Artificial knee joints are continuously loaded by higher contact stress than artificial hip joints due to a less conformity and much smaller contact area between the femoral and tibial surfaces. The higher contact stress causes severe surface damage such as pitting or delamination of polyethylene (PE) tibial inserts. To decrease the risks of these surface damages, the oxidation degradation of cross-linked polyethylene (PE) induced by residual free radicals resulting from gamma-ray irradiation for cross-linking or sterilization should be prevented. Vitamin E (VE), as an antioxidant, blended PE (PE(VE)) has been used to solve the problems. In addition, osteolysis induced by PE wear particles, bone cement and metallic debris is recognized as one of the important problems for total knee arthroplasty (TKA). To decrease the generation of PE wear particles, we have developed the bearing surface mimicking the articular cartilage; grafting a biocompatible polymer, poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), onto the PE surface having high wear resistance. In this study, we have evaluated the surface, mechanical under severe oxidative condition, and wear properties of PMPC-grafted cross-linked PE(VE) (PMPC-CLPE(VE)) material for artificial knee joints. Untreated and PMPC-grafted 0.1 mass% VE-blended PE (GUR1020E resin) with a gamma-ray irradiation of 100 kGy for cross-linking and 25 kGy for sterilization were prepared (CLPE(VE) and PMPC-CLPE(VE), respectively). Surface properties were evaluated by Fourier-transform infrared (FT-IR) spectroscopy and transmission electron microscope (TEM) observations. Surface wettability and frictional property were measured by static water contact angle measurement and ball-on-plate friction test. To evaluate the oxidation degradation resistance, mechanical and physical properties such tensile test, izod impact test, small punch test and cross-link density measurement before and after accelerated aging were measured. Wear properties of the tibial inserts were examined by using knee simulator in the combination of Co-Cr-Mo femoral components according to ISO14243-3. Gravimetric wear, volumetric penetration and the number of generated wear particles were measured. By the FT-IR measurements and TEM observation, P–O peaks attributed to MPC unit and uniform PMPC layer with 100–200 nm thick was observed only on PMPC-CLPE(VE) surface. Static water contact angle of CLPE(VE) was almost 100 degree, while that of PMPC-CLPE(VE) decreased significantly to almost 35 degree. There was no significant difference in the mechanical and physical properties between CLPE(VE) and PMPC-CLPE(VE). Moreover, both the CLPE(VE) and PMPC-CLPE(VE) maintained these properties even after the accelerated aging of 12 weeks [Fig. 1]. Blended VE in CLPE would act as radical scavengers to prevent oxidation degradation. In the knee simulator wear test, the PMPC-CLPE(VE) tibial inserts showed about a half gravimetric wear compared to the CLPE(VE) tibial inserts [Fig. 2]. This would be due to the significant differences observed in wettability of the surface. Water thin film formed on the hydrated PMPC graft layer, would act as significantly efficient lubricant. From these results, the PMPC-CLPE(VE) is expected to be one of the great bearing materials not only preventing surface damages due to higher contact stress and oxidation degradation but also improving wear resistance, and to provide much more lifelong artificial knee joints. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

Introduction. The combined incidence of anatomic (aTSA) and reverse total shoulder arthroplasties (rTSA) in the US is 90,000 per annum and rising. There has been little attention given to potential long-term complications due to periprosthetic tissue reactions to implant debris. The shoulder has been felt to be relatively immune to these complications due to lower acting loads compared to other joint arthroplasties. In this study, retrieved aTSAs and rTSAs were examined to determine the extent of implant damage and to characterize the nature of the corresponding periprosthetic tissue responses. Methods. TSA components and periprosthetic tissues were retrieved from 23 (eleven aTSA, twelve rTSA). Damage to the implants was characterized using light microscopy. Head/stem taper junction damage was graded 1–4 as minimal, mild, moderate or marked. Damage on polyethylene (PE) and metal bearing surfaces was graded 1–3 (mild, moderate, marked). H&E stained sections of periprosthetic soft tissues were evaluated for the extent and type of cellular response. A semi-quantitative system was used to score (1=rare to 4=marked) the overall number of particle-laden macrophages, foreign body giant cells, lymphocytes, plasma cells, eosinophils, and neutrophils. Implant damage and histopathological patterns were compared between the two TSA groups using the Mann-Whitney and Spearman tests. Results. The PE bearing surfaces of aTSAs were dominated by three-body wear and plastic deformation, whereas the rTSA PE components exhibited mainly polishing and scratching. Metal surface damage occurred in a few cases of both groups. Only one aTSA case exhibited marked taper corrosion. In both groups the primary nature of the inflammatory response was a moderate to marked macrophage response to wear particles (78% of cases). The particle-laden macrophages tended to occur in broad sheets and contained metal, PE, bone cement and suture debris. The extent of macrophage and foreign body giant cell responses was greater in the aTSA group (p≤0.001). Metal particles were seen in 63% of aTSAs and 83% of rTSAs. In the aTSA group, bone cement was seen in all cases and suture was observed in 9 cases, and their presence was larger compared to the rTSA group (p≤0.022). There was no difference in the number of other cell types between the groups. A mild lymphocyte response and chromium-phosphate debris was present within the tissue of the aTSA case with marked corrosion, which may be indicative of an early stage adverse local tissue reaction (ALTR) analog to total hip replacements with taper corrosion. Conclusion. Both groups exhibited a strong macrophage response to a combination of different types of implant debris—PE, metal, bone cement and suture. The prevalence of a marked macrophage response was larger in the aTSA group which may be explained by the larger overall presence of cement and suture within this group. PE particles may differ in size between groups due to different acting wear mechanisms which may also affect the extent of the macrophage response. Although corrosion within modular junctions was overall rare, the presence of one case with marked corrosion shows that taper corrosion and subsequent ALTRs are possible in TSAs. For any figures or tables, please contact authors directly

Introduction. Reverse total shoulder arthroplasty (RTSA) is a semi-constrained joint replacement with an articulating cobalt-chromium glenosphere and ultra-high molecular weight polyethylene (PE). Because of its limited load bearing, surgeons and implant manufacturers have not elicited the use of highly cross-linked PE in the shoulder, and to date have not considered excessive PE wear in the reverse shoulder a primary concern. As the number of shoulder procedures is expected to grow exponentially in the next decade, however, it is important to evaluate how new designs and bearing materials interact and to have an understanding of what is normal in well-functioning joint replacements. Currently, no in vivo investigation into RTSA PE wear has been conducted, with limited retrieval and simulation studies. In vitro and in silico studies demonstrate a large range in expected wear rates, from 14.3 mm. 3. /million cycles (MC) to 126 mm. 3. /MC, with no obvious relationship between wear rate and polyethylene diameter. The purpose of this study is to evaluate, for the first time, both volumetric and linear wear rates in reverse shoulder patients, with a minimum six-year follow-up using stereo radiographic techniques. Methods. To date, seven patients with a self-reported well-functioning Aequalis Reversed II (Wright Medical Group, Edina, MN, USA) RTSA implant system have been imaged (mean years from surgery = 7.0, range = 6.2 to 9). Using stereo radiographs, patients were imaged at the extents of their range of motion in internal and external rotation, lateral abduction, forward flexion, and with their arm at the side. Multiple arm positions were used to account for the multiple wear vectors associated with activities of daily living and the shoulder's six degrees of motion. Using proprietary software, the position and orientation of the polyethylene and glenosphere components were identified and their transformation matrices recorded. These transformation matrices were then applied to the CAD models of each component, respectively, and the apparent intersection of the glenosphere into the PE recorded. Using previously validated in-house software, volumetric and maximum linear wear depth measurements were obtained. Linear regression was used to identify wear rates. Results. The volumetric and linear wear rates for the 36 mm PE liners (n = 5) were 39 mm. 3. /y (r. 2. = 0.86, range = 24 to 42 mm. 3. /y) and 0.09 mm/y (r. 2. = 0.96, range = 0.08 to 0.11 mm/y), respectively. Only two patients with 42 mm PE liners were evaluated. For these, volumetric and linear wear rates were 110 mm. 3. /y (r. 2. = 0.81, range = 83 to 145 mm. 3. /y) and 0.17 mm/y (r. 2. = 0.99, range = 1.12 to 1.15 mm/y), respectively. Conclusion. For the first time, PE wear was evaluated in the reverse shoulder in vivo. More patients are required for conclusive statements, but preliminary results suggest first order volumetric and linear wear rates within those predicted by simulation studies. It is interesting to note the increased wear with larger PE size, likely due to the increased contact area between congruent faces and the potential for increased sliding distance during arm motion

Total knee arthroplasty has been the main treatment method among advanced osteoarthritis (OA) patients. The main post-operative evaluation considers the level of pain, stability and range of motion (ROM). The knee flexion level is one of the most important categories in the total knee arthroplasty patient's satisfaction in Asian countries due to consistent habits of floor-sitting, squating, kneeling and cross legged sitting. In this study, we discovered that the posterior capsular release enabled the further flexion angles by 14 degrees compared to the average ROM without posterior release group. Our objective was to increase the ROM using the conventional total knee arthroplasty by the posterior capsular release. Posterior capsular release is being used in order to manage the flexion contraction. Although the high flexion method extends the contact area during flexion by extending the posterior condyle by 2mm, the main problem has been the early femoral loosening. We searched for the method to get the deep knee flexion with the conventional knee prosthesis. 122 OA patients with less than preoperative 130 flexion that underwent conventional TKAs using Nexgen from January, 2014 to September, 2016 were reviewed. Posterior femoral osteophytes were removed as much as possible, but 74 cases were performed posterior capsular release, while 48 cases were not performed. After checking postoperative ROM after 6 months of operation, we compared 74 knees with a posterior capsular release and 48 knees without posterior capsular release. As a result, the average ROM in the posterior capsular release group was 132 degrees, but the average ROM without posterior release group is 118 degrees. No postoperative hyperextension was found when the adequate size of polyethylene (PE) thickness was utilized. Hence, the conventional TKA with a posterior capsular release showed satisfactory clinical outcomes in the deep knee flexion of Asians

Introduction. Durable bone fixation of uncemented porous-coated acetabular cups can be observed at a long-term, however, polyethylene (PE) wear and osteolysis may affect survivorship. Accurate wear measurements correlated with clinical data may offer unique research information of clinical interest about this highly debated issue. Objetive. We assessed the clinical and radiological outcome of a single uncemented total hip replacement (THR) after twenty years analysing polyethylene wear and the appearance of osteolysis. Materials and Methods. 82 hips implanted between 1992 and 1995 were prospectively evaluated with a mean follow-up of 20.6 years (range, 18 to 23). A hemispherical porous-coated acetabular cup matched to a proximally hydroxyapatite-coated anatomic stem and a 28 mm standard PE liner, sterilised by gamma irradiation in air, was used in all hips. Radiological position and the possible appearance of loosening and osteolysis were recorded over time. Penetration of the prosthetic head into the liner was measured by the Roentgen Monographic Analysis (ROMAN) Tool at 6 weeks, 6 months, one year and yearly thereafter. Results. Six cups were revised due to wear and four due to late dislocation. All cups were radiographically well-fixed and all stems showed radiographic ingrowth. Six un-revised hips showed osteolysis on the acetabular side and two on the proximal femoral side. Creep at one year was 0.30 (±0.23) mm. Mean total femoral head penetration was 1.23 mm at 10 years, 1.52 mm at 15 years and 1.92 mm at 23 years. Overall mean wear was 0.12 (± 0.1) mm/year and 0.09 (±0.06) mm/year after the creep period. Mean wear was 0.08 (± 0.06) mm/year in hips without osteolysis and 0.14 (±0.03) mm/year in revised hips or with osteolysis (p<0.001). Conclusions. Although continued durable fixation can be observed with a porous-coated cups and a proximally hydroxyapatite-coated anatomic stem, true wear continues to increase at a constant level over time. PE wear remains as the main reason for revision surgery and osteolysis in uncemented THR after twenty years

Introduction. The causes for revision of primary total hip arthroplasty (THA) are various and quite well known. The developing use of dual-mobility THA (DM-THA) seems a relevant option to decrease the risk of instability. Due to lack of long-term follow-up, this innovative retentive concept is suspected to increase the risk of polyethylene (PE) wear. The aim of the study was to analyse the causes for DM-THA revision and assess whether or not its occurrence is different from that of fixed-standard (FS) THA, particularly for aseptic loosening or wear and/or osteolysis. Materials and methods. The SoFCOT group conducted an observational prospective multicentre study from 1 January. 2010 to 31 December 2011. Inclusion criteria comprised an exhaustive collection of 2044 first-revision THAs with 251 DM-THAs and 1793 FS-THAs. After excluding complications linked to patient factors (infection and periprosthetic fractures), we performed a matched case–control study (matching ratio 1:1) comparing two groups of 133 THAs. Results. Revisions for aseptic loosening or osteolysis/wear were as frequent in DM-THA (58.7 %) as in FS-THA (57.1 %) (p 0.32); 7.5 % of DM-THAwere revised for dislocation versus 19.5 % of FS-THA (p 0.007). Discussion. Revision for osteolysis/wear and aseptic loosening were as frequent in DM-THA as in FS-THA; revision for dislocation was less frequent in DM-THA. This confirms the efficiency of the DM concept regarding the risk of dislocation. Causes for revision were different between groups, and revisions for dislocation were less frequent in DM-THA. Only prospective comparative studies could provide reliable information that may support broader use of the DM concept

Background and aim. A significant reduction in wear using Durasul highly cross-linked polyethylene (PE) versus Sulene polyethylene (sterilized with nitrogen) at 5 and 10 years have been reported previously. We ask if the improvement observed at the earlier follow-up continues at 15 years. Methods. Between 1999 and 2001, 90 hips underwent surgery using the same cementless cup and stem: 45 received Allofit cups with a Sulene-PE liner and 45 Allofit cups with a Durasul-PE liner, both associated with an Alloclassic stem (28 mm metallic femoral head). 66 hips of this prospective comparative study were available over a minimum follow-up of 15 years. Linear femoral head penetration was estimated digitally at 6 weeks, at 6 and 12 months and annually thereafter, using the Dorr method, given the nonspherical cup shape. All radiographs were evaluated by the same author, who was not involved in surgery. Results. 2 hips in the Sulene group showed proximal femoral osteolysis, one of these was revised for stem loosening at 12 years. There was no loosening of any other prosthetic component. Femoral head penetration in the one year postoperative radiographs was 0.23 mm (range, 0.08–0.23) for the Sulene group and 0.10 mm (0.04–0.11) for the Durasul group (p<0.001). The mean yearly linear femoral head penetration was 68.8 % lower for the Durasul group: 0.020+0.018 mm for the Durasul and 0.062+0.051 mm/year for the Sulene group (p<0.001). Mean linear femoral head penetration at 15 years was 64.5 % less in the Durasul group (0.394+0.27 mm) than in the Sulene group (1.108+0.78 mm)(p=0.001). Conclusions. There is a significant reduction in yearly linear femoral head penetration with the Durasul-PE. Confirmation that this reduction will result in less osteolysis requires continued follow-up studies

Introduction. In total hip arthroplasty, press-fit anchorage is one of the most common fixation methods for acetabular cups and mostly ensures sufficient primary stability. Nevertheless, implants may fail due to aseptic loosening over time, especially when the surrounding bone is affected by stress-shielding. The use of acetabular cups made of isoelastic materials might help to avoid stress-shielding and osteolysis. The aim of the present numerical study was to determine whether a modular acetabular cup with a shell made of polyetheretherketone (PEEK) may be an alternative to conventional titanium shells (Ti6Al4V). For this purpose, a 3D finite element analysis was performed, in which the implantation of modular acetabular cups into an artificial bone stock using shells made of either PEEK or Ti6Al4V, was simulated with respect to stresses and deformations within the implants. Methods. The implantation of a modular cup, consisting of a shell made of PEEK or Ti6Al4V and an insert made of either ceramic or polyethylene (PE), into a bone cavity made of polyurethane foam (20 pcf), was analysed by 3D finite element simulation. A two-point clamping cavity was chosen to represent a worst-case situation in terms of shell deformation. Five materials were considered; with Ti6Al4V and ceramic being defined as linear elastic and PE and PEEK as plastic materials. The artificial bone stock was simulated as a crushable foam. Contacts were generated between the cavity and shell (μ = 0.5) and between the shell and insert (μ = 0.16). In total, the FE models consisted of 45,282 linear hexahedron elements and the implantation process was simulated in four steps: 1. Displacement driven insertion of the cup; 2. Relief of the cup; 3. Displacement driven placement of the insert; 4. Load driven insertion of the insert (maximum push-in force of 500 N). The FE model was evaluated with respect to the radial deformations of the shell and insert as well as the principal stresses in case of the ceramic inserts. The model was experimentally validated via comparison of nominal strains of the titanium shells. Results. The maximum radial deformation of the shell made of PEEK was 581 μm (insertion) and 470 μm (relief) and therefore multiple times higher compared to the Ti6Al4V shell (42 μm and 21 μm). As a result, larger deformations occurred at the PE and ceramic inserts in combination with the PEEK shell. Partially, the deformations were above an usual clearance of 100 μm. When the ceramic insert was combined with the shell made of PEEK, maximum principal stresses in the ceramic insert amounted to 30 MPa and were clearly lower than approved bending strength of the ceramic material (948 MPa). Conclusion. The examined acetabular shell made of PEEK was intensively deformed during insertion compared to the geometrically identical Ti6Al4V shell and is therefore not suitable for modular acetabular cups. In future studies it should be clarified to what extent acetabular cups with shells made of carbon fiber reinforced PEEK materials with higher stiffness lead to reduced deformations during the insertion procedure

Introduction. Polyethylene (PE) wear is clearly linked to total hip arthroplasty (THA) failure, leading to osteolysis and decreasing survivorship rates. Dual mobility cups (DMC) are widely used to prevent or treat THA instability. However some studies have pointed PE wear risk as a “dual wear” risk. Hip wear simulation is usually used to understand factors influencing wear and to differentiate design, PE types and materials performances. To date, few works have been published studying dual mobility insert wear. Objectives. Our objective was to evaluate wear of DMC with comparison with a fixed single articulating hip design and to measure wear under same conditions (loading cycle, temperature, sterilization, material and surface roughness). Methods. The test bench includes one station for a control sample and one for dynamic test. Those are driven independently one from the other. Two electrical actuators applied the forces and two forces sensors putted on the fixing plate of the acetabular part gave the corresponding values. On the dynamic station, the angular movements are generated by an electric motor. Sleeves are installed on the bowls containing the testing liquid and on the supports of acetabular parts, in order to get a tight volume that excludes contaminant particles. Wear is measured by a gravimetric method. The simulator is stopped and implants have been removed from the simulators in order to achieve weighting and observations at 0.5, 1, 2, 3, 4 and 5 millions cycles. At the end, the sample PE insert and the control one are removed from their cup in the aim to measure the mass loss. Results. Under same conditions the gravimetric wear and the linear penetration of the head are perfectly comparable between a conventional and a dual mobility cup. Conclusion. In vitro, DMC wear is equal or less important than a standard single fixed cup and volumetric wear is lower than published data. Wear of the two joints of a DMC is not increased thanks to the recruitment phenomenon and the freedom induced by the concept

Introduction. Pelvic posterior tilt change (PPTC) after THA is caused by release of joint contracture and degenerative lumbar kyphosis. PPTC increases cup anteversion and inclination and results in a risk of prosthesis impingement (PI) and edge loading (EL). There was reportedly no component orientation of fixed bearing which can avoid PI and EL against 20°PPTC. However, dual mobility bearing (DM) has been reported to have a large oscillation angle and potential to withstand EL without increasing polyethylene (PE) wear against high cup inclination such as 60∼65°. Objective. The purpose of this study was to investigate the optimal orientation of DM-THA for avoiding PI and EL against postoperative 20°PPTC. Methods. Our study was performed with computer tomography -based three-dimensional simulation software (ZedHip. LEXI co. Japan). The CT data of hip was derived from asian typical woman with normal hips. Used prosthesises were 50mm cup and 42mm outer head of modular dual mobility system and Accolade II 127°(stryker). Femoral coordinate system was retrocondylar plane with z-axis from trochanteric fossa to intercondylar notch. Cup orientation was described as anatomical definition. The safe zone was calculated by the required hip range of motion which was defined as 130°flexion, 40°extension, 30°external rotation, and 50°internal rotation with 90°flexion and the maximum inclination of DM cup which was 60°in consideration of withstanding EL. Cup orientations withstanding 20°PPTC were defined as the primary cup orientation which changes consistently within the safe zone with the match of 20°PPTC. And among them cup orientation with lowest inclination was defined as the optimal cup orientation. result. The optimal orientations could be identified only within stem anteversion from 15°to 40°. The relationship between the optimal cup orientation and stem anteversion could be automatically identified. The correlation between stem anteversion and cup anteversion was linearly distributed and could be expressed as an approximated line of the formula that (stem anteversion)+(cup anteversion)=36.8. And likewise the relationship between stem anteversion and cup inclination was curved-linerly distributed and could be expressed as an approximated curved line of the formula that (cup inclination)=0.04(stem anteversion). 2. 2.18(stem anteversion)+74.8. Cup orientation calculated by the Widmer's combined anteversion theory is easily deviated from the safe zone by PPTC. The optimal cup orientation calculated in this study could be set more inclination and retroversion than it calculated by the Widmer's theory in contribution of large oscillation angle and admissibility of high inclination cup setting of DM. Therefore it could be possible to withstand 20°PPTC. Conclusion. Performing THA with considering postoperative PPTC is necessary for good long term outcome without dislocation and PE wear. The solution for 20°PPTC after THA is to apply dual mobility bearing and the formula of combined orientation theory calculated in this study

Each in vivo wear measurement method for total hip arthroplasty (THA) has strengths and weaknesses. The authors have developed a new manual wear measurement method (PowerPoint [PP] method) and validated that the PP method was found to have better repeatability, reproducibility and pick up differences in the radiographs than the previously established manual wear measurement methods. The primary aim of this study was to evaluate the reliability of the PP method by retrieval study. 17 retrieved polyethylene (PE) liners (16 patients) were enrolled in this study. The wear volumes of retrieved PE liners from clinical radiographs were calculated by the PP and Dorr and Wan method and they were compared with the wear volume of retrieved PE liners calculated by the triangulation three-dimensional (3D) laser scan. Spearman correlation coefficients results between PP method and 3D laser scan revealed excellent correlations (0.89 to 0.93). The Intraclass Correlation Coefficients values of the PP method showed excellent correlations (0.95 to 1.00). We suggest that the PP method will be a viable new technique for measuring wear of THA and a supplement method when computerized methods are not available

Articulation of the polyethylene (PE) insert between the metal femoral and tibial components in total knee replacements (TKR) results in wear of the insert which can necessitate revision surgery. Continuous PE advancements have improved wear resistance and durability increasing implant longevity. Keeping up with these material advancements, this study utilises model-based radiostereometric analysis (mbRSA) as a tool to measure in vivo short-term linear PE wear to thus predict long-term wear of the insert. Radiographic data was collected from the QEII Health Sciences Centre in Halifax, NS. Data consisted of follow-up RSA examinations at post-operative, six-, 12-, and 24-month time periods for 72 patients who received a TKR. Implanted in all patients were Stryker Triathlon TKRs with a fixed, conventional PE bearing of either a cruciate retaining or posterior stabilised design. Computer-aided design (CAD) implant models were either provided by the manufacturer or obtained from 3D scanned retrieved implants. Tibial and femoral CAD models were used in mbRSA to capture pose data in the form of Cartesian coordinates at all follow-ups for each patient. Coordinate data was manually entered into a 3D modeling software (Geomagic Studio) to position the implant components in virtual space as presented in the RSA examinations. PE wear was measured over successive follow-ups as the linear change in joint space, defined as the shortest distance between the tibial baseplate and femoral component, independently for medial and lateral sides. A linear best-fit was applied to each patient's wear data; the slope of this line determined the annual wear rate per individual patient. Wear rates were averaged to provide a mean rate of in vivo wear for the Triathlon PE bearing. Mean linear wear per annum across all 72 patients was 0.088mm/yr (SD: 0.271 mm/yr) for the medial condyle and 0.032 mm/yr (SD: 0.230 mm/yr) for the lateral condyle. Cumulative linear wear at the 2-year follow-up interval was 0.207mm (SD: 0.565mm) and 0.068mm (SD: 0.484mm) for the medial and lateral condyles, respectively. Linear PE wear measurements using mbRSA and Geomagic Studio resulted in 0.056mm/yr additional wear on the medial condyle than the lateral condyle. Large standard deviations for yearly wear rates and cumulative measurements demonstrate this method does not yet exhibit the accuracy needed to provide short-term in vivo wear measurement. Inter-patient variability from RSA examinations is likely a source of error when dealing with such small units of measure. Further analysis on patient age and body mass index may eliminate some variability in the data to improve accuracy. Despite high standard deviations, the results from this research are in proximity to previously reported linear wear measurements 0.052mm/yr and 0.054mm/yr. Linear wear analysis will continue upon completion of >100 patients, in addition to volumetric PE wear over the entire articulating surface

Unicompartmental knee arthroplasty (UKA) is often considered to be attractive alternate surgical technique to total knee arthroplasty (TKA) and high tibial osteotomy (HTO), in particular young patients. In addition, it is recently reported that preservation of joint line in UKA is crucial factor for positive long-term outcome, especially in revision case for UKA. However, the role of this joint line has neither been invested nor is it consciously bothered during surgical implantation. Validated finite element (FE) analysis was introduced in this study to investigate the effects of maximum contact stress on polyethylene (PE) insert and maximum compressive stress in opposite compartments for joint line in fixed-type UKA. As suggested by Weber et al., FE model for joint line was developed by means of determination of the angle between the pre-operative joint line and the reference line from lateral cortical is of the femur. Based on the method above, joint lines were modeled in −3, −2, −1, 0, +1, +2, and +3 mm cases and these seven FE models were compared and analyzed (Fig. 1). All implant components were modeled as linear elastic isotropic materials. However, the model was considered to have plastic characteristics of PE insert. FE analysis was performed using high kinematics displacement and rotation inputs, which were based on the kinematics of the natural knee. ISO standards were used for axial load and flexion (Fig. 2). The FE model was subjected to validation based on cadaveric experimental data available in the literature by Sohn et al. and from previous cadaveric tests conducted by current investigators. The maximum contact stress was found at around 43 % of the gait cycle in 0 mm case. There were no difference between ± 1 and 0 mm cases, but maximum contact stress on PE insert becomes greater in ± 3 mm cases. The maximum compressive stress of the lateral meniscus in 0 mm case occurred at 62 % of the gait cycle. There were no difference in positive joint line cases in maximum compressive stress, however maximum compressive stress of the lateral meniscus becomes greater in - 3 mm cases. This study emphasized the importance of joint line preservation after implantation of UKA. It would be critical to determine the joint line in UKA surgery in future based on the result showing that there has been no remarkable difference in stress but changed rapidly from the position beyond the joint line. In future study, it would be valuable study to compare between joint lines of fixed- and mobile-type UKA

Generic walking profiles applied to mechanical knee simulators are the gold standard in wear testing of total knee replacements (TKRs). Recently, there was a change in the international standard (ISO) for knee wear testing (ISO 14243-3): the direction of motion in the anterior/posterior (AP) and internal/external (IE) directions were reversed. The effects of this change have not been investigated, therefore it is not known whether results generated by following this new standard can be compared to historical wear tests which used the old standard. Using a finite element analysis (FEA) model of a TKR in parallel with an energy based wear model and adaptive remeshing, we investigated differences in wear between the newest ISO standard developed in 2014, and the previous ISO standard developed in 2004. CAD models of a left sided NexGen Cruciate Retaining (CR) TKR (Zimmer, Warsaw, IN) were used to create the FEA model (Figure 1). The loads and motions specified by simulator standards ISO 14243-3(2004) and ISO 14243-3(2014) were applied to the model. Analyses were run using ABAQUS v6.13-2 Standard (Dassault Systèmes, Waltham, MA). 8 node hexahedral elements were used to model the UHMWPE component. The contact was modeled as penalty contact, with the friction coefficient set to 0.04 on the articular surface. The cobalt chromium molybdenum femoral component was modeled as a rigid surface, utilizing a mix of 2. nd. order quadrilaterals and tetrahedrons. Wear of the polyethylene (PE) component was predicted to 1,000,000 cycles using a previously published frictional energy-based wear model. The wear model, developed from data generated in wheel-on-flat tests, utilizes two parameters defining the frictional energy required to remove a unit volume of material both parallel (3.86E8 J/mm. 3. ) and perpendicular (3.55E7 J/mm. 3. ) to the primary polyethylene fibril direction. Primary fibril direction for the analysis was set to the AP direction. Wear for each simulation of a gait cycle was scaled to 500,000 cycles. Two gait cycles were simulated representing 1,000,000 cycles in total. Adaptive remeshing was driven by the wear model, with the mesh being updated every time increment to simulate material ablation. The time step size was variable with a maximum of 0.01s. The FEA predicted higher wear rates for the newest ISO standard (7.34mg/million cycles) compared to the previous standard (6.04mg/million cycles) (Figure 2). Comparing the predicted wear scars (Figure 3), the new version of the standard covered a larger percentage of the total articular surface, with wear being more spread out as opposed to localized. This is more similar to what is seen in patient retrievals. The results of the study suggest that major differences between the old and the new ISO standard exist and therefore historical wear results are not comparable to newly obtained results. In addition, this study demonstrates the utility of FEA in wear analysis, though the wear model needs further work and validation before it can be used as a supplement to simulator testing. Validation of the wear model against simulator tests and pin-on-disk experiments is currently underway. For figures/tables, please contact authors directly.

Background. Wear and fatigue damage to polyethylene components remain major factors leading to complications after total knee and unicompartmental arthroplasty. A number of wear simulations have been reported using mechanical test equipment as well as computer models. Computational models of knee wear have generally not replicated experimental wear under diverse conditions. This is partly because of the complexity of quantifying the effect of cross-shear at the articular interface and partly because the results of pin-on-disk experiments cannot be extrapolated to total knee arthroplasty wear. Our premise is that diverse experimental knee wear simulation studies are needed to generate validated computational models. We combined five experimental wear simulation studies to develop and validate a finite-element model that accurately predicted polyethylene wear in high and low crosslinked polyethylene, mobile and fixed bearing, and unicompartmental (UKA) and tricompartmental knee arthroplasty (TKA). Methods. Low crosslinked polyethylene (PE). A finite element analysis (FEA) of two different experimental wear simulations involving TKA components of low crosslinked polyethylene inserts, with two different loading patterns and knee kinematics conducted in an AMTI knee wear simulator: a low intensity and a high intensity. Wear coefficients incorporating contact pressure, sliding distance, and cross-shear were generated by inverse FEA using the experimentally measured volume of wear loss as the target outcome measure. The FE models and wear coefficients were validated by predicting wear in a mobile bearing UKA design. Highly crosslinked polyethylene (XLPE). Two FEA models were constructed involving TKA and UKA XLPE inserts with different loading patterns and knee kinematics conducted in an AMTI knee wear simulator. Wear coefficients were generated by inverse FEA. Results. Predicted wear rates were within 5% of experimental wear rates during validation tests. Unicompartmental mobile bearing back-side wear accounted for 46% of the total wear in the mobile bearing. Wear during the swing phase was 38% to 44% of total wear. Discussion & Conclusions. Crosslinking polyethylene primarily decreased (by nearly 10-fold) the wear generated by cross-shear. This result can be explained by the reduced propensity of crosslinked polyethylene molecules to orient in the dominant direction of sliding. A highly crosslinked fixed-bearing polyethylene insert can provide high wear performance without the increased risk for mobile bearing dislocation. Finite element analysis can be a robust and efficient method for predicting experimental wear. The value of this model is in rapidly conducting screening studies for design development, assessing the effect of varying patient activity, and assessing newer biomaterials. This FEA model was experimentally validated but requires clinical validation

Introduction. Mobility at insert-tray articulations in mobile bearing knee implant accommodates lower cross-shear at polyethylene (PE) insert, which in turn reduces wear and delamination as well as decreasing constraint forces at implant-bone interfaces. Though, clinical studies disclosed damage due to wear has occurred at these mobile bearing articulations. The primary goal of this study is to investigate the effect of second articulations bearing mobility and surface friction at insert-tray interfaces to stress states at tibial post during deep flexion motion. Method & Analysis. Figure 1 shows the 3-D computational aided drawing model and finite element model of implant used in this study. LS-DYNA software was employed to develop the dynamic model. Four conditions of models were tested including fixed bearing, as well as models with coefficients of friction of 0.04, 0.10 and 0.15 at tibial-tray interfaces to represent healthy and with debris appearance. A pair of nonlinear springs was positioned both anteriorly and posteriorly to represent ligamentous constraint. The dynamic model was developed to perform position driven motion from 0° to 135° of flexion angle with 0°, 10° and 15° of tibial rotation. The prosthesis components were subjected with a deep squatting force. Results. Peak values of maximum shear stress for different coefficients of friction and fixed bearing, respectively, are shown in Figure 2. Peak value of maximum shear stress at tibial post of fixed bearing is significantly larger than mobile bearing with tibial rotation. The peak values are 63MPa and 46.7MPa with 10° and 15° tibial rotation respectively for fixed bearing while for mobile bearing the values range from 32MPa to 36.6MPa and from 35.3MPa to 40.6MPa with 10° and 15° tibial rotation respectively. It was found that peak value of maximum shear stress increases with coefficient of friction and tibial rotation. In contrast, with normal rotation, bearing mobility and surface friction do not give any significant effect on the shear stress at tibial post. Discussion & Conclusions. Appearance of second articulations in mobile bearing TKA provides an attribute in reducing force transmission via implant-bone interface which leads to lower shear stress induced in tibial post due to transmitted moment. However, higher surface friction will result in larger frictional force, which in turn induce larger moment at tibial post. Higher conformity will attribute to higher cross-shear level during knee motion. As a result, wear damage at tibiofemoral articular surface of mobile insert become worse

Numerous studies have shown highly cross-linked polyethylene (XLPE) to be an extremely low wear bearing surface for total hip arthroplasty (THA) at intermediate term follow-up. Wear rates and the incidence of osteolysis for CoCr femoral heads on XLPE liners appears to be considerably less than what is observed for conventional polyethylene (PE). This has been demonstrated even in younger, more active patients. Nevertheless, polyethylene wear and associated osteolysis are still a concern, since the indications for THA have been expanded to include younger and more active patients. Both wear simulator and clinical data suggest that ceramic femoral heads can reduce bearing surface wear of conventional PE. There is, however, extremely limited evidence supporting any advantage of ceramic femoral heads over CoCr femoral heads with regards to bearing surface wear of XLPE. This is perhaps due to the relative difficulty in measuring the low wear rates of XLPE bearings in general, regardless of material composition of the femoral head. Although ceramic femoral heads are more scratch resistant and less susceptible to third body wear, their current clinical use to reduce wear of XLPE bearings is, in reality, based on the unproven assumption that use of ceramic femoral heads will have a similar effect on wear reduction as is seen with ceramic on conventional PE bearing couples. Nevertheless, the use of ceramic femoral heads has become common in younger, more active patients. Recently, corrosion at the head neck junction of modular THA (trunnionosis), has been determined to be the possible source of metal debris and metal ions associated with adverse local tissue reactions (ALTR or ARMD) in THA, including ALVAL and pseudotumors. There is general agreement that trunnionosis results from mechanically assisted crevice corrosion (fretting) of the modular junctions common to nearly all contemporary THA designs. Several design, material and patient factors have been implicated as contributors to this problem including larger diameter femoral heads (>36 mm), reduced femoral neck and taper geometry, flexural rigidity of the taper, and patient body weight and activity level. Data from our multicenter implant retrieval program has shown that corrosion at the head-neck junction of contemporary modular THAs may be reduced with use of ceramic femoral heads. The use of ceramic femoral heads also eliminates the potential for release of cobalt and chromium ions from the taper junctions of titanium alloy stems. In younger patients, the long term effects of cobalt ions released from corrosion at the modular neck junction are still unknown. Although the surgeon's selection of a ceramic femoral head in combination with a XLPE acetabular liner is likely based on the desire to minimise PE wear, the impact of femoral head composition on taper neck corrosion and ALTR is perhaps more of a concern in 2015. Until the problem of taper neck corrosion is more thoroughly understood and effectively addressed by implant manufacturers, the use of ceramic femoral heads in THA should be considered in the younger or more active patient. The increased cost of ceramic femoral heads creates a dilemma in defining who is “young” enough and “active” enough to be considered an appropriate candidate for a ceramic femoral head in our current environment of bundled care payments, value based purchasing and concern about providing cost-effective health care to our patients

Introduction. In Total Hip Arthroplasty (THA), polyethylene wear reduction is key to implant longevity. Oxidized Zirconium (OxZi) unites properties of a ceramic bearing surface and metal head, producing less wear in comparison to standard Cobalt-Chromium (CoCr) when articulating with Cross-linked polyethylene (XLPE) in vitro. This study investigates in vivo polyethylene (PE) wear, outcomes and complications for these two bearing couples in patients at 5 year follow-up. Methods. 400 patients undergoing THA across four institutions were prospectively randomised into three groups. Group I received a cobalt-chrome (CoCr) femoral head/ cross-linked polyethylene (XLPE) liner; Group II received an OxZi femoral head/ ultrahigh molecular weight polyethylene (UHMWPE) liner; Group III received an OxZi femoral head/XLPE liner. All bearing heads were 32 mm. Linear wear rate was calculated with Martell computer software. Functional outcome and complications were recorded. Results. At median follow-up of 3.7 years, implant survivorship was 98% across all groups with no difference in SF-36, WOMAC, pain score or complications (p > 0.05). After the first 12 months of creep, rate of linear wear over 3 years was 0.07 mm for Group I, 0.16 mm for Group II, and 0.03 mm/year for Group III. A significant difference was detected when using UHMWPE (p = 0.012) but not when using XLPE (P = 0.75). Conclusion. At midterm follow-up, an XLPE acetabular liner is more important in reducing wear than the femoral head bearing. There is a trend towards lower wear when coupling OxZi rather than CoCr with XLPE; further long-term analysis is recommended to observe this pattern

In total hip arthroplasty (THA), aseptic loosening induced by polyethylene (PE) wear debris is the most important cause that limits the longevity of implants. Abrasive wear generated through the mechanism such that micrometer-roughened regions and small asperities on the metallic femoral heads surface locally plow through the PE cup surface. Abrasive wear results in the PE material being removed from the track traced by the asperity during the motion of the metallic femoral heads surface. For the purpose of reducing wear, alumina ceramics was introduced in Europe and Japan in 1970s. The clinical results of ceramic-on-PE bearings regarding the wear resistance have been superior to that of the metal-on-PE bearings. Compared with Co–Cr–Mo alloys, alumina ceramics is advantageous for precision machining because of its higher hardness, enable to form spherical and smooth surface. The fracture resistance of the alumina ceramics itself is related to grain size; the grain size reduction leads to the improvement of its resistance. In this study, we evaluated the roundness and the roughness of retrieved two distinct alumina ceramics having different grain size, and Co–Cr–Mo alloy heads. Fourteen retrieved alumina ceramic femoral heads; ten heads with a diameter of 28 mm made of small grain size alumina (SG-alumina; mean grain size is 3.4 μm) with clinical use for 16–28 years and four heads with a diameter of 26 mm made of extra-small grain size alumina (XSG-alumina; mean grain size is 1.3 μm) with clinical use for 14–19 years, were examined. Six retrieved Co–Cr–Mo alloy femoral heads with a diameter of from 22 to 32 mm with average clinical use for 12–28 years were examined. SG-alumina and XSG-alumina heads showed significantly lower roundness compared with Co–Cr–Mo alloy heads, due to higher precision machining [Fig. 1]. The surface roughness for the contact area of the heads increased in order of XSG-alumina, SG-alumina and Co–Cr–Mo alloy. The surface roughness of the non-contact area for all kinds of heads was lower than that for the contact area [Fig. 2]. Surface profiles of the SG-alumina and XSG-alumina showed the reentrant surface while Co–Cr–Mo alloy heads showed the protrusion surface. The roundness and roughness of the Co–Cr–Mo alloy or ceramic surface and the presence or absence of hard third-body particles correlate to the amount of abrasive PE wear. When the third-body was entrapped during the clinical use, a reentrant surface might be formed on the ceramic while protrusion surface formed on the Co–Cr–Mo alloy. The differences in clinical results may be due in part to the influence of third-body particles. The ceramic becomes more resistant than Co–Cr–Mo alloy against the scratching by the entrapped abrasive contaminants because of its harder surface. From the good clinical results of more than 20 years using SG-alumina, the greater long term clinical results using XSG-alumina will be expected

Background. The main reasons for hip prosthesis failure are aseptic loosening and periprosthetic joint infection (PJI). The real frequency of PJI is probably largely underestimated because of non-standardized definition criteria, diagnostic procedure, treatment algorithm and other confounders. Therefore, data from joint registries are not reflecting the frequency of PJI and can be misleading; particularly low-grade PJI can be frequently misdiagnosed as aseptic failure. Therefore, prospective clinical studies with standardized protocol, comprehensive diagnostic procedure and sufficient follow-up should be performed. Sonication of explanted prosthesis is highly sensitive for detection of biofilms on prosthetic surface and allows quantitative analysis of biofilm formation. We hypothesize that by using sonication, ceramic components (BIOLOX®delta, BIOLOX®forte) will show higher resistance against biofilm adhesion compared to polyethylene (PE) and metal (CoCrMo). Methods. In this prospective multicentre study (level of evidence: Ia), we included all consecutive adults ≥18 years of age, who underwent explantation of the hip prosthesis for infection or aseptic reason. Excluded were patients in whom part of the prosthetic components were retained. A standardized and comprehensive diagnostic algorithm was applied, including sonication of all removed prosthetic components for qualitative and quantitative microbiological analysis (ultrasound bath 40 kHz, 1 W/cm2, 1 min). Individual components (metal, PE, ceramic) were separately placed in sterile boxes for investigation. All patients were simultaneously included in the European Prosthetic joint infection cohort (EPJIC, . www.epjic.org. ) to ensure long-term follow-up. Results. Up to date, 79 patients were included, of whom 47 (60%) were diagnosed with aseptic failure and 32 (40%) with PJI. Mean age was 73 years (27–87 years), 32 (41%) were males. Table 1 summarizes the demographic characteristics. In 32 patients with PJI, most frequently isolated organisms were coagulase-negative staphylococci (n=12, 38%), Staphylococcus aureus (n=7, 22%) and Propionibacterium acnes (n=4, 13%), followed by enterococci (n=2; 6%) and gram-negative bacilli (n=2; 6%); 2 infections (6%) were polymicrobial and 3 were culture-negative (9%). Table 2 summarizes the microbiological results from sonication of removed components. Causative microorganism could be detected in sonication fluid from polyethylene in 100%, from metal in 92% and from ceramic in 69%. Significantly lower bacterial counts expressed as colony-forming units (CFU) were detected in sonication fluid from ceramic components (230 CFU/ml) than from PE (6’250 CFU/ml) and metal components (5’870 CFU / ml) (p < 0.01). Conclusions. These first results support the hypothesis that significantly less biofilm biomass is formed on ceramic surface, compared to PE and metal surfaces, potentially indicating higher ceramic “resistance” against bacterial adhesion. These findings should be confirmed with non-microbiological investigation such as imaging (fluorescent in situ hybridization, confocal laser scanning or electron microscopy). Furthermore, in 6 of 32 patients (19%) with PJI, an aseptic loosening was preoperatively suspected. Infection was found only by systematic application of an optimized diagnostic method, particularly sonication of the removed implant. Final study results are expected to be available by the end of 2016