Apport de l’analyse du liquide synovial au diagnostic des infections articulaires

Synovial fluid analysis is essential for the diagnosis and management of septic arthritis (SA). It allows to identify the pathogen (mainly bacterial) and to study the antibiotics sensitivity (essential for the therapeutic management). Nevertheless, the direct examination is often negative (positive in 15–40% of the cases) and the bacterial culture can be taken in default (positive in 75–85% of the cases) because of an antibiotic therapy set up before the joint puncture, a too small bacterial inoculum or in case of fragile/fastidious bacterial species. Molecular biology techniques (DNAr16S PCR or multiplex PCR) are only of value if positive, and do not seem to increase the sensitivity of bacterial detection during SA. Synovial biomarkers are therefore necessary to allow a diagnosis of SA without bacteriological documentation or to formally eliminate this diagnosis. A synovial white blood cells threshold ≥ 50,000/mm³ seems insufficient to discriminate SA from another diagnosis (metabolic, crystal-induced or reactive arthritis). Synovial biochemical parameters seem to be of particular interest (lactate, glucose, calprotectin, procalcitonin) while others should be abandoned (protides, LDH). This article reviews the performance of cytological, bacteriological and biochemical parameters of synovial fluid for the diagnosis of SA.