Fluid buildup in the knee after a fall usually does not require surgery if there is no damage to other tissues such as ligaments, cartilage, or meniscus. After a fall that injures the knee, tissue edema due to contusion of the tissues may result in excessive fluid buildup in the knee joint, a buildup that, more often than not, will self-absorb after a period of time. If you are not sure whether there is damage to other tissues such as bone, cartilage or ligaments, you should determine the severity of the damage under the guidance of MRI (Magnetic Resonance Imaging). If there is a torn meniscus, you should undergo surgery to repair the meniscus, and if there is an injury to the anterior cruciate ligament or the posterior cruciate ligament, you should determine whether you need to have surgery or not depending on your condition. In summary, after a fall, the knee simple fluid does not need surgery, if the combination of other important soft tissue, joint and cartilage damage, you need to judge whether to need surgical treatment.