Popliteal fossa is the popliteal fossa, and the pain in the leg fossa when the leg is bent is considered to be related to muscle strain, joint capsule and ligament injury, meniscus injury, osteoarthritis and so on. 1. Muscle strain: excessive strenuous exercise or unreasonable exercise posture will lead to strain of the popliteal muscle at the back of the popliteal fossa, resulting in localized pain. 2. Joint capsule and ligament injury: unreasonable exercise or external force causes injury to the joint capsule and ligament, which will cause local tissue congestion and edema, resulting in symptoms of pain in the leg socket. 3. Meniscus injury: if the knee joint is overly flexed and rotated in sports, it will easily lead to meniscus injury, which will cause obvious pain in the popliteal fossa when the knee is bent. 4. Osteoarthritis: the knee joint is a large weight-bearing joint in our body, with age, the knee joint will experience chronic strain, degeneration, osteoarthritis, and the involvement of the surrounding soft tissues, there may be popliteal fossa pain. There may be other causes of pain in the popliteal fossa when the leg is bent, such as popliteal cyst, popliteal bursitis, it is recommended to go to the hospital in a timely manner, improve the examination, clarify the cause of the disease and follow the doctor’s instructions for treatment.