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

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Abstract
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, pO2 and pCO2; 18 fluids were analyzed for lactate. pO2 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 pO2. pCO2 ranged between 34 and 150 mm Hg. pO2 correlated poorly with pCO2 (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 pCO2 (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 pO2 suggests that anaerobic glycolysis by an anoxic synovium may be the most important underlying factor.