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Osteomyelitis
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is an
Infection of
Bone , usually caused by
Pyogenic Bacteria or
Mycobacteria . It can be usefully subclassifed on the basis of the causative organism, the route, duration and anatomic location of the infection.
Generally microorganisms may be disseminated to bone hematogenously (''i.e.'', via the blood stream), spread contiguously to bone from local areas of infection, such as
Cellulitis , or be introduced by penetrating
Trauma including
Iatrogenic causes such as joint replacements or internal fixation of fractures.
Leukocyte s then enter the infected area, and in their attempt to
Engulf the infectious organisms, release enzymes that lyse bone.
Pus spreads into the bone's blood vessels, impairing the flow, and areas of devitalized infected bone, known as ''
Sequestra '', form the basis of a chronic infection. On
Histologic examination, these areas of necrotic bone are the basis for distinguishing between ''acute osteomyelitis'' and ''chronic osteomyelitis''. Osteomyelitis is an infective process which encompasses all of the bone (osseous) components, including the bone marrow. When it is chronic it can lead to bone sclerosis and deformity.
Because of the particulars of their blood supply, the
Tibia , the
Femur , the
Humerus , and the
Vertebra l bodies are especially prone to osteomyelitis.
Acute osteomyelitis almost invariably occurs in children. when adults are affected it may be because of compromised host resistance due to debilitation, disease or drugs (e.g.
Immunosuppressive therapy).
Osteomyelitis often requires prolonged
Antibiotic therapy, lasting a matter of weeks or months, and may require surgical
Debridement . Severe cases may lead to the loss of a limb.
The vast predominance of hematogenously seeded osteomyelitis is caused by ''
Staphylococcus Aureus ''. ''
Escherichia Coli '', and ''
Streptococci '' are other common
Pathogen s. In some subpopulations, including intravenous drug users and
Splenectomized patients,
Gram Negative bacteria, including enteric bacilli, are significant pathogens.
''Staphylococcus aureus'' is also the most common organism seen in osteomyelitis seeded from areas of contiguous infection, but here Gram negative organisms and
Anaerobe s are somewhat more common, and mixed infections may be seen.
In osteomyelitis involving the vertebral bodies, about half the cases are due to ''Staphylococcus aureus'', and the other half are due to
Tuberculosis (spread hematogenously from the
Lung s). Tubercular osteomyelitis of the spine was so common before the initiation of effective antitubercular therapy that it acquired a special name, ''
Pott's Disease '', by which it is sometimes still known.
