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KembaraXtra-Emergency and Acute Medicine - Osteomyelitis
Description: Osteomyelitis is an infection of bone characterized by ongoing inflammatory destruction. It is most commonly bacterial in origin, although fungal osteomyelitis can occur, particularly in immunocompromised patients. The disease may present as acute, subacute, or chronic infection, with chronic cases defined by persistence or recurrence and the presence of necrotic bone (sequestrum).
Etiology: Hematogenous osteomyelitis occurs when bacteria seed bone via the bloodstream and is most common in children, the elderly, and people who inject drugs. Children typically develop acute disease, often without a preceding illness, though up to one-third report recent trauma. Adults more often develop subacute or chronic disease. Staphylococcus aureus is the most common pathogen across all age groups. Neonates are additionally affected by Enterobacteriaceae, group A and B streptococci, and Escherichia coli. Children may also develop infection from Haemophilus influenzae, while Salmonella is classically associated with sickle cell disease. Adults may have infections caused by gram-negative rods, Pseudomonas, Staphylococcus epidermidis, and anaerobes. Vertebral osteomyelitis is uncommon but typically affects adults over 45 years, often in the setting of diabetes, malignancy, hemodialysis, long-term catheterization, or IV drug use, and may extend to cause epidural abscesses or deep paraspinal collections. Direct or contiguous osteomyelitis occurs following trauma, open fractures, surgery, or spread from adjacent soft tissue infection and is more common in adults and adolescents. Chronic osteomyelitis is associated with necrotic bone and commonly involves S. aureus, S. epidermidis, Pseudomonas aeruginosa, and gram-negative organisms.
Clinical features: Symptoms vary with disease duration. Patients often present with localized, deep, dull, or throbbing bone pain that may occur at rest or with movement. Fever and chills may be present in acute disease but are often absent in chronic infection. Other features include malaise, nausea, vomiting, reluctance to use an affected limb, nonhealing ulcers, or fracture nonunion. Risk factors include diabetes mellitus, vascular disease, IV drug use, trauma, and invasive procedures. Examination may reveal localized warmth, erythema, edema, tenderness, decreased range of motion, sinus tract drainage, or exposed bone. Deep ulcers with palpable bone and a positive “probe-to-bone” test strongly suggest osteomyelitis.
Evaluation: Initial workup includes complete blood count, erythrocyte sedimentation rate, C-reactive protein, plain radiographs, and blood and wound cultures. Leukocytosis may be absent, but inflammatory markers are usually elevated. Blood cultures are positive in approximately half of cases. Plain radiographs are often normal in the first two to three weeks; early findings include periosteal elevation, followed by cortical erosion and new bone formation. MRI is the imaging modality of choice, with high sensitivity and specificity, allowing early detection and assessment of marrow, cortical, and soft tissue involvement. CT is useful when MRI is contraindicated and for surgical planning. Bone scans and leukocyte scintigraphy may be helpful in selected cases, while ultrasound is increasingly useful in children. Definitive diagnosis is established by bone biopsy with histology and culture, which remains the gold standard.
Management: Initial management focuses on stabilization, particularly in septic patients or those with neurologic deficits from spinal involvement. Empiric intravenous antibiotics should be started after cultures are obtained, then tailored based on organism and sensitivities. Treatment typically requires four to six weeks of parenteral antibiotics, with shorter IV courses followed by oral therapy possible in selected pediatric cases. Orthopedic and infectious disease consultation is essential, and surgical intervention is often required for debridement of necrotic bone, infected hardware, or abscesses.
Disposition and follow-up: Patients with acute osteomyelitis should be admitted for intravenous antibiotics and monitoring. Chronic osteomyelitis often requires admission for surgical management and prolonged therapy. Selected subacute or chronic cases may be managed as outpatients if debridement has been performed, cultures obtained, and reliable home IV antibiotic therapy is available. Close follow-up is mandatory to monitor response and prevent recurrence.
Key points: A normal white blood cell count does not exclude osteomyelitis. Early radiographs may be normal, making MRI critical for early diagnosis. Wound cultures alone are often unreliable for guiding therapy, and bone biopsy provides the most accurate microbiologic diagnosis.
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