A, B. A 14-year-old male after reconstruction with a conventional modular tumor endoprosthesis. MSTS score – 60%. C. A 13-year-old male patient with mesenchymal chondrosarcoma of the proximal femur stage Ⅲ, reconstruction with a total femur expandable endoprosthesis, MSTS score – 73%. D. A 14-year-old female patient with malignant chondroblastoma of the distal femur stage ⅡA. Reconstruction was done with an expandable tumor endoprosthesis. MSTS score – 73%.