If the knee rattles when the leg is bent, it may be due to damage to the meniscus, cartilage, or infrapatellar fat pad in the knee joint, which may cause friction when moving the knee joint, resulting in a popping sound, accompanied by local pain and swelling, and affecting the flexion and extension of the knee joint. If there is osteoarthritis or rheumatoid arthritis in the knee joint, the joint space is narrowed due to bone proliferation and degeneration, which can also cause a popping sound due to cartilage friction when the patient moves the knee joint. In addition, due to changes in the force lines of the lower extremities, uneven forces are exerted in the knee joint, which can cause localized friction when flexing and extending the knee joint, resulting in a popping sound. Therefore, it is important to keep the knee warm and reduce weight bearing, and hot compresses can be applied to relieve this phenomenon.