There are several possible causes of pain behind the knee: 1. meniscal injury, when the posterior horn of the meniscus is torn, pain can occur at the back of the knee joint, which is often obvious when flexing the knee joint or working in a squatting position. 2. osteoarthritis, when osteoarthritis of the knee joint involves the soft tissues, pain can occur behind the knee, which can be diagnosed and treated with relevant knee x-ray. 3. 3, popliteal cysts, popliteal cysts can also appear in the popliteal fossa swelling pain, popliteal fossa can be touched cystic swelling. 4, popliteal bursitis, when the popliteal fossa bursa has chronic aseptic inflammation, it can appear behind the knee pain, this time to carry out nuclear magnetic examination of the knee for diagnosis and treatment.