1. Arthrocentesis is commonly referred to as a procedure in which a needle attached to a sterile syringe is inserted into the joint cavity to aspirate fluid from the joint. In some cases, the aspirated fluid can be followed by the injection of therapeutic drugs into the joint cavity. Joint cavity puncture can be used both to aid in the diagnosis of disease and to discover the cause of inflammation within the joint; it can also be used to treat certain diseases by draining fluid, relieving pain, and injecting medications. In most cases, the purpose of arthrocentesis is to identify infection and reduce joint swelling, or to perform routine tests for fluid aspiration. In cases of infection, arthrocentesis can identify whether a bacterial infection has caused inflammation. For non-bacterial inflammation of the joint, the purpose of the puncture is to aspirate fluid and reduce swelling and pain in the joint. After the fluid is aspirated, the pressure in the joint decreases and joint mobility can be improved. The fluid in the knee joint is usually only 2-3 ml. If the fluid accumulation exceeds 6-8 ml, the function of the quadriceps muscle will be affected. 3. Joint cavity aspiration can also be used to perform routine tests including white blood cell count, protein content, sugar content, and crystals, which reflect the body’s microenvironmental conditions. The higher the white blood cell count in the joint, the greater the likelihood of infection. A white blood cell count of 2,500 is usually sufficient to diagnose a joint infection. Gout often shows needle-shaped crystals, while pseudogout has diamond-shaped crystals. 4, the process of joint puncture first local sterilization of the joint, in some cases can also be local puncture site injection of anesthetic drugs or freezing pain, then you can use the puncture needle to joint puncture aspiration fluid, or further injection of drugs. The color of the joint fluid can help determine the type of disease initially. Is the fluid normal synovial fluid or is it purulent? If the fluid is bloody, there is a 75% or greater chance of anterior cruciate ligament or meniscal injury.