Figure 5: 10-year-old male with high-grade osteosarcoma of the femoral shaft on the left side (a/b). After neoadjuvant chemotherapy, en bloc tumor resection and reconstruction with a single free vascular pedicled fibula (from the right side) using microsurgical techniques, cancellous bone grafting and angle-stable plate osteosynthesis (Philos, Depuy Synthes) (c/d). Initial single FVFG (e), 3 years postoperatively, significant hypertrophy with good consolidation (f). After temporary release of the growth plate in the course of genu valgum on the left, an 8-plate was implanted in the left knee joint to gradually guide growth in the case of progressive genu valgum (g). The leg length discrepancy on the left is to be corrected using a magnetically driven intramedullary nail after completion of longitudinal growth.