When to request MRI in chronic osteomyelitis?

MRI Indications in Chronic Osteomyelitis

MRI should be requested in chronic osteomyelitis when radiographs are inconclusive, when there is a draining sinus tract, when there is persistent pain and swelling after treatment, or when planning surgical intervention. 1

Initial Evaluation

• Plain radiographs should always be the first imaging modality in suspected chronic osteomyelitis, but they have limited sensitivity in early disease and should not be the sole imaging modality 1
• Radiographic findings in chronic osteomyelitis include bone sclerosis and areas of destruction, but these changes may take weeks to develop 1

Specific Indications for MRI

• When radiographs are negative or inconclusive but clinical suspicion remains high 1
• Presence of a draining sinus tract, which is highly suggestive of underlying chronic osteomyelitis 1
• To evaluate the extent of bone and soft tissue involvement before surgical intervention 1
• When planning debridement to accurately define the margins of infected bone 1
• To differentiate between soft tissue infection and bone involvement when clinical assessment is unclear 1, 2

Advantages of MRI in Chronic Osteomyelitis

• MRI has high sensitivity and specificity for chronic osteomyelitis, with superior ability to detect:

  • Soft tissue and marrow edema 1
  • Alterations in tissue perfusion 1
  • Cortical erosions with high interobserver agreement 1
  • Presence of abscesses and fistulae 1

• MRI can accurately define the extent of infection, which is crucial for surgical planning 1, 2

Special Considerations

• Post-surgical or post-traumatic setting: MRI remains sensitive but interpretation is more challenging due to marrow signal heterogeneity from prior trauma or surgery 1
• Hardware presence: Metal artifacts can limit MRI evaluation, though modern sequences can reduce these artifacts 1
• Draining sinus: When a draining sinus is present, MRI is superior for detecting the connection between the sinus tract and bone involvement 1

Limitations and Alternatives

• In cases where MRI is contraindicated or unavailable, CT can be considered as it shows cortical thickening, destruction, and fistulae, though it is less sensitive than MRI 1
• FDG-PET may be particularly useful when hardware is present, with reported sensitivity of 94% and specificity of 87% in chronic post-traumatic osteomyelitis 1
• Bone scintigraphy has reasonable sensitivity (82%) but poor specificity (25%) in chronic osteomyelitis 1, 3

Clinical Pathway for Chronic Osteomyelitis Imaging

1. Initial plain radiographs for all patients 1
2. If radiographs are negative but clinical suspicion persists, proceed to MRI 1
3. If MRI is inconclusive or contraindicated, consider CT or nuclear medicine studies 1
4. When diagnosis remains uncertain after imaging, bone biopsy should be considered for definitive diagnosis 1

Important Pitfalls to Avoid

• Relying solely on radiographs for diagnosis, as they may be normal in early disease 1
• Misinterpreting post-surgical or post-traumatic changes as infection on MRI 1
• Failing to obtain contrast-enhanced MRI when evaluating soft tissue involvement 1
• Delaying MRI when clinical suspicion is high despite negative radiographs 1, 2