How to differentiate between deep tissue injury to the heel and osteomyelitis?

Differentiating Deep Tissue Injury to the Heel vs. Osteomyelitis

The most definitive way to diagnose osteomyelitis in the heel is through combined bone culture and histology, while deep tissue injury can be identified through clinical examination and imaging without bone involvement. 1

Initial Diagnostic Approach

• Begin with plain radiographs of the affected foot to look for bony abnormalities, soft tissue gas, and radio-opaque foreign bodies 1
• Perform a probe-to-bone (PTB) test for any open wound, which can help diagnose (when likelihood is high) or exclude (when likelihood is low) osteomyelitis 1
• Consider osteomyelitis as a potential complication of any infected, deep, or large foot ulcer, especially one that is chronic or overlies a bony prominence 1

Key Distinguishing Features

Deep Tissue Injury:

• Presents with soft tissue swelling, effacement of fat planes, and possible fluid collections 1
• Radiographs may show only soft tissue swelling without bony changes 1
• MRI shows soft tissue edema and enhancement without bone marrow signal abnormalities 2
• No periosteal reaction or bone destruction on imaging 3

Osteomyelitis:

• Characterized by periosteal reaction, focal bone lucency, and frank bone destruction on X-ray (though these findings may take 7-10 days to appear) 3
• MRI shows bone marrow edema, cortical disruption, and adjacent soft tissue inflammation 2
• Presence of a sinus tract or ulcer extending to the bone substantially increases risk 4
• May have negative plain radiographs in early stages (first 14 days) 1

Advanced Imaging

• MRI is the recommended imaging modality after initial radiographs when osteomyelitis is suspected 1, 2
• Negative MRI, defined as maintenance of intramedullary fat signal intensity and integrity of cortical signal, effectively rules out osteomyelitis 4
• If MRI is unavailable or contraindicated, consider a leukocyte or antigranulocyte scan combined with a bone scan 1
• CT can detect cortical bone destruction, sequestra, and sinus tracts, although it is less sensitive than MRI for early osteomyelitis 2

Definitive Diagnosis

• The most definitive way to diagnose osteomyelitis is through combined bone culture and histology 1
• When bone is debrided to treat suspected osteomyelitis, send a sample for culture and histology 1
• Bone biopsy should be considered when:
  • Diagnostic uncertainty exists
  • Soft tissue cultures are inconclusive
  • Infection fails to respond to empirical antibiotic therapy 1, 5

Important Diagnostic Pitfalls

• Soft tissue cultures often do not accurately predict bone pathogens - studies show only 42.8% agreement between bone and deep tissue cultures 6
• Relying solely on radiographs to rule out infection is inadequate, as early osteomyelitis may have normal radiographs 2
• In one study, wound cultures failed to predict bone culture results in 75% of patients 7
• Misinterpreting post-surgical or post-traumatic changes as infection on MRI can lead to incorrect diagnosis 2

Clinical Implications

• When osteomyelitis is confirmed, antibiotic therapy is typically needed for 2-3 weeks for moderate to severe infections 1
• For deep tissue injury without bone involvement, shorter antibiotic courses may be sufficient 1
• When a radical resection leaves no remaining infected tissue, antibiotic therapy may be prescribed for only a short duration (2-5 days) 1
• When there is persistent infected or necrotic bone, prolonged (≥4 weeks) antibiotic treatment is suggested 1

By following this diagnostic algorithm and understanding the key differences between deep tissue injury and osteomyelitis, clinicians can ensure appropriate treatment and improve patient outcomes.