The patient, Zhang, was in his early 40s. Three years ago, he found a lump on the back of his right knee that was not itchy or painful, and thought it was swelling from an accidental sprain. Recently, I found that the swelling had increased and I had pain in my right knee, and my squatting activities were slightly affected, so I went to a “native doctor” and applied herbs externally, but it did not improve. Then, one day while walking up the stairs, he suddenly developed severe pain in his right lower limb and could not walk. After the X-ray examination, he was considered to have a bone tumor and pathological fracture in the lower left femur. After further MRI examination and biopsy, it was confirmed that osteosarcoma of small cell type and fracture of the left lower femur. Osteosarcoma is a highly malignant bone tumor with a very low 5-year survival rate, and in the past, amputation was the only and best treatment. With the development of chemotherapeutic agents and chemotherapy regimens and the continuous improvement of medical technology, limb-sparing surgery has been widely performed in the last 20 years. Limb preservation surgery has become the main tool in the surgical treatment of malignant bone tumors, but the recovery of joint function and long-term complications are still problematic. What kind of surgical method can not only remove the tumor more completely but also ensure the better preservation of limb function? Can computer-aided design be applied to guide the precise resection of the tumor bone, preserve the bone and/or joint not invaded by the tumor bone, and perform tumor bone amputation for artificial prosthesis replacement or allograft bone graft and artificial prosthesis replacement to provide a new option to reduce the loss of joint structure and restore the function of the limb? This is the new orthopaedic technology we are going to introduce today. In recent years, the Department of Orthopedics of Shaoguan First People’s Hospital has carried out well the advanced technology of surgically preserving the function of the affected limb joint under computer-aided design for the treatment of primary malignant bone tumors, and has treated many patients with primary malignant bone tumors with limb-preserving artificial prosthesis or large segment allograft bone graft artificial joint replacement, achieving unprecedented results. Before surgery, CT 3D reconstruction and MRI are used to design the preoperative plan on the computer navigation workstation, to clarify the intramedullary and extramedullary extent of the lesion invasion, and to design and mark the extent of the resection of the tumor bone; the CT data is used to customize the tumor bone model, and under the guidance of computer navigation, the tumor bone model is registered and positioned on the tumor bone model, and the tumor bone model is truncated at the predetermined boundary of the navigation, and then the large segment allograft bone and artificial prosthesis are customized to match it. The prosthesis is then custom-made to match the large allograft bone and prosthesis. During the operation, the model designed under computerized navigation is registered and positioned point-to-point on the patient’s tumor bone, and the tumor bone is truncated according to the preoperative design, preserving the joint and ligament tissues as much as possible and assembling an artificial prosthesis or a large allograft bone graft for artificial prosthesis replacement. Postoperative combined with chemotherapy and limb functional rehabilitation exercises, very good results were achieved. With the progress of imaging technology and the increasing understanding of tumor biology, the invasive range of tumor can be more clearly shown, and the wide application of chemotherapy also provides a guarantee for oncologic surgery to reduce the local recurrence rate. In the limb-preserving treatment of malignant bone tumors, accurate evaluation of tumor surgical boundaries before and during surgery is crucial, and computer navigation technology can provide technical support. intraoperative guidance to complete prosthetic replacement or large allograft bone replacement. This can avoid the blind expansion of tumor resection and loss of valuable and important bone and joint structures due to the inability to accurately evaluate the tumor surgical boundary before and during surgery, thus creating conditions for the reconstruction of the limb structure, improving the level of limb function recovery and greatly improving the patient’s survival quality.