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

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

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. 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

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

Metal-on-metal retrieval studies indicated that MOM wear-rates could rise as high as 60–70mm3/year in short-term failures (Morlock, 2008). In contrast, some MOM and ceramic-on-ceramic (COC) devices of 1970's era performed admirably over 2–3 decades (Schmalzreid, 1996; Shishido, 2003). While technology has aided analysis of short-term MOM and COC failures (Morlock 2008; Lord 2011), information on successful THA remains scant. Lack of long-term data creates difficulties in setting benchmarks for simulator studies and establishing guidelines for use in standards. In this study we compared clinical and wear histories for a 30-year MOM and a 32-year COC to establish such long-term, wear-rates. The McKeeTM retrieval was cemented and made 100% of CoCr alloy (Fig. 1a). This patient had a right femoral fracture at 47 years of age, treated by internal-fixation, which failed. Her revision with a Judet implant also failed, leaving her right hip as a Girdlestone. At the age of 68, she had a McKee THA implanted in left hip, and used it until almost 98 years of age (Campbell, 2003). The COC case was a press-fit AutophorTM THA, head and cup made of alumina ceramic, with the only metal being the CoCr stem (Fig. 1c). This was implanted in a female patient 17-years of age active in sports (water-skiing). This modular THA was revised 32-years later due to hip pain from cup migration. Wear on these implants was identified by stereomicroscopy and stained red for photography (Fig. 1). Cup-to-neck impingement was denoted by circumferential neck notching, roughness was assessed by interferometry, and wear determined by CMM (Lord, 2011). McKee head wear covered 1092mm2 area (Figs. 1a, 2: hemi-area ratio 58%). There was no stripe wear and head roughness was 36nm (Ra). Cup wear covered an area of 1790mm2 (hemi-area 63%). Circumferential damage was noted on the supero-posterior femoral neck with scuff marks also on posterior collar (Fig. 2c). Head and cup wear amounted to 37.7 and 25.2mm3, respectively. Total MOM wear was 62.9mm3, indicating a wear-rate of 2.1mm3/year. Ceramic head wear consisted of two circular patterns (Fig. 1c), the major one of area 1790mm2 (hemi-area 79%). No wear stripes were identified. Non-worn and extensively worn surfaces had roughness (Ra) 17nm and 123nm, respectively. The cup showed 360o circumferential arc of rim wear with a small, non-wear zone inferiorly (Fig. 1c). Gray metallic transfer was evident, EDS revealing Co and Cr (Fig. 3a). Head and cup wear volumes were 77.2 and 54mm3, respectively. Total COC wear amounted to 131.2mm3 indicating a wear-rate of 4.1mm3/year. These two THA functioned successfully over 3 decades. The McKee retrieval had minor signs of impingement but no adverse “stripe wear”. This MOM performed satisfactorily due to good positioning and patient's advanced age (68 to 98Yrs of age). The COC patient was 17 years of age at index surgery and active. The ceramic cup showed 360o of edge wear, CoCr transfer and a COC wear-rate double that of the MOM retrieval. Thus the high ceramic wear-resistance protected this youthful patient

Introduction:. The addition of neck-stem modularity of femoral components allowed for increased versatility in controlling stability, head center, and limb length in total hip arthroplasty (THA). Recent reports of neck-stem corrosion, complicated by adverse local tissue reaction, have raised concern and prompted further patient evaluation for revision arthroplasty. Methods:. This was a single center, retrospective case series of thirteen hips in twelve patients. The cohort included eight women and four men, with an average age of 69.5 years (range 50–82), who underwent primary THA with a dual-taper femoral component with a titanium alloy stem, cobalt-chromium (CoCr) alloy modular neck and CoCr alloy head. Patients were followed an average of 34.3 months postsurgical (range 24–38.5 months). Each patient underwent serologic studies including metal ion levels, and Metal Artifact Reduction Sequence (MARS) magnetic resonance imaging (MRI) or Ultrasound. All patients were then referred for fluoro-assisted hip aspiration. Four patients underwent revision surgery. Results:. Ten of thirteen hips were symptomatic at the time of evaluation. ESR and CRP were normal in all patients. Serum Cobalt was elevated in 10/12 patients, with an average serum Cobalt level 4.16 mcg/L (range 1.7–9.4). Serum Chromium levels were normal in all patients. MRI was completed in eleven of twelve patients, with abnormal findings consistent with adverse local tissue reaction in nine hips. Three hips were normal by MRI. One patient had an abnormal ultrasound. Hip aspirations were positive in nine hips, negative in three, and indeterminate in one. Asymptomatic hips (3/13) all had elevated cobalt levels, and 2/3 had positive MRI and aspirates. One patient had a normal MRI and a negative aspirate. Of ten symptomatic hips, eight had elevated cobalt. 7/10 had an abnormal MRI, 2/10 a normal MRI, and 1 abnormal Ultrasound. 5/10 had aspirates that were consistent with the MRI. One aspirate was indeterminate. Four symptomatic patients had discrepancies between MRI findings and aspiration (negative MRI with positive aspirate, or vice versa); one patient had normal labs and MRI, but a positive aspirate, and was noted to have extensive adverse local tissue reaction at revision. Discussion:. Patients with dual-taper femoral stems are at risk of neck-stem corrosion and adverse local tissue reactions. The workup of these patients should include serologic studies as well as advanced imaging with MRI or Ultrasound. Hip aspiration may be a useful adjunct in identifying underlying soft tissue destruction in patients with normal or indeterminate labs or advanced imaging

Introduction. Comprehensive research and retrieval analyses of metal on metal / metal on polyethylene hip fretting and corrosion have been reported. Design choices such as modularity, material couples, geometry and offsets, as well as surgical variability and patient sensitivity have been cited as factors contributing to revision. Findings are informing new designs, surgical techniques and patient testing. However, similar efforts have not been performed on the shoulder. Do reduced joint reaction forces imply lower risk of fretting and corrosion? In this study we designed an accelerated corrosion fatigue (ACF) test specific for the shoulder to allow for evaluation of varying designs, and compared results to a reported shoulder retrieval study [Day ORS 2015]. Methods. Anatomic configuration and reverse shoulder ACF tests were developed with loads and orientations determined from instrumented shoulder data and reported literature. Scaled loads of 1480 N and 962 N were applied to anatomic (Fig 1.A) and reverse (Fig 1.B) prostheses, respectively (n=5 each, with additional assembly control), in potential worse case loading directions (α=25°, β=20°: anatomic; α=0°, β=0°: reverse), at 5 Hz for 3.0 Mc with R=0.1. Test environment included 0.9% NaCl solution at elevated temperature (50° C) and a decreased pH (3.5). Mass, roughness (Ra) and taper damage (modified Goldberg scoring system) measures were taken before and after testing. Taper connections were assembled at impact loads of 3600 N +/− 20% based on cadaveric studies. Goldberg scores for 79 humeral heads and 61 stems from an IRB approved collection served as the comparator. Results. The ACF test methodology caused only fretting in anatomic testing (Fig 2) but both fretting and corrosion in reverse tests (Fig 3). Alloys of Titanium (Ti-6V-4Al and Ti-6Al-7Nb) exhibited higher levels of fretting than CoCr alloys in both test configurations. Significant Ra decreases post-test were noted on all Ti based components, with Ra increases on CoCr based heads and glenospheres (p<0.05). The average mass loss measured in anatomical testing was 1.44 ± 0.35 mg with an average Goldberg score of 1.8 ± 0.3. In the reverse test mass loss was 1.51 ± 0.36 mg with a Goldberg score of 2.4 ± 0.3. Retrievals (implanted 4.6 ± 4.3 years) had weighted average Goldberg scores of 1.6 for heads compared to 2.0 for stems, with the majority of damage from fretting. Discussion. Anatomic and reverse shoulder ACF tests were created that result in levels of taper damage similar to those noted in clinical retrievals (Fig 2, Fig 3). Reverse implant tapers, under reduced loads compared to anatomic but with higher humeral load offset, tend to show higher levels of taper damage in vitro. Under the same assembly conditions, offset is a large contributor to micromotion, fretting, and likely corrosion. With offset and modularity as design options for the shoulder surgeon, care must be taken not to introduce offerings which may lead to significant metal and particle release in vivo. The proposed ACF testing may be one method to evaluate current and proposed shoulder designs

Introduction. Recent advances in nano-surface modification technologies are improving osseointegration response between implant materials and surrounding tissue. Living cells have been shown to sense and respond to cues on the nanoscale which in turn direct stem cell differentiation. One commercially practical surface treatment technique of particular promise is the modification of titanium implant surfaces via electrochemical anodization to form arrays of vertically aligned, laterally spaced titanium oxide (TiO2) nanotubes on areas of implants where enhanced implant–to-bone fixation is desired. Foundational work has demonstrated that the TiO2 nanotube surface architecture significantly accelerates osteoblast cell growth, improves bone-forming functionality, and even directs mesenchymal stem cell fate. The initial in vitro osteoblast cell response to such TiO2 nanotube surface treatments and corresponding in vivo rabbit tissue response are evaluated. Methods. Arrays of 30, 50, 70, 100nm diameter TiO2 nanotubes formed onto titanium surfaces were compared to grit blasted titanium controls in vitro (Figure 1). SEM micrographs of bovine cartilage chondrocytes (BCCs) on the nanotube surfaces were evaluated after 2 hours, 24 hours, and 5 days of culture. Additionally 20 samples each of various nanotube diameters and the non-nanotube treated titanium controls were evaluated after exposure to human mesenchymal stem cell (hMSC) after 2 hours and 24 hours. The left tibia and right tibia of four rabbits were implanted with disk shaped titanium implants (5.0 mm dia. × 1.5 mm) with and without TiO2 nanotubes. The front side of each implant faced the rabbit tibia bone and the back side of the implant had screw holes for post-in vivo tensile testing. After 4 weeks, the bones with implants were retrieved for mechanical testing and histology analysis. Comparative osteogenic behavior on metal oxide nanotube surfaces applied to other implant material surface chemistries including ZrO2, Ta, and Ta2O5 were also evaluated along with TiO2 nanotubes formed on a thin films of titanium on the surface of zirconia and CoCr alloy orthopedic implants. Results. A striking difference in ECM fibril formation and cell clustering on the nanotube substrates is evident in larger diameter nanotubes compared to non-treated titanium as shown by the arrows in Figure 2. The average fracture strength was significantly higher for TiO2 nanotube implants (10.8 N) compared to the grit blasted titanium control implants (1.2 N). The histology at week 4 shown in Figure 3 confirms direct bonded growth of new bone onto the nanotubes with a significantly less trapped amorphous tissue at the implant-bone interface compared to the control. Conclusions. The TiO2 nanotubes significantly enhanced the adhesion and growth of osteoblast cells (in vitro) by 300 to 400% as compared to non-nanostructure surfaces. In vivo implant tests indicate enhanced osseointegration of new bone cells on the TiO2 nanotube implant surface, with a 600% improvement in adhesion strength compared to conventional sand-blasted titanium surfaces. Discussion. Both in vitro and in vivo analysis indicates that TiO2 nanotubes enhance the speed and proliferation of osseointegration. This surface treatment technique can be applied to non-porous or porous surfaces on implants where optimized bone fixation is desired