Massive Post-traumatic Femoral Cyst Resulting in Pathologic Fracture in a Child: A Case Report

Case A 10-year-old boy experienced a pathologic diaphyseal femur fracture through a large cyst encompassing 40% of femoral length. At age 5, he had had a traumatic ipsilateral diaphyseal femur fracture, treated with flexible nailing. Biopsy at age 10 revealed a simple bone cyst with components of aneurysmal bone cyst. Curettage, antegrade nailing, and allograft resulted in successful osseous healing. Conclusion Post-traumatic cysts of long bones are rare and have not been reported to cause pathologic fracture in children. This case highlights that close scrutiny of follow-up radiographs of long bone fractures may identify clinically important post-traumatic cysts.