Diagnostic imaging

Radiographic features are as follows:

• radiographs may show only soft tissue swelling for the first two weeks
• periosteal new bone formation is visible by the end of the second week. Later, the sequestrum becomes rarefied and ragged
• neighbouring bone may become sclerotic - for example the femoral head scleroses during osteomyelitis of the proximal femur, suggesting avascularity of the sclerotic bone and possible necrosis

Other imaging includes:

• ultrasound may be very useful in localising subperiostial pus and guiding needle aspiration
• bone scan using 99m-Tc diphosphonates is very sensitive for osteomyelitis at all stages. Indium-labelled leukocytes may be more specific for infection
• MRI can distinguish pus from blood and may be helpful
  • a meta-analysis found that MRI performed well in the diagnosis of osteomyelitis of the foot and ankle and can be used to rule in or rule out the diagnosis.
    • magnetic resonance imaging performance was markedly superior to that of technetium Tc 99m bone scanning, plain radiography, and white blood cell studies

Reference:

1. Kapoor A et al. Magnetic resonance imaging for diagnosing foot osteomyelitis: a meta-analysis. Arch Intern Med. 2007 Jan 22;167(2):125-32