Xiaofeng is a junior high school student, just 12 years old this year, his head is close to 1 meter 7, smart and good at learning, love basketball. Before the Spring Festival, Xiao Feng found that his right knee sometimes had a vague pain around the joint, but his mother saw that it was not red or swollen, so she thought it might be twisted from playing basketball and did not care. A month later, Xiao Feng felt that the pain seemed to gradually increase. He went to a nearby hospital for a checkup, and no obvious abnormalities were found on the X-ray. The doctor considered that Xiao Feng was in a period of rapid growth and development, and that it might be “growing pains”. In early April, he went to the hospital for treatment. An MRI examination revealed a tumor-like lesion in the right lower middle femur, which was diagnosed as osteosarcoma after a puncture biopsy. Osteosarcoma is a relatively common primary malignant bone tumor in orthopedic clinics, commonly known as “bone cancer”, with high malignancy, high mortality and disability rates, and mostly occurs in children around 10 years old. Like other malignant tumors, early detection, diagnosis and treatment of malignant bone tumors are the key to successful treatment. However, due to the lack of specific symptoms in the early stage of malignant bone tumor, it is not easy to attract the attention of children and parents when it develops, and it is often misdiagnosed and missed due to growing pains or common trauma, so that many children lose the opportunity of early treatment. Malignant bone tumors are mostly found in long tubular bones such as femur, tibia and humerus, with the distal femur and proximal tibia, i.e. around the knee joint, being the most common. In the early stage, the main symptom is local pain, and the degree of pain varies, some of them only have slight soreness or discomfort, and the affected children may not feel the pain when they play happily, but feel the pain at night when they sleep, and wake up in the middle of sleep like Xiao Feng. As the disease progresses, the pain becomes progressively worse, the pain site is fixed, local swelling may gradually appear, the skin temperature is higher than the healthy side, some children may be accompanied by fever, poor appetite, anemia and other symptoms. Generally, pain in children is not easily associated with bone tumor, but pain is one of the main symptoms of bone tumor, especially at night when the pain worsens, which should be highly alerted. Therefore, when children have unexplained pain around the knee joint or the pain cannot be relieved after resting for more than one week after minor injury, they should be alerted to the possibility of malignant bone tumor and should be brought to a specialized hospital in time.