(water) – enters joint space from synovial capillary network
(from B cells) – glycosaminoglycan synthesized and secreted by B cells of the synovial membrane; composed of long chains of repeating disaccharides; steric configuration of these coils gives synovial fluid its high viscosity
(glucose, electroyles) – diffuse freely in and out of join space
(also from B cells in the synovial membrane) – intermediate-sized molecules which are moderately retarded in diffusion
Functions of synovial fluid
: lubricate joint and provide nutrition to the cartilage.
Examination of Synovial Fluid
can yield specific diagnosis (ex: gout), and can help limit the differential diagnosis (ex: <2000 WBC/mm3 = non-inflammatory), can reflect changes in the synovial membrane and supporting structures.
Tests to perform on SF:
(color and clarity)
: clear to pale straw colored.
: varies with degree of inflammation, usually yellow or green tinged with cloudiness depending on WBC count
: Hemarthrosis (hemophilia, joint trauma, etc.)
Note: bloody fluid with a fatty foam could result from a Tibial Plateau fracture.
(String sign is a quick measure of viscosity) – stretch a drop between thumb and forefinger
Decreased when PMN enzymes are released into joint fluid and degrade HA.
(3) Cell counts
normal – less than 200
grade I (non-inflammatory; acute traumatic arthritis, osteoarthritis) – 200-2000
grade II (inflammatory; RA, gout, SLE) – 2000-75,000
grade III (septic; infection, bacterial, mycobacterial, fungal) – 75,000