Knee pain and swelling with fluid may be caused by meniscus injury, knee synovitis, septic arthritis and other diseases, different diseases, different treatments, you can follow the doctor’s instructions to take general, medication, surgery and other ways to treat the cause. 1. Meniscus injury: it is caused by the combination of factors such as half-flexion, adduction or abduction of the knee joint, gravity extrusion and so on, which leads to severe pain in the knee joint, inability to straighten it, accompanied by swelling, and sometimes there will be blood accumulation in the joint. If there is blood accumulation, the blood can be drained under local anesthesia, and then pressure bandage can be applied, and if necessary, the affected limb can be immobilized with a long leg plaster cast. If conservative treatment is ineffective, surgical treatment such as meniscus repair or total/secondary meniscectomy can be considered. 2. Knee synovitis: refers to the degeneration of synovial membrane caused by mechanical or chemical stimulation of the knee joint. After acute joint trauma, the patient’s knee joint will be rapidly swollen and painful, and synovial reactive effusion will appear 6~8 hours after the injury. Stop moving the affected limb and extract the fluid from the joint as soon as possible, then use an elastic bandage to bandage the affected area with pressure or use a plaster to immobilize it. If the pain is severe, oral painkillers such as ibuprofen and diclofenac sodium can be taken as prescribed by the doctor. If the fluid in the joint is large and the tension is high, the fluid in the knee can be extracted and then sodium vitrate can be injected. If necessary, small incision treatment and arthroscopic treatment can be considered. 3. Septic arthritis: It is an inflammation that occurs when the pathogenic bacteria invade the joints through the bloodstream. It starts rapidly, and the patient may have systemic symptoms such as high fever, chills, etc. It may be accompanied by swelling and pain in the joints of the knee, elbow, and wrist, etc. In addition, it may be stimulated by inflammation and lead to an increase in the amount of pus in the joints. The affected limb can be immobilized with plaster and sensitive bacteria antibiotics, such as penicillin and vancomycin, can be injected intravenously as early as possible. In addition, the fluid in the joints of knee, elbow and wrist should be pumped out, and then rinsed with saline until the fluid is clear, and then antibiotics should be injected into the joints. If necessary, surgical treatment such as arthrotomy and drainage may be considered. In addition, there are many other causes of knee pain, swelling and fluid retention, patients are advised to go to the hospital in time to identify the cause of the disease, and then follow the doctor’s instructions for treatment. The use of the above medications should be in accordance with medical advice.