A 17-year-old girl diagnosed with osteosarcoma of the left proximal tibia who was treated by osteoarticular resection and modular prosthesis reconstruction. (A) Preoperative anteroposterior radiographic view showing a permeating sclerotic lesion of the proximal tibia. (B) A coronal-T1 magnetic resonance image showing the tumor located at the proximal tibia that extends to the diaphysis. Postoperative radiographs (C and D) show modular prosthesis reconstruction and intercalary massive bone allograft augmentation of the proximal tibia at the 12-month follow-up. The modular prosthesis was one of the treatments of choice in children at the end of their skeletal growth undergoing joint resection for bone sarcoma.