Formation of double contour as a repair reaction in the human femoral head.

Thirty-two femoral heads from autopsy material with arthrotic changes and 12 surgical specimens of femoral heads with different diseases have been examined with respect to their ability to form a 'double contour'. An additional bony plate within the cartilage, giving rise to the double contour, occurred only in the non-pressure zone of the articular cartilage. There were no major differences between autopsy and surgical material and these changes could also not be found in normal femoral heads. The origin of a double contour could be traced to tissue elements penetrating the subchondral bone from the bone marrow, and was the result of a gradual transformation with chondroid tissue as the starting material. We observed a similar transformation leading to lamellar bone in association with pannus.