Synovial fluid 1089772 225116942 2008-07-11T23:26:21Z 71.232.189.86 /* Composition */ Synovial fluid is a thick, stringy fluid found in the cavities of [[synovial joint]]s. With its egg-like consistency (''synovial'' comes from [[Latin language|Latin]] for "[[egg (biology)|egg]]"), synovial fluid reduces friction between the [[articular cartilage]] and other tissues in joints to lubricate and cushion them during movement. ==Overview== The inner membrane of synovial joints is called the [[synovial membrane]], which secretes synovial fluid into the joint cavity. This fluid forms a thin layer (approximately 50 [[micrometre]]s) at the surface of cartilage, but also seeps into microcavities and irregularities in the articular cartilage surface, filling any empty space <ref>http://www.ucl.ac.uk/~regfjxe/NORMALJOINT.htm</ref>. The fluid within articular cartilage effectively serves as a synovial fluid reserve. During normal movements, the synovial fluid held within the cartilage is squeezed out mechanically (so-called ''weeping lubrication'') to maintain a layer of fluid on the cartilage surface. ==Composition== 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 fluid|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 [[disaccharide]]s composed of D-glucuronic acid and D-N-acetyl[[glucosamine]] joined by alternating beta-1,4 and beta-1,3 [[glycosidic bond]]s <ref>[http://www.glycoforum.gr.jp/science/hyaluronan/HA01/HA01E.html GlycoForum / Science of Hyaluronan-1<!-- Bot generated title -->]</ref>. 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.<ref>[http://www.orthop.washington.edu/arthritis/general/joints/04 Arthritis - UW Medicine - Department of Orthopaedics and Sports Medicine<!-- Bot generated title -->]</ref> 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.<ref>[http://arthritis-research.com/content/5/S3/5 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<!-- Bot generated title -->]</ref> ==Health and disease== ===Collection=== Synovial fluid can be collected by syringe in a procedure termed [[arthrocentesis]], also known as joint aspiration. ===Classification=== Synovial fluid can be classified into normal, noninflammatory, inflammatory, septic, and hemorrhagic: {| border="1" cellpadding="3" style="border-collapse:collapse" |+ Classification of synovial fluid in an adult [[knee]] joint |- bgcolor="#cccccc" |bgcolor="#ffffff"| || Normal || Noninflammatory || Inflammatory || Septic || Hemorrhagic |- |bgcolor="#cccccc"| Volume (ml) || <3.5 || >3.5 || >3.5 || >3.5 || >3.5 |- |bgcolor="#cccccc"| [[Viscosity]] || High || High || Low || Mixed || Low |- |bgcolor="#cccccc"| Clarity || Clear || Clear || Cloudy || Opaque || Mixed |- |bgcolor="#cccccc"| Color || Colorless/straw || Straw/yellow || Yellow || Mixed || Red |- |bgcolor="#cccccc"| [[White blood cell|WBC]]/mm<sup>3</sup> || <200 || 200-2,000 || 2,000-75,000 || >100,000 || Same as blood |- |bgcolor="#cccccc"| [[Polysegmented neutrophil|Polys]] (%) || <25 || <25 || >50 || >75 || Same as blood |- |bgcolor="#cccccc"| [[Gram stain]] || Negative || Negative || Negative || Often positive || Negative |} ===Pathology=== Many synovial fluid types are associated with specific diagnoses <ref>[http://www.fpnotebook.com/RHE64.htm Lupus Anticoagulant<!-- Bot generated title -->]</ref> <ref>[http://www.rheumatology.org/publications/primarycare/number6/hrh0033698.asp?aud=mem American College of Rheumatology<!-- Bot generated title -->]</ref>: * 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 ** [[Tumor]]s ** [[Hemophilia]]/[[coagulopathy]] ** [[Scurvy]] ** [[Ehlers-Danlos syndrome]] ** Neuropathic arthropathy ===Joints cracking=== {{main|Cracking joints}} 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.<ref>[http://health.howstuffworks.com/question437.htm Howstuffworks "What makes your knuckles pop?"<!-- Bot generated title -->]</ref> The general term for this is [[cavitation]]. ==Additional images== <gallery> Image:Illu synovial joint.jpg|Synovial joint </gallery> ==References== {{reflist}} ==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 [http://arthritis-research.com/content/5/S3/5] * [http://www.glycoforum.gr.jp/science/hyaluronan/HA01/HA01E.html Hyaluronan: structure and properties] * {{FPnotebook|RHE62}} * {{FPnotebook|RHE64}} - white blood cell count * [http://www.ucl.ac.uk/~regfjxe/NORMALJOINT.htm Normal joint structure], from [[University College London]] {{Joints}} [[Category:Body fluids]] [[Category:Joints]] [[de:Synovia]] [[es:Líquido sinovial]] [[fr:Synovie]] [[pl:Maź stawowa]] [[pt:Líquido sinovial]]