Metal-on-metal bearings, inflammatory pseudotumours and their neurological manifestations

Ceramic prosthesis surfaces induce an inflammatory cell response and fibrotic tissue changes

Aims

Early evidence has emerged suggesting that ceramic-on-ceramic articulations induce a different tissue reaction to ceramic-on-polyethylene and metal-on-metal bearings. Therefore, the aim of this study was to investigate the tissue reaction and cellular response to ceramic total hip arthroplasty (THA) materials in vitro, as well as the tissue reaction in capsular tissue after revision surgery of ceramic-on-ceramic THAs.

Patients and Methods

We investigated tissue collected at revision surgery from nine ceramic-on-ceramic articulations. we compared our findings with tissue obtained from five metal-on-metal THA revisions, four ceramic-on-polyethylene THAs, and four primary osteoarthritis synovial membranes. The latter were analyzed to assess the amount of tissue fibrosis that might have been present at the time of implantation to enable evaluation, in relation to implantation time, of any subsequent response in the tissues.

Results

There was a significant increase in tissue fibrosis with implantation time for all implant types tested. Interestingly, the tissue fibrosis in ceramic-on-ceramic THAs was significantly increased compared with metal-on-metal and ceramic-on-polyethylene. Additionally, we found ceramic wear particles in the periprosthetic tissue of ceramic implants. Fibroblasts responded with expression of cytokines when cultured on alumina-toughened zirconia (ATZ) and zirconia-toughened alumina (ZTA) ceramic surfaces. This response was more pronounced on ATZ ceramics compared with ZTA ceramics. The same inflammatory response was observed with peripheral blood mononuclear cells (PBMCs) cultured on ZTA and ATZ.

Conclusion

Our findings therefore, corroborate the previous findings that ceramic-on-ceramic periprosthetic revision tissue is fibrous and offer an explanation for this observation. We detected a long-term inflammatory response of PBMCs and an inflammatory response of fibroblasts to ATZ and ZTA ceramic. These findings partially explain the fibrotic tissue change in periprosthetic tissue of ceramic-on-ceramic bearings. Cite this article: Bone Joint J 2018;100-B:882–90.

Environmental Factors Impacting Bone-Relevant Chemokines

Chemokines play an important role in normal bone physiology and the pathophysiology of many bone diseases. The recent increased focus on the individual roles of this class of proteins in the context of bone has shown that members of the two major chemokine subfamilies-CC and CXC-support or promote the formation of new bone and the remodeling of existing bone in response to a myriad of stimuli. These chemotactic molecules are crucial in orchestrating appropriate cellular homing, osteoblastogenesis, and osteoclastogenesis during normal bone repair. Bone healing is a complex cascade of carefully regulated processes, including inflammation, progenitor cell recruitment, differentiation, and remodeling. The extensive role of chemokines in these processes and the known links between environmental contaminants and chemokine expression/activity leaves ample opportunity for disruption of bone healing by environmental factors. However, despite increased clinical awareness, the potential impact of many of these environmental factors on bone-related chemokines is still ill defined. A great deal of focus has been placed on environmental exposure to various endocrine disruptors (bisphenol A, phthalate esters, etc.), volatile organic compounds, dioxins, and heavy metals, though mainly in other tissues. Awareness of the impact of other less well-studied bone toxicants, such as fluoride, mold and fungal toxins, asbestos, and chlorine, is also reviewed. In many cases, the literature on these toxins in osteogenic models is lacking. However, research focused on their effects in other tissues and cell lines provides clues for where future resources could be best utilized. This review aims to serve as a current and exhaustive resource detailing the known links between several classes of high-interest environmental pollutants and their interaction with the chemokines relevant to bone healing.

Cystic lesion around the hip joint

This article presents a narrative review of cystic lesions around the hip and primarily consists of 5 sections: Radiological examination, prevalence, pathogenesis, symptoms, and treatment. Cystic lesions around the hip are usually asymptomatic but may be observed incidentally on imaging examinations, such as computed tomography and magnetic resonance imaging. Some cysts may enlarge because of various pathological factors, such as trauma, osteoarthritis, rheumatoid arthritis, or total hip arthroplasty (THA), and may become symptomatic because of compression of surrounding structures, including the femoral, obturator, or sciatic nerves, external iliac or common femoral artery, femoral or external iliac vein, sigmoid colon, cecum, small bowel, ureters, and bladder. Treatment for symptomatic cystic lesions around the hip joint includes rest, nonsteroidal anti-inflammatory drug administration, needle aspiration, and surgical excision. Furthermore, when these cysts are associated with osteoarthritis, rheumatoid arthritis, and THA, primary or revision THA surgery will be necessary concurrent with cyst excision. Knowledge of the characteristic clinical appearance of cystic masses around the hip will be useful for determining specific diagnoses and treatments.

Particle characterisation and cytokine expression in failed small-diameter metal-on-metal total hip arthroplasties

The peri-prosthetic tissue response to wear debris is complex and influenced by various factors including the size, area and number of particles. We hypothesised that the ‘biologically active area’ of all metal wear particles may predict the type of peri-prosthetic tissue response.

Peri-prosthetic tissue was sampled from 21 patients undergoing revision of a small diameter metal-on-metal (MoM) total hip arthroplasty (THA) for aseptic loosening. An enzymatic protocol was used for tissue digestion and scanning electron microscope was used to characterise particles. Equivalent circle diameters and particle areas were calculated. Histomorphometric analyses were performed on all tissue specimens. Aspirates of synovial fluid were collected for analysis of the cytokine profile analysis, and compared with a control group of patients undergoing primary THA (n = 11) and revision of a failed ceramic-on-polyethylene arthroplasty (n = 6).

The overall distribution of the size and area of the particles in both lymphocyte and non-lymphocyte-dominated responses were similar; however, the subgroup with lymphocyte-dominated peri-prosthetic tissue responses had a significantly larger total number of particles.

14 cytokines (interleukin (IL)-1ß, IL-2, IL-4, IL-5, IL-6, IL-10, IL-13, IL-17, interferon (IFN)-γ, and IFN-gamma-inducible protein 10), chemokines (macrophage inflammatory protein (MIP)-1α and MIP-1ß), and growth factors (granulocyte macrophage colony stimulating factor (GM-CSF) and platelet derived growth factor) were detected at significantly higher levels in patients with metal wear debris compared with the control group.

Significantly higher levels for IL-1ß, IL-5, IL-10 and GM-CSF were found in the subgroup of tissues from failed MoM THAs with a lymphocyte-dominated peri-prosthetic response compared with those without this response.

These results suggest that the ‘biologically active area’ predicts the type of peri-prosthetic tissue response. The cytokines IL-1ß, IL-5, IL-10, and GM-CSF are associated with lymphocyte-dominated tissue responses from failed small-diameter MoM THA.

Cite this article: Bone Joint J 2015;97-B:917–23.

Importance of the HIF pathway in cobalt nanoparticle-induced cytotoxicity and inflammation in human macrophages

Recent, unexpected high failure rates of metal-on-metal hip implants have reintroduced the issue of cobalt toxicity. An adverse reaction to cobalt ions and cobalt-induced lung injury occurs during environmental exposure and is now strictly controlled. Currently adverse reaction occurs to cobalt nanoparticles during wear and tear of metal-on-metal hip implants of which the underlying mechanism is not fully understood. The putative role of the hypoxia-inducible factor (HIF) pathway in the mechanism of cobalt nanoparticle (Co-NPs) toxicity was examined using the U937 cell line, human alveolar macrophages and monocyte-derived macrophages. Co-NPs (5-20 μg/ml)-induced cytotoxicity (viability ranged from 75% to <20% of control, respectively) and reactive oxygen species (ROS), whereas a comparable concentration of cobalt ions (Co(II); up to 350 μM) did not. Co-NPs induced HIF-1α stabilization. Addition of ascorbic acid (100 µM) and glutathione (1 mM) both prevented the increased ROS. However, only treatment with ascorbic acid reduced HIF-1α levels and prevented cell death, indicating that a ROS-independent pathway is involved in Co-NPs-induced cytotoxicity. Replenishing intracellular ascorbate, which is crucial in preventing HIF pathway activation, modified Co-induced HIF target gene expression and the inflammatory response, by decreasing interleukin-1 beta (IL-1β) mRNA and protein expression. Addition of glutathione had no effect on Co-NPs-induced HIF target gene expression or inflammatory response. Thus, Co-NPs induce the HIF pathway by depleting intracellular ascorbate, leading to HIF stabilization and pathway activation. This suggests a strong, ROS-independent role for HIF activation in Co-NPs-induced cytotoxicity and a possible role for HIF in metal-on-metal hip implant pathology.

'Pseudotumour' invading the proximal femur with normal metal ions following metal on metal hip resurfacing

A 75-year-old woman who had undergone hybrid metal-on-metal hip resurfacing 8 years earlier underwent revision arthroplasty because of hip, groin and lateral thigh pain. The main differential was aseptic loosening; however, serum cobalt and chromium levels were normal. Multiple imaging modalities revealed a periprosthetic, cystic soft tissue mass adjacent to the proximal femur. A large 'pseudotumour' with proximal femoral invasion was found at revision arthroplasty. We report the first finding of a 'pseudotumour' invading the proximal femur with normal metal ions following metal on metal hip resurfacing.

Distributed analysis of hip implants using six national and regional registries: comparing metal-on-metal with metal-on-highly cross-linked polyethylene bearings in cementless total hip arthroplasty in young patients

BACKGROUND

The regulation of medical devices has attracted controversy recently because of problems related to metal-on-metal hip implants. There is growing evidence that metal-on-metal implants fail early and cause local and systemic complications. However, the failure associated with metal-on-metal head size is not consistently documented and needs to be communicated to patients and surgeons. The purpose of this study is to compare implant survival of metal on metal with that of metal on highly cross-linked polyethylene.

METHODS

Using a distributed health data network, primary total hip arthroplasties were identified from six national and regional total joint arthroplasty registries (2001 to 2010). Inclusion criteria were patient age of forty-five to sixty-four years, cementless total hip arthroplasties, primary osteoarthritis diagnosis, and exclusion of the well-known outlier implant ASR (articular surface replacement). The primary outcome was revision for any reason. A meta-analysis of survival probabilities was performed with use of a fixed-effects model. Metal-on-metal implants with a large head size of >36 mm were compared with metal-on-highly cross-linked polyethylene implants.

RESULTS

Metal-on-metal implants with a large head size of >36 mm were used in 5172 hips and metal-on-highly cross-linked polyethylene implants were used in 14,372 hips. Metal-on-metal total hip replacements with a large head size of >36 mm had an increased risk of revision compared with metal-on-highly cross-linked polyethylene total hip replacements with more than two years of follow-up, with no difference during the first two years after implantation. The results of the hazard ratios (and 95% confidence intervals) from the multivariable model at various durations of follow-up were 0.95 (0.74 to 1.23) at zero to two years (p = 0.698), 1.42 (1.16 to 1.75) at more than two years to four years (p = 0.001), 1.78 (1.45 to 2.19) at more than four years to six years (p < 0.001), and 2.15 (1.63 to 2.83) at more than six years to seven years (p < 0.001).

CONCLUSIONS

We conducted a comparison of large-head-size, metal-on-metal implants and metal-on-highly cross-linked polyethylene implants in younger patients with uncemented fixation. We found consistent and strong evidence worldwide that large-head-size, metal-on-metal implants were associated with increased risk of revision after two years compared with metal-on-highly cross-linked polyethylene implants, with the effect becoming more pronounced over time.

Metallic debris from metal-on-metal total hip arthroplasty regulates periprosthetic tissues

The era of metal-on-metal (MoM) total hip arthroplasty has left the orthopaedic community with valuable insights and lessons on periprosthetic tissue reactions to metallic debris. Various terms have been used to describe the tissue reactions. Sometimes the nomenclature can be confusing. We present a review of the concepts introduced by Willert and Semlitsch in 1977, along with further developments made in the understanding of periprosthetic tissue reactions to metallic debris. We propose that periprosthetic tissue reactions be thought of as (1) gross (metallosis, necrosis, cyst formation and pseudotumour); (2) histological (macrophage-dominated, lymphocyte-dominated or mixed); and (3) molecular (expression of inflammatory mediators and cytokines such as interleukin-6 and tumor necrosis factor-alpha). Taper corrosion and modularity are discussed, along with future research directions to elucidate the antigen-presenting pathways and material-specific biomarkers which may allow early detection and intervention in a patient with adverse periprosthetic tissue reactions to metal wear debris.

Metallic wear debris may regulate CXCR4 expression in vitro and in vivo

CXCR4, the chemokine receptor for CXCL12, also known as SDF-1 (stromal cell derived factor-1), has been shown to play a pivotal role in bone metastasis, inflammatory, and autoimmune conditions but has not been investigated in periprosthetic osteolysis. We co-cultured osteoblast-like cells with increasing concentrations of metallic (Co-35Ni-20Cr-10Mo and Co-28Cr-6Mo) and Co-ions simulating wear debris. Real-time polymerase chain reaction (RT-PCR) and Western blotting were used to quantify gene and protein expression of CXCR4. The expression of tumor necrosis factor-alpha (TNF-α) and the effects of AMD3100 (bicyclam) on both CXCR4 and TNF-α expression among these cells was investigated. RT-PCR showed an increase in CXCR4 mRNA (7.5-fold for MG63 and 4.0-fold for SaOs-2 cells) among cells co-cultured with metal alloy particles. Western blotting showed a time-dependent increase in protein expression of CXCR4. The attempted blockade of CXCR4 by its known competitive receptor agonist AMD3100 led to a significant inhibition TNF-α mRNA expression. Immunohistochemistry showed CXCR4 positivity among patients with failed metal-on-metal hip replacements and radiographic evidence of osteolysis. Our data collectively suggest that the CXCR4 chemokine is upregulated in a dose- and time-dependent manner in the presence of metallic wear debris.

Trunnionosis: A pain in the neck

Metal-on-metal (MoM) hip replacements have proven to be a modern day orthopaedic failure. The early enthusiasm and promise of a hard, durable bearing was quickly quashed following the unanticipated wear rates. The release of metal ions into the blood stream has been shown to lead to surrounding soft tissue complications and early failure. The devastating destruction caused has led to a large number of revision procedures and implant extractions. The resulting research into this field has led to a new area of interest; that of the wear at the trunnion of the prosthesis. It had been previously thought that the metal debris was generated solely from the weight bearing articulation, however with the evolution of modularity to aid surgical options, wear at the trunnion is becoming more apparent. The phenomenon of "trunnionosis" is a rapidly developing area of interest that may contribute to the overall effect of metallosis in MoM replacements but may also lead to the release of metal ions in non MoM hip designs. The aim of this paper is to introduce, explain and summarise the evidence so far in the field of trunnionosis. The evidence for this phenomenon, the type of debris particles generated and a contrast between MoM, non MoM and resurfacing procedures are also presented.

Large-diameter metal-on-metal total hip arthroplasties: a page in orthopedic history?

Large-diameter metal-on-metal (MoM) bearings evolved from the success of hip resurfacing. These implants were used in revision surgery in cases with well-fixed acetabular cups but loose or failed femoral stems, to avoid cup revision. Early data showed low rates of dislocation and potentially low wear profiles due to better fluid film lubrication. The risk of impingement was also thought to be low due to the increased head-neck ratio. Subsequently large-diameter MoM heads gained popularity in primary hip replacement. Recent data has emerged on the unacceptably high revision rates among patients with large-diameter MoM total hip arthroplasties (THAs), high blood levels of metal ions, and adverse tissue reactions. The head-neck (cone-taper) modular interface probably represents the weak link in large metal heads that have been used on conventional tapers. Increased torque of the large head, micromotion, and instability at the cone-taper interface, synergistic interactions between corrosion and wear, edge loading, low clearance, and psoas impingement are the likely causes for early failure of these prostheses.