Influence of orthopedic particulate biomaterials on inflammation and synovial microcirculation in the murine knee joint

Pathological analysis of periprosthetic soft tissue and modes of failure in revision total joint arthroplasty patients

Objectives

Implant failure leading to revision total joint arthroplasty can occur through a variety of different mechanisms which are typically associated with a soft tissue response adjacent to the implant that provide insight into the underlying etiology of implant failure. The objective of this study was to elucidate mechanisms of implant failure as they relate to histological classification and findings of adjacent periprosthetic tissue.

Methods

Histological analysis of soft tissue adjacent to the implant was performed in 99 patients with an average age of 64 years old and grouped into four categories based on the study conducted by Morawietz et al.:Type I (N = 47)Wear particle induced typeType II (N = 7)Infectious typeType III (N = 19)Combined type I and IIType IV (N = 26)Indeterminant typeModes of failure were categorized into five groupings based on the study conducted by Callies et al.: Instability (N = 35), Aseptic Loosening (N = 24), Hardware and/or Mechanical Failure (N = 15), Septic (N = 13), and Other failures (N = 12). We calculated odds ratios and conducted regression analysis to assess the relationship between modes of failure and histological findings as well as modes of failure and comorbidities.

Results

Hardware/mechanical failure was independently correlated with histological findings of anucleate protein debris, histiocytes, Staphylococcus epidermidis, and synovitis. Furthermore, hardware/mechanical failure was independently correlated with osteosarcoma as a co-morbidity. Septic failure was associated with histological findings of Enterococcus, granulation tissue, and tissue necrosis as well as comorbidities of Crohn's disease, deep venous thrombosis, lung disease, and rheumatoid arthritis. Infection was 5.8 times more likely to be associated with Type II histology. Aseptic loosening was associated with histologic findings of synovitis.

Conclusion

Our findings support the existing literature on periprosthetic tissue analysis in revision total joint arthroplasty which may improve surgeon understanding of the patholophysiological mechanisms that contribute to implant failure and revision surgery.

Activation of Bone Remodeling Compartments in BMP-2-Injected Knees Supports a Local Vascular Mechanism for Arthritis-Related Bone Changes

BACKGROUND

Synovial membrane-derived factors are implicated in arthritis-related bone changes. The route that synovial factors use to access subchondral bone and the mechanisms responsible for these bone changes remain unclear. A safety study involving intra-articular injection of bone morphogenetic protein-2 (BMP-2)/calcium phosphate matrix (CPM) or CPM addresses these issues.

METHODS

Knee joints in 21 monkeys were injected with CPM or 1.5 or 4.5 mg/mL BMP-2/CPM and were evaluated at 1 and 8 weeks. Contralateral joints were injected with saline solution. Knee joints in 4 animals each were injected with 1.5 or 4.5 mg/mL BMP-2/CPM. Contralateral joints were injected with corresponding treatments at 8 weeks. Both joints were evaluated at 16 weeks. Harvested joints were evaluated grossly and with histomorphometry. Knee joints in 3 animals were injected with 125I-labeled BMP-2/CPM and evaluated with scintigraphy and autoradiography at 2 weeks to determine BMP-2 distribution.

RESULTS

All treatments induced transient synovitis and increased capsular vascularization, observed to anastomose with metaphyseal venous sinusoids, but did not damage articular cartilage. Both treatments induced unanticipated activation of vascular-associated trabecular bone remodeling compartments (BRCs) restricted to injected knees. Bone volume increased in BMP-2/CPM-injected knees at 8 and 16 weeks. Scintigraphy demonstrated metaphyseal 125I-labeled BMP-2 localization restricted to injected knees, confirming local rather than systemic BMP-2 release. Autoradiography demonstrated that BMP-2 diffusion through articular cartilage into the metaphysis was blocked by the tidemark. The lack of marrow activation or de novo bone formation, previously reported following metaphyseal BMP-2/CPM administration, confirmed BMP-2 and synovial-derived factors were not free in the marrow. The 125I-labeled BMP-2/CPM, observed within venous sinusoids of injected knees, confirmed the potential for capsular and metaphyseal venous portal communication.

CONCLUSIONS

This study identifies a synovitis-induced venous portal circulation between the joint capsule and the metaphysis as an alternative to systemic circulation and local diffusion for synovial membrane-derived factors to reach subchondral bone. This study also identifies vascular-associated BRCs as a mechanism for arthritis-associated subchondral bone changes and provides additional support for their role in physiological trabecular bone remodeling and/or modeling.

CLINICAL RELEVANCE

Inhibition of synovitis and accompanying abnormal vascularization may limit bone changes associated with arthritis.

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.

Biological activity and migration of wear particles in the knee joint: an in vivo comparison of six different polyethylene materials

Wear of polyethylene causes loosening of joint prostheses because of the particle mediated activity of the host tissue. It was hypothesized that conventional and crosslinked polyethylene particles lead to similar biological effects around the knee joint in vivo as well as to a similar particle distribution in the surrounding tissues. To verify these hypotheses, particle suspensions of six different polyethylene materials were injected into knee joints of Balb/C mice and intravital microscopic, histological and immunohistochemical evaluations were done after 1 week. Whereas the biological effects on the synovial layer and the subchondral bone of femur and tibia were similar for all the polyethylenes, two crosslinked materials showed an elevated cytokine expression in the articular cartilage. Furthermore, the distribution of particles around the joint was dependent on the injected polyethylene material. Those crosslinked particles, which remained mainly in the joint space, showed an increased expression of TNF-alpha in articular cartilage. The data of this study support the use of crosslinked polyethylene in total knee arthroplasty. In contrast, the presence of certain crosslinked wear particles in the joint space can lead to an elevated inflammatory reaction in the remaining cartilage, which challenges the potential use of those crosslinked polyethylenes for unicondylar knee prostheses.

Polyethylene wear particles induce TLR 2 upregulation in the synovial layer of mice

A cellular and receptor mediated response to ultra-high-molecular-weight-polyethylene (UHMWPE) wear particles results in a release of proinflammatory cytokines and induces an inflammatory reaction causing osteolysis in total joint replacement. This investigation offers insight into the toll-like receptor (TLR) mediated activation by polyethylene wear particles in the synovial layer of mice. We hypothesized that, similar to recent in vitro results, UHMWPE particles lead to an upregulation of TLR 1 and 2 and TLR 4 in vivo in the synovial tissue of mice as well. Therefore, UHMWPE particles were generated in a common knee simulator according to the ISO standard, separated by acid digestion and determined by scanning electron microscopy. Endotoxin was removed using a method based on ultracentrifugation. A particle suspension (50 μl; 0.1 vol./vol.%) was injected into the left knee joint of female Balb/c mice (n = 8). In a control group, phosphate-buffered saline was injected into the left knee of Balb/c mice (n = 8). The mice were sacrificed after 7 days. Immunohistochemical staining was performed with TLR 1, 2 and 4 polyclonal antibodies for Balb/c mice and evaluated by light microscopy. The particle-stimulated group showed a thickened synovial layer, an increased cellular infiltration and a TLR 2-upregulation in the synovial layer compared to the control group. An increased expression of TLR 1 and TLR 4 could not be demonstrated. These results indicate a mainly TLR 2-induced inflammation to polyethylene wear debris in the synovial layer of mice.

Elevated cytokine expression of different PEEK wear particles compared to UHMWPE in vivo

Due to their mechanical properties, there has been growing interest in poly-ether-ether-ketone (PEEK) and its composites as bearing material in total and unicompartmental knee arthroplasty. The aim of this study was to analyze the biological activity of wear particles of two different (pitch and PAN) carbon-fiber-reinforced- (CFR-) PEEK varieties in comparison to ultra-high-molecular-weight-polyethylene (UHMWPE) in vivo. The authors hypothesized no difference between the used biomaterials. Wear particle suspensions of the particulate biomaterials were injected into knee joints of Balb/c mice, which were sacrificed after seven days. The cytokine expression (IL-1β, IL-6, TNF-α) was analyzed immunohistochemically in the synovial layer, the adjacent bone marrow and the articular cartilage. Especially in the bone marrow of the two CFR-PEEK varieties there were increased cytokine expressions compared to the control and UHMWPE group. Furthermore, in the articular cartilage the CFR-PEEK pitch group showed an enhanced cytokine expression, which could be a negative predictor for the use in unicondylar knee systems. As these data suggest an increased proinflammatory potential of CFR-PEEK and its composites in vivo, the initial hypothesis had to be refuted. Summarizing these results, CFR-PEEK seems not to be an attractive alternative to UHMWPE as a bearing material, especially in unicompartmental knee arthroplasty.

Polyethylene wear particles play a role in development of osteoarthritis via detrimental effects on cartilage, meniscus, and synovium

OBJECTIVE

While ultra-high molecular weight polyethylene (UHMWPE) wear particles are known to cause periprosthetic osteolysis, its interaction with other intra-articular tissues in the case of partial joint arthroplasties is not well understood. We hypothesized that UHMWPE particles per se would interact with intra-articular tissue, which by acting as inflammatory reservoirs, would subsequently induce osteoarthritic (OA) changes. Our goal was to assess the inflammatory response, phagocytic activity, as well as apoptosis of intra-articular cells in the presence of UHMWPE particles in vitro, and the in vivo response of those tissues after intra-articular injection of particles in a murine model.

DESIGN

Three cell types were used for the in vitro study; chondrocytes, meniscal fibrochondrocytes, and synoviocytes. Each cell type was cultured with two different concentrations of UHMWPE particles. Pro-inflammatory cytokine production, phagocytosis, and apoptosis were analyzed. In vivo experiments were done by injecting two concentrations of UHMWPE particles into normal and murine OA model knee joints.

RESULTS

In vitro experiments showed that UHMWPE particles increase pro-inflammatory cytokine and mediator (IL-1β, IL-6, TNF-α, Nitric Oxide, and Prostaglandin E2) production, phagocytosis of particles, and apoptosis in all cell types. In vivo experiment showed degeneration of cartilage and meniscus, as well as synovitis after particle injection.

CONCLUSIONS

UHMWPE wear particles per se exert detrimental effects in cartilage, synovium, and meniscus of the knee joint resulting in pro-inflammatory cytokine release, phagocytosis of particles and apoptosis. Particles induced and exacerbated OA changes in a murine model.

[Principles of tribological analysis of endoprostheses]

For the tribological characterization of artificial joints, various experimental methods are currently available. However, the in vitro test conditions applied are only comparable in a limited way and transferability to the in vivo situation is also restricted. This is due to the different wear simulation concepts used and partly insufficient simulation of clinical worst case situations. In the present paper current scientific methods and procedures for tribological testing of artificial joints are presented. In addition, the biological effects of wear products are described enabling clinicians to challenge tribological studies and to facilitate specific interpretation of scientific results taking the clinical situation into account.

Polyethylene and metal wear particles: characteristics and biological effects

This paper first presents a brief overview about the mechanism of wear particle formation as well as wear particle characteristics in metal-on-polyethylene and metal-on-metal artificial hip joints. The biological effects of such particles are then described, focusing on the inflammatory response induced by each type of particles as well as on how metal wear products may be the source of a T lymphocyte-mediated specific immune response, early adverse tissue responses, and genotoxicity. Finally, some of the current in vivo models used for the analysis of tissue response to various wear particles are presented.

Crosslinked polyethylene in knee arthroplasty: a simulator study evaluating the positive influence on the tribocontact area in the fixed-bearing knee

BACKGROUND

Crosslinked polyethylene (XPE) was developed to reduce the wear rate in hip as well as knee arthroplasty. The crosslinking process reduces the mechanical properties of ultra-high-molecular-weight polyethylene (UHMWPE), particularly its fatigue strength. UHMWPE fatigue occurs more frequently in the knee than in the hip joint due to its changing tribocontact areas (TCAs) combined with high weight bearing. This is why XPE is still controversially discussed for use in total knee arthroplasty. Therefore, the potential advantage of using XPE in the knee was analysed in a simulator study with a focus on potential fatigue wear mechanisms.

METHODS

Three different kinds of XPE and one conventional UHMWPE were tested over 5 million cycles in fixed-bearing knee designs. The TCAs were examined by replicas, and their extent was measured. The wear mechanism was analysed by scanning electron microscopy.

RESULTS

The extent of the TCAs was less than 5% for all XPEs, whereas 35% for the conventional UHMWPE. Fatigue wear mechanisms were not observed.

CONCLUSION

The measured small extent of the TCAs as a predictor of a low wear rate without any fatigue wear mechanism shows a possible advantage for the use of XPE even in knee arthroplasty.

[New perspectives in studies of the urogenital tract microcirculation--a decade of experience in Szeged, Hungary]

Investigations in microcirculation are an essential way to understand basic pathologic mechanisms and detect early signs of various diseases. Up until the last decade there was only limited amount of information available in the field of urological microcirculation. Due to advanced technologies, new methods and international cooperation of the research team of University of Szeged, promising new data became available in this interesting field.

Abriebpartikel

The aseptic prosthetic loosening of hip and knee prosthesis is the most important cause of implant insufficiency. Bone loss as a result of the biological effect of wear particles is the main cause of such loosening. Wear particles develop their biological activity along different cellular pathways, above all via macrophages, foreign body giant cells as well as fibroblasts of the periprosthetic membrane. These cells induce particle-dependent bone resorption by means of proinflammatory cytokines, such as IL-1beta, TNF-alpha, IL-6 and PGE2. These factors induce the activation of osteoclasts as well as the suppression of osteoblasts. Neutrophil granulocytes and lymphocytes do not play an important role in the process of aseptic loosening. The different wear particles, such as ultra-high molecular weight polyethylene, metal particles, ceramic particles and polymethylmethacrylate can be morphologically recognized very easily. From the clinical point of view, the differentiation between acute or chronic implant infection and particle induced prosthetic loosening is very important, with the histomorphological differential diagnosis between septic and aseptic loosening and their combination being the key clinicopathological factor.