The host and the skeletal infection: classification and pathogenesis of acute bacterial bone and joint sepsis.

Bone and joints are normally sterile areas. Bacteria may reach these sites by either haematogenous spread or spread from an exogenous or endogenous contiguous focus of infection. Bone infection, or osteomyelitis, is characterized by a progressive infectious process resulting in inflammatory destruction of bone, bone necrosis and new bone formation. Joint infections, or infectious arthritis, arise either from the haematogenous spread of organisms through the highly vascularized synovial membrane or from direct extension of a contiguous bone or soft tissue infection. The most commonly involved joints are the knee and the hip, although any joint can become infected. Infectious arthritis is monoarticular in 90% of cases. Some of the questions to be answered in this chapter include: how bacteria reach and cause damage in the bones and joints; what the current classification systems of bone and joint infections are; what some risk factors and host factors associated with bone and joint infection are; what some current characteristics of musculoskeletal infections are and whether the damage to joints can be diminished by treatment.