[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Histology](https://durgical.com/en/histology/) › [Connective tissue, cartilage and bone](https://durgical.com/en/histology/#a-connective) › Synovial joints: capsule, synovial membrane and articular cartilage [Histology](https://durgical.com/en/histology/) · [Connective tissue, cartilage and bone](https://durgical.com/en/histology/#a-connective) # Synovial joints: capsule, synovial membrane and articular cartilage - Tissue Movable joints are sealed bags of slippery fluid: a fibrous capsule, a thin lining that makes the fluid, and smooth cartilage on the bone ends. Updated 2026-11-01 **See it in 3D:** [Femoral cartilage](https://durgical.com/en/anatomy/articular-cartilage-of-femur/) · [Medial meniscus](https://durgical.com/en/anatomy/medial-meniscus/) · [Lateral meniscus](https://durgical.com/en/anatomy/lateral-meniscus/) ## Key points - The synovial lining is connective tissue, not epithelium: no basal lamina, no junctions. - Type A = macrophage-like (monocyte-derived); type B = fibroblast-like, makes hyaluronan. - Articular cartilage is hyaline, lacks perichondrium and is fed by synovial fluid. - RA begins in the synovium (pannus); OA begins in the cartilage (osteophytes). ## What it is A synovial (diarthrotic) joint is a cavity closed by a fibrous capsule and lined by the synovial membrane, a specialised connective tissue rather than an epithelium. Two kinds of synoviocytes keep the fluid clean and slippery, and the hyaline cartilage on the bone ends has no perichondrium and no blood vessels, so it lives on that fluid. Rheumatoid arthritis starts in the synovium; osteoarthritis starts in the cartilage. ## Structure - Fibrous capsule: dense connective tissue continuous with the periosteum, reinforced by ligaments. - Synovial membrane: folds and villi of loose or fatty connective tissue with many fenestrated capillaries; its surface layer of one to a few cells looks like an epithelium but has no basal lamina and no cell junctions. - Articular cartilage: hyaline cartilage with no perichondrium; collagen fibres run in arches whose tops face the joint surface. - Menisci and labra (where present): fibrocartilage pads attached to the capsule. ## Function - Type B cells make hyaluronan and lubricin that keep the fluid viscous and the surfaces gliding. - Type A cells clear wear debris from the fluid and help control joint inflammation. - Synovial fluid feeds the avascular cartilage with nutrients and oxygen; loading and unloading pumps it in and out. ## Synoviocytes and the two classic arthritides | Item | Origin or where it starts | What you see | Key point | | --- | --- | --- | --- | | Type A synoviocyte | Blood monocytes (bone marrow) | Rounded macrophage-like cells at the surface | Phagocytose debris; about a quarter of lining cells | | Type B synoviocyte | Local mesenchyme (fibroblast-like) | Spindle cells with abundant rough ER | Secrete hyaluronan and lubricin into the fluid | | [Rheumatoid arthritis](https://durgical.com/en/conditions/rheumatoid-arthritis/) | Synovium (autoimmune) | Thick villous synovium full of lymphocytes and plasma cells; pannus erodes cartilage and bone at the margins | Symmetric small joints; morning stiffness over an hour; RF and anti-CCP | | [Osteoarthritis](https://durgical.com/en/conditions/knee-osteoarthritis/) | Articular cartilage (wear and repair failure) | Fibrillated, thinned cartilage; eburnated bone, subchondral cysts, osteophytes | Weight-bearing joints; stiffness under 30 minutes; mild synovitis only | ## Clinical notes - Septic arthritis: bacteria reach the vascular synovium through the blood; Staphylococcus aureus is the usual cause in adults. - Gout: urate crystals in synovial fluid are needle-shaped and negatively birefringent; pseudogout crystals are rhomboid and positively birefringent. - Because adult cartilage has no vessels and few dividing chondrocytes, deep cartilage defects heal poorly, usually with fibrocartilage. ## In the lab - Joint aspiration: fluid viscosity, cell count, Gram stain, culture and polarised-light crystal search separate inflammatory, septic and crystal arthritis. ## Memory aid A for «Aspirator» (eats debris), B for «Builder» (builds the slippery fluid). ## Test yourself Think of the answer, then tap the question to see it. ## Why is the synovial lining not classified as an epithelium? Its surface cells sit on no basal lamina and are not joined by cell junctions; it is a specialised connective tissue. ## Which synoviocyte secretes hyaluronan into the joint fluid? The type B (fibroblast-like) synoviocyte, of mesenchymal origin. ## How is articular cartilage nourished? By diffusion from the synovial fluid, helped by loading; it has no blood vessels and no perichondrium. ## What tissue forms the pannus in rheumatoid arthritis? Inflamed, proliferating synovium with lymphocytes, plasma cells and new vessels that spreads over and erodes cartilage and bone. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/histology/synovial-joints-capsule-synovial-membrane-and-articular-cartilage/) ## See it in 3D The structures of Durgical's 3D anatomy where it is found. - [Femoral cartilage](https://durgical.com/en/anatomy/articular-cartilage-of-femur/) - [Medial meniscus](https://durgical.com/en/anatomy/medial-meniscus/) - [Lateral meniscus](https://durgical.com/en/anatomy/lateral-meniscus/) ## Related - [Cartilage: hyaline, elastic, fibrocartilage](https://durgical.com/en/histology/cartilage-hyaline-elastic-fibrocartilage/) - [Connective tissue proper: cells and fibres](https://durgical.com/en/histology/connective-tissue-proper-cells-and-fibres/) - [Extracellular matrix: collagen types, elastin, ground substance](https://durgical.com/en/histology/extracellular-matrix-collagen-types-elastin-ground-substance/) - [Bone tissue: cells, compact and spongy bone](https://durgical.com/en/histology/bone-tissue-cells-compact-and-spongy-bone/) ## Related conditions - [Rheumatoid arthritis](https://durgical.com/en/conditions/rheumatoid-arthritis/) - [Knee Osteoarthritis](https://durgical.com/en/conditions/knee-osteoarthritis/) - [Hip Osteoarthritis](https://durgical.com/en/conditions/hip-osteoarthritis/) - [Septic Arthritis of the Knee](https://durgical.com/en/conditions/septic-arthritis-of-the-knee/) - [Gout](https://durgical.com/en/conditions/gout/) - [Meniscus Tear](https://durgical.com/en/conditions/meniscus-tear/) ## Microorganisms - [Staphylococcus aureus](https://durgical.com/en/microbiology/staphylococcus-aureus/) [← All of histology](https://durgical.com/en/histology/) Educational content on normal microscopic structure and its clinical relevance; no substitute for studying slides or for a health professional's advice. Sources: [9.4 Synovial Joints](https://openstax.org/books/anatomy-and-physiology-2e/pages/9-4-synovial-joints) (OpenStax (Rice University), 2022); [Rheumatoid arthritis: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000431.htm) (MedlinePlus, US National Library of Medicine, 2026); [Osteoarthritis: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000423.htm) (MedlinePlus, US National Library of Medicine, 2026). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/histology/synovial-joints-capsule-synovial-membrane-and-articular-cartilage/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/histology/synovial-joints-capsule-synovial-membrane-and-articular-cartilage/