Transformation of Ischial Osteoblastoma Into High-Grade Osteoblastoma-Like Osteosarcoma

The authors report an osteoblastoma-like variant of osteosarcoma of the right ischial tuberosity in a 14-year-old boy. Radiographs initially showed a bone-forming lesion of the right ischial tuberosity. The patient underwent biopsy with curettage and bone grafting, with final pathology revealing osteoblastoma. Two years after the initial procedure, he presented with exuberant bone formation about the operative site concerning for recurrence. He underwent a second biopsy that showed transformation into a high-grade osteoblastoma-like osteosarcoma. Results from staging studies were negative for distant metastatic disease. The patient was treated with standard 3-drug chemotherapy along with wide resection of the right ischium with periacetabular reconstruction and total hip arthroplasty. [Orthopedics. 2019; 42(3):e343-e345.].