Synovial pH Is As Specific As Synovial Leukocyte Count But Less Sensitive For The Diagnosis of Chronic Prosthetic Joint Infection

Synovial fluid markers have been shown to be most accurate in diagnosing prosthetic joint infection (PJI). An inverse correlation for synovial leukocyte count and synovial pH is known assuming that leukocyte metabolism causes synovial fluid acidosis. This study analysis synovial pH as a potential marker for PJI. We prospectively included 92 patients who presented with painful total joint arthroplasty (TJA) of the hip (THA; n = 25) or knee (TKA, n = 67). Joints were diagnosed as infected (n = 30) or aseptic (n = 62) based on the Musculoskeletal Infection Society criteria of 2018. An ideal cut-off value for synovial pH and the sensitivity and specificity were calculated. Additionally, the sensitivity and specificity were calculated for synovial white blood cell (WBC) count (cut-off > 3000 leukocytes) and percentage of neutrophils (PMN%, cut-off > 80%). The median synovial pH level was significantly lower in the group with chronic PJI (7.09 vs. 7.27; p < 0.001) compared to implants with aseptic failure. The calculated optimal cut-off value was 7.11 (AUC 0.771) with a sensitivity of 53% and specificity of 89%. However, the sensitivity and specificity of synovial WBC count were 90% and 88% and for synovial PMN% 73% and 98%, respectively. Synovial pH may be a cost-effective parameter to diagnose chronic PJI.