Background: Preoperative aspiration of synovial fluid is not always possible. Intraoperative collection of synovial fluid for determination of cell count and differential may be a useful approach for diagnosing or excluding prosthetic joint infection (PJI). However, the value and accuracy of synovial fluid collected during surgery has not yet been prospectively investigated. We analysed intraoperatively collected synovial fluid cell count for rapid and accurate diagnosis of PJI.

Methods: Unselected patients undergoing total hip or knee revision surgery from 06/06-05/08 were prospectively included. During surgery, synovial fluid was collected for determination of cell count; the cut-off value for PJI was > 1700 leucocytes/mm³ and/or > 65% neutrophils (according to Am J Med2004;117:556). In addition, 6 intraoperative samples were obtained for microbiology and 1 for histopathology. PJI was defined as presence of intraoperative pus, acute inflammation in histopathology, or ≥2 tissue samples growing the same organism.

Results: 59 patients (median age, 69 years; 68% females) with hip (n = 41) and knee (n = 18) prostheses were included, of whom 20 (34%) had PJI. Synovial fluid cell counts were true-positive in 16, true–negative in 38, false–positive in 1 and false–negative 4 patients. Sensitivity of synovial fluid cell count was 80%, specificity 97%, positive and negative predictive values were 94% and 90%, respectively.

Conclusion: The intraoperative synovial fluid cell count analysis is a rapid, inexpensive and reliable test for predicting or excluding PJI, having a ≥90% positive and negative predictive value. This test may be used for making operative decisions during surgery.