Non-Traumatic Fracture of an Osteochondroma Mimicking Malignant Degeneration in an Adult with Hereditary Multiple Exostoses.

A 38-year-old man with a known history of hereditary multiple exostoses and no history of trauma presented with a painful right femur mass. While the clinical presentation was concerning for malignant degeneration or a large overlying bursitis, the radiologic evaluation demonstrated a large fractured pedunculated osteochondroma with a thick cartilage cap and underlying bone marrow edema. Traumatic fracture of an osteochondroma is an uncommon complication in patients with hereditary multiple exostoses. This case highlights an unusual presentation in which a patient with hereditary multiple exostoses and no history of trauma presented with a large fractured osteochondroma.