Significance of joint fluid uric acid levels in gout.

Thoughthepresence ofsynovial fluid injoints has beenknownsince thetimeofParacelsus, present concepts ofsynovial membranestructure andthe formation ofsynovial fluid areofrelatively recent origin. Mostworkers nowconsider thearticular cavities tobeconnective tissue spaces; thesynovial fluid istissue fluid, andtheembodied mucinisthe polysaccharide protein component ofother connective tissue. Thishypothesis issupported bythefact that nonelectrolytes diffuse readily ineither direction betweenblood andsynovial fluid andthatelectrolytes aredistributed inaccordance withtheGibbsDonnantheory ofmembraneequilibrium (Ropes, Bennett, andBauer,1939). Chloride andbicarbonate arepresent inhigher concentration inthe fluid thanintheserum,whileconcentrations of sodium, potassium, calcium, andmagnesium are lowerinthefluid. Themobility ofmanyionsin synovial tissue isthesameasinwaterbutthe bivalent cations havealowerapparent mobility in tissues thaninwater(Joseph, Reed, Steck, Folk, and Kaplan, 1948). Because ofthese facts, ithasusually beenassumed thatthesynovial fluid level ofuric acidfollows ata slightly lower level thanthatoftheserum, andthis assumption hasbeensupported bytheworkofRopes andBauer(1953) andTalbott (1957), whorefute the earlier observation byKling (1938) thatthelevel of joint fluid maybesignificantly raised abovethatof theseruminanacuteattack ofgout. Observations Ihavemade,however, support the original thesis ofKling, andsuggest thatthishigher level ofjoint fluid uricacidisassociated withthe formation ofuratecrystals inthejoint fluid.