The causes of knee pain during flexion are: first, the cause needs to be clarified, if it is induced by trauma, try not to bear weight or flex and extend the knee joint, most of which will induce knee pain, straighten the knee joint and pad it up, flush with the heart, which will help reduce swelling and pain, and can be targeted to choose blood activating drugs to reduce swelling and pain, such as drop pills and Panax notoginseng tablets. Second, exclude the presence of osteoarthritis of the knee joint, mostly in middle-aged and elderly people, from osteophytes, degeneration caused by aseptic inflammation of the knee joint, mostly in squatting, semi-squatting, flexion and extension joint pain, usually pay attention to reduce hiking, up and down stairs damaging knee movement, usually pay attention to the knee joint warmth, pain serious oral non-steroidal drugs, such as ibuprofen, aminophenol dihydrocodeine, celecoxib The pain can be temporarily relieved by the use of non-steroidal drugs such as ibuprofen, aminophenol dihydrocodeine, celecoxib, or local closed injections. Third, the knee joint interlocked by knee free body, meniscus injury, ligament injury, most of them will show pain when flexing and extending the knee joint, which can be accompanied by obvious compression, and arthroscopic treatment is feasible in severe cases.