Synovial Fluid

General Discussion of Synovial Fluid

(see also: glycosaminoglycans and proteoglycans; friction and lubrication)

• 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 the 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;

antibacterial properties:

• Antibacterial properties of synovial fluid in the knee.

changes in osteoarthritis

• Degeneration of normal articular cartilage induced by late phase osteoarthritic synovial fluid in beagle dogs.
• Synovial fluid depletion: successful arthrodesis without operative cartilage removal
• Human osteoarthritis synovial fluid and joint cartilage contain both aggrecanase- and matrix metalloproteinase-generated aggrecan fragments.
• Analysis of aggrecan in human knee cartilage and synovial fluid indicates that aggrecanase (ADAMTS) activity is responsible for the catabolic turnover and loss of whole aggrecan whereas other protease activity is required for C-terminal processing in vivo.
• Synovitis causes hypoxia and acidity in synovial fluid and subchondral bone

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;
• pH, references:
  • On the viscosity and pH of synovial fluid and the pH of blood.
  • Synovial pH in rheumatoid knee joints. II. The effect of local corticosteroid treatment.
  • Synovial pH in rheumatoid knee-joints. I. The effect of synovectomy.

References

• Synovial fluid tests. What should be ordered?
• Synovial fluid analysis. A critical reappraisal.
• [Septic arthritis? Gonococcal infection despite negative bacterial cultures]
• The value of synovial fluid assays in the diagnosis of joint disease: a literature survey.
• Brucellar arthritis of the knee: a case report with delayed diagnosis.
• Synovial ph in Rheumatoid arthritis
• The healing of freeze-dried rabbit flexor tendon in a synovial fluid environment.
• The synovial cavity as a "tissue culture in situ"--science or nonsense?
• Role of synovial fluid cells in the healing of flexor tendons.
• Experimental studies on cellular mechanisms involved in healing of animal and human flexor tendon in synovial environment.
• Experimental intrinsic healing of flexor tendons based upon synovial fluid nutrition.
• Identification of a Novel Fibronectin-Aggrecan Complex in the Synovial Fluid of Knees with Painful Meniscal Injury