A man who reported to hospital with a sore knee walked out and never came back after doctors told him his penis was turning to bone.

The bizarre case is detailed in the latest issue of journal Urology Case Reports, published online at the end of last week.

The 63-year-old had suffered a fall, hurting his buttocks and knee. He went to hospital, where doctors did an X-ray to see if there were any fractures. There weren't, but he told them he was also suffering pain in his privates.

The X-ray showed he had an "extensive plaque-like calcification along the expected distribution of the penis", and diagnosed him with penile ossification.