Synovitis and the risk of knee osteoarthritis: the MOST Study

Detection of synovitis in early knee osteoarthritis by MRI and serum biomarkers in Japanese general population

To investigate synovitis' influence on early knee osteoarthritis (EKOA) by serum biomarkers and magnetic resonance imaging (MRI) findings in Japanese women. We enrolled 255 women aged 30-70 without radiographic abnormalities (Kellgren-Lawrence grade ≥ 2). Knee injury, OA outcome scores (KOOS), clinical examinations, and standing radiograph were used for classification criteria of EKOA. Participants were classified into normal knee group and EKOA group. All participants underwent MRIs of their right knee. The amount of effusion-synovitis volume was quantified. We compared serum matrix metalloproteinases-3 levels (MMP-3), high-sensitivity C-reactive protein, interleukin-6, and adiponectin between the groups. The relationship between synovitis and EOKA was investigated using multiple linear regression. Fifty-four participants (21%) were classified as EKOA. Serum MMP-3 concentration and effusion-synovitis volume were higher in patients with EKOA (p = 0.025 and p = 0.001, respectively). Effusion-synovitis volume negatively correlated with all KOOS subscales and positively correlated with serum MMP-3 concentration. Serum MMP-3 concentration was associated with effusion-synovitis volume β = 0.60, p < 0.001). There was mildly active but definitive synovitis in EKOA. This was an observational study so that no conclusions can be drawn regarding cause-effect for synovitis and symptoms. Future studies should conduct follow-up of participants with synovitis to assess the progression of knee OA.

Association of Visceral Adiposity With Pain but Not Structural Osteoarthritis

OBJECTIVE

Osteoarthritis (OA) and pain are both made more severe by low-grade inflammation. This study was undertaken to examine whether visceral fat, a major source of inflammatory cytokines and adipokines, is associated with an increased risk of knee OA or musculoskeletal pain.

METHODS

Subjects in the Multicenter Osteoarthritis Study cohort, who were age 50-79 years and had or were at high risk of knee OA, underwent whole-body dual x-ray absorptiometry (DXA) at baseline. At baseline, 30 months, and 60 months radiographs and magnetic resonance images (MRIs) of the knees were obtained, and patients were asked to score the severity of their knee pain and to identify sites of joint pain using a body homunculus. Baseline DXA scans were used to measure total body fat and visceral and subcutaneous fat in the torso. The association of fat depot size with structural outcomes (incident radiographic OA and cartilage loss and synovitis on MRI) and with pain outcomes (worsening knee pain, number of painful joints, and widespread pain) was assessed. Regression analyses were adjusted for age, sex, race, education level, smoking status, physical activity, body mass index (BMI), and depressive symptoms.

RESULTS

Of the 2,961 participants at baseline, 60.7% were women. The mean age was 62.5 years and mean BMI was 30.5 kg/m2 . After adjustment for covariates, no fat measures were associated with any structural outcomes. However, total and visceral, but not subcutaneous, fat were positively associated with worsening knee pain (P = 0.0005 for total fat and P = 0.007 for visceral fat) and widespread pain (P = 0.001 for total fat and P = 0.02 for visceral fat), and the amount of visceral fat was associated with the number of painful joints (P = 0.07).

CONCLUSION

Our findings indicate that visceral fat is associated with an increased risk of musculoskeletal and widespread pain.

CD10/Neprilysin Enrichment in Infrapatellar Fat Pad-Derived Mesenchymal Stem Cells Under Regulatory-Compliant Conditions: Implications for Efficient Synovitis and Fat Pad Fibrosis Reversal

BACKGROUND

Synovitis and infrapatellar fat pad (IFP) fibrosis participate in various conditions of the knee. Substance P (SP), a neurotransmitter secreted within those structures and historically associated with nociception, also modulates local neurogenic inflammatory and fibrotic responses. Exposure of IFP mesenchymal stem cells (IFP-MSCs) to a proinflammatory/profibrotic environment (ex vivo priming with TNFα, IFNγ, and CTGF) induces their expression of CD10/neprilysin, effectively degrading SP in vitro and in vivo.

PURPOSE/HYPOTHESIS

The purpose was to test the therapeutic effects of IFP-MSCs processed under regulatory-compliant protocols, comparing them side-by-side with standard fetal bovine serum (FBS)-grown cells. The hypothesis was that when processed under such protocols, IFP-MSCs do not require ex vivo priming to acquire a CD10-rich phenotype efficiently degrading SP and reversing synovitis and IFP fibrosis.

STUDY DESIGN

Controlled laboratory study.

METHODS

Human IFP-MSCs were processed in FBS or either of 2 alternative conditions-regulatory-compliant pooled human platelet lysate (hPL) and chemically reinforced medium (Ch-R)-and then subjected to proinflammatory/profibrotic priming with TNFα, IFNγ, and CTGF. Cells were assessed for in vitro proliferation, stemness, immunophenotype, differentiation potential, transcriptional and secretory profiles, and SP degradation. Based on a rat model of acute synovitis and IFP fibrosis, the in vivo efficacy of cells degrading SP plus reversing structural signs of inflammation and fibrosis was assessed.

RESULTS

When compared with FBS, IFP-MSCs processed with either hPL or Ch-R exhibited a CD10^High phenotype and showed enhanced proliferation, differentiation, and immunomodulatory transcriptional and secretory profiles (amplified by priming). Both methods recapitulated and augmented the secretion of growth factors seen with FBS plus priming, with some differences between them. Functionally, in vitro SP degradation was more efficient in hPL and Ch-R, confirmed upon intra-articular injection in vivo where CD10-rich IFP-MSCs also dramatically reversed signs of synovitis and IFP fibrosis even without priming or at significantly lower cell doses.

CONCLUSION

hPL and Ch-R formulations can effectively replace FBS plus priming to induce specific therapeutic attributes in IFP-MSCs. The resulting fine-tuned, regulatory-compliant, cell-based product has potential future utilization as a novel minimally invasive cell therapy for the treatment of synovitis and IFP fibrosis.

CLINICAL RELEVANCE

The therapeutic enhancement of IFP-MSCs manufactured under regulatory-compliant conditions suggests that such a strategy could accelerate the time from preclinical to clinical phases. The therapeutic efficacy obtained at lower MSC numbers than currently needed and the avoidance of cell priming for efficient results could have a significant effect on the design of clinical protocols to potentially treat conditions involving synovitis and IFP fibrosis.

Differential patterns of pathology in and interaction between joint tissues in long-term osteoarthritis with different initiating causes: phenotype matters

OBJECTIVE

To determine if osteoarthritis (OA) progression and joint tissue-pathology associations link specific animal models to different human OA phenotypes.

DESIGN

Male 11-week-old C57BL6 mice had unilateral medial-meniscal-destabilization (DMM) or antigen-induced-arthritis (AIA). Joint tissue histopathology was scored day-3 to week-16. Tissue-pathology associations (corrected for time and at week-16) were determined by partial correlation coefficients, and odds ratios (OR) calculated for likelihood of cartilage damage and joint inflammation by ordinal-logistic-regression.

RESULTS

Despite distinct temporal patterns of progression, by week-16 joint-wide OA pathology in DMM and AIA was equivalent. Significant pathology associations common to both models included: osteophyte size and maturity (r > 0.4); subchondral bone (SCB) sclerosis and osteophyte maturity (r > 0.25); cartilage erosion and chondrocyte hypertrophy/apoptosis (r > 0.4), SCB sclerosis (r > 0.26), osteophyte size (r > 0.3), and maturity (r > 0.32). DMM-specific associations were between cartilage proteoglycan loss and structural damage (r = 0.56), osteophyte maturity (r = 0.49), size (r = 0.45), and SCB sclerosis (r = 0.28). AIA-specific associations were between SCB sclerosis and chondrocyte hypertrophy/apoptosis (r = 0.40) and osteophyte size (r = 0.37); and synovitis with cartilage structural damage (r = 0.18). No tissue-pathology associations were common to both models at week-16. Increased likelihood of cartilage structural damage was associated with: chondrocyte hypertrophy/apoptosis (OR>1.7), and osteophyte size (OR>2.3) in both models; SCB sclerosis (OR = 2.0) and proteoglycan loss (OR = 2.4) in DMM; and synovitis (OR = 1.2) in AIA. Joint inflammation was associated positively with cartilage proteoglycan loss (OR = 1.4) and inversely with osteophyte size (OR = 0.21) in AIA only.

CONCLUSION

This study highlights the importance of defining OA-models by initiating mechanisms and progression, not just end-stage joint-tissue pathology.

Early OA Stage Like Response Occurs after Dynamic Stretching of Human Synovial Fibroblasts

As events triggering early osteoarthritis onset can be related to mechanical stress and proinflammatory signaling, we investigated the effect of different mechanical strain protocols on the expression of proinflammatory genes, as well as extracellular matrix remodelling in human synovial fibroblasts. Three distinct models of tensile stretching were applied: static isotropic tensile strain at 0 Hz, 16% tension for 48 h; short-term high-frequency cyclic tension at 1 Hz, 10% tension for 4 h; and dynamic tensile stretching for 48 h, consisting of two blocks of moderate stretching at 0.2 Hz, 2%, advanced stretching at 0.5 Hz, 15%, or a combination of both. General signs of inflammation were present after static isotropic tension, whereas short-term high-frequency cyclic tension showed increased levels of IL-6 paired with diminished levels of IL-1β. Reduced inflammatory effects of TNF-α, IL-6, and IL-1β were observed when exposed to advanced stretching. Long-term tensile strain induced extracellular matrix remodelling at the gene and protein levels. While hyaluronan acid synthesis was increased with static tensile strain, dynamic tensile stretching had a reducing effect. Our study revealed that proinflammatory markers were activated by mechanical strain as seen in static isotropic tension and short-term high-frequency tensile strain, whereas long-term exposure induced extracellular matrix remodelling processes.

Interleukin-34 overexpression mediated through tumor necrosis factor-alpha reflects severity of synovitis in knee osteoarthritis

This study aimed to investigate whether interleukin-34 (IL-34) mRNA expression is aberrant and modulated by tumor necrosis factor-alpha (TNF-α) in knee osteoarthritis (OA) fibroblast-like synoviocytes (FLS) and determine associations of IL-34 mRNA and protein in the systemic and local joint environments with severity of knee OA synovitis. Transcriptional and translational IL-34 levels in FLS, synovium, synovial fluid, and plasma of knee OA were determined using real-time polymerase chain reaction, immunohistochemistry, and enzyme-linked immunosorbent assay. Relative mRNA expressions of NF-κB signaling molecules were further measured. In knee OA FLS stimulated with TNF-α, IL-34 mRNA expression was significantly up-regulated in a time-dependent manner. In knee OA synovium with severe synovitis, increased IL-34 mRNA expression was directly associated with IL-6, IκB, NF-κB, and MMP-13, in addition to knee OA FLS. Immunostaining score of IL-34 was considerably greater in knee OA synovium with severe synovitis than that in those with mild and no synovitis. Increments in joint fluid and plasma IL-34 levels in knee OA patients with severe synovitis were closely related to its mRNA and protein expressions in knee OA synovium. Transcriptional and translational expressions of IL-34 were positively correlated with synovitis severity. Collectively, IL-34 overexpression would reflect synovitis severity in knee OA.

CCL3/CCR1 mediates CD14+CD16- circulating monocyte recruitment in knee osteoarthritis progression

OBJECTIVES

Monocyte-derived macrophages, as the predominant immune cell type that is increased in inflamed synovium, play a vital role during knee osteoarthritis (KOA) progression. However, the mechanisms underlying the recruitment of circulating monocytes to osteoarthritic knees remain uncertain. Based on previous data obtained from plasma, we investigated the contributions of CCL2, CCL3, CCL4 and their cognate receptors in circulating monocyte chemotaxis and KOA development.

METHODS

Using flow cytometry staining, we characterized the expression patterns of the chemokine receptors in CD14⁺CD16^- circulating monocytes from KOA patients and healthy volunteers. The expression of chemokines in synovial fluids, synovium and cartilage was investigated in KOA patients and in patients without KOA. The role of chemokines and their cognate receptors in the chemotaxis of CD14⁺CD16^- circulating monocytes was assessed using chemokine neutralizing antibodies (NA) and receptor antagonists in vitro and in vivo.

RESULTS

The majority of CD14⁺CD16^- circulating monocytes were CCR1-and CCR2-positive. CCL2, CCL3 and CCL4 were elevated in synovial fluid of KOA patients compared with that of controls. The most likely source of these chemokines is inflamed synovium and cartilage in the osteoarthritic knee. The CCL3/CCR1 and CCL2/CCR2 axes showed substantial ability to recruit CD14⁺CD16^- monocytes in transwell assays. Similar results were confirmed in a mouse model of collagenase-induced KOA (CIA) in which blocking either the CCL3/CCR1 axis or the CCL2/CCR2 axis reduced synovial hyperplasia and F4/80⁺ macrophage infiltration.

CONCLUSIONS

Our findings suggested that, analogous to the CCL2/CCR2 axis, CCL3 produced in osteoarthritic knees can chemoattract circulating monocytes to the inflamed synovium through CCR1.

Macrophages regulate the progression of osteoarthritis

OA is now well accepted as a low-grade inflammatory disease affecting the whole joint. In addition to mechanical loading, inflammation (particularly synovitis), contributes significantly to OA. Synovial macrophages act as immune cells and are of critical importance in the symptomology and structural progression of OA. Activated macrophages are regulated by mTOR, NF-κB, JNK, PI3K/Akt and other signaling pathways, and are polarized into either M1 or M2 subtypes in OA synovial tissues, synovial fluid, and peripheral blood. The activation state and the M1/M2 ratio is highly associated with OA severity. Aside from autocrine interactions, paracrine interactions between macrophages and chondrocytes play a vital role in the initiation and development of OA by secreting inflammatory cytokines, growth factors, matrix metalloproteinases (MMPs) and tissue inhibitor of metalloproteinases (TIMPs), which lead to subsequent cartilage degradation and destruction. Treatments targeting synovial macrophages relieve pain, and protect from synovitis, cartilage damage, and osteophyte formation during OA development. Macrophage reprogramming of transformation from the M1 to M2 subtype, more than a decrease in the quantity of activated macrophages, appears to be an effective treatment option for OA. This review provides a broad understanding of the contributions of polarized macrophages to joint health and disease. Multifunctional agents with immunomodulatory effects on macrophage reprogramming can skew the inflammatory microenvironment towards a pro-chondrogenic atmosphere, and are thus, potential therapeutic options for the treatment of OA and other immune diseases.

Impact of Mononuclear Cell Infiltration on Chondrodestructive MMP/ADAMTS Production in Osteoarthritic Knee Joints-An Ex Vivo Study

Progressive loss of joint function in osteoarthritis (OA) is driven by degenerative and inflammatory processes and their complex interaction. Decoding the link between degeneration and inflammation is one of the most exciting approaches in understanding OA pathophysiology and holds the promise to open new therapeutic avenues. The overarching goal of this project was to analyze the impact of mononuclear cells (MNC) on enzymatic chondrodestructive processes (MMP/ADAMTS) in OA. Synovial membrane (SM), articular cartilage (AC) and peripheral blood (PB) were obtained from a total of 21 patients with advanced knee OA who underwent arthroplastic surgery. In supernatants of native synovial cell cultures, T cell-depleted synovial cell cultures and macrophage-depleted synovial cell cultures, the concentrations of various metalloproteinases were examined by Enzyme Linked Immunosorbent Assay (ELISA). Furthermore, ELISA was used to analyze concentrations of metalloproteinases in supernatants of chondrocyte monocultures and chondrocyte co-cultures with CD4⁺CD127^dim/- enriched peripheral blood mononuclear cells (PBMC), Treg depleted CD4⁺CD25^-CD127^dim/- enriched PBMC and CD4⁺CD25⁺CD127^dim/- Treg. Compared to native synovial cell culture, T cell depletion led to significantly lower levels of MMP-1, MMP-3 and MMP-9 and macrophage depletion led to a significant decline of MMP-1, MMP-3, MMP-9 and ADAMTS-5 concentration. Compared to T cell depletion, macrophage depletion resulted in a significantly stronger reduction of MMP-1, MMP-3, MMP-9 and ADAMTS-5. In chondrocyte co-culture with CD4⁺CD127^dim/- enriched PBMC the concentration of MMP-1 and ADAMTS-5 was significantly increased compared to chondrocyte monoculture. No significant differences were found between chondrocyte monoculture and chondrocyte co-culture with Treg as well as between co-culture with CD4⁺CD127^dim/- enriched PBMC containing Treg and co-culture with Treg-depleted CD4⁺CD25^-CD127^dim/- enriched PBMC. In conclusion, our data suggests that both synovial macrophages and T cells have a catabolic potential by inducing the release of chondrodestructive metalloproteinases in OA synovium. This study also supports the hypothesis that MNC affect the release of metalloproteinases by chondrocytes and are hereby involved in the cartilage-induced chondrodestructive process. In this study no suppressive effect of Treg was shown.

US detection of medial meniscus extrusion can predict the risk of developing radiographic knee osteoarthritis: a 5-year cohort study

OBJECTIVES

To clarify the relationship between the baseline value of medial meniscus extrusion (MME) and the radiographic change of knee osteoarthritis (KOA) through a 5-year follow-up.

METHODS

Overall, 472 participants and 944 knees were eligible. MME (mm) was measured at the baseline, and KOA was radiographically evaluated at both baseline and 5-year follow-up by Kellgren-Lawrence grade (KLG). Radiographic KOA (ROA) was defined as the knee showing KLG ≥ 2. Incident ROA (iROA) was defined if the baseline KLG of 0-1 increased to KLG ≥ 2 in 5 years. Progressive ROA (pROA) was defined if the baseline KLG of 2-3 worsened to a higher grade in 5 years. Receiver operating characteristic (ROC) curve and generalized estimating equations were used for analysis.

RESULTS

Of 574 non-ROA knees at the baseline, 43 knees (7.5%) developed iROA; of 370 ROA knees, 47 knees (12.7%) developed pROA. Based on the ROC curves, 4 mm was the optimal cutoff to detect the risk of iROA (area under curve [AUC] 0.639 [right knee]; AUC 0.641 [left knee]) and that of pROA (AUC 0.750 [right knee]; AUC 0.863 [left knee]). Multiple regression analysis showed that the 4-mm cutoff of MME was significantly associated with both the prevalence of iROA (regression coefficient [B] 1.909; p ≤ 0.001; adjusted odds ratio [aOR] 6.746) and that of pROA (B 1.791; p ≤ 0.001; aOR 5.993).

CONCLUSIONS

On ultrasonography, the participants with more extruded medial meniscus showed a higher prevalence of both iROA and pROA. Ultrasonography could identify patients who had a risk of developing KOA.

KEY POINTS

• Through a 5-year follow-up, the current cohort study was conducted to clarify the relationship between the baseline value of medial meniscus extrusion (MME) and the radiographic change of knee osteoarthritis (KOA). • More extruded medial meniscus evaluated by ultrasonography was associated with the development of radiographic KOA. • Ultrasonography could identify the patients who had a risk of developing KOA, and the 4-mm cutoff of MME was optimal to detect this risk.

Implication of HYBID (Hyaluronan-Binding Protein Involved in Hyaluronan Depolymerization) in Hyaluronan Degradation by Synovial Fibroblasts in Patients with Knee Osteoarthritis

Cell migration-inducing hyaluronidase 1 (CEMIP), also known as hyaluronan (HA)-binding protein involved in HA depolymerization (HYBID), plays a role in HA degradation. CEMIP2, also known as transmembrane protein 2 (TMEM2), possessing a sequence similarity with HYBID, is reported as a hyaluronidase in mice. However, the expression of these molecules in osteoarthritic synovium and their involvement in HA degradation in synovial fluid (SF) from patients with knee osteoarthritis remain elusive. This study examined their expression in synovial tissue and the relationship with molecular weight of HA in SF in knee osteoarthritis patients. Quantification of mRNA demonstrated that HYBID expression is significantly (5.5-fold) higher in osteoarthritic synovium than in normal control synovium, whereas TMEM2 expression level is similar between the two groups. By immunohistochemistry, HYBID was localized mainly to CD68-negative and fibroblast-specific protein 1-positive synovial lining cells and sublining fibroblasts in osteoarthritic synovium. The mRNA expression levels of HYBID, but not TMEM2, in osteoarthritic synovium positively correlated with distribution of lower-molecular-weight HA with below 1000 kDa in SF. HA-degrading activity in osteoarthritic synovial fibroblasts was abrogated by siRNA-mediated knockdown of HYBID. Among the 12 factors examined, IL-6 significantly up-regulated the HYBID expression and HA-degrading activity in osteoarthritic synovial fibroblasts. These data suggest that HYBID overexpressed by IL-6-stimulated synovial fibroblasts is implicated in HA degradation in osteoarthritic synovium.

Minimizing Posttraumatic Osteoarthritis After High-Energy Intra-Articular Fracture

This article serves to provide an overview of molecular and surgical interventions to minimize the progression of posttraumatic arthritis following high-energy intra-articular fractures. The roles of cartilage and the microcellular environment are discussed, as well as the response of the joint and cartilage to injury. Molecular therapies, such as glucocorticoids, mesenchymal stem cells, and bisphosphonates, are presented as potential treatments to prevent progression to posttraumatic arthritis. High-energy intra-articular fractures of the elbow, hip, knee, and ankle are discussed, with emphasis on restoring anatomic alignment, articular reduction, and stability of the joint.

Phenotypes of osteoarthritis: current state and future implications

In the most recent years, an extraordinary research effort has emerged to disentangle osteoarthritis heterogeneity, opening new avenues for progressing with therapeutic development and unravelling the pathogenesis of this complex condition. Several phenotypes and endotypes have been proposed albeit none has been sufficiently validated for clinical or research use as yet. This review discusses the latest advances in OA phenotyping including how new modern statistical strategies based on machine learning and big data can help advance this field of research.

Cartilage Wear Particles Induce an Inflammatory Response Similar to Cytokines in Human Fibroblast-Like Synoviocytes

The synovium plays a key role in the development of osteoarthritis, as evidenced by pathological changes to the tissue observed in both early and late stages of the disease. One such change is the attachment of cartilage wear particles to the synovial intima. While this phenomenon has been well observed clinically, little is known of the biological effects that such particles have on resident cells in the synovium. The present work investigates the hypothesis that cartilage wear particles elicit a pro-inflammatory response in diseased and healthy human fibroblast-like synoviocytes, like that induced by key cytokines in osteoarthritis. Fibroblast-like synoviocytes from 15 osteoarthritic human donors and a subset of three non-osteoarthritic donors were exposed to cartilage wear particles, interleukin-1α or tumor necrosis factor-α for 6 days and analyzed for proliferation, matrix production, and release of pro-inflammatory mediators and degradative enzymes. Wear particles significantly increased proliferation and release of nitric oxide, interleukin-6 and -8, and matrix metalloproteinase-9, -10, and -13 in osteoarthritic synoviocytes, mirroring the effects of both cytokines, with similar trends in non-osteoarthritic cells. These results suggest that cartilage wear particles are a relevant physical factor in the osteoarthritic environment, perpetuating the pro-inflammatory and pro-degradative cascade by modulating synoviocyte behavior at early and late stages of the disease. Future work points to therapeutic strategies for slowing disease progression that target cell-particle interactions. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1979-1987, 2019.

The exosome-like vesicles from osteoarthritic chondrocyte enhanced mature IL-1β production of macrophages and aggravated synovitis in osteoarthritis

Synovitis, a common clinical symptom for osteoarthritis (OA) patients, is highly related to OA pathological progression and pain manifestation. The activated synovial macrophages have been demonstrated to play an important role in synovitis, but the mechanisms about macrophage activation are still not clear. In this study, we found that the exosome-like vesicles from osteoarthritic chondrocytes could be a new biological factor to stimulate inflammasome activation and increase mature IL-1β production in macrophages. The degraded cartilage explants produced more exosome-like vesicles than the nondegraded ones, while the exosome-like vesicles from chondrocytes could enter into joint synovium tissue and macrophages. Moreover, the exosome-like vesicles from osteoarthritic chondrocytes enhanced the production of mature IL-1β in macrophages. These vesicles could inhibit ATG4B expression via miR-449a-5p, leading to inhibition of autophagy in LPS-primed macrophages. The decreased autophagy promoted the production of mitoROS, which further enhanced the inflammasome activation and subsequent IL-1β processing. Ultimately, the increase of mature IL-1β may aggravate synovial inflammation and promote the progression of OA disease. Our study provides a new perspective to understand the activation of synovial macrophages and synovitis in OA patients, which may be beneficial for therapeutic intervention in synovitis-related OA patients.

A machine learning approach to knee osteoarthritis phenotyping: data from the FNIH Biomarkers Consortium

OBJECTIVE

Knee osteoarthritis (KOA) is a heterogeneous condition representing a variety of potentially distinct phenotypes. The purpose of this study was to apply innovative machine learning approaches to KOA phenotyping in order to define progression phenotypes that are potentially more responsive to interventions.

DESIGN

We used publicly available data from the Foundation for the National Institutes of Health (FNIH) osteoarthritis (OA) Biomarkers Consortium, where radiographic (medial joint space narrowing of ≥0.7 mm), and pain progression (increase of ≥9 Western Ontario and McMaster Universities Osteoarthritis Index [WOMAC] points) were defined at 48 months, as four mutually exclusive outcome groups (none, both, pain only, radiographic only), along with an extensive set of covariates. We applied distance weighted discrimination (DWD), direction-projection-permutation (DiProPerm) testing, and clustering methods to focus on the contrast (z-scores) between those progressing by both criteria ("progressors") and those progressing by neither ("non-progressors").

RESULTS

Using all observations (597 individuals, 59% women, mean age 62 years and BMI 31 kg/m2) and all 73 baseline variables available in the dataset, there was a clear separation among progressors and non-progressors (z = 10.1). Higher z-scores were seen for the magnetic resonance imaging (MRI)-based variables than for demographic/clinical variables or biochemical markers. Baseline variables with the greatest contribution to non-progression at 48 months included WOMAC pain, lateral meniscal extrusion, and serum N-terminal pro-peptide of collagen IIA (PIIANP), while those contributing to progression included bone marrow lesions, osteophytes, medial meniscal extrusion, and urine C-terminal crosslinked telopeptide type II collagen (CTX-II).

CONCLUSIONS

Using methods that provide a way to assess numerous variables of different types and scalings simultaneously in relation to an outcome of interest enabled a data-driven approach that identified key variables associated with a progression phenotype.

Dihydroartemisinin derivative DC32 inhibits inflammatory response in osteoarthritic synovium through regulating Nrf2/NF-κB pathway

Synovitis is an aseptic inflammation that leads to joint effusion, pain and swelling. As one of the main drivers of pathogenesis in osteoarthritis (OA), the presence of synovitis contributes to pain, incidence and progression of OA. In our previous study, DC32 [(9α,12α-dihydroartemisinyl) bis(2'-chlorocinnmate)], a dihydroartemisinin derivative, was found to have an antirheumatic ability via immunosuppression, but the effect of DC32 on synovitis has not been fully illuminated. In this study, we chose to evaluate the effect and mechanism of DC32 on attenuating synovial inflammation. Fibroblast-like synoviocytes (FLSs) of papain-induced OA rats were isolated and cultured. And DC32 significantly inhibited the invasion and migration of cultured OA-FLSs, as well as the transcription of IL-6, IL-1β, CXCL12 and CX3CL1 in cultured OA-FLSs measured by qPCR. DC32 remarkably inhibited the activation of ERK and NF-κB pathway, increased the expression of Nrf2 and HO-1 in cultured OA-FLSs detected by western blot. DC32 inhibited the degradation and phosphorylation of IκBα which further prevented the phosphorylation of NF-κB p65 and the effect of DC32 could be relieved by siRNA for Nrf2. In papain-induced OA mice, DC32 significantly alleviated papain-induced mechanical allodynia, knee joint swelling and infiltration of inflammatory cell in synovium. DC32 upregulated the mRNA expression of Type II collagen and aggrecan, and downregulated the mRNA expression of MMP2, MMP3, MMP13 and ADAMTS-5 in the knee joints of papain-induced OA mice measured by qPCR. The level of TNF-α in the serum and secretion of TNF-α in the knee joints were also reduced by DC32 in papain-induced OA mice. In conclusion, DC32 inhibited the inflammatory response in osteoarthritic synovium through regulating Nrf2/NF-κB pathway and attenuated OA. In this way, DC32 may be a potential agent in the treatment of OA.

Degenerative Meniscal Tears and High Tibial Osteotomy: Do Current Treatment Algorithms Need to Be Realigned?

Degenerative medial meniscal tears (DMMTs) are a common feature of early knee osteoarthritis (OA). Varus alignment is a strong risk factor for medial compartment knee OA and its progression. We propose that high tibial osteotomy (HTO) should be considered much earlier in the treatment algorithm for patients presenting with recurring medial knee pain, varus alignment, and DMMT, absent of radiographic OA. We provide rationale for investigating HTO as a disease-modifying intervention for secondary prevention in knee OA, and present case examples as low-level proof of principle. Finally, caveats and challenges are discussed along with proposed future research.

Intra-articular corticosteroids and the risk of knee osteoarthritis progression: results from the Osteoarthritis Initiative

OBJECTIVE

A recent randomized clinical trial reported that repeated intra-articular corticosteroids (IACs) were associated with a greater cartilage loss. This study aimed to examine the relation of IACs to knee radiographic osteoarthritis (ROA) progression in a real-world setting.

DESIGN

A cohort that initiated IACs and a comparison cohort without IACs from participants with mild to moderate knee ROA in the Osteoarthritis Initiative (OAI) were assembled (from 0-month to 48-month). Two measures of knee ROA progression were assessed during the follow-up period: (1) an increase in Kellgren and Lawrence (KL) grade by ≥1 grade or having a knee replacement (i.e., KL grade worsening); and (2) a decrease in joint space width (JSW) by ≥0.7 mm or having a knee replacement (i.e., JSW worsening). The associations of IACs initiation using a propensity-score matched cohort study and continuous IACs using marginal structural models with the risk of knee ROA progression were examined.

RESULTS

Among 684 propensity-score matched participants at baseline (148 IACs initiators, 536 comparators), 65 knees (21.7/100 person-years) in the IACs initiation cohort and 90 knees (7.1/100 person-years) in the comparison cohort experienced KL worsening. The hazard ratios (HRs) of KL worsening from IACs initiation and continuous IACs were 3.02 (95% confidence interval [CI], 2.19-4.16) and 4.67 (95% CI, 2.92-7.47), respectively. The corresponding HRs of JSW worsening were 2.93 (95% CI, 2.13-4.02) and 3.26 (95% CI, 1.78-5.96), respectively. All HRs for continuous use of IACs were further away from the null.

CONCLUSIONS

IACs, especially continuous IACs, may be associated with an increased risk of knee ROA progression.

Is treated HIV infection associated with knee cartilage degeneration and structural changes? A longitudinal study using data from the osteoarthritis initiative

Background

Metabolic disorders presenting in HIV-infected patients on antiretroviral therapy (ART) may increase the risk of osteoarthritis. However, structural changes of the knee in HIV infected subjects are understudied. The aim of this study is to investigate knee cartilage degeneration and knee structural changes over 8 years in subjects with and without HIV infection determined based on the use of ART.

Methods

We studied 10 participants from the Osteoarthritis Initiative who received ART at baseline and 20 controls without ART, frequency matched for age, sex, race, baseline body mass index (BMI) and Kellgren & Lawrence grade. Knee abnormalities were assessed using the whole-organ magnetic resonance imaging score (WORMS) and cartilage T2 including laminar and texture analyses were analyzed using a multislice-multiecho spin-echo sequence. Signal abnormalities of the infrapatellar fat pad (IPFP) and suprapatellar fat pad (SPFP) were assessed separately using a semi-quantitative scoring system. Linear regression models were used in the cross-sectional analysis to compare the differences between ART/HIV subjects and controls in T2 (regular and laminar T2 values, texture parameters) and morphologic parameters (subscores of WORMS, scores for signal alterations of IPFP and SPFP). Mixed effects models were used in the longitudinal analysis to compare the rate of change in T2 and morphological parameters between groups over 8 years.

Results

At baseline, individuals on ART had significantly greater size of IPFP signal abnormalities (P = 0.008), higher signal intensities of SPFP (P = 0.015), higher effusion scores (P = 0.009), and lower subchondral cysts sum scores (P = 0.003) compared to the controls. No significant differences were found between the groups in T2-based cartilage parameters and WORMS scores for cartilage, meniscus, bone marrow edema patterns and ligaments (P > 0.05). Longitudinally, the HIV cohort had significantly higher global knee T2 entropy values (P = 0.047), more severe effusion (P = 0.001) but less severe subchondral cysts (P = 0.002) on average over 8 years.

Conclusions

Knees of individuals with HIV on ART had a more heterogeneous cartilage matrix, more severe synovitis and abnormalities of the IPFP and SPFP, which may increase the risk of incident knee osteoarthritis.

Electronic supplementary material

The online version of this article (10.1186/s12891-019-2573-5) contains supplementary material, which is available to authorized users.

The polyadenylation inhibitor cordycepin reduces pain, inflammation and joint pathology in rodent models of osteoarthritis

Clinically, osteoarthritis (OA) pain is significantly associated with synovial inflammation. Identification of the mechanisms driving inflammation could reveal new targets to relieve this prevalent pain state. Herein, a role of polyadenylation in OA synovial samples was investigated, and the potential of the polyadenylation inhibitor cordycepin (3’ deoxyadenosine) to inhibit inflammation as well as to reduce pain and structural OA progression were studied. Joint tissues from people with OA with high or low grade inflammation and non-arthritic post-mortem controls were analysed for the polyadenylation factor CPSF4 and inflammatory markers. Effects of cordycepin on pain behavior and joint pathology were studied in models of OA (intra-articular injection of monosodium iodoacetate in rats and surgical destabilisation of the medial meniscus in mice). Human monocyte-derived macrophages and a mouse macrophage cell line were used to determine effects of cordycepin on nuclear localisation of the inflammatory transcription factor NFĸB and polyadenylation factors (WDR33 and CPSF4). CPSF4 and NFκB expression were increased in synovia from OA patients with high grade inflammation. Cordycepin reduced pain behaviour, synovial inflammation and joint pathology in both OA models. Stimulation of macrophages induced nuclear localisation of NFĸB and polyadenylation factors, effects inhibited by cordycepin. Knockdown of polyadenylation factors also prevented nuclear localisation of NFĸB. The increased expression of polyadenylation factors in OA synovia indicates a new target for analgesia treatments. This is supported by the finding that polyadenylation factors are required for inflammation in macrophages and by the fact that the polyadenylation inhibitor cordycepin attenuates pain and pathology in models of OA.

Agkistrodon ameliorates pain response and prevents cartilage degradation in monosodium iodoacetate-induced osteoarthritic rats by inhibiting chondrocyte hypertrophy and apoptosis

ETHNOPHARMACOLOGICAL RELEVANCE

Osteoarthritis (OA), characterized by joint pain and cartilage degradation, is the most common form of joint disease worldwide but with no satisfactory therapy available. The ethanol extract of Agkistrodon acutus (EAA) has been widely used as a traditional Chinese medicine (TCM) for the treatment of arthralgia and inflammatory diseases, but there is no report regarding its efficacy on OA to date. Here, we determined the effects of EAA on the pain behavior and cartilage degradation in vivo and clarified its target genes and proteins associated with chondrocyte hypertrophy and apoptosis in vitro.

MATERIALS AND METHODS

In vivo OA model was established by intra-articular injection (1.5 mg) of monosodium iodoacetate (MIA) into rats and weekly treated by intra-articular administration of EAA at a dose range from 0.3 to 0.9 g/kg for four weeks. The pain behavior parameters, thermal withdrawal latency (TWL) and mechanical withdrawal threshold (MWT) were tested before and after the treatment. Then histopathologic, immunohistochemical and TUNEL analyses of the articular cartilage were conducted, followed by Mankin's scoring. In vitro, the effects of EAA on chondrocytes were evaluated via assays of cell viability, immunofluorescence, real time PCR, and Western blot. UPLC-MS was applied to determine the chemical composition of EAA.

RESULTS

The animal data showed that EEA not only attenuated the pain hypersensitivity but also blocked the cartilage degeneration by improving chondrocyte survival and suppressing chondrocyte apoptosis at a dose-dependent manner in OA rats. Furthermore, EAA remarkably restored the abnormal expression of collagen type II (Col2) and matrix metalloproteinase-13 (MMP13) in cartilage of OA rats. The cellular data showed that EAA significantly increased the cell viability of chondrocytes against OA-like damage and restored the abnormal expressions of Col2 and MMP13 in damaged chondrocytes. The molecular data showed that EAA significantly restored the abnormal mRNA expressions of Col2, Col10, MMP2 and MMP13 as well as the abnormal protein expressions of MMP13, PARP (total and cleaved) in chondrocytes under pathological condition. UPLC-MS analysis showed the known main components of EAA, including amino acides (glycine, L-aspartic acid, L-glutamic acid, and L-hydroxyproline), nucleoside (uridine), purines (xanthine and hypoxanthine), and pyrimidine (uracil).

CONCLUSIONS

Our data demonstrate that EAA exerts antinociceptive and chondroprotective effects on OA through suppressing chondrocyte hypertrophy and apoptosis with restoration of the molecular expressions of anabolism and catabolism in chondrocytes. It provides a promising TCM candidate of novel agent for OA therapy.

Osteoarthritis year in review 2018: clinical

Osteoarthritis (OA) is the most common joint disease in the world, with an age-associated increase in both incidence and prevalence. Clinical and epidemiologic research is crucial to better understand risk factors for disease, find the best treatments for symptoms, and identify therapies to slow down or even prevent disease progression. This paper is based on a systematic review of the osteoarthritis literature published in English between 2017/05/01 and 2018/04/25, with a focus on papers which have the potential to improve patient care, or which suggest novel areas for future research.

Osteoarthritis phenotypes and novel therapeutic targets

The success of disease-modifying osteoarthritis drug (DMOAD) development is still elusive. While there have been successes in preclinical and early clinical studies, phase 3 clinical trials have failed so far and there is still no approved, widely available DMOAD on the market. The latest research suggests that, among other causes, poor trial outcomes might be explained by the fact that osteoarthritis (OA) is a heterogeneous disease with distinct phenotypes. OA trials might be more successful if they would address and target a specific phenotype. The increasing availability of advanced techniques to detect particular OA characteristics expands the possibilities to distinguish between such potential OA phenotypes. Magnetic resonance imaging is among the key imaging techniques to stratify and monitor patients with changes in bone, cartilage and inflammation. Biochemical markers have mainly used as secondary parameters and could further delineate phenotypes. Moreover, post-hoc analyses of trial data have suggested the existence of distinct pain phenotypes and their relevance in the design of clinical trials. Although ongoing work in the field supports the concept of OA heterogeneity, this has not yet resulted in more effective treatment options. This paper reviews the current knowledge about potential OA phenotypes and suggests that combining patient clinical data, quantitative imaging, biochemical markers and utilizing data-driven approaches in patient selection and efficacy assessment will allow for more successful development of effective DMOADs.

MRI of synovitis and joint fluid

Synovitis and joint effusion are common manifestations of rheumatic disease and play an important role in the disease pathophysiology. Earlier detection and accurate assessment of synovial pathology, therefore, can facilitate appropriate clinical management and hence improve prognosis. Magnetic resonance imaging (MRI) allows unparalleled assessment of all joint structures and associated pathology. It has emerged as a powerful tool, which enables not only detection of synovitis and effusion, but also allows quantification, detailed characterization, and noninvasive monitoring of synovial processes. The purpose of this article is to summarize the pathophysiology of synovitis and to review the role of qualitative, semiquantitative, and quantitative MRI in the assessment of synovitis and joint fluid. We also discuss the utility of MRI as an outcome measure to assess treatment response, particularly with respect to osteoarthritis and rheumatoid arthritis. Emerging applications such as hybrid positron emission tomography / MRI and molecular imaging are also briefly discussed. Level of Evidence: 5 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2019.

Quantitative Signal Intensity Alteration in Infrapatellar Fat Pad Predicts Incident Radiographic Osteoarthritis: The Osteoarthritis Initiative

OBJECTIVE

To determine whether infrapatellar fat pad (IPFP) signal intensity measures are predictive of incident radiographic osteoarthritis (ROA) over 4 years in the Osteoarthritis Initiative study.

METHODS

Case knees (n = 355), as defined by incident ROA, were matched 1:1 with control knees, according to sex, age, and radiographic status. T2-weighted magnetic resonance images were assessed at P0 (the visit when incident ROA was observed on a radiograph), P1 (1 year prior to P0), and baseline and used to assess IPFP signal intensity semiautomatically. Conditional logistic regression analyses were performed to assess the risk of incident ROA associated with IPFP signal intensity alteration, after adjustment for covariates.

RESULTS

The mean age of the participants was 60.2 years, and most (66.7%) were female and overweight (mean body mass index 28.3 kg/m2 ). Baseline IPFP measures including the mean value and standard deviation of IPFP signal intensity, the mean value and standard deviation of IPFP high signal intensity, median and upper quartile values of IPFP high signal intensity, and the clustering effect of high signal intensity were associated with incident knee ROA over 4 years. All P1 IPFP measures were associated with incident ROA after 12 months. All P0 IPFP signal intensity measures were associated with ROA.

CONCLUSION

The quantitative segmentation of high signal intensity in the IPFP observed in our study confirms the findings of previous work based on semiquantitative assessment, suggesting the predictive validity of semiquantitative assessment of IPFP high signal intensity. The IPFP high signal intensity alteration could be an important imaging biomarker to predict the occurrence of ROA.

Effect of weight change on progression of knee OA structural features assessed by MRI in overweight and obese women

OBJECTIVE

To evaluate the effects of weight change on progression of knee osteoarthritis (OA) structural features by magnetic resonance imaging (MRI) in overweight and obese women without clinical knee OA.

DESIGN

347 participants from the Prevention of Knee Osteoarthritis in Overweight Females (PROOF) study were classified with latent class growth analysis into a subgroup with steady weight (n = 260; +0.1 ± 4.0 kg, +0.2 ± 4.4%), weight gain (n = 43; +8.6 ± 4.0 kg, +9.8 ± 4.1%) or weight loss (n = 44; -9.0 ± 7.2 kg, -9.8 ± 7.5%) over 2.5 years. Baseline and follow-up 1.5T MRIs were scored with MRI Osteoarthritis Knee Score (MOAKS) for progression of bone marrow lesions (BMLs), cartilage defects, osteophytes, meniscal abnormalities, meniscal extrusion and synovitis. Associations between subgroups and change in MRI features at knee-level were assessed using adjusted Generalized Estimating Equations.

RESULTS

687 knees from 347 women (median age 55.2 years, interquartile range (IQR) 5.5, median body mass index (BMI) 31.2 kg/m², IQR 5.3) were analyzed. Progression of synovitis was 18% in the weight gain vs 7% in the stable weight subgroup (OR 2.88; 95%CI 1.39-5.94). The odds for progression of patellofemoral (PF) BMLs and cartilage defects increased with 62% (OR 1.62; 95%CI 0.92-2.84) and 53% (OR 1.53; 95%CI 0.92-2.56) in the weight gain vs the stable weight subgroup.

CONCLUSIONS

In overweight and obese women, progression of synovitis increased more than 2.5 times in a weight gain compared to a stable weight subgroup over 2.5 years. Large effect sizes were also found for the difference in progression of PF BMLs and PF cartilage defects between the weight gain and stable weight subgroup.

Association of Changes in Effusion-Synovitis With Progression of Cartilage Damage Over Eighteen Months in Patients With Osteoarthritis and Meniscal Tear

OBJECTIVE

Synovitis is a feature of knee osteoarthritis (OA) and meniscal tear and has been associated with articular cartilage damage. This study was undertaken to examine the associations of baseline effusion-synovitis and changes in effusion-synovitis with changes in cartilage damage in a cohort with OA and meniscal tear.

METHODS

We analyzed data from the Meniscal Tear in Osteoarthritis Research (MeTeOR) trial of surgery versus physical therapy for treatment of meniscal tear. We performed semiquantitative grading of effusion-synovitis and cartilage damage on magnetic resonance imaging, and dichotomized effusion-synovitis as none/small (minimal) and medium/large (extensive). We assessed the association of baseline effusion-synovitis and changes in effusion-synovitis with changes in cartilage damage size and depth over 18 months, using Poisson regression models. Analyses were adjusted for patient demographic characteristics, treatment, and baseline cartilage damage.

RESULTS

We analyzed 221 participants. Over 18 months, effusion-synovitis was persistently minimal in 45.3% and persistently extensive in 21.3% of the patients. The remaining 33.5% of the patients had minimal synovitis on one occasion and extensive synovitis on the other. In adjusted analyses, patients with extensive effusion-synovitis at baseline had a relative risk (RR) of progression of cartilage damage depth of 1.7 (95% confidence interval [95% CI] 1.0-2.7). Compared to those with persistently minimal effusion-synovitis, those with persistently extensive effusion-synovitis had a significantly increased risk of progression of cartilage damage depth (RR 2.0 [95% CI 1.1-3.4]).

CONCLUSION

Our findings indicate that the presence of extensive effusion-synovitis is associated with subsequent progression of cartilage damage over 18 months. The persistence of extensive effusion-synovitis over time is associated with the greatest risk of concurrent cartilage damage progression.

Intra-Articular Injection of Fructus Ligustri Lucidi Extract Attenuates Pain Behavior and Cartilage Degeneration in Mono-Iodoacetate Induced Osteoarthritic Rats

Fructus Ligustri Lucidi (FLL) has been widely used as a traditional Chinese medicine (TCM) for treating soreness and weakness of waist and knees. It has potential for treating OA owing to its kidney-tonifying activity with bone-strengthening effects, but there is so far no report of its anti-OA effect. This study established a rat OA model by intra-articular (IA) injection of mono-iodoacetate (1.5 mg) and weekly treated by IA administration of FLL at 100 μg/mL for 4 weeks. Thermal withdrawal latency, mechanical withdrawal threshold, and spontaneous activity were tested for evaluation of pain behavior, and histopathological (HE, SO, and ABH staining) and immunohistochemical (Col2, Col10, and MMP13) analyses were conducted for observation of cartilage degradation. In vitro effect of FLL on chondrocytes was evaluated by MTT assay and qPCR analysis. Moreover, HPLC analysis was performed to determine its chemoprofile. The pain behavioral data showed that FLL attenuated joint pain hypersensitivity by increasing thresholds of mechanical allodynia and thermal hyperalgesia as well as spontaneous activity. The histopathological result showed that FLL reversed OA cartilage degradation by protecting chondrocytes and extracellular matrix in cartilage, and the immunohistochemical analysis revealed its molecular actions on protein expressions of MMP13, Col2, and Col10 in cartilage. The MTT assay showed its proliferative effects on chondrocytes, and qPCR assay clarified its mechanism associated with gene expressions of Mmp13, Col2, Col10, Adamts5, Aggrecan, and Runx2 in TNF-α treated chondrocytes. Our results revealed an anti-OA effect of FLL on pain behavior and cartilage degradation in OA rats and clarified a molecular mechanism in association with the suppression of chondrocyte hypertrophy and catabolism. IA FLL can be regarded as novel and promising option for OA therapy.

Comparing image analysis approaches versus expert readers: the relation of knee radiograph features to knee pain

OBJECTIVES

The relationship between radiographic evidence of osteoarthritis and knee pain has been weak. This may be because features that best discriminate knees with pain have not been included in analyses. We tested the correlation between knee pain and radiographic features taking into account both image analysis features and manual scores.

METHODS

Using data of the Multicentre Osteoarthritis Study, we tested in a cross-sectional design how well X-ray features discriminated those with frequent knee pain (one question at one time) or consistent frequent knee pain (three questions at three times during the 2 weeks prior to imaging) from those without it. We trained random forest models on features from two radiographic views for classification.

RESULTS

X-rays were better at classifying those with pain using three questions compared with one. When we used all manual radiographic features, the area under the curve (AUC) was 73.9%. Using the best model from automated image analyses or a combination of these and manual grades, no improvement over manual grading was found.

CONCLUSIONS

X-ray changes of OA are more strongly associated with repeated reports of knee pain than pain reported once. In addition, a fully automated system that assessed features not scored on X-ray performed no better than manual grading of features.

Bioinformatics analysis to identify key genes and pathways influencing synovial inflammation in osteoarthritis

Osteoarthritis (OA) is a chronic arthropathy that occurs in the middle-aged and elderly population. The present study aimed to identify gene signature differences between synovial cells from OA synovial membrane with and without inflammation, and to explain the potential mechanisms involved. The differentially expressed genes (DEGs) between 12 synovial membrane with inflammation and 12 synovial membrane without inflammation from the dataset GSE46750 were identified using the Gene Expression Omnibus 2R. The DEGs were subjected to enrichment analysis, protein-protein interaction (PPI) analysis and module analysis. The analysis results were compared with text-mining results. A total of 174 DEGs were identified. Gene Ontology enrichment results demonstrated that functional molecules encoded by the DEGs primarily had extracellular location, molecular functions predominantly involving ‘chemokine activity’ and ‘cytokine activity’, and were associated with biological processes, including ‘inflammatory response’ and ‘immune response’. The Kyoto Encyclopedia of Genes and Genomes results demonstrated that DEGS may function through pathways associated with ‘rheumatoid arthritis’, ‘chemokine signaling pathway’, ‘complement and coagulation cascades’, ‘TNF signaling pathway’, ‘intestinal immune networks for IgA production’, ‘cytokine-cytokine receptor interaction’, ‘allograft rejection’, ‘Toll-like receptor signaling pathway’ and ‘antigen processing and presentation’. The top 10 hub genes [interleukin (IL)6, IL8, matrix metallopeptidase (MMP)9, colony stimulating factor 1 receptor, FOS proto-oncogene, AP1 transcription factor subunit, insulin-like growth factor 1, TYRO protein tyrosine kinase binding protein, MMP3, cluster of differentiation (CD)14 and CD163] and four gene modules were identified from the PPI network using Cytoscape. In addition, text-mining was used to identify the commonly used drugs and their targets for the treatment of OA. It was initially verified whether the results of the present study were useful for the study of OA treatment targets and pathways. The present study provided insight for the molecular mechanisms of OA synovitis. The hub genes and associated pathways derived from analysis may be targets for OA treatment. IL8 and MMP9, which were validated by text-mining, may be used as molecular targets for the OA treatment, while other hub genes require further validation.

Effects of carrageenan induced synovitis on joint damage and pain in a rat model of knee osteoarthritis

OBJECTIVE

Knee osteoarthritis (OA) is associated with ongoing pain and joint damage that can be punctuated by acute flares of pain and inflammation. Synovitis in normal knees might resolve without long-term detriment to joint function. We hypothesised that osteoarthritis is associated with impaired resilience to inflammatory flares.

DESIGN

We induced synovitis by injecting carrageenan into rat knees with or without meniscal transection (MNX)-induced OA, and measured synovitis, weightbearing asymmetry (pain behaviour), and joint damage up to 35 days after OA induction (23 days after carrageenan-injection).

RESULTS

Carrageenan injection induced weightbearing asymmetry for 1 week, transient increase in knee diameter for 2 days, and a sustained increase in synovial macrophages, endothelial cell proliferation and vascular density compared with naive vehicle-injected controls. MNX surgery induced weightbearing asymmetry and histological evidence of OA. Carrageenan-injection in MNX-operated knees was followed for 2 days by increased weightbearing asymmetry compared either to MNX+vehicle or to sham+carrageenan groups. OA structural damage and synovitis at day 35 were greater in MNX+carrageenan compared to MNX+vehicle and sham+carrageenan groups. Carrageenan injection did not induce OA in Sham-operated knees.

CONCLUSION

Intra-articular injection of the pro-inflammatory compound carrageenan in OA and sham-operated control knees induced a short term increase in joint pain. Even though pain flares resolved in both groups and damage was not induced in sham-operated knees, carrageen injection exacerbated long-term joint damage in OA knees. OA knees display less resilience to inflammatory episodes. Preventing inflammatory flares may be particularly important in preventing symptoms and long term joint damage in OA.

Phenotypic instability of chondrocytes in osteoarthritis: on a path to hypertrophy

Articular chondrocytes are quiescent, fully differentiated cells responsible for the homeostasis of adult articular cartilage by maintaining cellular survival functions and the fine-tuned balance between anabolic and catabolic functions. This balance requires phenotypic stability that is lost in osteoarthritis (OA), a disease that affects and involves all joint tissues and especially impacts articular cartilage structural integrity. In OA, articular chondrocytes respond to the accumulation of injurious biochemical and biomechanical insults by shifting toward a degradative and hypertrophy-like state, involving abnormal matrix production and increased aggrecanase and collagenase activities. Hypertrophy is a necessary, transient developmental stage in growth plate chondrocytes that culminates in bone formation; in OA, however, chondrocyte hypertrophy is catastrophic and it is believed to initiate and perpetuate a cascade of events that ultimately result in permanent cartilage damage. Emphasizing changes in DNA methylation status and alterations in NF-κB signaling in OA, this review summarizes the data from the literature highlighting the loss of phenotypic stability and the hypertrophic differentiation of OA chondrocytes as central contributing factors to OA pathogenesis.

Relation of meniscus pathology to prevalence and worsening of patellofemoral joint osteoarthritis: the Multicenter Osteoarthritis Study

OBJECTIVE

To determine the relationship of meniscal damage to magnetic resonance imaging (MRI) features of compartment-specific patellofemoral joint (PFJ) osteoarthritis (OA) at baseline and 2 years later.

METHOD

Individuals from a prospective cohort of individuals aged 50-79 with or at risk of knee OA were included. At the 60-month and 84-month study visit, Whole-Organ MRI Score (WORMS) was used to assess meniscal tears and extrusions as well as cartilage damage and bone marrow lesions (BMLs) in the medial and lateral patella and trochlea. Worsening of structural features was defined as any increase in WORMS score from 60 to 84 months. Logistic regression was used to determine the cross-sectional and longitudinal relation of meniscus damage to features of compartment-specific PFJ OA.

RESULTS

Relative to knees without lateral meniscal pathology at baseline, those with grades 3-4 lateral meniscal tear and extrusion had greater risk of worsening of cartilage damage in the lateral PFJ 2 years later (Risk ratio: 1.7 [95% CI: 1.1-2.7) and (1.7 [1.2-2.5]), respectively. Relative to those without medial meniscal pathology at baseline, those with grades 1-2 (0.6 [0.4-0.9]) and 3-4 (0.7 [0.5-1.0]) medial meniscal tears had lower risk of worsening of BMLs in the medial PFJ 2 years later.

CONCLUSION

Meniscal tear and extrusion are associated with increased risk of medial and lateral PFJ OA and more severe meniscal pathology is associated with worsening of PFJ OA 2 years later. Lateral meniscal pathology appears to be more detrimental to the lateral PFJ.

Emerging Treatment Models in Rheumatology: Challenges for Osteoarthritis Trials

At a time when advancing understanding of osteoarthritis (OA) has created opportunities for new treatments, development of treatments has remained considerably behind advances in other rheumatic diseases. We describe elements of trial design and measurements that have inhibited success and offer suggestions that may help break the log jam. Among the problems with trials that include pain as an outcome measure are reliance on a single, non-optimal pain outcome, overestimation of likely effects of treatments on pain, and failure to identify patient subgroups most likely to respond to specific treatments. With regard to the use of structure modification as an outcome measure, demonstrating structure modification is often highly challenging, even with the use of magnetic resonance imaging. Many OA patients have advanced disease that is unlikely to respond to treatments that prevent cartilage loss. Further, prevention of cartilage loss and reduction of pain correlate weakly at best, and in at least some patients, reduction in pain may actually increase joint damage, making it impossible to demonstrate dual treatment effects on structure and pain in such scenarios. For structure outcomes, treatment effects on pain-sensitive structures such as bone and synovium may be more achievable than preventing cartilage loss. We suggest that changes in trial design related to some of these issues may increase the chances that new exciting and effective OA treatments will become available.

Changes in the structural features of osteoarthritis in a year of weight loss

OBJECTIVE

In patients undergoing bariatric surgery or medical management for obesity, we assessed whether those experiencing substantial weight loss had changes in innervated knee structures or in cartilage.

METHODS

Severely obese patients (body mass index (BMI) ≥35) with knee pain on most days were seen before bariatric surgery or medical weight management and at 1-year follow-up. Examinations included 3T MRI acquired at both time points for semi-quantitative scoring of bone marrow lesions (BML), synovitis, cartilage damage, and for quantitative measurement of cartilage thickness. Association of ≥20% vs <20% weight loss with change in semi-quantitative scores was evaluated using linear mixed-effects models, and that with cartilage thickness change used non-parametric and parametric methods. Sensitivity analyses tested different thresholds for weight loss, weight loss as a continuous measure, examined those with and without bariatric surgery, and with worse osteoarthritis (OA).

RESULTS

75 subjects (median age 49 years, 92% women) were included. At baseline, 61 subjects (81%) had Kellgren and Lawrence (KL) grade >0, and 16 (21%) had KL grade ≥3; 69 (92%) had cartilage damage. For BML, synovitis, and cartilage damage, the majority of knees had change in semi-quantitative scores of 0, and there was no difference between those with and without ≥20% weight loss. Similarly, in terms of cartilage thickness loss, in 14 of 16 sub-regions thickness loss was not associated with weight loss. Sensitivity analyses showed similar findings.

CONCLUSION

In middle-aged persons with mostly mild radiographic OA, structural features changed little over a year and weight loss was not associated with effects on structural changes.

Intraperitoneal injection of the SIRT1 activator SRT1720 attenuates the progression of experimental osteoarthritis in mice

Objectives

This study aimed to examine the effects of SRT1720, a potent SIRT1 activator, on osteoarthritis (OA) progression using an experimental OA model.

Methods

Osteoarthritis was surgically induced by destabilization of the medial meniscus in eight-week-old C57BL/6 male mice. SRT1720 was administered intraperitoneally twice a week after surgery. Osteoarthritis progression was evaluated histologically using the Osteoarthritis Research Society International (OARSI) score at four, eight, 12 and 16 weeks. The expression of SIRT1, matrix metalloproteinase 13 (MMP-13), a disintegrin and metalloproteinase with thrombospondin motifs-5 (ADAMTS-5), cleaved caspase-3, PARP p85, and acetylated nuclear factor (NF)-κB p65 in cartilage was examined by immunohistochemistry. Synovitis was also evaluated histologically. Primary mouse epiphyseal chondrocytes were treated with SRT1720 in the presence or absence of interleukin 1 beta (IL-1β), and gene expression changes were examined by real-time polymerase chain reaction (PCR).

Results

The OARSI score was significantly lower in mice treated with SRT1720 than in control mice at eight and 12 weeks associated with the decreased size of osteophytes at four and eight weeks. The delayed OA progression in the mice treated with SRT1720 was also associated with increased SIRT1-positive chondrocytes and decreased MMP-13-, ADAMTS-5-, cleaved caspase-3-, PARP p85-, and acetylated NF-κB p65-positive chondrocytes and decreased synovitis at four and eight weeks. SRT1720 treatment partially rescued the decreases in collagen type II alpha 1 (COL2A1) and aggrecan caused by IL-1β, while also reducing the induction of MMP-13 by IL-1β in vitro.

Conclusion

The intraperitoneal injection of SRT1720 attenuated experimental OA progression in mice, indicating that SRT1720 could be a new therapeutic approach for OA.Cite this article: K. Nishida, T. Matsushita, K. Takayama, T. Tanaka, N. Miyaji, K. Ibaraki, D. Araki, N. Kanzaki, T. Matsumoto, R. Kuroda. Intraperitoneal injection of the SIRT1 activator SRT1720 attenuates the progression of experimental osteoarthritis in mice. Bone Joint Res 2018;7:252-262. DOI: 10.1302/2046-3758.73.BJR-2017-0227.R1.

Relationship Between Patient-Reported Swelling and Magnetic Resonance Imaging-Defined Effusion-Synovitis in Patients With Meniscus Tears and Knee Osteoarthritis

OBJECTIVE

Synovitis is a prevalent feature in patients with knee osteoarthritis (OA) and meniscal tear and is associated with pain and cartilage damage. Patient-reported swelling is also prevalent in this population. The aim of this study was to investigate the cross-sectional association between patient-reported swelling and effusion-synovitis detected by magnetic resonance imaging (MRI) in patients with OA and meniscal tear.

METHODS

We used baseline data from a multicenter, randomized controlled trial, Meniscal Tear in Osteoarthritis Research (METEOR). MRI-identified effusion-synovitis, a proxy for effusion and synovitis on noncontrast MRIs, was graded as none/small versus medium/large. Using MRI-identified effusion-synovitis as the gold standard, we assessed the sensitivity, specificity, and positive predictive value of patient self-reported swelling in the previous week (none, intermittent, constant) to detect effusion and synovitis.

RESULTS

We analyzed data from 276 patients. Twenty-five percent of patients reported no swelling, 40% had intermittent swelling, and 36% had constant swelling. Fifty-two percent had MRI-identified medium/large-grade effusion-synovitis. As compared with MRI-identified effusion-synovitis, any patient-reported swelling (versus none) had a sensitivity of 84% (95% confidence interval [95% CI] 77-89), a specificity of 34% (95% CI 26-43), and a positive predictive value of 57% (95% CI 54-61). A history of constant swelling (versus none or intermittent) showed a sensitivity of 46% (95% CI 37-54), a specificity of 75% (95% CI 67-82), and a positive predictive value of 66% (95% CI 58-74).

CONCLUSION

We found that the sensitivity and specificity of patient-reported swelling were modest when compared with effusion-synovitis detected by MRI. These data urge caution against using patient-reported swelling as a proxy of inflammation manifesting as effusion-synovitis.

Bioluminescence and second harmonic generation imaging reveal dynamic changes in the inflammatory and collagen landscape in early osteoarthritis

Osteoarthritis (OA) is a leading cause of chronic disability whose mechanism of pathogenesis is largely elusive. Local inflammation is thought to play a key role in OA progression, especially in injury-associated OA. While multiple inflammatory cytokines are detected, the timing and extent of overall inflammatory activities in early OA and the manner by which joint inflammation correlates with cartilage structural damage are still unclear. We induced OA via destabilization of the medial meniscus (DMM) in NFκB luciferase reporter mice, whose bioluminescent signal reflects the activity of NFκB, a central mediator of inflammation. Bioluminescence imaging data showed that DMM and sham control joints had a similar surge of inflammation at 1-week post-surgery, but the DMM joint exhibited a delay in resolution of inflammation in subsequent weeks. A similar trend was observed with synovitis, which we found to be mainly driven by synovial cell density and inflammatory infiltration rather than synovial lining thickness. Interestingly, an association between synovitis and collagen structural damage was observed in early OA. Using Second Harmonic Generation (SHG) imaging, we analyzed collagen fiber organization in articular cartilage. Zonal differences in collagen fiber thickness and organization were observed as soon as OA initiated after DMM surgery, and persisted over time. Even at 1-week post-surgery, the DMM joint showed a decrease in collagen fiber thickness in the deep zone and an increase in collagen fiber disorganization in the superficial zone. Since we were able detect and quantify collagen structural changes very early in OA development by SHG imaging, we concluded that SHG imaging is a highly sensitive tool to evaluate pathological changes in OA. In summary, this study uncovered a dynamic profile of inflammation and joint cartilage damage during OA initiation and development, providing novel insights into OA pathology.

Novel Ex Vivo Human Osteochondral Explant Model of Knee and Spine Osteoarthritis Enables Assessment of Inflammatory and Drug Treatment Responses

Osteoarthritis of the knee and spine is highly prevalent in modern society, yet a disease-modifying pharmacological treatment remains an unmet clinical need. A major challenge for drug development includes selection of appropriate preclinical models that accurately reflect clinical phenotypes of human disease. The aim of this study was to establish an ex vivo explant model of human knee and spine osteoarthritis that enables assessment of osteochondral tissue responses to inflammation and drug treatment. Equal-sized osteochondral fragments from knee and facet joints (both n = 6) were subjected to explant culture for 7 days in the presence of a toll-like receptor 4 (TLR4) agonist and an inhibitor of transforming growth factor-beta (TGF-β) receptor type I signaling. Markers of inflammation, interleukin-6 (IL-6) and monocyte chemoattractant protein-1 (MCP-1), but not bone metabolism (pro-collagen-I) were significantly increased by treatment with TLR4 agonist. Targeting of TGF-β signaling resulted in a strong reduction of pro-collagen-I and significantly decreased IL-6 levels. MCP-1 secretion was increased, revealing a regulatory feedback mechanism between TGF-β and MCP-1 in joint tissues. These findings demonstrate proof-of-concept and feasibility of explant culture of human osteochondral specimens as a preclinical disease model, which might aid in definition and validation of disease-modifying drug targets.

Comparative analysis of quadriceps and hamstrings strength in knee osteoarthritis before and after total knee arthroplasty: a cross-sectional study

Objective

Compare the maximal isokinetic muscle strength of knee extensor and flexor muscles between patients with knee osteoarthritis and patients submitted to total knee arthroplasty.

Methods

Volunteers were divided into five groups (n = 20): Control; Ahlbäck I and II; Ahlbäck IV; six months after total knee arthroplasty; 12 months after total knee arthroplasty. An isokinetic knee strength evaluation was conducted for the quadriceps and hamstrings at 60°/s.

Results

Significant differences in the peak torque of the quadriceps and hamstrings were found among the groups (p < 0.001). The Ahlbäck IV, six-month, and 12-month postoperative groups demonstrated lower values when compared to the Control and Ahlbäck I and II groups. When percentage values were compared to the Control group, mean differences ranged from 7% to 41%.

Conclusion

Patients with healthy knees or early stage osteoarthritis have higher quadriceps and hamstrings strengths than those with a more advanced stage of the disease, even after knee replacement. These findings suggest that the traditional rehabilitation programs do not recover strength to levels observed in individuals without knee osteoarthritis.

Transcriptional profiling of synovium in a porcine model of early post-traumatic osteoarthritis

To determine the transcriptional profile of synovium during the molecular phase of post-traumatic osteoarthritis, anterior cruciate ligament transections (ACL) were performed in 36 Yucatan minipigs. Equal numbers were randomly assigned to no further treatment, ACL reconstruction or repair. Perimeniscal synovium for histopathology and RNA-sequencing was harvested at 1 and 4 weeks post-operatively and from six healthy control animals. Microscopic synovitis scores significantly worsened at 1 (p < 0.001) and 4 weeks (p = 0.003) post-surgery relative to controls, and were driven by intimal hyperplasia and increased stromal cellularity without inflammatory infiltrates. Synovitis scores were similar between no treatment, reconstruction, and repair groups (p ≥ 0.668). Relative to no treatment at 1 week, 88 and 367 genes were differentially expressed in the reconstruction and repair groups, respectively (227 and 277 at 4 weeks). Relative to controls and with the treatment groups pooled, 1,683 transcripts were concordantly differentially expressed throughout the post-surgery time-course. Affected pathways included, proteolysis_connective tissue degradation (including upregulations of protease-encoding MMP1, MMP13, and ADAMTS4), and development_cartilage development (including upregulations of ACAN, SOX9, and RUNX2), among others. Using linear regression, significant associations of post-surgery synovial expression levels of 20 genes with the articular cartilage glycosaminoglycan loss were identified. These genes were predominantly related to embryonic skeletal system development and included RUNX2. In conclusion, this study confirmed an increased synovial expression of genes that may serve as targets to prevent cartilage degradation, including MMP1, MMP13, and ADAMTS4, in knees with microscopic synovitis and cartilage proteoglycan loss. Attractive novel targets include regulators of embryonic developmental processes in synovium. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Osteoarthritis: Trauma vs Disease

Osteoarthritis (OA) is the most prevalent joint disease characterized by pain and degenerative lesions of the cartilage, subchondral bone, and other joint tissues. The causes of OA remain incompletely understood. Over the years, it has become recognized that OA is a multifactorial disease. In particular, aging and trauma are the main risk factors identified for the development of OA; however, other factors such as genetic predisposition, obesity, inflammation, gender and hormones, or metabolic syndrome contribute to OA development and lead to a more severe outcome. While this disease mainly affects people older than 60 years, OA developed after joint trauma affects all range ages and has a particular impact on young individuals and people who have highest levels of physical activity such as athletes. Traumatic injury to the joint often results in joint instability or intra-articular fractures which lead to posttraumatic osteoarthritis (PTOA). In response to injury, several molecular mechanisms are activated, increasing the production and activation of different factors that contribute to the progression of OA.In this chapter, we have focused on the interactions and contribution of the multiple factors involved in joint destruction and progression of OA. In addition, we overview the main changes and molecular mechanisms related to OA pathogenesis.

Comprehensive Expression Analysis of microRNAs and mRNAs in Synovial Tissue from a Mouse Model of Early Post-Traumatic Osteoarthritis

To better understand the molecular processes involved in driving osteoarthritis disease progression we characterized expression profiles of microRNAs (miRNA) and mRNAs in synovial tissue from a post-traumatic OA mouse model. OA was induced in 10–12 week old male C57BL6 mice by bilateral surgical destabilization of the medial meniscus (DMM). RNA isolated from the anterior synovium of mice at 1 and 6 weeks post-surgery was subject to expression profiling using Agilent microarrays and qPCR. OA severity was determined histologically. Anterior and posterior synovitis decreased with post-operative time after sham and DMM. No differences in synovitis parameters were evident between sham and DMM in the anterior synovium at either time. While expression profiling revealed 394 miRNAs were dysregulated between 1 and 6 week time-points in the anterior synovium, there were no significant changes in miRNA or mRNA expression between DMM and sham mice at both time-points. Bioinformatic analysis of the miRNAs and mRNAs differentially expressed in tandem with the resolution of anterior synovial inflammation revealed similar biological processes and functions, including organismal injury, connective tissue disorder and inflammatory responses. Our data demonstrates that early OA-specific patterns of synovial miRNAs or mRNAs dysregulation could not be identified in this model of post-traumatic OA.

Modulation of cartilage's response to injury: Can chondrocyte apoptosis be reversed?

Osteoarthritis is characterized by a chronic, progressive and irreversible degradation of the articular cartilage associated with joint inflammation and a reparative bone response. More than 100 million people are affected by this condition worldwide with significant health and welfare costs. Our available treatment options in osteoarthritis are extremely limited. Chondral or osteochondral grafts have shown some promising results but joint replacement surgery is by far the most common therapeutic approach. The difficulty lies on the limited regeneration capacity of the articular cartilage, poor blood supply and the paucity of resident progenitor stem cells. In addition, our poor understanding of the molecular signalling pathways involved in the senescence and apoptosis of chondrocytes is a major factor restricting further progress in the area. This review focuses on molecules and approaches that can be implemented to delay or even rescue chondrocyte apoptosis. Ways of modulating the physiologic response to trauma preventing chondrocyte death are proposed. The use of several cytokines, growth factors and advances made in altering several of the degenerative genetic pathways involved in chondrocyte apoptosis and degradation are also presented. The suggested approaches can help clinicians to improve cartilage tissue regeneration.

Immune Contributions to Osteoarthritis

PURPOSE OF THE REVIEW

Mounting evidence supports a role of low-grade inflammation in the pathophysiology of osteoarthritis (OA). We review and discuss the role of synovitis, complement activation, cytokines, and immune cell population in OA.

RECENT FINDINGS

Using newer imaging modalities, synovitis is found in the majority of knees with OA. Complement activation and pro-inflammatory cytokines play a significant role in the development of cartilage destruction and synovitis. Immune cell infiltration of OA synovial tissue by sub-populations of T cells and activated macrophages correlates with OA disease progression and pain. The innate and acquired immune system plays a key role in the low-grade inflammation found associated with OA. Targets of these pathways my hold promise for future disease-modifying osteoarthritis drugs (DMOADs).

The effect of pregabalin or duloxetine on arthritis pain: a clinical and mechanistic study in people with hand osteoarthritis

Osteoarthritis (OA) is the most prevalent arthritis worldwide and is characterized by chronic pain and impaired physical function. We hypothesized that heightened pain in hand OA could be reduced with duloxetine or pregabalin. In this prospective, randomized clinical study, we recruited 65 participants, aged 40–75 years, with a Numerical Rating Scale (NRS) for pain of at least 5. Participants were randomized to one of the following three groups: duloxetine, pregabalin, and placebo. The primary endpoint was the NRS pain score, and the secondary endpoints included the Australian and Canadian Hand Osteoarthritis Index (AUSCAN) pain, stiffness, and function scores and quantitative sensory testing by pain pressure algometry. After 13 weeks, compared to placebo, ANOVA found significant differences between the three groups (P=0.0078). In the intention-to-treat analysis, the pregabalin group showed improvement for NRS pain (P=0.023), AUSCAN pain (P=0.008), and AUSCAN function (P=0.009), but no difference between duloxetine and placebo (P>0.05) was observed. In the per protocol analysis, NRS pain was reduced for pregabalin (P<0.0001) and duloxetine (P=0.029) compared to placebo. We conclude that centrally acting analgesics improve pain outcomes in people with hand arthritis, offering new treatment paradigms for OA pain.

What drives osteoarthritis?-synovial versus subchondral bone pathology

Subchondral bone and the synovium play an important role in the initiation and progression of OA. MRI often permits an early detection of synovial hypertrophy and bone marrow lesions, both of which can precede cartilage damage. Newer imaging modalities including CT osteoabsorptiometry and hybrid SPECT-CT have underlined the importance of bone in OA pathogenesis. The subchondral bone in OA undergoes an uncoupled remodelling process, which is notably characterized by macrophage infiltration and osteoclast formation. Concomitant increased osteoblast activity leads to spatial remineralization and osteosclerosis in end-stage disease. A plethora of metabolic and mechanical factors can lead to synovitis in OA. Synovial tissue is highly vascularized and thus exposed to systemic influences such as hypercholesterolaemia or low grade inflammation. This review aims to describe the current understanding of synovitis and subchondral bone pathology and their connection in OA.