Mr. Yang was 37 years old and had occasional swelling and pain in his left thigh with no obvious cause 1 year ago. After the surgery, the pathology was considered as “left femoral proximal aneurysm-like bone cyst”, and the original discomfort was relieved and he was discharged. However, 4 months ago, the patient again developed pain in the left proximal thigh without any obvious cause, with gradual swelling, increased skin temperature and no obvious restriction of activity. More than half a month ago, the X-ray examination at the local hospital indicated “recurrence of the bone mass”. The local hospital was at its wits’ end due to technical limitations. The patient was desperate to seek medical help online and found the director of our joint surgery department, Wang Kun, on the Internet. Director Wang carefully analyzed the condition and explained carefully, which gave the patient hope and he came to our department for hospitalization as soon as possible. After admission, the MR indicated a mass in the left upper femur, and the possibility of recurrence of aneurysmal bone cyst after surgery was considered, and the possibility of malignant bone tumor was not excluded. The pathological slide from the outside hospital one year ago was considered: malignant bone giant cell tumor and malignant soft tissue tumor could not be excluded. The results suggested that malignant giant cell tumor could not be excluded. All the tests considered the mass as malignant possibility. After several detailed discussions and thorough preoperative planning, Director Wang Kun, Professor Shi Dehai and Professor Li Zhiyong decided to operate on the patient. During the operation, Director Wang Kun, Prof. Shi Dehai and Prof. Li Zhiyong, through their excellent surgical skills and close cooperation, completely removed the huge tumor of about 24cm*12cm*10cm and fitted the patient with a hip tumor prosthesis without any damage to the surrounding tissues and nerves. After the surgery, through active treatment and rehabilitation exercises, the patient was able to walk on the ground with the help of a walker and was successfully discharged home with the preserved limb. In the past, the treatment methods for giant malignant tumors of the upper and middle femur were hip dissection and hemipelvic amputation, both of which brought serious functional and psychological obstacles to the patients. In recent years, due to improved survival rates of patients with bone and soft tissue sarcomas, advances in bioengineering technology and improved surgical techniques, limb preservation can be performed for most primary sarcomas of the bone. It not only reconstructs limb function surgically, but also meets the marginal requirement for extensive tumor resection. The upper femur and middle femur are the most common sites for primary sarcoma of bone, and the upper femur is also a common site for metastatic bone tumors. Bone tumor prosthesis replacement surgery is one of the most difficult procedures in joint replacement surgery. As the first department in China to perform this procedure, our joint surgery department has helped a large number of patients overcome the disease and preserve their limbs. Our aim is to serve patients wholeheartedly.