Cobalt and chromium concentrations in patients with metal on metal total hip replacements

Survivability of Titanium Implant Materials: In Vitro Simulated Inflammatory and Infectious Environment

Titanium-based implants utilized in total joint arthroplasties could restore primary musculoskeletal function to patients suffering from osteoarthritis and other conditions. Implants are susceptible to failure stemming from aseptic loosening and infection at the joint site, eventually requiring revision surgery. We hypothesized that there might be a feedback loop by which metal degradation particles and ions released from the implant decrease cell viability and increase immune response, thereby creating biochemical conditions that increase the corrosion rate and release more metal ions. This study focused on the synergistic process through cell viability assays and electrochemical tests. From the results, inflammatory conditions from ion release resulting in cell death would further increase the corrosion rate at the metal implant site. The synergistic interaction in the implant surroundings in which infectious conditions produce Ti ions that contribute to more infection, creating a potential cycle of accelerating corrosion.

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.

3D Bioprinted Implants for Cartilage Repair in Intervertebral Discs and Knee Menisci

Cartilage defects pose a significant clinical challenge as they can lead to joint pain, swelling and stiffness, which reduces mobility and function thereby significantly affecting the quality of life of patients. More than 250,000 cartilage repair surgeries are performed in the United States every year. The current gold standard is the treatment of focal cartilage defects and bone damage with nonflexible metal or plastic prosthetics. However, these prosthetics are often made from hard and stiff materials that limits mobility and flexibility, and results in leaching of metal particles into the body, degeneration of adjacent soft bone tissues and possible failure of the implant with time. As a result, the patients may require revision surgeries to replace the worn implants or adjacent vertebrae. More recently, autograft - and allograft-based repair strategies have been studied, however these too are limited by donor site morbidity and the limited availability of tissues for surgery. There has been increasing interest in the past two decades in the area of cartilage tissue engineering where methods like 3D bioprinting may be implemented to generate functional constructs using a combination of cells, growth factors (GF) and biocompatible materials. 3D bioprinting allows for the modulation of mechanical properties of the developed constructs to maintain the required flexibility following implantation while also providing the stiffness needed to support body weight. In this review, we will provide a comprehensive overview of current advances in 3D bioprinting for cartilage tissue engineering for knee menisci and intervertebral disc repair. We will also discuss promising medical-grade materials and techniques that can be used for printing, and the future outlook of this emerging field.

Fretting-corrosion in hip taper modular junctions: The influence of topography and pH levels - An in-vitro study

Contemporary hip implants feature a modular design. Increased reported failure rates associated with the utilization of modular junctions have raised many clinical concerns. Typically, these modular interfaces contain circumferential machining marks (threads or microgrooves), but the effect of the machining marks on the fretting-corrosion behavior of total hip implant materials is unknown. This study reports the effects of microgrooves on the fretting-corrosion behavior of hip implant materials. The flat portions of two cylindrical, polished, CrCrMo alloy pins were loaded horizontally against one rectangular Ti alloy rod. Two surface preparation groups were used for the Ti6Al4V rod (polished and machined). The polished group was prepared using the same methods as the CoCrMo pins. The machined samples were prepared by creating parallel lines on the rod surfaces to represent microgrooves present on the stem tapers of head-neck modular junctions. Newborn calf serum (30 g/L protein content; 37 °C) at pH of levels of 7.6 and 3.0 were used to simulate the normal joint fluid and a lowered pH within a crevice, respectively. The samples were tested in a fretting corrosion apparatus under a 200N normal force and a 1Hz sinusoidal fretting motion with a displacement amplitude of 25 μm. All electrochemical measurements were performed with a potentiostat in a three-electrode configuration. The results show significant differences between machined samples and polished samples in both electrochemical and mechanical responses. In all cases, the magnitude of the drop in potential was greater in the machined group compared to the polished group. The machined group showed a lower total dissipated friction energy for the entire test compared to the polished group. Additionally, the potentiostatic test measurements revealed a higher evolved charge in the machined group compared to the polished group at both pH conditions (pH 7.6 and 3.0). The machined surfaces lowered the overall dissipated friction energy at pH 7.6 compared to pH 3.0, but also compromised electrochemical performance in the tested conditions. Therefore, the role of synergistic interaction of wear and corrosion with surface topographical changes is evident from the outcome of the study. Despite the shift towards higher electrochemical destabilization in the machined group, both polished and machined groups still exhibited a mechanically dominated degradation.

Biological Monitoring of Metal Ions Released from Hip Prostheses

The aim of this study was to evaluate the levels of As, Be, Bi, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Se, Tl, V, and Zn, by inductively coupled plasma-mass spectrometry (ICP-MS) in the urine of two groups of patients with two different types of metal-on-metal (MoM) total hip prostheses (ASR DePuy^®, group A, 25 patients; total Met-Met System Lima^®, group B, 28 patients). The determination of metals reflected a steady-state release (group A: 9 years after surgery and group B: 6 years after surgery). The results obtained confirmed the increase of Co and Cr urinary levels in both group when compared with the reference values for the general population adopted by the Italian Society of Reference Values (SIVR). In particular, Co and Cr levels exceeded the threshold values in urine, respectively, of 30 μg and 21 µg, adjusted to creatinine based on the threshold in whole blood of 7 μg/L proposed by the Medicines and Healthcare Products Regulatory Agency (MHRA). Regarding the other investigated metals, significantly higher values were found in Group A than in Group B. These differences could be due to the type of hip prosthesis implanted, the longer period of time since the implantation, as well as many other factors such as diet, age, drug consumption, physical activity, or presence of dental fillings. The continuous monitoring over the years of metal concentrations in patients carrying a prosthesis could be useful to better identify the sources of these metals.

Bioactive glass coatings on metallic implants for biomedical applications

Metallic implant materials possess adequate mechanical properties such as strength, elastic modulus, and ductility for long term support and stability in vivo. Traditional metallic biomaterials, including stainless steels, cobalt-chromium alloys, and titanium and its alloys, have been the gold standards for load-bearing implant materials in hard tissue applications in the past decades. Biodegradable metals including iron, magnesium, and zinc have also emerged as novel biodegradable implant materials with different in vivo degradation rates. However, they do not possess good bioactivity and other biological functions. Bioactive glasses have been widely used as coating materials on the metallic implants to improve their integration with the host tissue and overall biological performances. The present review provides a detailed overview of the benefits and issues of metal alloys when used as biomedical implants and how they are improved by bioactive glass-based coatings for biomedical applications.

Concordance between laboratories in metal ion testing in patients with metal-on-metal hip implants

BACKGROUND

Testing of whole blood or serum metal ion levels has become an important part of assessing and monitoring the performance of metal-on-metal bearings, both in hip resurfacing arthroplasty and in total hip replacement. The aim of this study was to determine the concordance between 2 laboratories testing cobalt and chromium ion levels in patients with metal-on-metal bearings.

METHODS

Serum and whole blood samples from patients who had undergone metal-on-metal resurfacing or large-diameter total hip arthroplasty were tested for cobalt and chromium ions in laboratory A (a recognized laboratory) and laboratory B (tasked with testing clinical specimens). Laboratory A performed cobalt and chromium testing on whole blood, and laboratory B performed cobalt testing on whole blood and chromium testing on serum.

RESULTS

Samples from 104 patients were tested. Laboratory B reported lower whole blood cobalt levels than laboratory A. Furthermore, laboratory A reported that all patients had elevated whole blood cobalt ion levels compared to the normal reference values for the laboratory, whereas laboratory B reported that 46 patients (44.2%) had whole blood cobalt ion levels within the normal reference range for the laboratory.

CONCLUSION

This comparative study highlights the importance of using a single laboratory for metal ion testing, as values generated from different laboratories may not be directly comparable. With recent literature suggesting that whole blood cobalt levels as low as 1 ppb may be a predictor of adverse reactions to metal debris, accurate clinical measurement needs to be increasingly exact.

Is end-organ surveillance necessary in patients with well-functioning metal-on-metal hip resurfacings?

Aims

Cardiac magnetic resonance (CMR) was used to assess whether cardiac function or tissue composition was affected in patients with well-functioning metal-on-metal hip resurfacing arthroplasties (MoMHRA) when compared with a group of controls, and to assess if metal ion levels correlated with any of the functional or structural parameters studied.

Patients and Methods

In all, 30 participants with no significant cardiac history were enrolled: 20 patients with well-functioning MoMHRA at mean follow-up of 8.3 years post-procedure (ten unilateral, ten bilateral; 17 men, three women) and a case-matched control group of ten non-MoM total hip arthroplasty patients (six men, four women). The mean age of the whole cohort (study group and controls) at the time of surgery was 50.6 years (41.0 to 64.0). Serum levels of cobalt and chromium were measured, and all patients underwent CMR imaging, including cine, T2* measurements, T1 and T2 mapping, late gadolinium enhancement, and strain measurements.

Results

None of the MoMHRA patients showed clinically significant cardiac functional abnormality. The MoMHRA patients had larger indexed right and left end diastolic volumes (left ventricular (LV): 74 ml/m2 vs 67 ml/m2, p = 0.045; right ventricular: 80 ml/m2 vs 71 ml/m2, p = 0.02). There was a small decrease in T2 time in the MoMHRA patients (median 49 ms vs 54 ms; p = 0.0003). Higher metal ion levels were associated with larger LV volumes and with shorter T2 time.

Conclusion

Although cardiac function is not clinically adversely affected in patients with well-functioning MoMHRA, modern imaging is able to demonstrate subtle changes in structure and function of the heart. As these changes correlate with systemic ion measurements, they may be consequences of wear debris deposition. Longer, longitudinal studies are necessary to determine whether cardiac function will become affected. Cite this article: Bone Joint J 2019;101-B:540–546.

Effect of the coexistence of albumin and H2O2on the corrosion of biomedical cobalt alloys in physiological saline

The corrosion of Co–28Cr–6Mo and Co–35Ni–20Cr–10Mo, as biomedical alloys, has been investigated for effects of typical species (albumin and H₂O₂) in physiological saline, with their coexistence explored for the first time. Electrochemical and long term immersion tests were carried out. It was found that Co alloys were not sensitive to the presence of albumin alone, which slightly promoted anodic dissolution of Co–35Ni–20Cr–10Mo without noticeably affecting Co–28Cr–6Mo and facilitated oxide film dissolution on both alloys. H₂O₂ led to a clear drop in corrosion resistance, favouring metal release and surface oxide formation and inducing much thicker but less compact oxide films for both alloys. The coexistence of both species resulted in the worst corrosion resistance and most metal release, while the amount and composition of surface oxide remained at a similar level as in the absence of both. The effect of H₂O₂ inducing low compactness of surface oxides should prevail on deciding the poor corrosion protection ability of passive film, while albumin simultaneously promoted dissolution or inhibited formation of oxides due to H₂O₂. Corrosion resistance was consistently lower for Co–35Ni–20Cr–10Mo under each condition, the only alloy where the synergistic effect of both species was clearly demonstrated. This work suggests that the complexity of the environment must be considered for corrosion resistance evaluation of biomedical alloys.

Corrosion of biomedical Co alloys were firstly studied in the presence of both albumin and H₂O₂.

A Randomized Seven-Year Study on Performance of the Stemmed Metal M2a-Magnum and Ceramic C2a-Taper, and the Resurfacing ReCap Hip Implants

BACKGROUND

The large-diameter metal-on-metal hip prostheses were expected to have low wear and reduced dislocation rate compared to the traditional metal-on-polyethylene implants. We compare 2 such prostheses, the ReCap resurfacing implant and the M2a-Magnum stemmed implant, with the C2a ceramic-on-ceramic stemmed implant as to clinical performance, serum concentrations of prosthesis metals, and the durability of the implants in a randomized, controlled clinical trial at 7 years of follow-up.

METHODS

All included patients had osteoarthritis. Preoperatively, the size of the implants was estimated from a magnetic resonance imaging (MRI) scan. Follow-up data included serum cobalt and chromium concentrations, Oxford and Harris Hip Scores, leg press and abduction force, 6-minute walk distance, WOMAC and SF-36 self-assessment scores, and from the 7th postoperative year also ultrasonography (US) examination of the soft tissue adjacent to the implant as well as MRI with metal artifact reduction sequence (MARS-MRI) when indicated.

RESULTS

One hundred fifty-two hips in 146 patients were included. The serum cobalt and chromium concentrations were significantly higher for the 2 metal-on-metal prostheses than for the ceramic-on-ceramic, with the M2a-Magnum as the highest. No significant difference was found between the groups concerning physical performance measurements and scores as well as dislocations and prosthesis survival. Five revisions were done and concerned all groups, for reasons of pain, high serum cobalt and chromium concentrations, cystic fluid collection around the joint, and infection. Metal concentrations, US, and MARS-MRI contributed to the decision making regarding prosthesis revision.

CONCLUSION

Metal concentrations were significantly higher for the metal-on-metal prostheses than for the ceramic-on-ceramic. The clinical performance was good in all 3 prosthesis groups. Metal concentrations, US, and MARS-MRI findings were of use to identify hips needing revision. ID Number in ClinicalTrials.gov PRS: NCT00284674.

Effect of sleeved ceramic femoral heads on titanium ion release

INTRODUCTION

Metal ion release from wear and corrosion at the femoral head-stem taper junction can evoke local adverse reactions to metal debris (ARMD). In a specific large-diameter head (LDH) total hip arthroplasty (THA) system, ceramic femoral heads of 44 to 48 mm are available with a titanium (Ti) adaptor sleeve, while heads of 36- to 40-mm come without sleeves. The hypothesis of this study is that the Ti adaptor sleeve with LDH ceramic-on-ceramic (CoC) bearings will not cause wear or corrosion at the taper junction and, thus, will not generate high whole blood Ti ion levels.

METHODS

We compared whole blood Ti levels at minimum 1-year follow-up in 27 patients with unilateral primary LDH CoC THA with head sizes ranging from 36 to 48 mm using a Ti stem and acetabular component.

RESULTS

Although Ti ion levels in patients with 36- to 40-mm head diameters without Ti sleeve were found to be statistically significantly higher (2.3 μg/l: 1.6-3.1, SD 0.44) compared to those with a Ti sleeve (1.9 μg/l: 1.6-2.2, SD 0.19) (p = 0.020), the found difference has no clinical importance. No patients presented clinical signs of ARMD, and the clinical results in both groups were similar.

CONCLUSIONS

LDH CoC THA Ti levels were low and probably related to unavoidable passive corrosion of implant surfaces. Measurement of Ti in subjects with ceramic LDH, with or without Ti adaptor sleeve, did not disclose undirected signs of trunnionosis.

Metallic Biomaterials: Current Challenges and Opportunities

Metallic biomaterials are engineered systems designed to provide internal support to biological tissues and they are being used largely in joint replacements, dental implants, orthopaedic fixations and stents. Higher biomaterial usage is associated with an increased incidence of implant-related complications due to poor implant integration, inflammation, mechanical instability, necrosis and infections, and associated prolonged patient care, pain and loss of function. In this review, we will briefly explore major representatives of metallic biomaterials along with the key existing and emerging strategies for surface and bulk modification used to improve biointegration, mechanical strength and flexibility of biometals, and discuss their compatibility with the concept of 3D printing.

Development of malignant lymphoma after metal-on-metal hip replacement: a case report and review of the literature

A number of previous studies have reported a potential risk of malignancy, particularly hematological malignancy, developing in patients receiving a metal-on-metal (MoM) hip replacement. We report a case of malignant lymphoma that arose in a patient who had an MoM hip arthroplasty complicated by development of a pseudotumour. The tumour was a B cell follicular lymphoma that involved lymph nodes and bone. Metal ions are known to have a genotoxic effect on lymphoid cells. Although epidemiological studies have not established that there is an increased risk of lymphoma associated with MoM implants, only a relatively short time period has elapsed since re-introduction of this type of implant and long-term follow-up of patients with MoM implants is indicated.

Cobalt toxicity in humans-A review of the potential sources and systemic health effects

Cobalt (Co) and its compounds are widely distributed in nature and are part of numerous anthropogenic activities. Although cobalt has a biologically necessary role as metal constituent of vitamin B₁₂, excessive exposure has been shown to induce various adverse health effects. This review provides an extended overview of the possible Co sources and related intake routes, the detection and quantification methods for Co intake and the interpretation thereof, and the reported health effects. The Co sources were allocated to four exposure settings: occupational, environmental, dietary and medical exposure. Oral intake of Co supplements and internal exposure through metal-on-metal (MoM) hip implants deliver the highest systemic Co concentrations. The systemic health effects are characterized by a complex clinical syndrome, mainly including neurological (e.g. hearing and visual impairment), cardiovascular and endocrine deficits. Recently, a biokinetic model has been proposed to characterize the dose-response relationship and effects of chronic exposure. According to the model, health effects are unlikely to occur at blood Co concentrations under 300μg/l (100μg/l respecting a safety factor of 3) in healthy individuals, hematological and endocrine dysfunctions are the primary health endpoints, and chronic exposure to acceptable doses is not expected to pose considerable health hazards. However, toxic reactions at lower doses have been described in several cases of malfunctioning MoM hip implants, which may be explained by certain underlying pathologies that increase the individual susceptibility for Co-induced systemic toxicity. This may be associated with a decrease in Co bound to serum proteins and an increase in free ionic Co²⁺. As the latter is believed to be the primary toxic form, monitoring of the free fraction of Co²⁺ might be advisable for future risk assessment. Furthermore, future research should focus on longitudinal studies in the clinical setting of MoM hip implant patients to further elucidate the dose-response discrepancies.

The Prevalence of Positive Findings on Metal Artifact Reduction Sequence Magnetic Resonance Imaging in Metal-on-Metal Total Hip Arthroplasty

BACKGROUND

We sought to assess the prevalence of soft tissue changes seen on magnetic resonance imaging (MRI) after metal-on-metal (MOM) total hip arthroplasty (THA) and determine if the presence of pseudotumors was associated with metal ion levels, acetabular cup position, outcomes scores, and femoral head size.

METHODS

After receiving an institutional review board exemption for secondary data analysis, we performed a cross-sectional study identifying 55 patients (55 hips) that underwent primary THA with a MOM articulation and had subsequent MRI imaging between February 2013 and February 2014 at a single academic medical center.

RESULTS

Twenty-four patients (44%) had no evidence of pseudotumors, 27 (49%) had type I pseudotumors, and 4 (7%) were classified as having type II pseudotumors. The presence and severity of pseudotumors were associated with higher serum chromium levels (P = .043). Neither acetabular inclination nor acetabular version was associated with the presence of pseudotumors, the severity of pseudotumors, or elevated serum metal ion levels (all P > .05). Increased metal ion levels were associated with lower Harris Hip Score and higher Harris Hip Score pain subscores (all P < .05).

CONCLUSION

In conclusion, pseudotumors on metal artifact reduction sequencing MRI may be present in both symptomatic and asymptomatic MOM THAs. Surgeons should therefore exercise caution in placing too much emphasis on isolated studies such as cross-sectional imaging. Instead, a structured approach to evaluation of MOM arthroplasty should be followed.

Hip resurfacing: history, current status, and future

Hip resurfacing arthroplasty (HRA) presents several advantages over conventional total hip arthroplasty (THA), including conservation and preservation of bone, reduced risk of dislocation, easy replication of hip biomechanics and easy revision if needed. It is a particularly appealing procedure for young patients. HRA has been performed for over 40 years following the same technological advances as THA. The bearing material used by most designs is metal-on-metal (MoM), which has the best compromise between strength and wear properties. However, MoM HRA has a specific set of possible complications. Aseptic femoral failures were initially the most prevalent cause for revision but progress in patient selection and surgical technique seem to have resolved this problem. Wear-related failures (high metal ion levels and adverse local tissue reactions) are now the main concern, and are essentially associated with poor acetabular component design and orientation, to which MoM is more sensitive than other bearing materials. The concept of functional coverage is key to understanding how MoM bearings are affected by edge wear. Only a 3-D assessment of cup position (e.g., the contact patch to rim distance) provides the necessary information to determine the role of cup positioning in relationship with abnormal bearing wear.The concept of hip resurfacing is more valid today than ever as the age of the patients in need of hip arthroplasty keeps getting lower. The recent publication of several excellent long-term survivorship results suggests that selection of a well-designed resurfacing system and accuracy in the placement of the cup can achieve long-term durability.

Metal ion concentrations and semen quality in patients undergoing hip arthroplasty: A prospective comparison between metal-on-metal and metal-on-polyethylene implants

PURPOSE

The widespread usage of metal-on-metal (MoM) articulations in total hip arthroplasty (THA) has been tempered by concerns of increased metal ion production. The purpose of the study is to evaluate the influence of metal ion exposure on semen quality in young male patients undergoing THA.

METHODS

Male patients who were scheduled for unilateral THA and aged between 20 and 45 years were prospectively enrolled. Patients were sorted into MoM and metal-on-polyethylene (MoP) groups with equal case number. Semen and blood metal ion levels were measured and sperm analysis was performed before, 6 months after, and 1 year after surgery.

RESULTS

Compared to preoperative baseline, patients (n = 50) in both groups had increased cobalt (Co) and chromium (Cr) concentrations in blood and seminal fluid after surgery. Between-group comparisons at 6 months and 1 year after surgery showed that patients in the MoM group both had a greater Co concentration in blood and semen and a greater Cr concentration in blood and semen. Patients receiving MoM prosthesis had a reduced percentage of morphologically normal sperm, and decreases from the preoperative level (44.7%) were significant at 6 months (36.8%, p = 0.03) and 1 year (33.8%, p = 0.004).

CONCLUSIONS

Our data shows a significantly greater concentration of metal ion in blood and semen in patients with MoM prosthesis with a reduced percentage of morphologically normal sperm. Despite small effects on sperm quality, some concerns remain. Further studies are necessary to determine sources of metal ion and to investigate effects on male fertility.

The Interchangeability of Plasma and Whole Blood Metal Ion Measurement in the Monitoring of Metal on Metal Hips

One hundred and twenty six paired samples of plasma and whole blood were measured with inductively coupled plasma mass spectrometry technique for metal ions analysis to determine a relationship between them. There was a significant difference between the mean plasma and whole blood concentrations of both cobalt (Co) and chromium (Cr) (p < 0.0001 for both Co and Cr). The mean ratio between plasma and whole blood Cr and Co was 1.56 (range: 0.39-3.85) and 1.54 (range: 0.64-18.26), respectively, but Bland and Altman analysis illustrated that this relationship was not universal throughout the range of concentrations. There was higher variability at high concentrations for both ions. We conclude that both these concentrations should not be used interchangeably and conversion factors are unreliable due to concentration dependent variability.

Do hardened femoral heads reduce blood metal ion concentrations after hip resurfacing?

BACKGROUND

Elevated cobalt and chromium ion concentrations have been associated with the use of metal-on-metal bearings in hip arthroplasty. The use of a differential hardness bearing may reduce metal particle release. The aim of our study was to compare circulating cobalt (Co) and chromium (Cr) ion levels between patients treated with a standard all 'as-cast' heat treated bearing and a differential hardness bearing.

MATERIALS AND METHODS

One hundred and thirty-two patients implanted with unilateral hip resurfacing arthroplasties and having had blood metal ion studies performed between one and six years after surgery were retrospectively selected. There were 73 patients in the standard all 'as cast' heat treated bearing group (group 1) and 59 in the differential hardness bearing group (group 2).

RESULTS

Clinical and quality of life scores were comparable between groups. The median Co in group 1 was 1.01 µg/L and 1.23 µg/L in group 2 (p = 0.0566). The median Cr in group 1 was 1.60 µg/L and 1.34 µg/L in group 2 (p = 0.0505).

CONCLUSION

Compared with conventional heat-treated CoCr bearings, differential hardness metal-on metal bearings do not confirm in vivo the hopes of a substantial reduction in circulating metal ions concentrations suggested by in vitro wear studies.

Interactions between mammalian cells and nano- or micro-sized wear particles: physico-chemical views against biological approaches

Total joint arthroplasty (TJA) is a more and more frequent approach for the treatment of end-stage osteoarthritis in young and active adults; it successfully relieves joint pain and improves function significantly enhancing the health-related quality of life. Aseptic loosening and other wear-related complications are some of the most recurrent reasons for revision of TJA. This review focuses on current understanding of the biological reactions to prosthetic wear debris comparing in vivo and in vitro results. Mechanisms of interactions of various types of cells with metal, polymeric and ceramic wear particles are summarised. Alternative views based on multidisciplinary approaches are proposed to consider physico-chemical, surface parameters of wear particles (such as: particle size, geometry and charge) and material (particle chemical composition and its nature) with biological effects (cellular responses).

Predictivity and fate of metal ion release from metal-on-metal total hip prostheses

Blood metal ion levels in 72 patients with large head metal-on-metal hip arthroplasty were studied to determine the correlation between the values measured in whole blood and urine. Urinary cobalt and chromium levels of 30μg and 21μg, respectively, adjusted to creatinine were found to correspond to the 7μg/l cut-off value that has been accepted in whole blood. Cobalt and chromium levels in whole blood and urine both significantly correlated with increased acetabular component inclination angle over 50 degrees and pain scores. There was no correlation with socket anteversion angle or femoral head diameter. The data support the use of urinary measurement of metal ions adjusted to creatinine to monitor patients with large head metal-on-metal total hip arthroplasty.

Femoral neck remodelling after hip resurfacing surgery: a radiological study

BACKGROUND

Narrowing of the femoral neck under the femoral component of the hip resurfacing has been noted previously and has raised concern. In this study we examined the X-rays of patients following Birmingham hip resurfacing surgery at 6-years follow-up.

METHODS

Bony changes proximally and distally were measured. Fifty-two patients were available for evaluation.

RESULTS

There were 40 (76.9%) men and 12 (23.1%) women, with a mean age of 52 years (25-64). The unoperated contralateral femoral neck was measured as a control. We found femoral neck narrowing proximally in 82.7% of patients and distally in 26.9% and on the contralateral side in 54.5%. The average narrowing was 3.6%. Widening was observed proximally in 17.3% and distally in 73.1% and on the contralateral side in 45.5%. The average widening was 3.9%. Four of the 52 patients had proximal narrowing exceeding 10% of the femoral neck diameter, and one of the 52 patients had inferior narrowing exceeding 10%.

CONCLUSION

Gender, body mass index, component size and age did not affect remodelling. We conclude that the observed findings are likely to be a manifestation of a generalized remodelling response in the femoral neck rather than a localized and isolated narrowing at the junction of the component and the femoral neck.

Potential release of in vivo trace metals from metallic medical implants in the human body: from ions to nanoparticles--a systematic analytical review

Metal ion release from metallic materials, e.g. metallic alloys and pure metals, implanted into the human body in dental and orthopedic surgery is becoming a major cause for concern. This review briefly provides an overview of both metallic alloys and pure metals used in implant materials in dental and orthopedic surgery. Additionally, a short section is dedicated to important biomaterials and their corrosive behavior in both real solutions and various types of media that model human biological fluids and tissues. The present review gives an overview of analytical methods, techniques and different approaches applied to the measurement of in vivo trace metals released into body fluids and tissues from patients carrying metal-on-metal prostheses and metal dental implants. Reference levels of ion concentrations in body fluids and tissues that have been determined by a host of studies are compiled, reviewed and presented in this paper. Finally, a collection of published clinical data on in vivo released trace metals from metallic medical implants is included.

Possible effects of metallosis on spermatozoal apoptotic genes expression in individuals with intramedullary nailing prosthesis

Seminal quality could be affected by metallosis caused by intramedullary nailing (IMN). Our objectives were to estimate metal ion levels in the seminal plasma of subjects with IMN, to determine their effects on semen parameters and on spermatozoal apoptotic gene expression, and to determine whether these expressed genes could be used as candidate biomarkers of seminal deterioration in individuals with IMN or not. Semen samples were collected from 60 subjects with IMN and 30 age-matched healthy controls. Seminal plasma contents of cobalt (Co), chromium (Cr), and molybdenum (Mo) were assayed. Spermatozoal Bcl-2 and Bax gene expressions were determined. Studied semen parameters were significantly lower in subjects with IMN for ≥5 years in relation to controls while the concentrations of Co, Cr, and Mo in the seminal plasma samples were significantly higher. There were significantly lower spermatozoal Bcl-2 expression, higher Bax expression, and lower Bcl-2/Bax ratio in subjects with IMN for ≥5 years than in controls. In subjects with IMN for ≥5 years, receiver operating characteristic (ROC) curve analysis of studied gene expressions and Bcl-2/Bax ratio were done showing priority of the ratio with 86.7 % sensitivity, 100 % specificity, 100 % positive predictive value, and 93.8 % negative predictive value at cutoff values ≤0.777. Co, Cr, and Mo metals are found at high concentrations in the seminal plasma of individuals with IMN leading to increased spermatozoal apoptotic activity. Spermatozoal Bcl-2/Bax ratio could be used as a candidate biomarker of reproductive disorders in individuals with intramedullary nailing.

Changes in blood ion levels after removal of metal-on-metal hip replacements: 16 patients followed for 0-12 months

BACKGROUND AND PURPOSE

In patients with metal-on-metal (MoM) hip prostheses, pain and joint effusions may be associated with elevated blood levels of cobalt and chromium ions. Since little is known about the kinetics of metal ion clearance from the body and the rate of resolution of elevated blood ion levels, we examined the time course of cobalt and chromium ion levels after revision of MoM hip replacements.

PATIENTS AND METHODS

We included 16 patients (13 female) who underwent revision of a painful MoM hip (large diameter, modern bearing) without fracture or infection, and who had a minimum of 4 blood metal ion measurements over an average period of 6.1 (0-12) months after revision.

RESULTS

Average blood ion concentrations at the time of revision were 22 ppb for chromium and 43 ppb for cobalt. The change in ion levels after revision surgery varied extensively between patients. In many cases, over the second and third months after revision surgery ion levels decreased to 50% of the values measured at revision. Decay of chromium levels occurred more slowly than decay of cobalt levels, with a 9% lag in return to normal levels. The rate of decay of both metals followed second-order (exponential) kinetics more closely than first-order (linear) kinetics.

INTERPRETATION

The elimination of cobalt and chromium from the blood of patients who have undergone revision of painful MoM hip arthroplasties follows an exponential decay curve with a half-life of approximately 50 days. Elevated blood levels of cobalt and chromium ions can persist for at least 1 year after revision, especially in patients with high levels of exposure.

Alternative bearing surfaces in total hip arthroplasty

Total hip arthroplasty continues to be one of the most effective surgical procedures currently available. The longevity of this otherwise very successful procedure is compromised by the wear of the bearing surface. In recent years, great advances have been made in the design of bearing surfaces that poise to offer extended performance to these artificial joints. The purpose of this review is to discuss the recent technologic advances in bearing surfaces and offer an insight to the potential benefits and concerns with the alternative bearing surfaces.

What happens to serum metal ion levels after a metal-on-metal bearing is removed?

Serum cobalt (Co) and chromium (Cr) levels are commonly used to screen for excessive wear of metal-on-metal hip replacements. However, it is unknown how rapidly these should decline after revision. 25 patients with average Co and Cr ion levels of 56.3 μg/L and 20.5 μg/L were followed with serial ion level testing post-revision. Over the first 6 weeks post-revision, the rate of decline for Co and Cr was approximately 2% per day and this slowed to approximately 1% decline per day over the ensuing 6 weeks. This translated to a decline of approximately 80% from the starting value after 6 weeks and a decline of approximately 90% after 12 weeks post-revision. The rate of decline for both Co and Cr was significantly faster during the first 6 weeks (P<0.001). In patients with ultra-high Cr levels>20 μg/L, the rate of Cr decline is less predictable and may be protracted leading to persistent elevation above 5 μg/L for one year or more post-revision in some cases.

Chromium level of salvaged blood in patients undergoing revision hip arthroplasty

PURPOSE. To evaluate the chromium level of the salvaged blood in patients undergoing revision total hip arthroplasty (THA). METHODS. Records of 7 women and one man aged 54 to 83 (mean, 64.3) years who underwent revision THA for aseptic loosening of the acetabular component (n=6), osteolysis of the acetabulum (n=1), or migration of the outer head (n=1) were reviewed, as were 2 controls who underwent primary THA. The initial THA entailed a metal-on-metal prosthesis (n=4), a metal-on-polyethylene prosthesis (n=3), and a bipolar head prosthesis (n=1). Chromium levels in the preoperative peripheral blood and intraoperative salvaged blood were measured using atomic absorption analysis. RESULTS. For controls and the patient with a bipolar head prosthesis, the mean chromium level in salvaged blood was 0.4 (range, 0.2-0.6) micrograms/l, which was significantly lower than that in the remaining 7 patients undergoing revision THA (mean, 5.6 micrograms/l; range, 1.2-9.8 micrograms/l). CONCLUSION. Salvaged blood of patients with a metal-on-metal prosthesis undergoing revision THA contained higher levels of chromium.

Improving cytocompatibility of Co28Cr6Mo by TiO2 coating: gene expression study in human endothelial cells

Cobalt-based materials are widely used for coronary stents, as well as bone and joint implants. However, their use is associated with high corrosion incidence. Titanium alloys, by contrast, are more biocompatible owing to the formation of a relatively inactive titanium oxide (TiO2) layer on their surface. This study was aimed at improving Co28Cr6Mo alloy cytocompatibility via sol-gel TiO2 coating to reduce metal corrosion and metal ion release. Owing to their role in inflammation and tissue remodelling around an implant, endothelial cells present a suitable in vitro model for testing the biological response to metallic materials. Primary human endothelial cells seeded on Co28Cr6Mo showed a stress phenotype with numerous F-actin fibres absent on TiO2-coated material. To investigate this effect at the gene expression level, cDNA microarray analysis of in total 1301 genes was performed. Compared with control cells, 247 genes were expressed differentially in the cells grown on Co28Cr6Mo, among them genes involved in proliferation, oxidative stress response and inflammation. TiO2 coating reduced the effects of Co28Cr6Mo on gene expression in endothelial cells, with only 34 genes being differentially expressed. Quantitative real-time polymerase chain reaction and protein analysis confirmed microarray data for selected genes. The effect of TiO2 coating can be, in part, attributed to the reduced release of Co(2+), because addition of CoCl2 resulted in similar cellular responses. TiO2 coating of cobalt-based materials, therefore, could be used in the production of cobalt-based devices for cardiovascular and skeletal applications to reduce the adverse effects of metal corrosion products and to improve the response of endothelial and other cell types.

An initial experience with hip resurfacing versus cementless total hip arthroplasty

BACKGROUND

Hip resurfacing is an alternative to total hip arthroplasty.

QUESTIONS/PURPOSE

We aimed to compare an experienced hip surgeon's initial clinical results of hip resurfacing with a new cementless total hip arthroplasty (THA).

METHODS

The first 55 consecutive hip resurfacing arthroplasties were compared to 100 consecutive cementless THAs using a cylindrical tapered femoral stem. The learning curve between the two procedures was compared utilizing the incidence of reoperation, complications, Harris Hip Scores (HHS), and implant survivorship.

RESULTS

The reoperation rate was significantly higher (p = 0.019) for hip resurfacing (14.5%) versus THA (4%). The overall complication rate between the two groups was not significantly different (p = 0.398). Preoperative HHS were similar between the two groups (p = 0.2). The final mean HHS was similar in both the resurfacing and THA groups (96 vs. 98.3, respectively, p < 0.65). Kaplan-Meier survival analysis with an endpoint of reoperation suggests complications occurred earlier in the resurfacing group versus the THA group (log-rank test, p = 0.007).

CONCLUSIONS

In comparison to our initial experience with a cementless THA stem, operative complications occur earlier and more often after hip resurfacing during the learning period. The clinical outcomes in both groups however are similar at 5 year follow-up.

Large diameter metal on metal articulations. Comparison of total hip arthroplasty and hip resurfacing arthroplasty

The use of large diameter metal bearing total hip arthroplasty (THA) and hip resurfacing arthroplasty (HRA) increased in popularity in the last decade. More recent literature has highlighted the effect of head size in patient outcomes. Data was obtained from the Australian Orthopaedic Association National Joint Replacement Registry (AOA-NJRR) to evaluate the Birmingham (MoM) bearing surface when used with THA and HRA. There is no difference in the overall rate of revision between the THA and HRA but head size has a significant effect on revision rate. The data show that small diameter metal bearings in HRA (below 50mm) have a higher rate of revision than large diameter metal bearings in HRA (equal to and above 50mm) (P<.001). Conversely the large diameter metal bearings in THA have a higher rate of revision than the small diameter metal bearings in THA (P=.027). The revision rate for large diameter HRA compared to small diameter THA is not significantly different P=.670. We recommend caution when choosing either a large diameter (≥50mm) metal on metal THA or small diameter (<50mm) HRA.

Prospective comparison study of one-year outcomes for all titanium total temporomandibular joint replacements in patients allergic to metal and cobalt-chromium replacement joints in patients not allergic to metal

We aimed to ascertain whether there are any early differences in outcome between all titanium temporomandibular joint (TMJ) prostheses in patients allergic to metal and standard cobalt-chromium prostheses in patients not allergic to metal. All patients who had primary TMJ prostheses placed with one-year follow-up between March 2003 and February 2011 were included. We reviewed the basic characteristics of patients. The outcome variables measured included disease, pain, mouth opening, and diet. A total of 55 patients with 77 joint replacements fulfilled the inclusion criteria. Forty patients had standard cobalt-chromium alloy (Co-Cr-Mo) prostheses (20 unilateral and 20 bilateral), and 15 had all titanium prostheses (13 unilateral and 2 bilateral). Osteoarthritis was the most common disease in both groups. There was significant improvement in pain score at reviews at 6 weeks (p=0.001) and 12 months (p=0.03). Values between groups were not significant (p=0.48 at 6 weeks, and p=0.10 at 1 year). Mouth opening in each group improved significantly with continued gains between assessments at 6 weeks and 12 months (p=0.001) but there were no significant differences between groups. Diet scores were significantly improved one year postoperatively in both groups (p=0.001), but differences between groups were not significant (p=0.90). At one year, outcomes for all titanium prostheses in patients allergic to metal were similarly favourable to those in patients who had no hypersensitivity to metal and had standard prostheses. No patient developed a hypersensitivity reaction, and no all titanium prosthesis failed during the one-year follow-up period.

Ten-year outcome of serum metal ion levels after primary total hip arthroplasty: a concise follow-up of a previous report*

We previously reported on the metal ion concentrations of cobalt, chromium, and titanium that were found in the serum of patients three years after they had undergone primary total hip arthroplasty as compared with the concentrations found in the serum of control patients who did not have an implant. This study is a concise update on the serum metal levels found in a cohort of these patients ten years after the time of hip implantation. Of the original seventy-five subjects, metal ion levels were available for forty patients (53%). Ten patients (hybrid group) had received a hybrid total hip replacement that consisted of a modular cobalt-alloy femoral stem with a cobalt-alloy femoral head that had been inserted with cement and a titanium acetabular socket that had been inserted without cement. Nine patients (cobalt-chromium [CoCr] group) had received an implant with an extensively porous-coated modular cobalt-alloy femoral stem and femoral head along with a titanium acetabular socket; the femoral and acetabular components had each been inserted without cement. Eight patients (titanium group) had undergone insertion of a proximally porous-coated modular titanium-alloy femoral stem with a cobalt-alloy femoral head and a titanium acetabular socket; the femoral and acetabular components had each been inserted without cement. Thirteen patients (control group) from the original control group of patients who had not received an implant served as control subjects. Serum metal levels were measured with use of high-resolution sector field inductively coupled plasma mass spectrometry. The hybrid total hip arthroplasty group had mean cobalt levels that were 3.2 times higher at 120 months than they were at baseline, and the cobalt levels in that group were significantly higher than those in the titanium total hip arthroplasty group at thirty-six, sixty, eighty-four, ninety-six, and 120 months (p < 0.01). The hybrid group had mean chromium levels that were 3.9 times higher at 120 months than they were at baseline, and the CoCr total hip arthroplasty group had chromium levels that were 3.6 times higher at 120 months than they were at baseline. The serum titanium levels were higher in the titanium group at all follow-up time intervals as compared with the levels in all other groups, and the level in the titanium group at 120 months was eighteen times higher than it was at baseline (p < 0.01). Patients with well-functioning primary metal-on-polyethylene total hip replacements had elevated serum metal levels for as many as ten years postoperatively. Furthermore, metal release at the modular femoral head-neck junctions, rather than passive dissolution from porous ingrowth surfaces, was likely the dominant source of serum cobalt and chromium.

CoCrMo metal-on-metal hip replacements

After the rapid growth in the use of CoCrMo metal-on-metal hip replacements since the second generation was introduced circa 1990, metal-on-metal hip replacements have experienced a sharp decline in the last two years due to biocompatibility issues related to wear and corrosion products. Despite some excellent clinical results, the release of wear and corrosion debris and the adverse response of local tissues have been of great concern. There are many unknowns regarding how CoCrMo metal bearings interact with the human body. This perspective article is intended to outline some recent progresses in understanding wear and corrosion of metal-on-metal hip replacement both in vivo and in vitro. The materials, mechanical deformation, corrosion, wear-assisted corrosion, and wear products will be discussed. Possible adverse health effects caused by wear products will be briefly addressed, as well as some of the many open questions such as the detailed chemistry of corrosion, tribochemical reactions and the formation of graphitic layers. Nowadays we design almost routinely for high performance materials and lubricants for automobiles; humans are at least as important. It is worth remembering that a hip implant is often the difference between walking and leading a relatively normal life, and a wheelchair.

Breast milk metal ion levels in a young and active patient with a metal-on-metal hip prosthesis

Metal-on-metal resurfacing arthroplasty of the hip has been used increasingly over the last 10 years in younger active patients. The dissolution of the metal wear particles results in measurable increases in cobalt and chromium ions in the serum and urine of patients with a metal-on-metal bearing. We measured the cobalt, chromium, and molybdenum ion levels in urine; serum; and breast milk in a young and active patient with a metal-on-metal hip prosthesis after a pathologic fracture of the femoral neck. Metal-on-metal hip prosthesis leads to increasing levels of molybdenum in breast milk in the short-term follow-up. There are no increasing levels of chromium and cobalt ions in breast milk. Besides the already known elevated concentrations in serum of chromium and cobalt after implantation of a metal-on-metal hip prosthesis, we found no increasing levels of chromium and cobalt in urine.

Metal-on-metal vs conventional total hip arthroplasty: a systematic review and meta-analysis of randomized controlled trials

Metal-on-metal (MOM) hip articulations represent a potential alternative to conventional metal-on-polyethylene total hip arthroplasty (THA). We performed a systematic review of the peer-reviewed literature in search of studies comparing MOM with conventional primary THA with regard to functional outcomes, radiographic outcomes, and complication rates. Four Level I randomized controlled trials remained following our screening process. The data published in these studies were extracted and aggregated using a Mantel-Haenszel cumulative fixed effects meta-analysis. We found no significant difference between MOM and conventional THA with regard to functional outcomes as measured by Harris hip scores and radiographic outcomes as measured by radiolucent lines. Patients with MOM THA did however demonstrate a 3.37 times greater complication rate (1.57, 7.26). In light of the lack of superiority, the increased complication rate, the greater cost, and the potential for adverse medical consequences associated with MOM THA, these bearing surfaces should be used with caution.

Corrosion at the cone/taper interface leads to failure of large-diameter metal-on-metal total hip arthroplasties

BACKGROUND

Metal-on-metal (MoM) THAs have reduced wear rates compared with metal-on-polyethylene. However, elevated serum metal ion levels and pseudotumors have been reported in large MoM articulations.

QUESTIONS/PURPOSES

We therefore determined (1) if corrosion occurred at the cone/taper interface leading to instability in patients with large-diameter THAs; (2) how patients presented clinically and radiographically; (3) if adverse periprosthetic tissue reactions occurred; (4) whether metal was released from the implants into the periprosthetic tissues; and (5) if head size correlated with metal release.

METHODS

We reviewed 114 patients who had revisions of large-diameter head MoM articulations. Mean time of implantation was 46 months. To identify adverse reactions and particle load, tissues were stained by hematoxylin and eosin and CD3/CD20/CD68 antibodies. Periprosthetic tissues were analyzed for metal content and distribution in different regions. Electrochemical reactions between the stem and adapter were investigated by a minicell electrode.

RESULTS

Electrochemical studies on the stem and the head adapter showed a risk for galvanic corrosion. Ninety-four percent of patients had instability at the cone/taper interface. All patients presented with early clinical symptoms; 59 patients had radiographic signs of loosening. One hundred four patients had foreign body reactions and necrosis. The largest amounts of metal released were titanium or iron. We found no correlation between head size and metal ion release.

CONCLUSIONS

These findings suggest that in modular cone/taper connections, friction of the MoM articulations may cause failure of the cone/taper interface leading to galvanic corrosion and loosening. It is unclear whether the design of this MoM system provides sufficient stability at the taper.

Wear-corrosion synergism in a CoCrMo hip bearing alloy is influenced by proteins

BACKGROUND

Although numerous in vitro studies report on the tribological performance of and, separately, on the corrosion properties of cobalt-based alloys in metal-on-metal (MoM) bearings, the few studies that take into account the synergistic interaction of wear and corrosion (tribocorrosion) have used canonical tribo-test methods. We therefore developed synergistic study using a test method that more closely simulates hip bearing conditions.

QUESTIONS/PURPOSES

(1) Is the total material loss during tribocorrosion larger than the sum of its components generated during isolated mechanical wear and isolated corrosion? (2) How is the tribocorrosive process affected by the presence of protein?

METHODS

High carbon CoCrMo alloy discs (18) were subjected to corrosion and tribocorrosion tests under potentiostatic conditions in an apparatus simulating hip contact conditions. The input variables were the applied potential and the protein content of the electrolyte (NaCl solution versus bovine serum, 30 g/L protein). The output variables were mass loss resulting from wear in the absence of corrosion, mass loss resulting from corrosion in the absence of wear, and the total mass loss under tribocorrosion, from which the additional mass loss resulting from the combined action of wear and corrosion, or synergism, was determined in the presence and absence of protein.

RESULTS

The degradation mechanisms were sensitive to the interaction of wear and corrosion. The synergistic component (64 μg) in the presence of protein amounted to 34% of total material loss (187 μg). The presence of protein led to a 23% decrease in the total mass loss and to a considerable reduction in the mean current (4 μA to 0.05 μA) under tribocorrosion.

CONCLUSIONS

Synergistic effects during tribocorrosion may account for a considerable portion of MoM degradation and are affected by proteins.

CLINICAL RELEVANCE

The in vivo performance of some large-diameter MoM joints is unsatisfactory. The synergistic component resulting from tribocorrosion may have been missed in conventional preclinical wear tests.

Metal-on-Metal Bearing: Is This the End of the Line? We Do Not Think So

BACKGROUND

Recent studies have recommended the discontinuation of metal-on-metal (MoM) components in total hip arthroplasty (THA) because of adverse effects reported with large-diameter MoM THA. This is despite favorable long-term results observed with 28 and 32 mm MoM bearings.

QUESTIONS/PURPOSES

The aim of this study was to assess the value of calls for an end to MoM bearings as THA components. Specifically, we wish to address the risks associated with MoM bearings including adverse soft tissue reactions, metal ion release, and carcinogenic risk.

METHODS

The study evaluates the arguments in the literature reporting on MoM (adverse soft tissue reactions, metal ion release, and carcinogenic risk) and the experience of the current authors who re-introduced these bearings in 1995. They are balanced by a benefit-risk review of the literature and the authors' experience with MoM use.

RESULTS

Adverse reactions to metallic debris as well as metal ion release are predictable and can be prevented by adequate design (arc of coverage, clearance), metallurgy (forged instead of cast alloy, high-carbide content), and appropriate component orientation. There is no scientific evidence that carcinogenicity is increased in subjects with MoM hip prostheses. MoM articulations appear to be attractive allowing safe hip resurfacing, decreasing the risk of THA revision in active patients, and providing secure THA fixation with cement in cages in severely deformed hips. MoM bearings in women of child-bearing age are controversial, but long-term data on metallic devices in adolescents undergoing spinal surgery seem reassuring.

DISCUSSION

Adequate selection of MoM articulations ensures their safe use. These articulations are sensitive to orientation. Fifteen years of safe experience with 28- and 32-mm bearings of forged alloy and high-carbide content is the main reason for retaining them in primary and revision THA.

Differential distribution of cobalt, chromium, and nickel between whole blood, plasma and urine in patients after metal-on-metal (MoM) hip arthroplasty

Evidence shows that raised cobalt (Co), chromium (Cr), and nickel (Ni) whole blood concentrations correlate with poor device outcome in patients following metal-on-metal (MoM) hip arthroplasty. To understand the local and systemic pathological effects of these raised metal concentrations it is important to define their distribution between whole blood, plasma, and urine. The metals were measured by Inductively Coupled Plasma Mass Spectrometry (ICPMS). Two hundred and five plasma, 199 whole blood, and 24 sets of urine samples were analyzed from 202 patients with Co-Cr alloy MoM hip prostheses implanted between 8 months to 12 years (mean 6.0 years) prior to analysis. Plasma Co (median 39.1 nmol/L) showed significantly positive 1:1 correlation with whole blood Co (median 45.9 nmol/L; R(2)  = 0.98, p < 0.001, slope = 1.0). Plasma Cr (median 53.8 nmol/L) and whole blood Cr (median 40.3 nmol/L) were also correlated; however, concentrations were significantly higher in plasma indicating relatively little blood cell uptake (R(2)  = 0.96, p < 0.001, slope = 1.6). Urinary Co was up to threefold higher than Cr (median 334.0 vs. 97.3 nmol/L respectively). Nickel concentrations in whole blood, plasma, and urine were low relative to Co and Cr. The analysis shows fundamental differences in the physiological handling of these metals: Co is distributed approximately equally between blood cells and plasma, whereas Cr is mainly in plasma, despite which, Cr had far less renal excretion than Co.

Silicon nitride films for the protective functional coating: blood compatibility and biomechanical property study

Behaviors of silicon nitride films and their relation to blood compatibility and biomechanical have been interesting subjects to researchers. A systematic blood compatibility and biomechanical property investigation on the deposition of silicon-nitride films under varying N₂ and CF₄ flows was carried out by direct current unbalanced magnetron sputtering techniques. Significant role of surface property, chemical bonding state of silicon nitride film and blood compatibility, mechanical properties for the films were observed. The chemical bonding configurations, surface topography, contact angle and mechanical properties were characterized by means of X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and nano-indentation technique and CSEM pin-on-disk tribometer. Blood compatibility of the films was evaluated by platelet adhesion investigation. The results of the platelet adhesion tests shown that the effect of fluorine and nitrogen-doped revealed an intimate relationship between the ratio of polar component and dispersion component of the surface energy and its hemocompatibility. Si-N-O coating can be a great candidate for developing antithrombogenic surfaces in blood contacting materials. The chemical bonding state made an adjustment in microstructured surfaces, once in the totally wettable configuration, may improve the initial contact between platelet and biomedical materials, due to the appropriate ratio of dispersion component and polar component. To resist wear, biomedical components require coatings that are tough and hard, have low friction, and are bio-inert. The study suggests that by Si-N coating the metal surfaces could be a choice to prolong the life of the sliding pair Co-Cr-Mo alloy/UHMWPE implants.