METHODS AND ERRORS IN MEASUREMENTS OF SYNOVIAL-FLUID VOLUME IN STIFLES WITH LOW-VOLUME AND HIGH-VISCOSITY SYNOVIAL-FLUID

Synovial fluid (SF) volume was calculated using various methods in the stifles of goats, in which the cranial cruciate ligament had been tra nsected on one side. Measurements were performed prior to surgery and again 4, 8, and 18 weeks following surgery, by measuring the dilution of an injected radioactive tracer diluted by the SF. Later, 7 months f ollowing surgery, SF volume measurements using simple arthrocentesis w ere performed on stifles in 9 of the goats, and the SF that could not be aspirated, was calculated using 2 indirect methods simultaneously o n identical fluids in 3 of these goats. SF was also collected directly during staged arthrotomy of the stifles in 4 goats. There were confli cting results between methods, but the resulting calculated SF volumes seemed to be larger in the operated stifles compared to the controls for all the methods at about the same degree. The 2 indirect methods u sed to calculate the fluid remaining in the joints following arthrocen tesis gave disparate volume calculations. The experiments revealed sou rces of error in all methods. Direct methods failed to acquire the tot al fluid volume, and indirect methods were subject to improper mixing and escape of the injected fluid or synovial fluid or both. It was con cluded that none of the methods could be used to measure the ''true'' volume of SF, if such a concept exists and can be defined. None of the methods were considered reliable to compare volumes in different type of joints containing this type of fluid. It was, however, concluded t hat all the methods gave indication of increased SF volume present on a relative basis when paired joints were compared.