A little swelling below the knee is usually caused by pathological factors, such as knee synovitis, tibial tuberosity epiphysitis, osteoarthritis and so on. 1. Knee synovitis: due to long-term strain, cold, infection, etc., knee synovitis is triggered, and fluid or blood accumulates in the joint cavity, which is manifested as persistent swelling and pain in the knee joint and limitation of activities. 2. Tibial tuberosity epiphysitis: acute or chronic recurrent injury to the tibial tuberosity causes edema at the tibial tuberosity, which manifests as swelling and pain below the knee, and the pain is aggravated when flexing or extending the knee. 3. Osteoarthritis: If degenerative changes occur in the articular cartilage, the synovial membrane in the joint is stimulated, triggering the synovial membrane edema, hyperplasia and exudation, which is usually manifested as pain and swelling in the knee joint. In addition to the above reasons, kidney disease, heart failure and so on may also cause lower limb edema. If there is a little bit of swelling below the knee, it is recommended to consult a doctor in time to identify the cause of the disease and then carry out targeted treatment.