Necrosis of the femoral head, X-ray microtomography (microCT) and histology of retrieved human femoral heads.

Aseptic osteonecrosis of the hip (AON) is a rare, but well-known pathology in rheumatology and orthopedic surgery that is a necrosis of the articular cartilage secondary to a necrosis of the subchondral bone. The microscopic aspect is well known, but the microCT aspect has never been reported or correlated with histopathological findings. The objective of this study was to improve the knowledge of the pathophysiology of AON using histochemistry and microCT. One hundred and sixty femoral heads with stage 3 or 4 AON were analyzed: one half of the head was sent for microCT analysis after impregnation with phosphotungstic acid (PTA) and the other half was used for histological analysis without decalcification. The microCT analysis provides relevant information on the cracked articular cartilage and the relationship with the necrotic subchondral trabecular bone well illustrated on three videos. In histology, Goldner's trichrome showed that the articular cartilage remains well preserved for a long time. In addition, toluidine blue staining reveals a modeling process, i.e. the apposition of new bone without prior resorption by osteoclasts. Rhodamine B staining (fluorescence analysis) reveals that the osteonecrotic trabeculae and subchondral bone were devoid of osteocytes. Areas of peri-necrotic osteosclerosis are due to direct bone formation on the surface of pre-existing necrotic trabeculae.