Synovial fluid

Synovial fluid

Synovial fluid is a thick, stringy fluid found in the cavities of synovial joints. With its egg-like consistency ("synovial" partially derives from "ovum", Latin for egg), synovial fluid reduces friction between the articular cartilage and other tissues in joints to lubricate and cushion them during movement.


The inner membrane of synovial joints is called the synovial membrane and secretes synovial fluid into the joint cavity. This fluid forms a thin layer (roughly 50 μm) at the surface of cartilage, but also seeps into microcavities and irregularities in the articular cartilage surface, filling all empty space [] . The fluid within articular cartilage effectively serves as a synovial fluid reserve. During movement, the synovial fluid held within the cartilage is squeezed out mechanically to maintain a layer of fluid on the cartilage surface (so-called "weeping lubrication").


Synovial tissue is composed of vascularized connective tissue that lacks a basement membrane. Two cells type (type A and type B) are present: type B produce synovial fluid. Synovial fluid is made of hyaluronic acid and lubricin, proteinases and collagenases. Synovial fluid exhibits non-Newtonian flow characteristics. The viscosity coefficient is not a constant, the fluid is not linearly viscous, and its viscosity increases as the shear rate decreases.

Normal synovial fluid contains 3-4 mg/ml hyaluronan (hyaluronic acid), a polymer of disaccharides composed of D-glucuronic acid and D-N-acetylglucosamine joined by alternating beta-1,4 and beta-1,3 glycosidic bonds [ [ GlycoForum / Science of Hyaluronan-1 ] ] . Hyaluronan is synthesized by the synovial membrane and secreted into the joint cavity to increase the viscosity and elasticity of articular cartilages and lubricate the surfaces between synovium and cartilage. [ [ Arthritis - UW Medicine - Department of Orthopaedics and Sports Medicine ] ]

Synovial fluid also contains lubricin secreted by synovial cells. It is chiefly responsible for so-called boundary-layer lubrication, which reduces friction between opposing surfaces of cartilage. There is also some evidence that it helps regulate synovial cell growth. [ [ Arthritis Research & Therapy | Full text | Delineating biologic pathways involved in skeletal growth and homeostasis through the study of rare Mendelian diseases that affect bones and joints ] ]

Health and disease


Synovial fluid can be collected by syringe in a procedure termed arthrocentesis, also known as joint aspiration.


Synovial fluid can be classified into normal, noninflammatory, inflammatory, septic, and hemorrhagic:


Many synovial fluid types are associated with specific diagnoses [ [ Lupus Anticoagulant ] ] [ [ American College of Rheumatology ] ] :

* Noninflammatory (Group I)
** Osteoarthritis, degenerative joint disease
** Trauma
** Rheumatic fever
** Chronic gout or pseudogout
** Scleroderma
** Polymyositis
** Systemic lupus erythematosus
** Erythema nodosum
** Neuropathic arthropathy (with possible hemorrhage)
** Sickle-cell disease
** Hemochromatosis
** Acromegaly
** Amyloidosis
* Inflammatory (Group II)
** Rheumatoid arthritis
** Reactive arthritis
** Psoriatic arthritis
** Acute rheumatic fever
** Acute gout or pseuodgout
** Scleroderma
** Polymyositis
** Systemic lupus erythematosus
** Ankylosing spondylitis
** Inflammatory bowel disease arthritis
** Infection (viral, fungal, bacterial) including Lyme disease
** Acute crystal synovitis
* Septic (Group III)
** Pyogenic bacterial infection
** Septic arthritis
* Hemorrhagic
** Trauma
** Tumors
** Hemophilia/coagulopathy
** Scurvy
** Ehlers-Danlos syndrome
** Neuropathic arthropathy

Joints cracking

When two parts forming a joint are pulled away from each other, the joint capsule increases in volume but the synovial fluid in the capsule no longer fills it all. Gases dissolved in the fluid quickly fill the empty space causing a sharp cracking sound. [ [ Howstuffworks "What makes your knuckles pop?" ] ] The general term for this is cavitation.



External links

* Warman W. "Delineating biologic pathways involved in skeletal growth and homeostasis through the study of rare Mendelian diseases that affect bones and joints." "Arthritis Res. Ther." 2003, 5(Suppl 3):5 []
* [ Hyaluronan: structure and properties]
* [ Normal joint structure] , from University College London

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Look at other dictionaries:

  • Synovial fluid — Synovial Syn*o vi*al, a. [Cf. F. synovial.] (Anat.) Of or pertaining to synovia; secreting synovia. [1913 Webster] {Synovial capsule}, a closed sac of synovial membrane situated between the articular surfaces at diarthrodial joints. {Synovial… …   The Collaborative International Dictionary of English

  • synovial fluid — noun viscid lubricating fluid secreted by the membrane lining joints and tendon sheaths etc. • Syn: ↑synovia • Derivationally related forms: ↑synovial (for: ↑synovia) • Hypernyms: ↑secretion …   Useful english dictionary

  • Synovial fluid — The slippery fluid that lubricates joints and provides nutrients to the cartilage. Also known as the synovia. * * * synovial fluid n a transparent viscid lubricating fluid secreted by a membrane of an articulation, bursa, or tendon sheath called… …   Medical dictionary

  • synovial fluid — viscous fluid secreted by a synovial membrane and used to lubricate joints (Anatomy) …   English contemporary dictionary

  • synovial fluid — noun Date: 1846 a transparent viscid lubricating fluid secreted by a membrane of an articulation, bursa, or tendon sheath …   New Collegiate Dictionary

  • synovial fluid — synovia …   The new mediacal dictionary

  • synovial fluid — UK [saɪˌnəʊvɪəl ˈfluːɪd] / US [saɪˌnoʊvɪəl ˈfluɪd] noun [uncountable] medical liquid in joints (= body parts where two bones meet) that allows your bones to move smoothly …   English dictionary

  • Синовия (Synovia), Жидкость Синовиальная (Synovial Fluid) — секретируемая синовиальной оболочкой вязкая бесцветная жидкость, которая находится в суставной полости, синовиальной сумке или синовиальном влагалище. Синовия, увлажняя суставные поверхности, облегчает движения в суставе и осуществляет питание… …   Медицинские термины

  • Synovial osteochondromatosis — (SOC) is a rare disease that creates a benign change or proliferation in the synovium or joint lining tissue which changes to form bone forming cartilage. Commonly there is only one joint affected, mostly either the knee, hip, or elbow. The… …   Wikipedia

  • Synovial sheath — Latin vagina synovialis Gray s subject #68 283 A synovial sheath is a layer of a tendon sheath containing tendons in the hand and foot. They lie internal to the fibrous tendon sheaths …   Wikipedia