Aims. Dual mobility implants in total hip arthroplasty are designed to increase the functional head size, thus decreasing the potential for dislocation. Modular dual mobility (MDM) implants incorporate a metal liner (e.g. cobalt-chromium alloy) in a metal shell (e.g. titanium alloy), raising concern for mechanically assisted crevice corrosion at the modular liner-shell connection. We sought to examine fretting and corrosion on MDM liners, to analyze the corrosion products, and to examine histologically the periprosthetic tissues. Methods. A total of 60 retrieved liners were subjectively scored for fretting and corrosion. The corrosion products from the three most severely corroded implants were removed from the implant surface, imaged using scanning electron microscopy, and analyzed using Fourier-transform infrared spectroscopy. Results. Fretting was present on 88% (53/60) of the retrieved liners, and corrosion was present on 97% (58/60). Fretting was most often found on the lip of the taper at the transition between the lip and the dome regions. Macrophages and particles reflecting an innate inflammatory reaction to corrosion debris were noted in six of the 48 cases for which periprosthetic tissues were examined, and all were associated with retrieved components that had high corrosion scores. Conclusion. Our results show that corrosion occurs at the interface between MDM liners and shells and that it can be associated with reactions in the local tissues, suggesting continued concern that this problem may become clinically important with longer-term use of these implants. Cite this article: Bone Joint J 2021;103-B(7):1238–1246

Introduction. In THA, fretting corrosion at the head-stem taper junction has emerged as a clinical concern that may result in adverse local tissue reactions, even in patients with a metal-on-polyethylene bearing [1]. Taper junctions that employ a ceramic head have demonstrated reduced corrosion at the interface [2]. However, during revision surgery with a well-fixed stem, a titanium sleeve is used in conjunction with a ceramic head to ensure proper fit of the head onto the stem and better stress distribution. In vitro testing has suggested that corrosion is not a concern in sleeved ceramic heads [3]; however, little is known about the in vivo fretting corrosion of the sleeves. The purpose of this study was to investigate fretting corrosion in sleeved ceramic heads. Materials and Methods. Between 2001 and 2014, 35 sleeved ceramic heads were collected during revision surgery as part of a multi-center retrieval program. The sleeves were all fabricated from titanium alloy and manufactured by 4 companies (CeramTec (n=14), Smith & Nephew (Richards, n=11), Stryker (n=5), and Zimmer (n=5)). The femoral heads were made from 3 ceramics (Alumina (n=7), Zirconia (n=11), and Zirconia-toughened Alumina (n=17)). Sleeve dimensions (length and thickness) were measured using calibrated calipers. Fretting corrosion of the sleeves and available associated stems was scored using a 4-point, semi-quantitative scoring system [4], with 1 being little-to-no damage, and 4 corresponded to severe fretting corrosion. Five sleeves could not be extracted; thus the external surface was not scored. Results. Moderate-to-severe fretting corrosion scores (Score ≥ 2) were observed in 97% (34/35) of internal tapers (sleeve-femoral stem contact), 57% (17/30) of external tapers (sleeve-femoral head contact), and 65% (11/17) of the stems. The internal sleeve had higher fretting corrosion scores than the external taper (Mean Score Difference [MSD] = 1.1; p = 0.001) and stem (MSD = 0.7; p = 0.016). Fretting corrosion scores were correlated with implantation time at all surfaces (Rho ≥ 0.53; p ≤ 0.015). Scores were not correlated with sleeve dimensions (p > 0.05). Fretting corrosion scores of the external sleeve correlated directly with activity level (p = 0.005) and inversely with patient age (p = 0.03). Discussion. The retrieval data shows that fretting corrosion can occur in these components, particularly on the internal surface of the sleeve. The corrosion scores were similar to levels observed in prior studies of tapers in CoCr heads [2]. Implantation time was the main predictor of increased fretting corrosion. The impact of ceramic material and sleeve design currently remain unclear as the analyses were confounded with implantation time. Thus, more detailed and quantitative analyses are required to fully determine the factors that influence fretting corrosion of sleeved ceramic heads in THA

Introduction. Fretting crevice-corrosion (tribocorrosion) of metallic biomaterials is a major concern in orthopedic, spinal, dental and cardiovascular devices. 1. Stainless steel (i.e., 316L SS) is one alloy that sees extensive use in applications where fretting, crevices and corrosion may be present. While fretting-corrosion of this alloy has been somewhat studied, the concept of fretting-initiating crevice corrosion (FICC), where an initial fretting corrosion process leads to ongoing crevice-corrosion without continued fretting, is less understood. This study investigated the susceptibility of 316L SS to FICC and the role of applied potential on the process. The hypothesis is crevice-corrosion can be induced in 316L SS at potentials well below the pitting potential. Materials and Methods. A pin-on-disk fretting test system similar to that of Swaminathan et al. 2. was employed. Disks were ∼35 mm in diameter and the pin area was ∼500 mm. Samples were polished to 600 mm finish, cleaned with ethanol and distilled water. An Ag/AgCl wire as the reference, a carbon counter electrode and phosphate buffered saline (PBS, pH 7.4, Room T) were used for electrochemical testing. Load was controlled with a dead-weight system, monitored with a six-axis load cell (ATI Inc.). Interfacial motion was captured with a non-contact eddy current sensor (0.5 mm accuracy). Motion and load data acquisition was performed with Labview (National Instruments). Samples were loaded to ∼2 N. The potential per tests was increased from −250 to 250 mV (50 mV increments) with new locations and pins used in each repeat (n=3). Testing incorporated a 1 min rest before fretting (5 min, 1.25 Hz, 60 mm displacement saw tooth pattern). Fretting ceased and the load was held while currents were captured for another 5 min to assess ongoing crevice corrosion. Results. Testing showed that crevice corrosion can be initiated within minutes of fretting (or in a few cycles depending on potential; Fig. 1). Potentials as low as −100 mV showed evidence of corrosion, while sustained crevice corrosion was seen at −50 mV. As the potential increased above −50 mV, susceptibility to FICC increased. Fig. 2 is a typical cyclic polarization curve for 316L SS in PBS without fretting. Pitting starts at 400 mV vs Ag/AgCl, and the protection potential in this case is around potentials where FICC can be induced. Discussion. This study showed that 316L SS is prone to FICC starting at −100 mV and the severity of the crevice-corrosion damage depends on the applied potential (Fig. 3). Current after cessation of fretting takes longer to return to baseline or does not return indicating ongoing corrosion without fretting (Fig. 1). If the pin and disk are separated, the crevice-corrosion process stops immediately. The region immediately outside the fretting contact was crevice-like with a very small separation distance between the pin and disk surface which allowed crevice corrosion to develop (Fig. 3). Conclusion. 316L SS can undergo FICC at potentials close to normal physiological electrode potential conditions. Few fretting cycles are required to develop conditions for continued crevice-corrosion. Higher potentials increased the susceptibility of FICC in 316L SS

Introduction. During revision surgery with a well-fixed stem, a titanium sleeve can be used in conjunction with a ceramic head to achieve better stress distribution across the taper surface. Previous studies have observed that the use of a ceramic head can mitigate the extent of corrosion damage at the taper. Moreover, in vitro testing suggests that corrosion is not a concern in sleeved ceramic heads [1]; however, little is known about the in vivo fretting corrosion of the sleeves. The purpose of this study was to investigate fretting corrosion in sleeved ceramic heads. Materials and Methods. Thirty sleeved ceramic heads (Biolox Option: CeramTec) were collected during revision surgery as part of a multi-center retrieval program. The sleeves were used in conjunction with a zirconia-toughened alumina femoral head. The femoral heads and sleeves were implanted between 0.0 and 3.25 years (0.8±0.9, Figure 1). The implants were revised predominantly for instability (n=14), infection (n=7), and loosening (n=5). Fifty percent of the retrievals were implanted during a primary surgery, while 50% had a history of a prior revision surgery. Fretting corrosion was scored using a previously described 4-point, semi-quantitative scoring system proposed by Higgs [2]. Results. Among the sleeved ceramic heads, mild-to-moderate fretting corrosion scores (Score = 2–3) were observed in 96% of internal tapers, 26% of external tapers, and 82% of the stems. On the internal taper surface, 5 sleeves had moderate fretting corrosion data (Score = 3, Figure 2). None of sleeves had severe (Score = 4) at any taper surface. Fretting corrosion scores were higher at the internal taper surface than the external taper. Implantation time was the main predictor of increased fretting-corrosion of the external sleeve tapers. Discussion. For the sleeved ceramic heads, we found that fretting corrosion can occur in these components, particularly on the internal surface of the sleeve. However, the fretting corrosion scores were predominantly mild, and lower than fretting scores of CoCr heads in metal on polyethylene bearings. Because the sleeves are Ti alloy, the corrosion products are considered to be less cytotoxic than Co and Cr. The primary limitation to this study is the short-term follow-up of these retrievals. As the fretting corrosion process is often associated with in vivo duration, future studies with longer-term implants are necessary to elucidate the long-term performance of these devices

Fretting corrosion of taper junctions is long known and of great concern, because of metal ion and particle release and their related adverse local and systemic effects on the human body (1–3). Orthopedic taper junctions are often comprised of CoCr29Mo6/TiAl6V4 pairings. Beside others the imprinting of the TiAlV-machining marks into the CoCrMo-taper is of clinical interest (4, 5). Thus, the multifactorial details and their interdependencies on the macro-, micro, and nanoscale are still a matter of research (6). This contribution presents the mechanisms of imprinting found in an in-vitro fretting corrosion test. The worn surfaces, the lubricant as well as its remains were analyzed after test and the findings brought into relation to the characteristic wear sub-mechanisms. The fretting tests were conducted by means of a cylinder-on-pin set-up. All details about the test and the sequence of analyses can be found in (7, 8). A marked tribofilm of C-rich organic matter and oxidized wear particles of both bodies was generated at the TiAlV/CoCrMo contact area (Figure 1a, c). After removing the tribofilm chemically, extremely fine scratches of sub-µm depth became visible on the CoCrMo body (Figure 1b). The TiAlV body showed shallow shelves leaving troughs filled with grainy debris (Figure 1d) mainly of Ti-oxide wear particles. The shelves stick to the surfaces and, therefore, move relatively to the counterbody. In combination with the grainy debris this brings about “Microploughing” on the CoCrMo surfaces. Microploughing is known for destroying any passive film resulting in “Tribocorrosion”. The question remains how the shelves are formed. From the surface analyses one could conclude that they point towards “Delamination”. But this would also mean that they would not stick rigidly to the surfaces but be ejected from the contact area. Focused Ion Beam (FIB) cuts were done in order to investigate the near- and subsurface structure of the shelves in order to clarify the governing mechanisms (Figure 2). Below the platinum protection layer appears a laminated structure of highly deformed nanocrystalline and amorphous areas. EDS confirmed that the lighter intermediate layers consist mainly of Ti-oxide. This microstructure is supposedly formed by severe plastic deformation and the generation of shear bands, which under fretting pile up on top of each other. This cannot be connected to “Delamination”. We therefore propose to categorize the formation mechanism of these shelves as a specific form of microploughing. Thus, imprinting is neither driven by any galvanic effects (9) nor by hardness differences of TiO. 2. and Cr. 2. O. 3. (10) but by microploughing on the TiAlV-body leading to tribocorrosion at specific sites of CoCrMo what imprints the surface grooves of the softer TiAlV into the harder CoCrMo. For any figures or tables, please contact the authors directly

Introduction. Fretting corrosion of the modular taper junction in total hip arthroplasty has been studied in several finite element (FE) investigations. In FE analyses, different parameters can be varied to study micromotions and contact pressures at the taper interface. However, to truly study taper wear, the simulation of micromotions and contact pressures in non-adaptive FE models is insufficient, as over time these can change due to interfacial changes caused by the wear process. In this study we developed an FE approach in which material removal during the wear process was simulated by adaptations to the taper geometry. The removal of material was validated against experiments simulating the clinical fretting wear process. Method. Experimental test: An accelerated fretting screening test was developed that consistently reproduced fretting wear features observed in retrievals. Biomet Type-1 (4°) tapers and +9 mm offset adaptors were assembled with a 4 kN force (N=3). A custom head fixture was used to create an increased offset and torque. The stems were potted in accordance with ISO 7206–6:2013. The set-up was submerged in a 37°C PBS solution with a pH adjusted to 3 using HCL and NaCl concentration of 90gl. −1. The components were cyclically loaded between 0.4 – 4 kN for 10 million cycles. After completion, the volumetric and linear wear was measured using a Talyrond-585 roundness measurement machine. FE model: This was created to match the experimental set up (Figure 1). Taper geometry and experimental material data were obtained from the manufacturer (Zimmer Biomet). The coefficient of friction of the studied combination of components was based on previous experiments (Bitter, 2016). After each change in load the geometry was updated by moving nodes inwards perpendicular to the taper surface. Archard's Law (Archard, 1953) was used to calculate the wear with the following equation: H=k*p*S. Where H is the linear wear depth in mm, k is a wear factor (mm³/Nmm), p is the contact pressure (MPa) and S is the sliding distance (mm). The 10 million experimental cycles were simulated using a range of 5 to 200 computational cycles. For this purpose, the wear factor (k) was scaled for each simulation to match the volumetric wear found in the experiments. Results. The accelerated fretting experiments resulted in an average volumetric wear of 0.79 mm³ after 10 million cycles. A thumbprint shaped wear patch was observed on the inferior-distal and superior-proximal side of the taper (Figure 2). Optimal results were found using 100 simulated cycles, and a wear factor of 1.25*10. −6. (mm. 3. /N*mm), balancing accurate results with computational time. The maximum wear depth found in the experiments was found to be 15 µm whereas the simulations predicted a maximum linear wear of 9.5 µm(Figure 3). Discussion and Conclusion. In this study we have shown that we can accurately model wear at the taper junction. The model was validated with experiments using the measured volumetric and linear wear. With this model we will look at the effect of several patient, implant, and surgical parameters on the volumetric wear

Background. Fretting at modular junctions is thought to be a ‘mechanically assisted’ corrosion phenomenon, initiated by mechanical factors that lead to increased contact stresses and micromotions at the taper interface. We adopted a finite element approach to model the head-taper junction, to analyse the contact mechanics at the taper interface. We investigated the effect of assembly force and angle on contact pressures and micromotions, during loads commonly used to test hip implants, to demonstrate the importance of a good assembly during surgery. Methods. Models of the Bimetric taper and adaptor were created, with elastic-plastic material properties based on material tests with the actual implant alloy. FE contact conditions were validated against push-on and pull-off experiments. The models were loaded according to ISO 7206-4 and −6, after being assembled at 2-4-15kN, both axially and at a 30° angle. Average micromotions and contact pressures were analysed, and a wear score was calculated based on the contact pressures and micromotions. Results. The average contact pressure decreased when a higher assembly force was used, with loads being distributed over a larger contact area, but increased when tested at a 30° angle. Average micromotions reduced with a higher assembly load, except when assembled at a 30° angle. The wear score decreased with increasing assembly force, when applied perpendicularly, while when assembled at a 30° angle, the wear score did not reduce with assembly force. Conclusions. The location and patterns of micromotions were consistent with retrieved tapers and those generated in in-vitro test models. Increased impaction loads reduced the average amount of micromotion and fretting. We intend to apply more complex loading regimes in future analyses, enabling to study phenomena such as edge loading and frictional torque. Level of evidence. IIb - Experimental study. Disclosure. This study was financially supported by Biomet UK Healthcare Ltd

Introduction. Fretting corrosion at the taper interface has been implicated as a possible cause of implant failure. Using in-vitro testing, fretting wear observed at tapers of retrieved implants may be reproduced (Marriott, EORS-2014). In order to reduce time and cost associated with experimental testing, a validated finite element method (FE) can be employed to study the mechanics at the taper. In this study we compared experimental and representative FE simulations of an accelerated fretting test set-up. Comparison was made by between the FE wear score and volumetric material loss from the testing. Methods. Experimental test set-up: An accelerated wear test was developed that consistently reproduced fretting wear features observed in retrievals. Biomet stems with smooth 4° Type-1 tapers were combined with Ti6Al4V Magnum +9 mm adaptors using a 2 or 15 kN assembly force. The head was replaced with a custom head fixture to increase the offset and apply a torque at the taper interface. The stems were potted according to ISO 7206-6:2013. The set-up was submerged in a test medium containing PBS and 90gl-1 NaCl. The solution was pH adjusted to 3 using HCl and maintained at 37°C throughout the tests. For each assembly case, n=3 tests were cyclically loaded between 0.4–4 kN for 10 Million cycles. Volumetric wear measurements were performed using a Talyrond-365 roundness measurement machine. The FE model was created to replicate the experimental set up. Geometries and experimental material data were obtained from the manufacturer (Biomet). The same assembly forces of 2 and 15 kN were applied, and the same head fixture was used for similar offset and loading conditions. The 4 kN load was applied at the same angles in accordance with ISO 7206-6:2013. Micromotions and contact pressures were calculated, and based on these a wear score was determined by summation over all contact points. Results. The FE wear score showed a significant drop after an assembly force of 15 kN has been applied. The micromotion scores were similar, and the contact pressure was higher due to the larger assembly force. The volumetric wear measurements did not show a significant difference between the two assembly cases due to the large variation in measured values. A downward trend can be observed when applying higher assembly forces, similar to the trend seen at the FE wear score (figure 1, table1). Discussion. This study shows a correlation between experimental and FE simulation, however highlights the difficulty in validating a FE model with complex in-vitro experiments. Due to the nature of experimental testing, it is impossible to remove all sources of error associated with the set-up. The use of a single static load and the absence of fluids and corrosion processes means that the full mechanics of the wear process could not be fully replicated. Despite these deficiencies the general trends and wear patterns observed in the experimental setup were reproduced. Further studies will focus on including the interplay between the aforementioned properties, to provide a better simulation of the fretting processes occurring at the taper junction

INTRODUCTION. The role and importance of fretting and corrosion in modular hip endoprostheses has become of more and more interest within the last years. Especially bearing couples with large diameters may experience high friction moments leading to an increase of relative micro movements between the surfaces of the taper connections. Recently published studies show that the risk of fretting and corrosion is significantly reduced by using ceramic ball heads compared to metal ball heads. OBJECTIVES. Goal of this study was to investigate the risk of fretting and corrosion as well as possible loosening of large ceramic ball heads with metal sleeves. METHODS. BIOLOX. ®. OPTION systems have been investigated, consisting of ceramic ball heads (BIOLOX. ®. delta) with sleeves (Ti6Al4V) using generic tapers made of different metals (Ti6Al4V, FeCrNiMo, CoCrMo):. Fretting test according to ASTM F1875-98 (IIb). Corrosion test under in-vivo-like fatigue loading. Simulator test creating large frictional moments. Ad B): If corrosion occurs under in-vivo-like conditions and compromises the connection between the modular parts, was investigated using three different consecutive scenarios. At first, a fatigue test was performed in a corrosive medium with 4.5Mio. cycles under a load of 4.5kN. Afterwards, a very high axial load of 10kN was applied for 0.5Mio. cycles. Finally, pull-off tests were performed and compared to reference samples. RESULTS. In the ASTM test, for all taper materials under investigation, decreasing corrosion currents on a comparatively low level have been measured. The interface strength between both the taper/sleeve surface and the sleeve/ball head surface did not changed significantly after fatigue loading and storage in a corrosive medium. Even though large bending moments and torques were applied in the simulator test, no loosening between the components was observed. The analysis of the involved surfaces exhibited only plastic deformation of the microstructure and tribochemical reaction layers as expected. No signs of excessive corrosion was found. CONCLUSIONS. The results of the fretting and corrosion tests of ceramic ball heads with adapter sleeves exhibited no signs of noticeable corrosion even under adverse conditions (large ball head diameter, high inclination, large bending moments and torques). No loosening events have been observed. The proper assembling of the involved modular components (dry, no debris between the surfaces) according to the manufacturer´s Instructions For Use is an essential requirement hereby

Introduction:. Modular necks allow intra-operative adjustment of neck length, offset, and version, enabling the surgeon to better match leg length and accommodate anatomical differences. However, there have been recent reports of early fatigue failures of the neck initiating from the neck/stem taper, and some retrieved components exhibit severe fretting corrosion. 1. Fatigue testing according to ISO 7206-6 (10/9 orientation) has been shown to replicate the clinical fatigue failures, but results in relatively minor fretting and corrosion. The purpose of this pilot study was to evaluate techniques for accelerating fretting corrosion with the goal of replicating the most severely corroded clinical retrieval cases. Methods:. Constructs tested in this study consisted of a single stem and neck design (PROFEMUR modular, Wright Medical Technology). The worst case long varus neck design was evaluated in two materials: Ti6Al4V and wrought CoCr. In vitro fatigue testing in the 10/9 configuration was conducted at 10 Hz in unbuffered, aerated saline. Fretting mass loss, distraction force, and assessment of taper corrosion via SEM/EDS were measured. Methods used to exacerbate fretting corrosion are shown in Figure 2. Results:. Test results & conditions are shown in Figure-2. All of the constructs impacted per surgical technique survived 5 Mc and were similar to constructs tested under standard conditions (Figure-1a). In contrast, Ti neck constructs that were hand assembled failed in fatigue after a surprisingly small number of cycles. The hand-assembled constructs that survived 5 Mc of loading exhibited lower distraction forces, higher than normal fretting mass loss, and moderate to severe corrosion of the taper. In particular, constructs that were hand-assembled and tested at elevated temperature with a rest period had much higher fretting mass loss and a level of corrosion that is qualitatively similar to corroded retrievals (Figures-1b, d). The CoCr necks that were hand assembled survived 10 Mc, but one of them fractured during distraction, and they exhibited higher fretting and corrosion at 5 Mc (Figure-1c). The effect of adding acidified saline to the stem pocket was unclear, but elevating the temperature and adding a rest period resulted in a significant increase in fretting and corrosion. Discussion:. Pallini et al. 2. recommended light tapping based on tests that showed distraction forces were equal between hammer impacted necks and hand assembly followed by simulated normal walking. The simulated gait loads in Pallini's study were applied in line with the neck taper's axis, whereas in the present study, they were applied in the 10/9 orientation, which is considerably off-axis. It is also notable that while the CoCr necks performed significantly better than Ti necks after hand-assembly, their performance was still markedly reduced compared to well-impacted constructs. Conclusion:. This study has shown conclusively that failure to impact modular neck connections can have a devastating effect on taper fretting and corrosion, leading to early fatigue failure. Applicability to other designs and to lightly impacted necks requires further study

Introduction. MDM implants can enhance stability in total hip replacement (THR), but complications include malseated liners and corrosion between the cobalt-chrome liner and titanium acetabular shell increased systemic metal ion levels. The liner-shell junction has the potential for fretting corrosion, and the corrosion could be exacerbated in malseated liners. We determined the potential for fretting corrosion in malseated versus well-seated liners using a mechanical electrochemical corrosion chamber. Methods. Four pristine MDM liners and shells were tested. Two liners were well-seated into their shells; two were canted at 6°. The liner-shell couples were assembled with a 2kN force after wetting the surfaces to promote a crevice environment conducive to corrosion. Couples were fixed in an electrochemical chamber at 40° inclination/20° anteversion to the load axis. The chamber was filled with phosphate buffered saline and setup as a three-electrode configuration: the shell as the working, a saturated calomel electrode as the reference, and a carbon rod as the counter electrode. A potentiostat held the system at −50mV throughout testing. After equilibration, couples underwent cyclic loading of increasing magnitudes from 100 to 3400N at 3 Hz. Fretting current was measured throughout, and the onset load for fretting was determined from the increase in average current. Results. Well-seated liners showed lower fretting current values at all peak compressive loads greater than 800 N (p<0.05). Canted liners demonstrated a fretting onset load of 2400 N, and fretting currents at greater than 2400 N were larger than those at lower peak compressive loads (p<0.05). Conclusion. The clinical consequences of MDM liner malseating remain unknown, but our results demonstrate earlier fretting current onset at lower peak loads when compared to well-seated liners. The onset loads were consistent with physiologic loads for daily activities. Our findings are significant given the potential for metallosis and adverse local tissue reactions. For any tables or figures, please contact the authors directly

Introduction. Bearing surfaces of metal-on-metal (MoM) hip resurfacing devices and total hip replacements (THRs) are a known source of metallic debris. Further, large diameter heads and the high friction of a MoM joint are thought to lead to fretting and corrosion at the taper interface between modular components. 1. The metal debris generated can cause significant problems on the joint area. 2. This paper investigated fretting and corrosion of femoral head-neck junctions. Variables of the head-neck junction which may have an effect on fretting and corrosion were identified with the aim of determining the key drivers so that their risk on fretting and corrosion could be reduced through design. Additionally, a Chromium Nitride (CrN) coating was assessed to determine the effect on fretting and corrosion of coating the stem (male), head (female) or both trunnion interfaces. As there is currently no standard specification for a head-neck trunnion interface and trunnion designs vary significantly across the market, this work may lead to a positive change in the design and materials used in head-neck taper interfaces for all THR devices. Methods. Suitable head and stem combinations were identified to enable individual variables such as; coating, medial-lateral (M-L) offset, head offset and taper angle to be isolated (Figure 1 and Figure 2). For the coated components a 3 μm CrN coating was applied to trunnion using electron beam physical vapour deposition (Tecvac, Cambridge, UK). Fretting and corrosion testing was carried out in accordance with ASTM F1875-98 (2009) method II procedure B. 3. following assembly of the components under a 2 kN load. Results. For the majority of the testing the CrN coating reduced the fretting and corrosion. Tests showed that increasing the M-L offset decreased the dynamic current but increased the static current. The results also demonstrated that increasing the head offset increases the fretting and corrosion. Taper angle did not appear to significantly alter either fretting or corrosion. Discussion. There are many peer reviewed papers regarding fretting and corrosion observed in vivo and the consequence of this on the patient. 4,5,6. To the author's knowledge this systematic identification of individual variables accountable for damaged caused to the taper junction is the first of its kind. Previous issues have been identified with CrN coatings. 7. , however the coating used here has already been shown to be very durable as a bearing surface coating under long term tests. 8. The results presented here are therefore encouraging as they also demonstrate that both fretting and corrosion can be reduced by the addition of a CrN coating to trunnion surfaces. The M-L offset results indicated that fretting may have different root causes to corrosion, as different trends were seen for dynamic and static currents. Increasing the head length increased fretting and corrosion, while altering the taper angle had no significant effect. Further work is therefore required to establish additional trends to enable design optimisation

Background:. Previous studies regarding modular head-neck taper corrosion were largely based on cobalt chrome (CoCr) alloy femoral heads. Less is known about head-neck taper corrosion with ceramic femoral heads. Questions/purposes:. We asked (1) whether ceramic heads resulted in less taper corrosion than CoCr heads; (2) what device and patient factors influence taper fretting corrosion; and (3) whether the mechanism of taper fretting corrosion in ceramic heads differs from that in CoCr heads. Methods:. One hundred 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 50 ceramic head-stem pairs were matched with 50 CoCr head-stem pairs based on implantation time, lateral offset, stem design, and flexural rigidity. Results:. Fretting and corrosion scores were lower for the stems in the ceramic head cohort (p = 0.03). Stem alloy (p = 0.004; TMZF) and lower stem flexural rigidity (Spearman's rho = −0.32, p = 0.02) predicted stem fretting and corrosion damage in the ceramic head cohort but not in the metal head cohort. The mechanism of mechanically assisted crevice corrosion was similar in both cohorts although in the case of ceramic femoral heads, only one of the two surfaces (the male metal taper) engaged in the oxide abrasion and repassivation process. Conclusions:. The results suggest that by using a ceramic femoral head, CoCr fretting and corrosion from the modular head-neck taper may be mitigated but not eliminated. Clinical Relevance:. The findings of this study support further study of the role of ceramic heads in potentially reducing femoral taper corrosion

Introduction:. High failure rates with large diameter, metal on metal hip replacements have highlighted a potential issue with the head/stem taper junction as one of the significant sources of metal ion release. Postulated reasons as to why this may be such a problem with large head metal on metal hip replacements is due to the increased torque achieved by the larger head size. This may be responsible for applying greater micromotion between the head and stem taper and consequently greater amounts of fretting corrosion. The aim of this study was to perform short term in vitro electrochemical tests to assess the effect of increasing head diameter and torque on the fretting corrosion susceptibility of the head/stem taper interface and to investigate its effect on different material combinations. Methods:. 36 mm Cobalt Chrome (CoCr) femoral heads were coupled with either a CoCr or Titanium (Ti) stem with 12/14 tapers, all with a smooth surface finish. Increasing perpendicular horizontal offsets in the sagittal plane created incremental increases in torque. Offset increments of 0 mm, 5.4 mm and 7.5 mm were selected (Figure 1) to simulate the torque force equivalent to 9 Nm, 12 Nm and 17 Nm. An inverted hip replacement setup was used (ASTM F1875-98) (Figure 2). Components were statically loaded at 0 kN and 2.3 kN prior to sinusoidal cyclic loading and electrochemical testing. Mean & fretting currents were calculated every 50 cycles up to a maximum of 1000 cycles of sinusoidal cyclic loading at 3 Hz along with the Overall Mean Current (OMC), Overall Mean Fretting Current (OMFC) and Overall Current change (OCC). Results:. There was a significant increase in the mean current (R = 0.992, p = 0.008) and fretting current (R = 0.929, p = 0.071) for CoCr-CoCr and in the mean current (R = 0.780, p = 0.005) and fretting current (R = 0.810, p = 0.006) for CoCr-Ti material combinations, with increasing femoral offsets. The highest currents (mean and fretting) were produced at 7.5 mm and the lowest at 0 mm offsets. The proportional relationship between torque and corrosion was observed for both CoCr-CoCr and CoCr-Ti material combinations. With low torques we saw higher OMC and OMFC with the Co-Ti material combination however with higher torques we saw higher OMC and OMFC with the CoCr-CoCr combination (Figure 3). Conclusion:. Increasing torque leads to increased susceptibility to fretting corrosion at the modular head/stem taper interface of total hip replacements for both head stem material combinations. This study highlights the risk of high frictional torque, independent of material combination, on the head/ stem with the use of large heads. This is particularly relevant with the increasing use of larger diameter femoral heads across all bearing material combinations, in current hip arthroplasty practice

Introduction. Fretting corrosion at the Head-Neck taper interface of Large Metal on Metal (MoM), Metal on Polymer (MoP) and Ceramic on Ceramic (CoC) total hip arthroplasty (THA) remains a clinical concern. Ceramic femoral heads have gained a lot of attention more recently as a possible way to mitigate/reduce the dissolution of Cobalt Chromium ions. The objective of this study is to assess the fretting corrosion currents emanating from four material combinations for which Ti6Al4V and Co28Cr6Mo are the neck components of Co28Cr6Mo and BIOLOX®delta femoral heads at three different cyclic loads. Method. 12/14 Ti6Al4V and Co28Cr6Mo spigots (designed to geometrically represent the stem) were impacted against Ø36mm Co28Cr6Mo and BIOLOX®delta femoral heads with a static force of 2kN as shown in Figure 1. The tapers were immersed in 25% v/v diluted Foetal Bovine Serum, PBS balance and 0.03% Sodium Azide at room temperature. In-situ electrochemistry was facilitated using a 3-eletrode cell arrangement whereby the neck components were the working electrode, Ag/AgCl was the reference electrode and a platinum counter electrode completed the cell. All combinations were held at a potential of 0V vs. Ag/AgCl and the cyclic load applied unto each couple were 1kN, 3kN and 5kN at 1Hz consecutively (see Figure 2). The fretting corrosion currents were converted into cumulative charge transferred (Q) by integrating the wear enhanced corrosion current. Results and Discussion. Bergmann et al.1 plotted the loading profile of a patient weighing 1000N doing various daily living activities. In their study, the range in loading cycles vary from 1kN (standing on one leg) to ∼9kN (stumbling). For this study, Figure 2 shows the sinusoidal loading profile used and the corresponding charge transferred as a result of wear enhanced corrosion. The results reveal an increase in the cumulative charge for all four combinations as cyclic load increases. While for all combinations, no negligible amount of cumulative charge was measured at 1kN, no significant difference was observed at 3kN and at 5kN, the charge transferred from both MoM and CoM fretting couples where Ti6Al4V is the neck component were significantly lower than the couples with Co28Cr6Mo neck (see figure 3). The BIOLOX®delta – Ti6Al4V couple was observed to generate the least wear enhanced corrosion current. This, we observe, is due to thick agglomerated oxides resulting from wear and corrosion products which can adhere to the anodic fretting interface (see figure 3). Conclusion. This study reveals that for both MoM and CoM combinations, the charge transferred through wear enhanced corrosion of Ti6Al4V prove to be significantly lower than the combinations with Co28Cr6Mo alloy. Furthermore, this study proposes that the agglomeration of wear and corrosion products (oxides) can lead to the reduction of fretting corrosion currents at modular fretting interfaces as seen in combinations involving Ti6Al4V alloys. This is relevant as titanium alloys are known to form thick oxides at fretting contacts. For figures/tables, please contact authors directly.

Introduction. Wear debris generation in metal-on-metal (MOM) total hip arthroplasty (THA) has emerged as a compelling issue. In the UK, clinically significant fretting corrosion was reported at head-taper junctions of MOM hip prostheses from a single manufacturer (Langton 2011). This study characterizes the prevalence of fretting and corrosion at various modular interfaces in retrieved MOM THA systems used in the United States. Methods and Materials. 106 MOM bearing systems were collected between 2003 and 2012 in an NIH-supported, multi-institutional retrieval program. From this collection, 88 modular MOM THA devices were identified, yielding 76 heads and 31 stems (22 modular necks) of 7 different bearing designs (5 manufacturers) for analysis. 10 modular CoCr acetabular liners and 5 corresponding acetabular shells were also examined. Mean age at implantation was 58 years (range, 30–85 years) and implantation time averaged 2.2 ± 1.8 years (range, 0–11.0 years). The predominant revision reason was loosening (n=52). Explants were cleaned and scored at the head taper, stem taper, proximal and distal neck tapers (for modular necks), liner, and shell interfaces in accordance with the semi-quantitative method of Goldberg et al. (2002). Results. Fretting and corrosion were observed on 68/76 (89%) head tapers, 21/31 (68%) stem tapers, 15/22 (68%) proximal modular neck tapers, 20/22 (91%) distal modular neck tapers, 10/10 (100%) modular liners and 5/5 (100%) modular shells. Scores were lower at proximal stem tapers than within the head tapers (p = 0.001) but were positively correlated (ρ = 0.56, p = 0.001). At the head-neck interface, significantly more damage was noted on head tapers of devices with modular necks (p<0.001). At the neck-stem interface, damage to modular necks was localized at the curved medial and lateral surfaces. A significant correlation was observed between implantation time and corrosion/fretting score at this region (ρ = 0.78, p < 0.001). Damage was noted at all shell-liner interfaces, manifested primarily as scratching with discoloration on the backside rim of liners and circular fretting patterns on shells. Discussion. These results support the inclusion of fretting and corrosion evaluation in standardized MOM retrieval inspection protocols. Adaptation of the method developed by Goldberg and colleagues is suitable for the variety of modular connections in contemporary MOM THA implants, which may incorporate modular femoral and/or acetabular components. Further quantitative assessment of wear at modular interfaces of retrieved MOM devices is therefore warranted

Introduction. Recent implant design trends have renewed concerns regarding metal wear debris release from modular connections in THA. Previous studies regarding modular head-neck taper corrosion were largely based on cobalt chrome (CoCr) alloy femoral heads. Comparatively little is known about head-neck taper corrosion with ceramic femoral heads or about how taper angle clearance influences taper corrosion. This study addressed the following research questions: 1) Could ceramic heads mitigate electrochemical processes of taper corrosion compared to CoCr heads? 2) Which factors influence stem taper corrosion with ceramic heads? 3) What is the influence of taper angle clearance on taper corrosion in THA?. Methods. 100 femoral head-stem pairs were analyzed for evidence of fretting and corrosion. A matched cohort design was employed in which 50 ceramic head-stem pairs were matched with 50 CoCr head-stem pairs based on implantation time, lateral offset, stem design and flexural rigidity. Fretting corrosion was assessed using a semi-quantitative scoring scale where a score of 1 was given for little to no damage and a score of 4 was given for severe fretting corrosion. The head and trunnion taper angles were measured using a roundness machine (Talyrond 585, Taylor Hobson, UK). Taper angle clearance is defined as the difference between the head and trunnion taper angles. Results. The fretting corrosion scores were significantly lower for the stems in the ceramic head cohort when compared with the CoCr cohort. Stem alloy and stem flexural rigidity were predictors of stem fretting and corrosion damage in the ceramic head cohort, however not for the CoCr cohort. The mechanism of mechanically assisted crevice corrosion was the same in the two cohorts, with the exception being that, only one of the two surfaces (i.e., the trunnion) engaged in the oxide abrasion and repassivation process in the ceramic cohort. There was no significant correlation observed between taper angle clearance and visual fretting-corrosion scores for trunnions in the ceramic cohort (Rho=−0.17), trunnions in the CoCr cohort (Rho=0.24), or the femoral head tapers in the metal cohort (Rho=−0.05) (Figure 1). Additionally, visual fretting-corrosion scores in the metal cohort were similar between components with distal contact (negative taper angle clearance) and components with proximal contact (positive taper angle clearance) (p=0.43 and 0.56 for head and trunnion scores, respectively). Conclusions. The results suggest that by using a ceramic femoral head, CoCr fretting and corrosion from the modular head-neck taper may be mitigated, but not completely eliminated. The findings of this study support further study of the role of ceramic heads in potentially reducing femoral taper corrosion. Taper angle clearance was not correlated with the visual fretting-corrosion scores in the ceramic or CoCr cohort in the present study. The effects of taper angle clearance may not be significant compared to other factors leading to material loss or the lack of correlation may be due to the limitations in the visual scoring method. Research is underway quantify the volume of material release from explants to better understand the reasons for reduced fretting and corrosion observed in the ceramic head cohort

INTRODUCTION. Modular metal-on-metal hip implants show increased revision rates due to fretting and corrosion at the interface. High frictional torque potentially causes such effects at the head-taper interface, especially for large hip bearings. The aim of this study was to investigate fretting and corrosion of sleeved ceramic heads for large ceramic-on-ceramic (CoC) bearings. METHODS. The investigated system consists of a ceramic head (ISO 6474-2; BIOLOX® Option), a metal sleeve (Ti-6Al-4V, ISO 5832-3) and different metal stem tapers (Ti-6Al-4V, ISO 5832-3; stainless steel, ISO 5832-1; CoCrMo, ISO 5832-12). Three different test methods were used to assess corrosion behaviour and connection strength of head-sleeve-taper interfaces: . –. Fretting corrosion acc. to ASTM F1- Corrosion under in-vivo relevant loads. –. Frictional torque under severe i like conditions. Standardized fretting corrosion tests were carried out. Additionally, a long term test (0.5 mio. cycles) under same conditions was performed. Corrosion effects under 4.5 kN (stair climbing) and 10 kN (stumbling) were determined for three groups. One group was fatigue tested applying 4.5 mio. cycles at 4.5 kN and 0.5 mio. cycles at 10 kN in a corrosive fluid. In parallel two control groups (heads only assembled at same load levels) were stored in the same fluid for same time period. Pull-off tests were performed to detect the effect of corrosion on the interface strength. A new designed test was performed to analyse the connection strength and fretting-corrosion effects on the head-sleeve taper interfaces caused by frictional torque of large CoC bearings (48 mm). Two separate loading conditions were investigated in a hip joint simulator. One created bending torque (pure abduction/adduction), the other set-up applied rotational torque (pure flexion). A static axial force of 3 kN and movements with a frequency of 1 Hz up to 5 mio. cycles in the same corrosive fluid as in the second set of tests were applied for both tests. Surface analysis of the taper and sleeve surfaces was peformed. In order to detect loosening caused by frictional torque, torque-out tests were conducted after simulator testing. RESULTS. The measured currents (static and dynamic) from standard ASTM testing showed low values for all investigated taper materials even for long term testing (0.5 mio. cycles). The strength of the head-sleeve-taper connection was not affected by storing and fatigue testing in corrosive fluid at 4.5 kN and 10 kN. No critical increase or decrease of pull-off force could be observed. No loosening of the head-taper-sleeve connection was detected after hip simulator testing applying high frictional torque. For large CoC bearings (48 mm) with titanium alloy sleeves on appropriate stem tapers no critical corrosion effects could be found. Even testing low corrosion resistant stainless steel tapers as a worst case material showed only tribo-chemical layers and plastic deformation of the taper surfaces. CONCLUSION. All different tests of large ceramic modular heads (48 mm) with titanium adapters on various taper materials exhibited only minor effects on the surfaces of the modular connections. Even worst case material combinations, high loads, corrosive fluid and high frictional torque did not show any critical results using such aggressive test methods

Introduction. Mechanically assisted crevice corrosion (MACC) of head-neck modular taper junctions is prevalent in virtually all head neck tapers in use today. To date, no clear in vitro tests of design, material or surgical elements of the modular taper system have been reported that show which factors principally affect MACC in these tapers. Possible elements include seating load, head-neck offset, surface roughness, taper engagement length, material combination, angular mismatch, and taper diameter. The goals of this study were to use an incremental fretting corrosion test method. 1. to assess the above 7 elements using a design of experiments approach. The hypothesis is that only one or two principal factors affect fretting corrosion. Methods. A 2. 7-2. design of experiment test (7 factors, ¼ factorial, n=32 total runs, 16 samples per condition per factor) was conducted. Factors included: Assembly Force (100, 4000N), Head Offset (1.5, 12 mm), Taper Locking Position (Mouth, Throat), Stem Taper Length (0.44, 0.54 in), Stem Taper Roughness (Ground, Ridged), Taper Diameter (9/10, 12/14), and Stem Material (CoCrMo, Ti-6Al-4V). The heads were CoCrMo coupled with taper coupons (DePuy Synthes, Warsaw, IN). Test components were assembled wet and seated axially with 100 or 4000N assembly force. The assemblies were immersed in PBS and potentiostatically held at −50mV vs. Ag/AgCl. Incremental cyclic loads were applied vertically to the head at 3Hz until a 4000N maximum load was reached (See Fig. 1). Fretting currents at 4000 N cyclic load were used for comparisons while other parameters, including onset load, subsidence, micromotion and pull off load were also captured. Statistical analysis was performed using Pareto charts and Student's T-tests for single factor comparisons (P < 0.05 was statistically significant). Results. Average fretting corrosion currents at 4000 N cyclic load ranged from 0 to 23 µA for all test specimens. The primary factors that statistically affected fretting corrosion currents were head-neck offset (P<0.05) and assembly load (P<0.05). Test factors with the most significance are shown in the Pareto chart of effects (Fig 2). Assembly force, head offset, and the interaction between these two factors were the most significant effects (see Fig 3). All other factors had diminishing effects on fretting current. Note that there is a correlation between fretting currents and pull off load (Fig. 3c). A number of interactive effects were seen between factors on various output parameters (e.g., subsidence, pull off load, onset load) as well. Discussion. This work demonstrates that the principal factors affecting fretting corrosion are seating load and head-neck offset. Material combination, taper diameter, engagement length, roughness and angular mismatch were less significant effectors of fretting corrosion. This test assesses early fretting corrosion response but does not necessarily predict long-term performance where crevices and solution changes may be important. Significance. This work shows a relative comparison of the effects of multiple design, material and surgical elements on the early fretting corrosion behavior of modular tapers in vitro. Head offset and seating loads represent the most significant factors amongst those studied. For figures, please contact authors directly

Aims

This study investigates head-neck taper corrosion with varying head size in a novel hip simulator instrumented to measure corrosion related electrical activity under torsional loads.