A case report of autogenous bone grafting using fibula regenerated from beta-tricalcium phosphate for a bone tumor: application of the in vivo bioreactor principle

Reconstruction of large bone defects after tumor resection remains a major challenge in orthopedic surgery. Although autologous bone grafts have excellent osteogenic potential, their application is limited by the small volume available for harvest. Conversely, artificial bone substitutes, such as β-tricalcium phosphate (β-TCP), can be produced in large quantities but possess limited osteoinductive capacity. We present a case in which hybrid grafting using irradiated bone and β-TCP–derived regenerated fibula was performed to reconstruct a large segmental defect following resection of a recurrent bone tumor, achieving successful bone union. A 10-year-old boy with fibrous dysplasia of the proximal femur initially underwent curettage, fibular strut grafting, and β-TCP implantation, including cylindrical β-TCP placement at the fibular donor site. At age 28, local recurrence was suspected, and the possibility of an intermediate malignant bone tumor could not be excluded. Therefore, a wide resection was selected after careful clinical consideration. The resulting segmental defect was reconstructed using an intercalary extracorporeally irradiated autograft, augmented with the regenerated fibula derived from the previous β-TCP implantation. At 1 year postoperatively, radiographic findings demonstrated bone union not only at the femoral osteotomy sites but also between the regenerated fibula and irradiated bone. Objective imaging analyses were performed to evaluate bone regeneration around the reconstructed segment using postoperative radiographs and CT as part of postoperative follow-up. Grayscale values at the osteotomy gaps reached levels comparable to cortical bone on radiographs. Computed tomography further revealed a significant increase in Hounsfield unit values at the bridging region between the regenerated fibula and irradiated bone. Hybrid grafting using a β-TCP–derived regenerated fibula and irradiated bone successfully reconstructed a large femoral defect, highlighting the biological potential of regenerated bone. This reconstruction was based on the in vivo bioreactor concept, and objective imaging analysis proved useful for evaluating bone regeneration adjacent to the recycled bone.