- See:
-
Synovium
- General Properties:
- synovial fluid is an ultrafiltrate of blood plasma plus hyaluronic acid and glycoproteins;
- synovial fluid resembles material in interstices of loose connective tissue in respect to both components;
- rate and method of passage of substances into & out of synovial fluid depend upon the molecular size of the substance;
- gases & crystalloids diffuse rapidly in both directions;
- larger proteins appear to leave fluid by way of lymphatics;
- particulate matter is taken up by macrophages, and its egress from the joint cavity is quite slow;
- inflamed
synovium contains large clefts which probably permit passage of molecules of almost any size;
- one of main functions of the lining cells of synovium is to secrete certain components of the
synovial fluid;
- in addition to substances secreted by lining cells, synovial fluid contains proteins that are electrophoretically and immunologically identical to plasma proteins;
- these proteins come from blood that circulates in synovial membranes;
-
hyaluronic acid
-
friction and lubrication:
-
synovial fluid is a non-newtonian fluid;
- non-newtonian fluids are notable because their viscosity is not constant and inversely depends on shear rate;
- relationship between viscosity and shear rate is determined by the alignment of the long-chain hyaluronate molecules as the fluid is sheared;
- Synovial-Fluid Analysis (septic arthritis:
)
- all studies can be performed with only 1 to 2 ml of fluid.
- even a few drops may be adequate for Cx, Gm stain, & wet prep;
-
total leukocyte count:
-
crystal examination of synovial fluid:
-
cx & gm staining of synovial fluid:
- viscosity:
-
RA: expect decreased viscosity and poor mucin clot formation;
- glucose:
- low level of synovial-fluid glucose is suggestive of an infected joint, but low glucose levels are present in only about 50 % of patients with septic joints
and can also occur in
RA;
- fasting glucose levels are usually reduced to less than half of the simultaneously obtained blood levels;
Synovial fluid tests: What should be ordered? Shmerling RH, Deblanco TL, Tosteson AN, et al: JAMA 264:1009-1014, 1990
A critical reappraisal. Rheum Dis Clin North Am 20: 503-512, 1994. Shmerling RH: Synovial fluid analysis:
Antibacterial properties of synovial fluid in the knee.
Towards evidence based emergency medicine: Best BETs from the Manchester Royal Infirmary. BET 3: Is the white cell count of the joint aspirate sufficiently sensitive/specific to rule in/out septic arthritis?
The value of synovial fluid assays in the diagnosis of joint disease: a literature survey.
