Exfoliative osteochondritis is a type of joint disease characterized by localized ischemic necrosis of articular cartilage and its subchondral bone, and separation from surrounding normal bone, caused by various reasons. Etiology: The exact cause and pathogenesis of the disease are still unclear. According to clinical studies, it is suggested that the following factors are involved: 1. Sports injury More scholars currently propose that it is a sports factor, especially repeated small energy trauma, which can easily lead to local cartilage injury and produce subchondral fractures, but there are scholars like Mubarak and others who deny the trauma theory because exfoliative osteochondritis have special sites of onset rather than random traumatic places. 2. Local ischemia says that Infection inflammation and other factors lead to the local blood supply is impaired, so that part of the cartilage and its subchondral bone lack of nutrition, leading to the occurrence of the disease, but the pathology of some cases without obvious ischemic necrosis, etc. 3, hereditary theory that the occurrence of the disease has a certain heredity, when the organism in some special role, leading to local chondritis. Combining the above factors, further research is needed on its etiology. Pathology: In the early stage, it is seen that the necrotic area of cartilage shows localized bone fracture, there is a band of congestion around the necrotic area, cartilage matrix and cell degeneration, no inflammatory cell infiltration, as the disease gradually progresses, cartilage necrosis is obvious, a few necrotic cartilage into the joint cavity, but there is usually a tip connection, this tip includes new mature chondrocytes and naive prechondrocytes and some fibrocartilage, some small cartilage is absorbed by the body Some of the small cartilage is absorbed by the body, while the large cartilage remains in the joint cavity and causes joint dysfunction. In contrast, the chondrogenic defect area is proliferated and mechanized by the surrounding granulation tissue, and finally the defect area is filled with fibrocartilage. Clinical manifestations: It occurs in adolescents and adults who love sports. The knee and elbow joints are most commonly involved, while the hip, shoulder, ankle or metatarsophalangeal joints are less common. The affected bones include the medial and lateral femoral condyles, the patellofemoral articular surface, the humeral epicondyle, the radial tuberosity, and the talus of the ankle joint. The disease usually erodes one joint and has no systemic symptoms. Its main clinical symptoms include joint pain, aggravated by activity and reduced by rest, and there may be joint swelling. If a free body is present in the joint cavity, there are symptoms of joint strangulation. Physical examination reveals joint swelling, pressure pain, and restricted movement. Imaging manifestations: 1, X examination The abnormal changes are early joint surface cartilage limited gap, bone small sorghum sparse; to cartilage displacement is visible after the cartilage local upturn, round, oval, dotted stripes, below the depressed bone defect; late displacement body into the joint cavity, visible cavity density, sharp edge of the density shadow, the relative joint surface appears irregular sclerotic defect, sclerotic defect edge with a line In the early stage, it is possible to detect cartilage edema, before the formation of the displaced body, and to clarify whether there is a tip connected, a small residual body, joint fluid, etc. Diagnosis and differential diagnosis: The diagnosis can be confirmed based on the medical history, physical signs and X-ray and MRI. Diseases to be differentiated 1. Infected bone destruction Patients usually have local redness, swelling, pressure pain, skin temperature change, and systemic signs of toxicity, including fever and poor nasal function, which can mostly be differentiated; 2. Articular surface cartilage fracture Most of them have a clear history of trauma, with obvious local joint cavity knotted blood and restricted movement, and X-ray and MRI can help to diagnose. Treatment and prognosis: Consider according to the disease progression and age at the time of consultation. For early stage of the disease, including the bone block is not completely separated, dislodged, and the symptoms are mild, conservative treatment is generally used to make the lesion heal again by local stopping and avoiding strenuous movement; if the symptoms are still obvious or even aggravated after conservative treatment, or if small free bone is found, surgical treatment is feasible, such as minimally invasive arthroscopic surgery; if the displaced bone block is large and the symptoms are obvious, in situ internal fixation should be performed surgically to restore the consistency of the joint surface.