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

Introduction. Mechanically assisted crevice corrosion (MACC) in metal-on-polyethylene (MOP) total hip arthroplasty (THA) is of concern, but its prevalence, etiology and natural history are incompletely understood. Methods. From January 2003 to December 2012, 1356 consecutive THA surgeries using a titanium stem, cobalt chromium alloy femoral head, highly crosslinked polyethylene and a tantalum or titanium acetabular shell were performed. Patients were followed at 1 year, and 5 year intervals for surveillance, but also seen earlier if they had symptoms. Any patient with osteolysis or unexplained pain underwent exam, radiographs, CBC, ESR and CRP, as well as serum cobalt (Co) and chromium (Cr) level. MARS MRI was performed if the Co level was > 1 ppb. Results. Symptomatic MACC was present in 39/1356 patients (2.9%). Yearly MACC prevalence ranged from 0 % (0/139, 2005) to 9.9 % (16/162, 2009). 22/39 (56%) patients have undergone revision surgery, and 17/39 (44%) have opted for ongoing surveillance. Of the surveillance patients, serial serum metal ion levels appear to increase over time. Time of symptoms is correlated with tissue necrosis at time of revision. Conclusions. The prevalence of MACC in MOP hips is higher in this cross-sectional study than previously reported. The highest prevalence was found in 2009 with this vendor. Based on how common this finding is in symptomatic patients from 2009, we may consider asking asymptomatic patients to obtain baseline serum ion levels. The goal of our ongoing research is to understand how to avoid permanent soft tissue loss from adverse local tissue reactions caused by MACC

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

Introduction. The process of wear and corrosion at the head-neck junction of a total hip replacement is initiated when the femoral head and stem are joined together during surgery. To date, the effects of the surface topography of the femoral head and metal stem on the contact mechanics during assembly and thus on tribology and fretting corrosion during service life of the implant are not well understood. Therefore, the objective of this study was to investigate the influence of the surface topography of the metal stem taper on contact mechanics and wear during assembly of the head-neck junction using Finite Element models. Materials and Methods. 2D axisymmetric Finite Element models were developed consisting of a simplified head-neck junction incorporating the surface topography of a threaded stem taper to investigate axial assembly with 1 kN. Subsequently, a base model and three modifications of the base model in terms of profile peak height and plateau width of the stem taper topography and femoral head taper angle were calculated. To account for the wear process during assembly a law based on the Archard equation was implemented. Femoral head was modeled as ceramic (linear-elastic), taper material was either modeled as titanium, stainless steel or cobalt-chromium (all elastic-plastic). Wear volume, contact area, taper subsidence, equivalent plastic strain, von Mises stress, engagement length and crevice width was analyzed. Results. Titanium tapers showed largest wear volume throughout all simulations, followed by stainless steel and cobalt-chromium. A larger head taper angle resulted in an increase of the wear volume for all taper materials while the increase of the plateau width resulted in a decrease of the wear volume. Taper subsidence, von Mises stress and equivalent plastic strain followed the same trends. Contact area was largest for the models with a large plateau width for all taper materials. Other taper parameters had little effect on contact area. A pure increase of the angular mismatch (AM) resulted in the strongest decrease of the engagement length, while a combined increase of the AM and plateau width showed only a moderate decrease. The smallest effect concerning the engagement length was found when a combined increase of the profile peak height and AM was simulated. Crevice width was largest for a pure increase of the AM and for a combined increase of the AM and profile peak height for all taper materials. Discussion. This study showed that depending on the surface topography and material of the stem taper, wear and taper mechanics during assembly could be affected. For the examined surface topographies wear is distinctively elevated by increasing the AM and the profile peak height due to the resulting higher mechanical loading. More parameter studies under in vivo loading and the study of other taper surface parameters like the peak-to-peak distance have to be conducted to get a deeper insight into taper mechanics and wear effects. However, this study demonstrates the importance of good manufacturing practice of components for hip replacement systems to guarantee reproducible taper mechanics. For any figures or tables, please contact authors directly

Taper corrosion and Trunionnosis are recognized as a major complication of hip replacement surgery presenting in a variety of clinical manifestations commonly referred to as Adverse Local Tissue Reactions. Metal debris is produced through Mechanically Assisted Crevice Corrosion with several implicating factors including mixed alloy components, taper design, head offset, femoral head size, and taper impaction techniques (including magnitude of force, control of alignment and environmental factors). Our project has focused singularly on taper impaction techniques and surgeon controlled factors, as we believe the process of head impaction unto a trunnion is non-standardized, which often times dooms the trunionn to failure. We have contemplated a standardization process, such that given the right tool, the surgeon can control the quality of the taper interlock, which may produce a “cold weld” or perfect taper interlock, eliminate micro motion, mechanically assisted crevice corrosion, and trunionnosis. We have considered four specific problems with current head to trunionn impaction techniques: 1. The magnitude of applied force is uncontrolled, haphazard, and non-standardized. 2. Non-axial application of force is the norm, which produces canting, leading to micro-motion and tribocorrosion. 3. The transfer of energy from the head to the trunionn interface is highly inefficient, such that the energy produced by the surgeon is mostly dissipated in a non-constrained system. 4. No in vitro studies exist to guide surgeons as to the magnitude of force required for a proper interlock. Regardless of the design, including taper angles, larger heads, offset heads, mixed alloy components, shorter and slimmer trunionns there is a widespread problem with the process of head impaction onto the trunionn and the engagement of the modular taper interface that dooms the trunionn interface to failure. The deficiencies noted in current techniques are addressed with a simple tool and minor modification of the femoral stem. We present a new concept/apparatus for head to trunionn taper assembly that fully controls the magnitude and direction of assembly force within a constrained, dry and contaminant free environment. This tool allows application of a perfectly axial and high insertional forces without risk of damage to the femoral stem/bone interface to obtain a cold weld and perfect taper interlock with no chance for canting, micro motion and tribocorrosion. The concept has been verified through several prototypes and can be adopted in order to standardize the process of taper assembly, making this procedure independent of surgeon skill and strength, and minimizing the incidence of trunionnosis

INTRODUCTION. The lifetime of total hip replacements (THR) is often limited by adverse local tissue reactions to corrosion products generated from modular junctions. Two prominent damage modes are the imprinting of the rougher stem topography into the smoother head taper topography (imprinting) and the occurrence of column-like troughs running parallel to the taper axis (column damage). It was the purpose of this study to identify mechanisms that lead to imprinting and column damage based on a thorough analysis of retrieved implants. METHODS. 776 femoral heads were studied. Heads were visually inspected for imprinting and column damage. Molds were made of each head taper and scanned with an optical coordinate measuring machine. The resulting intensity images were used to visualize damage on the entire surface. In selected cases, implant surfaces were further analyzed by means of scanning electron microscopy (SEM) and white light interferometry. The alloy microstructure was characterized for designs from different manufactures. RESULTS. 165 heads exhibited moderate to severe damage (modified Goldberg scale). Out of those heads 83% had imprinting and 28% exhibited column damage. In most cases with imprinting, the entire contact area between stem and head was affected (Figure 1). Several cases exhibited early signs of imprinting, usually starting on the distal-inferior and distal superior side. High resolution SEM imaging revealed that imprinting was a fretting driven process that was independent of the hardness and material of the stem and head. The SEM images showed that the main mechanism was surface fatigue under partial slip fretting. The generated wear debris was the primary driver of imprinting by three-body fretting. The effect was detrimental on the smoother head surface, but less severe on the rougher stem, where debris was pushed into the troughs of the machining mark topography. 90% of cases with column damage also exhibited imprinting. The other ten percent were either cases in which column damage was too extensive to identify imprinting, or the stem taper was smooth and therefore could not induce imprinting. Metallographic analysis showed that column damage was dictated by the alloy microstructure. Wrought alloy heads frequently exhibited banding related to slight alloy segregations. The process of column damage was entirely chemically driven with etching occurring along the banded microstructure eventually resulting in troughs that were several tens of micrometers deep (Figure 2). DISCUSSION. Imprinting and column damage are common damage modes in THR femoral heads. Imprinting is fretting (miro-motion) driven while column damage is caused chemically, but is also dictated by the alloy micro-structure. However, the results suggest that these two damage modes may be related. The damage process starts with local fretting slowly progressing to a large area of imprinting. The imprinting process leads to widening of the crevice, enabling joint fluid and biological constituents (protein, cells, etc.) to enter the taper interface. This change in local chemistry within a confined crevice environment can cause an etching process that leads to column damage, but only if the femoral head alloy has a banded microstructure

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

Corrosion at metal/metal modular interfaces in total hip arthroplasty was first described in the early 1990s, and the susceptibility of modular tapers to mechanically assisted crevice corrosion (MACC), a combination of fretting and crevice corrosion, was subsequently introduced. Since that time, there have been numerous reports of corrosion at this taper interface, documented primarily in retrieval studies or in rare cases of catastrophic failure. We have reported that fretting corrosion at the modular taper may produce soluble and particulate debris that can migrate locally or systemically, and more recently reported that this process can cause an adverse local tissue reaction (ALTR). Based on the type of tissue reaction and the presence of elevated serum metal ion levels, this process appears quite similar to ALTRs secondary to metal on metal bearing surfaces. While modularity in total hip replacement has demonstrable clinical benefits, modular junctions increase the risk of tribocorrosion and the types of ALTRs seen in patients with accelerated metal release from metal-on-metal bearing total hip replacements. The use of modular connections should be minimised in routine primary total hip replacement to avoid tribocorrosion-induced ALTRs

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

Corrosion at metal/metal modular interfaces in total hip arthroplasty was first described in the early 1990's, and the susceptibility of modular tapers to mechanically assisted crevice corrosion (MACC), a combination of fretting and crevice corrosion, was subsequently introduced. Since that time, there have been numerous reports of corrosion at this taper interface, documented primarily in retrieval studies or in rare cases of catastrophic failure. We have reported that fretting corrosion at the modular taper may produce soluble and particulate debris that can migrate locally or systemically, and more recently reported that this process can cause an adverse local tissue reaction. Based on the type of tissue reaction and the presence of elevated serum metal ion levels, this process appears quite similar to adverse local tissue reactions secondary to metal-on-metal bearing surfaces. While modularity in THR has demonstrable clinical benefits, modular junctions increase the risk of corrosion and the types of adverse soft tissue reactions seen in patients with accelerated metal release from metal-on-metal bearing THRs

Corrosion at metal/metal modular interfaces in total hip arthroplasty was first described in the early 1990's, and the susceptibility of modular tapers to mechanically assisted crevice corrosion (MACC), a combination of fretting and crevice corrosion, was subsequently introduced. Since that time, there have been numerous reports of corrosion at this taper interface, documented primarily in retrieval studies or in rare cases of catastrophic failure. We have reported that fretting corrosion at the modular taper may produce soluble and particulate debris that can migrate locally or systemically, and more recently reported that this process can cause an adverse local tissue reaction. Based on the type of tissue reaction and the presence of elevated serum metal ion levels, this process appears quite similar to adverse local tissue reactions secondary to metal on metal bearing surfaces. While modularity in THR has demonstrable clinical benefits, modular junctions increase the risk of corrosion and the types of adverse soft tissue reactions seen in patients with accelerated metal release from metal-on-metal bearing THRs

Corrosion at metal/metal modular interfaces in total hip arthroplasty was first described in the early 1990's, and the susceptibility of modular tapers to mechanically assisted crevice corrosion (MACC), a combination of fretting and crevice corrosion, was subsequently introduced. Since that time, there have been numerous reports of corrosion at this taper interface, documented primarily in retrieval studies or in rare cases of catastrophic failure. We have reported that fretting corrosion at the modular taper may produce soluble and particulate debris that can migrate locally or systemically, and more recently reported that this process can cause an adverse local tissue reaction. Based on the type of tissue reaction and the presence of elevated serum metal ion levels, this process appears quite similar to adverse local tissue reactions secondary to metal on metal bearing surfaces. While modularity in THR has demonstrable clinical benefits, modular junctions increase the risk of corrosion and the types of adverse soft tissue reactions seen in patients with accelerated metal release from metal-on-metal bearing THRs

Introduction. Dual modular femoral stems for total hip arthroplasty were initially introduced to optimize joint biomechanics. These implants have been recalled due to fretting and crevice corrosion at the stem-neck interface, ultimately necessitating revision in a significant number of patients. At our institution we had experience with the Rejuvenate (Stryker, Mahwah, NJ) dual modular stem from 2009 until 2011 before it's recall in 2012. This study identifies complications encountered in patients requiring revision of this prosthesis. Methods. We retrospectively identified all patients who had one particular dual modular stem using our registry database. All patients’ charts and imaging was reviewed using our electronic medical records and digital imaging programs. Patients’ age, gender, revision date, intraoperative and postoperative complications, need for subsequent surgery were identified. Results. 118 femoral stems were implanted in 107 patients (61 male & 46 female) with average follow up of over 3 years. 40 stems (34%) were revised in 36 patients with an average time to revision of 2.7 years. Women had a revision rate of 42% versus 28% in men for an odds ratio of 1.5. Complications were also increased overall with a predilection for women. 7 (15%) of revisions required an extended trochanteric osteotomy (ETO), and 5 (12.5%) had greater trochanter (GT) fractures. The most common complication postoperatively was dislocation in 25% of patients, 7 of which required reoperation. One patient had an infection after revision requiring 2-stage revision. Discussion and Conclusion. Dual modular femoral stems are associated with a high early failure rate due to fretting and crevice corrosion. Women in particular are at higher risk for need for revision and have a higher complication rate during and after revision. A significant number of our patients required an ETO or had a GT fracture intraoperatively. Additionally, adverse local tissue reactions (ALTR) are shown to affect the abductor muscles and joint capsule. These two factors likely contribute to the high dislocation rate after revision. Preoperatively counsel patients on the higher complication rate and revision should be carried out carefully to prevent fracture and maximize stability of the hip

Introduction. Manifestation of high interface stresses coupled with micromotion at the interface can render the taper lock joint in a modular hip replacement prosthesis at risk for failure. Bending can lead to crevice formation between the trunnion and the head and can potentially expose the interface to the biological fluids, generating interface corrosion. Additionally, development of high stresses can cause the material to yield, ultimately leading to irreversible damage to the implant. The objective of this study is to elucidate the mechanical response of taper junction in different material combination assemblies, under the maximum loads applied during everyday activities. Methods. Computer simulations were executed using a verified FE model. A stable hexahedral mesh (33648 elements) was generated for the trunnion (taper size: 12/14mm) and a tetrahedral mesh (51182 elements) for the head (CoCr, size: 32mm). An assembly load of 4000N was applied along the trunnion axis followed by the application of a load of 230–4300N at 25° and 10° angle to the trunnion axis in the frontal and sagittal planes. A linear static solution was set up using Siemens NX Nastran. Two material combinations were tested - cobalt-chrome head with a titanium alloy trunnion and cobalt chrome head with a cobalt-chrome trunnion. Results. Table1 compares the results obtained from the simulation to those observed in experimental simulations performed under similar loading conditions in our lab. Larger vertical interface displacement was observed in the CoCr-CoCr assembly during toggle-inducing loads. The trunnion bending inside the femoral head was higher in the Ti-CoCr assembly (0.056) compared to the CoCr-CoCr assembly (0.027) with the overall bending of the Ti-CoCr assembly also observed to be much higher (Fig.1). Negligible difference between the stress measured in the femoral head and taper was observed (Fig.2). Discussion. Bending could potentially lead to the development of higher stresses especially under multiple cycles of loading. Fatigue and plastic deformation could result in irreparable damage to the interface leading to implant failure. Additionally, bending causes a separation of the interfaces at the trunnion-head junction, leading to crevice formation, triggering corrosion by exposure to the surrounding physiological environment. Thus, it is crucial that we understand the mechanics of the trunnion-head junction especially under conditions of functional loading

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

Introduction. Taper corrosion has been identified to be major problem in total hip replacement during the past years. Patients may suffer from adverse local tissue reactions (ALTR) due to corrosion products that are released from modular taper connection. So far, the mechanism that leads to taper corrosion in taper connections is not fully understood. Some retrieval studies tried to correlate implant related design parameters to the incidence and the severeness of taper corrosion. For example Kocagöz et al.[1] have not seen an influence of the taper clearance to taper corrosion. Hothi et al.[2] showed that shorter and rougher tapers increase taper corrosion. One limitation of retrieval studies may be that the analysed tapers are used and may have been altered during in vivo service. Beside the effect of taper corrosion many surgeons are not aware that the tapers may vary among different manufactors. With our study we want to provide taper related data that may be used for comparison and correlation (e.g. retrieval studies). Therefore we aimed to assess and compare geometric and topographic design parameters of currently available hip stem tapers from different manufacturers. Material. For comparison well established cementless hip stems made of titanium alloy were choosen. All of them have a 12/14-taper. The analysed implants are shown in Fig. 1. As geometrical parameters the taper angle, the opening taper diameter and the taper length were measured using a coordinate measuring machine (CMM) (MarVision MS 222, Mahr, Göttingen, Germany; accuracy: ±2.3 µm). Several topographical parameters (e.g. Ra, Rz, etc.) were determined using a tactil roughness measurement instrument (Perthometer M2, Mahr, Göttingen, Germany; accuracy: 12 nm). Three independent samples of each taper were measured five times. Results. In Fig. 2 the geometrical parameters like taper angle and opening diameter are given. As roughness parameters the average roughness (Ra) and the average maximum height of the profile (Rz) are presented in Fig. 3. Discussion and conclusion. As expected, this study shows that the tapers differ among the manufactures. Regarding the geometry, high variations in taper length were seen whereas the taper angle and opening taper diameter vary only to a small extent. However, if the combination of taper angle and opening diameter are considered these small differences may become relevant regarding the contact situation in the taper junction. Clearly, the tapers differed in topography. The surface roughness parameters vary to a large extent from smooth to very rough values. In combination all these parameters will influence the crevice of the taper junction. Considering that taper corrosion is mostly initiated within the crevice, further studies may help to understand the influence of taper variations to the corrosion mechanism

Introduction. Dual modular hip prostheses were introduced to optimize the individual and intra-surgical adaptation of the implant design to the native anatomics und biomechanics of the hip. The downside of a modular implant design with an additional modular interface is the potential susceptibility to fretting, crevice corrosion and wear [1–2]. The purpose of this study was to characterize the metal ion release of a modular hip implant system with different modular junctions and material combinations in consideration of the corrosive physiological environment. Methods. One design of a dual modular hip prosthesis (Ti6Al4V, Metha®, Aesculap AG, Germany) with a high offset neck adapter (CoCrMo, CCD-angle of 130°, neutral antetorsion) and a monobloc prosthesis (stem size 4) of the same implant type were used to characterize the metal ion release of modular and non-modular hip implants. Stems were embedded in PMMA with 10° adduction and 9° flexion according to ISO 7206-6 and assembled with ceramic (Biolox® delta) or CoCrMo femoral heads (XL-offset) by three light impacts with a hammer. All implant options were tested in four different test fluids: Ringer's solution, bovine calf serum and iron chloride solution (FeCl3-concentration: 10 g/L and 114 g/L). Cyclic axial sinusoidal compressive load (Fmax = 3800 N, peak load level of walking based on in vivo force measurements [3]) was applied for 10 million cycles using a servohydraulic testing machine (MTS MiniBionix 370). The test frequency was continuously varied between 15 Hz (9900 cycles) followed by 1 Hz (100 cycles). The metal ion concentration (cobalt, chromium and titanium) of the test fluids were analysed using ICP-OES and ICP-MS at intervals of 0, 5·105, 2·106 and 10·106 cycles (measuring sensitivity < 1 µg/L). Results. Due to the additional modular interface between stem and neck adapter the total metal ion release of the modular hip endoprosthesis system increased significantly and is comparable to the coupling of a monobloc stem and a CoCrMo femoral head (Fig. 1). The application of ceramic femoral heads reduced the total cobalt and chromium release in the stem-head taper interface of non-modular and modular stems. In comparison between the four test fluids could be observed that lower pH-values and higher FeCl3-concentrations increased the metal ion release (Fig 2). In contrast, the use of bovine calf serum decreased the metal ion release of modular junctions due to the presence of proteins and other organic components. Discussion. For testing hip implants with proximal femoral modularity according to ISO and ASTM standards, sodium chloride solutions are frequently used to determine the fatigue strength and durability of the stem-neck connection. The present study illustrate that the expansion of standard requirements of biomechanical testing and the use of alternative test fluids is necessary to simulate metal ion release by electro-chemical processes. A promising approach is the use of adapted iron-chloride solutions (10 g/L FeCl3, pH 2) to evaluate the susceptibility of modular hip junctions to fretting, crevice and contact corrosion

Introduction. Total hip arthroplasty (THA) is a commonly performed procedure to relieve arthritis or traumatic injury. However, implant failure can occur from implant loosening or crevice corrosion as a result of inadequate seating of the femoral head onto the stem during implantation. There is no consensus—either by manufacturers or by the surgical community—on what head/stem assembly procedure should be used to maximize modular junction stability. Furthermore, the role of “off-axis” loads—loads not aligned with the stem taper axis—during assembly may significantly affect modular junction stability, but has not been sufficiently evaluated. Objective. The objective of this study was to measure the three-dimensional (3D) head/stem assembly loads considering material choice—metal or ceramic—and the surgeon experience level. Methods. A total of 29 surgeons of varying levels (Attending, Fellow, Resident) were recruited and asked to perform a benchtop, head/stem assembly using an instrumented apparatus simulating a procedure in the operating room (Figure 1). The apparatus comprised of a 12/14 stem taper attached to a 3D load sensor (9347C, Kistler® USA, Amherst, NY). Surgeons were randomly assigned a metal or ceramic femoral head and instructed to assemble the taper using their preferred surgical technique. This procedure was repeated five times. Surgeons were brought back to test the opposite material after four weeks. Output 3D load data was analyzed for differences in peak vertical load applied, angle of deviation from the stem axis—termed off-axis angle, variability between trials, and impaction location. Results. Preliminary results suggest no significant differences between the loads applied to the metal heads and the ceramic heads. Across the two materials tested, both attendings and residents applied greater loads than fellows (p=0.33; Residents=9.0 kN vs Fellow=7.2 kN: p=0.27; Attendings=8.9 kN vs 7.2 kN) with significantly less variability (Attendings: σ= 1.58; Fellows: σ= 3.26; Residents: σ= 2.86). Attending surgeons also exhibited applied loads at significantly lower off-axis angles compared to fellows (p=0.01; 4.6° vs Fellow=7.2°) (Figure 2). However, all of our clinicians assembled ceramic head tapers with a greater off-axis angle as compared to assembling metal heads. In addition, metal heads were impacted more on-axis for all surgeon experience levels (Figure 3). While the impaction load plots suggest that the first impact strike is the most crucial for head stability, it was determined that the number of strikes is not as important as the maximum impaction load applied. Conclusion. Differences in impaction load when assembling metal and ceramic femoral heads were not apparent; however, variability of technique and load was observed across the different surgical experience levels as well as within surgeons of the same level. Understanding assembly mechanics and surgical habits for THA will provide insight to the best assembly procedures for these implants. For any figures or tables, please contact authors directly

Introduction. The use of bone cement as a fixation agent has ensured the long-term functionality of THA implants . 1. However, some studies have shown the undesirable effect of wear of stem-cement interface, due to the release of metals and polymeric debris lead to implant failure . 2,3. Debris is generated by the micromotion together with a severely corrosive medium present in the crevice of stem-cement interface . 3,4. FEA studies showed that micromotion can affect osseointegration and fretting wear . 5,6. The aim of this research is to investigate if the micromotions measures from in silico analysis of the stem-cement correlate with the fretting-corrosion damage observed on in vitro testing. Methods. The in vitro fretting-corrosion testing was made with positioning and loading based on ISO 7206-4 and ISO 7206-6. It was used Exeter stems embedded in bone cement (PMMA) and immersed in a saline solution (9.0 g/L of NaCl). A fatigue testing system (Instron 8872, USA) was used to conduct the test, applying a sinusoidal cyclic load at 5.0 Hz. The tests were finished after 10 million cycles and images of stem surfaces were taken with a photographic camera (Canon EOS Rebel T6i, Japan) and a stereoscope (Leica M165C, Germany). For the computational analysis, the same testing configurations were modeled on software ANSYS. The analysis was performed using linear isotropic elasticity for both stem (E=193GPa; ⱱ=0.27; σ. y. =400MPa) and PMMA cement (E=2.7GPa; ⱱ=0.35; σ. u. =76MPa). 7,8. . A second-order tetrahedral element was used to mesh all components with a size of 0.5 mm in the stem-cement contact area, increasing until 1.0 mm outside from them. A frictional contact (µ=0.25) with an augmented Lagrange formulation was used. The third cycle of loading was evaluated and a variation of sliding distance less than 10% was set as convergence criteria. The micromotion was measured as the sliding distance on the stem-cement interface. Results and Discussion. The in silico analysis showed the presence of areas almost without micromotion in the proximal lateral and distal medial regions. In these regions, there is no evidence of fretting-corrosion after the in vitro testing. The lack of micromotion is caused by the debonding due to testing configurations and implant design. The absence of contact doesn't allow wear by abrasion or third body, avoiding the fretting-corrosion damage. For the regions distal lateral and proximal medial, it is possible to observe fretting-corrosion due to micromotions, which is supported by the in silico analysis results. The region proximal medial had the highest micromotion on computational analysis and the fretting-corrosion was more severe on laboratory testing, reinforcing the relevance of micromotion in the fretting-corrosion damage on the stem-cement interface. Conclusion. The results indicate a correlation of micromotion calculated by in silico analysis and fretting-corrosion damage observed on in vitro testing. The developed FEA model may be a useful tool to predict the fretting-corrosion damage on the THA implants on pre-clinical testing. Additional efforts are needed to apply this tool on bone-implant systems to predict fretting-corrosion damage observed in vivo. For any figures or tables, please contact authors directly

Introduction. Are there really ‘conventional’ bearings, offering more security and less risk than the ‘alternative’ bearings that feature in the programme?. Alternative, when used as an adjective has 2 meanings:. offering or expressing a choice, as in several alternative plans. different from or functioning outside the usual or conventional:. eg alternative newspaper, alternative rock music, alternative medicine. This paper reviews the elements that make up the bearing couples available today in the developed world, and tests each bearing against these meanings. Materials. what are the alternatives?. The materials available today fall into the following broad families:. Metals. Stainless Steel and Cobalt-Chromium Alloy, are the dominant metals available. There is no variation in the Steel, but the characterisation of the Co-Cr does vary. Several manufacturers use different carbide content for the femoral and acetabular components, and different processes. One has been withdrawn from the market, and others may be at risk of this, although it is not the material itself that seems to be the main issue. Ceramics include alumina and zirconia ceramics. Alumina has been available unchanged for over 40 years, although delta ceramic (a zirconia toughened alumina) has only been available unchanged since 2001, making in available for 10 years. Polymers. a huge range of polyethylenes are now available, with different individual claims. All claim superior wear resistance, and oxidation resistance. More than 20 unique products are available in the EU, each with a proprietary formula giving individual characteristics. Coatings and surface treatments. these are now available today from many companies, who either ceramicise the surface of cobalt chrome or titanium with titanium nitride, or use oxinium (a proprietary product from a single company). Bearing couples. what are the alternatives Symmetric and Asymmetric bearings are currently offered. Symmetric bearings are available for Ceramic on Ceramic and Metal on Metal bearings only. Asymmetric bearings are available with metals, including metal on poly, and metal on peek. Ceramics can couple with metal or polymers. Bearing Sizes. Larger than 32mm should be considered ‘alternative’. The larger metal bearings have seen the start of crevice corrosion at the taper between titanium and Co-Cr, and even between different Co-Cr alloys. This new class of complication seems to be unique to metal femoral heads. Bearing-stem compatibility. Larger metal on metal head bearings have brought an entirely new world of complications. The choices of trunion are mainly twofold: the 12/14 tapers which differ significantly between products, and the V40 taper still used by one manufacturer. Neither was designed for use with a larger diameter head. Conclusions. The use of the word ‘alternative’ implies a ‘standard’ or conventional bearing. Ceramic bearings have changed least, have been immune from the metallosis and crevice corrosion seen with large ball Metal head whether bearing on metal or polyethylene. They also have reassuring long term results. In 2011 they should be considered the standard bearing for the young and active patient. The large diameter metal on highly cross-linked poly bearings should now be considered ‘alternative’