Bilateral protusio acetabuli following pelvic irradiation.

A 77 year old man developed bilateral protrusio acetabuli three years following pelvic irradiation for transitional cell carcinoma of the prostatic urethra. There was no evidence of metastasis or coexistent systemic arthritis. Aseptic necrosis of acetabular bone is the postulated etiology. Gross and pathologic evidence of aseptic necrosis of both femoral heads was observed. Vascular fibrosis was a prominent pathologic finding, as was eosinophilia of the synovial fluid and joint tissue. Protrusio appears to be an infrequently described complication of pelvic irradiation.