How is osteomyelitis diagnosed?
• Gold standard = bone biopsy for culture and pathology.
• Probe-to-bone = using a blunt metal tool to evaluate diabetic foot ulcers; if a hard gritty surface is noted, this is 87% sensitive and 83% specific for osteomyelitis.
• Plain radiographs = can detect osteomyelitis after ∼2 weeks of symptoms (may miss early osteomyelitis).
• MRI = highest sensitivity with detection within 3 to 5 days of symptom onset.
• CT = more sensitive than plain radiographs, less sensitive than MRI. Useful for evaluating for the presence of sequestra and involucrum.
• Laboratory tests will usually reveal leukocytosis and elevations in ESR/CRP. Blood cultures are positive in ∼50% acute hematogenous osteomyelitis cases.
Pearl: Cultures of sinus tracts are not predictive of the organisms found in bone with the exception of S. aureus.