The pain in the fossa behind the knee may have the following causes: first, bursitis of the popliteal fossa, bursitis of the popliteal fossa is due to chronic aseptic inflammation of the popliteal bursa, which should be diagnosed and treated with relevant physical examination as well as ultrasound of the popliteal fossa and MRI; second, popliteal cysts, popliteal cysts can also be present in the popliteal fossa of the knee pain behind the knee, which should be diagnosed and treated with relevant physical examination, which can palpate a cystic swelling with a feeling of swelling and pain. The cystic swelling can be touched, and there is a feeling of distension and pain, and then the ultrasound of popliteal fossa as well as MRI examination should be carried out for diagnosis and treatment; third, meniscus injury, when the posterior horn of the meniscus is injured, pain at the back of the knee can occur, and then the MRI examination of the meniscus should be carried out for diagnosis and treatment; fourth, osteoarthritis, osteoarthritis can involve soft tissues around the knee, and it can cause pain at the back of the knee, and then the pain at the back of the knee can occur; and then the pain at the back of the knee can occur. Fourth, osteoarthritis, osteoarthritis can involve the soft tissues around the knee joint and can cause pain behind the knee, which should be diagnosed and treated by X-ray examination of the relevant knee joint.