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Key Clinical Questions Osteomyelitis
How does bone become infected?
What parts of the history and physical examination are most helpful in diagnosis?
What treatment options should be considered?
How is the response to treatment monitored?
Septic Arthritis How should possible acute bacterial (septic) arthritis be evaluated?
When should empiric antibiotics be used in suspected septic arthritis? Which antibiotics?
What are the key elements of treatment of septic arthritis?
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Osteomyelitis is infection of bone, with accompanying inflammation and destruction. In healthy adults, osteomyelitis is rare. Bone infection usually requires predisposing factors. These include adjacent soft-tissue infections, such as diabetic foot ulcers and stage IV pressure sores, hematogenous seeding, as may occur in endocarditis, or direct inoculation of bone during trauma or surgery.
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Once microbes invade bone, they attach to host cells and extracellular matrix, as well as prosthetic biomaterials, if present. Bacteria in bone may produce biofilm, a slimy polymer that acts as a physical barrier against both antibiotics and the host immune system. Bacteria embedded in biofilm are less metabolically active, making them even less susceptible to antibiotics. Inflammation associated with bacterial toxins and the host immune response leads to bone lysis. Over time, as infection becomes chronic, suppuration leads to vascular congestion, raised intraosseous pressure, and ischemia of infected bone. The necrotic bone separates from healthy bone to form a sequestrum, a diagnostic finding of chronic osteomyelitis. If the dead bone cannot be resorbed, healthy new bone may form around it, encasing the sequestrum in an involucrum. The walled-off sequestrum may act like an abscess, with bacterial growth continuing in a pocket of necrotic tissue inaccessible to immune policing and antibiotics. As pressure in the sequestrum builds, infection may erupt through the involucrum, leading to subperiosteal or soft-tissue abscesses, or a sinus tract through overlying soft tissue.
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Bone resists infection under normal circumstances. Factors that influence the establishment and progression of osteomyelitis include pathogen virulence, inoculum size, bone health, presence of foreign objects, host immunity, and duration of infection. Patients should be asked about risk factors for osteomyelitis, such as diabetes, vascular disease, intravenous drug use, sickle cell disease, and recent trauma or surgery.
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In osteomyelitis, regardless of cause, cure often requires both medical and surgical intervention, with prolonged antibiotics as well as debridement of infected bone and soft tissue. When debridement is extensive, reconstructive surgery may be necessary, including bone grafts and muscle and skin flaps. Sufficient vascular supply is a critical element to healing; revascularization procedures may be necessary. Because of the multispecialty approach required for diagnosis and treatment, patients with suspected osteomyelitis should be admitted for further evaluation. Infectious disease and orthopedic surgery consultation is recommended, and input from vascular surgery and plastic surgery may also be indicated.
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OSTEOMYELITIS—GENERAL EVALUATION AND MANAGEMENT
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