The common reasons for the sound of bone crumbs in the knee include chondromalacia patella, osteoarthritis, free body, synovial chondromatosis and meniscus injury. 1. Chondromalacia patella: mostly due to trauma or chronic degeneration resulting in patellar spalling, exposed subchondral bone, friction during knee activities, can cause the knee as if crushed bone crumbs sound. Treatment, mainly nutritional articular cartilage treatment, oral glucosamine hydrochloride capsules under the guidance of a doctor. 2. Osteoarthritis: It is mostly due to the serious degeneration of the knee joint, narrowing of the joint space, degeneration of the articular cartilage, stripping, and exposure of the bone under the cartilage, which causes direct friction between the bone and the bone when the knee joint is moving, and results in the ringing of the knee as if it were broken bone crumbs. The main treatment is knee joint surface replacement surgery. 3. Free body: The cartilage is peeled off due to trauma or degeneration of the knee joint and falls off in the joint cavity, forming a free body, which slides between the femur and tibia surfaces when the knee joint flexes and extends. The main treatment is to remove the free body. 4. Synovial chondromatosis: The synovial membrane in the knee joint is inflamed and forms chondromas, which are stuck between the femur and tibia, and when the knee joint moves, the friction of the cartilage surface of the tibia increases, resulting in the phenomenon that the knee seems to be rattling like a broken bone crumb. The main treatment is surgical resection. 5. Meniscus injury: If the meniscus is torn, it can also cause the knee to sound like broken bones. Treatment, need to take early surgical treatment, such as arthroscopic meniscus suture. There are many reasons that lead to the sound of bone crumbs in the knee, and it is recommended that patients find out the cause of the disease in time.