Hybrid Prosthetic and Biological Reconstruction Using Extracorporeal Radiotherapy for Long-Segment Humeral Osteosarcoma: A Case Report.

INTRODUCTION: Osteosarcoma, the most prevalent malignant primary bone tumor in children and adolescents, can present formidable challenges when involving long segments of the humerus. Reconstruction options must balance oncological clearance with long-term limb function, particularly in skeletally immature patients. CASE REPORT: We report a case of a 15-year-old female diagnosed with high-grade osteosarcoma involving the proximal epiphysis and most of the diaphysis of the right humerus, sparing only the distal 3 cm. Following neoadjuvant chemotherapy, the patient underwent wide tumor excision and a novel hybrid limb-salvage reconstruction using a custom proximal prosthesis combined with biological reconstruction of the diaphysis via extracorporeal radiotherapy (ECRT). The tumor-bearing bone was irradiated with 50 Gy ex vivo and reimplanted, fixed to the preserved distal humerus with a locking plate. At 18-month follow-up, the patient remained disease-free, with radiographic evidence of graft incorporation and preserved elbow function. CONCLUSION: This case highlights the viability of combining prosthetic and biological methods in complex pediatric osteosarcoma, especially when distal joint preservation is possible. ECRT provides a cost-effective, anatomically compatible solution that maintains structural integrity, especially when used with proximal prosthetic support. This hybrid method represents an optimal limb-salvage strategy in selected pediatric cases involving long bone tumors.