How to evaluate and treat cellulitis of the leg with suspected hardware (prosthetic) involvement, considering the use of computed tomography (CT) scan?

Evaluation and Management of Leg Cellulitis with Suspected Hardware Involvement

For cellulitis of the leg with suspected hardware involvement, MRI with and without IV contrast is the preferred imaging modality due to its superior ability to detect both soft tissue infection and potential osteomyelitis. 1

Initial Assessment

• Begin with plain radiographs to evaluate for radiodense foreign bodies, hardware complications (loosening, fracture), and to establish baseline anatomic detail 1
• Look for cardinal manifestations of infection: purulent secretions, redness, warmth, swelling/induration, and pain/tenderness 1
• Assess for systemic signs of infection including fever, altered mental status, and elevated inflammatory markers 2
• Document the extent of cellulitis, depth of involvement, and any drainage characteristics 1

Imaging Algorithm

First-line imaging:

• Plain radiographs to evaluate hardware status and exclude alternative diagnoses 1
• MRI with and without IV contrast is the recommended next step for suspected hardware-associated infection 1
  • Highest sensitivity and specificity for detecting both soft tissue infection and osteomyelitis 1
  • Can delineate the anatomic extent of infection and identify complications requiring intervention 1
  • Metal artifact reduction techniques have improved hardware imaging, particularly in appendicular skeleton 1

Alternative imaging options (if MRI contraindicated):

• CT with IV contrast (rating 7/9) 1

  • Useful for detecting hardware complications, fluid collections, and sequestra 1
  • Can identify abscesses requiring drainage 1
  • Less sensitive than MRI for early osteomyelitis but better for visualizing cortical bone 1

• Labeled leukocyte scan with Tc-99m sulfur colloid marrow scan (rating 7/9) 1

  • Alternative when extensive hardware is present causing significant artifact 1
  • Particularly useful when MRI and CT are limited by hardware artifact 1

Clinical Considerations

• CT for extremity cellulitis has shown low yield (5.5%) for detecting deep infection in lower extremities 3

• Ultrasound has limited utility in hardware-associated infections (rating 1/9) due to:

  • Metal artifact limitations 1
  • Inability to adequately assess bone abnormalities 1
  • Limited visualization of deeper structures 1

• Recent surgery or trauma can complicate imaging interpretation as bone marrow and soft tissue edema may persist and mimic infection 1

Management Implications

• If abscess is identified, consider image-guided aspiration or surgical drainage 1
• Obtain cultures before initiating antibiotic therapy when possible 1
• Deep tissue specimens provide more accurate culture results than superficial swabs 1
• Positive imaging findings consistent with hardware-associated infection may require surgical consultation for potential hardware removal or debridement 2

Common Pitfalls

• Relying solely on CT for cellulitis evaluation may lead to unnecessary radiation exposure with limited yield 3
• Inflammation due to recent surgery or trauma can decrease accuracy of all imaging modalities 1
• Metal artifacts can significantly limit imaging quality - use metal artifact reduction techniques when available 1
• Polymicrobial infections are common in hardware-associated infections, requiring broad-spectrum antibiotics initially 4