Popliteal nerve injury, popliteal cyst, lumbar disc herniation may be the cause of pain in the posterior fossa of the leg. 1. Popliteal nerve injury: because when performing leg stretching activities, the knee may be over-extended, causing injury to the popliteal nerve behind the knee by excessive stretching, so pain occurs in the posterior fossa of the leg. 2. Popliteal cyst: due to knee degeneration, knee arthritis or trauma, the bursa in the deep popliteal fossa of the knee joint is enlarged or the synovial sac is bulging, and the cyst may compress the surrounding tissues, causing pain in the posterior fossa of the leg. 3. Lumbar disc herniation: due to chronic fatigue, cold, prolonged sedentary standing and other reasons, caused by lumbar disc herniation, the protruding disc compression of the nerves, which may lead to lower limb radiating pain, so the phenomenon of pain in the posterior fossa of the leg. It is recommended that patients with pain in the posterior fossa of the leg go to the hospital in time for a detailed examination and standardized treatment under the guidance of the doctor.