Chapter 58 Osteomyelitis
PATHOPHYSIOLOGY
Osteomyelitis is an infection of the bone that can occur in any bone in the body. The most common locations are the femur and the tibia. The humerus and the hip are rarely affected. The skull is a common location in infants. Usually a predisposing condition such as poor nutrition or poor hygiene exists.
Bacterial emboli reach the small arteries in the metaphysis, where circulation is sluggish. An abscess forms and replaces bone, causing increased pressure and secondary necrosis. This abscess eventually can rupture into the subperiosteal space. The infection spreads beneath the periosteum, thrombosing vessels and causing increased necrosis. The cycle of impaired circulation is thus established. A sinus can form and extend the infection to the skin. Extension to a joint results in septic arthritis. The condition can become chronic and thus quite resistant to therapy, often necessitating involved surgical intervention. The epiphysis is usually spared because it has a separate circulation.
There are several classsifications of osteomyelitis. One classification is by the duration of the disease: acute or chronic. Acute osteomyelitis is considered to occur over several days or weeks, and the chronic form is considered to be a long-standing infection. A second classification is by the source of the infection. The first is the hematogenous route, referring to circumstances when the infection originates from a bacteremia or by seeding through the bloodstream. This is the more common route, and sources include furuncles, skin abrasions, upper respiratory tract infections, otitis media, abscessed teeth, and pyelonephritis. The second is the contiguous route, where the infection originates in the nearby tissue as in the following: contamination from penetrating wounds, open fractures, or surgical wounds, or secondary extension through an abscess, burn, or wound. The third route is the presence of systemic disease or vascular insufficiency that causes the infection.
CLINICAL MANIFESTATIONS
LABORATORY AND DIAGNOSTIC TESTS
See Appendix D for normal values and ranges of laboratory and diagnostic tests.
1. Complete blood count—marked leukocytosis, indicates presence of infection
2. Erythrocyte sedimentation rate—elevated, indicates presence of infection
3. Blood culture and sensitivity test—positive culture in 50% of cases; common causative organisms vary with age and other factors; determine causative organism and preferred antibiotic
4. Radiographic studies—findings are normal in first 10 to 12 days until bone destruction occurs (soft tissue swelling is evident early)
