Comparison of synovial fluid, urine, and serum ion levels in metal-on-metal total hip arthroplasty at a minimum follow-up of 18 years

Do Intra-articular Metal Ion Levels Predict Adverse Local Tissue Reaction in Revision Total Hip Arthroplasty for Mechanically Assisted Crevice Corrosion?

BACKGROUND

Mechanically assisted crevice corrosion is a complication that may occur in vivo at modular metal interfaces following metal-on-polyethylene total hip arthroplasty (THA). Metal ions released in vivo may be associated with adverse local tissue reactions (ALTRs). While there is no definitive value, high serum ion levels are implicated as contributors to ALTR, and various screening levels have been recommended. The purpose of this investigation was to evaluate the relationship between synovial fluid (SF) cobalt and chromium ion levels and the risk of developing ALTR.

METHODS

This was a retrospective cohort study of 552 patients who underwent 621 metal-on-polyethylene primary THAs. A total of 69 patients underwent revision THA due to symptomatic primary failure with elevated serum metal ions levels. There were 28 who had preoperative serum and intraoperative SF chromium and cobalt samples. Patient demographics, surgical, and laboratory data were collected. Descriptive statistics, Mann-Whitney U, analysis of variance tests, and linear regression analyses were performed.

RESULTS

There were 40.6% of revisions that had preoperative serum and intraoperative SF samples. The mean time to revision was 5.7 (range, 3.8 to 7.6) years. Mean SF cobalt and chromium levels were 870.9mcg/L (range, 1.1 to 8,300.0) and 573.5mcg/L (range, 1.3 to 10,000.0). Mean serum and SF cobalt-chromium ratios were 4.0 (range, 0.9 to 7.1) and 6.4 (range, 0 to 15.1), respectively. Elevated serum cobalt levels were predictive of ALTR (P = 0.002), SF levels were not. Analysis of preoperative serum to SF cobalt-chromium ratios showed poor correlation (R2 = 0.05).

CONCLUSIONS

There was no correlation between SF ion levels and ALTR. Also, serum and intra-articular ion levels did not correlate. The SF levels did not provide additional value over serum levels for diagnosis or prognosis of mechanically assisted crevice corrosion. Further studies are needed to better understand the relationship between serum and SF ion levels and its relationship to ALTR.

Cobalt ions induce a cellular senescence secretory phenotype in human synovial fibroblast-like cells that may be an early event in the development of adverse local tissue reactions to hip implants

Objectives

Total hip arthroplasty is a successful procedure for treating advanced osteoarthritis (OA). Metal bearing surfaces remain one of the most widely implanted prosthesis, however approximately 10% of patients develop adverse local tissue reactions (ALTRs), namely lymphocytic predominant soft tissue reaction with or without necrosis and osteolysis resulting in high revision rates. The mechanism(s) for these reactions remains unclear although T lymphocyte mediated type IV hypersensitivity to cobalt (Co) and chromium (Cr) ions have been described. The purpose of this study was to determine the prolonged effects of Co and Cr metal ions on synovial fibroblasts to better understand the impact of the synovial membrane in the development of ALTRs.

Methods

Human synovial fibroblast-like cells were isolated from donors undergoing arthroplasty. DNA content and Alamar blue assay were used to determine cellular viability against exposure to Co and Cr. A beta-galactosidase assay was used to determine the development of cellular senescence. Western blotting and RT-qPCR were employed to determine changes in senescent associated secretory factors, signaling and anti-oxidant enzyme expression. A fluorescent assay was used to measure accumulation of hydrogen peroxide.

Results

We demonstrate that prolonged cobalt exposure results in a downregulation of the enzyme catalase resulting in cytosolic accumulation of hydrogen peroxide, decreased Akt activity and cellular senescence. Senescent fibroblasts demonstrated upregulation of proinflammatory cytokines IL-1β and TNFα in addition to the neurotrophic factor NGF.

Conclusion

Our results provide evidence that metal ions induce a senescent associated secretory phenotype in synovial fibroblasts that could contribute to the development of adverse local tissue reactions.

Critically high metal ion levels found in metal-on-metal modular hinged knee arthroplasty : a comparison of two different systems

AIMS

This study compared the cobalt and chromium serum ion concentration of patients treated with two different metal-on-metal (MoM) hinged total knee arthroplasty (TKA) systems, as well as a titanium nitride (TiN)-coated variant.

METHODS

A total of 63 patients (65 implants) were treated using either a MoM-coated (n = 29) or TiN-coated (n = 7) hinged TKA (GenuX mobile bearing, MUTARS; Implantcast, Germany) versus the BPKS (Brehm, Germany) hinged TKA (n = 27), in which the weight placed on the MoM hinge is diffused through a polyethylene (PE) inlay, reducing the direct load on the MoM hinge. Serum cobalt and chromium ion concentrations were assessed after minimum follow-up of 12 months, as well as functional outcome and quality of life.

RESULTS

No differences in mean age (69 years, 40 to 86), mean age adapted Charlson Comorbidity Index (3.1 (SD 1.4)), mean BMI (29.2 kg/m² (SD 5.8)), or number of other implants were observed between groups. Significant improvements in outcome scores and pain levels were achieved for all groups, and there was no difference in quality of life (12-Item Short-Form Health Survey questionnaire (SF-12)). Mean cobalt and chromium ion levels were significantly higher for the GenuX versus the BPKS hinged TKA (GenuX vs BPKS: cobalt: 16.3 vs 9.4 µg/l; chromium: 9.5 vs 5.2 µg/l). The TiN-coated implants did not appear to confer improvement in the metal ion levels. Metal ion concentrations above 7 µg/l were detected in 81%(29/36) of GenuX patients versus 41% (11/27) in the BPKS group. No GenuX patients had normal levels under 2 µg/l, versus 22% of BPKS patients. No significant reduction in outcome scores was observed regardless of the metal ion levels, whereas higher work-related activity was correlated with higher chromium concentrations.

CONCLUSION

Hinged TKA, using MoM hinges, resulted in critically high cobalt and chromium ion concentrations. The BPKS hinged TKA showed significantly lower metal ion concentrations compared with the GenuX TKA. No benefits were observed using TiN coating. The different weightbearing mechanics might influence the wear of the component materials. Higher workloads and physical activity could influence chromium levels. Cite this article: Bone Joint J 2022;104-B(3):376-385.

Concentration-Dependent Effects of Cobalt and Chromium Ions on Osteoarthritic Chondrocytes

OBJECTIVE

Cobalt and chromium (CoCr) ions from metal implants are released into the joint due to biotribocorrosion, inducing apoptosis and altering gene expression in various cell types. Here, we asked whether CoCr ions concentration-dependently changed viability, transcriptional activity, and inflammatory response in human articular chondrocytes.

DESIGN

Human articular chondrocytes were exposed to Co (1.02-16.33 ppm) and Cr (0.42-6.66 ppm) ions and cell viability and early/late apoptosis (annexin V and 7-AAD) were assessed in 2-dimensional cell cultures using the XTT assay and flow cytometry, respectively. Changes in chondrocyte morphology were assessed using transmitted light microscopy. The effects of CoCr ions on transcriptional activity of chondrocytes were evaluated by quantitative polymerase chain reaction (qPCR). The inflammatory responses were determined by measuring the levels of released pro-inflammatory cytokines (interleukin-1β [IL-1β], IL-6, IL-8, and tumor necrosis factor-α [TNF-α]).

RESULTS

CoCr ions concentration-dependently reduced metabolic activity and induced early and late apoptosis after 24 hours in culture. After 72 hours, the majority of chondrocytes (>90%) were apoptotic at the highest concentrations of CoCr ions (16.33/6/66 ppm). SOX9 expression was concentration-dependently enhanced, whereas expression of COL2A1 linearly decreased after 24 hours. IL-8 release was enhanced proportionally to CoCr ions levels, whereas IL-1β, IL-6, and TNF-α levels were not affected by the treatments.

CONCLUSIONS

CoCr ions showed concentration- and time-dependent effects on articular chondrocytes. Fractions of apoptotic articular chondrocytes were proportional to CoCr ion concentrations. In addition, metabolic activity and expression of chondrocyte-specific genes were decreased by CoCr ions. Furthermore, exposure to CoCr ions caused a release of pro-inflammatory cytokines.

Synovial Fluid Metal Ion Levels are Superior to Blood Metal Ion Levels in Predicting an Adverse Local Tissue Reaction in Failed Total Hip Arthroplasty

BACKGROUND

Adverse local tissue reactions (ALTR) are associated with total hip arthroplasty (THA) failure in patients with metal-on-metal bearings and/or taper corrosion, which can also occur in metal-on-polyethylene articulations. Patients are monitored with blood cobalt (Co) and chromium (Cr) concentrations which do not always correlate with the degree of soft tissue reaction at revision THA. The purpose of this study was to determine how the blood and prosthetic hip synovial fluid levels of Co and Cr correlate with one another, and determine which concentration is more predictive of ALTR.

METHODS

Synovial fluid and blood samples were collected at the time of revision THA in patients with (n = 26) and without ALTR (n = 27). Whole blood, serum, and synovial fluid metal ion concentrations were correlated with one another and clinical findings.

RESULTS

The ratio of synovial fluid to whole blood Co concentration in ALTR and non-ALTR hips was 120:1 and 18:1 (P = .006). The mean ratio of synovial fluid to whole blood Cr concentration in ALTR and non-ALTR hips was 414:1 and 24:1 (P = .01). The mean synovial fluid Co/Cr concentrations were elevated in patients with ALTR compared with those without (2007.3 vs. 12.4 ppb, P = .007) and (3188.2 vs. 10.3 ppb, P = .02). The synovial fluid Co concentration was the most accurate test for detecting ALTR (cut off: 19.75 PPB, AUC 0.973).

CONCLUSION

In patients with ALTR, synovial fluid Co and Cr levels were 120 times higher and 414 times higher than whole blood Co and Cr levels. Synovial fluid Co ion concentration was the most accurate in predicting ALTR.

LEVEL OF EVIDENCE

Diagnostic level II.

Pseudotumors in Small-Head Metal-on-Metal Total Hip Arthroplasties at a Minimum Follow-Up of 20 Years

BACKGROUND

Metal-on-metal (MOM) surfaces in total hip arthroplasty (THA) have been used widely. Serum cobalt and chromium levels have been the standard investigation for follow-up examinations, but magnetic resonance imaging (MRI) with metal artifact reducing sequences has shown good results in detecting pseudotumors. The aim of this study is to survey a significant correlation among MRI findings, serum metal levels, and clinical scores in patients with small-head MOM implants and if serum cobalt and chromium levels are sufficient in detecting patients with pseudotumors in the long-term follow-up.

METHODS

At a minimum follow-up of 20 years, 26 patients (29 THAs) of the original 98 patients (105 THAs) included in this study between November 1992 and May 1994 were available for follow-up examination. Clinical scores, serum metal ion levels, and MRIs were obtained.

RESULTS

We found mean serum cobalt levels of 1.87 μg/L (±3.44) and chromium levels of 2.23 μg/L (±2.96) and very good clinical and functional results (mean Harris Hip Score 88.6) in the long-term follow-up. Pseudotumors were detected in MRIs of 21 hips. There were no significant differences between patients with or without pseudotumors regarding serum metal levels and the correlation for clinical outcome scores, demographic data, and cup inclination. The cumulative rate of survival was still at 91.4% at 22.8 years.

CONCLUSION

This study presents the first published data on small-head MOM hips, comparing metal ion levels, pseudotumors, clinical, and radiological results in a follow-up period of more than 20 years and reveals that serum metal levels are not significantly higher in patients with pseudotumors.

LEVEL OF EVIDENCE

Therapeutic Level III.

Do cobalt or chromium accumulate in metal-on-metal hip arthroplasty patients who have mild, moderate, or severe renal insufficiency?

AIMS

To find out if there is an inverse association between estimated glomerular filtration rate (eGFR) and whole blood cobalt (Co) and chromium (Cr) levels in patients with metal-on-metal (MoM) hip arthroplasties and renal insufficiency, suggesting that renal insufficiency could cause accumulation of Co and Cr in blood.

METHODS

Out of 2,520 patients with 3,013 MoM hip arthroplasties, we identified 1,244 patients with whole blood Co, Cr, and creatinine measured within no more than a one-year interval. We analyzed the correlation of blood metal ion levels and eGFR to identify a potential trend of accumulating Co or Cr with decreasing eGFR.

RESULTS

Of the 1,244 patients, 112 had normal renal function (eGFR > 90 ml/min/1.73 m²), 715 had mild renal insufficiency (eGFR 60 to 89), 384 had moderate renal insufficiency (eGFR 30 to 59), 27 had severe renal insufficiency (eGFR 15 to 29), and six had end-stage renal insufficiency (eGFR < 15). Median eGFR was 68 ml/min/1.73 m² (interquartile range (IQR) 56 to 82), median whole blood Co was 3.3 µg/l (IQR 1.1 to 9.9), and median Cr was 2.0 µg/l (IQR 1.2 to 3.6). We did not observe an association between decreased eGFR and increased whole blood Co and Cr concentrations, but instead both increased Co and Cr were associated with higher eGFR, indicating better kidney function.

CONCLUSION

As patients with MoM hip arthroplasties get older, the prevalence of renal insufficiency among them will increase, and orthopaedic surgeons will increasingly have to evaluate whether or not this affects patient follow-up. The USA Food and Drug Administration suggests that closer follow-up may be needed for MoM patients with renal insufficiency. We did not observe accumulation of blood Co or Cr in MoM hip arthroplasty patients with mild to severe renal insufficiency. Cite this article: Bone Joint J 2021;103-B(7):1231-1237.

Metal Ion Release, Clinical and Radiological Outcomes in Large Diameter Metal-on-Metal Total Hip Arthroplasty at Long-Term Follow-Up

Total hip arthroplasty (THA) with metal-on-metal (MoM) bearings have shown problems of biocompatibility linked to metal ion release at the local level causing an adverse reaction to metal debris (ARMD) and at a systemic level. The aim of this study was to evaluate clinical and radiological outcomes, and metal ion concentrations in the blood and urine of patients who underwent THA with the LIMA Met-Met hip system. Patients with ceramic-on-ceramic (CoC) bearings were included as a control group. In this study, 68 patients were enrolled: 34 with MoM THAs and 34 with CoC THAs. Patients were evaluated clinically (Harris Hip Score, SF-36) and radiologically at a median of 7.4 years after surgery. Whole blood and urinary cobalt and chromium levels were also assessed. Both types of implants were comparable in terms of clinical and functional results. Ion levels were significantly higher in the MoM group compared with CoC group 7 years after surgery. No correlations were found between metal ion levels and patient demographics, functional and radiological outcomes, and prosthesis features. Patient monitoring is thus advised to establish if prosthesis revision is necessary, especially in the case of MoM THA.

Synthetic periprosthetic synovial fluid development for in vitro cell-tribocorrosion testing using the Taguchi array approach

Synovial fluid is dynamic in vivo with biological components changing in ratio and size depending on the health of the joint space, making it difficult to model in vitro. Previous efforts to develop synthetic synovial fluid have typically focused on single organic-tribological interactions with implant surfaces, thus ignoring interplay between multiple solution components. Using a Taguchi orthogonal array, we were able to isolate the individual effects of five independent synovial fluid composition variables: ratios of (1) hyaluronic acid to phospholipids (HA:PL) and (2) albumin to globulin (A:G), and concentrations of (3) hydrogen peroxide (H₂ O₂ ), (4) cobalt (Co²⁺ ) and (5) chromium (Cr³⁺ ) ions on macrophage viability and reduced glutathione production, local solution pH and the comprehensive CoCrMo alloy electrochemical response. While no single synovial fluid variable significantly affected the collective response, HA:PL ratio resulted in the largest impact factor (Δ) on 12 of the 13 measured responses with significant effects (p < .05) on the average macrophage survival rate and electrochemical capacitive state of the CoCrMo surface. Cluster analysis separated significant responses from all trials into three groups, corresponding to healthy, mild, or severely inflamed fluids, respectively; with the healthy synovial fluid composition having mid-range HA:PL ratios with no Co²⁺ ions, and the severely inflamed fluids consisting of low and high HA:PL ratios with H₂ O₂ and Co²⁺ ions. By utilizing the Taguchi approach in combination with cluster analysis, we were able to advance our knowledge of complex multivariate synthetic synovial fluids influence on macrophage and electrochemical behavior at the cell-solution-metal interface.

Serum cobalt concentrations remain at low levels at a minimum of 20 years following metal-on-metal total hip arthroplasty

Aims

Second-generation metal-on-metal (MoM) articulations in total hip arthroplasty (THA) were introduced in order to reduce wear-related complications. The current study reports on the serum cobalt levels and the clinical outcome at a minimum of 20 years following THA with a MoM (Metasul) or a ceramic-on-polyethylene (CoP) bearing.

Methods

The present study provides an update of a previously published prospective randomized controlled study, evaluating the serum cobalt levels of a consecutive cohort of 100 patients following THA with a MoM or a CoP articulation. A total of 31 patients were available for clinical and radiological follow-up examination. After exclusion of 11 patients because of other cobalt-containing implants, 20 patients (MoM (n = 11); CoP (n = 9)) with a mean age of 69 years (42 to 97) were analyzed. Serum cobalt levels were compared to serum cobalt levels five years out of surgery.

Results

The median cobalt concentration in the MoM group was 1.04 μg/l (interquartile range (IQR) 0.64 to 1.70) at a mean of 21 years (20 to 24) postoperatively and these values were similar (p = 0.799) to cobalt levels at five years. In the CoP control group, the median cobalt levels were below the detection limit (< 0.3 μg/l; median 0.15 μg/l, IQR 0.15 to 0.75) at 20 years. The mean Harris Hip Score was 91.4 points (61 to 100) in the MoM group and 92.8 points (63 to 100) in the CoP group.

Conclusion

This study represents the longest follow-up series evaluating the serum cobalt levels after 28 mm head MoM bearing THA and shows that serum cobalt concentrations remain at low levels at a mean of 21 years (20 to 24) after implantation.

Cite this article:Bone Joint Res. 2020;9(3):145–150.

Local Biological Reactions and Pseudotumor-Like Tissue Formation in relation to Metal Wear in a Murine In Vivo Model

Metal wear debris and released ions (CoCrMo), which are widely generated in metal-on-metal bearings of hip implants, are also found in patients with metal-on-polyethylene bearings due to the mechanically assisted crevice corrosion of modular taper junctions, including head-neck and neck-stem taper interfaces. The resulting adverse reactions to metal debris and metal ions frequently lead to early arthroplasty revision surgery. National guidelines have since been published where the blood metal ion concentration of patients must consistently be monitored after joint replacement to prevent serious complications from developing after surgery. However, to date, the effect of metal particles and metal ions on local biological reactions is complex and still not understood in detail; the present study sought to elucidate the complex mechanism of metal wear-associated inflammation reactions. The knee joints in 4 groups each consisting of 10 female BALB/c mice received injections with cobalt chrome ions, cobalt chrome particles, and ultra-high-molecular-weight polyethylene (UHMWPE) particles or PBS (control). Seven days after injection, the synovial microcirculation and knee joint diameter were assessed via intravital fluorescence microscopy followed by histological evaluation of the synovial layer. Enlarged knee diameter, enhanced leukocyte to endothelial cell interactions, and an increase in functional capillary density within cobalt chrome particle-treated animals were significantly greater than those in the other treatment groups. Subsequently, pseudotumor-like tissue formations were observed only in the synovial tissue layer of the cobalt chrome particle-treated animals. Therefore, these findings strongly suggest that the cobalt chrome particles and not metal ions are the cause for in vivo postsurgery implantation inflammation.

Mechanisms of Adverse Local Tissue Reactions to Hip Implants

Adverse Local Tissue Reactions (ALTRs) are one of the main causes of hip implant failures. Although the metal release from the implants is considered as a main etiology, the mechanisms, and the roles of the released products are topics of ongoing research. The alloys used in the hip implants are considered biocompatible and show negligible corrosion in the body environment under static conditions. However, modularity and its associated mechanically assisted corrosion have been shown to release metal species into the body fluids. ALTRs associated with metal release have been observed in hip implants with metal-on-metal articulation initially, and later with metal-on-polyethylene articulation, the most commonly used design in current hip replacement. The etiological factors in ALTRs have been the topics of many studies. One commonly accepted theory is that the interactions between the metal species and body proteins and cells generate a delayed type IV hypersensitivity reaction leading to ALTRs. However, lymphocyte reactions are not always observed in ALTRS, and the molecular mechanisms have not been clearly demonstrated. A more accepted mechanism is that cell damage generated by metal ions may trigger the secretion of cytokines leading to the inflammatory reactions observed in ALTRs. In this inflammatory environment, some patients would develop hypersensitivity that is associated with poor outcomes. Concerns over ALTRS have brought significant impact to both the clinical selection and development of hip implants. This review is focused on the mechanisms of ALTRs, specifically, the metal release process and the roles of the metal species released in the etiology and pathogenesis of the disease. Hopefully, our presentation and discussion of this biological process from a material perspective could improve our current understanding on the ALTRs and provide useful guidance in developing preventive solutions.

Does metal porosity affect metal ion release in blood and urine following total hip arthroplasty? A short term study

INTRODUCTION

The surface area of exposed metal in a trabecular-titanium acetabular component is wider compared to traditional-titanium implants. The purpose of this study is to establish if this increase in surface area can lead to a significant increase in systemic metal levels.

METHODS

19 patients with conventional acetabular component and 19 with trabecular-titanium cup were compared. Aluminum, Vanadium and Titanium in blood and urine were assessed before surgery and at intervals for 2 years. The samples were analysed using an inductively coupled plasma mass spectrometry.

RESULTS

Patients with trabecular-titanium did not have significantly higher metal ion levels compared to patients with conventional cups up to 2 years. A trend over time was statistically significant in both blood and urine for aluminum and titanium concentrations.

CONCLUSIONS

The three-dimensionality and the wide surface of the trabecular-titanium acetabular component did not affect metal ion release compared to traditional implants after 2 years.

Mechanical tests, wear simulation and wear particle analysis of carbon-based nanomultilayer coatings on Ti6Al4V alloys as hip prostheses

Carbon-based nanomultilayer coatings were deposited on medical-grade Ti₆Al₄V alloy using a magnetron sputtering technique under a graded bias voltage.

Osteocyte physiology and response to fluid shear stress are impaired following exposure to cobalt and chromium: Implications for bone health following joint replacement

The effects of metal ion exposure on osteocytes, the most abundant cell type in bone and responsible for coordinating bone remodeling, remain unclear. However, several studies have previously shown that exposure to cobalt (Co²⁺ ) and chromium (Cr³⁺ ), at concentrations equivalent to those found clinically, affect osteoblast and osteoclast survival and function. In this study, we tested the hypothesis that metal ions would similarly impair the normal physiology of osteocytes. The survival, dendritic morphology, and response to fluid shear stress of the mature osteocyte-like cell-line MLO-Y4 following exposure to clinically relevant concentrations and combinations of Co and Cr ions were measured in 2D-culture. Exposure of MLO-Y4 cells to metal ions reduced cell number, increased dendrites per cell and increased dendrite length. We found that combinations of metal ions had a greater effect than the individual ions alone, and that Co²⁺ had a predominate effect on changes to cell numbers and dendrites. Combined metal ion exposure blunted the responses of the MLO-Y4 cells to fluid shear stress, including reducing the intracellular calcium responses and modulation of genes for the osteocyte markers Cx43 and Gp38, and the signaling molecules RANKL and Dkk-1. Finally, we demonstrated that in the late osteoblasts/early osteocytes cell line MLO-A5 that Co²⁺ exposure had no effect on mineralization, but Cr³⁺ treatment inhibited mineralization in a dose-dependent manner, without affecting cell viability. Taken together, these data indicate that metal exposure can directly affect osteocyte physiology, with potential implications for bone health including osseointegration of cementless components, and periprosthetic bone remodeling. © 2016 The Authors. Journal of Orthopaedic Research Published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 35:1716-1723, 2017.

Elevated Intra-Articular Cobalt and Chromium Levels in Mechanically Assisted Crevice Corrosion in Metal-on-Polyethylene Total Hip Arthroplasty

BACKGROUND

Failed total hip arthroplasty (THA) caused by mechanically assisted crevice corrosion (MACC) has serious consequences such as adverse local tissue reaction (ALTR). Serum cobalt (Co) and chromium (Cr) ion levels have been used to diagnose taper corrosion, but have not been shown to be an accurate measure of the severity of MACC or associated ALTRs. Additionally, elevated serum ions are not specific in patients with multiple artificial joints.

METHODS

We examined the relationship between serum and intra-articular (IA) Co and Cr levels in a cohort of 20 patients undergoing revision THA, 16 who had symptomatic MACC. IA Co and Cr levels in MACC patients were compared with demographic, pre-operative, and operative findings.

RESULTS

Serum and IA metal levels were found to be relatively low in THA patients undergoing revision surgery for isolated instability, aseptic loosening, or infection (average serum Co 0.03 ppb [parts per billion], IA Co 1.4 ppb, serum Cr 0.32 ppb, IA Cr 3.3 ppb). In patients with MACC, average IA Co (940 ppb) was significantly higher than serum Co (5.1 ppb) (P = .0003) and IA Cr (491 ppb) was significantly higher than serum Cr (1.3 ppb) (P = .0003). IA Co level was associated with shorter time of hip symptoms to revision surgery (P = .0043).

CONCLUSION

Serum levels of Co and Cr correlated with joint levels in the entire cohort, but IA levels of MACC patients were 100 times greater than serum levels. IA Co and Cr levels may be useful in confirming MACC in a specific joint and the striking elevation may explain symptoms and ALTR with relatively low serum values.

Mid-term changes in blood metal ion levels after Articular Surface Replacement arthroplasty of the hip

AIMS

Our first aim was to determine whether there are significant changes in the level of metal ions in the blood at mid-term follow-up, in patients with an Articular Surface Replacement (ASR) arthroplasty. Secondly, we sought to identify risk factors for any increases.

PATIENTS AND METHODS

The study involved 435 patients who underwent unilateral, metal-on-metal (MoM) hip resurfacing (HRA) or total hip arthroplasty (THA). These patients all had one measurement of the level of metal ions in the blood before seven years had passed post-operatively (early evaluation) and one after seven years had passed post-operatively (mid-term evaluation). Changes in ion levels were tested using a Wilcoxon signed-rank test. We identified subgroups at the highest risk of increase using a multivariable linear logistic regression model.

RESULTS

There were significant increases in the levels of metal ions for patients who underwent both MoM HRA (Chromium (Cr): 0.5 parts per billion (ppb); Cobalt (Co): 1.1 ppb) and MoM THA (Cr: 0.5 ppb; Co: 0.7 ppb). In a multivariable model considering MoM HRAs, the change in the levels of metal ions was influenced by female gender (Co: Odds Ratio (OR) 1.42; p = 0.002 and Cr: OR 1.08; p = 0.006). The change was found to be irrespective of the initial level for the MoM HRAs, whereas there was a negative relationship between the initial level and the change in the level for those with a MoM THA (Co: OR -0.43; p < 0.001 and Cr: OR -0.14; p = 0.033).

CONCLUSION

The levels of metal ions in the blood increase significantly over the period until mid-term follow-up in patients with both a MoM HRA and those with a MoM THA. We recommend that the levels of metal ions be measured most frequently for women with a MoM HRA. While those with a MoM THA appear to stabilise at a certain level, the accuracy of this trend is not yet clear. Vigilant follow-up is still recommended. Cite this article: Bone Joint J 2017;99-B(4 Supple B):33-40.

pH and metal concentration of synovial fluid of osteoarthritic joints and joints with metal replacements

BACKGROUND

Due to degradation and metal dissolution during articulation of metal joint replacements the chemical periprosthetic environment may change. The aim was to establish whether metal replacements cause the local changes in pH and elevated metal concentrations.

METHODS

pH was measured on samples from 167 patients: native hip and knee osteoarthritic joints, joints with hip and knee replacements revised for aseptic or septic reasons. pH of synovial fluid and periprosthetic tissue was measured perioperatively using a microelectrode and pH indicator papers for removed metal components. Metal concentrations were measured in 21 samples using inductively coupled plasma mass spectrometry.

RESULTS

The mean pH value of synovial fluid at native osteoarthritic joints (n = 101) was 7.78 ± 0.38. The mean pH value of synovial fluid at revision aseptic operation (n = 58) was 7.60 ± 0.31, with statistically significant difference (p = 0.002) compared to native osteoarthritic joints. The mean pH value of synovial fluid at revision septic operation (n = 8) was 7.55 ± 0.25, with statistically significant difference (p = 0.038) compared to native osteoarthritic joints. Measurements in tissue and at stems were not reliable. In the majority of samples taken at revision increased levels of cobalt and chromium were measured.

CONCLUSION

A small but statistically significant difference was observed in the pH of synovial fluid between natural joints with degenerative diseases and joints treated with metal replacements. Based on the increased metal levels we expected the value of pH to be lower, but the influence of metal ions is counteracted by the buffering capacity of human body. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2507-2515, 2017.

[Are the cobalt hip prosthesis dangerous?]

The placement of a hip prosthesis is one of the most common orthopedic surgical procedures. Some implants contain metal and are therefore capable of releasing metal particles like cobalt in patients who wear metal prostheses. Cobalt can be responsible of local toxicity (including metallosis, hypersensitivity reaction, and benign tumor) or systemic toxicity (including cardiomyopathy, polycythemia, hypothyroidism, and neurological disorders). To monitor potential toxicity of metal hip prostheses, an annual monitoring of patients implanted is recommended and includes clinical examination, radiological examination and blood cobalt determination. The cobalt concentration in blood allows to estimate the risk of toxicity and to evaluate the performance of the implant. The currently recommended threshold value is equal to 7 µg of cobalt per liter of blood. Our study, conducted on 251 patients over a period of 4 years, has shown that the cobalt concentration average was 2.51 µg/l in blood, with 51 patients having a cobaltemia higher than the threshold of 7 µg/l.

Biological responses of preosteoblasts to particulate and ion forms of Co-Cr alloy

This study compared the particulate and ion forms of a cobalt-chrome (Co-Cr) alloy on the differentiation/activation of preosteoblasts. Mouse preosteoblasts (MC3T3-E1) were cultured in an osteoblast-induction medium in the presence of particulate and ion forms of a Co-Cr alloy, followed by cell proliferation and cytotoxicity evaluations. The maturation and function of osteoblasts were assessed by alkaline phosphatase (ALP) assay and related gene expressions. Both particulate and ion forms of the metals significantly reduced the proliferation of MC3T3-E1 cells in a dose-dependent manner. Similarly, cells challenged with high concentrations of particles and ions exhibited a marked cytotoxic effect and diminished expression of ALP. Real-time (RT) polymerase chain reaction (PCR) data have suggested that cells with Co-Cr particles dramatically promoted over-expression of monocyte chemo-attractant protein-1 (MCP-1), tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6), whereas Co(2+) ions treatment predominately up-regulated expressions of receptor activator of nuclear factor kappa-B ligand (RANKL), nuclear factor of activated T-cells cytoplasmic 1 (NFATc1), and down-regulated expression of osteoprotegerin (OPG) and Osterix (Osx). Overall, this study provides evidence that both Co-Cr alloy particles and metal ions interfered with the MC3T3-E1 cells for their growth, maturation, and functions. Further, Co-Cr particles exhibited stronger effects on inflammatory mediators, while metal ions showed more influence on inhibition of osteoblast differentiation and promotion of osteoclastogenesis.

Understanding the tissue effects of tribo-corrosion: uptake, distribution, and speciation of cobalt and chromium in human bone cells

Cobalt and chromium species are released in the local tissues as a result of tribo-corrosion, and affect bone cell survival and function. However we have little understanding of the mechanisms of cellular entry, intracellular distribution, and speciation of the metals that result in impaired bone health. Here we used synchrotron based X-ray fluorescence (XRF), X-ray absorption spectroscopy (XAS), and fluorescent-probing approaches of candidate receptors P2X7R and divalent metal transporter-1 (DMT-1), to better understand the entry, intra-cellular distribution and speciation of cobalt (Co) and chromium (Cr) in human osteoblasts and primary human osteoclasts. We found that both Co and Cr were most highly localized at nuclear and perinuclear sites in osteoblasts, suggesting uptake through cell membrane transporters, and supported by a finding that P2X7 receptor blockade reduced cellular entry of Co. In contrast, metal species were present at discrete sites corresponding to the basolateral membrane in osteoclasts, suggesting cell entry by endocytosis and trafficking through a functional secretory domain. An intracellular reduction of Cr6+ to Cr3+ was the only redox change observed in cells treated with Co2+, Cr3+, and Cr6+. Our data suggest that the cellular uptake and processing of Co and Cr differs between osteoblasts and osteoclasts.