Definition and research guide
This page combines a MeSH definition, publication statistics and selected research abstracts. It is a starting point for reading the literature, not a medical textbook or a systematic evidence review.
Content available: 4 complete abstracts (801 words), 10 references. Full article text is not stored or reproduced here; follow the PMID, DOI or PMC links to read the original sources and their access terms.
Definition
The clear, viscous fluid secreted by the synovial membrane. It contains mucin, albumin, fat, and mineral salts and serves to lubricate joints.
Definition: NLM Medical Subject Headings (MeSH) scope note (Public domain (U.S. National Library of Medicine); attribution requested). View the MeSH record.
Also known as: Fluids, Synovial; Fluid, Synovial; Synovial Fluids; Synovia.
Where it fits in the MeSH classification
- Broader topics
- Synovial Membrane; Extracellular Fluid
Related concepts
Research landscape
PubMed indexes 14,514 records tagged with the MeSH heading “Synovial Fluid” (counts retrieved 2026-10-31). 1,642 of them (11.3%) were published from 2020 onward, and the busiest period so far is through 1999 with 7,479 records.
Reviews account for 1,011 records (7.0%) and meta-analyses for 59. Randomized controlled trials number 192 (1.3%) as a share of all records on the topic. Randomized trials make up only a small share of this literature, so much of what is known comes from laboratory, observational or descriptive work.
Show the data
| Period | Records |
|---|---|
| through 1999 | 7,479 |
| 2000-2009 | 2,395 |
| 2010-2019 | 2,998 |
| 2020 onward | 1,642 |
Publication-type chart data
| Type | Records | Share |
|---|---|---|
| Reviews | 1,011 | 7.0% |
| Meta-analyses | 59 | 0.4% |
| Randomized controlled trials | 192 | 1.3% |
Method: PubMed query "Synovial Fluid"[MeSH Terms] with publication-type and date filters, retrieved 2026-10-31.
Reading the evidence in anatomy and physiology
Anatomy describes how body structures are built and physiology describes how they normally work, so most findings here are descriptive or mechanistic rather than evidence about treatment. Much of what is known comes from dissection, imaging, tissue studies and experiments in animals, and measurements in healthy volunteers can differ from those in people with disease or at different ages. Normal ranges vary between individuals and populations. Check whether a result was measured in people or in another species, the age and health of the participants, and the method used.
Evidence from open-access studies
These open-access studies come from PubMed’s best-match results for this heading (papers whose main topic it is), ranked here by citation count, with one recent addition. Each abstract is reproduced in full under its recorded open licence so that you can read the authors’ own words. They illustrate the literature; they are not a systematic summary of it. Citation counts measure attention, not reliability or clinical benefit.
Rheumatoid Arthritis Synovial Fluid Neutrophils Drive Inflammation Through Production of Chemokines, Reactive Oxygen Species, and Neutrophil Extracellular Traps [1]
Abstract reading summary — source excerpts
- Opening excerpt
- Rheumatoid arthritis (RA) is a chronic inflammatory disorder affecting synovial joints.
- Closing excerpt
- We propose that this activated SF neutrophil phenotype contributes to the chronic inflammation and progressive damage to cartilage and bone observed in patients with RA.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (170 words)
Rheumatoid arthritis (RA) is a chronic inflammatory disorder affecting synovial joints. Neutrophils are believed to play an important role in both the initiation and progression of RA, and large numbers of activated neutrophils are found within both synovial fluid (SF) and synovial tissue from RA joints. In this study we analyzed paired blood and SF neutrophils from patients with severe, active RA (DAS28>5.1, n=3) using RNA-seq. 772 genes were significantly different between blood and SF neutrophils. IPA analysis predicted that SF neutrophils had increased expression of chemokines and ROS production, delayed apoptosis, and activation of signaling cascades regulating the production of NETs. This activated phenotype was confirmed experimentally by incubating healthy control neutrophils in cell-free RA SF, which was able to delay apoptosis and induce ROS production in both unprimed and TNFα primed neutrophils (pvia recruitment and activation of both innate and adaptive immune cells. We propose that this activated SF neutrophil phenotype contributes to the chronic inflammation and progressive damage to cartilage and bone observed in patients with RA.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 33469455 · DOI · PMC7813679
Single-cell sequencing reveals clonal expansions of pro-inflammatory synovial CD8 T cells expressing tissue-homing receptors in psoriatic arthritis [2]
Abstract reading summary — source excerpts
- Opening excerpt
- Psoriatic arthritis (PsA) is a debilitating immune-mediated inflammatory arthritis of unknown pathogenesis commonly affecting patients with skin psoriasis.
- Closing excerpt
- Our data thus provide a quantitative molecular insight into the cellular immune landscape of psoriatic arthritis.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (148 words)
Psoriatic arthritis (PsA) is a debilitating immune-mediated inflammatory arthritis of unknown pathogenesis commonly affecting patients with skin psoriasis. Here we use complementary single-cell approaches to study leukocytes from PsA joints. Mass cytometry demonstrates a 3-fold expansion of memory CD8 T cells in the joints of PsA patients compared to peripheral blood. Meanwhile, droplet-based and plate-based single-cell RNA sequencing of paired T cell receptor alpha and beta chain sequences show pronounced CD8 T cell clonal expansions within the joints. Transcriptome analyses find these expanded synovial CD8 T cells to express cycling, activation, tissue-homing and tissue residency markers. T cell receptor sequence comparison between patients identifies clonal convergence. Finally, chemokine receptor CXCR3 is upregulated in the expanded synovial CD8 T cells, while two CXCR3 ligands, CXCL9 and CXCL10, are elevated in PsA synovial fluid. Our data thus provide a quantitative molecular insight into the cellular immune landscape of psoriatic arthritis.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 32958743 · DOI · PMC7505844
Synovial fluid monocyte/macrophage subsets and their correlation to patient-reported outcomes in osteoarthritic patients: a cohort study [3]
Abstract reading summary — source excerpts
- Opening excerpt
- BackgroundChronic, low-grade inflammation of the synovium (synovitis) is a hallmark of osteoarthritis (OA), thus understanding of OA immunobiology, mediated by immune effectors, is of importance.
- Closing excerpt
- Knee OA SF MΦ subsets could serve as knee OA function biomarkers and as targets of novel therapeutics.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (334 words)
BackgroundChronic, low-grade inflammation of the synovium (synovitis) is a hallmark of osteoarthritis (OA), thus understanding of OA immunobiology, mediated by immune effectors, is of importance. Specifically, monocytes/macrophages (MΦs) are known to be abundantly present in OA joints and involved in OA progression. However, different subsets of OA MΦs have not been investigated in detail, especially in terms of their relationship with patient-reported outcome measures (PROMs). We hypothesized that levels of synovial fluid (SF) MΦ subsets are indicative of joint function and quality of life in patients with OA, and can therefore serve as biomarkers and therapeutic targets for OA.MethodsIn this cohort study, synovial fluid leukocytes (SFLs, N = 86) and peripheral blood mononuclear cells (n = 53) from patients with knee OA were characterized. Soluble MΦ receptors and chemokine (sCD14, sCD163, CCL2, CX3CL1) levels were detected in SF using immunoassays. Linear models, adjusted for sex, age and body mass index, were used to determine associations between SF MΦs and soluble factors with PROMs (N = 83). Pearson correlation was calculated to determine correlation between MΦ subsets, T cells and soluble factors.ResultsSF MΦs were the most abundant SFLs. Within these, the double-positive CD14+CD16+-MΦ subset is enriched in knee OA SF compared to the circulation. Importantly, MΦ subset ratios correlated with PROMs, specially stiffness, function and quality of life. Interestingly, the SF CD14+CD16+-MΦ subset ratio correlated with SF chemokine (C-C motif) ligand 2 (CCL2) levels but not with levels of sCD163 or sCD14; we found no association between PROMs and either SF CCL2, sCD163, sCD14 or CX3CL1 (which was below detection levels). All SF MΦs displayed high levels of HLA-DR, suggesting an activated phenotype. Correlation between OA SF MΦ subsets and activated CD4+ T cell subsets suggests modulation of CD4+ T cell activation by MΦs.ConclusionSF MΦ subsets are associated with knee OA PROMs and display an activated phenotype, which may lead to modulation of CD4+ T cell activation. Knee OA SF MΦ subsets could serve as knee OA function biomarkers and as targets of novel therapeutics.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 30658702 · DOI · PMC6339358
Large-scale molecular endotype discovery in synovial fluid reveals osteoarthritis as a single biological continuum [4]
Abstract reading summary — source excerpts
- Opening excerpt
- Knee osteoarthritis affects 40% of people during their lifetime, significantly impacting societies worldwide.
- Closing excerpt
- These findings support knee OA as a biological continuum, identify common and phenotype-enriched targetable pathways, and a rationale for stratification in clinical trial design.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (149 words)
Knee osteoarthritis affects 40% of people during their lifetime, significantly impacting societies worldwide. Its molecular pathogenesis remains poorly understood and variable clinical phenotypes suggest it may be more than one disease. We established Synovial fluid To detect Endotypes by Unbiased Proteomics in OA (STEpUP OA) to search for molecular endotypes in knee OA synovial fluid, and to reveal key pathobiological pathways across 1361 individuals with knee OA. Using unsupervised clustering, a single cluster representing a biological continuum is observed, primarily driven by "Epithelial Mesenchymal Transition". Distinct molecular endotypes are not detected. "Angiogenesis", "Complement" and "Coagulation" are enriched for after stratification by clinical phenotype (obesity status, biological sex). Complement and coagulation are associated with the inflammatory marker, C-reactive protein. Associations with patient-reported knee pain are weaker. These findings support knee OA as a biological continuum, identify common and phenotype-enriched targetable pathways, and a rationale for stratification in clinical trial design.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 42230587 · DOI · PMC13230806
Key reviews and meta-analyses
The most cited review-type papers among PubMed’s best-match results for this heading, listed with bibliographic details only. Follow the links for the full text and access terms.
- Research article Lubrication of Articular Cartilage [5]
- Research article Effector Functions of CD4+ T Cells at the Site of Local Autoimmune Inflammation-Lessons From Rheumatoid Arthritis [6]
- Research article Functions of hyaluronan [7]
- Research article The value of synovial fluid assays in the diagnosis of joint disease: a literature survey [8]
- Research article A systems biology approach to synovial joint lubrication in health, injury, and disease [9]
- Research article Synovial Fluid Biomarkers for the Diagnosis of Periprosthetic Joint Infection: A Systematic Review and Meta-Analysis [10]
References
- Wright HL, Lyon M, Chapman EA, Moots RJ, Edwards SW. Rheumatoid Arthritis Synovial Fluid Neutrophils Drive Inflammation Through Production of Chemokines, Reactive Oxygen Species, and Neutrophil Extracellular Traps. . 2020. PMID 33469455 · DOI · PMC7813679
- Penkava F, Velasco-Herrera MDC, Young MD, Yager N, Nwosu LN, Pratt AG, et al.. Single-cell sequencing reveals clonal expansions of pro-inflammatory synovial CD8 T cells expressing tissue-homing receptors in psoriatic arthritis. . 2020. PMID 32958743 · DOI · PMC7505844
- Gómez-Aristizábal A, Gandhi R, Mahomed NN, Marshall KW, Viswanathan S. Synovial fluid monocyte/macrophage subsets and their correlation to patient-reported outcomes in osteoarthritic patients: a cohort study. . 2019. PMID 30658702 · DOI · PMC6339358
- Perry TA, Deng Y, Hulley PA, Maciewicz RA, Mitchelmore J, Larsson S, et al.. Large-scale molecular endotype discovery in synovial fluid reveals osteoarthritis as a single biological continuum. . 2026. PMID 42230587 · DOI · PMC13230806
- Jahn S, Seror J, Klein J. Lubrication of Articular Cartilage. Annu Rev Biomed Eng. 2016. PMID 27420572 · DOI
- Chemin K, Gerstner C, Malmström V. Effector Functions of CD4+ T Cells at the Site of Local Autoimmune Inflammation-Lessons From Rheumatoid Arthritis. Front Immunol. 2019. PMID 30915067 · DOI · PMC6422991
- Laurent TC, Laurent UB, Fraser JR. Functions of hyaluronan. Ann Rheum Dis. 1995. PMID 7794055 · DOI · PMC1005610
- Swan A, Amer H, Dieppe P. The value of synovial fluid assays in the diagnosis of joint disease: a literature survey. Ann Rheum Dis. 2002. PMID 12006320 · DOI · PMC1754135
- Hui AY, McCarty WJ, Masuda K, Firestein GS, Sah RL. A systems biology approach to synovial joint lubrication in health, injury, and disease. Wiley Interdiscip Rev Syst Biol Med. 2012. PMID 21826801 · DOI · PMC3593048
- Lee YS, Koo KH, Kim HJ, Tian S, Kim TY, Maltenfort MG, et al.. Synovial Fluid Biomarkers for the Diagnosis of Periprosthetic Joint Infection: A Systematic Review and Meta-Analysis. J Bone Joint Surg Am. 2017. PMID 29257013 · DOI
About this article
- Sources
- NLM Medical Subject Headings (definition, synonyms); NCBI PubMed (counts, identifiers); Europe PMC (open-access abstracts and citation counts).
- Verification
- Every reference was resolved against PubMed on 2026-10-31; title, year and DOI matched.
- Review state
- automated source verified; no human expert review has been recorded yet.
- Version
- 1, last updated 2026-10-31.
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Evidence strength
EvidenceHelix's computed view of the study designs behind this topic: how common meta-analyses, randomized trials and reviews are, how recent the literature is, and a plain-language reading. It describes the design mix of the literature. It is not a quality appraisal of any study, and it is not medical advice.