There was a patient who sprained his knee 3 years ago. At that time, his right knee was swollen and painful, and his movement was limited. However, a year ago, his right knee started to hurt again and he often felt a lump moving around in his knee, and he often felt weak when walking and had a weak leg. The photos showed that he had an anterior cruciate ligament (a ligament in the joint that stabilizes the joint) stop point avulsion fracture that had not healed and had been in a free state, so his joint was unstable and the degeneration of the joint (commonly known as aging) was obvious. Although he is only in his twenties, this film looks like the film of a person over 45 years of age who does heavy physical work regularly. The lateral view shows a free bone fragment in the intercondylar spine, which is the bone of his anterior cruciate ligament stop. There was also a bone mass at the superior edge of the pancreas, which was a free body. We performed arthroscopic surgery on him and removed a 1.5×2.5 cm free body. He is not feeling any more movement of the swelling in his knee (we have removed the free body), and no more weakness in his leg (ACL function has been restored), but there is nothing we can do to bring him back from the degeneration of his joint.