Synovial fluid pH, lactate, oxygen and carbon dioxide partial pressure in various joint diseases

Fifty‐five samples from knee joints of 44 patients with a wide variety of joint diseases were analyzed by routine gross and microscopic examination, and for pH, pO 2 and pCO 2 ; 18 fluids were analyzed for lactate. pO 2 values ranged from 8–78 mm Hg. Lower values were found generally in fluids of the inflammatory type. pH values ranged between 6.6 and 7.41 units and correlated poorly with pO 2 . pCO 2 ranged between 34 and 150 mm Hg. pO 2 correlated poorly with pCO 2 ( r = −0.22) but better with lactate ( r = −0.67). In the same 18 samples, lactate correlated better with pH ( r = −0.9) than did pCO 2 ( r = −0.38). No single entity could be identified with a given degree of physiologic abnormality. These changes appear to be nonspecific. The good correlation between lactate and both pH and pO 2 suggests that anaerobic glycolysis by an anoxic synovium may be the most important underlying factor.