Knee flexion pain may be caused by excessive recent exercise, accidental strain, arthritis, meniscus injury, knee ligament injury, synovitis, popliteal cysts, etc. 1, when the recent excessive exercise, will lead to muscle strain, knee flexion and extension activities will also aggravate the injury, then you need to bed rest, reduce the ground activities, local physical therapy, hot compresses, can take oral ibuprofen or fenbid anti-inflammatory and analgesic treatment. 2, accidental strain, tendon injury or laceration, easy to appear local swelling and pain in the knee, knee flexion and extension activities are limited, after the injury need 24-48 hours of cold compresses, after local heat, physical therapy, avoid ground activities, swelling can be used to reduce swelling drug treatment. 3, arthritis and synovitis, local inflammation of the knee joint, swelling, pain, limited knee movement, you can take oral ibuprofen and other drugs for anti-inflammatory and analgesic treatment, oral medicine to reduce swelling. In addition, oral aminoglycans and other nutritional joint cartilage drugs are needed for treatment, and if necessary, arthroscopic surgery. 4. Meniscal injury and knee ligament injury can cause knee pain and restricted movement, which can result in a “clicking” sound or joint locking and inability to move. In this case, local physical therapy, hot compresses, intra-articular injection of sodium vitreous acid, after a period of treatment, if persistently not relieved, consider arthroscopic surgery treatment. These are the common causes of knee flexion pain, which require reduction of downward activities and systematic treatment. If we do not take them seriously and actively cooperate with the treatment, it may lead to aggravation of symptoms and even inability to move downward.