Acidosis of synovial fluid correlates with synovial fluid leukocytosis

The antibacterial activity of aminoglycoside antibiotics is significantly reduced by lowering the pH of the incubation medium. Since gram-negative septic arthritis responds poorly to aminoglycoside antibiotic therapy, we sought to determine whether synovial fluid acidosis contributes to this poor outcome. Synovial fluid samples from 22 patients with various forms of acute and chronic arthritis were examined for white blood cell count and pH. A close correlation (r = -0.92, p < 0.001) between an increasing white blood cell count and a decreasing pH was demonstrated. Since septic arthritis is associated with high white blood cell counts, in synovial fluid, the resultant low pH may contribute to the poor response of gram-negative septic arthritis treated with aminoglycoside antibiotics.