[Is bone infection of endogenous or exogenous origin? A pathophysiological approach]

Osteomyelitis is a bacterial implant in bone matrix. Infection occurs as a result of a bacteremia, an inoculation during aseptic or orthopedic surgery, or a contiguous infectious focus. Persistent and relapsing infection may be due to three situations: underlying conditions such as diabetes mellitus or rheumatoid arthritis, presence of foreign surgical implant, and a causative bacterial strain. The pathogenesis of osteomyelitis has been explored through various experimental models, involving mostly Staphylococcus (S. aureus, S. epidermidis) and has given new insights. Bacterial adherence to implanted devices or bone matrix via surface proteins is critical for bacterial survival. Further bacterial growth depends on various mechanisms: the capacity to exhibit matrix-embedded lifestyle known as biofilm and the ability for bacterial subpopulations to switch to a dormant metabolic state known as small colony variants. In addition to bacterial factors, the presence of foreign material induces a defect in local inflammatory response partly responsible for the high susceptibility to infection.