Recently, she received a patient from abroad, a farmer, who suddenly had severe pain in her left knee while working in a field sometime in 2013, which meant that she could not move at that time, went home and rested for a month, took some medication prescribed by the local hospital, gradually improved and even could walk normally, and had a similar attack again in December 2014, but this time it could not be relieved until she came to the clinic in March this year, and on examination she found that her left knee could not be fully straightened, and that she could not walk in extreme flexion. The patient complained of limping when walking, but did not feel significant pain. After she visited several local hospitals, the doctors informed her that she needed knee replacement, so the patient came to our hospital accompanied by her family with the same straightforward purpose of requesting hospitalization for joint replacement. Based on the patient’s symptoms and signs, I considered that the most likely cause was an intra-articular free body, but the patient did not exhibit the typical interlocking sign. However, I still wanted the patient to undergo arthroscopy and joint debridement and free body removal at the same time. It took some patience to communicate with the patient, after all, the patient spent money on arthroscopy and the symptoms could not be improved. The arthroscopy was done, and it was found that the cartilage in the joint had degenerated significantly, but there was no exfoliation and no exposed subchondral bone. The patient was informed that his left knee joint could continue to be used.