1. Clinical data The patient was a male, 19 years old. He came to the hospital with right ankle pain after a basketball sprain. On examination, there was no swelling in the right ankle, and the pain was worse when the joint was internally rotated and dorsiflexed, and when walking fast and running and jumping. 1.2 X-ray There were no obvious abnormal signs in the talus. 1.3 CT and MRI CT showed a 4×4 mm {density or normal density bone mass under the superior articular surface in the talar talus, surrounded by a circular soft tissue density translucent zone, with sclerosis of the bone at the periphery of the translucent zone; MRI showed a low signal and mixed signal at T1 and a heterogeneous increase in T2 signal intensity. 2.Surgery The lesion was scraped under epidural anesthesia, and the scraped material was white hyperplastic tissue. The residual cavity was implanted with a mixture of autologous bone and artificial bone containing BMP. 3.Discussion Exfoliative osteochondritis (osteochondritis, dissecans) is a limited ischemic necrosis of the subchondral bone of the joint. Trauma is the main cause, and the injured osteochondral tissue is gradually surrounded by reparative fibrous granulation tissue, which can be gradually repaired by crawling replacement; it can also be separated from the surrounding normal bone and fall into the joint cavity, forming a free body. The disease occurs in young adults aged 16-40 years old, with more males. It occurs in the medial and lateral femoral condyles, the femoral head, the patella, the humeral tuberosity, the talar tuberosity, the talar talus, the bone and the navicular bone. The diagnosis of osteochondritis of the talus is rarely reported in the literature, and it is easily missed or misdiagnosed as articular ligament injury because of the obvious abnormalities on X-ray. CT or MRI is of high diagnostic value, and it can be differentiated from bone cyst, endogenous chondroma, intraosseous hematoma, ankle ligament and cartilage injury based on the signal condition and sclerosis of the lesion. The diagnosis can be made by CT and MRI examination if a round or ovoid high-density bone mass or abnormal signal area under the articular cartilage of several millimeters or centimeters in length is found, and a circular low-density translucent band is formed around the patient as the disease progresses.