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. Methods. In all, six 28 mm and six 36 mm titanium stem-cobalt chrome head pairs with polyethylene sockets were tested in a novel instrumented hip simulator. Samples were tested using simulated gait data with incremental increasing loads to determine corrosion onset load and electrochemical activity. Half of each head size group were then cycled with simulated gait and the other half with gait compression only. Damage was measured by area and maximum linear wear depth. Results. Overall, 36 mm heads had lower corrosion onset load (p = 0.009) and change in open circuit potential (OCP) during simulated gait with (p = 0.006) and without joint movement (p = 0.004). Discontinuing gait’s joint movement decreased corrosion currents (p = 0.042); however, wear testing showed no significant effect of joint movement on taper damage. In addition, 36 mm heads had greater corrosion area (p = 0.050), but no significant difference was found for maximum linear wear depth (p = 0.155). Conclusion. Larger heads are more susceptible to taper corrosion; however, not due to frictional torque as hypothesized. An alternative hypothesis of taper flexural rigidity differential is proposed. Further studies are necessary to investigate the clinical significance and underlying mechanism of this finding. Cite this article: Bone Jt Open 2021;2(11):1004–1016

Objectives. This study aimed to characterise and qualitatively grade the severity of the corrosion particles released into the hip joint following taper corrosion. Methods. The 26 cases examined were CoC/ABG Modular (n = 13) and ASR/SROM (n = 13). Blood serum metal ion levels were collected before and after revision surgery. The haematoxylin and eosin tissue sections were graded on the presence of fibrin exudates, necrosis, inflammatory cells and corrosion products. The corrosion products were identified based on visible observation and graded on abundance. Two independent observers blinded to the clinical patient findings scored all cases. Elemental analysis was performed on corrosion products within tissue sections. X-Ray diffraction was used to identify crystalline structures present in taper debris. Results. The CoC/ABG Modular patients had a mean age of 64.6 years (49.4 to 76.5) and ASR/SROM patients had a mean age of 58.2 years (33.3 to 85.6). The mean time in situ for CoC/ABG was 4.9 years (2 to 6.4) and ASR/SROM was 6.1 years (2.5 to 8.1). The blood serum metal ion concentrations reduced following revision surgery with the exception of Cr levels within CoC/ABG. The grading of tissue sections showed that the macrophage response and metal debris were significantly higher for the ASR/SROM patients (p < 0.001). The brown/red particles were significantly higher for ASR/SROM (p < 0.001). The taper debris contained traces of titanium oxide, chromium oxide and aluminium nitride. Conclusion. This study characterised and qualitatively graded the severity of the corrosion particles released into the hip joint from tapers that had corrosion damage. Cite this article: S. Munir, R. A. Oliver, B. Zicat, W. L. Walter, W. K. Walter, W. R. Walsh. The histological and elemental characterisation of corrosion particles from taper junctions. Bone Joint Res 2016;5:370–378. DOI: 10.1302/2046-3758.59.2000507

Aims. To present a surgically relevant update of trunnionosis. . Materials and Methods. Systematic review performed April 2017. Results. Trunnionosis accounts for approximately 2% of the revision total hip arthroplasty (THA) burden. Thinner (reduced flexural rigidity) and shorter trunnions (reduced contact area at the taper junction) may contribute to mechanically assisted corrosion, exacerbated by high offset implants. The contribution of large heads and mixed metallurgy is discussed. Conclusion. Identifying causative risk factors is challenging due to the multifactorial nature of this problem. Cite this article: Bone Joint J 2018;100-B(1 Supple A):44–9

The aim of this study was to assess the effect of frictional torque and bending moment on fretting corrosion at the taper interface of a modular femoral component and to investigate whether different combinations of material also had an effect. The combinations we examined were 1) cobalt–chromium (CoCr) heads on CoCr stems 2) CoCr heads on titanium alloy (Ti) stems and 3) ceramic heads on CoCr stems. In test 1 increasing torque was imposed by offsetting the stem in the anteroposterior plane in increments of 0 mm, 4 mm, 6 mm and 8 mm when the torque generated was equivalent to 0 Nm, 9 Nm, 14 Nm and 18 Nm. In test 2 we investigated the effect of increasing the bending moment by offsetting the application of axial load from the midline in the mediolateral plane. Increments of offset equivalent to head + 0 mm, head + 7 mm and head + 14 mm were used. Significantly higher currents and amplitudes were seen with increasing torque for all combinations of material. However, Ti stems showed the highest corrosion currents. Increased bending moments associated with using larger offset heads produced more corrosion: Ti stems generally performed worse than CoCr stems. Using ceramic heads did not prevent corrosion, but reduced it significantly in all loading configurations. Cite this article: Bone Joint J 2015;97-B:463–72

We present a series of 35 patients (19 men and 16 women) with a mean age of 64 years (36.7 to 75.9), who underwent total hip replacement using the ESKA dual-modular short stem with metal on-polyethylene bearing surfaces. This implant has a modular neck section in addition to the modular head. Of these patients, three presented with increasing post-operative pain due to pseudotumour formation that resulted from corrosion at the modular neck-stem junction. These patients underwent further surgery and aseptic lymphocytic vaculitis associated lesions were demonstrated on histological analysis. Retrieval analysis of two modular necks showed corrosion at the neck-stem taper. Blood cobalt and chromium levels were measured at a mean of nine months (3 to 28) following surgery. These were compared with the levels in seven control patients (three men and four women) with a mean age of 53.4 years (32.1 to 64.1), who had an identical prosthesis and articulation but with a prosthesis that had no modularity at neck-stem junction. The mean blood levels of cobalt in the study group were raised at 50.75 nmol/l (5 to 145) compared with 5.6 nmol/l (2 to 13) in control patients. Corrosion at neck-stem tapers has been identified as an important source of metal ion release and pseudotumour formation requiring revision surgery. Finite element modelling of the dual modular stem demonstrated high stresses at the modular stem-neck junction. Dual modular cobalt-chrome hip prostheses should be used with caution due to these concerns

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

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

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

Aims. Taper corrosion has been widely reported to be problematic for modular total hip arthroplasty implants. A simple and systematic method to evaluate taper damage with sufficient resolution is needed. We introduce a semiquantitative grading system for modular femoral tapers to characterize taper corrosion damage. Methods. After examining a unique collection of retrieved cobalt-chromium (CoCr) taper sleeves (n = 465) using the widely-used Goldberg system, we developed an expanded six-point visual grading system intended to characterize the severity, visible material loss, and absence of direct component contact due to corrosion. Female taper sleeve damage was evaluated by three blinded observers using the Goldberg scoring system and the expanded system. A subset (n = 85) was then re-evaluated following destructive cleaning, using both scoring systems. Material loss for this subset was quantified using metrology and correlated with both scoring systems. Results. There was substantial agreement in grading among all three observers with uncleaned (n = 465) and with the subset of cleaned (n = 85) implants. The expanded scoring criteria provided a wider distribution of scores which ultimately correlated well with corrosion material loss. Cleaning changed the average scores marginally using the Goldberg criteria (p = 0.290); however, using the VGS, approximately 40% of the scores for all observers changed, increasing the average score from 4.24 to 4.35 (p = 0.002). There was a strong correlation between measured material loss and new grading scores. Conclusion. The expanded scoring criteria provided a wider distribution of scores which ultimately correlated well with corrosion material loss. This system provides potential advantages for assessing taper damage without requiring specialized imaging devices. Cite this article: Bone Joint Res 2023;12(3):155–164

Aims. To report our experience with trunnion corrosion following metal-on-polyethylene total hip arthroplasty, in particular to report the spectrum of presentation and determine the mean time to presentation. Patients and Methods. We report the presenting symptoms and signs, intraoperative findings, and early results and complications of operative treatment in nine patients with a mean age of 74 years (60 to 86). The onset of symptoms was at a mean of seven years (3 to 18) after index surgery. Results. Patients presented with a variety of symptoms including pain, limp and rash. The preoperative mean serum cobalt level was 7.1 ppb (2.2 to 12.8) and mean serum chromium level was 2.2 ppb (0.5 to 5.2). Metal artifact reduction sequence (MARS) MRI showed fluid collection and possible pseudotumour formation in five hips, fluid collection in two hips, and synovitis/debris in one hip, with no MRI in one patient. Acetabular revision was performed in three patients, six patients underwent liner and head exchange only. The postoperative metal levels decreased in all patients: mean cobalt 0.5 ppb (0 to 1.8) and mean chromium 0.9 ppb (0 to 2.6) at a mean of five months (3 to 8) postoperatively. Seven patients had good pain relief and no complications at one year. There were two major complications requiring reoperation: acute infection at six weeks, for which the patient required two-stage reimplantation; and recurrent dislocation, for which the patient was revised to a dual mobility component. Conclusion. Trunnion corrosion in metal-on-polyethylene THA has a range of presenting symptoms, and may present later than previously described. A high index of suspicion is warranted, and serum cobalt and chromium levels are recommended for diagnosis. Patients should be counselled about possible postoperative complications. Cite this article: Bone Joint J 2018;100-B:898–902

There is increasing global awareness of adverse reactions to metal debris and elevated serum metal ion concentrations following the use of second generation metal-on-metal total hip arthroplasties. The high incidence of these complications can be largely attributed to corrosion at the head-neck interface. Severe corrosion of the taper is identified most commonly in association with larger diameter femoral heads. However, there is emerging evidence of varying levels of corrosion observed in retrieved components with smaller diameter femoral heads. This same mechanism of galvanic and mechanically-assisted crevice corrosion has been observed in metal-on-polyethylene and ceramic components, suggesting an inherent biomechanical problem with current designs of the head-neck interface. We provide a review of the fundamental questions and answers clinicians and researchers must understand regarding corrosion of the taper, and its relevance to current orthopaedic practice. Cite this article: Bone Joint J 2016;98-B:579–84

Titanium alloys are one of the most used for orthopaedic implants and the fabrication of them by 3D printing technology is a raising technology, which could effectively resolve existing challenges. Surface modification of Ti surfaces is often necessary to improve biocorrosion resistance, especially in inflammatory conditions. Such modification can be made by coatings based on hydrogels, like alginate (Alg) - a naturally occurring anionic polymer. The properties of the hydrogel can be further enhanced with calcium phosphates like octacalcium phosphate (OCP) as a precursor of biologically formed hydroxyapatite. Formed Alg-OCP matrices have a high potential in wound healing, delivery of bioactive agents etc. but their effect on 3D printed Ti alloys performance was not well known. In this work, Alg-OCP coated 3D printed samples were studied with electrochemical measurements and revealed significant variations of corrosion resistance vs. composition of the coating. The potentiodynamic polarization test showed that the Alg-OCP-coated samples had lower corrosion current density than simple Alg-coated samples. Electrochemical impedance spectroscopy indicated that OCP incorporated hydrogels had also a high value of the Bode modulus and phase angle. Hence Alg-OCP hydrogels could be highly beneficial in protecting 3D printed Ti alloys especially when the host conditions for the implant placement are inflammatory. AcThis work was supported by the European Union Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Actions GA860462 (PREMUROSA). The authors also acknowledge the access to the infrastructure and expertise of the BBCE – Baltic Biomaterials Centre of Excellence (European Union Horizon 2020 programme under GA857287)

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

Aims. This combined clinical and in vitro study aimed to determine the incidence of liner malseating in modular dual mobility (MDM) constructs in primary total hip arthroplasties (THAs) from a large volume arthroplasty centre, and determine whether malseating increases the potential for fretting and corrosion at the modular metal interface in malseated MDM constructs using a simulated corrosion chamber. Methods. For the clinical arm of the study, observers independently reviewed postoperative radiographs of 551 primary THAs using MDM constructs from a single manufacturer over a three-year period, to identify the incidence of MDM liner-shell malseating. Multivariable logistic regression analysis was performed to identify risk factors including age, sex, body mass index (BMI), cup design, cup size, and the MDM case volume of the surgeon. For the in vitro arm, six pristine MDM implants with cobalt-chrome liners were tested in a simulated corrosion chamber. Three were well-seated and three were malseated with 6° of canting. The liner-shell couples underwent cyclic loading of increasing magnitudes. Fretting current was measured throughout testing and the onset of fretting load was determined by analyzing the increase in average current. Results. The radiological review identified that 32 of 551 MDM liners (5.8%) were malseated. Malseating was noted in all of the three different cup designs. The incidence of malseating was significantly higher in low-volume MDM surgeons than high-volume MDM surgeons (p < 0.001). Pristine well-seated liners showed significantly lower fretting current values at all peak loads greater than 800 N (p < 0.044). Malseated liner-shell couples had lower fretting onset loads at 2,400 N. Conclusion. MDM malseating remains an issue that can occur in at least one in 20 patients at a high-volume arthroplasty centre. The onset of fretting and increased fretting current throughout loading cycles suggests susceptibility to corrosion when this occurs. These results support the hypothesis that malseated liners may be at risk for fretting corrosion. Clinicians should be aware of this phenomenon. Cite this article: Bone Joint J 2020;102-B(7 Supple B):20–26

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

Summary. Corrosion and fretting damage at the head-neck interface of artificial hip joints is more severe with larger head sizes. This is a concern, as the release of metal particles and ions can cause adverse tissue reactions, similar to those observed high wear metal-on-metal articulations. Introduction. In the last few years corrosion was increasingly observed at head-neck interfaces of artificial hip joints, especially in joints with larger heads. There has always been evidence of some corrosion at modular junctions of artificial joints, but except for few designs, it was not seen as a real problem. It is important to better understand the factors contributing to corrosion at modular interfaces, so that necessary improvements can be made to minimise or completely avoid corrosion, in order to avoid possible adverse tissue reactions. Methods. Over 100 retrieved stems and heads of 28, 32, 36, 40 and larger heads with metal-on-polyethylene (MoP) and metal-on-metal (MoM) articulations were scored for corrosion and fretting damage, in order to get a better picture of the magnitude of the problem. For some of the head sizes it was possible to assess the fretting and corrosion damage separately from implants from two different manufacturers. The tapers of the stem and head were subdivided into eight regions each, and scored for the severity of fretting and corrosion damage, as well as of the affected area within each sub-section. The scoring was undertaken by three persons with a fair intraclass correlation. The fretting and corrosion scores were also assessed based on the location of the center of the head with respect to the center of the taper. The distance between these two centers influences the toggling motion between the head and neck, as the main load is about 30 degrees out of axis during walking and other activities of daily living. Results. It was found that head-neck interfaces of two manufacturers of 36mm heads had significantly more corrosion than 28mm heads. There is a significant relationship between head and neck fretting damage, and between corrosion and fretting damage. There is also more corrosion damage in 32, 40 and larger heads, but these groups were from different manufacturers, so that it was not possible to perform statistical tests. More corrosion was observed when the centre of the head was at a larger distance from the centre of the head, leading to an increased toggling moment due to the out-of-axis loading. Discussion. It is of some concern that more corrosion is being observed with larger heads. Corrosion generally gets worse over time, which could negatively impact on the long-term behavior of these hip joints. Furthermore, it is possible that the metal particle and ion release due to corrosion and fretting could have adverse soft tissue reactions, similar to those observed at some MoM articulations. The fact that there are significant differences in the observed corrosion and fretting damage between the head-neck interfaces of two companies, indicates that even subtle changes in the geometry and the machined taper surface are important. A better understanding of these factors is required to make sure that the corrosion and fretting damage is minimised, or even better eliminated for all heads of artificial joints

Adhered bacteria on titanium surfaces are able to decrease its corrosion potential and impedance values at the lowest frequencies. This result points to the detrimental influence of the biofilm on the passive film formed on the surfaces, independently on the surface finishes. Titanium is one of the most used metallic biomaterials for biological and implant applications. The spontaneous formation of a protective passive film around 2–5 nm thick, make titanium unique as a biomaterial for implants. Its composition has been described by a three-layer model: TiO2/Ti2O3/TiO and its stability is ultimately responsible for the success of osseointegrated titanium implants. The cases of breakdown of the protective passive film are associated with highly acidic environments induced by bacterial biofilms and/or inflammatory processes that lead to localized corrosion of titanium and, in extreme cases, implant failure. Bearing in mind that the surface design of a titanium implant is a key element involved in the healing mechanisms at the bone-implant interface, the surface modifications have sought to enhance the biomechanical anchorage of the implant and promote osseointegration at the cell-biomolecular level. However, little attention has been paid to the effects of these surface modifications in the microbiologically induced corrosion (MIC). The aim of this work is to evaluate the potential for MIC of titanium in the short term under viable bacterial cells of Streptococcus mutansas a representative microorganism of oral biofilm considered to be a highly cariogenic pathogen. Discs of 64 mm. 2. surface area of commercially pure titanium, grade 4, were supplied by Biotechnology Institute (BTI, Vitoria, Spain). Four surface treatments were studied: two acid etchings (low roughness, opN and high roughness, opV). In addition, acid etched plus anodic oxidation (opNT). For comparative purposes, two surface finishes have been included: high roughness – corresponding with sandblasting-large grit plus acid (SLA); and, as-machined titanium (mach). The oral strain used for assessing the biofilm formation on the corrosion behavior of Ti surfaces was Streptococus mutansATCC 25175, obtained from the Spanish Type Culture Collection (CECT). The study of MIC from Streptococcus mutanson surfaces of Ti was carried out in an electrochemical cell specifically designed and patented by some of the present authors [1]. A three set up configuration of the electrochemical cell was used in the experiments. The measurement of the corrosion potential and electrochemical impedance was performed at different periods of incubation of bacteria: 2, 7, 15, 21 and 28 days. Out Slight but continuous decrease in the corrosion potential and impedance values at the lowest frequencies indicate the deleterious influence of the biofilm on the passive film formed on the surfaces, independently on the surface finishes. This research suggests that the most appropriate surface modification for the dental implant portion at the bone level would be the acid etched of high roughness (opV) surface

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

1. A total of 564 metal components from 109 patients have been examined. 2. Corrosion was detected on 228 components. 3. Most implants were removed for reasons other than corrosion. 4. In at least twelve cases corrosion was the reason for removal of the implant. 5. No corrosion of cobalt-chromium-molybdenum implants has been detected by the methods described in this paper. 6. Corrosion of ferrous alloy implants occurs in the human body. 7. The most common site for corrosion is the junction between components of implants. 8. The most corrosion-resistant type of ferrous alloy for implant uses is 18/8/Mo steel, which falls within specification En58.J of the British Standards Institute, and specification 316/317 of the American Iron and Steel Institute. 9. About 13 per cent of components removed (and by no means only when something was amiss) showed "face" corrosion when all the components of the implant were made of 18/8/Mo steel. 10. Four per cent of 18/8/Mo components of implants showed corrosion at sites other than the interface between components. 11. On the basis of corrosion resistance it is preferable to use cobalt-chromium-molybdenum alloys for implants that are to be left in the body for an indefinite period. 12. The corrosion resistance of the high alloy steels examined (18/8, 18/8/Ti, 18/8/Mo) does not appear to be related to hardness. 13. The marking of components, either by punching or by electrolytic methods, has not predisposed to corrosion. 14. All hollow 18/8/Mo implants should have a clean and metallurgically satisfactory internal surface. 15. The figures in this report do not permit a full statistical survey of corrosion in surgical implants because it has not been possible to examine a satisfactorily random sample. Many patients cannot be followed up and others die with the implant still in the body

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

Aims. Head-taper corrosion is a cause of failure in total hip arthroplasty (THA). Recent reports have described an increasing number of V40 taper failures with adverse local tissue reaction (ALTR). However, the real incidence of V40 taper damage and its cause remain unknown. The aim of this study was to evaluate the long-term incidence of ALTR in a consecutive series of THAs using a V40 taper and identify potentially related factors. Methods. Between January 2006 and June 2007, a total of 121 patients underwent THA using either an uncemented (Accolade I, made of Ti. 12. Mo. 6. Zr. 2. Fe; Stryker, USA) or a cemented (ABG II, made of cobalt-chrome-molybdenum (CoCrMo); Stryker) femoral component, both with a V40 taper (Stryker). Uncemented acetabular components (Trident; Stryker) with crosslinked polyethylene liners and CoCr femoral heads of 36 mm diameter were used in all patients. At a mean folllow-up of 10.8 years (SD 1.1), 94 patients (79%) were eligible for follow-up (six patients had already undergone a revision, 15 had died, and six were lost to follow-up). A total of 85 THAs in 80 patients (mean age 61 years (24 to 75); 47 (56%) were female) underwent clinical and radiological evaluation, including the measurement of whole blood levels of cobalt and chrome. Metal artifact reduction sequence MRI scans of the hip were performed in 71 patients. Results. A total of 20 ALTRs were identified on MRI, with an incidence of 26%. Patients with ALTR had significantly higher median Co levels compared with those without ALTR (2.96 μg/l (interquartile range (IQR) 1.35 to 4.98) vs 1.44 μg/l (IQR 0.79 to 2.5); p = 0.019). Radiological evidence of osteolysis was also significantly associated with ALTR (p = 0.014). Median Cr levels were not significantly higher in those with ALTR compared with those without one (0.97 μg/l (IQR 0.72 to 1.9) v 0.67 μg/l (IQR 0.5 to 1.19; p = 0.080). BMI, sex, age, type of femoral component, head length, the inclination of the acetabular component, and heterotopic ossification formation showed no significant relationship with ALTR. Conclusion. Due to the high incidence of local ALTR in our cohort after more than ten years postoperatively, we recommend regular follow-up investigation even in asymptomatic patients with V40 taper and metal heads. As cobalt levels correlate with ALTR occurrence, routine metal ion screening and consecutive MRI investigation upon elevation could be discussed. Cite this article: Bone Joint J 2022;104-B(7):852–858

Aims. Surgeons have commonly used modular femoral heads and stems from different manufacturers, although this is not recommended by orthopaedic companies due to the different manufacturing processes. We compared the rate of corrosion and rate of wear at the trunnion/head taper junction in two groups of retrieved hips; those with mixed manufacturers (MM) and those from the same manufacturer (SM). . Materials and Methods. We identified 151 retrieved hips with large-diameter cobalt-chromium heads; 51 of two designs that had been paired with stems from different manufacturers (MM) and 100 of seven designs paired with stems from the same manufacturer (SM). We determined the severity of corrosion with the Goldberg corrosion score and the volume of material loss at the head/stem junction. We used multivariable statistical analysis to determine if there was a significant difference between the two groups. . Results. We found no significant difference in the corrosion scores of the two groups. The median rate of material loss at the head/stem junction for the MM and SM groups were 0.39 mm. 3. /year (0.00 to 4.73) and 0.46 mm. 3. /year (0.00 to 6.71) respectively; this difference was not significant after controlling for confounding factors (p = 0.06). . Conclusion. The use of stems with heads of another manufacturer does not appear to affect the amount of metal lost from the surfaces between these two components at total hip arthroplasty. Other surgical, implant and patient factors should be considered when determining the mechanisms of failure of large diameter metal-on-metal hip arthroplasties. Cite this article: Bone Joint J 2016;98-B:917–24

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

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

Background. Adverse local tissue reactions (ALTR) in metal-on-polyethylene (MoP) total hip arthroplasty (THA) with head-neck taper corrosion is likely to be multifactorial involving implant and patient factors. However, there is a paucity of clinical data on implant parameters as predisposing factors in MoP head-neck taper corrosion. The aim of this study was to identify any potential implant factors associated with failed MoP THA due to head-neck taper corrosion. Methods. A total of 67 MoP THA patients in two groups was investigated: 1) ALTR (n=38) on MARS MRI and 2) non-ALTR (n=29) on MARS MRI. All patients had highly cross-linked polyethylene liners with cobalt-chromium femoral heads with a single head-neck modularity. Parameters compared between groups included: acetabular component orientation, femoral neck shaft angle, radiographic measurement of medial and vertical femoral offsets, limb length discrepancy, component size, femoral head offset, implant type, femoral stem alloy and taper design. Results. The occurrence of ALTR was associated with increased femoral head offset (non-ALTR vs. ALTR, 0.5 ± 3.7 vs. 4.1 ± 3.6, p = 0.008), increased radiographic femoral stem offset (35.9 ± 7.4 mm vs 40.7 ± 7.1mm, p = 0.018), and the use of TMZF alloy stems (p = 0.051). The presence of ALTR was significantly associated with higher cobalt (9.1 µg/L vs. 0.4µg/L, p=0.001) and chromium (2.6µg/L vs. 0.4µg/L). A significant correlation was identified between the serum cobalt level and the femoral stem offset (R=0.375, p=0.009). Conclusions. Although the occurrence of head-neck taper corrosion in MoP THA is likely to be an interplay between implant and patient factors, the results of this study identified increased femoral head and stem offset and the use of TMZF alloy stems as risk factors associated with clinically relevant ALTR due to head-neck taper corrosion in MoP THA patients. The study provides evidenced-based information in risk stratification of symptomatic MoP THA patients for head-neck taper corrosion. For any tables or figures, please contact the authors directly

Introduction: To investigate the head/neck interface of total hip replacements and to see whether the use of small spigots (minispigots) results in enhanced wear and corrosion of tapers compared to standard spigots and the influence of the surface finish on this. Methods: In the total hip replacement combinations the heads were made of cobalt-chrome (CoCr) and the stems of titanium alloy (Ti). Firstly wear and corrosion of minisigots were compared with standard spigots (Test 1) and secondly, these minispigots were compared with another minispigot with a smoother taper surface finish (Test 2). The samples were immersed in aerated Ringers solution (37°C) and loaded for 10 million cycles. The specimens surface parameters and profiles were measured before & after the test. Electrochemical static corrosion tests were carried out on the rough & smooth minispigots from Test 2 where the current was measured with constant potential under loaded and non-loaded conditions. A cyclical sinusoidal load of 1500-200 Newtons for 1000 cycles at ~1 Hz was used. Pitting tests measured the current while increasing and then decreasing the potential of non-loaded and loaded specimens. Two newly manufactured rough and smooth minispigots were subjected to the same electrochemical corrosion tests. Results: In Test 1 the results demonstrated that pre-test the surfaces of the female tapers were similar for all heads. Post-testing the Ra values on the female tapers had become greater for the minispigots compared with standard spigots. An abrupt change was noted on the surface profile of the female taper where it was in contact with the male Ti taper, indicating the the CoCr head had corroded. The Ti male tapers were unchanged. Scanning electron microscopy showed that the coarser profile in the corroded region of the CoCr was similar to the profile on the Ti male taper. Pitting corrosion was evident in the grooves on the CoCr. In Test 2 the smooth spigots were not affected, but in the rough minispigots, Ra values had increased in the female tapers. Static corrosion tests showed evidence of fretting in the rough but not the smooth minispigots. When comparing new rough & smooth minispigots, static corrosion testing with clyclical loading showed that for minispigots with a rough finish the current fluctuated with each cycle. Pitting scans showed a greater hysteresis with the rough minispigot compared with the smooth minispigot indicating potentially greater corrosion in the former. Conclusion: The cobalt-chrome/titanium alloy combinations where the surface finish on the male taper was coarse, corrosion was increased in minispigots compared with standard spigots. This was due to the smaller area of contact of the minispigot at the interface. This corrosion appears to be mediated through the mechanism of fretting corrosion. Surface finish was crucial and corrosion of the minispigot was reduced if the surface finish was smooth. Manufacturers should investigate the effect of surface finish on the corrosion of their tapers particularly where cobalt-chrome/titanium alloy combinations are used

Aim:. The aim of this study was test the amount of corrosion occurring at the (Ti) /cobalt chrome (CoCr) interface comparing this with Ti and Ti interfaces. This was compared with retrieved metal work visualised under a scanning electron microscope (SEM). Methods:. The interface of interest is the interface between rod and the screw. We investigated corrosion seen at that interface with a CoCr rod coupled to a Ti screw versus a Ti rod coupled to a Ti screw (6 screws were used) Implants were loaded according to the ASTM F2193 – 02 Standard Specifications and Test Methods for Components Used in the Surgical Fixation of the Spinal Skeletal System. Pitting potentials were monitored using cyclic potentiodynamic polarization tests (ASTM F2129 – 08 Standard Test Method for Conducting Cyclic Potentiodynamic Polarisation Measurements) to determine corrosion susceptibility. Retrieved implants were visualised under (SEM) to confirm corrosion. Results:. Mean fretting current for titanium and cobalt chrome was 7.94 (μA) and for titanium on titanium 5.89 (μA). The results of SEM showed evidence of fretting and galvanic corrosion. Discussion:. Cobalt chrome ions in hip implants have raised concern amongst the orthopaedic community. This study showed that metal ion production occurs due to fretting and galvanic corrosion. This corrosion is increased in cobalt chrome and titanium constructs but statistically more tests are required to confirm this. Further research is required to understand this interface as cobalt chrome ions pose a potential hazard to patients with their reproductive years ahead. Conflict Of Interest Statement: No conflict of interest

Adverse reaction to wear and corrosion debris is a cause for concern in total hip arthroplasty (THA). Modular junctions are a potential source of such wear products and are associated with secondary pseudotumour formation. . We present a consecutive series of 17 patients treated at our unit for this complication following metal-on-highly cross-linked polyethylene (MoP) THA. We emphasise the risk of misdiagnosis as infection, and present the aggregate laboratory results and pathological findings in this series. The clinical presentation was pain, swelling or instability. Solid, cystic and mixed soft-tissue lesions were noted on imaging and confirmed intra-operatively. Corrosion at the head–neck junction was noted in all cases. No bacteria were isolated on multiple pre- and intra-operative samples yet the mean erythrocyte sedimentation rate was 49 (9 to 100) and C-reactive protein 32 (0.6 to 106) and stromal polymorphonuclear cell counts were noted in nine cases. . Adverse soft–tissue reactions can occur in MoP THA owing to corrosion products released from the head–neck junction. The diagnosis should be carefully considered when investigating pain after THA. This may avoid the misdiagnosis of periprosthetic infection with an unidentified organism and mitigate the unnecessary management of these cases with complete single- or two-stage exchange. Cite this article: Bone Joint J 2015;97-B:1024–1030

Metallic contacts in hip replacements are susceptible to wear and corrosion processes which lead to the release of particles and metal ions. Adverse local tissue reactions (ALTRs) and systemic manifestations to solid and soluble debris can be debilitating for the patients. It is believed that particles originating from CoCrMo taper junctions trigger more severe body reactions compared to debris from MoM hip bearings. The body's reaction is highly dependent on particle characteristics, such as size, morphology, composition and aggregation state, which can reflect the specific wear and corrosion conditions at the site of release. Here we proposed to investigate wear and corrosion flakes collected from around CoCrMo tapers at the time of revision. The particles were initially characterised with scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). This revealed the microstructure of the corrosion products, which appeared to be made of smaller metallic aggregates, entrapped in a biological matrix. The in depth characterisation of the particles released from the organo-metallic composite, was performed with transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM), both fitted with EDX. The investigation revealed clusters and individual nanoparticles, as small as 3 nm, which represent the building blocks of the large corrosion flakes, reported and characterised in the past mainly with low resolution microscopy techniques. The majority of the particles consisted of Cr and O, potentially in the form of chromium oxides, with little evidence of Co and Mo. Particles size distribution (PSD) provided by STEM and TEM characterisation showed statistically different results. The STEM technique was able to resolve tiny particles found in close proximity and provided a PSD shift towards the smaller end of the size range. The study is the first to show microscopy evidence of Cr rich nanoparticles (3–60 nm) released in vivo from the modular taper interface, which can have important health implications caused by their increased potential to disseminate and corrode within the body

Introduction. The possibility of corrosion at the taper junction of hip replacements was initially identified as a concern of generating adverse reactions in the late 1980s. Common clinical findings of failure are pain, clicking, swelling, fluid collections, soft tissue masses, and gluteal muscle necrosis identified intra operatively. Methodology. The joint replacement surgery was performed utilizing a posterior approach to the hip joint. The data from all surgical, clinical and radiological examinations was prospectively collected and stored in a database. Patients were separated into two groups based on bearing material, where group 1 had a CoC bearing and ABG modular stem whilst group 2 had a MoM bearing and SROM stem, with each group having 13 cases. Pre-operative revision surgery and post-operative blood serum metal ion levels we collected. Cup inclination and anteversion was measured using the Ein-Bild-Roentgen-Analyse (EBRA) software. A range of 2–5 tissue sections was examined per case. 2 independent observers that were blinded to the clinical patient findings scored all cases. The tissue grading for the H&E tissue sections were graded based on the presence of fibrin exudates, necrosis, inflammatory cells, metallic deposits, and corrosion products. The corrosion products were identified into 3 groups based on visible observation and graded based on abundance. A scanning electron microscope (SEM) Hitachi S3400 was used to allow for topographic and compositional surface imaging. Unstained tissue sections were used for imaging and elemental analysis. X-Ray diffraction was the analytical technique used for the taper debris that provided identification on the atomic and molecular structure of a crystal. Result. Group 1 patients showed a significant reduction (p = 0.0002) in the Co, however the decrease of Cr ion concentration had no statistical significance (p = 0.48). The Co (p = 0.001) and Cr (p = 0.02) levels significantly reduced after revision surgery for patients within group 2. The largest differences in the abundance between the two groups were for the brown/red corrosion particles where group 2 is highly significant (p<0.001) compared to group 1. The specific identification was determined using a mapping technique that showed the red/brown colour consisted of evenly scattered Ti (green) and Cr (red) particles (figure 1). Elemental analysis of the green shards showed chromium as a major metallic element with traces of cobalt (figure 2). The ABG modular collected debris matched the peaks of the following crystaline strucutes: chromium oxide (CrO), titantium oxide (TiO2), and chromium oxide (Cr2O3), and iron titanium oxide (Fe2Ti3O9) (figure 2). The peaks from the XRD scan were assessed against these possible elements which showed the most were aluminium nitride and chromium oxide (Cr2O3). Both implant configurations produced an ALTR response indicative from the tissue sections graded and visually observed. Conclusion. This study has characterized the corrosion products produced at taper junctions. The histology presented with similar results across the two groups suggestive that due to the same corrosion products found between both groups this was expected

Introduction. The release of metal debris and ions has raised concerns in joint arthroplasty. In THA metal debris and ions can be generated by wear of metal-on-metal bearing surfaces and corrosion at modular taper interfaces, currently understood to be mechanically assisted crevice corrosion (MACC) [1]. More recently, inflammatory-cell induced corrosion (ICIC) has been identified as a possible source of metal debris and/or ions [2]. Although MACC has been shown to occur at modular junctions in TKA, little is known about the prevalence of other sources. The purpose of this study was to determine the sources of metallic debris and ion release in long-term implanted (in vivo > 15y) TKA femoral components. Specific attention was paid to instances of ICIC as well as damage at the implant-bone interface. Methods. 1873 retrieved TKA components were collected from 2002–2013 as part of a multi-center, IRB-approved retrieval program. Of these, 52 CoCr femoral condyles were identified as long term TKA (Average: 17.9±2.8y). These components were predominantly revised for loosening, PE wear and instability. 40/52 of the components were primary surgeries. Components were examined using optical microscopy to confirm the presence of 5 damage mechanisms (polyethylene failure, MACC corrosion of modular tapers, corrosion damage between cement and backside, third-body wear, and ICIC). Third-body wear was evaluated using a semi-quantitative scoring method based on the percentage of damaged area. A score of 1 had minimal damage and a score of 4 corresponded to severe damage. Polyethylene components were scored using the Hood method and CoCr components were scored similarly to quantify metal wear. The total area damaged by ICIC was quantified using photogrammetry. Images were taken using a digital SLR with a calibrated ruler in the same focal plane. Using known pixel dimensions, the ICIC damaged area was calculated. Results. Surface damage indicative of corrosion and/or CoCr debris release was identified in 92% (n=48) of the components. Third-body wear was the most prevalent damage mechanism identified in 77% (n=40/52; Figure 1) of these components. ICIC was identified in 38% (n=20/52, figure 2) of the components. The polyethylene damage scores were predominantly a score of 4 out of a maximum score of 4 (89%). The corresponding femoral components had moderate to severe damage scores, with 39% with a score of 2, 37% scoring 3 and 22% scoring 4 out of a maximum score of 4. The total ICIC damaged area was an average of 0.11 ± 0.12 mm. 2. (Range: 0.01–0.46mm. 2. ). Discussion. In this study, we sought to identify mechanisms that could lead to the release of CoCr debris/ions in TKA. Five different mechanisms of potential metal release were observed. The most prevalent were third-body wear and ICIC damage. However the clinical implications remain unclear for several mechanisms because none of the devices were revised due to adverse local tissue reactions or biologic reactions to CoCr. Although we documented the prevalence of each damage mechanism, the quantity of metal removal was not investigated, warranting future studies

Objectives. Mechanical wear and corrosion at the head-stem junction of total hip arthroplasties (THAs) (trunnionosis) have been implicated in their early revision, most commonly in metal-on-metal (MOM) hips. We can isolate the role of the head-stem junction as the predominant source of metal release by investigating non-MOM hips; this can help to identify clinically significant volumes of material loss and corrosion from these surfaces. Methods. In this study we examined a series of 94 retrieved metal-on-polyethylene (MOP) hips for evidence of corrosion and material loss at the taper junction using a well published visual grading method and an established roundness-measuring machine protocol. Hips were retrieved from 74 male and 20 female patients with a median age of 57 years (30 to 76) and a median time to revision of 215 months (2 to 324). The reasons for revision were loosening of both the acetabular component and the stem (n = 29), loosening of the acetabular component (n = 58) and infection (n = 7). No adverse tissue reactions were reported by the revision surgeons. Results. Evidence of corrosion was observed in 55% of hips. The median Goldberg taper corrosion score was 2 (1 to 4) and the annual rate of material loss at the taper was 0.084 mm. 3. /year (0 to 0.239). The median trunnion corrosion score was 1 (1 to 3). Conclusions. We have reported a level of trunnionosis for MOP hips with large-diameter heads that were revised for reasons other than trunnionosis, and therefore may be clinically insignificant. Cite this article: H. S. Hothi, D. Kendoff, C. Lausmann, J. Henckel, T. Gehrke, J. Skinner, A. Hart. Clinically insignificant trunnionosis in large-diameter metal-on-polyethylene total hip arthroplasty. Bone Joint Res 2017;6:52–56. DOI: 10.1302/2046-3758.61.BJR-2016-0150.R2

Objectives. The Precice nail is the latest intramedullary lengthening nail with excellent early outcomes. Implant complications have led to modification of the nail design. The aim of this study was to perform a retrieval study of Precice nails following lower-limb lengthening and to assess macroscopical and microscopical changes to the implants and evaluate differences following design modification, with the aim of identifying potential surgical, implant, and patient risk factors. Methods. A total of 15 nails were retrieved from 13 patients following lower-limb lengthening. Macroscopical and microscopical surface damage to the nails were identified. Further analysis included radiology and micro-CT prior to sectioning. The internal mechanism was then analyzed with scanning electron microscopy and energy dispersive x-ray spectroscopy to identify corrosion. Results. Seven male and three female patients underwent 12 femoral lengthenings. Three female patients underwent tibial lengthening. All patients obtained the desired length with no implant failure. Surface degradation was noted on the telescopic part of every nail design, less on the latest implants. Microscopical analysis confirmed fretting and pitting corrosion. Following sectioning, black debris was noted in all implants. The early designs were found to have fractured actuator pins and the pin and bearings showed evidence of corrosive debris. The latest designs showed evidence of biological deposits suggestive of fluid ingress within the nail but no corrosion. Conclusion. This study confirms less internal corrosion following modification, but evidence of titanium debris remains. We recommend no change to current clinical practice. However, potential reuse of the Precice nail, for secondary limb lengthening in the same patient, should be undertaken with caution. Cite this article: V. C. Panagiotopoulou, K. Davda, H. S. Hothi, J. Henckel, A. Cerquiglini, W. D. Goodier, J. Skinner, A. Hart, P. R. Calder. A retrieval analysis of the Precice intramedullary limb lengthening system. Bone Joint Res 2018;7:476–484. DOI: 10.1302/2046-3758.77.BJR-2017-0359.R1

INTRODUCTION. Due to increasing interest into taper corrosion observed primarily in hip arthroplasty devices with modular tapers, efforts towards characterizing the corrosion byproducts are prevalent in the literature [1–4]. As a result of this motivation, several studies postulate cellular induced corrosion due to the presence of remarkable features in the regions near taper junction regions and articulating surfaces [3–5]. Observations made on explanted devices from a retrieval database as well as laboratory tests have led to the alternative proposal of electrocautery-electrosurgery damage as the cause of these features. These surgical instruments are commonly used for hemostasis or different degrees of tissue dissection. METHODS. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to evaluate the features observed on retrieved devices. Retrieved devices consisted of OXINIUM and cobalt-chromium-molybdenum (CoCrMo) femoral implants, a Titanium-alloy hip stem, and a CoCrMo metal-on-metal femoral head. Electrocautery-electrosurgery damage was created using a SurgiStat II (Valleylab, Colorado) onto various components (CoCrMo, OXINIUM femoral heads as well as Ti-6Al-4V and CoCrMo alloy test stem constructs). Test components were evaluated using the same methods as the retrieved devices. RESULTS. Remarkable features were present on retrieved devices (Figure 1) which were similar to previous studies (3–5). The appearance of these features could be described as crater-like, pitted, scratched, molten or splattered material, and ruffled. These features were present on articulating and non-articulating regions as well as near taper junctions. Testing performed on samples using the SurgiStat II, created features that were similar in appearance (Figure 1). Additionally, material transfer that included an iron peak based on EDS in addition to the cobalt and chromium (present due to native material) was detected in the regions of contact (Figure 2). CONCLUSIONS. It was possible to re-create damage features similar to those previously characterized as remarkable features created by cellular-induced corrosion [3–5]. It is theorized that the high-voltage based electrocautery (commonly Bovie) or high-frequency based electrosurgical devices can result in localized degradation/alteration of oxides and passive regions of commonly used orthopaedic alloys. These surgical instruments, specifically the cutting electrodes, are frequently made of stainless steels which can result in iron transfer during contact with the device. During the surgical use of the electrocautery-electrosurgery instrument, it may be necessary to remove tissue, bone, or cauterize near the implant or explant which may have led to the damage features noted in this study and the previous literature [3–5]. If this damage occurs during the initial implantation of the devices, it may further exacerbate corrosion in the damaged region and/or alter the mechanical integrity of the constructs (i.e. fatigue performance)

Wear and corrosion debris generated from total hip replacements (THR) can cause adverse local tissue reactions (ALTR) or osteolysis, often leading to premature implant failure. The tissue response can be best characterized by histopathological analysis, which accurately determines the presence of cell types, but is limited in the characterization of biochemical changes (e.g. protein conformation alteration). Fourier transform infrared micro-spectroscopy imaging (FTIRI) enables rapid analysis of the chemical structure of biological tissue with a high spatial resolution, and minimal additional sample preparation. The data provides the most information through multivariate method carried out by hierarchical clustering analysis (HCA). It is the goal of this study to demonstrate the beneficial use of this multivariate approach in providing pathologist with biochemical information from cellular and subcellular organization within joint capsule tissue retrieved from THR patients. Joint capsule tissue from 2 retrieved THRs was studied. Case 1: a metal-on-polyethylene THR, and Case 2: a dual modular metal-on-metal THR. Prior to FTIRI analysis, tissue samples were formalin-fixed paraffin-embedded and 5μm thick microtome sectioned samples were prepared and mounted on BaF. 2. discs and deparaffinized. FTIRI data were collected using high-definition transmission mode (pixel size: ∼1.1 μm. 2. ). Hyperspectral images were exported to CytoSpec V2.0.06 for processing and reconstruction into pseudo-color maps based on cluster assignments. Case 1 exhibited a strong presence of lymphocytes and macrophages (Fig. 1a). Since the process of taking second derivatives reduces the half width of the spectral peaks, it increases the sensitivity toward detecting shoulders or second peaks that may not be apparent in the raw spectra (Fig. 1b). Thus, areas occupied by lymphocytes and macrophages can be easily distinguished providing a fast tissue screening method. Here, HCA was able to distinguish macrophages and lymphocytes based on the infrared response, even in areas where both occurred intermixed. (Fig. 1c) The tissue in direct proximity to cells had a slightly altered collagenous structure. Case 1 also exhibited multiple glassy, green particles which can typically observed around THRs that underwent taper corrosion (Fig. 2a). HCA image was able to visualize and distinguish large CrPO. 4. particles, embedded within fibrin exudate rich areas, collagenous tissue without inflammatory cells, and a nearby area with a strong macrophage presence and some finer CrPO. 4. particles (Fig. 2d). Moreover, this method can not only locate macrophages, but distinguish particle-laden macrophages depending the type of particles within the cells. In Case 2 (Fig. 3a), clustering results (Fig. 3 b&c) are consistent with the fact that different particle types are associated with MoM bearing surface wear (Co rich particles), corrosion of the CoCrMo taper junctions (Cr-oxides and –phosphate), fretting of Ti-alloy dual modular tapers (Ti-oxides, Ti alloy particles), and even suture debris, which all occurred in this case. Although details of debris types are not available, specifications are possible by coupling other techniques. The results demonstrate that multivariate FTIRI based spectral histopathology is a powerful tool to characterize the chemical structure and foreign body response within periprosthetic tissue, thus providing insights into the biological impact of different types of implant debris. For any figures or tables, please contact the authors directly

In metal-on-metal (MoM) total hip arthroplasty, the taper interface is where the femoral head (female taper surface) attaches to the trunnion (male taper) of the femoral stem. Corrosion is well reported in metal-on-polyethylene hips but little is known about taper corrosion in MoM devices. The aim of this study was to quantify corrosion in modern-generation stemmed MoM hip systems and gain insight into the nature of the underlying corrosive attack. Taper corrosion was quantified in 161 failed MoM components (head components n=128; femoral stem n=33) from nine hip types with the use of a qualitative subjective scoring system. An unanticipated finding on preliminary inspection of the hips was a region on the female taper surface that contained ridges that directly corresponded with the ridged microthread on the trunnion. The ridges were not present on unimplanted (control) female taper surfaces and therefore a novel four-scale subjective scoring system was devised to quantify the prevalence and severity of this ‘imprinting’ phenomenon. Evidence of corrosion was observed in 81% (131/161) of components, with at least moderate corrosion observed in 58% (94/161). Corrosion was greater on the female taper surface than on the male taper (p=0.034) and the two scores were associated (r=0.784, p=0.001). Imprinting affected all manufacturers and was observed in 64% (82/128) of head components. The corrosion and imprinting scores were strongly correlated (r=0.694, p=0.001). Corrosion was largely confined to the area of the female taper interface where imprinting had occurred i.e. the region that had been in contact with the trunnion microthread. Scanning electron microscopy showed evidence of fretting corrosion and substantial mechanical wear within the ridged region on the female taper surface. Our study indicates that MoM hips are susceptible to taper corrosion. We believe it occurs by a process of “mechanically-assisted crevice corrosion,” involving the following sequence of events: joint fluid enters the taper junction as a result of pumping of fluid along the machined microthread of the trunnion. This results in galvanic corrosion of the anodic surface (the cobalt-chromium femoral head or taper sleeve). The pattern of corrosion of the head taper is determined by the surface profile of the screw thread of the trunnion, thus leaving an imprinted appearance. Historically the ridged microthread was introduced to trunnions to minimise the risk of burst fracture of ceramic heads. However this study indicates that the ridges are detrimental in MoM hips by causing extensive mechanical wear. Thus the possibility that cobalt-chrome and ceramic femoral head components require different trunnion designs needs urgent investigation