TAILIEUCHUNG - Chapter 120. Osteomyelitis

Osteomyelitis, an infection of bone, is caused most commonly by pyogenic bacteria and mycobacteria. As a useful framework for evaluating a patient and planning treatment, cases are classified on the basis of the causative agent; the route by which organisms gain access to bone; the duration of infection; the anatomic location of infection; and the local and systemic host factors that have a bearing on pathogenesis and outcome. Pathogenesis and Pathology Microorganisms enter bone by hematogenous dissemination, by spread from a contiguous focus of infection, or by a penetrating wound. Trauma, ischemia, and foreign bodies enhance the susceptibility of. | Chapter 120. Osteomyelitis Osteomyelitis an infection of bone is caused most commonly by pyogenic bacteria and mycobacteria. As a useful framework for evaluating a patient and planning treatment cases are classified on the basis of the causative agent the route by which organisms gain access to bone the duration of infection the anatomic location of infection and the local and systemic host factors that have a bearing on pathogenesis and outcome. Pathogenesis and Pathology Microorganisms enter bone by hematogenous dissemination by spread from a contiguous focus of infection or by a penetrating wound. Trauma ischemia and foreign bodies enhance the susceptibility of bone to microbial invasion by exposing sites to which bacteria can bind and by impeding host defenses. Phagocytes attempt to contain the infection and in the process release enzymes that lyse bone. Bacteria escape host defenses by adhering tightly to damaged bone by entering and persisting within osteoblasts and by coating themselves and underlying surfaces with a protective polysaccharide-rich biofilm. Pus spreads into vascular channels raising intraosseous pressure and impairing the flow of blood as the untreated infection becomes chronic ischemic necrosis of bone results in the separation of large devascularized fragments sequestra . When pus breaks through the cortex subperiosteal or soft tissue abscesses form and the elevated periosteum deposits new bone an involucrum around the sequestrum. Microorganisms infiltrates of neutrophils and congested or thrombosed blood vessels are the principal histologic findings of acute osteomyelitis. The distinguishing feature of chronic osteomyelitis is necrotic bone which is characterized by the absence of living osteocytes. Mononuclear cells predominate in chronic infections and granulation and fibrous tissues replace bone that has been resorbed by osteoclasts. In the chronic stage organisms may be too few to be seen on staining. Hematogenous Osteomyelitis .

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