Knee bending pain may be related to knee joint injury, chondromalacia patella or knee arthritis, etc. It can be treated by medication or surgery according to the cause. 1. Knee injury: If the knee joint is injured during sports, such as sprain or strain, it will cause pain when bending the knee, which can be treated by arthroscopy, ligament reconstruction, and surgery such as incision and repositioning. 2. Chondromalacia patella: refers to chronic damage to the cartilaginous surface of the patella, generally manifested as infrapatellar pain, anterior knee pain and knee pain, etc., and there will be obvious pain when bending the knee, which can be treated by limited chondroplasty and drilling or artificial joint replacement surgery. 3. Knee osteoarthritis: Knee osteoarthritis is a disease characterized by degeneration of knee cartilage and osteophytes, which is mainly manifested by knee pain and swelling and may lead to activity limitation. It can be treated by Celecoxib tablets, Erythroxib tablets, etc., and can be treated by arthroscopic clean-up, osteotomy, and fusion surgery, etc., if necessary. As there are many factors that can cause pain in the bent knee, it is recommended to go to the hospital in time when symptoms occur, so that the cause of the disease can be clarified as soon as possible and positive treatment measures can be taken to avoid delaying the disease.