroplasty (THA), but the safety of using thinner HXLPE liners to maximize femoral head size remains uncertain. The objective of this study was to analyze clinical survival and radiological wear rates of patients with HXLPE liners, a 36 mm femoral head, and a small acetabular component with a minimum of ten years’ follow-up. Methods. We retrospectively identified 55 patients who underwent primary THA performed at a single centre, using HXLPE liners with 36 mm cobalt-chrome heads in acetabular components with an outer diameter of 52 mm or smaller. Patient demographic details, implant details, death, and all-cause revisions were recorded. Cox regression and Kaplan-Meier survival was used to determine all-cause and liner-specific revision. Of these 55 patients, 22 had a minimum radiological follow-up of seven years and were assessed radiologically for linear and volumetric wear. Results. Overall survival rate for all-cause revision was 94.5% (95% confidence interval (CI) 81.7% to 97.2%) at a mean follow-up of 12.8 years (10.9 to 18.7). Three patients were revised, none for liner wear, fracture, or dissociation. A total of 22 patients were included in the radiological analysis (mean follow-up 9.9 years (7.5 to 13.7)). Mean linear liner wear was 0.085 mm (95% CI -0.086 to 0.257) and the volumetric wear rate was 11.097 mm. 3. /year (95% CI -6.5 to 28.7). Conclusion. Using HXLPE liners with 36 mm heads in 52 mm acetabular components or smaller is safe, with excellent survival and low rates of linear and volumetric wear at medium-term follow-up. Patients did not require revision surgery for liner complications such as fracture, dissociation, or wear. Our results suggest that the advantages of using larger heads outweigh the potential risks of using thin HXLPE liners. Cite this article: Bone Joint J 2023;105-B(1):29–34

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

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