Introduction. Previous studies of long-term CoCr alloy femoral components for TKA have identified 3rd body abrasive wear and inflammatory cell induced corrosion (ICIC). The extent of femoral condyle surface damage in contemporary CoCr femoral components is currently unclear. The purpose of this study was to investigate the prevalence and morphology of damage (3rd body scratches and ICIC) at the bearing surface in retrieved TKA femoral components from contemporary designs. Methods. 308 CoCr femoral TKA components were collected as part of an ongoing, multi-institutional orthopedic implant retrieval program. The collection included contemporary designs from Stryker (Triathlon n=48, NRG n=10, Scorpio n=31), Depuy Synthes (PFC n=27) and Zimmer (NexGen n=140, Persona n=1) and Biomet (Vanguard n=51). Hinged knee designs and unicondylar knee designs were excluded. Components were split into groups based on implantation time: short-term (1–3y, n=134), intermediate-term (3–5y, n=73) and long-term (6–15y, n=101). Each grouping was mainly revised for instability, infection and loosening. Third-body abrasive wear of CoCr was evaluated using a semi-quantitative scoring method similar to the Hood method (Figure 1). A score of 1 had minimal damage and a score of 4 corresponded to damage covering more than 50% of the evaluated area. ICIC damage was reported as location of affected area. A white light interferometer (Zygo New View 5000) was also used to analyze the topography of severe damage of the bearing surface. For this analysis, three representative components from each cohort were selected and analyzed in three locations on the apex of the bearing surface. We analyzed the following roughness parameters: Ra, Rsk, and Rku. Results. On the CoCr bearing surface, the primary damage mechanisms were large scratches, small random scratches, and ICIC damage (Figure 2). Mild to severe damage (Damage Score ≥ 2) was observed in 96% of the short-term, 98% intermediate-term and 94% of long-term components. Severe damage (Damage Score = 4) was observed in 43% of the short-term, 50% intermediate-term and 56% of long-term components. ICIC damage observed on a portion of the bearing surface was detected in 43% of the short-term components, 30% of the intermediate-term components and 26% of the long term components. Apparent ICIC damage on the bearing and/or a non-bearing region of the component was observed in 85% of the short-term components, 75% of the intermediate-term components and 80of long-term TKA components. The Ra, Rsk, and Rku were similar between cohorts (Table 1). Discussion. Abrasive wear of the femoral components was frequently observed in retrieved contemporary femoral components for TKA, regardless of their implantation time, and can most likely be attributed to third body damage caused by bone or bone cement debris. The prevalence of severe CoCr damage scores was highest in the long-term cohort, while the appearance of ICIC damage was lowest in the long-term cohort. Surface roughness parameters were similar in all three cohorts suggesting that the mechanism for this damage is comparable throughout the first 15 years of service. Future work is necessary to quantify the in vivo release of CoCr from abrasive wear and corrosion mechanisms, and the effects of increased surface roughness on wear of the polyethylene counter face

Femoral components with an oxidized zirconium-niobium (OxZr) gradient ceramic surface (Oxinium, Smith & Nephew, Memphis, TN) were introduced as an alternative to cobalt-chromium (CoCr) alloy femoral components for the purpose of PE wear reduction in total knee replacements [1]. In the present study, the surface damage and clinical performance of both CoCr alloy and OxZr femoral components were investigated. By matching CoCr alloy and OxZr femoral components for clinical factors, as done by Heyse et al. [2], the surface damage on retrieved CoCr alloy and OxZr femoral component was assessed. Twenty-six retrieved cobalt-chromium (CoCr) alloy femoral components were matched with twenty-six retrieved oxidized zirconium (OxZr) femoral components for implantation period, body-mass index, patient gender, implant type (cruciate ligament retaining/substituting), and polyethylene insert thickness. Detailed surface profilometry was performed on retrieved femoral condyles in areas that had not been damaged by gouging [3] with the specific purpose of investigating the in vivo wear behaviour of undamaged OxZr surface. In addition, the cumulative survivorships were calculated for patients who had received CoCr alloy or OxZr femoral components from our orthopaedic database. In order to identify factors that affect the clinical performance of CoCr alloy and OxZr femoral components, the findings from the retrieval analysis and the survivorship analysis were combined. The Rp, Rpm, and Rpk-values for the retrieved CoCr alloy femoral components were found significantly higher than the Rp, Rpm, and Rpk-values for the retrieved OxZr femoral components (p ≤ 0.031). The roughness parameters values (Ra, Rq, Rz, Rp, Rpm, Rpk, Rv, and Rsk) for the retrieved CoCr alloy femoral components were found significantly higher than the values of the new, never implanted CoCr alloy femoral components (p ≥ 0.001). The surface roughness was higher on the medial condyles than the lateral condyles of the retrieved CoCr alloy femoral components; such a difference was not observed on the retrieved OxZr femoral components. The OxZr bearing surface appeared to protect the femoral components from abrasive wear in vivo. At 8.5-years follow up, the cumulative survivorship for the CoCr alloy femoral components (98%) was not found to be statistically significantly different (p = 0.343, Breslow test) from the OxZr femoral components (97.5%). Therefore, OxZr femoral components appeared to possess low wear characteristics and could be particularly suitable for younger, heavier patients to ensure long-term durability

Purpose. Ion implantation with a high kinetic energy has advantages in controlling the size and distribution of coating materials, helping to overcome the limitations of conventional methods. This method resulted in uniformly and homogeneously distributed in a CoCr alloy even without a further annealing process. The study was to investigate the wear rate of UHMWPE on CoCr alloy for metal head by plasma immersion ion implantation (PIII) treatments. MATERIALS AND METHODS. Commercially CoCr alloy (ISO 5832-12, ASTM F1537, alloy 1) were used as the substrate. PIII surface treatments were performed in a high-vacuum chamber with a radio frequency plasma source. We divided with two groups: PIII CoCr alloy, CoCr ally as control. Wear amount of UHMWPE (ISO 5834-2, ASTM F648, Type 1) on CoCr alloy specimens (three samples per group) was evaluated after 500,000 and 1,000,000 cycles using pin-on disk wear tester. After test, surface morthology was examined by SEM, and surface roughness was calculated in both groups. RESULTS. The wear amount of UHMWPE was 0.00030g on PIII CoCr, and 0.00042g on control group (p=0.032). We observed statistical difference (p = 0.021) in surface roughness in the PIII CoCr and control group: 0.086 and 0.112, respectively. SEM images after 1,000,000 cycles shows the abrasion tracks on both groups. CONCLUSIONS. PIII treatment could reduce the wear amount of UHMWPE for acetabular liner application. The surface roughness of PIII CoCr was lower than CoCr alloy

Revision of fractured ceramic-on-ceramic total hip replacements with a cobalt-chromium (CoCr) alloy-on-polyethylene articulation can facilitate metallosis and require further expensive revision surgery [1–3]. In the present study, a fifty-two year old male patient suffered from fatal cardiomyopathy after undergoing revision total hip arthroplasty. The patient had received a polyethylene-ceramic acetabular liner and a ceramic femoral head as his primary total hip replacement. The polyethylene-ceramic sandwich acetabular liner fractured in vivo after 58 months and the patient underwent his first revision surgery where he received a Vitamin E stabilized acetabular Polyethylene (PE) liner and a CoCr alloy femoral head with documented synovectomy at that time. After 15 months, the patient was admitted to hospital in cardiogenic shock, with retrieval of the bearing components. Before the second revision surgery, peak serum cobalt levels measured 6,521 μg/L, 78-times greater than serum cobalt levels of 83μg/L associated with cobalt poisoning [4]. Serum titanium levels found in the patient measured 17.5 μg/L) normal, healthy range 0–1.4 μg/L). The retrieved CoCr alloy femoral head had lost a total of 28.3g (24% or an estimated amount of 102 × 10. −9. wear particles (∼2 μm diameter) [1]) within 16 months of in vivo service. Despite initiating a cobalt chelating therapy, the patients' cardiac left ventricular ejection fraction remained reduced at 6%. This was followed by multi-organ failure, and ultimately the patient passed away shortly after being taken off life support. Embedded ceramic particles were found on the backside and articular surfaces of the Vitamin E-stabilized PE acetabular liner. Evidence of fretting wear on the titanium (Ti) alloy acetabular shell was present, possibly explaining the increased serum Ti levels. Scanning electron microscopy and energy dispersive X-ray analyses confirmed Ti alloy transfer on the embedded ceramic particles on the backside PE liner surface and CoCr alloy transfer on the embedded ceramic particles on the articular PE liner surface. A fractured ceramic-on-ceramic total hip replacement should not be revised to a CoCr alloy-on-polyethylene articulation irrespective of concurrent synovectomy [5] as it can cause severe, third-body wear to the CoCr alloy femoral head that can lead to metallosis with fatal, systemic consequences

Introduction: A renewal of interest in large metal-on-metal bearings has been seen due to the introduction of resurfacing prostheses. According to lubrication theory, large metal-on-metal bearings may obtain a film fluid lubrication. The mode of lubrication may be described by the lambda coefficient λ, which is the ratio between the thickness of the lubricant hc and the root mean square roughness of the bearing Rq. If this coefficient λ is higher than 3, a fluid film lubrication is expected. To have this situation, the following parameters must be optimized: diametral clearance and roughness. This presentation investigates the role of these two parameters, based on two commercially available products. Methods: To determine the λ coefficient, the thickness hc of the lubricant must be determined, as well as the roughness of the bearing Rq. The Hamrock – Dawson equation (. 1. ) allows the determination of the thickness hc as a function of the bearing parameters. The roughness Rq is measured by a stylus profilometer. Results: With a typical load of 3000 N, an angular velocity of 1 rad/s, and a viscosity of 0.005 Pas, the Hamrock – Dawson equation gives the following film thickness hc for a 50 mm metal-on-metal bearing with different diametral clearances:. Diametral clearance [μm] 100 150 200 250 300< . Minimum thickness hc [nm] 64.9 47.5 38.1 32.1 27.9. The following roughnesses Rq were measured for two types of resurfacing prosthesis:. As cast CoCr alloy (BHR by MMT): 23 ± 6 nm. Wrought-forged CoCr alloy (DUROM by Zimmer): 5 ± 2 nmThe as cast resurfacing prosthesis has a 250 μm diametral clearance and the wrought-forged resurfacing prosthesis has a 150 μm diametral clearance. Therefore, the following λ coefficients for a 50 mm metal-on-metal bearing are obtained:. As cast CoCr alloy: 0.99. Wrought-forged CoCr alloy: 6.72. This large difference in the λ coefficients indicates that the lubrication mode of these two different prostheses is probably different. Based on this analysis, the wrought-forged component has ideal lubrication (λ > 3) whereas the as cast does not reach ideal lubrication (λ < 3). Conclusions: This investigation shows that minute differences in the geometry and in the roughness of a metal-on-metal prosthesis may significantly influence their lubrication behaviour as well as the wear resistance

Wear of the polyethylene (PE) insert in total knee replacements can lead to wear-particle and fluid-pressure induced osteolysis. One major factor affecting the wear behaviour of the PE insert in-vivo is the surface characteristics of the articulating femoral components. Contemporary femoral components available in Canada are either made of cast Cobalt Chromium (CoCr) alloy or have an oxidized zirconium surface (Oxinium). The latter type of femoral components have shown to have increased abrasive wear resistance and increased surface wettability, thus leading to reduced PE wear in-vitro compared with conventional cast CoCr components. Although surface damage has been reported on femoral components in general, there have been no reports in the literature as to what extent the recommended operating techniques affect the surface tribology of either type of femoral component. Twenty-two retrieved total knee replacements were identified with profound surface damage on the posterior aspect of the femoral condyles. The femoral components were of three different knee systems: five retrievals from the NexGen(r) total knee system (Zimmer Inc., Warsaw, IN), twelve retrievals from the Genesis II(r) total knee system (CoCr alloy or Oxinium; Smith & Nephew Inc., Memphis, TN), and five retrievals from the Duracon(r) total knee system (Stryker Inc., Mahwah, NJ). Reasons for revision were all non-wear-related and included aseptic loosening in two cases, painful flexion instability, and chronic infection. All retrieved femoral components showed evidence of surface damage on the condyles, at an average of 99° flexion (range, 43° – 135° flexion). Titanium (Ti) alloy transfer and abrasive surface damage were evident on all retrieved CoCr alloy femoral components that came in contact with Ti alloy tibial trays. Surface damage on the retrieved Oxinium femoral components was gouging, associated with the removal and cracking of the oxide and exposure of the zirconium alloy substrate material. CoCr alloy femoral components that had unintended contact with CoCr alloy tibial trays also showed evidence of gouging and abrasive wear. All femoral components showed severe surface damage in the posterior aspect of the condyles. The femoral surface was heavily scratched and the oxidized zirconium coating surface appeared removed. The surface analysis suggested that the surface damage most likely occurred during the time of initial implantation. In particular, it appeared that the femoral condyles were resting on the posterior aspect of the tibial tray in flexion, thus scratching the femoral components. Such scratches could potentially lead to accelerated PE insert wear and reduced implant longevity, thus making expensive revisions surgery necessary. The authors strongly suggest a revision of the current operating techniques recommended by the implant manufacturer to prevent this type of surface damage from occurring

Distal neck modularity places a modular connection at a mechanically critical location, which is also the location that confers perhaps the greatest clinical utility. The benefits of increased clinical options at that location must be weighed against the potential risks of adding an additional junction to the construct. Those risks include prosthetic neck fracture, taper corrosion, metal hypersensitivity, and adverse local tissue reaction. Further, in-vitro testing of ultimate or fatigue strength of femoral component designs has repeatedly failed to predict behavior in-vivo, raising questions about the utility of in-vitro testing that does not incorporate the effect of mechanically assisted crevice corrosion into the test design. The material properties of Ti alloy and CoCr alloy place limits on design considerations in the proximal femur. The smaller taper junctions that are necessary for primary reconstruction are particularly vulnerable to failure whereas larger taper junctions commonly used in revision modular femoral component designs have greater opportunity for success. Modular junctions of CoCr alloy on conventional Ti alloy have been shown to have a greater incidence of clinically significant mechanically assisted crevice corrosion and adverse reaction. Designs that have proven clinical strength and utility universally have larger, more robust junctions, that extend into the metaphysis of the femur. While these designs are primarily designed for revision total hip replacement (THR), they are occasionally indicated for primary THR. Overall, however, while design options at the neck-stem junction have unmatched clinical utility, no design that does not extend into the metaphysis has proven to be universally reliable. While routine use of modular neck components for primary THR does not appear to be clinically indicated based on current evidence, modular designs with proven successful proximal junctions appear to be indicated for revision THR and rare primary THR with extreme version or other anatomical circumstances

Background. When reversing the hard-soft articulation in inverse shoulder replacement, i.e. hard inlay and soft glenosphere, the tribological behaviour of such a pairing has to be tested thoroughly. Therefore, two hard materials for the inlay, CoCr alloy and alumina toughened zirconia ceramic (ATZ) articulating on two soft materials, conventional UHMWPE and vitamin E stabilised, highly cross-linked PE (E-XLPE) were tested. Methods. The simulator tests were performed analogue to standardised gravimetric wear tests for hip prosthesis (ISO 14242-1) with load and motion curves adapted to the shoulder. The test parameters differing from the standard were the maximum force (1.0 kN) and the range of motion. A servo-hydraulic six station joint simulator (EndoLab, Rosenheim) was used to run the tests up to 5 times 106 cycles with diluted calf serum at 37° C as lubricant. Results. The wear rates measured in the simulator when the CoCr alloy inlay articulated on UHMWPE and E-XLPE were respectively 32.50 +/− 3.48 mg/Mcycle and 10.65 +/− 2.36 mg/Mcycle. In comparison, when the ATZ inlay articulated on UHMWPE and E-XLPE the wear rates were 20.34 +/− 1.14 mg/Mcycle and 5.99 +/− 0.79 mg/Mcycle respectively. Conclusions. The simulator wear rate of the standard articulation CoCr – UHMWPE is similar to that found in the corresponding pairing for hip endoprosthesis. Replacing UHMWPE by E-XLPE, the wear rate is reduced to about 1/3 for both hard counterparts, CoCr and ZTA, respectively. Replacing the CoCr inlay by a part made from ZTA lowers wear by about 37 % in articulation against UHMWPE and about 44 % against E-XLPE. The lowest wear rate, with a reduction of about 80 % compared to the standard CoCr – UHMWPE, exhibits the pairing of both advanced materials, ZTA – E-XLPE. However, long-term clinical follow-up will confirm if this in-vitro wear reduction leads to longer in-vivo survival. Level of evidence. Laboratory test on sample implants. Study financed by Mathys Orthopaedie GmbH

Introduction. In these three years, many troubles have occurred in the arthroplasty by hip joint prostheses with metal on metal sliding surfaces. Anomalous reaction including a pseudotumor, which is supposed to be caused by the metal ions released from the implant surfaces, is the most serious problem for the patients. 1). This problem seriously confused us because there is the fact that ion release has not hardly occurred between a head and an acetabulum, where usual wear proceeds. The important clue was the stain that was sometimes found on the surfaces of the taper junction of retrieved prostheses. This stain has been generally estimated the evidence of the fretting corrosion. It has not been clarified why short range sliding enhances the corrosion, yet. In the present study, to elucidate this problem, we observed the behavior of the passive film of implant surfaces under the sliding conditions of fretting, which is presumed on the taper junction. Materials and Methods. In the present study, electric potential was measured as an indicator to assess the removal of the passive film of cobalt chromium (CoCr) alloy under the fretting conditions. A wear simulator (FPR-2100, RHESCA, Tokyo, Japan) was used for the testing apparatus with reciprocating motion. A Co-28Cr-6Mo alloy pin (Smith & Nepew, London, UK) specimen was 10 mm in diameter and abraded with the common material plate (Fig. 1). A load of 1 N was applied to a pin. The electronic potential between the pin and the Ag/AgCl reference electrode (HX-R5, HOKUTO DENKO, Tokyo, Japan) soaking in the PBS(−) as simulated biological fluid were measured using a high impedance electrometer (HE-104, HOKUTO DENKO, Tokyo, Japan) (Fig. 2). The sliding width was chosen 0.5–10 mm. The reciprocating cycle was chosen 0.5–2 Hz. The changes in the electronic potential of CoCr alloy were recorded during the sliding motion together with under the static conditions before and after the sliding motion. Results and Discussion. The electronic potential lowered with the onset of the sliding motion (Fig. 3). The reduction in the potential enlarged with the increase in the cycle at any sliding width. The return of the potential, which might correspond with the repassivation on the damaged surface, was observed after the halt of the sliding motion. On the other hand, the time constant of the return curve of the potential rose with the expansion of the sliding width. From these results, it was found that the passive film of CoCr alloy that was removed with the sliding motion can repassivate when the interval of the motion is sufficiently long. On the other hand, repassivation is slow when the interval of the motion is short. This means the small amplitude, as the fretting, must enhance the metal ion release

Introduction. Cobalt-Chromium-Molybdenum (CoCr) and Titanium-Aluminium-Vanadium (Ti) alloys are the most commonly used alloys used for Total Hip Replacement due to their excellent biocompatibility and mechanical properties. However, both are susceptible to fretting corrosion In-vivo. The objective of this study was to understand the damage mechanism of both combinations through a sub-surface damage assessment of the alloys at various fretting amplitudes using the Transmission Electron Microscopy (TEM – CM200 FEGTEM). The TEM was used to attain a cross sectional view of the alloys in orderto see the effect of high shear stress on the grain structure. Methods. The two combinations were fretted at a maximum contact pressure of 1 GPa in a Ball – on – Plate configuration for displacement amplitudes of 10μm, 25μm, 50μm and 150μm. The contact was lubricated with 25% v/v Foetal Bovine Serum (FBS), diluted with Phosphate Buffered Saline (PBS). The material loss through wear and corrosion from the fretting contact were quantified using the Visual Scanning Interferometry (VSI). The TEM samples were obtained using the Focused Ion Beam (FIB – FEA Nova 200 Nanolab). Samples were obtained from regions of high stress (shaded in red) [Fig. 1] for both CoCr and Ti flat of the CoCr–CoCr and CoCr–Ti couples respectively. Result. Total volume loss result vs. Dissipated Energy was plotted from displacement amplitudes of 10μm, 25μm and 50μm for both couples consecutively [Fig. 2]. The TEM images [Fig. 3] of CoCr alloy (denoted as CC) reveal a progressive damage to the topmost surface of the alloy and loss of nano-crystalline layer. Evidence of severe grain damage from the topmost surface can also be seen at 50μm. On the other hand, the Ti alloy (denoted as CT) at [Fig. 3 (CT–25μm)] reveal some recrystallization at the topmost surface and a progressive recrystallization of the bulk alloy was observed at 150μm. Damage to the surface was also visible at this displacement amplitude which initiated a crack as circled in red in the image [Fig. 3 (CT–150μm)]. Discussion. Fouvry et al1 discussed the effect of the interfacial shear work done (dissipated energy) on a fretted material; this energy is mainly expended on material structure transformation (as observed in Ti alloy) and/or wear generation (as observed in CoCr alloy) [Fig. 2]. This intermediate damage mechanism helps to identify that CoCr–CoCr follows a wear dominated mechanism while CoCr–Ti preferably exhibits fatigue behaviour until large displacement amplitudes are applied leading to accelerated wear of the top surface [Fig. 3 (CT–150μm)]. The recrystallization was observed over 2μm below the surface at displacement amplitude of 150μm. Consequentially, this could modify the metallurgy of the Ti alloy and may contribute to the clinically observed phenomena whereby, the softer Ti wears the harder CoCr component2. Conclusion. TEM micrographs reveal large granular damage on the CoCr alloy and deep bulk recrystallization of the Ti alloy as a result of interfacial shear stress. This suggests that the Ti alloy may experience a change in its mechanical behaviour. On the other hand, it is identified that a CoCr–CoCr couple experiences a wear dominated mechanism

Introduction. Backside wear of polyethylene (PE) inlays in fixed-bearing total knee replacement (TKR) generates high number of wear debris, but is poorly studied in modern plants with improved locking mechanisms. Aim of study. Retrieval analysis of PE inlays from contemporary fixed bearing TKRs - to evaluate the relationship between backside wear and liner locking mechanism and material type and roughness of the tibial tray. Methods. MATERIAL. We included five types of implants, revised after min. 12 months (14–71): three models with a peripheral locking rim and two models with a dove-tail locking mechanism. Altogether this study included 15 inlays were removed from TKRs with CoCr alloy tray with a roughened surface and a peripheral locking lip liner (Stryker Triathlon, Ra 5,61 µm), 9 from CoCr trays with peripheral locking lip and untreated surface (Aesculap Search, Ra 0,81 µm), 13 from Ti alloy trays with peripheral locking lip and untreated surface (DePuy PFC Sigma 0,61 µm), 11 from Ti alloy trays with untreated surface and dovetail locking mechanism (Zimmer NexGen, 0,34 µm), and 9 from iplants with a Ti alloy tibial tray with mirror polished surface and dovetail locking mechanism (Smitn&Nephew Genesis II, 0,11 µm). METHODS. Wear of bearing surface and back side of retrieved inlays was examined in 10 sectors under a light microscope. Seven modes of wear were analysed and quantified according to the Hood scale: surface deformation, pitting, embedded third bodies, pitting, scratching, burnishing (polishing), abrasion and delamination. Damage of inlays caused by backside wear was also evaluated using scanning electron microscopy (SEM). Roughness of tibial tray was evaluated using a contact profilometer. Results. We found no differences between wear scores on the articulating surface in all group, they did not correlate with backside wear scores in all groups as well. Compared to all other groups, backside wear scores were significantly higher in implants with untreated Ti alloy tibial tray (P<0,001 Wilcoxon test). Lowest wear rates were found in implants from both Ti and CoCr alloys and peripheral locking rim. Interestingly there was no difference between wear of implants with polished and untreated surface (Fig. 1). SEM analysis demonstrated different wear modes in implants with dovetail mechanism and peripheral rim. The first group demonstrated signs of gross rotational instability, with severe abrasion with an arch-shaped pattern and delaminated PE (Fig 2). In one design we observed severe extrusion of PE into screw holes of the tibial tray. Inlays from trays with peripheral rim presented two types of wear: flattening of machining marks or protrusion of the material caused by the rough surface (Fig 3). Conclusions. This study demonstrates that backside wear is still a problem in modern TKR. Our findings suggest that it is predominantly affected by type of locking mechanism (with peripheral rim performing better), to a lesser extent by surface roughness of the tibial component, while material type does not seem to play an important role. This study was funded by a grant from the National Science Centre nr 2012/05/D/NZ5/01840. To view tables/figures, please contact authors directly

Introduction: Symptomatic abnormal soft-tissue masses relating to the hip joint, such as those described as pseudotumours, are being increasingly reported following metal-on-metal hip resurfacing arthroplasty (MoMHRA). These were found to be locally destructive, requiring revision surgery in a high proportion (75%) of patients. Lymphocyte infiltrations seen in pseudotumours were similar to aseptic lymphocyte vascular associated lesion (ALVAL), which is thought to represent a T-lymphocyte-mediated delayed type hypersensitivity. Therefore, a delayed hypersensitivity reaction to nickel (Ni), chromium (Cr) or cobalt (Co) has been suggested to play a role in pseudotumour aetiology. In patients with bilateral MoMHRA who presented with symptoms on one side, subsequent scans have demonstrated pseudotumours both on the symptomatic and asymptomatic side. Thus, there are concerns that there may be an appreciable number of asymptomatic pseudotumours that surgeons are unaware of and these may eventually become symptomatic. Aim: The aims of this study were:. to determine the prevalence of asymptomatic pseudotumours after MoMHRA; and. to measure Co and Cr ion levels as well as lymphocyte proliferation responses to Ni, Co and Cr (the principal elements in the CoCr alloy used in MoMHRA) in MoMHRA patients with and without asymptomatic pseudotumours. Methods: A total of 201 MoMHRA implanted hips in 158 patients (97 male, 61 female) with a mean age of 56 years (range 33–73 years) were evaluated. The mean follow-up was 61 months (range 13–88 months). Resurfacing devices implanted included 128 Birmingham Hip Resurfacing, 66 Conserve Plus and seven ReCap. The control groups included additional 20 patients, 10 male and 10 female (a mean age 68 years, range 57–80 years) with metal-on-polyethylene total hip arthroplasty and a further 22 age-matched patients (a mean age 55 years) without any metal implants. Ultrasound was used as the initial imaging modality and MRI was used to assess the extent of the identified masses. Patients with a soft-tissue mass had ultrasound-guided aspiration or core biopsy performed. Venous blood samples were collected in all patients for serum cobalt and chromium ion levels analysis using Inductively-Coupled Plasma Mass Spectrometer and lymphocyte transformation tests (LTT). The Oxford Hip Score (OHS) was used to measure the functional outcomes of patients. Acetabular component abduction angle was measured from standardised anteroposterior pelvis radiographs. Results: Prevalence – Pseudotumours were found in 7 patients (6 female and 1 male). The overall prevalence of asymptomatic pseudotumours was 4%, with a relatively very high (30%) prevalence in females with bilateral implants. Histological examinations showed extensive necrosis of connective tissue, in which there were scattered aggregates of metal particles and a diffuse lymphocyte infiltrate. Metal Ion Levels – The presence of pseudotumour was associated with significantly higher median serum cobalt levels (9.2mg/L vs. 1.9mg/L, p< 0.001), chromium levels (12.0mg/L vs. 2.1mg/L, p< 0.001), hip aspirate cobalt levels (1182 mg/L vs. 86.2mg/L, p=0.003), and aspirate chromium levels (883mg/L vs. 114.8mg/ L, p=0.006), as well as with inferior functional scores (OHS 41 vs. 47 p< 0.001). There was no significant difference in acetabular cup inclination angle (p=0.51). Lymphocyte Reactivity: A higher incidence and level of enhanced lymphocyte reactivity to Ni (p=0.001), but not to Co or Cr (the principal elements in the CoCr alloy used in metal-on-metal hip resurfacing implants), was found in patients with MoMHRA compared to the patients without MoM implants. However, lymphocyte reactivity to Co, Cr and Ni did not significantly differ in patients with pseudotumours compared to those patients without pseudotumours. Conclusion: The prevalence of asymptomatic pseudotumours in females was high, especially in females with bilateral MoMHRA implants (30%). The patients with ‘asymptomatic’ pseudotumours were in fact mildly symptomatic. Lymphocyte reactivity to Co, Cr and Ni did not differ in patients with pseudotumour compared to those patients without pseudotumours, suggesting that systemic hypersensitivity type IV reactions, mediated by lymphocyte reactivity to these metals, is not the dominant mechanism in pathogenesis of the soft tissue pseudotumours. Furthermore, pseudotumours were not detected in those patients who had normal levels of cobalt and chromium ions. This suggests that pseudotumours do not occur if MoM articulations are well functioning. Therefore, pseudotumours are likely to be a biological consequence of the large amount of metal debris generated in vivo due to excessive wear

INTRODUCTION. In theory, Finite Element Analysis (FEA) is an attractive method for elucidating the mechanics of modular implant junctions, including variations in materials, designs, and modes of loading. However, the credence of any computational model can only be established through validation using experimental data. In this study we examine the validity of such a simulation validated by comparing values of interface motion predicted using FEA with values measured during experimental simulation of stair-climbing. MATERIALS and METHODS. Two finite element models (FEM) of a modular implant assembly were created for use in this study, consisting of a 36mm CoCr femoral head attached to a TiAlV rod with a 14/12 trunnion. Two head materials were modelled: CoCr alloy (118,706 10-noded tetrahedral elements), and alumina ceramic (124,710 10-noded tetrahedral elements). The quasi-static coefficients of friction (µ. s. ) of the CoCr-TiAlV and Ceramic-TiAlV interfaces were calculated from uniaxial assembly (2000N) and dis-assembly experiments performed in a mechanical testing machine (Bionix, MTS). Interface displacements during taper assembly and disassembly were measured using digital image correlation (DIC; Dantec Dynamics). The assembly process was also simulated using the computational model with the friction coefficient set to µ. s. and solved using the Siemens Nastran NX 11.0 Solver. The frictional conditions were then varied iteratively to find the value of µ providing the closest estimate to the experimental value of head displacement during assembly. To validate the FEA model, the relative motion between the head and the trunnion was measured during dynamic loading simulating stair-climbing. Each modular junction was assembled in a drop tower apparatus and then cyclically loaded from 230–4300N at 1 Hz for a total of 2,000 cycles. The applied load was oriented at 25° to the trunnion axis in the frontal plane and 10° in the sagittal plane. The displacement of the head relative to the trunnion during cyclic loading was measured by a three-camera digital image correlation (DIC) system. The same loading conditions were simulated using the FEA model using the optimal value of µ derived from the initial head assembly trials. RESULTS. For both head materials, the predicted values of axial displacement of the head on the trunnion closely approximated the measured values derived from DIC measurements, with differences of −0.17% to +6.5%, respectively. Larger differences were calculated for individual components of motion for the stair climbing activity. However, the predicted magnitude of interface motion was still within 10% of the observed values, ranging from −7% to −5%. CONCLUSIONS. Our simulations closely approximated physical testing using complex loading, coming within 7% of the target values. By generating a validated computational model of a modular junctions with varying head materials, we will be able to simulate additional activities of daily living to determine micromotion and areas of peak pressure and contact stresses generated. For any figures or tables, please contact authors directly

Background. As the number of ceramic THR bearings used worldwide is increasing, the number of implants that experience off-normal working conditions, e.g. edge loading, third bodies in the joint, soft tissues laxity, dislocation/subluxation of the joint, increases too. Under all such conditions the bearing surfaces can be damaged, leading eventually to a limitation of the expected performances of the implant. Methods. We characterised the damage resistance of different bearing surfaces (alumina matrix composite BIOLOXdelta, alpha-alumina BIOLOXforte, zirconia 3Y-TZP, oxidized zirconium alloy Zr-2.5Nb, CoCr-alloy) by scratch tests performed following the European standard EN 1071–3:2005. Also the scratch hardness of same materials has been assessed. Results. The Lc1 value (i.e., the load for the onset of a scratch) measured for BIOLOXdelta is about fivefold the one measured for the oxidized zirconium alloy (OXZr) surface and about tenfold the Lc1 measured for the CoCr alloy. The height of ridges along the scratch edges due to plastic flow in the composite ceramic BIOLOXdelta are only 21% in height than in CoCr, and only a small fraction (0.04%) of the height of ridges measured on OXZr surfaces. The scratch hardness of the metal samples tested (CoCr, OXZr) results one order of magnitude lower than the ones of ceramics. This behavior is not influenced by of the presence of the coating on OXZr surface. Conclusions. The transformation toughened ceramics tested (BIOLOXdelta, 3Y-TZP) are the materials that exhibit the higher resistance to scratching. Ridges at scratch edges are lower in ceramics than in coated or uncoated metals. The result show the superior scratch resistance behavior of toughened ceramics for THR wear couples with respect to coated or bare alloys. Level of Evidence. Level 1

Distal neck modularity places a modular connection at a mechanically critical location which is also the location that confers perhaps the greatest clinical utility. Assessment of femoral anteversion in 342 of our total hip replacement (THR) patients by CT showed a range from −24 to 61 degrees. The use of monoblock stems in some of these deformed femurs therefore must result in a failure to appropriately reconstruct the hip and have increased risks of impingement, instability, accelerated bearing wear or fracture, and adverse local tissue reaction (ALTR). However, the risks of failing to properly reconstruct the hip without neck modularity must be weighed against the additional risks introduced by neck modularity. There are several critical design, material, and technique variables that are directly associated with higher or lower incidences of problems associated with modular neck femoral components. Unfortunately, in vitro testing of the fatigue strength of these constructs has failed to predict their behavior in vivo. Designs predicted to tolerate loads that far exceed those experienced in vivo still fail at unacceptably high rates. Titanium alloy neck components subjected to the stresses at the neck-stem junction continue to fail at an unacceptable incidence. CoCr alloy neck components, while theoretically stronger, still fracture and are further compromised by mechanically assisted crevice corrosion, metal hypersensitivity, and rarely, adverse tissue reaction. Designs that have proven clinical strength and utility universally have larger, more robust junctions that extend into the metaphysis of the femur. While these designs are primarily designed for revision THR, they are occasionally indicated for primary THR. Overall, however, while design options at the neck-stem junction have unmatched clinical utility, no design that does not extend into the metaphysis has proven to be universally reliable. While routine use for primary THR does not appear clinically indicated based on current evidence, modular designs with proven successful proximal junctions appear to be indicated for extreme version or anatomical circumstances

Expectations for ceramic-on-metal (COM) bearings included (i) optimal lubrication due to smoother ceramic heads (ii), reduction of metal ions due to elimination of CoCr heads, and (iii) ‘differential hardness’ reducing adhesive wear and squeaking (Firkins 2001, Williams 2007). Additional benefits included (iv) use of heads larger than for ceramic-on-ceramic (COC), (v) reduction in taper corrosion and (vi) simulator studies clearly demonstrated metal ions and wear both reduced compared to MOM (Firkins 2001, Williams 2007, Ishida 2007). However, contemporary ‘3rd body wear’ paradigms focused only on metal debris size range 0.025–0.035um (Firkins 2001). Thus, neglected was the effect of hip impingement, provoking release of large metal particles sized 20–200um (Clarke 2013). In this study, we compared COM retrievals using hypotheses that adverse COM cases would demonstrate a combination of (a) steeply inclined cups, (b) liner “edge-loading”, (c) Ti6Al4V contamination on ceramic, and (d) evidence of 3rd-body CoCr wear by large particles. As a case example, this 51-year old female had her metal-polyethylene (MPE) bearing revised to COM in June 2011. She reported no symptoms 1-year post-op, but scans revealed a palpable mass in the inguinal region of left hip. By March 2013 the patient reported mild pain in her hip, which progressed to severe by April 2014. Scans showed a solid and cystic iliopsoas bursitis while cup position had changed from 43o to 73o inclination. Revision was performed in June 2014, her joint tissues were found extensively stained due to metal contamination, and histology described formation of a large pseudotumor. Analysis of retrieved components was by interferometry, SEM and EDS. Detailed maps were made of wear areas in heads and cups and volumetric wear was determined by CMM techniques. This adverse COM example revealed large diametral mismatch (595um) compared to COM controls (75–115um). The ceramic head had a broad polar stripe of CoCr contamination, roughness 0.1–0.3um high. Equatorial ceramic areas showed arrays of thin metal smears that demonstrated elemental Ti and Al. The CoCr liner revealed wear area into cup rim, as “edge loading”, and also featured a focal rim-defect over 18o circumferential arc. Liner scratches were 20um wide and larger, and wear-rate of CoCr liner averaged approximately 50mm3 per year. In contrast, ceramic head had minimal wear. Our study highlights the underappreciated risk of impingement by metallic prosthetic components. Prior studies of ceramic heads showed black metallic smears. With COM we can anticipate that the broad polar smear will be CoCr alloy (wear of liner on head). However, Ti6Al4V smearing on ceramic heads is a notable signpost indicating impingement by the Ti6Al4V acetabular shell. The femoral neck (Ti6Al4V: CoCr), may also be damaged. Release of large metal particles, 1500-times larger than prior predictions, provoke a particularly adverse ‘3rd body wear’ (Halim, 2015). Such cases confirm our four hypotheses, that COM bearings will then fail in a way similar to MOM. In contrast, COC bearings are immune to such impingement and 3rd-body metal damage

Introduction. Originally, the vertical expandable titanium rib (VEPTR™) was developed to treat children with Thoracic insufficiency syndrome secondary to fused ribs and congenital scoliosis. Over the years its usage has widen and is currently being used to treat all etiology of early onset scoliosis (EOS). A major draw back remains the size of the titanium VEPTR™ implant. In keeping with the new trend of chrome-cobalt alloy (CoCr). spinal implants, we set out to explore if redesigning the VEPTR™ was mechanically sound. The aim of this study was twofold. Firstly, we investigate the mechanical properties of a VEPTR™ made with CoCr alloy compared to that of titanium alloy. Secondly we investigated how much we could down size the VEPTR™. Materials & Methods. Finite element analyses were performed on 3 different VEPTR™ designs (rod diameter of 6mm, 5mm and 4mm) subjected to a compressive load of 500N (equivalent to a 50Kg child). For each configuration, two materials, titanium alloy and chrome-cobalt alloy, were used. Maximum Von Mises stress distribution (VMSD), plastic strain (PS) and total displacement (TD) of the VEPTR™ were measured as indicators of mechanical properties of the implant. Results. Results for the maximum Von Mises stress distribution (VMSD), plastic strain and total displacement (TD) can be seen on the table 1. Discussion. Results confirm that yield strength of titanium material is greater than that of Co-Cr, while Plastic strain (PS) is greater for a CoCr VEPTR™ than for titanium VEPTR™. As expected a 6 mm CoCr VEPTR resist displacement almost twice as a 6 mm titanium VEPTR. Little difference is noted in plastic strain and VonMises stress at 6mm. Down sizing the implant to 5 mm in titanium or CoCr may runs the risk of implant failure as both exceeds their failure point and they both deform 0.29% and 6.6% respectively, placing the 5mm CoCr at higher risk of failure. Our results suggest that the VEPTR™ design could be reduced to 5mm however requires a new design to minimize the risk of failure. 4mm rods will not withstand a 50kg load

Introduction. Previous studies of CoCr alloy femoral components for total knee arthroplasty (TKA) have identified 3. rd. body abrasive wear, and apparent inflammatory cell induced corrosion (ICIC) [1] as potential damage mechanisms. The association between observed surface damage on the femoral condyle and metal ion release into the surrounding tissues is currently unclear. The purpose of this study was to investigate the damage on the bearing surface in TKA femoral components recovered at autopsy and compare the damage to the metal ion concentrations in the synovial fluid. Methods. 12 autopsy TKA CoCr femoral components were collected as part of a multi-institutional orthopedic implant retrieval program. The autopsy components included Depuy Synthes Sigma Mobile Bearing (n=1) and PFC (n=1), Stryker Triathlon (n=1) and Scorpio (n=3), and Zimmer Nexgen (n=4) and Natural Knee (n=2). Fluoro scans of all specimens prior to removal was carried out to assure no signs of osteolysis or aseptic loosening were present. Third-body abrasive wear of CoCr was evaluated using a semi-quantitative scoring method similar to the Hood method [2]. ICIC damage was reported as location of affected area and confirmed using a digital optical microscope with 4000X magnification. Synovial fluid was aspirated from the joint capsule prior to removal of the TKA device. The synovial fluid was spun at 1600 rpm for 20 minutes in a centrifuge with the cell pellet removed. The supernatant was analyzed in 1 mL quantities for ICP-MS (inductively coupled plasma mass spectrometry) by Huffman Hazen Laboratories. Data was expressed as ppb. Results. Mild to severe damage (Damage Score ≥ 2) was observed on 92% of the components in at least one quadrant, with no severe damage (Damage Score = 4) observed. ICIC damage was observed on three components in three different regions (the posterior lateral, anterior, and medial bearing surface). These observations were confirmed with digital optical microscopy, where we observed as interconnecting pits and indentations with a spiraling or trailing region, consistent with prior observation of ICIC in retrievals (Figure 1). Cobalt was detected in 7 cases, however the metal levels were not as high as levels observed in patients with a failed joint replacement (Table 1). There was no correlation between the metal ion concentration and the damage score on the CoCr femoral condyle. Discussion. This study documents the damage mechanics and associated metallic release into the synovial fluid of “well-functioning” TKA components retrieved at autopsy. It has been suggested that ICIC damage is actually damage from electrocautery during surgery. However, we observed ICIC damage on autopsy retrievals in which the use of electrocautery is unlikely. The damage mechanisms observed on the autopsy TKA components were similar but less severe compared to mechanisms observed in long-term TKA components from revision surgery [1]. More research is needed to better understand the metal release from CoCr femoral components and periprosthetic tissue reactions in TKA

Background. When reversing the hard-soft articulation in inverse shoulder replacement, i.e. hard inlay and soft glenosphere (cf. Figure 1), the tribological behaviour of such a pairing has to be tested thoroughly. Therefore, two hard materials for the inlay, CoCr alloy and alumina toughened zirconia ceramic (ceramys®) articulating on two soft materials, conventional UHMWPE and vitamin E stabilised, highly cross-linked PE (vitamys®) were tested in a joint simulator. Methods. The simulator tests were performed at Endolab GmbH, Rosenheim, Germany, analogue to standardised gravimetric wear tests for hip prosthesis (ISO 14242-1) with load and motion curves adapted to the shoulder. The test parameters differing from the standard were the maximum force (1.0 kN) and the range of motion. A servo-hydraulic six station joint simulator (EndoLab) was used to run the tests up to 5*106 cycles with diluted calf serum at 37° C as lubricant. Visual inspection and mass measurements were done at 0.1, 0.5, 1, 2, 3, 4 and 5 million cycles using a high precision scale and a stereo microscope, respectivly. Results. The wear rates measured in the simulator are summarised in the table below and illustrated in Figure 2. The simulator wear rate of the standard articulation CoCr – UHMWPE is similar to that found in the corresponding pairing for hip endoprosthesis, although the articulation diameter of the glenospheres tested is larger (42 mm compared to 28 – 32 mm in hip joints). Replacing UHMWPE by the cross-linked vitamys®, the wear rate is reduced to about 1/3 for both hard counterparts, CoCr and ceramys®, respectively. Replacing the CoCr inlay by a part made from ceramys® lowers wear by about 37 % in articulation against UHMWPE. This difference is significant (p = 0.002, significance level 5 %). And comparing CoCr and ceramys® against vitamys®, yields a reduction of about 44 %. Which is significant again (p = 0.015, significance level 5 %). The lowest wear rate, with a reduction of about 80 % compared to the standard CoCr – UHMWPE, exhibits the pairing of both advanced materials, ceramys® – vitamys®. Conclusions. Long-term clinical follow-up will confirm if this in-vitro wear reduction leads to longer in-vivo survival of reverse total shoulder arthroplasty. Such a study is under ethic approval, currently. However, the ceramys® inlay offers the benefits of a nickel free inverse shoulder replacement with less x-ray opacity, compared to CoCr. To view tables/figures, please contact authors directly

Introduction. Previous studies of retrieved CoCr alloy femoral heads have identified imprinting of the stem taper surface features onto the interior head bore, leading researchers to hypothesize that stem taper microgrooves may influence taper corrosion. However, little is known about the role of stem taper surface morphology on the magnitude of in vivo corrosion damage. We designed a matched cohort retrieval study to examine this issue. Methods. From a multi-institutional retrieval collection of over 3,000 THAs, 120 femoral head-stem pairs were analyzed for evidence of fretting and corrosion using a visual scoring technique based on the severity and extent of fretting and corrosion damage observed at the taper. A matched cohort design was used in which 60 CoCr head-stem pairs with a smooth stem taper were matched with 60 CoCr head-stem pairs having a micro-grooved surface, based on implantation time, flexural rigidity, apparent length of taper engagement, and head size. This study was adequately powered to detect a difference of 0.5 in corrosion scores between the two cohorts, with a power of 82% and 95% confidence. Both cohorts included CoCr and Ti-6-4 alloy femoral stems. A high precision roundness machine (Talyrond 585, Taylor Hobson, UK) was used to measure surface morphology and categorize the stem tapers into smooth vs. micro-grooved categories. Fretting and corrosion damage at the head/neck junction was characterized using a modified semi-quantitative adapted from the Goldberg method by three independent observers. This method separated corrosion damage into four visually determined categories: minimal, mild, moderate and severe damage. Results. Mild to severe damage (Fretting Corrosion Score ≥ 2) was observed in 75% of the 120 CoCr femoral heads (78% of the heads mated with micro-grooved stems (47/60), Fig. 1A) and 72% of the heads mated with smooth stems (43/60, Fig 1B). Fretting and corrosion damage was not significantly different between the two cohorts when evaluated at the CoCr femoral head bore (p =0.105, Mann Whitney test, Fig. 2A) or the male stem tapers (p =0.428, Fig. 2B). No implant or patient factors were associated with fretting corrosion; corrosion scores were not significantly associated with stem alloy in the two cohorts (p=0.669, Mann-Whitney test). Discussion. The results of this matched cohort retrieval study do not support the hypothesis that taper surfaces with micro-grooved stems exhibit increased in vivo fretting corrosion. We accounted for implant, patient, and clinical factors that may influence in vivo taper corrosion with the matched cohort design and by post hoc statistical analyses. However, this study is limited by the semi-quantitative method used for evaluating damage in these components. Therefore, additional research will be necessary to quantify the volume of metal release from these two cohorts. To view tables/figures, please contact authors directly