Aims. This study aims to enhance understanding of clinical and radiological consequences and involved mechanisms that led to corrosion of the Precice Stryde (Stryde) intramedullary lengthening nail in the post market surveillance era of the device. Between 2018 and 2021 more than 2,000 Stryde nails have been implanted worldwide. However, the outcome of treatment with the Stryde system is insufficiently reported. Methods. This is a retrospective single-centre study analyzing outcome of 57 consecutive lengthening procedures performed with the Stryde nail at the authors’ institution from February 2019 until November 2020. Macro- and microscopic metallographic analysis of four retrieved nails was conducted. To investigate observed corrosion at telescoping junction, scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDX) were performed. Results. Adjacent to the nail’s telescoping junction, osteolytic changes were observed in bi-planar radiographs of 20/57 segments (35%) after a mean of 9.5 months (95% confidence interval 7.2 to 11.9) after surgery. A total of 8/20 patients with osseous alterations (40%) reported rest and ambulation pain of the lengthened segment during consolidation. So far, 24 Stryde nails were retrieved and in 20 (83%) macroscopic corrosion was observed at the nail’s telescoping junction. Before implant removal 11/20 radiographs (55%) of lengthened segments with these 20 nails revealed osteolysis. Implant retrieval analysis by means of SEM showed pitting and crevice corrosion. EDX detected chromium as the main metallic element of corrosion. Conclusion. Patients are exposed to the risk of implant-related osteolysis of unclear short- and long-term clinical consequences. The authors advocate in favour of an early implant removal after osseous consolidation. Cite this article: Bone Joint Res 2021;10(7):425–436

Introduction. Since the introduction of modular hip taper junctions, corrosion has been studied yet the clinical effect remains unclear. Mechanically assisted corrosion and crevice corrosion are thought to be the primary clinical processes driving taper corrosion. Like all corrosion reactions, these processes require the taper junction to be in contact with an electrolyte. This study investigates the effect of sealing the taper junction from the environment on the mechanically-induced corrosion of a modular hip taper junction. Methods. A short-term corrosion fatigue test was conducted with Ti6Al4V 12/14 taper coupons coupled with CoCrMo 12/14 taper 28mm+12 heads (DePuy Synthes, Warsaw, IN). Ten specimens were assembled with a 1.1 kN press load and sealed with silicone sealant (Dow-Corning 732 Multi-Purpose Sealant). Prior to assembly five of these specimens were assembled with the taper junction having been wetted with phosphate buffered saline before assembly; the rest were assembled dry. Specimens were then immersed in phosphate buffered saline and a potentiostat was used to maintain the potential of the specimen at −50mV vs. Ag/AgCl. Incrementally larger loads were applied to the head of the specimen until a 4000N maximum load was reached. The average currents generated during this test was used to assess the corrosion performance of the specimens. The data from the sealed specimens was compared to a control group, which were wetted before assembly but not sealed. Results. In all cases the corrosion of the sealed specimens did not appear to increase in response to the cyclic load; throughout the test, the corrosion did not increase over the baseline anodic current of roughly 0.25 μA. In contrast, the unsealed controls experienced average corrosion currents of around 5 μA at the maximum load, and an average current of 2.0±0.93 µA over the entire test. The wet and dry sealed assembly specimens both resulted in significantly lower average currents of 0.24±0.09 µA and 0.25±0.09 µA, respectively. Discussion. Test specimens with sealed taper junctions to prevent fluid and ion ingress and egress resulted in no measurably increased corrosion currents compared to the baseline currents in the ambient fluid. The wetted sealed specimens might possibly be subject to corrosion; however the corrosion process and effects in this case may be isolated within the taper junction. This test indicates mechanically assisted corrosion does not occur if the taper junction is not exposed to an electrolyte. Significance. This study demonstrates that mechanically induced corrosion can be greatly reduced or prevented by sealing the taper junction to prevent the ingress of electrolyte

INTRODUCTION. Mechanically assisted crevice corrosion of taper interfaces was raised as a concern in total hip arthroplasty (THA) approximately 20 years ago (Gilbert 1993). In total shoulder replacement, however, comparatively little is known about the prevalence of fretting assisted crevice corrosion or the biomechanical and patient factors that influence this phenomenon. Given the comparatively lower loading experienced in the shoulder compared to the hip, we asked: (1) What is the prevalence of fretting assisted corrosion in modular total shoulder replacements, and (2) What patient and implant factors are associated with corrosion?. METHODS. Modular components were collected from 48 revision shoulder arthroplasties as part of a multi-center, IRB approved retrieval program. For anatomic shoulders, this included 40 humeral heads, 32 stems and four taper adapters from seven manufacturers. For reverse shoulders, there were eight complete sets of retrieved components from three manufacturers. The components were predominantly revised for instability, loosening and pain. Anatomical shoulders were implanted for an average of 3.1 years (st dev 3.8; range 0.1–14.5). Reverse shoulders were implanted for an average of 2.2 years (st dev 0.7; range 1.3–3.3). Modular components were disassembled and examined for taper damage. The modular junctions were scored for fretting corrosion using a semi-quantitative four-point scoring system adapted from Goldberg, et al. (Goldberg, 2002, Higgs 2013). The scoring system criteria was adapted from Goldberg and Higgs which is comprised of a one to four grading system (with one indicating little-to-no fretting/corrosion and four indicating extensive fretting/corrosion). The component alloy composition was determined using the manufacturer's laser markings and verified by x-ray fluorescence. Patient age, gender, hand dominance, alloy, flexural rigidity of the trunnion and taper geometry were assessed independently as predictors for fretting corrosion. RESULTS. Moderate to severe fretting corrosion (score > 2) was observed in 23% of the anatomic modular components (Figure 1) and 22% of the reverse shoulder components. An example with severe damage is included in Figure 1. There was no significant relation between corrosion scores and any of the assessed factors. DISCUSSION AND CONCLUSION. It has been suggested that fretting assisted crevice corrosion may be a concern in THA, particularly with large head metal-on-metal articulations. We have identified the presence of moderate to severe corrosion on approximately one quarter of all retrieved shoulder arthroplasties. This is similar to the proportion observed in retrieved modular hips (Goldberg, 2002). While the expected loading of the shoulder is less than that in the hip (Westerhoff, 2009), the offset between the effective center of the prosthetic humeral head and the taper connecter is often larger and the size of the taper is smaller. This can increase the effect of bearing surface loading on the taper. We were unable to detect significant associated biomechanical or patient factors. This was probably due to the limited sample size of our population. At the present time, the clinical effects of taper corrosion in shoulder arthroplasty remain unknown

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

Little is known about the relationship between head-neck corrosion and its effect on the periprosthetic tissues and distant organs of patients hosting well-functioning devices. The purpose of this study was to investigate in postmortem retrieved specimens the degree and type of taper damage, and the corresponding histologic responses in periprosthetic tissues and distant organs. Fifty postmortem THRs (34 primaries, 16 revisions) retrieved after 0.5 to 26 years were analyzed. Forty-three implants had a CoCrMo stem and seven had a Ti6Al4V stem. All heads were CoCrMo and articulated against polyethylene cups (19 XLPE, 31 UHMWPE). H&E sections of joint pseudocapsules, liver, spleen, kidneys and lymph nodes were graded 1–4 for the intensity of various inflammatory cell infiltrates and tissue characteristics. Corrosion damage of the taper surfaces was assessed using visual scoring and quantitated with an optical coordinate measuring machine. SEM analysis was used to determine the acting corrosion mode. Polyethylene wear was assessed optically. The majority of tapers had minimal to mild damage characterized by local plastic deformation of machining line peaks. Imprinting of the stem topography onto the head taper surface was observed in 18 cases. Column damage on the head taper surface occurred in three cases. All taper surfaces scored moderate or severe exhibited local damage features of fretting and/or pitting corrosion. Moderate or severe corrosion of the head and/or trunnion was present in nine hips. In one asymptomatic patient with bilateral hips, lymphocyte-dominated tissue reactions involving perivascular infiltrates of lymphocytes and plasmacytes were observed. In this patient, mild, focal lymphocytic infiltrates were also present in the liver and kidneys, and there was focal histiocytosis and necrosis of the para-aortic lymph nodes. These two implants, which had been in place for 58.6 and 60.1 months, had severe intergranular corrosion of the CoCrMo trunnion, and column damage and imprinting on the head taper. In the other 41 hips, macrophage responses in the joint pseudocapsule to metallic and/or polyethylene wear particles ranged widely from minimal to marked. Focal necrosis in the pseudocapsules of 12 arthroplasties was related to high concentrations of CoCrMo, TiAl4V, TiO, BaSO4 and polyethylene wear particles. High concentrations of these particles were also detected in para-aortic lymph nodes. Rare to mild macrophages were observed in liver and spleen. This is a comprehensive study of wear and corrosion within well-functioning postmortem retrieved THRs, and the resulting local and distant tissue reactions. One of eight patients with moderate or severe corrosion did have a subclinical inflammatory response dominated by lymphocytes after five years. To what extent such an inflammatory process might progress to become symptomatic is not known. Ionic and particulate products generated by corrosion disseminated systemically. The minor lymphocytic infiltrate in the liver and kidneys of one subject with bilateral severely corroded head-neck junctions might suggest possible metal toxicity. The diagnosis of adverse tissue reactions to corrosion of modular junctions can be challenging. Postmortem retrieval studies add to our understanding of the nature and progression of lymphocyte-dominated adverse local and potentially systemic tissue reactions to corrosion of modular junctions

Uncemented metal-on-polyethylene total hip arthroplasties (THAs) have had a modular cobalt-chrome alloy head since their introduction in the early 1980's. Retrieval analysis studies and case reports in the early 1990's first reported corrosion between the femoral stem trunnion (usually titanium alloy) and cobalt-chrome alloy femoral head. However, then this condition seemed to disappear for about two decades? There are now numerous recent case series of this problem after metal-on-polyethylene THA, with a single taper or dual taper modular femoral component. Metal ion elevation, corrosion debris, and effusion are caused by mechanically assisted crevice corrosion (MACC). These patients present with diffuse hip pain, simulating trochanteric bursitis, iliopsoas tendinitis, or even deep infection. Trunnion corrosion, with adverse local tissue reaction, is a diagnosis of exclusion, after infection, loosening, or fracture. The initial lab tests recommended are: ESR, CRP, and serum cobalt and chromium ions. With a metal-on-polyethylene THA, a cobalt level > 1ppb is abnormal. Plain radiographs are usually negative, but may show calcar osteolysis or acetabular erosion or cyst. MARS MRI may be the best imaging study to confirm the diagnosis. Hip aspiration for culture and cell-count may be necessary. The operative treatment is empiric, with debridement, and head exchange with a ceramic head-titanium sleeve (or oxidised zirconium head) placed on the cleaned trunnion. The femoral component may have to be removed if there is “whole trunnion failure”. This usually relieves the symptoms, but the complication rate of this procedure may be high

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

Introduction. Corrosion at modular junctions of total hip replacements has been identified as a potential threat to implant longevity, resulting in efforts to determine appropriate countermeasures. Visual scoring and volumetric material loss measurements have been useful tools to elucidate various clinical and design factors associated with corrosion damage. However, corrosion involves electron exchange that results in chemical changes to biomedical alloys, and electrochemical assessment may therefore be a more appropriate approach to understand the phenomenon. The purpose of this pilot study was to electrochemically distinguish the severity of corrosion in retrieved femoral heads. A secondary goal was to identify the potential of electrochemical impedance spectroscopy (EIS) as a method to identify different forms of corrosion damage. Methods. Twenty femoral heads were identified from a larger study of total hip replacements, obtained as part of an ongoing multi- center IRB-approved retrieval program. Using a previously established 4-point scoring method, components were binned by taper damage: 10 components were identified as having severe damage, 7 with moderate damage and 2 with mild damage. One (1) unimplanted control was included to represent minimal corrosion damage. All components were then characterized using electrochemical impedance spectroscopy under the frequency domain: a 10 mV sinusoidal voltage, ranging from 20 kHz to 2 mHz, was applied to the taper of a femoral head (working electrode) filled with a 1M solution of PBS, a platinum counter electrode and a chlorided silver reference electrode. Absolute impedance at 2 mHz (|Z. 0.002. |), and max phase angle (θ) were assessed relative to taper damage severity. After least-squares fitting of the EIS data to a Randles circuit with a constant phase element, circuit elements: polarization resistance (Rp), CPE-capacitance, and CPE-exponent were also evaluated. The seven (7) most severely corroded components were further examined with scanning electron microscopy to identify corrosion modes. For all statistical analyses, significance was determined at alpha=0.05. Results. Taper damage was strongly correlated with both |Z. 0.002. | (ρ = −0.857, p<0.001) and CPE-capacitance (ρ=0.913, p<0.001). Taper damage was moderately associated with max phase angle (ρ= −0.483, p=0.031), CPE-exponent (ρ= −0.653, p=0.002) and Rp (ρ=0.556, p=0.011). Log-log plots of the strongest predictors of taper damage (|Z. 0.002. | and CPE- capacitance) identified some clustering among severely corroded components. SEM analysis identified evidence of grain/phase boundary corrosion on four components, all with log CPE-capacitance ≥ −4.4. Discussion. The results of this pilot study highlight that electrochemical impedance spectroscopy is useful in determining corrosion severity in retrieved femoral heads, and may also identify intergranular corrosion attack. For an undamaged taper, the self- passivating behavior of CoCrMo creates a surface that opposes charge transfer, but greater corrosion appears to compromise this barrier. The observed trend of low impedance but high capacitance for severely corroded components with intergranular corrosion may signal charge storage at the boundaries of individual grains. Additional work is underway to characterize this behavior

Introduction. The corrosion of modular taper junctions in hip implants is becoming an area of increased research focus. Many design factors have been hypothesized to contribute to this kind of corrosion. The authors' previous research indicated femoral stem taper roughness may influence taper corrosion. The purpose of this study is to determine whether taper roughness significantly affects taper performance. Methods. A 2. 2. design of experiment was conducted with Ti6Al4V 12/14 taper coupons coupled with CoCrMo 12/14 taper 28mm+12 heads (DePuy Synthes, Warsaw, IN) with n=3 samples per test run for a total of 12 samples. The femoral heads and taper coupons were manufactured with “smooth” finishes ranging from R. t. 100–200 µin and “rough” finishes ranging from R. t. 900–1000 µin. Test components were assembled wet (dipped in saline solution and drained) and pressed together with a 4400 N assembly force. The assemblies were immersed in phosphate buffered saline and a potentiostat was used to maintain the potential of the specimen at −50mV vs. Ag/AgCl. Incrementally larger cyclic loads were applied vertically to the head at 3Hz until a 4000N maximum load was reached, then this cyclic load was maintained for an additional 1 million cycles. Results. The long-term average corrosion test results ranged from 0.26 to 2.98 µA among the groups. The “Rough Head – Rough Stem” (Group 1) resulted in the highest average corrosion currents of 1.53 ± 0.75 µA. The “Smooth Head – Smooth Stem” (Group 4) showed the lowest average corrosion currents of 0.20 ± 0.05 µA. ANOVA analysis revealed significant differences between the groups (p>0.05), Tukey-Kramer post-hoc analysis showed a significant difference between groups 1 and 4 only. Discussion. Femoral heads and femoral stems with a smoother taper roughness specification resulted in less measured corrosion compared to components with higher taper roughness specifications under the specified test conditions. Significance. This study demonstrates taper surface roughness is a relevant design factor which could influence taper corrosion

Introduction. Modularity is being increasingly used throughout the world for both primary and revision total hip arthroplasty. Recently there have been concerns of increased corrosion and fretting at the modular junctions. In the SROM® modular hip system, two modular junctions are the head-neck taper junction and the stem-sleeve taper junction. The aim of this study was to investigate corrosion at these junctions with the use of different bearing materials. Methods. Between 1994 and 2012, fourty-two patients were revised with SROM® stems. Reasons for revision included aseptic loosening of the cup or stem (11), periprosthetic fracture (2), osteolysis (8), dislocation (13) and other reasons (7). One was revised for stem breakage, and this was excluded from this study. We examined 41 retrieved S-ROM® comprised of 6 metal-on-metal (MOM), 12 metal-on-polyethylene (MOP), 7 ceramic-on-polyethylene (COP) and 16 ceramic-on-ceramic (COC). The orientation for all components was marked at the time of revision surgery. Both the proximal sleeve/stem and the femoral head-neck modular junctions were examined under 10X magnification, and graded by two independent observers. The head tapers were divided into 4 regions, and graded using a previously published 3 point scoring system for fretting and corrosion damage (Goldberg et al, Kop et al), for a total corrosion damage score of 12. The SROM stems were also assessed at the sleeve/stem taper junction. Each stem was divided into 8 quadrants, and graded for corrosion and fretting using the same system as the taper. In addition to severity, we also quantified area of corrosion damage of the stem at the sleeve-stem junction from 0–3, which was multiplied by the severity of damage, to give a score out of 9 for each quadrant (maximum total score of 72 for the stem). The bearing type was unknown to the investigators, so the grading was done in a blinded fashion. Corrosion scores were divided by time to account for differences in time to revision. Results. Corrosion at the head-neck taper junction was higher for 17 stems with metal heads compared to 23 stems with ceramic heads (p=0.008). The average corrosion rate at the stem-sleeve taper junction in hips with hard-on-hard bearings (COC and MOM) was higher than polyethylene (MOP and COP) bearings, but this was not significant (p=0.07). Conclusions. Corrosion at the head-neck modular junction of hips with metal heads was greater than ceramic heads, likely due to galvanic corrosion in a mixed-metal system. Greater corrosion was found at the stem-sleeve taper junction in stems with hard-on-hard bearings. This may be related to friction in the bearings

Background. Distal femoral replacements (DFR) are used in children for limb-salvage procedures after bone tumor surgery. These are typically modular devices involving a hinged knee axle that has peripheral metal-on-polyethylene (MoP) and central metal-on-metal (M-M) articulations. While modular connections and M-M surfaces in hip devices have been extensively studied, little is known about long-term wear or corrosion mechanisms of DFRs. Retrieved axles were examined to identify common features and patterns of surface damage, wear and corrosion. Methods. The cobalt chromium alloy axle components from 13 retrieved DFRs were cleaned and examined by eye and with a stereo microscope up to 1000× magnification. Each axle was marked into 6 zones for visual inspection: the proximal and distal views, and the middle (M-M) and 2 peripheral (MoP) zones. The approximate percentage of the following features were recorded per zone: polishing, abrasion or scratching, gouges or detectable wear, impingement wear (i.e. from non- intentional articulation), discoloration and pitting. Results. In each case, the middle M-M zones showed more damage features compared with peripheral MoP zones. Brown discoloration, presumably due to tribofilm deposits, was the predominant M-M area feature, particularly at the junction between the MoP and M-M zones. Higher magnification showed areas of polishing underlying the discoloration, suggesting repetitive removal of the surface metal and re-deposition of tribofilms (Fig 2B). 9 cases demonstrated reflective patches resembling “thumbprint” or “fish scale” markings, which, under higher magnification, showed signs of scratching and grooving in a radial pattern (Figs 2D, 3A). Pits were occasionally present but appeared to be from third-body damage as signs of corrosion were absent. Features that resembled carbides, sometimes with associated “comet” patterns of scratching were apparent under higher magnification in some areas. The MoP zones showed variable scratching, abrasion and wear polishing. The MoP to M-M junctional areas were demarcated by a distinct band corresponding, in some cases, to a narrow wear groove or gouge. 3 axles showed evidence of severe impingement wear on one proximal end. Discussion. This study of retrieved axle components demonstrated varying types of surface wear damage but no clear evidence of corrosion. This is presumably because these parts are in nearly constant motion during gait. Third-body damage may have resulted from the breakdown of surface carbides, leading to scratching, abrasion and wear polishing under high contact stress. Severe impingement wear presumably occurred after catastrophic damage to the polyethylene bushings, allowing eccentric loading and extensive metal wear. The components were revised for a range of clinical reasons including aseptic loosening and the need to expand the prosthesis during growth. With the exception of the few cases with severe impingement, it is unlikely that the wear features seen here contributed to the need for revision. While it was reassuring that corrosion was not a prominent feature of these modular M-M articulations, retrieval analysis of DFR components should be continued to confirm this finding, better document the in vivo wear processes and point to design features that might be improved for future patients. For any figures or tables, please contact the authors directly

Introduction. Modern hip replacements all have encapsulated the design concept of proximal modularity. The factors contributing to the increased wear and corrosion at the taper junction are trunnion geometry, surface characteristics, head size, impaction forces, and material coupling. This study maps the inferior and superior region of the trunnion and bore to provide a visual identification of the corrosion severity. The corrosion/wear generated inferiorly and superiorly at the bore and trunnion will be quantified to understand how corrosion is affected by mechanical stresses in relation to anatomical orientation. Methodology. Three neck tapers generated from bar stock containing a threaded trunnion Ti-6Al-4V and 3× 32mm femoral heads (Co-Cr-Mo) with a +4 offset manufactured by Signature Orthopaedics were used within this study. Rectangular Rozzette strain gauges (Tokyo Sokki Kenkyujo Co., Ltd.) were adhered onto the inferior and superior sections of the neck section. The tapers were fatigued in accordance to ISO 7206 at 5Hz for 5 million cycles at 37 degrees Celsius in phosphate buffered saline. The tapers were sectioned from the center of the femoral head to split both trunnion and bore into superior and inferior components. SEM imaging of all surface areas for each component, per taper (4) was done under ×100 magnification. The images were used to quantify the corrosion present across the surface area using a MATLAB based program called Histomorph. To obtain a visual observation of the variation of corrosion across the bore and trunnion the proximal, medial, and distal regions were mapped together for both the superior and inferior sections. Results. The superior region of the trunnion had a dominant tensile strain in comparison to the inferior region, which had a dominant compressive strain. Corrosion/wear of the inferior section of the trunnion was significantly higher (p<0.05) in comparison to the superior section (Figure 1). The bore had more corrosion/wear on the superior side in comparison to the inferior side however the difference was not significant. The mapping of the trunnion shows corrosion/wear along the whole length of the inferior side and dominantly at the distal region for the superior side (Figure 2 & 3). The superior section of the trunnion had higher corrosion/wear damage across the center and distal regions of the trunnion. The subdivision of the superior section reveals that the majority of the distal section contains higher wear/corrosion damage. However the central region also has sufficient corrosion/wear extending across the width of the bore. Conclusion. The corroded regions have shown that the type of stress present on the regions of the taper junction determines the severity of corrosion. The inferior section of the trunnion under compressive stress has significantly (p<0.05) higher corrosion/wear in comparison to the superior section dominated by tensile stress

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. Little is known about the relationship between head-neck corrosion and its effect on periprosthetic tissues and distant organs in the majority of patients hosting apparently well-functioning devices. We studied the degree and type of taper damage and the histopathologic response in periprosthetic tissue and distant organs. Methods. A total of 50 contemporary THRs (34 primary, 16 revision) retrieved postmortem from 40 patients after 0.4–26 years were studied. Forty-three femoral stems were CoCrMo and 7 were Ti6Al4V. In every case, a CoCrMo-alloy head articulated against a cementless polyethylene cup (19 XLPE and 31 UHMWPE). H&E and IHC sections of the joint pseudocapsules and liver were graded 1–4 for the intensity of various inflammatory cell infiltrates and tissue necrosis. The nature of the tissue response in the joint capsule, liver, spleen, kidneys and lymph nodes was assessed. Wear and corrosion products in the tissues were identified using SEM and EDS. Taper surfaces were graded for corrosion damage using modified Goldberg scoring and examined by SEM to determine the acting corrosion mode. Correlations between damage scores and the histologic variables were generated using the Spearman test. Results. No correlation was seen between taper damage scores and the macrophage response in the joint pseudocapsule. The distribution of corrosion scores for heads and femoral trunnions is shown in Figure 1. Moderate or severe corrosion of the head and/or trunnion was present in 9 hips (8 CoCr/CoCr and 1 CoCr/TiAlV). One patient with bilateral hips had local ALVAL-like lymphocyte-dominated tissue reactions (Figure 2) and mild focal lymphocytic infiltrates in the liver and kidneys (Figure 3). This was associated with severe intergranular corrosion of the CoCrMo trunnion and column damage on the head taper. Particle-laden macrophages in pseudocapsules were significantly correlated with liver macrophages (r=.382, p=0.012) and liver lymphocytes (r=.367, p=0.013). Pseudocapsule macrophage responses to metallic and/or polyethylene wear particles ranged widely from minimal to marked. Focal tissue necrosis was related to high concentrations of particulate wear debris. A minimal number of metallic particle-laden macrophages were also detected in the liver and spleen; and macrophage granulomas were present in para-aortic lymph nodes, especially in revision cases. DISCUSSION. The generation of metal ions and particulates at corroded CoCrMo heads and CoCrMo or Ti6Al4V trunnions was a significant contributor to the presence of perivascular lymphocytes within the joint pseudocapsule, with 1 patient showing a histologic pattern consistent with ALVAL. Patient factors and the rate of corrosion are among variables influencing whether an ALVAL-type reaction will develop and whether or not it will become symptomatic. Macrophages in the joint pseudocapsules were positively correlated with inflammatory cells in the liver. In this study, the intensity of inflammatory infiltrates in distant organs was mild. However, several cases of organ dysfunction have been reported in association with catastrophic wear of CoCrMo components. It continues to be essential to minimize the generation of metal ions and particulates and to improve strategies for identifying and managing patients exposed to high levels of degradation products. For any figures or tables, please contact the authors directly

Since the advent of total hip arthroplasty (THA), there have been many changes in implant design that have been implemented in an effort to improve the outcome of the procedure and enhance the surgeon's ability to reproducibly perform the procedure. Some of these design features have not stood the test of time. However, the introduction of femoral stem head/neck modularity made possible by the Morse taper has now been a mainstay design feature for over two decades. Modularity at the head-neck junction facilitates intraoperative adjustments. ‘Dual Taper’ modular stems in total hip arthroplasty have interchangeable modular necks with additional modularity at the neck and stem junction. This ‘dual taper’ modular femoral stem design facilitates adjustments of the leg length, the femoral neck version and the offset independent of femoral fixation. This has the potential advantage of optimizing hip biomechanical parameters by accurately reproducing the center of rotation of the hip. More recently, however, there is increasing concern regarding the occurrence of adverse local tissue reactions in patients with taper corrosion, which is emerging as an important reason for failure requiring revision surgery. Although adverse tissue reactions or ‘pseudotumor’ were initially described as a complication of metal-on-metal (MoM) bearings, the presence of pseudotumor in patients with taper corrosion is thought to result from corrosion at the neck-stem taper junction, secondary to reciprocating movement at the modular junction leading to fretting corrosion in a process described as mechanically assisted crevice corrosion (MACC). Therefore, the focus of this presentation is to summarise clinical challenges in diagnosis and treatment of patients with adverse tissue reactions due to taper corrosion and review up-to-date evidence

Introduction. Titanium and its alloys are attractive biomaterials attributable to their desirable corrosion, mechanical, biocompatibility and osseointegration properties. In particular, β – titanium alloys like the TMZF possess other advantages such as its lower modulus compared to Ti6Al4V alloy. This reduces stress shielding effect in Total Hip Arthroplasty (THA) and the replacement of V in the Ti6Al4V alloy, eliminates in-vivo V-induced toxicity. Unfortunately, implants made of TMZF were later recalled by the FDA due to higher than acceptable revision rates. The purpose of this study was to compare the fretting corrosion characteristics of Ti6Al4V and TMZF titanium alloys. It is hoped the findings will inform better design of β – titanium alloys for future applications in THA. Method. A ball-on-flat configuration was utilised in this study to achieve a Hertzian point contact for CoCrMo – Ti6Al4V and CoCrMo – TMZF material combinations. These were assessed at a fretting displacement of ±50 µm at an initial contact pressure of 1 GPa. Each fretting test lasted 6000 cycles at a frequency of 1 Hz. A two-electrode cell set-up was used to monitor in-situ open circuit potential (OCP). The simulated physiological solution consisted of Foetal Bovine Serum (FBS) diluted to 25% with Phosphate Buffered Saline (PBS) and 0.03% Sodium Azide (SA) balance. The temperature was kept at ∼37°C. Corrosion products on the worn surfaces and subsurface transformations in both alloys were characterised using the Scanning and Transmission Electron Microscopy (SEM/TEM) to obtain high resolution micrographs. The samples were prepared using a FIB-SEM. Bright-field, dark-field and selected area electron diffraction (SAED) patterns were all captured using a scanning TEM (STEM) and Energy Dispersed X-Ray spectroscopy (EDX) mapping was carried out. Results. The results showed that fretting regime transition from partial-slip to gross slip was delayed a few hundred cycles for TMZF relative to the Ti6Al4V (Figure 1). This indicates that the lower modulus of TMZF influences the degree of elastic deformation accommodated prior to the initiation of plastic shear at the fretting interface. The OCP directly corresponded to the fretting regime for both material combinations (Figure 2). Surface and subsurface characterisation of both alloys show differences in the structure of their mechanically mixed corrosion products and metallurgical transformations. Interestingly, an amorphous Co-rich layer was seen across the TMZF surface (Figure 3) whereas, pitting corrosion products from the CoCrMo alloy was seen on the Ti6Al4V alloy. Conclusion. In summary, the difference in the fretting behavior of Ti6Al4V and TMZF directly corresponds to the combined differences in their elastic modulus and surface chemistry. This corresponds to the differences observed in their electrochemical behavior. However, the main differences observed were the properties of their corrosion products and subsurface metallurgical transformations. These observed characteristic differences are to be considered in further examination of the cause of higher failure rates in TMZF alloys. For any figures or tables, please contact the authors directly

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. There are increasing reports of total hip replacement (THR) failure due to corrosion within modular taper junctions, and subsequent adverse local tissue reactions (ALTRs) to corrosion products. Modular junction corrosion is a multifactorial problem that depends on material, design, patient and surgical factors. However, the influence of alloy microstructure on corrosion has not been studied sufficiently. Especially for cast CoCrMo, there are concerns regarding microstructure variability with respect to grain size and hard-phase volume fraction. Therefore, it was the goal of this study to (1) identify different types of microstructures in contemporary implants, and (2) determine implications of alloy microstructure on the occurring corrosion modes. Methods. Fifteen surgically retrieved femoral stems made from cast CoCrMo alloy were analyzed for this study. Damage on the taper surfaces was investigated by scanning electron microscopy (SEM) and damage was assessed with the Goldberg Score. The alloy microstructure was evaluated by standard metallographic techniques. Alloy samples were sectioned off the femoral stem, and microstructural features were visualized by chemical etching. Cyclic potentio-dynamic polarization tests were carried out with alloy samples from two implants with different commonly occurring types of microstructures. Both had a similar grain size, but type 1 had no hard-phases, where as type 2 exhibited hard-phases along the grain boundaries, as well as intra-granular hard-phase clusters. Tests were performed in bovine serum at 37°C with a saturate calomel reference electrode and a graphite counter electrode. In vitro generated corrosion damage was then compared to in vivo generated damage features on the taper surfaces of the corresponding implants. Results. Tapers with high damage scores exhibited varying degrees of grain and phase boundary corrosion, along with fretting and pitting corrosion. In several cases thick chromium oxide films were observed. The metallographic analysis showed that nominally identical alloys (ASTM F75) exhibited a broad variability in grain size (250 micrometers to several millimeters), hard-phase volume fraction (0–6%), and hard-phase type (carbides and intermetallic phases). The corrosion tests revealed that the alloy without hard-phases (type 1) had a significantly higher pitting potential (p=0.001) than type 2 alloy without hard-phases. After testing, both alloys exhibited grain boundary corrosion. However, type 2 had a higher degree of material loss due to hard-phase detachment. Additionally, type 2 exhibited pitting within the grains around hard-phases, along with the formation of thick oxide films which was consistent with the lower pitting potential. The results also corresponded with the damage features on the corresponding tapers, where type 1 exhibited only mild damage features, and type 2 underwent severe grain and phase boundary corrosion along with thick oxide films (Figure 3). Discussion. It appears that the alloy microstructure drives local modes of corrosion. Additional phase boundaries due to hard-phase content promote corrosion. The fact that the same alloy can differ broadly even within the same design shows that material standards are currently not sufficient. Optimizing implant alloys will help to reduce in vivo corrosion processes, and subsequently the risk of implant failure due to ALTRs. For figures/tables, 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

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