Although aseptic loosening of the
prosthesis is a long-term complication after
total joint replacement, the detailed mechanism of
osteolysis remains unknown. We examined 82 samples from 40 patients with aseptic loosened
hip prostheses histologically, and compared the distribution of particles, macrophages/histiocytes, and foreign body giant cells in the retrieved tissue from capsules and around
prostheses. Furthermore, to investigate the mechanism of
osteolysis, we cultured tissue from a patient with
massive osteolysis and examined the effects of the
conditioned medium on osteoblasts in vitro. Numerous multinucleated giant cells and histiocytes were present, and
polyethylene particles ranging from medium to large were identified in the polarized light. However, the distribution was heterogeneous, and no particles were found microscopically in about 30%-40% of periprosthetic tissues, and in 60% of capsules. The amount of particles correlated with giant cells, but not with histiocytes. The
conditioned medium of the granulation tissue culture stimulated osteoblasts to produce
interleukin-6 in both
protein and
mRNA, and this was in part inhibited by anti-
tumor necrosis factor-alpha or the
interleukin-1beta antibody, suggesting that
interleukin-6 production is mediated by several
cytokines. These findings suggest that
interleukin-6, which is produced not only by macrophages but also by osteoblasts, is a contributing factor to aseptic loosening.