Osteonecrosis, fractures, and protrusio acetabuli secondary to x-irradiation therapy for prostatic carcinoma

Two years after pelvic irradiation for prostatic cancer, bilateral protrusio acetabuli and collapse of the right femoral head requiring prosthetic arthroplasty developed in a 73-year-old man with chronic rheumatoid arthritis. There was no evidence of metastases. Histologic evaluation showed empty lacunae in the bone but no evidence of obliterative endarteritis. Osteonecrosis and pathologic fractures constitute a rare complication of high voltage irradiation.