The popliteal fossa is called popliteal fossa in medicine, and the causes of popliteal fossa a little swollen may be soft tissue injury, fasciitis, popliteal cyst, knee osteoarthritis and so on. 1. Soft tissue injury: In the process of work or sports, it may cause injury to the muscles and tendons in the popliteal fossa and other soft tissues, and local pain and swelling will occur. 2. Fasciitis: Aseptic inflammation of the fascia of the knee joint due to exertion, cold, etc. may also cause swelling in the popliteal fossa. 3. Popliteal cyst: Popliteal cyst is a benign soft tissue swelling in the popliteal fossa that causes swelling in the popliteal fossa. 4. Knee arthritis: Osteoarthritis of the knee, gouty arthritis, rheumatoid arthritis, etc. may cause swelling in the popliteal fossa due to fluid accumulation in the knee joint cavity. A little bit of swelling in the posterior leg fossa may also have other reasons, such as knee joint infection, tumor, etc., if the persistence of non-relief, it is recommended to go to the hospital in a timely manner to improve the relevant examinations to identify the cause of the disease, and then comply with the doctor’s instructions to carry out targeted treatment, so as to avoid delaying the condition.