Osteomyelitis is a progressive infectious process involving the various components of bone, namely periosteum, cortical bone, and the medullary cavity. The disease is characterized by progressive, inflammatory destruction of bone; by necrosis; and by new bone apposition.

Acute osteomyelitis evolves over several days to weeks: the term acute is used in opposition to chronic osteomyelitis, a disease characterized by clinical symptoms that persist for several weeks followed by long-standing infection evolving over months or even years, by the persistence of microorganisms, by lowgrade inflammation, by the presence of necrotic bone (sequestra) and foreign material, and by fistulous tracts. The terms acute and chronic do not have a sharp demarcation and are often used somewhat loosely. Nevertheless, they are useful clinical concepts in infectious diseases because they describe two different patterns of the same disease, caused by the same microorganisms, but with different evolutions.

CLINICAL MANIFESTATIONS AND CHARACTERISTICS OF THE PATHOGEN

From a practical point of view, it is useful to distinguish three types of osteomyelitis, which are described separately. Hematogenous osteomyelitis follows bacteremic spread, is seen mostly in prepubertal children and in elderly patients, and is characterized by local proliferation of bacteria within bone during septicemia. In most cases, infection is located in the metaphyseal area of long bones or in the spine. Osteomyelitis secondary to a contiguous focus of infection without vascular insufficiency follows trauma, organ perforation, or an orthopedic procedure. It implies an initial infection, which by continuity gains access to bone.