[Pathophysiology of implant-associated infections: From biofilm to osteolysis and septic loosening].

Biofilm formation is the key factor in the pathogenesis of implant-associated infections. The most common pathogens isolated are Staphylococcus species, opportunists belonging to the physiological flora of the skin. Biofilm formation starts with the adhesion of bacteria and colonisation preferentially occurs on the surfaces of the foreign body material. As an interactive symbiotic "city of microbes," biofilm formation represents an efficient survival strategy for bacteria. In clinically apparent infections the biofilm induces a local host response with infiltration of phagocytic immune cells. The proinflammatory microenvironment results in a stimulation of osteoclastogenesis, with local osteolysis, and finally septic loosening of the implant. According to the biofilm theory, retaining the implant in primary revision surgery is only recommended in early-stage infections with a stable implant; in late-stage infections, or when loosening occurs, the implant should be removed. Results of previous anti-biofilm therapies have not been satisfactory; therefore, current research is focused on prevention strategies, especially the modification of implant surfaces. Basic knowledge of the underlying pathophysiology is a prerequisite for the development of innovative interdisciplinary therapy and prevention strategies; in this context, essential aspects of biofilm formation, its consequences, and its relevance to diagnosis and therapy are described and discussed.