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

INTRODUCTION. The specific factors affecting wear of the ultrahigh molecular weight polyethylene (UHMWPE) tibial component of total knee replacements (TKR) are poorly understood. One recent study demonstrated that lower conforming inserts produced less wear in knee simulators. The purpose of this study is to investigate the effect of insert conformity and design on articular surface wear of postmortem retrieved UHMWPE tibial inserts. METHODS. Nineteen NexGen cruciate-retaining (NexGen CR) and twenty-five NexGen posterior-stabilized (NexGen PS) (Zimmer) UHWMPE tibial inserts were retrieved at postmortem from fifteen and eighteen patients respectively. Articular surfaces were scanned at 100×100μm using a coordinate measuring machine (SmartScope, OGP Inc.). Autonomous mathematical reconstruction of the original surface was used to calculate volume loss and linear penetration maps of the medial and lateral plateaus. Wear rates for the medial, lateral and total articular surface were calculated as the slope of the linear regression line of volume loss against implantation time. Volume loss due to creep was estimated as the regression intercept. Student t-tests were used to check for significant. RESULTS. The NexGen CR and NexGen PS patient groups were approximately the same age at time of implantation (mean±SD: 72.1±9.9 and 68.7±8.8 years respectively, p=0.260) and implantation times were not significantly different (8.7±3.1 and 9.1±3.7 years, p=0.670). Both groups showed high variability in wear scars. No significant difference in wear rates on the total surface (mean±SE: 11.89±5.01 mm. 3. /year vs. 11.09±4.18 mm. 3. /year, p=0.905). However, NexGen CR components showed significantly higher volume loss due to creep than NexGen PS components (70.22±47.07 mm. 3. vs. 31.30±41.15 mm. 3. , p=0.007). These results were reflected on the medial and lateral sides, with no significant differences in wear rates on the medial side (p=0.856) or lateral side (p=0.633) and higher volume losses due to creep associated with the NexGen CR components. While NexGen CR and NexGen PS showed a near equal mean percentage of volume loss on the medial side (CR: 52.4±11.7%, PS: 52.5±11.6%), a paired t-test showed that NexGen PS components showed a higher volume loss on the medial side (p=0.056), NexGen CR components did not (p=0.404). DISCUSSION. The combination of higher conformity and more kinematic constraint in NexGen CR components may create larger contact areas with higher stresses, leading to higher volume loss due to creep observed in this study. However, these factors did not produce increased wear rates in the population. Constrained components may maintain more loading on medial side and limit sliding distance on lateral side, causing more wear medially. Total wear rates were very similar and resembled the previously reported rate of 12.9 ± 5.97 mm. 3. /year for retrieved Miller-Galante II (Zimmer) components, which features a near flat articulating surface. These findings indicate that materials factors may be most important in producing wear and that higher conformity alone does not decrease wear. For any figures or tables, please contact authors directly

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. Metal-on-polyethylene (MoP) is the most commonly used bearing couple in total hip replacements (THRs). Retrieval studies (Cooper et al, 2012, JBJS, Lindgren et al, 2011, JBJS) report adverse reactions to metal debris (ARMD) due to debris produced from the taper-trunnion junction of the modular MoP THRs. A recent retrospective observational study (Matharu et al, 2016, BMC Musc Dis) showed that the risk of ARMD revision surgery is increasing in MoP THRs. To the authors' best knowledge, no hip simulator tests have investigated material loss from the taper-trunnion junction of contemporary MoP THRs. Methods. A 6-station anatomical hip joint simulator was used to investigate material loss at the articulating and taper-trunnion surfaces of 32mm diameter metal-on-cross-linked polyethylene (MoXLPE) joints for 5 million cycles (Mc) with a sixth joint serving as a dynamically loaded soak control. Commercially available cobalt-chromium-molybdenum (CoCrMo) femoral heads articulating against XLPE acetabular liners (7.5Mrad) were used with a diluted new-born-calf-serum lubricant. Each CoCrMo femoral head was mounted on a 12/14 titanium alloy trunnion. The test was stopped every 0.5Mc, components were cleaned and gravimetric measurements performed following ISO 14242-2 and the lubricant was changed. Weight loss (mg) obtained from gravimetric measurements was converted into volume loss (mm. 3. ) and wear rates were calculated from the slopes of the linear regression lines in the volumetric loss versus number of cycles plot for heads, liners and trunnions. Additionally, volumetric measurements of the head tapers were obtained using a coordinate measuring machine (CMM) post-test. The surface roughness (Sa) of all heads and liners was measured pre and post-test. At the end of the test, the femoral heads were cut and the roughness of the worn and unworn area was measured. Statistical analysis was performed using a paired-t-test (for roughness measurements) and an independent sample t-test (for wear rates). Results and Discussion. The mean volumetric wear rates for CoCrMo heads, XLPE liners and titanium trunnions were 0.019, 2.74 and 0.013 mm. 3. /Mc respectively. There was a statistically significant decrease (p<0.001) in the Sa of the liners post-test. This is in contrast to the femoral heads roughness in which no change was observed (p = 0.338). This head roughness result matches with a previous MoP in vitro test (Saikko, 2005, IMechE-H). The Sa of the head tapers on the worn area showed a statistically significant increase (p<0.001) compared with unworn, with an associated removal of the original machining marks. The mean volumetric wear rate of the head tapers obtained using the CMM (0.028 ± 0.016 mm. 3. /Mc) was not statistically different (p=0.435) to the mean volumetric wear rate obtained gravimetrically (0.019 ± 0.020 mm. 3. /Mc) for the femoral heads. Therefore, wear of the heads arose mainly from the internal taper. The mean wear rates of the CoCrMo taper and titanium trunnion are in agreement with a MoP explant study (Kocagoz et al, 2016, CORR). Conclusion. This is the first long-term hip simulator study to report wear generated from the taper-trunnion junction of MoP hips

INTRODUCTION. Studies of retrieved TKR components demonstrate that in vivo wear on the articular surface of polyethylene liners exhibits a much higher variability on their in vitro counterparts. Only one study has attempted to validate a patient-specific model of wear with a clinically retrieved component. The purpose of this study is to investigate the relationship between observed TKR contact conditions during gait and measured volume loss on retrieved tibial components. METHODS. Eleven retrieved ultra-high molecular weight polyethylene (UHMWPE) cruciate-retaining tibial liner components from ten separate patients (implantation time = 8.6±5.6 years) had matching gait trials of normal level walking for each knee. Volume loss on retrieved components was calculated using a coordinate measuring machine and autonomous reconstruction. Motion analysis of normal level walking gait had been conducted between 1986 and 2005 for various previous studies and stored in a consented Human Mechanics Repository, ranging from pre-operative to long-term post- operative testing. Contact location between the femoral component and the tibial component on the medial and lateral plateaus were calculated throughout stance. A previously validated and fine-tuned parametric numerical model was used to calculate TKR contact forces for each gait trial. Vertical contact forces and contact paths on the medial and lateral plateaus were input as normal force and sliding distance to a simplified Archard equation for wear with material wear constant averaged from literature (2.42 × 10. −7. mm. 3. /Nm) to compute average wear per gait cycle. Wear rates were calculated using linear regression, and Pearson correlation examined correlations between modeled and measured wear. RESULTS. Secondary motions at the knee from gait testing showed distinct grouping between trials of each patient. Three components demonstrated severe polyethylene delamination and were excluded from wear rate analyses. Calculated wear rates for measured and modeled volume loss showed excellent agreement on total surface (15.9 vs. 16.4 mm. 3. /year), medial sides (11.4 vs. 11.7 mm. 3. /year) and lateral sides (4.4 vs. 4.7 mm. 3. /year) and were not significantly different. Volumes were significantly correlated between measured and modeled wear for the total part (r=0.758, p=0.017) and on the medial side (r=0.780, p=0.012), but not for the lateral side (r=0.482, p=0.154). DISCUSSION. Measured wear rates were comparable to a previous study of a large population of retrieved MGII components. Medial wear volumes for six of eight mild wearing components were closely tracked by their modeled counterparts. Because the Archard equation produces wear volumes that are linearly related to time in situ, deviations from linear predictions arise from patient-specific variations in contact forces and tibiofemoral pathways during normal walking gait. As suggested by the results of the current study, these variations in gait between patients result in meaningful differences to the wear of the UHMWPE component. Despite many assumptions, this study demonstrates the feasibility of a patient-specific model of wear using a rare population of gait-matched retrievals

Introduction. This study was performed to investigate the failure mechanism of one specific hip arthroplasty cup design that has shown a high clinical failure rate. The aim of this study was to identify general design problems of this polyethylene inlay. Material and Methods. 55 consecutive retrievals of a cementless screw ring (Mecron) were collected. In any case a 32 mm ceramic head was used. All implants failed due to aseptic loosening. The follow-up of the implants was 3 to 16 years. We recorded backside wear, fatigue of the polyethylene at the flanges on the outer rim and at the cup opening (32 mm inner diameter). To assess the deformation of the inlay, the smallest and the median diameter of the cup opening were measured using a 3 dimensional coordinate measuring machine (Multisensor, Mahr, Germany). Results. 90% of the explants showed signs of wear on the backside of the inlay. Another typical and so far not described alteration was collar fatigue in 68%. 38% of the inlays showed rim creep: Examples for Backside wear, collar fatigue and rim creep are illustrated in Fig. 1. 90% had a diameter of 32.1 mm or less, and even 46% had a diameter less than 32 mm. Discussion. The investigated design is at the lower limit of the allowed machining tolerance of the cup opening (32 + 0.1 mm) and has no additional clearance (which some manufacturers add). It seems that the inlays yield at the dome because of the viscoelastic properties of polyethylene and the open dome area of the attached screw ring. This leads to excessive wear at the dome area and it triggers a “brake drum” effect at the cup opening. Thereby torsional stresses at the implant bone interface increase which lead to failure of the implant. To avoid this type of failure, PE inlays should have enough clearance at the cup opening and the inlay should have dome contact to the closed metal shell

Introduction. Ultra-high molecular weight polyethylene (UHMWPE) is the sole polymeric material currently used for weight- bearing surfaces in total joint replacement. However, the wear of UHMWPE in the human body after total joint replacement causes serious clinical and biomechanical reactions. Therefore, the wear phenomenon of UHMWPE is now recognized as one of the major factors restricting the longevity of artificial joints. In order to minimize the wear of UHMWPE and to improve the longevity of artificial joints, it is necessary to clarify the factors influencing the wear mechanism of UHMWPE. Materials and Methods. In a previous study (Cho et al., 2016), it was found that roundness (out-of-roundness) of the retrieved UHMWPE acetabular cup liner [Figure 1(a)] had a tendency to increase with increasing roundness of the retrieved metal femoral head [Figure 1(b)]. It appears that roundness of the femoral head contributes to increase of wear of the polyethylene liners. We focused on the roundness of femoral head as a factor influencing the wear of polyethylene liner in hip prosthesis. In this study, further roundness measurements for 5 retrieved metal femoral heads were performed by using a coordinate measuring machine. The elasto-plastic contact analyses between femoral head and polyethylene liner using the finite element method (FEM) were also performed in order to investigate the influence of femoral head roundness on the mechanical state and wear of polyethylene liner in hip prosthesis. Results. The range of roundness of the 5 retrieved metal femoral heads measured in this study was 14.50∼44.70 µm. Two examples of the results of FEM contact analyses are shown in Figure 2. Figure 2(a) is the results of the repeated contact analysis between femoral head and polyethylene liner under constant axial loading of 1000 N. Figure 2(b) is the results of the repeated contact analysis between femoral head and polyethylene liner under hip joint loading during normal gait. These figures show the distribution of the contact stress (von Mises equivalent stress) in the polyethylene liner. The graph in Figure 3 shows the changes in the maximum contact stress in the polyethylene liner with the flexion/extension angle of femoral head. Discussion and Conclusions. As the results of a series of the FEM contact analyses, it was found that repeated high contact stresses which exceed the yield stress of UHMWPE caused by roundness of the metal femoral head occurred in the polyethylene liner as shown in Figures 2 and 3. It was also found that the magnitude and amplitude of the repeated contact stresses had a tendency to increase with increasing roundness of the femoral head and axial loading applied to the femoral head. The results of this analytical study suggest that the roundness (out-of- roundness) of the femoral head is associated with accelerating and/or increasing wear of the UHMWPE acetabular cup liner in a hip prosthesis after total hip replacement. For any figures or tables, please contact 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

Hemi shoulder arthroplasty is an attractive treatment for shoulder arthritis in particular if the natural glenoid is still intact. However, comparing the clinical results of hemi and total shoulder arthroplasty clearly shows lower survival for the hemi arthroplasty. One of the most common reasons for revision surgery is gleniod erosion, where the cartilage or bone is worn of. Aim of the current study was to analyse if the metallic articular surface of retrieved hemi shoulder arthroplasty is different from new implants. We hypothesized that the surface roughness will increased due the articulation and that metallic wear is detectable on the implants. Twelve retrieved and three brand new hemi shoulder arthroplasty were included. The surface roughness (Ra, Rz, Rmax, Rsk) was measured on different sites of the surface (center of the head and at the edge). The implants were further measured using a coordinate measuring machine to gain information on volumetric wear and geometrical alterations. Compared to new implants the surface roughness on the retrievals was significantly increased (Tab. 1), except for skewness. Although the roughness parameters within the retrieval group were generally higher at the center of the head compared to the edge, this difference was not significant. Apart from form deviations no volumetric wear was detectable on the heads (Fig. 1). The current results indicate that the metallic articular implant surface changes in vivo and that the material is hurt due to the articulation against the softer cartilage or bone. Although it can't be finally clarified by that study, to what extend the higher roughness is taking part in the process of the clinically observed erosion of the gleniod, it can be assumed that an increased roughness is disadvantageous. Possibly, the observed surface alterations won't occur clinically with harder materiel (e.g. ceramic), but this even needs to be validated

Purpose. The goal of Total Ankle Arthroplasty (TAA) is to relieve pain and restore healthy function of the intact ankle. Restoring intact ankle kinematics is an important step in restoring normal function to the joint. Previous robotic laxity testing and functional activity simulation showed the intact and implanted motion of the tibia relative to the calcaneus is similar. However there is limited data on the tibiotalar joint in either the intact or implanted state. This current study compares modern anatomically designed TAA to intact tibiotalar motion. Method. A robotic testing system including a 6 DOF load cell (AMTI, Waltham, MA) was used to evaluate a simulated functional activity before and after implantation of a modern anatomically designed TAA (Figure 1). An experienced foot and ankle surgeon performed TAA on five fresh-frozen cadaveric specimens. The specimen tibia and fibula were potted and affixed to the robot arm (KUKA Robotics Inc., Augsburg, Germany) while the calcaneus was secured to a fixed pedestal (Figure 1). Passive reflective motion capture arrays were fixed to the tibia and talus and a portable coordinate measuring machine (Hexagon Metrology Group, Stockholm, Sweden) established the location of the markers relative to anatomical landmarks palpated on the tibia. A four camera motion capture system (The Motion Monitor, Innovative Sports Training, Chicago, IL) recorded the movement of the tibia and talus. The tibia was rotated from 30 degrees plantar flexion to 15 degrees dorsiflexion to simulate motions during the stance phase of gait. At each flexion angle the robot found the orientation which zeroed all forces and torques except compressive force, which was either 44N or 200N. Results. Preliminary data indicates the tibiotalar motion of the TAA is similar to the intact ankle. The pattern and magnitude of tibiotalar translations and rotations are similar between the intact and implanted states for both 44N and 200N compressive loads (Figure 2). The most variation occurs with internal-external rotation. Increased translation especially in the anterior-posterior directions was observed in plantarflexion while the mediolateral translation remained relatively centered moving less than a millimeter. The intact talus with respect to the calcaneus had less than 3 degrees of rotation over the whole arc of ankle flexion (Figure 3). The angular motion of the implanted talus was similar in pattern to the intact talus, however there were offsets in all three angular directions which changed depending on the loading (Figure 3). This indicates that most of the motion that occurs between the intact tibial calcaneal complex occurs in the tibiotalar joint. Conclusion. Although more investigation is required, this study adds to the limited available tibiotalar kinematic data. This current study suggests the anatomical TAA design allows the tibiotalar joint to behave in similar way to the intact tibiotalar joint. Restoring intact kinematics is an important step in restoring normal function to the joint. For figures/tables, please contact authors directly.

Introduction. Recently, the combination of press-fit acetabular cup with ceramic articulation is a widely used for implanting cementless acetabular components and has been shown to provide good initial stability. However, these methods may lead to elevating stresses, changing in the bearing geometries, and increasing wear due to deformation of the cup and insert. In addition, there is a potential for failure of ceramic inserts when a large ball head was used because it should be assembled with shallow thickness of the acetabular cup. For risk reduction of it, we applied direct metal tooling (DMT) based on 3D printing for porous coating on the cup. Due to its capability of mechanical strength, DMT coated cup could be feasible to provide better stability than conventional coating. Therefore, we constructed laboratory models for deformation test simulating an press-fit situation with large ceramic ball head to evaluate stability of the DMT coated cup compared with conventional coated cup. Materials and Methods. The deformation test was performed according to the test setup described by Z. M. Jin et al. The under reaming of the cavity in a two-point pinching cavity models of polyurethane (PU) foam block (SAWBONES, Pacific Research Laboratories, USA) with a grade 30 were constructed. Titanium plasma spray (TPS) and direct metal tooling (DMT) coated acetabular cups (BENCOX Mirabo and Z Mirabo Cup, Corentec Co. Ltd., KOREA) with a 52 mm size (n=3, respectively) were used for the test. These cups were implanted into the PU foam blocks, and followed by impaction of the inserts (BIOLOX delta, Ceramtec, GE) with a 36/44 size (n=6) into the acetabupar cups as shown in Fig. 1. Roundness and inner diameter of the acetabular cups and inserts were measured using a coordinate measuring machine (BHN 305, Mitutoyo Neuss, GE) in three levels; E2, E3, and E4 (3, 5, and 7 mm below the front face, respectively). Also, these parameters of the acetabular cup were measured in two level; E1 and E5 (5 and 11 mm below the front face) as shown in Fig. 2. Changes in roundness and inner diameter of the cup and insert were measured to evaluate deformation in relation to porous coating on the acetabular cups. Results. Before implantation cups and inserts, roundness and inner diameters were shown good values. When inserts were impacted into the PU foam blocks, there are no significant change in the inner diameters of the cup and insert. However, changes in roundness of the insert which impacted into the DMT coated cup were less deformable than the TPS coated cup's, especially, in E2 level of the inserts (the nearest region of the acetabular rim) as shown in Fig. 3. Conclusions. We demonstrated that deformation of the acetabular cup was affected by the porous coating methods. Although it was limited to few specimens, our results suggested that DMT coated cup would provide more initial stability than TPS coated cup. For figures/tables, please contact authors directly.

Introduction. Highly cross-linked (HXL) polyethylene has demonstrated clinical advantages as a wear resistant acetabular bearing material in total hip arthroplasty (THA) [1]. In vitro wear testing has predicted a tenfold reduction in the wear rate of HXL polyethylene, as compared to its conventional, non-HXL counterpart [2]. To date, radiographic studies of head penetration represent the state-of-the-art in determining clinical wear of polyethylene hip liners [3]. However, as the amount of wear drops to very low levels, it becomes important to develop a precise and reliable method for measuring wear, facilitating a comparison of clinical results to expectations. This study focuses on locating and quantifying the maximum linear wear of retrieved acetabular poly liners using a coordinate measuring machine (CMM). Specifically, HXL liners are compared to a baseline of conventional, non-HXL bearings. Methods. An IRB-approved retrieval laboratory received 63 HXL acetabular bearing retrievals from 5 manufacturers with in vivo durations of 1.01–14.85 years. These were compared with 32 conventional, non-HXL controls (including gas plasma, gamma-barrier and EtO) from 3 manufacturers with in vivo durations of 1.03–20.89 years. Liners were mounted in a tripod of axial contacts with the liner face positioned in a vertical plane. Each bearing was scanned with a CMM dual-probe head, with one horizontal probe scanning the articular surface and the other scanning the non-articular, sequentially. Surface-normal wall thickness values along each latitude were calculated using a custom developed algorithm (Figure 1). Because the liners are axially symmetric as manufactured, deviation in wall thickness at a given latitude represents linear wear [4]. Results. Total wear penetration for the HXL liners ranged from 0.02 to 1.03 mm, and for the conventional, non-HXL controls ranged from 0.07 to 6.85 mm. The HXL liners had an average linear wear rate of 0.02 mm/year, compared to 0.20 mm/year for the conventional, non-HXL controls (Figure 2). The direction of maximum wear, as measured in degrees from the cup pole, ranged from 8.32 to 73.86 degrees. Differences in wear rates as a function of crosslinking dose, as well as presence/absence of a lip can be identified. Discussion. This wear measurement study of retrievals is the first application of a novel CMM technique to locate and quantify wear in HXL liners compared to conventional polyethylene controls. The study confirms the expectations of a tenfold reduction in wear rates that were based on in vitro testing [2]. The results are consistent with those of radiographic studies that have documented lower wear of HXL polyethylene in the hip compared to conventional polyethylene [3]. However, the current technique offers higher precision and reliability, and eliminates the large proportion of negative wear measurements common amongst radiographic methods. A sufficient number of liners have been measured to begin to differentiate wear between different radiation doses

Introduction. Wear debris from polyethylene tibial inserts has been associated with limited longevity of total knee replacements (TKRs). While material factors were studied extensively and considerable progress has been made, there is little knowledge about surgical factors, particularly on how the wear rate is related to implant positioning. It was the purpose of this study to determine the combined effect of patient and implant positioning factors on the volumetric wear rate of TKRs. Our hypothesis was that implant alignment has a significant impact on the wear rate when controlled for other patient factors. Methods. This study included 59 tibial inserts of a cruciate retaining TKR design (Nexgen, Zimmer Inc.). The patients' age, sex, weight, height, and implant size were obtained. All implants were scanned with a coordinate measuring machine. Volumetric wear was determined using an autonomous mathematical reconstruction method (Figure 1). Radiographs were used to determine the anatomic lateral distal femoral angle (aLDFA), anatomic medial proximal tibial angle (aMPTA), femoral tilt angle (FTA) and posterior tibial slope (PTS). Also, the patella position was assessed using the Blackburne-Peel Index (BPI) and the Insall-Salvati Ratio (Figure 2). General linear modeling (SPSS) was conducted in order to determine the most significant patient and implant positioning factors on wear rate. Results. After adjustment for creep, the mean volumetric wear rate was 11.6 mm. 3. /yr (Figure 2). According to the linear regression model wear increased with younger age (p=0.0014) and male sex (p<0.001). The wear rate was independent of patient weight (p=0.17). From the multiple positioning factors only BPI and tibial slope were significant and inversely correlated with wear (p=0.009 and 0.026, respectively). The average ISR was normal before and after surgery, whereas the BPI was only in the normal range prior to surgery, and dropped postop into pseudo-baja (p<0.001, Figure 3). Discussion. The effect of male sex on wear volume can partially be explained by a larger average implant size; however, other unknown confounding factors may play a role too. The effect of younger age is likely related to higher patient activity. Based on previous gait analysis, we speculate that increasing tibial slope results in larger AP translations of the knee joint and thus more wear. Interestingly, BPI remained a highly significant factor when controlled for all other factors. The average BPI clearly dropped post-operatively, whereas the average ISR did not, indicating that not true patella baja, but a joint line elevation occurred due to the reconstruction. Joint line elevation may affect the quadriceps mechanism leading to higher contact forces and subsequent higher wear. Post-operative joint line elevation can be explained by the intention to keep bone loss at a minimum, while using thick polyethylene inserts. Further studies are needed to determine the trade-offs between bone conservation and reduction of wear rate. However, this study has revealed the importance of surgical factors regarding polyethylene wear reduction in TKR. Acknowledgements. This study was funded by NIH grant R01AR059843. For figures/tables, please contact authors directly.

Background. Fretting corrosion at the junction of the modular head neck interface in total hip arthroplasty is an area of substantial clinical interest. This fretting corrosion has been associated with adverse patient outcomes, including soft tissue damage around the hip joint. A number of implant characteristics have been identified as risk factors. However, much of the literature has been based on metal on metal total hip arthroplasty or subjective scoring of retrieved implants. The purpose of this study was to isolate specific implant variables and assess for material loss in retrieved implants with a metal on polyethylene bearing surface. Methods. All 28mm and 32 mm femoral heads from a 12/14 mm taper for a single implant design implanted for greater than 2 years were obtained from our institutional implant retrieval laboratory. This included n = 56 of the 28 mm heads (−3: n = 10, +0: n = 24, +4: n = 13, and +8: n = 9), and n = 23 of the 32 mm heads (−3: n = 2, +0: n = 8, +4: n = 1, and +8: n = 6). There were no differences between groups for age, gender, BMI, or implantation time. A coordinate measuring machine was used to acquire axial scans within each head, and the resulting point clouds were analyzed with a custom Matlab program. Maximum linear wear depth (MLWD) was calculated as the maximum difference between the material loss and as-machined surface. Differences in MLWD for head length, head diameter, stem material, and stem offset were determined. Results. Within the 28 mm head diameter group, there was no difference (p = 0.65) in MLWD between head lengths (−3: 4.0 ± 1.7 µm, +0: 10.4 ± 15.2 µm, +4: 4.4 ± 1.7 µm, +8: 4.3 ± 1.8 µm). There was no difference (p = 0.12) between the 28 mm (6.7 ± 10.9 µm) and 32 mm (5.5 ± 6.2 µm) head diameters. There was also no difference (p = 0.97) between titanium (7.3 ± 11.4 µm) or cobalt-chromium (5.9 ± 5.6 µm) stems, and no difference (p = 0.20) between regular (7.0 ± 10.0 µm) or high-offset (5.7 ± 8.0 µm) stems. Discussion. The development of fretting corrosion at the head neck junction of metal on polyethylene total hip replacements is of substantial clinical importance. In a single taper design, head diameter, head length, stem material and stem offset were all not found to be contributory to magnitude of wear depth. This is in contrast to current literature, which is controversial regarding the role of head diameter, but head length is thought to be contributory. However, as this study using precise tools does not illustrate these proposed biomechanic factors of fretting corrosion, other factors influencing tribocorrosion such as trunnion surface finish, flexural rigidity, interface geometry and biochemical factors may need to be considered

Introduction. We conducted independent wear analysis of retrieved metal on metal (MoM) hip components from around the world. All patients with resurfaced hips who developed adverse reactions to metal debris (ARMD) were found to have increased wear of the bearing surfaces. This was untrue in patients with large diameter (?36mm) MoM total hip replacements. This led us to search for other factors leading to ARMD. Methods. MoM THR explants retrieved from 78 patients suffering ARMD underwent full volumetric wear analysis of bearing surface and taper-junctions using coordinate measuring machine. Scanning electron microscopy (SEM) used to characterise material composition of specific areas. Results. 34 MoM THRs were found to have relatively low bearing surface wear (< 3mm. 3. /year). In each of these cases, material loss up to 60 microns wear depth was identified on the internal taper-junctions of femoral components. However, volumetric loss was rarely >5mm. 3. Similarly only 65% of metal ion levels of these patients were found to be greater than the MHRA guidance figure (7µg/L). Patterns of material loss at the tapers were consistent with antero-posterior force splaying open the taper-junction. This characteristic pattern was identified in number of commercially available devices (titanium and cobalt chromium stems). Soft tissue lesions were severe in patients found to have taper damage. Histology confirmed severe ALVAL with lymphoid neogenesis in majority cases, suggesting that wear debris from taper junctions may have greater potential to stimulate adverse immune response. Discussion. The results suggest that forces transmitted from large diameter hard-on-hard bearing surfaces are sufficient to cause mechanical damage to modular junctions with secondary localised corrosion. We urge caution in the use of these designs and recommend a re-evaluation of the stem head interface

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 and Aims. In order to improve the longevity and design of an implant, a wide range of pre-clinical testing conditions should be considered including variations in surgical delivery, and patients' anatomy and biomechanics. The aim of this research study was to determine the effect of the acetabular cup inclination angle with different levels of joint centre mismatch on the magnitude of dynamic microseparation, occurrence and severity of edge loading and the resultant wear rates in a hip joint simulator. Methods. The six-station Leeds Mark II Anatomical Physiological Hip Joint Simulator and 36mm diameter ceramic-on-ceramic bearings (BIOLOX® delta) were used in this study. A standard gait cycle, with a twin-peak loading (2.5kN peak load and approximately 70N swing phase load), extension/flexion 15°/+30° and internal/external ±10° rotations, was applied. Translational mismatch in the medial-lateral axis between the centres of rotation of the head and the cup were considered. In this study, mismatches of 2, 3 and 4 (mm) were applied. Two acetabular cup inclination angles were investigated; equivalent to 45° and 65° in-vivo. These resulted in a total of six conditions [Figure 1] with n=6 for each condition. Three million cycles were completed under each condition. The lubricant used was 25% (v/v) new-born calf serum supplemented with 0.03% (w/v) sodium azide to retard bacterial growth. The wear of the ceramic bearings were determined using a microbalance (XP205, Mettler Toledo, UK) and a coordinate measuring machine (Legex 322, Mitutoyo, UK). The stripe wear was analysed using RedLux software. The dynamic microseparation displacement was measured using a linear variable differential transformer. Mean wear rates and 95% confidence limits were determined and statistical analysis (one way ANOVA) completed with significance taken at p<0.05. Results Increasing the medial-lateral joint centre mismatch from 2 to 3 to 4mm resulted in an increased dynamic microseparation [Figure 2]. A similar trend was observed for the wear. A higher level of medial-lateral mismatch increased the wear rate under both 45° and 65° cup inclination angle conditions [Figure 3]. The mean wear rates obtained under 65° were significantly higher compared to those obtained under the 45° cup inclination angle conditions for a given medial-lateral mismatch in the joint centre (p=0.02 for 2mm mismatch, p=0.02 for 3 mm mismatch, and p<0.01 for 4mm mismatch). Conclusions. The condition with the acetabular cups positioned at an inclination of 45° exhibited greater resistance to dynamic microseparation for any given medial-lateral mismatch in the centres of rotation. Higher wear rates correlated with higher levels of dynamic microseparation. These results highlight how different conditions can alter the severity of edge loading, and highlight the necessity of understanding how the surgical positioning can affect the occurrence of edge loading and wear. Future studies will look into the other factors which can influence the microseparation conditions such as joint laxity, swing phase load and version angles

Background. We have previously described the relationship between wear rates of MOM components and soft tissue necrosis. In this study we investigated the link between wear rates, metal ion concentrations and osteolysis. Methods. All unilateral patients who underwent revision of hip resurfacings at our centre were included. Retrieved components were analysed using a coordinate measuring machine to determine total volumetric material loss and rates of wear. Given the accuracy of the wear calculations (which we have previously published), wear rates were considered “abnormal” if ≥3mm. 3. /yr. ROC curves were constructed to determine a Co concentration which would be clinically useful to detect abnormal wear. During revision, the presence/absence of osteolysis was documented. Results. There were 65 patients in total (mean time to revision was 41 months (2 to 98). 60 patients had suffered ARMD. 2 hips were revised for infection, 1 for osteolysis and 1 due to a loose cup and 1 for unexplained pain. A blood cobalt concentration >5µg/l was found to be 100%(62.2–100) specific and 94.4%(84.2–98.6) sensitive for the detection of abnormal wear. All patients with wear rates greater than 12mm. 3. /yr (n=21) were found to have osteolysis (the minimum total loss of material in this group of patients was 16mm3). ROC analysis showed that a blood cobalt ≥44.6µg/l was 97.2% specific for the detection of this rate of wear. 3 of the 21 patients with these rates of wear were asymptomatic. They decided on revision after discussion with the surgeon. Two were revised following acute femoral collapse but were completely pain free prior to these events. Conclusion. These data suggest that a blood cobalt concentration of 5µg/l can reliably identify an abnormally wearing resurfacing prosthesis. Elevated metal ion concentrations are associated with osteolysis, even in the absence of symptoms

Introduction. Increased wear rates [1, 2] and acetabular rim fracture [3] of hip replacement bearings reported clinically have been associated with edge loading, which could occur due to rotational and/or translational mal-positioning [4]. Surgical mal-positioning can lead to dynamic microseparation mechanisms resulting in edge loading conditions. In vitro microseparation conditions have replicated stripe wear and the bi-modal wear debris distribution observed clinically [5, 6]. The aim of this study was to investigate the effect of steep cup inclination, representing rotational mal-positioning, on the magnitude of dynamic microseparation, severity of edge loading, and the resulting wear rate of a ceramic-on-ceramic bearing, under surgical translational mal-positioning conditions. Materials and Methods. Ceramic-on-ceramic bearings where the ceramic liner was inserted into a titanium alloy cup (BIOLOX® delta and Pinnacle® respectively, DePuy Synthes, UK) were tested on the six-station Leeds II hip simulator. The first test was run with the cups inclined at an angle equivalent, clinically, to 45° (n=6) and the second test was run with the cups inclined at an angle equivalent, clinically, to 65° (n=6). A standard gait cycle was run. A fixed surgical translational mal-positioning of 4mm between the centres of rotations of the head and the cup in the medial/lateral axis was applied on all stations. Both tests ran for three million cycles each. The lubricant used was 25% new-born calf serum. Wear was assessed gravimetrically using a microbalance (XP205, Mettler Toledo, UK) and geometrically using a coordinate measuring machine (CMM, Legex 322, Mitutoyo, UK). Statistical analysis was done using one way ANOVA with significance taken at p<0.05. Results. The magnitude of dynamic microseparation was significantly (p<0.01) higher when the inclination angle of the cup was steeper (Figure 1) under the same level of translational mal-positioning of 4mm. This has resulted in significantly (p<0.01) higher wear rates of 1.01mm. 3. /million cycles for the steep cup inclination group of 65° compared to 0.32mm. 3. /million cycles for the 45° inclined cups group (Figure 2). Furthermore, the penetration on the femoral heads was significantly (p<0.01) higher for the steep cup inclination angle group with a mean (±95% confidence limit) penetration of 33±6µm under the 65° cup inclination angle condition and 15±3µm under the 45° cup inclination angle condition (Figure 3). Discussion and Conclusion. This study showed that cup inclination angle affects the magnitude of dynamic microseparation for a given surgical translational mal-position, thus leading to severe edge loading and increased wear rates with increased cup inclination angles. The occurrence and severity of the resulting edge loading causing increased wear in hip bearings will depend on the combinations of surgical variations, such as steep inclination angle, excessive version angle, medialised cups, head offset deficiencies, stem subsidence, and joint laxity. Future work will include studying the effect of these variables on the level of dynamic microseparation, severity of edge loading, the offset frictional torque and level of resulting wear

Introduction. Detailed analysis of retrieved total hip replacements (THRs) is valuable for assessing implant and material successes and failures. Reduction of bearing wear and corrosion and fretting of the head-neck trunnion is essential to implant durability and patient health. This research quantifies and characterizes taper and bearing surface damage on retrieved oxidized zirconium THRs. Methods. Initially, 11 retrieved oxidized zirconium femoral heads were examined along with their associated femoral stems. Relevant patient and retrieval data was collected from clinical charts and radiographs. Taper corrosion (Figure 1) and fretting damage (Figure 2) scoring was performed following the Dyrkacz [1] method. A coordinate measuring machine was used to obtain a detailed surface map of the male and female taper surfaces. Taper surface maps were best-fit with an idealized cone followed by volume subtraction to quantify the amount of material removed as a result of fretting and corrosion processes. Scanning electron microscopy was performed on select samples to identify specific damage modes. Unique surface bumps were noted on the articular surface of select femoral heads (Figure 3). Seventeen femoral heads were added to the analysis specifically for identification of these bumps. Articular surfaces were searched under SEM magnification and bumps were identified and counted. Parametric statistical correlations were performed with SAS v9.3. Results. Mean patient age was 61 years (Range: 35–95) with mean implantation period being 2.0 years (Range: 0.1–11.4) and mean body mass index of 29 kg/m. 2. (Range: 22–46). Revision for infection (n=11), peri-prosthetic fracture (n=5) and dislocation (n=5) were the main reasons for revision. Mean corrosion damage scores were 2.0 and 3.6 (head, neck) while mean fretting damage scores were 8.5 and 5.8 (head, neck). Fretting damage score was weakly correlated with implantation period (p=0.07) while corrosion damage score was not. Mean corrosion and fretting volume measured 0.40 mm. 3. and 0.87 mm. 3. (head, neck). Volume of corrosion and fretting damage did not correlate with implantation period; however neck volume correlated with inclination angle of the acetabular cup (p<0.01). Bearing diameter was not found to correlate with corrosion and fretting damage score or volume. The unique surface bumps were identified in 12 of 28 samples, with 3 samples having <10 bumps. Presence of these bumps did not appear to be related to bearing diameter, implantation period, or any damage metrics. Conclusion. Fretting damage was found to correlate with implantation period, suggesting that is a continuous in vivo process; however, this was not found for corrosion damage. Fretting damage volume correlated with acetabular cup angle; however, this may be coincidence as only 8 samples were included in the analysis. Overall, our corrosion damage scores (2.0–3.6) were lower than previously published values for 28mm & 36mm cobalt-chrome heads (4.5–13.1) [1]. However, our fretting damage scores (5.8–8.5) were higher than previously published (2.8–4.4) [1]. Greater fretting damage on the oxidized zirconium heads may be explained by the softer zirconium alloy compared to that of cobalt-chromium. Further subsurface investigation of the surface bumps is underway using a focused ion beam mill