Histopathology of femoral head osteonecrosis in rheumatoid arthritis: the relationship between steroid therapy and lipid degeneration in the osteocyte.

To investigate the pathology of osteonecrosis of the femoral head (ON) in patients with rheumatoid arthritis (RA), we examined 26 hips clinically and histologically. In this study, we diagnosed ON by both the radiological evidence of femoral head collapse, with or without narrowing of the joint space, and by histological evidence of extensive areas of bone necrosis with surrounding reparative new bone. Thus 14 hips were diagnosed as ON, and 12 hips were not. All of the patients with ON had a history of steroid medication. The frequency of lipid-containing osteocytes observed in the subchondral area of the femoral head significantly correlated with the occurrence of ON (P less than 0.05). In electron micrographs, these osteocytes showed degenerative features, with their nuclei pressed towards one side of the cell by plump fatty droplets (fatty degeneration). In patients with RA, there was a significant correlation between the appearance of lipid-containing osteocytes and steroid medication (P less than 0.05). No relationship existed between the severity of RA synovitis and the occurrence of ON. These data suggest that ON in rheumatoid hips may relate to the administration of a steroid and the fatty degeneration of osteocytes.