Aseptic loosening and other wear-related complications are one of the most frequent late reasons for revision of total knee arthroplasty (TKA). Periprosthetic osteolysis (PPOL) predates aseptic loosening in many cases indicating the clinical significance of this pathogenic mechanism. A variety of implant-, surgery-, and host-related factors have been delineated to explain the development of PPOL. These factors influence the development of PPOL due to changes in mechanical stresses within the vicinity of the prosthetic device, excessive wear of the polyethylene liner, and joint fluid pressure and flow acting on the peri-implant bone. The process of aseptic loosening is initially governed by factors such as implant/limb alignment, device fixation quality, and muscle coordination/strength. Later large numbers of wear particles detached from TKAs trigger and perpetuate particle disease, as highlighted by progressive growth of inflammatory/granulomatous tissue around the joint cavity. An increased accumulation of osteoclasts at the bone-implant interface, an impairment of osteoblast function, mechanical stresses, and an increased production of joint fluid contribute to bone resorption and subsequent loosening of the implant. In addition, hypersensitivity and adverse reactions to metal debris may contribute to aseptic TKA failure but should be determined more precisely. Patient activity level appears to be the most important factor when the long-term development of PPOL is considered. Surgical technique, implant design, and material factors are the most important preventative factors because they influence both the generation of wear debris and excessive mechanical stresses. New generations of bearing surfaces and designs for TKA should carefully address these important issues in extensive preclinical studies. Currently, there is little evidence that PPOL can be prevented with pharmacological interventions.
The generation of wear debris is an inevitable result of normal usage of joint replacements. Wear debris particles stimulate local and systemic biological reactions resulting in chronic inflammation, periprosthetic bone destruction, and eventually, implant loosening and revision surgery. The latter may be indicated in up to 15% patients in the decade following the arthroplasty using conventional polyethylene. Macrophages play multiple roles in both inflammation and in maintaining tissue homeostasis. As sentinels of the innate immune system, they are central to the initiation of this inflammatory cascade, characterized by the release of pro-inflammatory and proosteoclastic factors. Similar to the response to pathogens, wear particles elicit a macrophage response, based on the unique properties of the cells belonging to this lineage, including sensing, chemotaxis, phagocytosis, and adaptive stimulation. The biological processes involved are complex, redundant, both local and systemic, and highly adaptive. Cells of the monocyte/ macrophage lineage are implicated in this phenomenon, ultimately resulting in differentiation and activation of bone resorbing osteoclasts. Simultaneously, other distinct macrophage populations inhibit inflammation and protect the bone-implant interface from osteolysis. Here, the current knowledge about the physiology of monocyte/macrophage lineage cells is reviewed. In addition, the pattern and consequences of their interaction with wear debris and the recent developments in this field are presented.
It is expected that the projected increased usage of implantable devices in medicine will result in a natural rise in the number of infections related to these cases. Some patients are unable to autonomously prevent formation of biofilm on implant surfaces. Suppression of the local peri-implant immune response is an important contributory factor. Substantial avascular scar tissue encountered during revision joint replacement surgery places these cases at an especially high risk of periprosthetic joint infection. A critical pathogenic event in the process of biofilm formation is bacterial adhesion. Prevention of biomaterial-associated infections should be concurrently focused on at least two targets: inhibition of biofilm formation and minimizing local immune response suppression. Current knowledge of antimicrobial surface treatments suitable for prevention of prosthetic joint infection is reviewed. Several surface treatment modalities have been proposed. Minimizing bacterial adhesion, biofilm formation inhibition, and bactericidal approaches are discussed. The ultimate anti-infective surface should be “smart” and responsive to even the lowest bacterial load. While research in this field is promising, there appears to be a great discrepancy between proposed and clinically implemented strategies, and there is urgent need for translational science focusing on this topic.
Numerous studies provide detailed insight into the triggering and amplification mechanisms of the inflammatory response associated with prosthetic wear particles, promoting final dominance of bone resorption over bone formation in multiple bone multicellular units around an implant. In fact, inflammation is a highly regulated process tightly linked to simultaneous stimulation of tissue protective and regenerative mechanisms in order to prevent collateral damage of periprosthetic tissues. A variety of cytokines, chemokines, hormones and specific cell populations, including macrophages, dendritic and stem cells, attempt to balance tissue architecture and minimize inflammation. Based on this fact, we postulate that the local tissue homeostatic mechanisms more effectively regulate the pro-inflammatory/pro-osteolytic cells/pathways in patients with none/mild periprosthetic osteolysis (PPOL) than in patients with severe PPOL. In this line of thinking, ‘particle disease theory’ can be understood, at least partially, in terms of the failure of local tissue homeostatic mechanisms. As a result, we envision focusing current research on homeostatic mechanisms in addition to traditional efforts to elucidate details of pro-inflammatory/pro-osteolytic pathways. We believe this approach could open new avenues for research and potential therapeutic strategies.
Clinical studies, as well as in vitro and in vivo experiments have demonstrated that byproducts from joint replacements induce an inflammatory reaction that can result in periprosthetic osteolysis (PPOL) and aseptic loosening (AL). Particle-stimulated macrophages and other cells release cytokines, chemokines, and other pro-inflammatory substances that perpetuate chronic inflammation, induce osteoclastic bone resorption and suppress bone formation. Differentiation, maturation, activation, and survival of osteoclasts at the bone–implant interface are under the control of the receptor activator of nuclear factor kappa-Β ligand (RANKL)-dependent pathways, and the transcription factors like nuclear factor κB (NF-κB) and activator protein-1 (AP-1). Mechanical factors such as prosthetic micromotion and oscillations in fluid pressures also contribute to PPOL. The treatment for progressive PPOL is only surgical. In order to mitigate ongoing loss of host bone, a number of non-operative approaches have been proposed. However, except for the use of bisphosphonates in selected cases, none are evidence based. To date, the most successful and effective approach to preventing PPOL is usage of wear-resistant bearing couples in combination with advanced implant designs, reducing the load of metallic and polymer particles. These innovations have significantly decreased the revision rate due to AL and PPOL in the last decade.
Aseptic loosening and osteolysis are considered the main long-term problems of hip arthroplasty. Pathogenesis of periprosthetic osteolysis is multifactorial, and both the biological and mechanical factors seem to play an important role. Bearing surfaces continuously generate excessive amounts of micron and submicron particles provoking an adverse inflammatory response of periprosthetic connective tissues. In general, a key role has been attributed to macrophages. Cytokines, growth factors, PGE2, and enzymes are secreted with activated periprosthetic cells resulting in formation of osteolytic granulomas. The final osteolytic step is taken predominantly by osteoclasts which are getting ready for action mainly by an osteoprotegerin ligand (RANKL) and TNFalpha. Rankl is expressed by activated macrophages, osteoblasts, and lymphocytes. In parallel, a repetitive hydraulic effect of the joint fluid is manifested on the susceptible bone.
Aseptic loosening and osteolysis are the most frequent late complications of total hip arthroplasty (THA) leading to revision of the prosthesis. This review aims to demonstrate how histopathological studies contribute to our understanding of the mechanisms of aseptic loosening/osteolysis development. Only studies analysing periprosthetic tissues retrieved from failed implants in humans were included. Data from 101 studies (5532 patients with failure of THA implants) published in English or German between 1974 and 2013 were included. “Control” samples were reported in 45 of the 101 studies. The most frequently examined tissues were the bone-implant interface membrane and pseudosynovial tissues. Histopathological studies contribute importantly to determination of key cell populations underlying the biological mechanisms of aseptic loosening and osteolysis. The studies demonstrated the key molecules of the host response at the protein level (chemokines, cytokines, nitric oxide metabolites, metalloproteinases). However, these studies also have important limitations. Tissues harvested at revision surgery reflect specifically end-stage failure and may not adequately reveal the evolution of pathophysiological events that lead to prosthetic loosening and osteolysis. One possible solution is to examine tissues harvested from stable total hip arthroplasties that have been revised at various time periods due to dislocation or periprosthetic fracture in multicenter studies.
MicroRNAs (miRNAs) represent the most abundant class of regulators of gene expression in humans: they regulate one‐third of human protein‐coding genes. These small noncoding ∼22‐nucleotides (nt)‐long RNAs originate by multistep process from miRNA genes localized in the genomic DNA. To date, more than 1420 miRNAs have been identified in humans (miRBase v17). The main mechanism of miRNA action is the posttranscriptional regulation via RNA interference with their target mRNAs. The majority of target mRNAs (more than 80%) undergo degradation after recognition by complementary miRNA; the translational inhibition with little or no influence on mRNA levels has been also reported. Each miRNA may suppress multiple mRNA targets (average ∼200), and at the same time, one mRNA can be targeted by many miRNAs enabling to control a spectrum wide range of cellular processes. Recently, the role of miRNAs in the development of immune cells and the maintenance of immune system homeostasis gained attention, and the involvement of miRNAs in the pathogenesis of several immune system diseases has emerged. This review focuses on the role of miRNAs in autoimmune disorders (systemic lupus erythematosus, rheumatoid arthritis, multiple sclerosis, inflammatory bowel disease and psoriasis), inflammatory pathologies of distinct organ (atherosclerosis, osteoarthritis and atopic eczema) and/or systemic locations such as allergy. The role of miRNAs, their predicted and known mRNA targets and description of their actions in physiological immune reactions and in the pathological processes ongoing in immune‐mediated human disorders will be discussed. Finally, miRNA‐based diagnostics and therapeutic potentials will be highlighted.
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