Diagnostic indications of knee joint fluid – current state ofknowledge

Synovial fluid (synovia) plays a complex role in the knee joint due to the multi-stage physiologicalprocesses taking place there. The biomechanics of the knee joint is based on the jointfluid as the main shock absorber in the system of friction forces. The diagnosis of synovialfluid is of particular importance in the process of treatment and diagnosis of the disease. Itturns out to be helpful not only to surgeons and orthopedists, but also to clinical physiotherapists.Any pathologies within the knee joint therefore directly affect the composition andbiorheology of the synovial fluid.The literature review consisted of articles collected in the following databases: PubMed and CochraneLibrary regarding changes in the composition of knee joint fluid over the last 20 years.The collected articles were divided into groups with the greatest clinical significance: cytokines, immune system cells, mesenchymal stem cells, collagen, biomarkers, enzymes, nitric oxide(NO), neurotransmitters. Each group presents the latest data on individual groups of compoundspresent in the composition of the synovial fluid of the knee joint, quantitative data ofthese substances and the role they play in the pathophysiological processes of the joint.The collected research reports allow us to observe trends in the progress of research on thesynovial fluid of the knee joint and to distinguish groups of compounds that are the area ofresearch interest in modern synovial fluid diagnostics. Cytokines that are involved in inflammatoryand immunomodulatory processes are of the greatest interest. The most importantof them belong to the groups of interleukins, extracellular matrix metalloproteinases and fibroblastgrowth factor. Studies on collagen breakdown and markers of its degradation duringosteoarthritis and in the initial stages of joint injury are also the subject of broader researchinterest in the pathophysiology of knee joint fluid. The fewest scientific reports concernedenzymes and neurotransmitters, of which only acetylcholine and choline transporters (CTL,OCT) were sparsely described in the world literature.