The common causes of knee bending pain include excessive exercise, meniscus injury, cartilage degeneration and so on. 1. Excessive exercise: when the patient has too much exercise recently, it leads to muscle strain or crack, and when the knee bends, the symptoms of pain will appear. 2. Meniscus injury: Meniscus injury will cause knee bending pain and movement limitation. It is accompanied by symptoms such as clicking sound or joint strangulation and inability to move. 3. Cartilage degeneration: Bone degeneration is the degeneration of cartilage caused by various reasons, such as primary osteoarthropathy, secondary osteoarthropathy, etc. After the knee joint is damaged, the symptom of bending pain will appear. When the patient appears after the knee bending pain can not be relieved, should consult the doctor well in time, under the guidance of professional doctors, clear causes, choose to target effective treatment.