**6.1 Histological examination**

Histological examination of the periprosthetic tissues showed large amounts of metal and polyethylene debris and a nonspecific chronic inflammatory reaction. Wear debris, macrophages that had phagocytosed small metal and polyethylene particles, fibroid necrosis, and proliferation of capillaries were seen more commonly in granulomas (Fig. 1).

Fig. 1. Polyethylene and metal particles in the interstitium, giant cells and macrophages (Perle's iron stain, x500)

In contrast, stroma rich of connective tissue, abundance of fibroblasts with less frequent macrophages were more prevalent in the fibrous pseudocapsule (Fig. 2).

Fig. 2. Periprosthetic tissue from 72-year-old male, 9 years after implantation of cementless prosthesis. Adjacent to the implant synovia-like membrane with 1-2 cell layers (arrow), interstitial matrix rich of fibrous tissue with abundance of fibroblasts and macrophages digested wear debris (open arrow) (haematoxylene staining, x500).
