Histological analysis and biological effects of granulation tissue around loosened hip prostheses in the development of osteolysis

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-lbeta 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.