Introduction. Revision of total hip replacements (THRS) is predominantly due to aseptic loosening, pain and infection [1]. The current method used to address the risk of infection is to administer antibiotics and to include antibacterial agents into bone cement (if used) and on implant coatings [2–4]. Currently, silver (Ag) coatings have only been applied to titanium hip stems [3]. Cobalt chromium alloy (CoCr) is a widely used orthopaedic alloy which is commonly used as a bearing surface; revisions of joints using this material often describe adverse reactions to the particulate wear debris [1]. This study considers an Ag containing CrN based coating on a CoCr substrate with the aim to reduce cobalt (Co) release and promote antibacterial silver release. Methods. Silver Chromium Nitride (CrNAg) coatings were developed and applied onto the bearing surfaces of 48 mm diameter metal-on-metal THRs. Three coatings were evaluated: high Ag at the surface (CrNAg+), low Ag at surface (CrNAg-) and uniform Ag (CrNAg=). All bearings were tested under ISO 14242-3 conditions for 0.17 million cycles (mc) representing approximately 2 months use in vivo. Wear was determined gravimetrically; Ag and Co levels in the lubricant were measured using graphite furnace atomic absorption spectroscopy. Testing of the CrNAg= bearings were continued to 2mc under standard conditions; CrNAg- bearings to 5mc incorporating lateralisation, which created separation at swing phase and rim contact at heel strike. Wear volume and Ag/Co release were monitored at 0.33, 0.67, 1mc and every mc thereafter. Results. All bearings produced low levels of wear and released silver into the lubricating fluid. An increase in silver concentration at the surface of the bearings was found to increase both the silver released and wear, Figure 1. Negligible cobalt was released. Testing of the CrNAg= coating to 2mc showed the wear rate to decrease after 0.17mc, Figure 2. Ag release continued up to 2mc but at a decreased rate. The CrNAg- coating tested under lateralisation conditions to 5mc showed no coating failure and negligible cobalt release. Wear and silver release showed similar patterns and reached a steady state after 1mc, Figure 3. Discussion. The AgCrN coatings on bearing surfaces of a hip joint are capable of releasing Ag at concentrations within the ‘No Observable Adverse Effect Limit’ [5]. These coatings also prevented Co release while maintaining a low wear rate. All coatings remained intact and did not delaminate, even under adverse conditions. These coatings have been tested in a metal-on-metal hip bearing surface, the most controversial and challenging condition for a coating, wearing against itself. CoCr is used as a bearing surface against polyethylene in hips and knees, in stems and tapers, as tibial trays in knee replacement and as shells for acetabular cups. This coating may be applied to a wide range of applications, removing some of the challenges over the use of CoCr while reducing infections

PURPOSE:. Wright Medical has a long history of modular neck hip implants but had fracture issues with the original titanium necks. They subsequently changed to chrome cobalt modular necks. Direct contact between these dissimilar metal parts in the modular femoral component brings into consideration the possibility of similar adverse reactions of metal-on-metal articulations that have been previously described in other designs. METHODS:. A retrospective review of 10 patients with Wright Medical chrome cobalt modular necks who were evaluated with chromium and cobalt metal ion levels as well as Metal Artifact Reduction Sequence (MARS) MRI's was performed. Pseudotumors were classified by MRI based on wall thickness, T1/T2 signal, shape, and location and given a corresponding type of I, II, or III. For each patient, symptoms or lack thereof were recorded, and time since surgery noted. RESULTS:. Of 10 patients tested, 9 were symptomatic, and 1 was asymptomatic. The patient that was asymptomatic at last clinical visit at 14 months post-op while symptomatic patients averaged 18 months since initial surgery before symptoms began. Those with metal-poly articulation had an average cobalt level of 1.6, ceramic-ceramic articulation had level of <1, and metal-on-metal had level of 2.9. Five patients had pseudotumor by MRI (2 type I, 1 type II, and 2 type III pseudotumors). CONCLUSION:. It appears that an unintended consequence of changing from titanium to chrome cobalt modular neck may be occurring secondary to corrosion at neck-stem junction. SIGNIFICANCE: This reaction does not appear to be design-specific as these findings are similar to our findings in Stryker Rejuvenate stems. Surgeons evaluating patients with these and other similar stems should be aware of this complication and consider ion testing and MARS MRI

Introduction. Wear debris and metal ions originating from metal on metal hip replacements have been widely shown to recruit and activate macrophages. These cells secrete chemokines and pro-inflammatory cytokines that lead to an adverse local tissue reaction (ALTR), frequently requiring early revision. The mechanism for this response is still poorly understood. It is well documented that cobalt gives rise to apoptosis, necrosis and reactive oxygen species generation. Additionally, cobalt stimulates T cell migration, although the effect on macrophage motility remains unknown. This study tests the hypothesis that cobalt ions and nanoparticles affect macrophage migration stimulating an ALTR. Methods. This study used Co. 2+. ions (200µM) and cobalt nanoparticles (CoNPs, 100µM, 2–60nm diameter). PMA differentiation of the U937 cell line was used as macrophage-like cells. The effect of cobalt on macrophage migration was investigated by live cell imaging. After 12 hours of each treatment, timelapse images of 20 cells were collected over a 6 hour period with images captured every 5 min. Migration of individual cells was tracked in 2D using ImageJ software. The transwell migration assay was also applied to study the effect of cobalt on macrophage directional migration. U937 cells in serum free medium were added to the upper chamber of a 8µm pore size Transwell insert in the presence of cobalt, whilst the lower chamber was filled with medium plus 10% FBS. After 6 hours treatment, cells remaining on the membrane were fixed, stained with crystal violet and counted. Cellular F-actin and podosomes were visualized by labeling with TRITCconjugated phalloidin and anti-vinculin antibody after 12 hours of cobalt exposure (Co. 2+. and CoNPs). Results. Cells incubated with cobalt ions and nanoparticles showed a substantial reduction in cell migration compared with control cells. The total migration path length of cells treated with Co. 2+. (362.4±96.6µm) and CoNPs (217.3±128.1µm) were significantly shorter than those for untreated cells (801.1±198.3µm). The ability of macrophages to migrate through the transwell membrane was significantly impaired by pre-treatment with cobalt, with 16±4 and 18± migrated cells/field for Co. 2+. and CoNPs respectively with the control at 42±7 migrated cells/field. In addition, cobalt influenced macrophage morphology and actin cytoskeletal organization with a dramatic increase in the presence of intracellular podosome-type adhesions structure. Discussion. Co. 2+. ions and nanoparticles dramatically inhibited the migration of U937 macrophages in contrast to the enhanced migration reported for T cells. We propose that macrophages recruited into the area of CoCr implants would lose their responsiveness to migration signals and be retained in situ due to cobalt-induced cytoskeleton rearrangement. This enhanced macrophage accumulation and cobalt-induced formation of podosomes may therefore represent a mechanism through which cobalt wear debris and metal ions from joint prostheses exacerbate the ALTR leading to revision surgery

Introduction. Improvements in material properties of total joint prostheses and methods of fixation mean that arthroplasty is the most effective means of restoring mobility in osteoarthritic patients. Aseptic loosening is the major cause of long-term failure of prostheses. Cobalt particles may act directly on osteoblasts, decreasing bone formation and potentially playing a role in osteolysis and aseptic loosening. Objectives. To assess gene expression profiles of primary human osteoblasts exposed to cobalt ions in a temporal manner, and to identify gene clusters underpinning the osteoblast response to cobalt. Methods. Primary human osteoblasts were exposed to cobalt ions at a concentration of 10ppm. To determine gene expression profiles, comparisons were made between control and 12, 24, 48 and 72 hour time exposures. RNA isolation and cDNA synthesis were performed. Gene profiling was carried out using the Affymetrix Human Genome UI33 Plus 2.0 array. Data was normalised using RMA express and an average expression measure for each time point used to identify alterations in gene expression. Validation was achieved by performing quantitative real time RT-PCR on selected genes. Results. Oligonucleotide microarray profiling identified significant alterations in osteoblast gene expression in response to cobalt exposure. Distinct phase patterns were observed, with significant altered expression following 12, 24 and 48 hours cobalt ion exposure. Of the 22,233 gene sequences represented on the Affymetrix microarray, 4.8% (1077 genes), 4.1% (930 genes), and 2.13% (486 genes) were significantly altered. We identified dysregulation of key functional families in response to cobalt ions, including alterations in cellular proliferation, development and and inflammation. Conclusion. These data will provide novel avenues for exploration to further characterise the molecular mechanisms underpinning the initiation and progression of osteolysis

Introduction. There is a demand for longer lasting arthroplasty implants driving the investigation of novel material combinations. PEEK has shown promise as an arthroplasty bearing material, with potentially relatively bio inert wear debris [1]. When coupled with an all-polyethylene tibial component this combination shows potential as a metal-free knee. In this study, the suitability of PEEK Optima® as an alternative to cobalt chrome for the femoral component of total knee replacements was assessed using experimental knee wear simulation under two kinematic conditions. Methods. Three cobalt chrome and three injection moulded PEEK Optima® (Invibio Biomaterial Solutions, UK) femoral components of similar geometry and surface roughness (mean surface roughness (Ra) ∼0.02µm) were coupled with all-polyethylene GUR1020 (conventional, unsterilised) tibial components in a 6 station ProSim knee simulator (Simulation Solutions, UK). 3 million cycles (MC) of wear simulation were carried out under intermediate kinematics (maximum anterior-posterior (AP) displacement 5mm) followed by 3MC under high kinematics (AP 10mm) [2] with 25% serum as the lubricant. The wear of the tibial component was assessed gravimetrically. At each measurement point, the surface roughness of the femoral components was determined using contacting profilometry and throughout testing, the bulk lubricant temperature was monitored close to the articulating surfaces. Statistical analysis was carried out using ANOVA, with significance at p<0.05. Results. Figure 1 shows the wear rate of the all-polyethylene tibial components. After 3MC of intermediate kinematics, the mean wear rate of UHMWPE articulating against cobalt chrome was 1.0±2.3mm3/MC and against PEEK was similar (p=0.06) 2.5±0.8mm3/MC. Scratches were apparent on the surface of the PEEK implant in the AP direction significantly (p<0.05) increasing mean surface roughness of the PEEK components (Table 1) compared to pre-test values. The surface topography of the cobalt chrome components (Table 2) was similar to pre-test measurements. Increasing AP displacement caused no significant increase in the wear of the tibial inserts against either material. Under intermediate kinematics, the mean bulk lubricant temperature was 28.0±0.7°C for cobalt chrome and significantly higher (p<0.001) for PEEK, 29.5±0.1°C; kinematic conditions had no effect on the lubricant temperature. Conclusions. This study showed a similar wear rate of all-polyethylene tibial components against PEEK and cobalt chrome femoral components of similar initial surface topography and geometry. Wear simulation with a higher AP displacement did not increase the wear of the polyethylene, in contrast to other designs of knee replacements, potentially due to the low conforming geometry of the implant [3]. The linear scratching on the surface of the PEEK implants did not increase the wear rate of the tibial components and the surface did not deteriorate further between 3 and 6 MC. A higher mean lubricant temperature was measured with PEEK femoral components, which was attributed to the higher friction of the PEEK-PE bearing couple. However it is not known whether this is clinically relevant or an artefact of the continuous running of the simulator. PEEK Optima® shows promise as the femoral component in a metal-free knee

Introduction. The observation of elevated heavy metal ions in arthroplasty patients in association with complications has led to concern on the part of patients and surgeons. The aim of this study was to determine the levels of cobalt chromium ions in three compartments, the joint fluid, plasma, and CSF. Method. Patients were divided into 3 groups:. 239 without any implant(M132F108). 50 having a supplementary implant, with a well performing contralateral THR. – 16 large head MoM arthroplasty (Birmingham modular M7F9). – 44 a Birmingham resurfacing(M39F5). 6 revisions of MoM bearings(M3F3). Blood and CSF specimens were harvested at the time of induction of anaesthesia. Joint fluid was aspirated before the surgical incision was made under sterile conditions. Cobalt was assayed using an Agilent7500ce inductively coupled plasma mass spectrometer. Chromium was assayed with a graphite furnace atomic absorption spectrometer (Varian240zlGFAAS). Bivariate correlations were used to determine similarities between group. Results. All results are in nanomoles/litre. Primary group. Blood: Co4.62±3.86; Cr6.10+I-4.17. CSF: Co2.43±3.44; Cr4.82±3.24. Supplementary group:. THR. Blood: Co37.3±62.96; Cr29.2±45.2. CSF: Co3.7±2.6;Cr7.4±4.9. BHR. Blood: Co35.2+I-48.8; Cr66.5+I-1 01.03. CSF: Co4.7±11.6;Cr6.6-'-I-4.1. Revision Group. Joint Fluid: Co5184.5±4662.9; Cr4452.7 ±3302.9. Blood: Col 07.5+1–77.6, Cr127.5±90.2. CSF: Co6.3±3.0, Cr8.3+I-6.2. Comparing with total hip with resurfacing patients, cobalt levels were not significantly different, but chromium levels were higher in resurfacing patients. The CSF levels, however, were not significantly different in the two groups. The CSF chromium level in all circumstances was higher than the cobalt. In patients with well functioning prostheses the blood ion levels were some 50% to 100% higher than patients without prostheses. While cobalt was higher in the joint fluid and the blood measurements, chromium was higher in the CSF. CSF measurements in the three groups of patients with pre-existing implant either well functioning or not, were not significantly different. The blood levels obtained are consistent with that described as reference values” for cobalt and chromium provided in pathology reports. On that basis, we believe that the CSF levels in the samples tested are an accurate representation of the levels. Conslusion. Blood sample chromium levels were higher than cobalt levels with the exception of total hip replacements. In spite of high levels and joint fluid, and less than 5% of the ion level was found in the blood. Of the blood level, less than 15% of was reflected in the CSF

We report a case of fatal heart failure caused by cobalt intoxication after revision THR in the patient who successfully underwent re-revision THR. 53-year old male presented to emergency room in our hospital with progressive shortness of breath. Symptom was started about 6 months ago so he visited local hospital. He worked up for worsening dyspnea. Simple chest radiograph and enhanced heart MRI study were performed and they showed bilateral pericardial and pleural effusion. There was no evidence of ischemic change. Transthoracic echocardiogram showed the evidence of heart failure, left ventricular ejection fraction(EF) was 40%. He was admitted at local hospital and started on vasopressors but urine output was decreased and follow-up echocardiogram showed a 25% of EF. Patient recommended heart transplantation and transferred our hospital emergency room. He underwent sequential bilateral total hip arthroplasties using CoP bearing surfaces. At 12 years postoperatively, he presented to the other hospital with acute onset of left hip pain. He was diagnosed ceramic head fracture on his left hip. Head and liner change revision surgery was performed using Cobalt-Chrome alloy 28mm metal head and Protruded cross-linked polyethylene liners. In our hospital, the patient admitted cardiovascular department of internal medicine. Patient complained nonspecific fatigue and general weakness but had no other symptoms such as visual and hearing loss, cognitive dysfuction. During work-up, patient presented progressive left hip pain and complaint of discomfort for the mass on the left groin. He also complained Left leg weakness and numbness. Simple radiograph and enhanced CT study was done. Simple radiograph image shows radiodense area around the hip joint and radiologist suspected heterotopic ossification. The cardiovascular department consulted orthopedic department. In the image findings showed huge mass combined hemorrhagic component lining acetabular component extending psoas compartment and eccentric wear on cobalt-chrome alloy metal head. Also highly radiodense material was seen around neck inferor portion and severly deformed metal head was seen. It was highly suspected that metal related granuloma, which means severe metallosis. Performed heavy metals screen, cobalt levels were 397,800 μg/Land chrome levels were 236,000 μg/L suggesting cobalt toxicity. Hip joint aspiration was done for decompression as radiologic intervention and EDTA (ethylenediamine tetraacetate) chelation therapy started immediately. After 10 cycle chelating therapy, metal level was lowered cobalt levels by 255.2μg/L and chrome levels by 39.5 μg/L. When hospital day after 134, Medical condition of the patient was getting improved, we underwent revision surgery using ceramic on ceramic bearing surface. The patient discharged postoperative 79 days. Final heavy metals screen results were 27.79μg/L on cobalt and 22.17μg/L on chrome. Although there were also reported a good clinical result of revision surgery using MoP bearing, and some surgeons reluctant to use CoC articulation because of concerns about re-fracture of ceramic. But take into account like this devastating complication after cobalt-chrome wear caused by remained ceramic particles, we should carefully select which bearing is safer

Aim. Adverse tissue reactions have been a concern in relation to metal components, particularly in hip replacements. We look at a possible correlation between hip joint effusion and metal ion levels. Materials and methods. 56 patients,(42M, 14F) agreed to the study. All had metal-on-mental arthroplasties. Average age was 64.2 (SD 9.8). All patients were asymptomatic. Ultrasound examination performed by one ultrasonographer, using a Sonosite M-Turbo machine with a C60X/5-2 MHz transducer. Cobalt levels were assessed using an inductively coupled plasma mass spectrometer. Chromium levels were assessed using a graphite furnace atomic absorption spectrometer. Results. Average blood ion levels were:. Cobalt 39.02 nmol/L. (SD41.18) range 3 to 215. Chromium 52.51 nmol/L (SD47.48) range 5 to 284. Average Volume: 10.38ml (SD21.3) Range 0 to 219. Conclusion. There was no statistically significant correlation between joint effusion and metal ion levels

INTRODUCTION. Many studies have looked at the effects of titanium tibial baseplates compared to cobalt chrome baseplates on backside wear. However, the surface finish of the materials is usually different (polished/unpolished) [1,2]. Backside wear may be a function not only of tray material but also of the locking mechanism. The purpose of this study was to evaluate the wear performance of conventional polyethylene inserts when mated with titanium tibial trays or cobalt chrome tibial trays that both have non-polished topside surfaces. MATERIALS AND METHODS. Three titanium (Ti) trays were used along with three cobalt chrome (CoCr) trays. The Ti trays underwent Type II anodization prior to testing. All trays were Triathlon® design (Stryker Orthopaedics, Mahwah, NJ). Tibial inserts were manufactured from GUR 1020 conventional polyethylene then vacuum/flush packaged and sterilized in nitrogen (30 kGy). Appropriate sized CoCr femoral components articulated against the tibial inserts (Triathlon®, Stryker Orthopaedics, Mahwah, NJ). Surface roughness of the tibial trays was taken prior to testing using white light interferometry (Zygo Corp, Middlefield, CT). A 6-station knee simulator (MTS, Eden Prairie, MN) was used for testing. Two phases were conducted. The first phase used a normal walking profile, as dictated by ISO 14243-3 [3]. The second phase used waveforms created specifically for stair climbing kinematics. Testing was conducted at a frequency of 1 Hz for 2 million cycles for each test with a lubricant of Alpha Calf Fraction serum (Hyclone Labs, Logan, UT) diluted to 50% with a pH-balanced 20-mMole solution of deionized water and EDTA (protein level = 20 g/l) [4]. The serum solution was replaced and inserts were weighed for gravimetric wear at least every 0.5 million cycles. Standard test protocols were used for cleaning, weighing and assessing the wear loss of the tibial inserts [5]. Soak control specimens were used to correct for fluid absorption with weight loss data converted to volumetric data (by material density). Statistical analysis was performed using the Student's t-test (p<0.05). RESULTS. White light interferometry measurements (Figure 1) showed a significant difference in surface roughness between the Ti and CoCr tibial trays (p < 0.01). Figure 2 displays the results of wear testing after 2 million cycles for walking and stair climbing kinematics and showed no significant difference in wear rate between the two tibial trays for either test. The large standard deviation for the CoCr trays during stair climbing kinematics is due to one outlier that had 60% higher wear than the remaining two stations. Without this station, the average of the remaining two CoCr stations was 7.6 mm. 3. /mc, which was similar to the average obtained using Ti tibial trays. Figure 3 shows the backside surfaces of the polyethylene inserts after 2 million cycles using the stair climbing kinematics. Visually, the inserts mated with the Ti trays showed less of a stenciling effect that those mated with CoCr trays. The location of the stenciled area corresponded to the location of the femoral condyle during the loading cycle. DISCUSSION. Although Ti has different material properties than CoCr, the results of this study show that the wear performance was not adversely affected when Ti tibial trays were substituted for standard CoCr tibial trays under normal walking and stair climbing kinematics. Even though there are differences between the two materials, the documented wear was not significantly different possibly owing to the specific locking mechanism tested

Metal on metal total hip arthroplasty provides the potential improvement in articular wear and the use of large-diameter femoral heads following the prospect for reduction in the risk of dislocation. The purpose of this study was to compare the clinical and radiographic outcomes as well as serum metal ion level between the two different component designs with small and large femoral heads in metal on metal total hip arthroplasty. We studied 39 patients with large head (Magnum®, Biomet; cup size minus 6 mm) and 37 patients with small head (M2a taper®, Biomet; 28 or 32 mm head) of metal on metal total hip arthroplasty between December 2009 to October 2011 with follow-up of 2.1 years (1.0–3.3 years) after surgery. Harris Hip Score, UCLA activity score, EQ-5D, radiographic assessment, and serum cobalt and chromium ion levels were evaluated. Harris Hip Score, UCLA activity score, and EQ-5D were improved after surgery in small and large head groups, however, no significant differences were observed between both groups. Cup inclination was below 50 degree in all prosthesis. No loosening and no osteolysis were observed. Cobalt and chromium ion was not detected before surgery; however, metal ion levels of both groups were increased after surgery in time dependent manner. There was no significant difference between two groups at one year after surgery. One patient in each group showed the increase of cobalt ion level over 7 ppb (15.4 ppb, 12.9 ppb) without any clinical symptom including pain. Cup inclination was 29 degree in both patients and cup anteversion was 38 and 41 degree, respectively. There was no significant difference of ion levels between both groups. No dislocation was observed in large head group while one dislocation occurred in small head group. No patients required the revision surgery. This metal on metal component, especially with large femoral heads, showed the good clinical results at the maximum follow up of 3.3 year after surgery. However, the ion level of two patients increased over 7 ppb and longer follow-up will be needed

Introduction. Total hip replacement with metal-on-polymer (MoP) hip prostheses is a successful treatment for late-stage osteoarthritis. However, the wear debris generated from the polymer acetabular liners remains a problem as it can be associated with osteolysis and aseptic loosening of the implant. This has led to the investigation of more wear resistant polymers in orthopaedics. Cross-linked polyethylene (XLPE) is now the gold-standard acetabular liner material. However, we asked if carbon fibre reinforced polyether ether ketone (CFR-PEEK) might be a lower wear material. In addition, we sought to understand the influence of contact stress on the wear of both XLPE and CFR-PEEK as this has not previously been reported. Materials and Methods. A 50-station circularly translating pin-on-disc (SuperCTPOD) machine was used to wear test both XLPE and CFR-PEEK pins against cobalt chromium (CoCr) discs to investigate the influence of contact stress on their wear rates. Fifty XLPE and 50 CFR-PEEK pins were articulated against CoCr discs. The pins, 9 mm in outer diameter and 12 mm in height, were drilled with different diameter holes to generate different sized annuli and thus, different contact areas. The pins were tested at 1.10, 1.38, 1.61, 2.00 and 5.30 MPa, which are typical contact stresses observed in the natural hip joint. An additional pin for every test group was used as a control to track the lubricant uptake. The discs were polished to 0.015 μm Sa prior to testing. The test stations contained 16 ml of diluted newborn calf serum (protein concentration: 22 g/L). Wear was measured gravimetrically with a balance (resolution: 10 μm) every 500,000 cycles. A standardised cleaning and weighing protocol was followed. Results and Discussion. The wear rates for the XLPE pins were calculated as 1.05, 0.90, 0.77, 0.48 and 0.28 mg/million cycles for the different pin stress groups respectively. The wear rates decreased with increasing contact stress, which was similar to what was observed for ultra-high molecular weight polyethylene (UHMWPE). The change in weight of the discs was insignificant (p-value:0.85). For the CFR-PEEK pin groups, the wear rates were calculated as 0.56, 0.65, 0.61, 0.58 and 0.65 mg/million cycles respectively. The difference between the wear rates was insignificant (p-value: 0.92). However, the weight of the discs decreased significantly (p-value: 0.00). At 1.11 MPa and taking data for UHMWPE tested in the same way, comparison of the three polymers showed that CFR-PEEK produced the lowest wear against CoCr. Although the wear rates for CFR-PEEK were found to be the lowest, the decrease in weight of the CoCr discs articulated against CFR-PEEK was indicative of metallic wear. Conclusion. CFR-PEEK should not be used against orthopaedic metals. XLPE articulating against CoCr was found to be the optimum combination, producing low wear without causing weight change from the counterface, under varying contact stresses

Introduction. The metal-on-metal (MoM) total hip prosthesis is widely used. However, the adverse reactions such as pseudotumor around the total hip prosthesis are observed. This is considered the effect of the corrosion of alloy which includes metal ion release and the wear particle generation. As materials for total hip prostheses, cobalt chromium (Co-Cr) alloy is used because of the wear resistance and corrosion resistance. The passive film on the surface of alloy contributes to corrosion resistance. The passive film is removed easily with friction. Therefore, metal ion is released from bare metal. However, this removal of passive film can be restored because of oxidation reaction with neighboring environment. The modular MoM total hip prosthesis such as acetabular component-femoral head or taper junction which connect femoral head and stem have friction interfaces. The friction amplitudes must be different among these interfaces. However, how sliding amplitude affects on removal of a passive film is unclear. The main purpose of this study was to investigate the effect of the sliding amplitude of the reciplocating micromotion on removal and reformation of the passive film of Co-Cr alloy. Methods. The behavior of the passive film was observed by measuring the electric potential of the alloy. Co-Cr alloy (ASTM F75) pin specimen and common tablet specimen were immersed in simulated body fluid PBS(−) and abraded with friction testing machine. The electronic potential between the pin and the Ag/AgCl reference electrode (RE-1C, ALS, Tokyo, Japan) were measured using a high impedance electrometer (HE-104E, HOKUTO DENKO, Tokyo, Japan). The friction amplitude was chosen from 0.2–2 mm. The reciprocating cycle was 1 Hz. The load of 10 N applied on the pin by a weight. Results and discussion. The electric potential neared equilibrium before the friction, and the passive film was stable. Electric potential dropped with the onset of friction and gradually increased with the cessation of friction. The potential difference ΔV and a time constant τ of the rise in electric potential after the friction were estimated. Those ΔV and τ were used as the indicator of the passive film destruction and restoration, respectively. At the friction amplitude of 0.2 mm, ΔV was lowest among at the other amplitudes. On the other hand, τ tended to be longer (Fig. 2). It showed that the reformation of passive film was delayed. When the removal of the passive film was repeated on local area of the friction interfaces, it was presumed similar to a phenomenon of the crevice corrosion. To view tables/figures, please contact authors directly

The PFC Sigma Cobalt Chrome Sigma (PFCSCC) was introduced in 2006, an update of the PFC Sigma designed to reduce backside wear. To help identify any significant early failures following its introduction, we prospectively identified all recipients over a one-year period. The patient's clinical, demographic and radiographic data, American Knee Society scores (AKSS), Oxford Knee scores (OKS) and SF-12 scores was recorded pre-operatively and at one, three and five years. 233 patients underwent 249 primary knee arthroplasties with the PFCSCC. Seventeen patients (19 knees) died and 29 patients (30 knees) were also lost to follow up at the five year point. The mean age was 66.6 (34–80) with 47.6% of the cohort being male. The mean five year follow-up was 1836 days (1530–2307). Five knees (2.2%) were revised for infection and three were revised for pain. The 5–year cumulative survival rate was 96.6% for any failure and 98.6% for aseptic failure. AKSS 32.6 (0–86.6) preoperatively, 80.7 (29–95) 5 years P < 0.001. OKS was 39.0 (22–53) preoperatively, 23.5 (4.7–42.3) 5 years P < 0.001. These results demonstrate a good early survivorship when compared to the old design PFC Sigma, however further follow-up to ten years is required

The aim of this study was to compare the outcome of cemented TKR using either oxidized zirconium (oxinium) or cobalt chrome (CoCr) femoral components in patients undergoing simultaneous bilateral TKR. Patients involved in the study received one of each prosthesis, thereby acting as their own control. The hypothesis was that there would be no difference in the clinical and radiographic outcome between the two prosthetic materials. Forty consecutive patients who were undergoing bilateral Genesis ll TKR consented to participate in the study. Patients were assessed preoperatively, at five days, six weeks and one, two and five years, postoperatively. The outcome measures included the KOOS, Knee Society Score, BOA Patient Satisfaction Scale, and radiographs at six weeks and one, two and five years. In two patients polyethlylene exchange was performed at 56 months from surgery during patellofemoral resurfacing. The four retrieved polyethylene liners were studied for wear with the aid of a stereo zoom microscope and an environmental scanning electron microscope (ESEM). Both the patients and the all examiners were blinded as to the prosthesis type throughout the study. Forty patients (80 knees) were included in the study. At five years, three patients were deceased and two had developed senile dementia. No patients were lost to follow up. At five years from surgery the CoCr knee was preferred by 41% of patients compared to 13% who preferred the Oxinium knee (p=0.009). There was no significant difference in range of motion between the two prosthesis at five days, six weeks or one, two and five years. There were also no significant differences between the two prostheses in any of the other variables assessed. The four retrieved polyethylene inserts showed similar patterns of wear in terms of both wear types and patterns under examination with both the stereo zoom and scanning electron microscope with no clear differences between CoCr and Oxinium bearing against the polyethlylene. There was no difference in the grade or incidence of radiographic lucencies between the two prosthesis at five years. At five years after surgery the only significant difference between the Genesis II Oxinium prosthesis and the CoCr prosthesis was a subjective preference for the CoCr prosthesis by a higher proportion of patients. There were no unexpected complications associated with the use the Oxinium femoral implants. In the four retrieved polyethylene liners, no significant differences were identified between the two prosthesis materials in terms of detectable wear type and patterns. Continued follow up of this cohort is planned to establish whether Oxinium femoral implants have an improved survivorship compared to CoCr femoral component in total knee replacement to warrant the additional cost

Purpose. Total disc replacement (TDR) devices have been restricted to designs with large, congruent articulations due to the limited wear properties of available materials. TDRs with more natural motion could be designed if materials were available which could resist the higher wear conditions. A novel TriLobe TDR design is self-centering and energetically stable, emulating the natural motion of the intact motion segment, but is not feasible using traditional materials due to small incongruent articulating surfaces. The objective of this study was to compare the wear properties of a medical grade polycrystalline diamond with wear properties of cobalt chrome (CoCr) and ultrahigh molecular weight polyethylene (UHMWPE) in aggressive high wear conditions. Methods. A modified pin-on-disc, crossing-path wear test was used to measure the wear rates of PCD-on-PCD, CoCr-on-CoCr, and CoCr-on-UHMWPE. The discs were placed in the inferior position on an oscillating plate, moving in a 10mm by 5mm figure-eight pattern. Pins had an initial 11.5mm radius and were loaded at 133N normal to the disc. In a typical pin-on-disc test, a wear flat develops on the pin and the wear rate is reduced as the contact area increases. The TriLobe design uses three lobes sliding in three non-conforming lenses which prevents wear flats from developing. To approximate this condition, the fixture holding the disc was placed on an air bearing and was allowed to rock in concert with movement of the load. The test was conducted in 25% bovine serum at a speed of less than two Hertz. Two sets of each material were tested, one set to 2.0 million cycles and the other set to 14.0 million cycles. Wear rates on the rocking-discs were measured using a high resolution coordinate measuring machine because the wear in the PCD specimens was not detectable gravimetrically. Results. The diamond specimen averaged 0.0036mm. 3. /MC of wear over the first 2 million cycles. The CoCr-on-CoCr specimens averaged 1.4mm. 3. /MC and the CoCr-on-UHMWPE averaged 4.7mm. 3. /MC over 2 million cycles. The PCD specimen taken to 14 million cycles had and average wear of 0.0022mm. 3. /MC compared to 2.4mm. 3. /MC and 9.5mm. 3. /MC for CoCr-on-CoCr and CoCr-on-UHMWPE respectively. Conclusions. Using the pin-on-rocking-disc test to approximate small, non-congruent articulating surface wear, both CoCr-on-CoCr and CoCr-on-UHMWPE wore at rates that were orders of magnitude greater than medical grade PCD. At two million cycles, CoCr-on-CoCr had worn nearly 400 times more than PCD and CoCr-on-UHMWPE wore more than 1300 times greater. During the last 12 million cycles the wear in non-diamond specimen accelerated, while the diamond wear rate decreased. At the end of 14 million cycles CoCr on itself and on UHMWPE specimens had worn at more than 1100 times and nearly 4300 times greater than PCD, respectively. Coupled with the inherent biocompatibility, high strength and toughness, and ultra low friction of diamond, the performance of PCD makes it an attractive material for TDR applications. PCD could be used in current designs to alleviate concern over wear debris and ion release and to increase the space for the next generation of TDR devices

Implant related hypersensitivity is an infrequent complication after total knee replacement. It remains a relatively unpredictable and poorly understood cause of failure of an implant. We present a report of five patients who presented with persistent hypertrophic synovitis after total knee replacement using a cobalt chrome component. Extensive preoperative and intraoperative attempts ruled out infection as a cause of symptoms. The knees had good ligamentous balance and were well aligned and fixed. The clinical condition improved after revision to a zirconium femoral and titanium metal backed tibial components. Intraoperative histopathology revealed thickened synovium with a predominantly monocellular (lymphocytic or histiocytic) response. Where infection has been excluded as a cause of persistent pain and swelling, consideration should be given to metal allergy as a cause of failure in primary knee replacement surgery

Demand for TKR surgery is rising, including a more diverse patient demographic with increasing expectations [1]. Therefore, greater efforts are being devoted to laboratory testing. As a result, laboratory testing may set a clinical performance presumption for surgeons and patients. For example, oxidized ZrNB (Oxinium) femoral components have been projected to show 85% less wear than CoCr femoral components in bench-top testing [2]. However, recent clinical data show no difference in outcomes between Oxinium® and CoCr for the same design [3]. While it does not show lagging peformance for the Oxinium components, it does call into question the predictive ability of simulation. To better understand the performance of these two materials, a non standardized simulator evaluation was conducted. One commercially available design (Legion PS) was evaluated with two variations of femoral component material (n = 3/material) Oxinium® and Cobalt Chromium. All testing was conducted using a 7.5 kGy moderately crosslinked UHMWPE (XLPE). A 6-station knee simulator was utilized to simulate stair-climbing kinematics. The lubricant used was Alpha Calf Fraction serum which was replaced every 0.5 million cycles for a total of 5 million cycles. Soak controls were used to correct for fluid absorption and statistical analysis was performed using the Student's t-test. Total wear rate results for the tibial inserts are shown in Figure 1. There was no statistical difference in volume loss (p = 0.8) or wear rate (p = 0.9) for the Oxinium® system when compared to the CoCrsystem under stair-climbing kinematics. Visual examination revealed typical wear scars and features on the condylar surfaces, including burnishing. These results corroborate the recent clinical data showing no difference between Oxinium® components and their CoCr analogs [3]. The kinematics used here are not a combination of normal level walking with stair-climbing conditions as was published originally for the Oxinium® material [2], but stair-climbing kinematics only. Even though the stair-climbing profile utilized here does not represent standardized kinematics, it provided results that are in line with clinical observations for these femoral materials. Logic suggests that a combined duty cycle is more representative of patient behavior so there must be additional test factors contributing to the prediction previously reported. The goal of bench top testing is to simulate actual clinical performance so test models must be validated as clinicaly relevant in order to be predictive. Furthermore, the results of this test indicate that the different femoral materials evaluated in this study do not alter the wear characteristics of this TKR. This is further supported by a similar previous study showing the relative contribution of design versus materials in terms of wear behavior [4]. The main determination comes from clinical evidence, and as it has been demonstrated by Kim, et al [3], there is no significant difference in the clinical results of the two TKR devices analyzed

Trunnionosis in modular hip arthroplasty has recently been recognised to be clinically important. Gaining an understanding of how the material interface at the head-trunnion affects the tribology at the modular junctions has current clinical implications as well as an implication on future implant selection and material choice. This matched-cohort study aims to compare tribocorrosion between ceramic and cobalt-chromium trunnions and to investigate other factors that contribute to the difference in tribocorrosion if present.

All hip prostheses retrieved between 1999 and 2015 at one centre were reviewed. Fifty two ceramic heads were retrieved, and these were matched to a cobalt-chromium cohort according to taper design, head size, neck length and implantation time in that order. The two cohorts were similar in male:female ratio (p=0.32) and body mass index (p=0.15) though the ceramic group was younger than the cobalt-chromium group (56.6 (+/−)13.5 years for ceramic group vs 66.3 (+/−14.4) years for cobalt-chromium group; p=0.001). There was no significant difference in the reasons for revision between the two groups (p=0.42). The femoral head trunnions were examined by two independent observers using a previously published 4-point scoring technique. The trunnions were divided into three zones: apex, middle and base. The observers were blinded to clinical and manufacturing data where possible.

Ceramic head trunnions demonstrated a lower median fretting and corrosion score at the base zone (p<0.001), middle zone (p<0.001) and in the combined score (p<0.001). In a subgroup analysis by head size, ceramic heads had a lower fretting and corrosion score at 28mm head diameter (p<0.001). Within the ceramic group, taper design had a significant effect on fretting and corrosion in the apex zone (p=0.04). Taper design also had a similar effect in the cobalt-chromium group in the apex zone (p=0.03). For the ceramic trunnions, the largest effect was contributed by the difference between the 11/13 taper and the 12/14 taper. For the cobalt-chromium trunnions, the largest effect was contributed by the difference between the 5 degree 38′ 37″ taper and type 1 taper.

Ceramic head trunnions showed a significantly lower fretting and corrosion score as compared to cobalt-chromium trunnions. Ceramic heads had a lower score than cobalt-chromium heads at 28mm head diameter. Taper design had an effect on fretting and corrosion within each cohort.

Introduction

Silicon nitride (SiN) is a recently introduced bearing material for THR that has shown potential in its bulk form and as a coating material on cobalt-chromium (CoCr) substrates. Previous studies have shown that SiN has low friction characteristics, low wear rates and high mechanical strength. Moreover, it has been shown to have osseointegration properties. However, there is limited evidence to support its biocompatibility as an implant material. The aim of this study was to investigate the responses of peripheral blood mononuclear cells (PBMNCs) isolated from healthy human volunteers and U937 human histiocytes (U937s) to SiN nanoparticles and CoCr wear particles.

Introduction. Metal-on-Metal (MoM) bearing surfaces were historically used for young patients undergoing total hip arthroplasty, and remain commonplace in modern hip resurfacing. In theory, it has been postulated that metal ions released from such implants may cross the placental barrier and cause harm to the fetus. In light of this potential risk, recommendations against the use of MoM components in women of child-bearing age have been advocated. The purpose of this systematic review was to evaluate: 1) the Metal-on-Metal bearing types and ion levels found; 2) the concentrations of metals in maternal circulation and the umbilical cord; and 3) the presence of abnormalities in the fetus. Methods. A comprehensive literature review was conducted of studies published between January 1st, 1975 and April 1st, 2019 using specific keywords. (See Fig 1). We defined the inclusion criteria for qualifying studies for this review as follows: 1) studies that reported on the women who experienced pregnancy and who had a Metal-on-Metal hip implant; 2) studies that reported on maternal metal ions blood and umbilical cord levels; and 3) studies that reported on the occurrence of fetal complications. Data on cobalt and chromium ion levels in the maternal blood and umbilical cord blood, as well as the presence of adverse effects in the infant were collected. Age at parturition and time from MoM implant to parturition were also collected. A total of 6 studies were included in the final analysis that reported on a total of 21 females and 21 infants born. The mean age at parturition was 40 years (range, 24–41 years), and the mean time from MoM implantation to parturition was 47.2 months (range, 11–119 months). Results. Maternal blood cobalt levels were found as a weighted average of 33.94ug/L (0.972–143), while umbilical cord blood cobalt levels were found to be 22.07 ug/L(0.486–75). Cobalt levels were reduced by an average of 35% between maternal and umbilical cord blood. Maternal cord blood chromium levels were found as a weighted average of 9.25 ug/L (1–25), while umbilical cord chromium levels were found to be 1.30 ug/L(0.288–2.3). Chromium levels were reduced by an average of 86% between maternal and umbilical cord blood. No cobalt or chromium was detected in the umbilical cord blood of three patients. Out of the 21 infants born to women with MoM implants, 20 were born healthy with no adverse effects or complications. Conclusion. To date, there is a lack of consensus as to whether Metal-on-Metal hip arthroplasty implants are to be avoided in the child-bearing female population and whether it constitute a hazard to the fetus in-utero. Both chromium and cobalt ions were markedly reduced in levels when transitioning from maternal to cord blood. In particular, chromium showed a greater reduction on average than cobalt (86% vs. 35%). Based on the current evidence, there appears to be no correlation between the presence of metal ions in umbilical cord blood and complications, particularly congenital malformations in the fetus, as none of the infants experienced abnormalities uniquely attributable to the presence of metal ions. For any figures or tables, please contact the authors directly