Free bodies are more common in the knee joint, mainly from exfoliative osteochondritis, synovial osteochondromatosis, osteophytes, articular surface fractures, and injured menisci. Free bodies can be fibrinous, fibrous, or osteochondral. Fibrinous free bodies can be secondary to intra-articular hemorrhage with a polarized blood clot composition. Fibrous free bodies are often self-shedding hypertrophic synovial villi. Cartilaginous free bodies are mainly from trauma or various pathological conditions, such as synovial osteochondromatosis, exfoliative osteochondritis, and neuroarthritis. The clinical manifestations of various intra-articular free bodies are the same, mainly as follows: 1. Sudden onset of severe knee pain during activity, sometimes the patient may fall. The knee joint may suddenly lock up and cannot be extended or flexed. 2. Swelling of the joint, often after an attack, early as effusion, which over time produces chronic synovitis. X-rays may show osteochondral free bodies, but not free bodies of other nature. Arthrography and arthroscopy can make a clear diagnosis. Prevention and treatment methods: 1. For patients with gout, the main thing is to pay attention to dietary control, eat less food containing seafood, animal offal and beer, and reduce uric acid through medication as appropriate. For conservative treatment, patients with poor efficacy can undergo minimally invasive arthroscopic surgery, which can achieve good results. 2. For some patients with synovial chondromatosis, if repeated knee swelling and recurrent symptoms of interlocking are ineffective with conservative treatment, arthroscopic free body removal of the knee is required. 3, For repeated patellar dislocation, repeated patellar dislocation leading to cartilage loss and formation of free body, early arthroscopic free body removal + patellofemoral osteoplasty is recommended. 4. For patients with exfoliative chondromalacia and formation of free body, it is recommended to avoid physical work, and if frequent symptoms of interlocking appear, early arthroscopic free body removal is recommended.