Unilateral knee pain on bending is less likely to be cancer, and is commonly associated with orthopedic conditions such as osteoarthritis, meniscus injuries, and other injuries that may be caused by sports. If unilateral knee pain occurs in an older person, the first consideration is osteoarthritis. With the degeneration of cartilage, osteophytes and calcification, middle-aged and elderly people are prone to knee pain, especially in the case of more activities and exposure to cold, the symptoms will be more obvious. In addition, if the soft tissues around the knee joint are strained or strained, local inflammatory foci will also form, and the inflammatory metabolic products will stimulate the peripheral nerves around the knee joint, and pain will also occur. In this case, the patient’s knee can not be completely straightened, the location of the pain is relatively fixed, mostly accompanied by redness and swelling symptoms. In the case of meniscus injuries caused by trauma or prolonged physical labor, the patient may experience pain when the knee is bent to a specific angle. Therefore, patients with unilateral knee pain when bending do not need to worry too much, you can go to the orthopedic department for knee MRI examination, to clarify the specific cause of the disease and then take appropriate treatment.