The knee pain when straightening is considered to be related to trauma, osteoarthritis, chondromalacia patella, etc.; it can be treated by general treatment, physical therapy, medication, surgery, etc. according to the cause. 1. Trauma: After knee injury, if there is soft tissue injury, fracture, etc., it will cause knee pain when straightening. After the injury, pay attention to rest, you can apply cold compresses in the acute period and hot compresses in the recovery period. Non-steroidal anti-inflammatory analgesic drugs, such as diclofenac sodium and other treatment can also be applied. If the injury is more serious, serious fracture, etc., need surgical incision and fixation treatment. 2. Osteoarthritis: mostly seen in elderly patients, there will be joint cartilage damage, when the knee is straightened, the damaged cartilage rubbing against each other and cause pain. Usually pay attention to rest, can apply diclofenac sodium and other treatment. It can also be treated with heat therapy and microwave. In the late stage of the disease, artificial joint replacement surgery is feasible. 3. Chondromalacia patella: It is an osteoarthropathy in which the cartilage of the patella is chronically damaged and patellofemoral arthritis is formed. As the cartilage is damaged, it will cause pain when the knee is straightened. Usually pay attention to rest, pay attention to keep warm, can apply diclofenac sodium and other treatment. If the symptoms are serious, surgery can be performed, such as patellar chondroplasty. When there is pain when the knee joint is straightened, you can go to the hospital to further identify the cause of the disease, and then targeted treatment. The above drugs need to be applied under the guidance of a physician, avoid self-medication.