Patient: Description: Patient female, previously in good health, half a year ago a cyst in the knee joint, action is very inconvenient, do not want surgery, what is a good treatment plan? Luo Dianzhong, Department of Orthopedics, The First Affiliated Hospital of the PLA General Hospital: N-fossa cysts in elderly patients are usually caused by osteoarthritis of the knee joint, mostly occurring in the posterior medial side. Cysts are generally classified as communicating and non-communicating; the former is more common. A communicating N-fossa cyst increases in size, pain, and limited knee flexion with increased activity; a noncommunicating cyst is not affected by the amount of knee activity. They can be treated with rest, reduced activity, oral anti-inflammatory and analgesic drugs (Fotaralin, Fentanyl, etc.), and joint injections, etc. Symptoms can be significantly relieved in 2-3 weeks, but the cyst remains in place. Excision of the N-fossa cyst alone (incision or arthroscopy) has moderate results in the near future, but is prone to recurrence and incomplete relief of knee pain because the osteoarthritis has not been effectively treated. In most patients, osteoarthritis of the knee has progressed to a point where knee replacement therapy with removal of the cystic synovium is required, which is the complete treatment option. Anteromedial, or medial, cysts of the knee in young people are mostly cysts following meniscal injury. There is also a rare history of hemangioma, lipoma, hematoma mechanicum, and nerve sheath tumor, which need to be carefully identified.