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Osteomyelitis is an infection of bone or bone marrow, usually caused by pyogenic bacteria or mycobacteria. It can be usefully subclassified on the basis of the causative organism, the route, duration and anatomic location of the infection.
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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, internal fixation of fractures or root-canalled teeth. Leukocytes 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. Often, the body will try to create new bone around the area of necrosis. The resulting new bone is often called an involucrum. 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, the vertebra, the maxilla and the mandibular bodies are especially susceptible to osteomyelitis. 
In children, the long bones are usually affected. In adults, the vertebrae and the pelvis are most commonly affected.
Acute osteomyelitis almost invariably occurs in children. When adults are affected, it may be because of compromised host resistance due to debilitation, intravenous drug abuse, infectious root-canalled teeth, other disease or drugs (e.g. immunosuppressive therapy).
Osteomyelitis often requires prolonged antibiotic therapy. IV antibiotics are generally used to combat the infection, with a course lasting a matter of weeks or months. A PICC line or central venous catheter is often placed for this purpose. Osteomyelitis also may require surgical debridement. Severe cases may lead to the loss of a limb. Initial first line antibiotic choice is determined by the patient's history and regional differences in common infective organisms.
American artist Thomas Eakins in 1875 depicted a surgical procedure for osteomyelitis in a famous oil painting titled "The Gross Clinic," now part of Jefferson Medical College.
Staphylococcus aureus is the organism most commonly isolated from all forms of osteomyelitis.
Hematogenously seeded osteomyelitis is seen most frequently in children, and nearly 90% of cases are caused by Staphylococcus aureus. In infants, S. aureus, Group B streptococci and Escherichia coli are commonly isolated; in children from 1 to 16 years of age, S. aureus, Streptococcus pyogenes, and Haemophilus influenzae are common. In some subpopulations, including intravenous drug users and splenectomized patients, Gram negative bacteria, including enteric bacilli, are significant pathogens.
The most common form of the disease in adults is caused by injury exposing the bone to local infection. Staphylococcus aureus is again the most common organism seen in osteomyelitis seeded from areas of contiguous infection, but anaerobes and Gram negative organisms, including Pseudomonas aeruginosa, E. coli, and Serratia marcescens, are also common, and mixed infections are the rule rather than the exception.
Systemic mycotic (fungal) infections may also cause osteomyelitis. The two most common are Blastomyces dermatitidis and Coccidioides immitis.
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 lungs). 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.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Osteomyelitis". A list of authors is available in Wikipedia.|