Taper corrosion and fretting have been associated with oxide layer abrasion and fluid ingress that contributes to adverse local tissue reactions with potential failure of the hip joint replacement. [1,2]. Both mechanisms are considered to be affected by the precise nature of the taper design. [3]. Indeed relative motion at the taper interface that causes fretting damage and wear effects, such as pistoning and rocking, have been described following analysis of implants at retrieval. [4,5]. However, there is much less reported about the mechanisms that allow the fluid ingress/egress at the taper interface which would drive corrosion. Thus the aim of the present study was to investigate the effect of trunnion design on the gap opening and taper relative motions under different load scenarios and taper designs. A 3-D finite element model of a 40mm CoCr modular femoral head and a Ti6Al4V trunnion was established in Abaqus CAE/2018. Femoral head and trunnion geometries were meshed with an element (C3D8) size of 0.17mm. Tapers were assembled by simulating a range of impact forces (AF); taper interface behaviour was evaluated under physiological forces and frictional moments simulated during walking activity. [6]. , assuming different coefficients of friction (CF), Figure 1. The output involved the total and normal relative motion of the surfaces at the taper interface. The model predicted for a taper mismatch of 0.36° which, when combined with an assembly force of 2kN, generated the largest taper gap opening (59.2mm) during walking, Figure 2. In all trunnion designs the largest normal relative motion coincided with heel strike in the gait cycle (0–5%). The taper gap and normal relative motions were related to the initial taper lock area. Furthermore, the direction of the total motion was different in all three taper mismatches, with a shift in the direction towards the normal of the surface as the taper mismatch increased, Figure 3. By contrast, the direction of the normal relative motions did not change with different trunnion designs. Contact patterns were asymmetrical and contact areas varied throughout the walking activity; contact pressure and the largest taper gap were located on the same side of the taper, suggesting toggling of the trunnion. The relationship between taper gap opening and initial taper lock contact area suggests that the taper contact area functions as a fulcrum in a lever mechanism. Large taper mismatches create larger relative motions that will not only create more wear and fretting damage but also larger normal relative motions. This may allow fluid ingress into the taper interface and/or the egress of fluid along with any metal wear particles into the body. This increased understanding of the taper motion will result in improved designs and ultimately taper performance. For any figures or tables, please contact the authors directly

Introduction. Hip stem taper wear and corrosion is a multifactorial process involving mechanical, chemical and biological damage modes. For the most cases it seems likely that the mechanically driven fretting wear is accompanied by other damage modes like pitting corrosion, galvanic corrosion or metal transfer. Recent retrieval studies have reported that the taper surface topography may affect taper damage resulting from fretting and corrosion [1]. Therefore, the current study aimed to examine effects of different taper topography parameters and material combinations on taper mechanics and results regarding wear and corrosion have been investigated. Materials and Methods. Combined experimental and numerical studies were conducted using titanium, cobalt-chromium and stainless steel generic tapers (Figure1). Uniaxial tensile tests were performed to determine the mechanical properties of the materials examined. For the taper studies macro-geometry of ceramic ball heads (BIOLOX. ®. delta) and tapers were characterized using a coordinate measuring machine, and assembly experiments according to ISO7206-10 were conducted up to 4kN. Before and after loading, taper subsidence was quantified by assembly height measurements. Taper micro-geometry, taper surface deformation, and contact area were determined by profilometry. Initial numerical studies determined coefficients of friction for the three material combinations. Macro- and micro-geometries of the tapers were modelled, and taper subsidence and assembly load served as boundary conditions. Further studies used simplified models to examine effects of varying profile depths and angular gaps on surface deformation, taper subsidence, contact area, engagement length and pull-off force. Results. Largest coefficient of friction and pull-off forces were calculated for steel (µ=0.32), cobalt-chromium revealed the lowest with µ=0.18. Titanium showed largest deformations and taper subsidence throughout all calculations (Figure2, Figure3). Taper subsidence, engagement length and deformations increased with increasing profile depth while contact area decreased. Pull-off forces were almost constant for different profile depths while they increased for increasing angular gaps. Taper subsidence and deformations also increased with increasing angular gap while engagement length decreased and contact area almost remained constant. Discussion. In order to decrease wear and corrosion micromotions should be minimized. Therefore, smaller angular gaps and smaller profile depths seems to be beneficial since deformation and taper subsidence are reduced. Literature data confirmed the results for different angular gaps showing that a larger angular gap is associated with larger amounts of micromotion and wear [2, 3]. Additionally, larger angular gaps and larger profile depths result in larger plastic deformation facilitating subsurface crack initiation and propagation. A large angular gap may also facilitate particle release [4]. Larger pull-off forces can indicate larger resistance against micromotion. Therefore, steel may tend to later develop fretting-corrosion in situ. However, among the metals examined steel also showed the largest equivalent plastic strain. This study is limited to pairings involving ceramic heads. These can help mitigating fretting corrosion resulting from micromotion between ball head and cobalt-chromium or titanium alloy tapers [5]. However, future studies will include other ball head materials. In conclusion, this study showed that taper surface topography affects taper mechanics and is important in terms of wear and corrosion

Introduction. Taper corrosion and fretting has been identified to be a major problem in total hip replacement during the past years. Taper design and manufacturing are not been standardised, and therefore it can be assumed that the tapers vary among different implant manufacturers. This can lead to variable contact situations and stresses in the taper junction depending on the combination. It can be assumed that the taper strength will influence the occurrence and magnitude of micromotions which are known to influence corrosion. Therefore, the aim of this study was to assess the influence of the taper angle clearance on the taper connection strength. Material & Methods. For the investigation stem dummys with different taper angles were used that were manufactured from titanium alloy. The stem dummys were combined with ceramic heads with identically taper angles. Out of this, there were seven groups ranging from distal contact through full contact up to proximal contact. Three samples were used in each group and five repetitive measurements per samples were performed. All taper connections were impacted with different forces (1 kN, 3 kN, 6 kN and 10 kN) and afterwards an increasing torque was applied until the head disconnected. The maximal torque off value was used as a measure for the taper strength. Results. A greater taper clearance leads to a higher taper strength (Fig. 1). However, this effect is also influenced by the assembly force and becomes even stronger with higher assembly forces. When comparing a distal, full and proximal contact situation the full contact shows the lowest taper strength, whereas the distal contact situation leads to the highest taper strength. Discussion and conclusion. The design variability in taper connections influences its strength. A smaller contact area leads to higher local contact pressure. It is assumed that this increases local plastic deformations of the surface structure which is beneficial for this self-locking mechanism of the junction. However, the effect of the assembly force seems to overcome the effect of the taper clearance. Therefore taper junctions should be firmly connected in total hip replacements. Furthermore, surgeons should be aware that in a clinical case of a Mix & Match the taper strength may be reduced depending on the combined components. 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. The femoral head/stem taper modular junction has several advantages; it also has the potential to result in fretting [1]. Stability of the taper junction is critical in reducing the risk associated with fretting. The purpose of this test was to measure the strength of various commercially available head-stem taper combinations under torsional loads to determine the effect of taper geometry and material on the strength of this taper junction. Methods and Materials. CoCr femoral heads were tested with trunnions that were machined with both a large and small taper geometry, replicating commercially available stem taper designs, V40 (small) and C (large) (Table-1, Stryker Orthopaedics, NJ). The femoral heads were assembled onto the trunnions with a 2 kN axial force. A multi-axis test frame (MTS Corp, MN) was used to test the head-trunnion combination by dynamically loading with a torque of ± 5Nm and a constant axial load of 2450N for 1000 cycles at 1.5 Hz (Figure 1). Samples were submerged in 25% diluted Alpha Calf Fraction Serum (Hyclone, UT). Upon completion of the dynamic test, a static torque to failure test was performed where the axial force of 2450N was maintained and the trunnion was rotated to 40° at a rate of 3°/sec. The torque required to rotate the trunnion by 1° was determined for each specimen. Also, the torsional resistance, defined as change in torque/change in angle in the linear region of the torque-angular displacement data curve, was calculated for all the specimens. A limitation associated with the static test was that at 1° rotation it was difficult to differentiate between rotation of the trunnion inside the femoral head and physical twisting of the trunnion. Specimen groups were compared with a single-factor ANOVA test and a Tukey post hoc test at 95% confidence level. Results. The dynamic test did not generate any rotation between the trunnion and the head. The difference in torque at 1° of rotation and torsional resistance was not statistically significant between any two specimen groups (Table 2, p > 0.05). Discussion. The results of this study indicate that neither taper surface area nor material have a significant effect on the strength of the taper junctions under torsional loads, within the range of designs and material combinations tested. Alternatively, the results suggest that taper junctions are appropriately designed to eliminate the effects of taper surface area and material on their strength. Previously in a similar test setup, it was determined that the average torque generated with CoCr femoral heads articulating against a press-fit acetabular shell/polyethylene liner assembly is 3.86 Nm [3]. In the present study, the trunnion-head combinations were cyclically loaded with 5 Nm of torque for 1000 cycles and the strength of the taper junction upon completion of the static test was at minimum six-times greater than the torque generated at the articulating surfaces

Background. Complications of metal-on-metal hip resurfacing, leading to implant failure, include femoral notching, neck fracture, and avascular necrosis. Revision arthroplasty options include femoral-only revision with a head, however mis-matching radial clearance could accelerate metal ion release. Alternatively, revision of a well-fixed acetabular component could lead to further bone loss, complicating revision surgery. We have developed a ceramic hip resurfacing system with a titanium-ceramic taper junction; taking advantage of the low frictional torque and wear rates that ceramic affords. Taking a revision scenario into account, the ceramic head has a deep female taper for the resurfacing stem, but also a superficial tapered rim. Should revision to this resurfacing be required, any femoral stem with a 12/14 taper can be implanted, onto which a dual taper adaptor is attached. The outer diameter of the taper adaptor then becomes the male taper for the superficial taper of the ceramic head; ultimately allowing retention of the acetabular component. In an in-vitro model, we have compared the fretting corrosion of this taper adaptor to existing revision taper options: a titanium-cobalt chrome (Ti-CoCr) taper junction, and a titanium-titanium sleeve-ceramic (Ti-Ti-Cer) taper junction. Methods. To simulate gait, sinusoidal cyclical loads between 300N-2300N, at a frequency of 3Hz was applied to different neck offsets generating different bending moments and torques. Bending moment and frictional torque were tested separately. An electrochemical assessment using potentiostatic tests at an applied potential of 200mV, was used to measure the fretting current (μA) and current amplitude (μA). In a short term 1000 cycle test with bending moment, four neck lengths (short to x-long) were applied. For frictional torque, four increments of increasing torque (2-4-6-8Nm) were applied. In a long-term test using the taper adaptor, the combination of worst-case scenario of bending and torque were applied, and fretting currents measured every million cycles, up to 10 million cycles. Results. Short-term test: When adjusting bending moment the taper adaptor displayed equivalent fretting currents for the short and medium neck lengths. Using the long neck the taper adaptor displayed a higher fretting current, though this was not significant (Kruskal-Wallis test). However, using the X-Long adaptor the fretting current was significantly higher than the other tapers (Fig. 1). Across the range of frictional torques, the taper adaptor displayed equivalent fretting currents to the Ti-CoCr single taper. The Ti-Ti-Cer displayed the lowest fretting currents but this was not significant when compared to the other combinations (Fig. 2). Long-term test: combining the worst case bending (X-Long) and torque (8Nm) showed consistent fretting currents and current amplitudes across 10 million cycles, with no significant variance of the median values (Fig. 3). Conclusion. Electro-chemical testing has highlighted caution if revision arthroplasty is performed using the X-Long taper adaptor. However for shorter neck lengths, fretting corrosion is comparable to existing revision tapers. The LIMA ceramic resurfacing arthroplasty is an integrated system and can be safely revised to a conventional hip system using a dual taper head, and taper adaptor

The vast majority of total hip replacements (THR) implanted today enable modularity by means of a tapered junction; based on the Morse taper design introduced for cutting tools in the 19. th. Century . 1. Morse-type tapers at the head-stem junction provide many benefits, key for a successful surgical outcome such as wider component selection and restoration of better biomechanics . 2. However, moving from mono-block to modular designs has not been without its issues. Fluid ingress and motion at the interface has led to a complex multifactorial degradation mechanism better known as fretting-corrosion . 3. Fretting-corrosion products created at the junction are commonly associated with adverse local tissue reactions . 4. . There is a wide variation in the taper junction of THR differing quite significantly from Morse's original design. Performance of the taper junction has been found to vary with different designs . 5,6. However, there is still a lack of common understanding of what design inputs makes a ‘good’ modular taper interface. The aim of this study was to better understand the links between implant design and fretting-corrosion initially focussing on the role of angular mismatch between male and female taper. A combination of experimental approaches with the aid of computational models to assist understanding has been adopted. A more descriptive understanding between taper design, engagement, motion and fretting-corrosion will be developed. Three different sample designs were created to represent the maximum range of possible angular mismatches seen in clinically available THR modular tapers (Matched: 0.020 ±0.002 °, Proximal: 0.127 ±0.016 °, Distal: −0.090 ±0.002 °). Head-stem components were assembled at 2 kN. Motion and fretting-corrosion at the interface was simulated under incremental uniaxial sinusoidal loading between 0.5–4 kN at 8 intervals of 600 cycles. The different types of motions at the interface was measured using a developed inductance circuit composed of four sensing coils, digital inductance converter chip (LDC1614, Texas Instruments, US) and microcontroller (myRIO, National Instruments, US). Fretting-corrosion was measured using potentiostatic electrochemical techniques with an over potential of +100 mV vs OCP (Ivium, NL). Complimentary finite element (FE) models were created in Ansys (Ansys 19.2, US). Under uniaxial loading, the ‘matched’ modular taper assemblies corroded most and allowed the greatest pistoning motion due to a seating action. ‘Distal’ and ‘proximal’ engaged modular tapers showed reduced corrosion and seating when compare to the ‘matched’ components. However the kinetics of corrosion and motion were interface dependent. It is hypothesized, and complimented by FEA analysis, that lower initial contact stress in the ‘matched’ modular tapers allows for greater subsidence and depassivation of the oxide layer and higher corrosion. ‘Matched’ modular tapers allowed less rotational and toggling motions compared to mismatched tapers, suggesting a reduced mismatch might perform better once the heads have seated over time. Future work involves tests conducted under a surgically relevant impaction force and physiological loading kinematics to develop this descriptive link between taper design, engagement and performance

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. Improper seating during head/stem assembly can lead to unintended micromotion between the femoral head and stem taper—resulting in fretting corrosion and implant failure. There is no consensus—either by manufacturers or by the surgical community—on what head/stem taper assembly method maximizes modular junction stability in total hip arthroplasty (THA). A 2018 clinical survey found that orthopedic surgeons prefer applying one strike or three, subsequent strikes when assembling head/stem taper. However, it has been suggested that additional strikes may lead to decreased interference. Additionally, the taper surface finish—micro-grooves—has been shown to affect taper interference and may be influenced by assembly method. Objective. The objective of this study was to employ a novel, micro-grooved finite element (FEA) model of the hip taper interface and assess the role of head/stem assembly method—one vs three strikes—on modular taper junction stability. Methods. A two-dimensional, axisymmetric model representative of a CoCrMo femoral head taper and Ti6Al4V stem taper was created using median geometrical measurements taken from over 100 retrieved implants. Surface finish—micro-grooves—of the head/stem taper were modeled using a sinusoidal function with amplitude and period corresponding to median retrieval measurements of micro-groove height and spacing, respectively (“smooth” stem taper: height=2µm, spacing=50µm; “rough” stem taper: height=11µm, spacing=200µm; head taper: height=2µm, spacing=50µm). All models had a 3’ (0.05°), proximal-locked angular mismatch between the tapers. To simulate modular assembly during surgery, multiple dynamic loads (4kN, 8kN, and 12kN) were applied to the femoral head taper as either one or three sequence of strikes. The input load profile (Figure 1) used for both cases was collected from surgeons assembling an experimental setup with a three-dimensional load sensor. Models were assembled and meshed in ABAQUS Standard (v 6.17) using four-node linear hexahedral, reduced integration elements. Friction was modeled between the stem and head taper using surface-to-surface formulation with penalty contact (µ=0.2). A total of 12 implicit, dynamic simulations (3 loads x 2 assembly sequences x 2 stem taper surface finishes) were run, with 2 static simulations at 4kN for evaluating inertial effects. Outcome variables included contact area, contact pressure, equivalent plastic strain, and pull-off force. Results. As expected, increasing assembly load led to increased contact area, pressures, and plasticity for both taper finishes. Rough tapers exhibited less total contact area at each loading level as compared to the smooth taper. Contact pressures were relatively similar across the stem taper finishes, except the 3-strike smooth taper, which exhibited the lowest contact pressures (Figure 2) and pull-off forces. The models assembled with one strike exhibited the greatest contact pressures, pull-off forces, and micro-groove plastic deformation. Conclusion. Employing 1-strike loads led to greater contact areas, pressures, pull-off forces, and plastic deformation of the stem taper micro-grooves as compared to tapers assembled with three strikes. Residual energy may be lost with subsequent assembly strikes, suggesting that one, firm strike maximizes taper assembly mechanics. These models will be used to identify the optimal design factors and impaction method to maximize stability of modular taper junctions. For any figures or tables, please contact authors directly

Perioperative glucocorticoids have been used as a successful non-opioid analgesic adjunct for various orthopaedic procedures. Here we describe an ongoing randomized control trial assessing the efficacy of a post-operative methylprednisolone taper course on immediate post-operative pain and function following surgical distal radius fixation. We hypothesize that a post-operative methylprednisolone taper course following distal radius fracture fixation will lead to improved patient pain and function. This study is a randomized control trial (NCT03661645) of a group of patients treated surgically for distal radius fractures. Patients were randomly assigned at the time of surgery to receive intraoperative dexamethasone only or intraoperative dexamethasone followed by a 6-day oral methylprednisolone (Medrol) taper course. All patients received the same standardized perioperative pain management protocol. A pain journal was used to record visual analog pain scores (VAS-pain), VAS-nausea, and number of opioid tablets consumed during the first 7 post-operative days (POD). Patients were seen at 2-weeks, 6-weeks, and 12-weeks post-operatively for clinical evaluation and collection of patient reported outcomes (Disabilities of the Arm, Shoulder and Hand Score [qDASH]). Differences in categorical variables were assessed with χ2 or Fischer's exact tests. T-tests or Mann-Whitney-U tests were used to compare continuous data. Forty-three patients were enrolled from October 2018 to October 2019. 20 patients have been assigned to the control group and 23 patients have been assigned to the treatment group. There were no differences in age (p=0.7259), Body Mass Index (p=0.361), race (p=0.5605), smoking status (p=0.0844), or pre-operative narcotic use (p=0.2276) between cohorts. 83.7% (n=36) of patients were female and the median age was 56.9 years. No differences were seen in pre-operative qDASH (p=0.2359) or pre-operative PRWE (p=0.2329) between groups. In the 7 days following surgery, patients in the control group took an average of 16.3 (±12.02) opioid tablets, while those in the treatment group took an average of 8.71 (±7.61) tablets (p=0.0270). We see that significant difference in Opioid consumption is formed at postoperative day two between the two groups with patients in the control group taking. Patient pain scores decreased uniformly in both groups to post-operative day 7. Patient pain was not statistically from POD0 to POD2 (p=0.0662 to 0.2923). However, from POD4 to POD7 patients receiving the methylprednisolone taper course reported decreased pain (p=0.0021 to 0.0497). There was no difference in qDASH score improvement at 6 or 12 weeks. Additionally, no differences were seen for wrist motion improvement at 6 or 12 weeks. A methylprednisolone taper course shows promise in reducing acute pain in the immediate post-operative period following distal radius fixation. Furthermore, although no statistically significant reductions in post-operative opioid utilization were noted, current trends may become statistically significant as the study continues. No improvements were seen in wrist motion or qDASH and continued enrollment of patients in this clinical trial will further elucidate the role of methylprednisolone for these outcomes

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. Recent literature demonstrates that the assembly load to connect ball head and femoral stem affects the taper junction fretting wear evolution in THR [1]. During assembly the surface profile peaks of the mostly threaded tapers are deformed. This contributes to the taper locking effect. Very little is known about this deformation process and its role in the evolution of fretting and wear. Therefore, this study aimed to experimentally determine the deformation of the profile peaks after the initial assembly process. Materials and Methods. 36 tapers of three different stem materials acc. to ISO5832-3 (titanium), ISO5832-9 (steel), ISO5832-12 (cobalt chromium) and 36 ceramic ball heads were tested under quasi-static (4kN) and dynamic (impaction) (3.7±0.3kN) axial assembly. Before and after loading 4 surface profiles in 90° offset were measured on each taper. Height differences of profile peaks and areas under profile curves were calculated and compared. Both parameters provide insights into the deformation behavior of the surface structure. Additionally, subsidence of tapers into ball heads was measured and subsidence rates were calculated with regard to varying impaction forces. Due to different thermal expansion coefficients tapers could be disconnected from ball heads by utilizing liquid nitrogen. Thus, further surface damage due to disassembly was avoided. Statistical analysis was performed using a Wilcoxon test (p<0.05). Results. Almost no differences of the subsidence rate were found among the taper materials in both assembly groups while it was higher for dynamic assembly (Figure 1). Peak height difference decreased with increasing number of profile peak (Figure 2) and increased in the dynamic assembly group. Largest peak height differences were found for titanium tapers, while steel and cobalt chromium tapers showed almost identical values, especially in the dynamic assembly group. Differences in area under profile showed varying results for the three taper materials (Figure 3). Almost no changes were found for steel tapers, while titanium and cobalt chromium tapers showed distinct differences. Discussion. This study describes the deformation behavior of the taper surface structure of three commonly used metallic materials coupled with ceramic ball heads. Since titanium has the lowest Young's modulus it seems reasonable that highest subsidence rates and peak height differences were found. Nevertheless, this material also showed the largest differences in area under profile which could be interpreted as a parameter of material removal. In contrast, steel tapers showed lowest material removal, but also lowest peak height differences and subsidence rates corresponding to the finding of almost none metal transfer at the ceramic counterface. These low subsidence rates could be influenced by frictional forces since this material combination has the highest friction coefficient [2,3]. The results provide insights into the mechanical behavior of stem tapers from commonly used metallic materials in THR and will be used for calibration of finite element models examining interface contact mechanics and wear. For figures, please contact authors directly

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

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

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

Introduction. Corrosion products from modular taper junctions of hip prostheses have been implicated in adverse local tissue reactions after THR. Numerous factors have been proposed as the root causes of this phenomenon, including implant design and materials, manufacturing variables, intraoperative assembly, and patient lifestyle. As significant taper damage only occurs in a few percent of cases of THR, we have addressed this complication using a “forensic” examination of retrieval specimens to gain insight into the factors initiating the cascade leading to irreversible damage of the modular interface. In this study we report the categorization of over 380 retrievals into groups having shared damage patterns, metallic composition, and interface surface geometries to isolate the genesis of mechanically-assisted corrosion and its relation to intraoperative assembly, manufacturing, and postoperative loading. Methods. A total of 384 femoral components were examined after retrieval at revision THR. The implants were produced by a diverse range of manufacturers, 271 in CoCr, and 113 in TiAlV, with both smooth (253) and machined (131) tapers. Initially, the implants were sorted into groups based on composition and taper roughness. Each trunnion was then cleaned to remove organic deposits and examined by stereomicroscopy at X6-X31. After an initial pilot study, we developed a classification system consisting of 8 basic patterns of damage (Table 1). We then classified all 384 trunnions according to this 8-group system. The prevalence of each pattern was calculated on the basis of both composition and surface texture of the trunnion. Results. Overall, 81% of the trunnions had visible areas of surface damage, which varied as a function of composition (CoCr: 77%; TiAlV: 90%; p=0.002) and finish (smooth: 88%; machined: 67%; p<0.001). The most common pattern of damage was a circumferential ring at the base of the taper (24%) followed by a group with slight fretting or assembly damage distributed over the entire taper (19%). Damage to one quadrant at the bottom third was seen in approximately 18%. When combining material types, 41% of smooth tapers had circumferential patterns of damage corresponding to groups 2, 3, and 5. Conversely, 77% of the machined tapers had damage limited to one side or on two opposite sides (Patterns 4, 6, 7, 8, and 9). Discussion. Our results show that the pattern and location of damage is influenced not only by composition and surface texture, but can also be an indicator of component fit. The damage patterns observed on almost half (45%) of the trunnions were not circumferential (Chart 2), suggesting that misalignment of the head during assembly may be responsible for initiating the corrosion cascade in stems with machined taper surfaces. Summary. We categorized over 380 implant retrievals into groups having shared damage patterns, metallic composition, and interface surface geometries to isolate the genesis of corrosion

In recent years, cementless stems have dominated the North American market. There are several categories of cementless stems, but in the past 20 years, the two most popular designs in the United States have been the extensively coated cylindrical cobalt-chrome (Co-Cr) stem and the proximally coated tapered titanium stem, which in recent years has become the most common. The 10 year survival for both stem types has been over 95% with a distinction made on factors other than stem survival, including thigh pain, stress shielding, complications of insertion, and ease of revision. Conventional wisdom holds that proximally coated titanium stems have less stress shielding, less thigh pain, and a higher quality clinical result. Recent studies, however, including randomised clinical trials have found that the incidence of thigh pain and clinical result is essentially equivalent between the stem types, however, there is a modest advantage in terms of stress shielding for a tapered titanium stem over an extensively coated Co-Cr stem. One study utilising pain drawings did establish that if a Co-Cr cylindrical stem was utilised, superior clinical results in terms of pain score and pain drawings were obtained with a fully coated versus a proximally coated stem. In spite of the lack of a clinically proven advantage in randomised trials, tapered titanium stems have been favored because of the occasional occurrence of substantial stress shielding, the increased clinical observation of thigh pain severe enough to warrant surgical intervention, ease of use of shorter tapered stems that involve removal of less trochanteric bone and less risk of fracture both at the trochanter and the diaphysis due to the shorter, and greater ease of insertion through more limited approaches, especially anterior approaches. When tapered stems are utilised, there may be an advantage to a more rectangular stem-cross-section in patients with type C bone. In spite of the numerous clinical advantages of tapered titanium stems, there still remains a role for more extensively coated cylindrical stems in patients that have had prior surgery of the proximal femur, particularly for a hip fracture, which makes proximal fixation, ingrowth, and immediate mechanical stability difficult to assure consistently. Cement fixation should also be considered in these cases. While the marketplace and the clinical evidence strongly support routine use of tapered titanium proximally coated relatively short stems with angled rather than straight proximal lateral geometry in the vast majority of cases, there still remains a role for more extensively coated cylindrical and for specific indications

Introduction. Ceramic ball heads are well known in hip arthroplasty for their superior tribology performance and high burst strength. To assess the ball head performance and the in-vivo fracture risk Pandorf et al 2008 examined the burst strength of BIOLOX®forte (pure aluminium oxide ceramic, CeramTec GmbH, Plochingen, Germany) ball heads on clean standard test tapers and contaminated test tapers. They found that fat tissue and scratches are reducing the burst strength to 40% and to 20% of the reference burst strength, respectively. The aim of this work is to investigate if BIOLOX®delta (alumina matrix ceramic, CeramTec GmbH, Plochingen, Germany) ball heads show a similar behaviour as BIOLOX®forte ball heads with respect to taper contamination. Materials and Methods. Each test series consisted of n=5 BIOLOX®delta 28–12/14 L ball heads and n=5 metal test tapers (Ti-6Al-4V, ISO 5832-3). For the reference series the metal tapers remained untouched representing the CeramTec standard test procedure. For the fluid series the ball heads were filled up with tap water or calf blood serum. For the solid series the metal test tapers were contaminated with small particles of bovine bone, commercially available bone cement and porcine fat tissue in the engagement zone. A chisel and a slight hammer tap were used to scratch the proximal region of the metal test taper. The ball heads were then manually attached to the contaminated metal test tapers without further force appliances. An apparatus according to ISO 7206-10 was used for burst testing. The tests were performed at CeramTec in-house test laboratory. Results. The contamination of the taper region showed an influence on the resulting burst strength which was qualitatively similar to the previously performed investigations with pure alumina ball heads. Discussion. Sterilized water is used for cleaning the surgical wound before attaching the ball head on the metal taper. A contamination of the metal taper with water is reducing the burst strength of BIOLOX®delta ball heads to 80% reference burst strength. Remains of blood and bone particles on the metal taper can lead to 63% of the reference burst strength. Remains of fat tissue on the metal taper can lead to 38% of the reference burst strength. The fat tissue is reducing the coefficient of friction, which leads in further consequence to a change of the stress distribution and a raise of the stress magnitude in the ceramic ball head. Scratches and grooves have the ability to reduce the burst strength to only 29% reference burst strength. The results confirm that the taper connection of the components have to be clean and dry in order to provide a sufficient and strong connection

Introduction. In hip arthroplasty, it has been shown that assembly of the femoral head onto the stem remains a non-standardized practice and differs between surgeons [1]. Pennock et al. determined by altering mechanical conditions during seating there was a direct effect on the taper strength [2]. Furthermore, Mali et al. demonstrated that components assembled with a lower assembly load had increased fretting currents and micromotion at the taper junction during cyclic testing [3]. This suggests overall performance may be affected by head assembly method. The purpose of this test was to perform controlled bench top studies to determine the influence of impaction force and compliance of support structure (or damping) on the initial stability of the taper junction. Materials and Methods. Test Specimens. Testing was performed on 36mm +5mm CoCr heads combined with prototype Ti6Al4V locking taper analogs both machined with approximately a 5.67º taper angle. To minimize sample variation, the locking taper analogs were dimensionally matched with CoCr femoral heads to maintain a uniform angle difference. Prior to testing, samples were cleaned with isopropanol and allowed to dry. Effect of Peak Force Magnitude. Testing was performed on a rigid setup where a 10N preload was applied to the femoral head axially. Heads were assembled with loads ranging from 2kN–10kN using an impaction tower and seating loads were recorded at a collection rate of 273kHz. After assembly, tensile loads were applied until the taper junction was fully disassembled and distraction loads were recorded at a collection rate of 500Hz. Effect of Damping. 40 durometer rubber pads were placed underneath the trunnions as well as to the striking surface of the impaction tower to simulate compliance in the supporting structure and the surgical instruments. Aside from the added damping, testing was performed identical to the rigid setup tests. Results. Taper stability (as assessed by disassembly forces) increased linearly with peak assembly force with an R2 value of 0.95 for both rigid and compliant groups (Figure 1). On average a 46% larger input energy was required in the compliant group to achieve a comparable impaction force to the rigid group (Figure 2). However, the correlation between the assembly load and distraction force was not affected. Discussion. As shown in previous studies, impact force has a large effect on initial taper stability. An interesting finding in this study was that system compliance has a large effect on the applied assembly force. The addition of a compliant setup was intended to simulate a surgical scenario where factors such as the patient's leg positioning, patient mass, surgical instruments, and surgical approach may influence the resulting compliance due to the dissipation of impaction energy and reducing the applied impaction force. Based on test results, surgical procedure as well as patient variables may have a significant effect of initial taper stability. For any figures or tables, please contact authors directly (see Info & Metrics tab above).