Sudden pain in the knee joint is usually due to local acute inflammation, bone lesions or injuries are common, acute inflammation may be septic arthritis and other problems. Acute inflammation is usually accompanied by local redness and swelling, and there are even systemic symptoms of systemic toxicity such as high fever and loss of appetite, which can be determined by a combination of knee MRI, blood tests and other indicators. There is also knee gout, which is usually triggered by drinking beer, eating seafood, etc., and can be determined by uric acid examination. Other causes such as giant cell tumor of bone, tumor rupture and bleeding, and knee capillary rupture and bleeding may also cause sudden pain. This condition usually has no redness or swelling in appearance, and the pain level is more intense, and the condition can be determined by examination such as knee CT or MRI. If there is trauma, it may be a traumatic fracture or meniscal injury that causes sudden pain in the knee joint, which can be determined by taking a film or doing an MRI.