Osteomyelitis
A pyogenic bone infection, osteomyelitis may be chronic or acute. It commonly results from a combination of local trauma—usually quite trivial but resulting in hematoma formation—and an acute infection originating elsewhere in the body. Although osteomyelitis may remain localized, it can spread through the bone to the marrow, cortex, and periosteum.
Acute osteomyelitis is typically a blood-borne disease that usually affects rapidly growing children. Chronic osteomyelitis, although rare, is characterized by multiple draining sinus tracts and metastatic lesions.
Age AlertOsteomyelitis occurs more commonly in children than in adults—and particularly in boys—usually as a complication of an acute localized infection. The most common sites in children are the lower end of the femur and the upper end of the tibia, humerus, and radius. In adults, the most common sites are the pelvis and vertebrae, generally the result of contamination associated with surgery or trauma.
The incidence of both chronic and acute osteomyelitis is declining, except in drug abusers. With prompt treatment, the prognosis for acute osteomyelitis is good; for chronic osteomyelitis, which is more prevalent in adults, the prognosis is still poor.
Causes
The most common pyogenic organism in osteomyelitis is Staphylococcus aureus; others include Streptococcus pyogenes, Pneumococcus, Pseudomonas aeruginosa, Escherichia coli, and Proteus vulgaris. Typically, these organisms find a culture site in a hematoma from recent trauma or in a weakened area, such as the site of local infection (for example, furunculosis), and spread directly to bone.
As the organisms grow and form pus within the bone, tension builds within the rigid medullary cavity, forcing pus through the haversian canals. This forms a subperiosteal abscess that deprives the bone of its blood supply and eventually may cause necrosis. In turn, necrosis stimulates the periosteum to create new bone (involucrum); the old bone (sequestrum) detaches and works its way out through an abscess or the sinuses. By the time sequestrum forms, osteomyelitis is chronic.
Signs and symptoms
Onset of acute osteomyelitis is usually rapid, with sudden pain in the affected bone, and tenderness, heat, swelling, and restricted movement over it. Associated systemic signs and symptoms include tachycardia, sudden fever, nausea, and malaise.
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