Synovial inflammation in patients undergoing arthroscopic meniscectomy: molecular characterization and relationship to symptoms

Cartilage Injuries: Basic Science Update

The last several decades have brought about substantial development in our understanding of the biomolecular pathways associated with chondral disease and progression to arthritis. Within domains relevant to foot and ankle, genetic modification of stem cells, augmentation of bone marrow stimulation techniques, and improvement on existing scaffolds for delivery of orthobiologic agents hold promise in improving treatment of chondral injuries. This review summarizes novel developments in the understanding of the molecular pathways underlying chondral damage and some of the recent advancements within related therapeutics.

A Standardized Approach To Evaluation And Reporting of Synovial Histopathology In Two Surgically Induced Murine Models Of Osteoarthritis

OBJECTIVE

Synovial pathology has been linked to osteoarthritis (OA) pain in patients. Microscopic grading systems for synovial changes in human OA have been described, but a standardized approach for murine models of OA is needed. We sought to develop a reproducible approach and set of minimum recommendations for reporting of synovial histopathology in mouse models of OA.

METHODS

Coronal and sagittal sections from male mouse knee joints subjected to destabilization of medial meniscus (DMM) or partial meniscectomy (PMX) were collected as part of other studies. Stains included Hematoxylin and Eosin (H&E), Toluidine Blue (T-Blue) and Safranin O/Fast Green (Saf-O). Four blinded readers graded pathological features (hyperplasia, cellularity, and fibrosis) at specific anatomic locations. Inter-reader agreement of each feature score was determined.

RESULTS

There was acceptable to very good agreement when using 3-4 individual readers. After DMM and PMX, expected medial predominant changes in hyperplasia and cellularity were observed, with fibrosis noted at 12 weeks post-PMX. Synovial changes were consistent from section to section in the mid-joint area. When comparing stains, H&E and T-blue resulted in better agreement compared to Saf-O stain.

CONCLUSIONS

To account for the pathologic and anatomic variability in synovial pathology and allow for a more standardized evaluation that can be compared across studies, we recommend evaluating a minimum set of 3 pathological features at standardized anatomic areas. Further, we suggest reporting individual feature scores separately before relying on a single summed "synovitis" score. H&E or T-blue are preferred, inter-reader agreement for each feature should be considered.

The mediating role of synovitis in meniscus pathology and knee osteoarthritis radiographic progression

Meniscus pathologies (damage, extrusion) and synovitis are associated with knee osteoarthritis (KOA); however, whether synovitis mediates the relationship between meniscus pathologies and KOA radiographic progression remains unclear. We conducted an observational study in the Osteoarthritis Initiative (OAI) cohort, with a 48-month follow-up. Meniscus pathology and synovitis were measured by MRI osteoarthritis knee score (MOAKS) at baseline and 24 months, and a comprehensive synovitis score was calculated using effusion and Hoffa synovitis scores. The knee osteoarthritis radiographic progression was considered that Kellgren-Lawrence (KL) grade and joint space narrowing (JSN) grade at 48 months were increased compared to those at baseline. This study included a total of 589 participants, with KL grades mainly being KL1 (26.5%), KL2 (34.1%), and KL3 (30.2%) at baseline, while JSN grades were mostly 0 at baseline. A logistic regression model was used to analyze the relationship between meniscus pathology, synovitis, and KOA progression. Mediation analysis was used to evaluate the mediation effect of synovitis. The average age of the participants was 61 years old, 62% of which were female. The medial meniscus extrusion was longitudinally correlated with the progression of KL (odds ratio [OR]: 2.271, 95% confidence interval [CI]: 1.412-3.694) and medial JSN (OR: 3.211, 95% CI: 2.040-5.054). Additionally, the longitudinal correlation between medial meniscus damage and progression of KOA (OR: 1.853, 95% CI: 1.177-2.941) and medial JSN (OR: 1.655, 95% CI: 1.053-2.602) was significant. Synovitis was found to mediate the relationship between medial meniscus extrusion and KL and medial JSN progression at baseline (β: 0.029, 95% CI: 0.010-0.053; β: 0.022, 95% CI: 0.005-0.046) and beyond 24 months (β: 0.039, 95% CI: 0.016-0.068; β: 0.047, 95% CI: 0.020-0.078). However, we did not find evidence of synovitis mediating the relationship between meniscal damage and KOA progression. Synovitis mediates the relationship between medial meniscus extrusion (rather than meniscus damage) and KOA progression.

Identification of CD64 as a marker for the destructive potential of synovitis in osteoarthritis

OBJECTIVES

OA is characterized by cartilage degeneration and persistent pain. The majority of OA patients present with synovitis, which is associated with increased cartilage damage. Activated synovial macrophages are key contributors to joint destruction. Therefore, a marker that reflects the activation of these cells could be a valuable tool to characterize the destructive potential of synovitis and benefit monitoring of OA. Here, we aimed to investigate the use of CD64 (FcγRI) as a marker to characterize the damaging potential of synovitis in OA.

METHODS

Synovial biopsies were obtained from end-stage OA patients that underwent joint replacement surgery. CD64 protein expression and localization was evaluated using immunohistochemistry and immunofluorescence and quantified using flow cytometry. qPCR was performed to measure the expression of FCGR1 and OA-related genes in synovial biopsies, and in primary chondrocytes and primary fibroblasts stimulated with OA conditioned medium (OAS-CM).

RESULTS

Our data exposed a wide range of CD64 expression in OA synovium and showed positive correlations between FCGR1 and S100A8, S100A9, IL1B, IL6 and MMP1/2/3/9/13 expression. CD64 protein correlated with MMP1, MMP3, MMP9, MMP13 and S100A9. Furthermore, we observed that synovial CD64 protein levels in source tissue for OAS-CM significantly associated with the OAS-CM-induced expression of MMP1, MMP3 and especially ADAMTS4 in cultured fibroblasts, but not chondrocytes.

CONCLUSION

Together, these results indicate that synovial CD64 expression is associated with the expression of proteolytic enzymes and inflammatory markers related to structural damage in OA. CD64 therefore holds promise as marker to characterize the damaging potential of synovitis.

Arthroscopic Linear Chain Fixation for the Treatment of Medial Meniscus Posterior Root Tear: A Case Study

BACKGROUND

The repair and reconstruction of medial meniscus posterior root tears (MMPRTs) is an important issue in the field of orthopedic sports medicine. This study reports the first application of arthroscopic linear chain fixation for the treatment of MMPRTs.

CASE PRESENTATION

A 78-year-old female patient presented with a 1.5-month history of right knee pain accompanied by a locked facet joint. The patient underwent surgery with the new linear chain fixation method. In this method, the suture and the loop part of the buckle-strap titanium plate were combined into a linear chain mechanical complex, and the tension of the posterior root stump was gradually increased by pulling on the two attachment lines at the external mouth of the tibial tunnel. The postoperative Lysholm score was 89, and the visual analogue scale score was 0.9, indicating a significant improvement in knee joint function. At the 7-month and 1-year post-surgery follow-up, physical and MRI examinations confirmed satisfactory healing of the MMPRTs.

CONCLUSION

This surgical approach offers several benefits, including a simplified instrumentation setup, preservation of natural anatomical structures, and reliable residual stump fixation. It has the potential for clinical implementation.

Preoperative Synovial Tissue and Synovial Fluid Biomarkers as Predictors for Outcomes After Knee Arthroscopy and ACL Reconstruction: A Narrative Review

Background

Biomarkers collected in synovial tissue and fluid have been identified as potential predictors of outcomes after arthroscopy.

Purpose

To provide a narrative review of the current literature that assesses the associations between preoperative biomarkers in the synovial fluid or synovial tissue and patient outcomes after knee arthroscopy.

Study Design

Narrative review.

Methods

We searched the PubMed database with keywords, "biomarkers AND arthroscopy," "biomarkers AND anterior cruciate ligament reconstruction," and "biomarkers AND meniscectomy." To be included, studies must have collected synovial fluid or synovial tissue from patients before or during arthroscopic knee surgery and analyzed the relationship of biomarkers to postoperative patient outcomes. Biomarkers were classified into 4 main categories: metabolism of aggrecan in cartilage, metabolism of collagen in cartilage (type II collagen), noncollagenous proteins in the knee, and other. When biomarker levels and outcomes were expressed with continuous variables, we abstracted the Pearson or Spearman correlation coefficients as the effect measure. If the biomarker values were continuous and the outcomes binary, we abstracted the mean or median biomarker values in those with favorable versus unfavorable outcomes. We calculated effect sizes as the difference between means of both groups divided by the standard deviation from the mean in the group with better outcomes.

Results

Eight studies were included in the review. Each study reported different patient outcomes. Biomarkers associated with metabolism of aggrecan, type II collagen metabolism, and noncollagenous proteins as well as inflammatory biomarkers had statistically significant associations with a range of patient outcomes after knee arthroscopy. Difference across studies in sample size and outcome measures precluded choosing a single biomarker that best predicted patient outcomes.

Conclusion

The findings suggest that biomarkers associated with metabolism of aggrecan, type II collagen metabolism, noncollagenous proteins, as well as inflammatory biomarkers may help surgeons and their patients anticipate surgical outcomes.

Intra-Articular Injection of Adipose-Derived Stromal Vascular Fraction in Osteoarthritic Temporomandibular Joints: Study Design of a Randomized Controlled Clinical Trial

INTRODUCTION

Temporomandibular joint (TMJ) osteoarthritis is a degenerative disease of the TMJ. It is characterized by progressive degradation of the extracellular matrix components of articular cartilage, with secondary inflammatory components leading to pain in the temporomandibular region and reduced mouth opening. Current treatments do not halt disease progression, hence the need for new therapies to reduce inflammation and, consequently, improve symptoms. The aim of our randomized controlled clinical trial protocol is to investigate the efficacy of adjuvant intra-articular injections of autologous tissue-like stromal vascular fraction (tSVF), compared to arthrocentesis alone, in reducing pain and improving mouth opening in TMJ osteoarthritis patients.

MATERIALS AND METHODS

The primary endpoint analysis will consist of the visual analogue scale (VAS) for pain. The secondary endpoint analyses will include maximal interincisal mouth opening measurements; assessment of oral health and mandibular function based on the oral health impact profile (OHIP) questionnaire and mandibular functional impairment questionnaire (MFIQ); complications during the follow up; synovial cytokine analysis at baseline and after 26 weeks; and nucleated cells and tSVF (immuno)histochemistry analyses of the intervention group.

DISCUSSION

Our randomized clinical trial protocol will be applied to evaluate the efficacy of a new promising tSVF injection therapy for TMJ osteoarthritis. The safety of intra-articular injections of tSVF has been proven for knee osteoarthritis. However, since a tSVF injection is considered a heterologous application of cell therapy, the regulatory requirements are strict, which makes medical ethical approval challenging.

Construction of a diagnostic model for osteoarthritis based on transcriptomic immune-related genes

Background

Osteoarthritis (OA) is a leading cause of disability globally, affecting over 500 million individuals worldwide. However, accurate and early diagnosis of OA is challenging to achieve. Immune-related genes play an essential role in OA development. Therefore, the objective of this study was to develop a diagnostic model for OA based on immune-related genes identified in synovial membrane.

Methods

The gene expression profile of OA were downloaded based on four datasets. The significantly differentially expressed genes (DEGs) between OA and control groups were selected. The differential immune cells were analyzed, followed by immune-related DEGs screening. WGCNA was used to screen module genes and these genes were further selected through optimization algorithm. Then, nomogram model was constructed. Chemical drug small molecule related to OA was predicted. Finally, expression levels of several key genes were validated by qRT-PCR through construction of OA rat models.

Results

The total 656 DEGs were obtained. Eight immune cells were significantly differential between two groups, and 317 immune-related DEGs were obtained. WGCNA identified three modules. The genes in modules were significantly involved in 15 pathways, involving in 65 genes. Then 12 DEGs were screened as the final optimal combination of DEGs, such as CEBPB, CXCL1, JUND, GABARAPL2 and PDGFC. The Nomogram model was also constructed. Furthermore, the chemical small molecules, such as acetaminophen, aspirin, and caffeine were predicted. The expression levels of CEBPB, CXCL1, GABARAPL2 and PDGFC were validated in OA rat models.

Conclusion

A diagnostic model based on twelve immune related genes was constructed. These model genes, such as CEBPB, CXCL1, GABARAPL2, and PDGFC, may serve as diagnostic biomarkers and immunotherapeutic targets.

Imaging mass cytometry reveals tissue-specific cellular immune phenotypes in the mouse knee following ACL injury

Objective

To develop an imaging mass cytometry method for identifying complex cell phenotypes, inter-cellular interactions, and population changes in the synovium and infrapatellar fat pad (IFP) of the mouse knee following a non-invasive compression injury.

Design

Fifteen male C57BL/6 mice were fed a high-fat diet for 8 weeks prior to random assignment to sham, 0.88 ​mm, or 1.7 ​mm knee compression displacement at 24 weeks of age. 2-weeks after loading, limbs were prepared for histologic and imaging mass cytometry analysis, focusing on myeloid immune cell populations in the synovium and IFP.

Results

1.7 ​mm compression caused anterior cruciate ligament (ACL) rupture, development of post-traumatic osteoarthritis, and a 2- to 3-fold increase in cellularity of synovium and IFP tissues compared to sham or 0.88 ​mm compression. Imaging mass cytometry identified 11 myeloid cell subpopulations in synovium and 7 in IFP, of which approximately half were elevated 2 weeks after ACL injury in association with the vasculature. Notably, two monocyte/macrophage subpopulations and an MHC IIhi population were elevated 2-weeks post-injury in the synovium but not IFP. Vascular and immune cell interactions were particularly diverse in the synovium, incorporating 8 unique combinations of 5 myeloid cell populations, including a monocyte/macrophage population, an MHC IIhi population, and 3 different undefined F4/80+ myeloid populations.

Conclusions

Developing an imaging mass cytometry method for the mouse enabled us to identify a diverse array of synovial and IFP vascular-associated myeloid cell subpopulations. These subpopulations were differentially elevated in synovial and IFP tissues 2-weeks post injury, providing new details on tissue-specific immune regulation.

Recommendations For a Standardized Approach to Histopathologic Evaluation of Synovial Membrane in Murine Models of Experimental Osteoarthritis

Background

Synovial pathology has been linked to osteoarthritis (OA) pain in patients. Microscopic grading systems for synovial changes in human OA have been described, but a standardized approach for murine models of OA is needed. We sought to develop a reproducible approach and set of minimum recommendations for synovial histopathology in mouse models of OA.

Methods

Coronal and sagittal sections from male mouse knee joints subjected to destabilization of medial meniscus (DMM) or partial meniscectomy (PMX) were collected as part of other studies. Stains included Hematoxylin and Eosin (H&E), Toluidine Blue (T-Blue) and Safranin O/Fast Green (Saf-O). Four blinded readers graded pathological features (hyperplasia, cellularity, and fibrosis) at specific anatomic locations in the medial and lateral compartments. Inter-reader reliability of each feature was determined.

Results

There was acceptable to very good agreement between raters. After DMM, increased hyperplasia and cellularity and a trend towards increased fibrosis were observed 6 weeks after DMM in the medial locations, and persisted up to 16 weeks. In the PMX model, cellularity and hyperplasia were evident in both medial and lateral compartments while fibrotic changes were largely seen on the medial side. Synovial changes were consistent from section to section in the mid-joint area mice. H&E, T-blue, and Saf-O stains resulted in comparable reliability.

Conclusions

To allow for a standard evaluation that can be implemented and compared across labs and studies, we recommend using 3 readers to evaluate a minimum set of 3 pathological features at standardized anatomic areas. Pre-defining areas to be scored, and reliability for each pathologic feature should be considered.

Identification of Diagnostic Markers in Synovial Tissue of Osteoarthritis by Weighted Gene Coexpression Network

Osteoarthritis (OA) is a serious threat to human health. However, the etiology and pathogenesis of the disease are not fully understood. Most researchers believe that the degeneration and imbalance of articular cartilage, extracellular matrix, and subchondral bone are the fundamental causes of osteoarthritis. However, recent studies have shown that synovial lesions may precede cartilage, which may be an important precipitating factor in the early stage of OA and the whole course of the disease. This study aimed to conduct an analysis based on sequence data from the Gene Expression Omnibus (GEO) database to investigate the presence of effective biomarkers in the synovial tissue of osteoarthritis for the diagnosis and control of OA progression. In this study, the differentially expressed OA-related genes (DE-OARGs) in osteoarthritis synovial tissues were extracted in the GSE55235 and GSE55457 datasets using the Weighted Gene Co-expression Network Analysis (WGCNA) and limma. Least-Absolute Shrinkage and Selection Operator (LASSO) algorithm was used to select the diagnostic genes based on the DE-OARGs by glmnet package. 7 genes were selected as diagnostic genes including SAT1, RLF, MAFF, SIK1, RORA, ZNF529, and EBF2. Subsequently, the diagnostic model was constructed and the results of the Area Under the Curve (AUC) demonstrated that the diagnostic model had high diagnostic performance for OA. Additionally, among the 22 immune cells of the Cell type Identification By Estimating Relative Subsets Of RNA Transcripts (CIBERSORT) and the 24 immune cells of the single sample Gene Set Enrichment Analysis (ssGSEA), 3 immune cells and 5 immune cells were different between the OA and normal samples, respectively. The expression trends of the 7 diagnostic genes were consistent in the GEO datasets and the results of the real-time reverse transcription PCR (qRT-PCR). The results of this study demonstrate that these diagnostic markers have important significance in the diagnosis and treatment of OA, and will provide further evidence for the clinical and functional studies of OA.

Sexual dimorphism of the synovial transcriptome underpins greater PTOA disease severity in male mice following joint injury

OBJECTIVE

Osteoarthritis (OA) is a disease with sex-dependent prevalence and severity in both human and animal models. We sought to elucidate sex differences in synovitis, mechanical sensitization, structural damage, bone remodeling, and the synovial transcriptome in the anterior cruciate ligament rupture (ACLR) mouse model of post-traumatic OA (PTOA).

DESIGN

Male and female 12-week-old C57/BL6J mice were randomized to Sham or noninvasive ACLR with harvests at 7d or 28d post-ACLR (n = 9 per sex in each group - Sham, 7d ACLR, 28d ACLR). Knee hyperalgesia, mechanical allodynia, and intra-articular matrix metalloproteinase (MMP) activity (via intravital imaging) were measured longitudinally. Trabecular and subchondral bone (SCB) remodeling and osteophyte formation were assessed by µCT. Histological scoring of PTOA, synovitis, and anti-MMP13 immunostaining were performed. NaV1.8-Cre;tdTomato mice were used to document localization and sprouting of nociceptors. Bulk RNA-seq of synovium in Sham, 7d, and 28d post-ACLR, and contralateral joints (n = 6 per group per sex) assessed injury-induced and sex-dependent gene expression.

RESULTS

Male mice exhibited more severe joint damage at 7d and 28d and more severe synovitis at 28d, accompanied by 19% greater MMP activity, 8% lower knee hyperalgesia threshold, and 43% lower hindpaw withdrawal threshold in injured limbs compared to female injured limbs. Females had injury-induced catabolic responses in trabecular and SCB, whereas males exhibited 133% greater normalized osteophyte volume relative to females and sclerotic remodeling of trabecular and SCB. NaV1.8+ nociceptor sprouting in SCB and medial synovium was induced by injury and comparable between sexes. RNA-seq of synovium demonstrated similar injury-induced transcriptomic programs between the sexes at 7d, but only female mice exhibited a transcriptomic signature indicative of synovial inflammatory resolution by 28d, whereas males had persistent pro-inflammatory, pro-fibrotic, pro-neurogenic, and pro-angiogenic gene expression.

CONCLUSION

Male mice exhibited more severe overall joint damage and pain behavior after ACLR, which was associated with persistent activation of synovial inflammatory, fibrotic, and neuroangiogenic processes, implicating persistent synovitis in driving sex differences in murine PTOA.

Transient inhibition of meniscus cell migration following acute inflammatory challenge

Meniscus tears represent a common orthopedic injury that often requires surgery to restore pain-free function. The need for surgical intervention is due, in part, to the inflammatory and catabolic environment that inhibits meniscus healing after injury. In other organ systems, healing is dependent on the migration of cells to the site of injury; however, in the meniscus, it is currently unknown how the microenvironment dictates cell migration in the postinjury inflamed setting. Here, we investigated how inflammatory cytokines alter meniscal fibrochondrocyte (MFC) migration and sensation of microenvironmental stiffness. We further tested whether an FDA approved interleukin-1 receptor antagonist (IL-1Ra; Anakinra) could rescue migratory deficits caused by inflammatory challenge. When cultured in the presence of inflammatory cytokines (tumor necrosis factor-α [TNF-α] or interleukin-1β [IL-1β]) for 1 day, MFC migration was inhibited for 3 days before returning to control levels at Day 7. This migratory deficit was clear in three-dimensional as well, where fewer MFCs exposed to inflammatory cytokines migrated from a living meniscal explant compared with control. Notably, addition of IL-1Ra to MFCs previously exposed to IL-1β restored migration to baseline levels. This study demonstrates that joint inflammation can have negative impacts on meniscus cell migration and mechanosensation, affecting their potential for repair, and that resolution of this inflammation with concurrent anti-inflammatories can reverse these deficits. Future work will apply these findings to mitigate the negative consequences of joint inflammation and promote repair in a clinically relevant meniscus injury model.

Evaluation of mechanistic serum and urine biomarkers for secondary osteoarthritis associated with developmental dysplasia of the hip

Objective

Determine measurable differences for mechanistic urine and serum biomarkers in patients with developmental dysplasia of the hip (DDH) prior to, and following, secondary hip osteoarthritis (OA) when compared to controls.

Design

Urine and serum were collected from individuals with developmental dysplasia of the hip (n = 39), prior to (Pre-OA DDH, n = 32) and following diagnosis of secondary hip OA (Post-OA DDH, n = 7), age-matched Pre-OA controls (n = 35), and age-matched Post-OA controls (n = 12). Samples were analyzed for protein biomarkers with potential for differentiation of hip status through a Mann-Whitney U test with a Benjamini-Hochberg correction.

Results

Several interleukin and degradation related proteins were found to be differentially expressed when comparing DDH-related hip status prior to and following diagnosis of hip OA. In addition, MCP-1 and TIMP-1 were significantly different between younger and older patients in the control cohorts.

Conclusion

These results provide initial evidence for serum and urine protein biomarkers that define clinically relevant stages of symptomatic DDH and its progression to secondary hip osteoarthritis categorized by known mechanisms of disease.

Level of evidence

III.

A Gel-Based Proteomic Analysis Reveals Synovial α-Enolase and Fibrinogen β-Chain Dysregulation in Knee Osteoarthritis: A Controlled Trial

BACKGROUND

The identification of synovial fluid (SF) biomarkers that could anticipate the diagnosis of osteoarthritis (OA) is gaining increasing importance in orthopaedic clinical practice. This controlled trial aims to assess the differences between the SF proteome of patients affected by severe OA undergoing Total Knee Replacement (TKR) compared to control subjects (i.e., subjects younger than 35, undergoing knee arthroscopy for acute meniscus injury).

METHODS

The synovial samples were collected from patients with Kellgren Lawrence grade 3 and 4 knee osteoarthritis undergoing THR (study group) and young patients with meniscal tears and no OA signs undergoing arthroscopic surgery (control group). The samples were processed and analyzed following the protocol defined in our previous study. All of the patients underwent clinical evaluation using the International Knee Documentation Committee (IKDC) subjective knee evaluation (main outcome), Knee Society Clinical Rating System (KSS), Knee injury and Osteoarthritis Outcome Score (KOOS), and Visual Analogue Scale (VAS) for pain. The drugs' assumptions and comorbidities were recorded. All patients underwent preoperative serial blood tests, including complete blood count and C-Reactive Protein (CRP).

RESULTS

The synovial samples' analysis showed a significantly different fibrinogen beta chain (FBG) and alpha-enolase 1 (ENO1) concentration in OA compared to the control samples. A significant correlation between clinical scores, FBG, and ENO1 concentration was observed in osteoarthritic patients.

CONCLUSIONS

Synovial fluid FBG and ENO1 concentrations are significantly different in patients affected by knee OA compared with non-OA subjects.

Therapeutic Perspectives for Inflammation and Senescence in Osteoarthritis Using Mesenchymal Stem Cells, Mesenchymal Stem Cell-Derived Extracellular Vesicles and Senolytic Agents

Osteoarthritis (OA) is the most common cause of disability worldwide among the elderly. Alarmingly, the incidence of OA in individuals less than 40 years of age is rising, likely due to the increase in obesity and post-traumatic osteoarthritis (PTOA). In recent years, due to a better understanding of the underlying pathophysiology of OA, several potential therapeutic approaches targeting specific molecular pathways have been identified. In particular, the role of inflammation and the immune system has been increasingly recognized as important in a variety of musculoskeletal diseases, including OA. Similarly, higher levels of host cellular senescence, characterized by cessation of cell division and the secretion of a senescence-associated secretory phenotype (SASP) within the local tissue microenvironments, have also been linked to OA and its progression. New advances in the field, including stem cell therapies and senolytics, are emerging with the goal of slowing disease progression. Mesenchymal stem/stromal cells (MSCs) are a subset of multipotent adult stem cells that have demonstrated the potential to modulate unchecked inflammation, reverse fibrosis, attenuate pain, and potentially treat patients with OA. Numerous studies have demonstrated the potential of MSC extracellular vesicles (EVs) as cell-free treatments that comply with FDA regulations. EVs, including exosomes and microvesicles, are released by numerous cell types and are increasingly recognized as playing a critical role in cell-cell communication in age-related diseases, including OA. Treatment strategies for OA are being developed that target senescent cells and the paracrine and autocrine secretions of SASP. This article highlights the encouraging potential for MSC or MSC-derived products alone or in combination with senolytics to control patient symptoms and potentially mitigate the progression of OA. We will also explore the application of genomic principles to the study of OA and the potential for the discovery of OA phenotypes that can motivate more precise patient-driven treatments.

Synovial Fluid Proteomics From Serial Aspirations of ACL-Injured Knees Identifies Candidate Biomarkers

BACKGROUND

Anterior cruciate ligament (ACL) tears often result in knee effusion and an increased risk for developing knee osteoarthritis (OA) in the long run. The molecular profile of these effusions could be informative regarding initial steps in the development of posttraumatic OA after an ACL tear.

HYPOTHESIS

The proteomics of knee synovial fluid changes over time after ACL injury.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Synovial fluid was collected from patients with an acute traumatic ACL tear presenting to the office for evaluation (18.31 ± 19.07 days from injury) (aspiration 1) and again at the time of surgery (35.41 ± 58.15 days after aspiration 1 (aspiration 2). High-resolution liquid chromatography mass spectrometry was used to assess the quantitative protein profile of synovial fluid, and differences in protein profile between the 2 aspirations were determined computationally.

RESULTS

A total of 58 synovial fluid samples collected from 29 patients (12 male, 17 female; 12 isolated ACL tear, 17 combined ACL and meniscal tear) with a mean age and body mass index of 27.01 ± 12.78 years and 26.30 ± 4.93, respectively, underwent unbiased proteomics analysis. The levels of 130 proteins in the synovial fluid changed over time (87 high, 43 low). Proteins of interest that were significantly higher in aspiration 2 included CRIP1, S100A11, PLS3, POSTN, and VIM, which represent catabolic/inflammatory activities in the joint. Proteins with a known role in chondroprotection and joint homeostasis such as CHI3L2 (YKL-39), TNFAIP6/TSG6, DEFA1, SPP1, and CILP were lower in aspiration 2.

CONCLUSION

Synovial fluid from knees with ACL tears exhibits an increased burden of inflammatory (catabolic) proteins relevant to OA with reduced levels of chondroprotective (anabolic) proteins.

CLINICAL RELEVANCE

This study identified a set of novel proteins that provide new biological insights into the aftermath of ACL tears. Elevated inflammation and decreased chondroprotection could represent initial disruption of homeostasis, potentially initiating the development of OA. Longitudinal follow-up and mechanistic studies are necessary to assess the functional role of these proteins in the joint. Ultimately, these investigations could lead to better approaches to predict and possibly improve patient outcomes.

Increased Effusion Synovitis for Those With a Dysregulated Inflammatory Response After an Anterior Cruciate Ligament Injury

Introduction The progression to posttraumatic osteoarthritis (PTOA) after an anterior cruciate ligament (ACL) injury is likely multifactorial, involving biological, mechanical, and psychosocial factors. Following acute joint trauma, there appears to be a subset of patients that demonstrate a dysregulated inflammatory response. This pro-inflammatory phenotype, or "Inflamma-type," is characterized by an amplified pro-inflammatory response combined with a lack of attendant anti-inflammatory response and has been observed following both an ACL injury and an intra-articular fracture. The aims of this study were to: 1) compare magnetic resonance imaging (MRI)-measured effusion synovitis between those with vs. without a dysregulated inflammatory response, and 2) assess the correlations between effusion synovitis and synovial fluid concentrations of proinflammatory cytokines, degradative enzymes, and synovial fluid biomarkers of cartilage degradation. Methods A cluster analysis was previously performed with synovial fluid concentrations of biomarkers of inflammation and cartilage degradation from 35 patients with acute ACL injuries. Patients were then categorized into two groups: a pro-inflammatory phenotype ("Inflamma-type") and those with a more normal inflammatory response to injury (NORM). Effusion synovitis measured from each patient's preoperative clinical MRI scan was compared between the Inflamma-type and NORM groups using an independent, two-tailed t-test. In addition, Spearman's rho non-parametric correlations were calculated to evaluate the relationship between effusion synovitis and each of the synovial fluid concentrations of pro-inflammatory cytokines, degradative enzymes, and biomarkers of cartilage degradation and bony remodeling. Results Effusion synovitis was significantly greater for the Inflamma-type (10.9±3.8 mm) than the NORM group (7.4±4.4 mm, p=0.04, Cohen's d=0.82). Effusion synovitis significantly correlated with matrix metalloproteinase-3 (rho=0.63, p<0.001), matrix metalloproteinase-1 (rho=0.50, p=0.003), and sulfated glycosaminoglycan (rho=0.42, p=0.01). No other significant correlations were present. Conclusion Effusion synovitis was significantly greater for those that demonstrated a dysregulated inflammatory response after acute ACL injury than those with a more normal response to injury. Effusion synovitis was also found to significantly correlate with synovial fluid concentrations of degradative enzymes and a biomarker of early cartilage degradation. Future work is needed to determine if non-invasive methods, such as MRI or ultrasound, may accurately identify patients within this pro-inflammatory phenotype and whether this subset is more prone to more rapid PTOA changes after injury.

The Corticosteroid Meniscectomy Trial of Extended-Release Triamcinolone Injection After Arthroscopic Partial Meniscectomy: Protocol for a Double-Blind Randomized Controlled Trial

Background

Meniscal tear in older adults often accompanies knee osteoarthritis and is commonly treated with arthroscopic partial meniscectomy (APM) when patients have persistent pain after a trial of physical therapy. Cross-sectional evidence suggests that synovitis is associated with baseline pain in this patient population, but little is known about the relationship between synovitis and postoperative recovery or progression of knee osteoarthritis.

Purpose/Hypothesis

Intra-articular extended-release triamcinolone may reduce inflammation and thereby improve outcomes and slow disease progression. This article presents the rationale behind the Corticosteroid Meniscectomy Trial (CoMeT) and describes its study design and implementation strategies.

Study Design

Randomized controlled trial.

Methods

CoMeT is a 2-arm, 3-center, randomized placebo-controlled trial designed to establish the clinical efficacy of extended-release triamcinolone administered via intra-articular injection immediately after APM. The primary outcome is change in Knee injury and Osteoarthritis Outcome Score Pain subscore at 3-month follow-up. Synovial biopsy, joint fluid aspirate, and urine and blood sample analyses will examine the associations between various objective measures of baseline inflammation and pre- and postoperative outcome measures and clinical responses to triamcinolone intervention. Quantitative 3-T magnetic resonance imaging will evaluate cartilage and meniscal composition and 3-dimensional bone shape to detect early joint degeneration.

Results

We discuss methodologic innovations and challenges.

Conclusion

To our knowledge, this is the first randomized double-blind clinical trial that will analyze the effect of extended-release triamcinolone acetonide on pain, magnetic resonance imaging measures of structural change and effusion/synovitis, soluble biomarkers, and synovial tissue transcriptomics after APM.

Study on the mechanism and pharmacokinetics of HB-NC4 based on C5b-9 target in the treatment of osteoarthritis

Osteoarthritis (OA) is a chronic degenerative disease that mostly occurs in elderly individuals over 60 years old. The detailed pathogenesis of OA is unclear. Medicines available on the market are nonsteroidal anti-inflammatory drugs. Therefore, in this study, a fusion protein was introduced, and the detailed mechanism that could alleviate OA was discussed. As a targeted protein, HB-NC4 showed better binding ability to chondrocytes, and its half-life period was prolonged compared to NC4 alone. In addition, HB-NC4 can not only affect the levels of C3 and C5, but also inhibit the formation of the membrane-attack complex (MAC, C5b-9), thereby further affecting the expression of MAPK signalling pathway-related proteins to achieve the goal of treating OA. Thus, in this study, we demonstrate the pharmacokinetics of HB-NC4 and its mechanism to alleviate OA by regulating the complement system and MAPK signalling pathway. This study provides a new method for OA therapy based on fusion proteins.

Failure Rates of Repaired Bucket-Handle Tears of the Medial Meniscus Concomitant With Anterior Cruciate Ligament Reconstruction: A Cohort Study of 253 Patients From the SANTI Study Group With a Mean Follow-up of 94 Months

BACKGROUND

Failure rates of repaired bucket-handle medial meniscal tears (BHMMTs) concomitant with anterior cruciate ligament reconstruction (ACLR) are as high as 20%. The outcomes of posteromedial portal suture hook repair have not been compared with all-inside repair techniques for this subtype of meniscal lesion.

PURPOSE/HYPOTHESIS

The aim of this study was to evaluate the outcomes and failure rates of patients who underwent BHMMT repair concomitant with ACLR using an all-inside technique, suture hook + all-inside technique, or suture hook + outside-in technique. It was hypothesized that no significant differences in failure rates would be found between the groups.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

A retrospective analysis was performed on patients diagnosed with a BHMMT who underwent meniscal repair during primary ACLR and had a minimum follow-up of 2 years. Patients were grouped based on the meniscal repair technique used: all-inside repair, suture hook + all-inside repair, or suture hook + outside-in repair. At the end of the study period, secondary medial meniscectomy rates were determined.

RESULTS

The study population comprised 253 patients who underwent repair of a BHMMT with concomitant ACLR with a mean follow-up of 94.0 ± 47.6 months. A total of 114 patients (45.1%) underwent all-inside repair, 61 patients (24.1%) underwent suture hook + all-inside repair, and 78 patients (30.8%) underwent suture hook + outside-in repair. Overall, there were 36 failures. The failure rates were 20.2%, 14.8%, and 5.1%, respectively (P = .0135). All-inside repairs were >4 times more likely to fail than suture hook + outside-in repairs (hazard ratio [HR], 4.103; 95% CI, 1.369-12.296; P = .0117). Failure was also 3 times higher (HR, 2.943; 95% CI, 1.224-7.075; P = .0159) for patients <30 years of age compared with those aged ≥30 years. An additional anterolateral ligament reconstruction (ALLR) was also found to reduce the failure rate of repaired BHMMTs concomitant with ACLR.

CONCLUSION

Combined suture hook + outside-in repair of BHMMTs resulted in significantly fewer failures than all other techniques. Furthermore, age <30 years and no additional ALLR were associated with higher failure rates.

STS loaded PCL-MECM based hydrogel hybrid scaffolds promote meniscal regeneration via modulating macrophage phenotype polarization

Meniscus injury has a limited ability to heal itself and often results in the progression to osteoarthritis. After a meniscus injury, there is an obvious acute or chronic inflammatory response in the articular cavity, which is not conducive to tissue regeneration. M2 macrophages are involved in tissue repair and remodeling. Regenerative medicine strategies for tissue regeneration by enhancing the phenotypic ratio of M2 : M1 macrophages have been demonstrated in a variety of tissues. However, there are no relevant reports in the field of meniscus tissue regeneration. In this study, we confirmed that sodium tanshinone IIA sulfonate (STS) could transform macrophages from M1 to M2 polarization. STS protects meniscal fibrochondrocytes (MFCs) against the effects of macrophage conditioned medium (CM). Moreover, STS attenuates interleukin (IL)-1β-induced inflammation, oxidative stress, apoptosis, and extracellular matrix (ECM) degradation in MFCs, possibly by inhibiting the interleukin-1 receptor-associated kinase 4 (IRAK4)/TNFR-associated factor 6 (TRAF6)/nuclear factor-kappaB (NF-κB) signaling pathway. An STS loaded polycaprolactone (PCL)-meniscus extracellular matrix (MECM) based hydrogel hybrid scaffold was fabricated. PCL provides mechanical support, the MECM based hydrogel provides a microenvironment conducive to cell proliferation and differentiation, and STS is used to drive M2 polarization and protect MFCs against the effects of inflammatory stimuli, thus providing an immune microenvironment conducive to regeneration. The results of subcutaneous implantation in vivo showed that hybrid scaffolds could induce M2 polarization in the early stage. In addition, the hybrid scaffolds seeded with MFCs could achieve good meniscus regeneration and chondroprotective effects in rabbits.

Mechanism of immune infiltration in synovial tissue of osteoarthritis: a gene expression-based study

BACKGROUND

Osteoarthritis is a chronic degenerative joint disease, and increasing evidences suggest that the pathogenic mechanism involves immune system and inflammation.

AIMS

The aim of current study was to uncover hub genes linked to immune infiltration in osteoarthritis synovial tissue using comprehensive bioinformatics analysis and experimental confirmation.

METHODS

Multiple microarray datasets (GSE55457, GSE55235, GSE12021 and GSE1919) for osteoarthritis in Gene Expression Omnibus database were downloaded for analysis. Differentially expressed genes (DEGs) were identified using Limma package in R software, and immune infiltration was evaluated by CIBERSORT algorithm. Then weighted gene co-expression network analysis (WGCNA) was performed to uncover immune infiltration-associated gene modules. Protein-protein interaction (PPI) network was constructed to select the hub genes, and the tissue distribution of these genes was analyzed using BioGPS database. Finally, the expression pattern of these genes was confirmed by RT-qPCR using clinical samples.

RESULTS

Totally 181 DEGs between osteoarthritis and normal control were screened. Macrophages, mast cells, memory CD4 T cells and B cells accounted for the majority of immune cell composition in synovial tissue. Osteoarthritis synovial showed high abundance of infiltrating resting mast cells, B cells memory and plasma cells. WGCNA screened 93 DEGs related to osteoarthritis immune infiltration. These genes were involved in TNF signaling pathway, IL-17 signaling pathway, response to steroid hormone, glucocorticoid and corticosteroid. Ten hub genes including MYC, JUN, DUSP1, NFKBIA, VEGFA, ATF3, IL-6, PTGS2, IL1B and SOCS3 were selected by using PPI network. Among them, four genes (MYC, JUN, DUSP1 and NFKBIA) specifically expressed in immune system were identified and clinical samples revealed consistent change of these four genes in synovial tissue retrieved from patients with osteoarthritis.

CONCLUSION

A 4-gene-based diagnostic model was developed, which had well predictive performance in osteoarthritis. MYC, JUN, DUSP1 and NFKBIA might be biomarkers and potential therapeutic targets in osteoarthritis.

Electroacupuncture activated local sympathetic noradrenergic signaling to relieve synovitis and referred pain behaviors in knee osteoarthritis rats

Introduction

Recent research has focused on the local control of articular inflammation through neuronal stimulation to avoid the systemic side effects of conventional pharmacological therapies. Electroacupuncture (EA) has been proven to be useful for inflammation suppressing and pain reduction in knee osteoarthritis (KOA) patients, yet its mechanism remains unclear.

Methods

In the present study, the KOA model was established using the intra-articular injection of sodium monoiodoacetate (MIA) (1 mg/50 μL) into the knee cavity. EA was delivered at the ipsilateral ST36-GB34 acupoints. Hind paw weight-bearing and withdrawl thresholds were measured. On day 9, the histology, dep enrichment proteins, cytokines contents, immune cell population of the synovial membrane of the affected limbs were measured using HE staining, Masson staining, DIA quantitative proteomic analysis, flow cytometry, immunofluorescence staining, ELISA, and Western Blot. The ultrastructure of the saphenous nerve of the affected limb was observed using transmission electron microscopy on the 14th day after modeling.

Results

The result demonstrated that EA intervention during the midterm phase of the articular inflammation alleviated inflammatory pain behaviors and cartilage damage, but not during the early phase. Mid-term EA suppressed the levels of proinflammatory cytokines TNF-α, IL-1β, and IL-6 in the synovium on day 9 after MIA by elevating the level of sympathetic neurotransmitters Norepinephrine (NE) in the synovium but not systemic NE or systemic adrenaline. Selective blocking of the sympathetic function (6-OHDA) and β2-adrenergic receptor (ICI 118,551) prevented the anti-inflammatory effects of EA. EA-induced increment of the NE in the synovium inhibited the CXCL1-CXCR2 dependent overexpression of IL-6 in the synovial macrophages in a β2-adrenergic receptor (AR)-mediated manner.

Discussion

These results revealed that EA activated sympathetic noradrenergic signaling to control local inflammation in KOA rats and contributed to the development of novel therapeutic neurostimulation strategies for inflammatory diseases.

Grinding, Clicking, and Pivot Pain Resolve in Most Patients After Knee Arthroscopy

PURPOSE

To determine whether knee arthroscopy alleviates the symptom constellation of knee grinding/clicking, catching/locking, and pivot pain.

METHODS

One-year follow-up data from 584 consecutive subjects who underwent knee arthroscopy from August 2012 to December 2019 were collected prospectively. Subjects reported frequency of knee grinding/clicking, catching/locking, and/or pivot pain preoperatively and 1 and 2 years postoperatively. A single surgeon performed each procedure and documented all intraoperative pathology. We measured the postoperative resolution or persistence of these symptoms and used multivariable regression models to identify preoperative demographic and clinical variables that predicted symptom persistence. We also assessed changes in the Pain, Activities of Daily Living, and Quality of Life subscales of the Knee Injury and Osteoarthritis Outcome Score (KOOS).

RESULTS

Postoperative symptom resolution was more likely for grinding/clicking (65.6%) and pivot pain (67.8%) than for catching/locking (44.1%). Smoking status, overweight/obesity, absence of meniscal tear, and number of compartments with focal cartilage lesions predicted persistence of 1 or more patient-reported knee symptoms. KOOS subscale scores consistently improved by at least one standard deviation. Individuals who had resolution of patient-reported knee symptoms exhibited roughly 2-fold improvements in KOOS Pain, ADL and Quality of Life scores compared with those whose symptoms persisted. Persistence of pivot pain was associated with the least improvement of the 3 KOOS subscales.

CONCLUSIONS

Two in three patients with grinding/clicking or pivot pain experience symptom resolution after knee arthroscopy, although catching/locking is more likely to persist. Smoking status, overweight/obesity, absence of meniscal tear, and number of compartments with focal cartilage lesions predict symptom persistence after knee arthroscopy.

LEVEL OF EVIDENCE

Therapeutic Level IV, retrospective cohort analysis of prospective data.

Infiltration Profile of Regulatory T Cells in Osteoarthritis-Related Pain and Disability

Emerging evidence indicates that regulatory T cells (Treg) intervene in the inflammatory processes that drive osteoarthritis (OA). However, whether polarized Tregs affect clinical features of the disease in the short- or long-term, and if so, what their role in OA-related pain and functional disability really is, remains elusive. Thus, the aim of the current study was to characterize the infiltration profile of Tregs in systemic (peripheral blood) and joint-derived (synovial fluid and synovial membrane) samples from patients with knee OA in relation to OA-induced symptoms. To this end, Treg infiltration (CD4⁺CD25^+/high CD127^low/−) was analyzed in matched samples of peripheral blood (PB), synovial fluid (SF) and synovial membrane (SM) from a total of 47 patients undergoing elective knee arthroplasty using flow cytometry. At the same time, knee pain and function were assessed and correlated with Treg proportions in different compartments (PB, SF, SM). Interestingly, matched-pair analysis revealed significantly higher Treg proportions in joint-derived samples than in PB, which was mainly attributed to the high Treg frequency in SF. Moreover, we found significant associations between infiltrating Tregs and OA-related symptoms which indicate that lower Treg proportions—especially in the SM—are related to increased pain and functional disability in knee OA. In conclusion, this study highlights the importance of local cellular inflammatory processes in OA pathology. Intra-articular Treg infiltration might play an important role not only in OA pathogenesis but also in the development of OA-related symptoms.

Post-traumatic knee osteoarthritis; the role of inflammation and hemarthrosis on disease progression

Knee injuries such as anterior cruciate ligament ruptures and meniscal injury are common and are most frequently sustained by young and active individuals. Knee injuries will lead to post-traumatic osteoarthritis (PTOA) in 25–50% of patients. Mechanical processes where historically believed to cause cartilage breakdown in PTOA patients. But there is increasing evidence suggesting a key role for inflammation in PTOA development. Inflammation in PTOA might be aggravated by hemarthrosis which frequently occurs in injured knees. Whereas mechanical symptoms (joint instability and locking of the knee) can be successfully treated by surgery, there still is an unmet need for anti-inflammatory therapies that prevent PTOA progression. In order to develop anti-inflammatory therapies for PTOA, more knowledge about the exact pathophysiological mechanisms and exact course of post-traumatic inflammation is needed to determine possible targets and timing of future therapies.

Pulsed Electromagnetic Field Enhances Healing of a Meniscal Tear and Mitigates Posttraumatic Osteoarthritis in a Rat Model

BACKGROUND

Meniscal tears in the avascular region are thought to rarely heal and are a considerable challenge to treat. Although the therapeutic effects of a pulsed electromagnetic field (PEMF) have been extensively studied in a variety of orthopaedic disorders, the effect of a PEMF on meniscal healing has not been reported.

HYPOTHESIS

PEMF treatment would promote meniscal healing and prevent osteoarthritis progression.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 72 twelve-week-old male Sprague-Dawley rats with full-thickness longitudinal medial meniscal tears in the avascular region were divided into 3 groups: control (G_con), treatment with a classic signal PEMF (G_classic), and treatment with a high-slew rate signal PEMF (G_HSR). Macroscopic observation and histological analysis of the meniscus and articular cartilage were performed to evaluate the meniscal healing and progression of osteoarthritis. The synovium was harvested for histological and immunofluorescent analysis to evaluate the intra-articular inflammation. Meniscal healing, articular cartilage degeneration, and synovitis were quantitatively evaluated according to their scoring systems.

RESULTS

Dramatic degenerative changes of the meniscus and articular cartilage were noticed during gross observation and histological evaluation in G_con at 8 weeks. However, the menisci in the 2 treatment groups were restored to normal morphology, with a smooth surface and shiny white color. Particularly, the HSR signal remarkably enhanced the fibrochondrogenesis and accelerated the remodeling process of the regenerated tissue. The meniscal healing scores of the PEMF treatment groups were significantly higher than those in G_con at 8 weeks. Specifically, the HSR signal showed a significantly higher meniscal repair score than did the classic signal at week 8 (P < .01). Additionally, the HSR signal significantly downregulated the secretion levels of interleukin 1 beta (IL-1β) and tumor necrosis factor alpha (TNF-α) in the meniscus and synovium as compared with the control group. When compared with the 2 treatment groups, G_con had significantly higher degeneration scores (G_con vs G_classic, P < .0001; G_con vs G_HSR, P < .0001). The HSR signal also exhibited significantly lower synovitis scores compared with the other two groups (G_con vs G_classic, P < .0001; G_classic vs G_HSR, P = .0002).

CONCLUSION

A PEMF promoted the healing of meniscal tears in the avascular region and restored the injured meniscus to its structural integrity in a rat model. As compared with the classic signal, the HSR signal showed increased capability to promote fibrocartilaginous tissue formation and modulate the inflammatory environment, therefore protecting the knee joint from posttraumatic osteoarthritis development.

CLINICAL RELEVANCE

Adjuvant PEMF therapy may offer a new approach for the treatment of meniscal tears attributed to the enhanced meniscal repair and ameliorated osteoarthritis progression.

Synovial Macrophages: Past Life, Current Situation, and Application in Inflammatory Arthritis

Inflammatory arthritis is an inflammatory disease that involves the joints and surrounding tissues. Synovial hyperplasia often presents when joints become inflamed due to immune cell infiltration. Synovial membrane is an important as well as a highly specific component of the joint, and its lesions can lead to degeneration of the joint surface, causing pain and joint disability or affecting the patients’ quality of life in severe cases. Synovial macrophages (SMs) are one of the cellular components of the synovial membrane, which not only retain the function of macrophages to engulf foreign bodies in the joint cavity, but also interact with synovial fibroblasts (SFs), T cells, B cells, and other inflammatory cells to promote the production of a variety of pro-inflammatory cytokines and chemokines, such as TNF-α, IL-1β, IL-8, and IL-6, which are involved in the pathogenic process of inflammatory arthritis. SMs from different tissue sources have differently differentiated potentials and functional expressions. This article provides a summary on studies pertaining to SMs in inflammatory arthritis, and explores their role in its treatment, in order to highlight novel treatment modalities for the disease.

Macroscopic Synovial Inflammation Correlates with Symptoms and Cartilage Lesions in Patients Undergoing Arthroscopic Partial Meniscectomy: A Clinical Study

Background: The aim of the study was to examine the relationship among patients’ characteristics, intraoperative pathology and pre/post-operative symptoms in a cohort of patients undergoing arthroscopic partial meniscectomy for symptomatic meniscal tears. Methods: Clinical data were collected (age, sex, body mass index, time to surgery, trauma). Intraoperative cartilage pathology was assessed with Outerbridge score. Meniscal tears were graded with the ISAKOS classification. Synovial inflammation was scored using the Macro-score. Patient symptoms were assessed pre/post-operatively using the KOOS instrument. Results: In the series of 109 patients (median age 47 years), 50% of the meniscal tears were traumatic; 85% of patients showed mild to moderate synovitis; 52 (47.7%) patients had multiple cartilage defects and 31 (28.4%) exhibited a single focal chondral lesion. Outerbridge scores significantly correlated with patient age, BMI and synovial inflammation. There was a correlation between severity of chondral pathology and high-grade synovial hyperplasia. Pre-operative KOOS correlated with BMI, meniscal degenerative changes and symptom duration. Obesity, time to surgery, presence of high-grade synovial hyperplasia and high-grade cartilage lesions were independent predictors of worse post-operative pain and function. Conclusion: We demonstrated that pre-operative symptoms and post-operative outcomes correlate with synovitis severity and cartilage pathology, particularly in old and obese patients that underwent arthroscopic partial meniscectomy. Importantly, patients with a degenerative meniscal pattern and with longer time to surgery experienced more severe cartilage damage and, consequentially, pain and dysfunction. These findings are fundamental to identify patients suitable for earlier interventions.

Potential Methods of Targeting Cellular Aging Hallmarks to Reverse Osteoarthritic Phenotype of Chondrocytes

Osteoarthritis (OA) is a chronic degenerative joint disease that causes pain, physical disability, and life quality impairment. The pathophysiology of OA remains largely unclear, and currently no FDA-approved disease-modifying OA drugs (DMOADs) are available. As has been acknowledged, aging is the primary independent risk factor for OA, but the mechanisms underlying such a connection are not fully understood. In this review, we first revisit the changes in OA chondrocytes from the perspective of cellular hallmarks of aging. It is concluded that OA chondrocytes share many alterations similar to cellular aging. Next, based on the findings from studies on other cell types and diseases, we propose methods that can potentially reverse osteoarthritic phenotype of chondrocytes back to a healthier state. Lastly, current challenges and future perspectives are summarized.

Is interleukin-17 implicated in early knee osteoarthritis pathogenesis as in rheumatoid arthritis?

Background

Interleukin-17 (IL-17) is a cytokine that promotes activation of multiple catabolic pathways resulting in cartilage and tissue damage. It has features making it increasingly attractive as a biological marker, especially in rheumatoid arthritis (RA) and osteoarthritis (OA). However, its expression is heterogeneous; not all patients’ exhibit high IL-17 levels, and its level along the disease course is still challenging to predict.

Aim of the work

The objectives of this study were to compare serum IL-17 levels in patients with early knee OA and in RA patients, to determine its correlation with disease activity in RA and to determine if it is correlated with functional scores in both RA and OA.

Subjects and methods

Twenty early knee OA patients (32.7 ± 3.7) years were included. Diagnosis of early OA was based on Luyten et al. 2012 early knee OA classification (early OA 2012). This study also included 25 RA patients aged 32.8 ± 5.1 years, and the diagnosis was according to 2010 ACR-EULAR classification criteria for RA. The current work also included a control group of 20 healthy volunteers aged 31.9 ± 3.2 years. The serum IL-17 level was assessed by using the ELISA technique.

Results

Serum IL-17 level was significantly high in early knee OA patients (5.2 pg/ml) and was significantly higher in RA patients (5.9 pg/ml) compared to the control group (4.9 pg/ml) (P < 0.001).

Conclusions

The increased serum IL-17 level in patients with early knee OA suggests its pathogenic role in the disease. Serum IL-17 positive correlation with the severity of knee OA-related pain proposes that it may be a potential marker to target for early treatment of knee OA-related pain.

Exercise for Osteoarthritis: A Literature Review of Pathology and Mechanism

Osteoarthritis (OA) has a very high incidence worldwide and has become a very common joint disease in the elderly. Currently, the treatment methods for OA include surgery, drug therapy, and exercise therapy. In recent years, the treatment of certain diseases by exercise has received increasing research and attention. Proper exercise can improve the physiological function of various organs of the body. At present, the treatment of OA is usually symptomatic. Limited methods are available for the treatment of OA according to its pathogenesis, and effective intervention has not been developed to slow down the progress of OA from the molecular level. Only by clarifying the mechanism of exercise treatment of OA and the influence of different exercise intensities on OA patients can we choose the appropriate exercise prescription to prevent and treat OA. This review mainly expounds the mechanism that exercise alleviates the pathological changes of OA by affecting the degradation of the ECM, apoptosis, inflammatory response, autophagy, and changes of ncRNA, and summarizes the effects of different exercise types on OA patients. Finally, it is found that different exercise types, exercise intensity, exercise time and exercise frequency have different effects on OA patients. At the same time, suitable exercise prescriptions are recommended for OA patients.

Targeted transcriptomic analyses of RNA isolated from formalin-fixed and paraffin-embedded human menisci

Formalin-fixed and paraffin-embedded (FFPE) biospecimens are a valuable and widely-available resource for diagnostic and research applications. With biobanks of tissue samples available in many institutions, FFPE tissues could prove to be a valuable resource for translational orthopaedic research. The purpose of this study was to characterize the molecular profiles and degree of histologic degeneration on archival fragments of FFPE human menisci obtained during arthroscopic partial meniscectomy. We used FFPE menisci for multiplexed gene expression analysis using the NanoString nCounter® platform, and for histological assessment using a quantitative scoring system. In total, 17 archival specimens were utilized for integrated histologic and molecular analyses. The median patient age was 22 years (range: 14-62). We found that the genes with the highest normalized counts were those typically expressed in meniscal fibrocartilage. Gene expression differences were identified in patient cohorts based on age (≤40 years), including genes associated with the extracellular matrix and tissue repair. The majority of samples showed mild to moderate histologic degeneration. Based on these data, we conclude that FFPE human menisci can be effectively utilized for molecular evaluation following a storage time as long as 11 years. Statement of Clinical Significance: The integration of histological and transcriptomic analyses described in this study will be useful for future studies investigating the basis for biological classification of meniscus specimens in patients. Further exploration into the genes and pathways uncovered by this study may suggest targets for biomarker discovery and identify patients at greater risk for osteoarthritis once the meniscus is torn.

Synovial inflammation in osteoarthritis progression

Osteoarthritis (OA) is a progressive degenerative disease resulting in joint deterioration. Synovial inflammation is present in the OA joint and has been associated with radiographic and pain progression. Several OA risk factors, including ageing, obesity, trauma and mechanical loading, play a role in OA pathogenesis, likely by modifying synovial biology. In addition, other factors, such as mitochondrial dysfunction, damage-associated molecular patterns, cytokines, metabolites and crystals in the synovium, activate synovial cells and mediate synovial inflammation. An understanding of the activated pathways that are involved in OA-related synovial inflammation could form the basis for the stratification of patients and the development of novel therapeutics. This Review focuses on the biology of the OA synovium, how the cells residing in or recruited to the synovium interact with each other, how they become activated, how they contribute to OA progression and their interplay with other joint structures.

Characterization of Microfragmented Adipose Tissue Architecture, Mesenchymal Stromal Cell Content and Release of Paracrine Mediators

The use of microfragmented adipose tissue (µFAT) for the treatment of musculoskeletal disorders, especially osteoarthritis (OA), is gaining popularity, following positive results reported in recent case series and clinical trials. Although these outcomes were postulated to rely on paracrine signals, to date, a thorough fingerprint of released molecules is largely missing. The purpose of this study was to first characterize both structure and cell content of unprocessed lipoaspirate (LA) and µFAT, and further identify and frame the array of signaling factors in the context of OA disease, by means of high throughput qRT-PCR for extracellular-vesicle (EV) embedded miRNAs and proteomics for tissue and secreted factors. Cell count showed reduction of blood cells in µFAT, confirmed by histological and flow cytometry analyses, that also showed a conserved presence of structural, endothelial and stromal components and pericytes. In the secretome, 376 and 381 EV-miRNAs in LA and µFAT, respectively, were identified. In particular, most abundant and µFAT upregulated EV-miRNAs were mainly recapitulating those already reported as ASC-EVs-specific, with crucial roles in cartilage protection and M2 macrophage polarization, while only a scarce presence of those related to blood cells emerged. Furthermore, secretome proteomic analysis revealed reduction in µFAT of acute phase factors driving OA progression. Taken together, these results suggest that processing of LA into µFAT allows for removal of blood elements and maintenance of tissue structure and stromal cell populations, and possibly the increase of OA-protective molecular features. Thus, microfragmentation represents a safe and efficient method for the application of adipose tissue properties in the frame of musculoskeletal disorders.

Do Synovial Inflammation and Meniscal Degeneration Impact Clinical Outcomes of Patients Undergoing Arthroscopic Partial Meniscectomy? A Histological Study

The menisci exert a prominent role in joint stabilization and in the distribution of mechanical loading. Meniscal damage is associated with increased risk of knee OA. The aim of this study was to characterize the synovial membrane and meniscal tissues in patients undergoing arthroscopic partial meniscectomy for meniscal tear and to evaluate association with clinical outcomes. A total of 109 patients were recruited. Demographic and clinical data were collected. Visual Analogic Scale (VAS) measuring pain and Knee injury and Osteoarthritis Outcome Score (KOOS) were recorded at baseline and at 2-years follow-up. Histological and immunohistochemical characterizations were performed on synovial membranes and meniscal tissues. More than half of the patients demonstrated synovial mononuclear cell infiltration and hyperplasia. Synovial fibrosis was present in most of the patients; marked vascularity and CD68 positivity were observed. Inflammation had an impact on both pain and knee symptoms. Patients with synovial inflammation had higher values of pre-operative VAS and inflammation. Higher pre-operative pain was observed in patients with meniscal MMP-13 production. In conclusion, multivariate analysis showed that synovial inflammation was associated with pre-operative total KOOS scores, knee symptoms, and pain. Moreover, meniscal MMP-13 expression was found to be associated with pre-operative pain in multivariate analysis. Thus, targeting inflammation of the synovial membrane and meniscus might reduce clinical symptoms and dysfunction at the time of surgery.

Histologic and molecular features in pathologic human menisci from knees with and without osteoarthritis

The objective of this study was to evaluate histologic and molecular features of meniscus degeneration in cohorts of patients with and without osteoarthritis (OA) of the knee. Menisci were obtained from patients undergoing total knee arthroplasty for OA (TKA) or arthroscopic partial meniscectomy (APM) for a torn knee meniscus. Degenerative meniscal tears were among the most common tear type in the APM group based on the pattern. Using an integrative workflow for molecular evaluation of formalin-fixed and paraffin-embedded tissues, human menisci underwent blinded histologic evaluation and NanoString gene expression analyses. Histology revealed increased proteoglycan content in TKA menisci compared to APM menisci, but otherwise no significant differences in the total pathology score or sub-scores between patients based on age or cohort. NanoString analyses revealed differential expression of genes primarily associated with the PI3K-AKT signaling pathway, cell cycle, and apoptosis. These data provide new insights into histological and molecular features of meniscus degeneration in patients with and without knee OA. Histologic assessment of menisci showed similar severity of overall degeneration between cohorts, but there were differences at the molecular level. The dysregulated pathways identified in this study could contribute to early-onset meniscus degeneration, or to a predisposition to meniscus tears and subsequent knee OA. Further studies that validate genes and pathways uncovered in this study will allow us to evaluate novel approaches to assess and treat meniscal degeneration.

Erosive hand osteoarthritis: latest findings and outlook

Osteoarthritis (OA) most commonly affects knee joints, and the next most commonly affected sites are the hands and hips. Three distinct hand OA phenotypes have been described: erosive hand OA (EHOA), nodal hand OA - also known as non-erosive hand OA (non-EHOA) - and first carpometacarpal joint OA. EHOA predominantly affects women and is the most aggressive form of hand OA, characterized by a severe clinical onset and progression, leading to joint damage, disability and reduction of quality of life. Clinical signs of inflammation associated with EHOA include the acute onset of pain, swelling and redness. Moreover, EHOA is characterized by radiographic features such as central erosion, saw-tooth and gull-wing lesions and, rarely, ankylosis. The aim of this Review is to report the latest findings on epidemiology, clinical features, pathology and aetiopathogenesis, biomarkers, imaging modalities and treatments for EHOA. The ongoing development of new hand OA classification criteria should facilitate standardization between studies.

Monocytes, Macrophages, and Their Potential Niches in Synovial Joints - Therapeutic Targets in Post-Traumatic Osteoarthritis?

Synovial joints are complex structures that enable normal locomotion. Following injury, they undergo a series of changes, including a prevalent inflammatory response. This increases the risk for development of osteoarthritis (OA), the most common joint disorder. In healthy joints, macrophages are the predominant immune cells. They regulate bone turnover, constantly scavenge debris from the joint cavity and, together with synovial fibroblasts, form a protective barrier. Macrophages thus work in concert with the non-hematopoietic stroma. In turn, the stroma provides a scaffold as well as molecular signals for macrophage survival and functional imprinting: “a macrophage niche”. These intricate cellular interactions are susceptible to perturbations like those induced by joint injury. With this review, we explore how the concepts of local tissue niches apply to synovial joints. We introduce the joint micro-anatomy and cellular players, and discuss their potential interactions in healthy joints, with an emphasis on molecular cues underlying their crosstalk and relevance to joint functionality. We then consider how these interactions are perturbed by joint injury and how they may contribute to OA pathogenesis. We conclude by discussing how understanding these changes might help identify novel therapeutic avenues with the potential of restoring joint function and reducing post-traumatic OA risk.

Arthroscopic partial meniscectomy: did it ever work?

Arthroscopic partial meniscectomy (APM) is one the most common orthopedic surgical procedures. The most common indication for APM is a degenerative meniscal tear (DMT). High-quality evidence suggests that APM does not provide meaningful benefits in patients with DMTs and may even be harmful in the longer term. This narrative review focuses on a fundamental question: considering the history and large number of these surgeries, has APM ever actually worked in patients with DMT? A truly effective treatment needs a valid disease model that would biologically and plausibly explain the perceived treatment benefits. In the case of DMT, effectiveness requires a credible framework for the pain-generating process, which should be influenced by APM. Basic research, pathoanatomy, and clinical evidence gives no support to these frameworks. Moreover, treatment of DMT with an APM does not align with the traditional practice of medicine since DMT is not a reliable diagnosis for knee pain and no evidence-based indication exists that would influence patient prognosis from APM. A plausible and robust explanation supported by both basic research and clinical evidence is that DMTs are part of an osteoarthritic disease process and do not contribute to the symptoms independently or in isolation and that symptoms are not treatable with APM. This is further supported by the fact that APM as an intervention is paradoxical because the extent of procedure and severity of disease are both inversely associated with outcome. We argue that arthroscopic treatment of DMT is largely based on a logical fallacy: post hoc ergo propter hoc.

Current State of Synovial Fluid Biomarkers in Sports Medicine

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While the gross mechanical abnormalities contributing to posttraumatic osteoarthritis (PTOA) have been well described, new research is demonstrating that these insults to the articular cartilage may also initiate changes in the joint microenvironment that seed the development of PTOA.

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A growing amount of literature has identified key biomarkers that exhibit altered expression in the synovial fluid following a knee injury, with a portion of these molecules remaining elevated in the years following an injury.

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These biomarkers have the potential to aid in the early detection of PTOA before radiographic evidence becomes apparent. Furthermore, deciphering the processes that occur within the articular microenvironment after trauma may allow for better identification of therapeutic targets for the prevention and earlier treatment of PTOA.

Immunofluorescence Analysis of NF-kB and iNOS Expression in Different Cell Populations during Early and Advanced Knee Osteoarthritis

Synovitis of the knee synovium is proven to be a precursor of knee osteoarthritis (OA), leading to a radiologically advanced stage of the disease. This study was conducted to elucidate the expression pattern of different inflammatory factors—NF-kB, iNOS, and MMP-9 in a subpopulation of synovial cells. Thirty synovial membrane intra-operative biopsies of patients (ten controls, ten with early OA, and ten with advanced OA, according to the Kellgren–Lawrence radiological score) were immunohistochemically stained for NF-kB, iNOS, and MMP9, and for different cell markers for macrophages, fibroblasts, leukocytes, lymphocytes, blood vessel endothelial cells, and blood vessel smooth muscle cells. The total number of CD68+/NF-kB+ cells/mm² in the intima of early OA patients (median = 2359) was significantly higher compared to the total number of vimentin+/Nf-kB+ cells/mm² (median = 1321) and LCA+/NF-kB+ cells/mm² (median = 64) (p < 0.001 and p < 0.0001, respectively). The total number of LCA+/NF-kB+ cells/mm² in the subintima of advanced OA patients (median = 2123) was significantly higher compared to the total number of vimentin+/NF-kB+ cells/mm² (median = 14) and CD68+/NF-kB+ cells/mm² (median = 29) (p < 0.0001). The total number of CD68+/iNOS+ cells/mm² in the intima of both early and advanced OA patients was significantly higher compared to the total number of vimentin+/iNOS+ cells/mm² and LCA+/iNOS+ cells/mm² (p < 0.0001 and p < 0.001, respectively). The total number of CD68+/MMP-9+ cells/mm² in the intima of both early and advanced OA patients was significantly higher compared to the total number of vimentin+/MMP-9+ cells/mm² and CD5+/MMP-9+ cells/mm² (p < 0.0001). Macrophages may have a leading role in OA progression through the NF-kB production of inflammatory factors (iNOS and MMP-9) in the intima, except in advanced OA, where leukocytes could have a dominant role through NF-kB production in subintima. The blocking of macrophageal and leukocyte NF-kB expression is a possible therapeutic target as a disease modifying drug.

Synovial Macrophages in Osteoarthritis: The Key to Understanding Pathogenesis?

Effective treatment of osteoarthritis (OA) remains a huge clinical challenge despite major research efforts. Different tissues and cell-types within the joint contribute to disease pathogenesis, and there is great heterogeneity between patients in terms of clinical features, genetic characteristics and responses to treatment. Inflammation and the most abundant immune cell type within the joint, macrophages, have now been recognised as possible players in disease development and progression. Here we discuss recent findings on the involvement of synovial inflammation and particularly the role of synovial macrophages in OA pathogenesis. Understanding macrophage involvement may hold the key for improved OA treatments.

Study of chondroitin sulfate E oligosaccharide as a promising complement C5 inhibitor for osteoarthritis alleviation

Osteoarthritis (OA) is a degenerative joint disease which is highly prevalent worldwide. However, no therapy for blocking OA pathogenesis is available currently. In this study, chondroitin sulfate (CS) E oligosaccharides were prepared and we identified disaccharide as the functional unit showing the strongest anti-complement activity and screened out complement C5 as its target in the complement system. We determined that CS-E disaccharide produced anti-inflammatory effects to treat OA by regulating the complement system: it inhibited the formation of complement-dependent complexes such as the membrane-attack complex (MAC) by targeting C5 and suppressed MAC-induced protein expression and the activation of downstream MAPK and NF-κB signaling pathways accordingly. By identifying CS-E disaccharide which could be regarded as a complement regulator or inhibitor exhibiting high anti-complement activity and revealing its OA-alleviating mechanism, this study not only provides a new strategy for OA treatment and drug development, but also potentially offers a promising C5 target therapy for other associated diseases.

Extensive cytokine analysis in synovial fluid of osteoarthritis patients

OBJECTIVE

Osteoarthritis (OA) is a joint disease characterized by articular cartilage loss and afflicts many people worldwide. However, diagnostic methods and treatment options remain limited and are often characterized by low sensitivity and low efficacy. The focus of the present study was to identify proteomic biomarkers in synovial fluid to improve diagnosis and therapy of OA patients.

METHODS

Antibody array technology was utilized for protein expression profiling of synovial fluid from 24 OA patients and 24 healthy persons.

RESULTS

Compared with healthy persons, twenty proteins showed lower expression levels in OA patients, while thirty proteins had higher levels. Among these differential proteins, GITRL, CEACAM-1, FSH, EG-VEGF, FGF-4, PIGF, Cystatin EM and NT-4 were found for the first time to be differentially expressed in OA. Bioinformatics analysis showed that most of these differential proteins were involved leukocytes events, and some differentially expressed proteins including IL-18, CXCL1, CTLA4, MIP-3b, CD40, MMP-1, THBS1, CCL11, PAI-1, BAFF, aggrecan, angiogenin and follistatin were located in central positions of the protein-protein interaction (PPI) network.

CONCLUSION

We speculate that leukocyte proliferation and migration to the joint may be an important pathogenesis of OA, which needs a further validation. The central proteins of the PPI network may play a more pivotal role in OA. The newly identified differentially expressed proteins may be novel biomarkers for OA diagnosis and targets for OA therapy.

Low-Intensity Pulsed Ultrasound Suppresses Synovial Macrophage Infiltration and Inflammation in Injured Knees in Rats

This study was designed to investigate how low-intensity pulsed ultrasound (LIPUS) suppresses traumatic joint inflammation and thereafter affects the progression of posttraumatic osteoarthritis. Intra-articular fracture (IAF) was created in the right knee of rats. LIPUS was applied to the knees with IAFs for 20 min/d for 2 wk-LIPUS(+) group. The study controls included rats that underwent sham surgery but no LIPUS treatment (control group) or underwent IAF surgery without LIPUS treatment-LIPUS(-) group. By histology, at 4 wk, leukocyte infiltration in the synovium was reduced in the LIPUS(+) group. Furthermore, LIPUS treatment reduced CD68⁺ macrophages in the synovium and limited their distribution mostly in the subintimal synovium. Measured with enzyme-linked immunosorbent assay, interleukin-1β (IL-1β) in the joint fluid of the LIPUS(+) group was reduced to about one-third that in the LIPUS(-) group. By reducing synovial macrophages and lowering IL-1β in the joint fluid, LIPUS is potentially therapeutic for posttraumatic osteoarthritis.