Osteochondroma, also known as exophytic bone warts, is a benign bone tumor that is most common in adolescence. There are two types of osteochondroma: solitary and multiple, and solitary is common. The most common occurrence is near the knee and ankle joints, often bilaterally symmetrical and hereditary, also known as hereditary multiple exophytic warts. Osteochondroma consists of a fibrous tissue envelope, a cartilage cap, and a bony base. The base can be elongated and tip-like or broad. At the age of growth, the osteochondroma itself has its own epiphyseal plate. Therefore, at the end of the growth age, the growth of the osteochondroma also stops. Bursa can be produced by friction between osteochondroma and surrounding tissues. About 1% of solitary osteochondroma can be malignant, but 10-20% of multiple osteochondromas develop malignant transformation into chondrosarcoma. Radiographic manifestations: 1. narrow basal type 2. broad basal type 3. multiple type (osteochondromatosis) Radiographic manifestations are bony lesions protruding from the dorsal aspect of the epiphysis toward the joint, which are generally smaller than those seen clinically, because the cartilage cap and bursa are not visible, and the bony image of the tumor is identical to the bony structure of the epiphysis where it is located, so it is not easy to distinguish. For example, osteochondroma of distal femur grows toward femur, and tumor of proximal tibia grows toward distal tibia, its shape varies, it may have a very long tip and narrow base, or very short and thick with broad base, and the tip of larger tumor is inflated like cauliflower. Diagnosis 1.Most often occurs in adolescents, usually in the long bone epiphysis, single or multiple, multiple often accompanied by abnormal bone development. 2.Tumor starts from the epiphysis, the shape is different, nerve compression symptoms or joint dysfunction may appear. Malignant transformation is rare, but if the tumor continues to grow rapidly in adulthood, malignant transformation should be suspected as chondrosarcoma. 4.X-ray film and pathological examination can confirm the diagnosis. Treatment 1.The tumor is small and most of the tumors stop growing after the development stops, no special treatment is needed. 2.If there is local discomfort, the tumor is large and presses the surrounding tissues to produce symptoms and continues to grow after the development stops, it should be removed surgically in time. When resecting, the fibrous envelope, cartilage cap and tumor body including osteochondroma should be removed together with the normal bone tissue at the base. If the thickness of cartilage cap is more than 2cm, malignant change is highly suspected and surgery is needed. 3. Pathological examination should be performed after resection of tumor.