Osteomyelitis

Background

• Osteomyelitis is typically a bacterial infection of the bone but rarely may be fungal or mycobacterial.
• Illness may present as an acute or chronic infection.
• Incidence rates range widely with respect to the type of osteomyelitis and specific populations.
• The incidence of chronic osteomyelitis has increased due to the rising prevalence of risk factors such as diabetes and peripheral vascular disease.
• The mechanisms of infection include:
  • hematogenous seeding of bone, which most commonly occurs in children, causing acute infection
  • contiguous spread from adjacent soft tissues and joints, causing subacute to chronic infection
  • direct inoculation of microorganisms into bone due to wound contamination during surgery or trauma
• Acute osteomyelitis is typically caused by a single organism, while chronic osteomyelitis is more likely polymicrobial.
• Staphylococcus aureus is the most common pathogen in both acute and chronic osteomyelitis, coagulase-negative staphylococci are also common in chronic infection. Other important pathogens include; streptococci, Enterobacteriaceae, Pseudomonas, and anaerobes.

Evaluation

• Suspect osteomyelitis in patients with any of the following:
  • acute onset of fever with pain, erythema, and swelling at the affected site
  • chronic pain, persistent sinus tract or wound drainage, and soft tissue damage, particularly in patients with diabetes and peripheral vascular disease
• Definite diagnosis of chronic osteomyelitis requires a bone biopsy for pathology and culture.
• Supportive diagnostic testing for chronic osteomyelitis may include:
  • probe-to-bone test with a metal probe
  • blood tests - may show elevated inflammatory markers including erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP)
  • imaging studies, such as:
    • x-ray - low sensitivity early in course (acute osteomyelitis), serial x-rays may be performed to monitor suspected diabetic foot infections
    • magnetic resonance imaging (MRI) - good resolution and delineation of bone and soft tissue
    • computed tomography (CT) - useful for guiding a needle biopsy and in identifying sequestra (necrotic bone) or soft tissue extension
    • nuclear imaging - sensitive but not specific

Management

• Treatment goals include eradication of infection, restoration of function, and maintenance of stability as well as pain relief.
• When possible, wait to give antibiotics until after deep cultures at the time that debridement or bone biopsy are obtained.
  • Once samples are obtained, initiate empiric antibiotics guided by the patient's history, type of osteomyelitis, and any preliminary Gram stain or pathology available.
  • Narrow to pathogen-directed antibiotic therapy once the culture speciation and sensitivities are available.
  • The duration of therapy is usually 4-6 weeks, but is guided by the organism, location of infection, completeness of surgical debridement, presence of hardware, and clinical course. Long-term suppressive therapy may be considered in patients not suitable for surgery, particularly in the setting of retained infected hardware .
• A surgical approach may be required in patients with antibiotic failure, infected surgical hardware, or chronic osteomyelitis with necrotic bone and soft tissue.
• Early and specific treatment prior to bone destruction and necrosis is associated with a better prognosis.
• Recurrence rates remain high (up to 31% reported) despite surgery and long-term antibiotic therapy.