Does a patient with ongoing leukocytosis (elevated white blood cell count) and recent ankle surgery show signs of osteomyelitis (bone infection) on X-ray?

X-ray Cannot Rule Out Osteomyelitis in This Clinical Scenario

Your patient's normal ankle X-ray does NOT exclude osteomyelitis, and you must proceed with advanced imaging—specifically MRI with IV contrast—given the combination of persistent leukocytosis and recent surgical hardware. 1, 2

Why Plain Radiographs Are Inadequate Here

• Plain X-rays have poor sensitivity for early osteomyelitis, particularly in the post-surgical setting where it can take 2-4 weeks for radiographic changes (cortical erosion, periosteal reaction, lucency) to become visible 1, 3
• In the presence of surgical hardware, X-ray specificity drops even further because normal post-operative bone remodeling mimics infection radiographically 1
• The ACR explicitly states that normal initial radiographs in suspected post-surgical osteomyelitis require advanced imaging for definitive evaluation 1, 2

Critical Clinical Context

A common pitfall: Leukocytosis alone is actually a poor indicator of osteomyelitis in many clinical contexts. One study found that 54% of patients with proven acute osteomyelitis had normal white blood cell counts 4. However, persistent leukocytosis in your post-operative patient warrants investigation regardless.

Your Next Steps (ACR-Recommended Algorithm)

Immediate Actions:

• Order MRI with IV contrast of the left ankle as the definitive next imaging study 1, 2

  • Modern metal artifact reduction sequences allow excellent evaluation despite hardware 2
  • MRI has the highest sensitivity and specificity for acute osteomyelitis (superior to all other modalities) 1, 3
  • IV contrast improves soft tissue evaluation for abscess/sinus tracts but doesn't improve bone infection diagnosis itself 1

• Check inflammatory markers immediately: ESR and CRP 2, 3

  • These are more reliable than WBC count for osteomyelitis 1, 4
  • ESR is elevated in 96% of osteomyelitis cases 4

• Review operative notes to understand baseline hardware configuration 2

• Arrange urgent orthopedic surgery consultation within 24-48 hours 2

Alternative Imaging (If MRI Unavailable or Contraindicated):

• FDG-PET/CT is an excellent alternative IF surgery occurred >6 months ago 1, 2
  • Sensitivity 83-100% and specificity 76-100% for post-traumatic osteomyelitis with hardware 1
  • However, in the acute post-operative period (<6 months), normal surgical inflammation causes false positives 1

Imaging Modalities to AVOID:

• 3-phase bone scan: Specificity <50% in post-surgical patients due to normal bone remodeling 1
• WBC scan alone: Variable sensitivity/specificity, particularly poor in central skeleton 1, 5
• CT without contrast: Insensitive for acute osteomyelitis, though useful for identifying fluid collections or sequestra in chronic cases 1

If MRI Confirms Osteomyelitis

• Obtain tissue cultures at time of surgical debridement (not before surgery unless there's a drainable fluid collection) 1, 2, 3
• Bone biopsy-guided antibiotic therapy has significantly better outcomes than empiric treatment (56% vs 22% success) 1
• Hardware removal is typically required for cure of hardware-associated osteomyelitis 2
• Expect prolonged antibiotic therapy (typically 4-6 weeks minimum) and possible staged reconstruction 2

What to Look for on MRI

Concerning findings that suggest osteomyelitis with hardware include:

• Sinus tracts from hardware to skin (pathognomonic for chronic osteomyelitis) 2
• Bone marrow edema/signal changes 1
• Periosteal reaction, especially if exuberant 2
• Lucency around screws/hardware 2
• Soft tissue abscesses or fluid collections 1, 2

Bottom line: Normal X-rays mean nothing in this scenario. Get the MRI now to avoid missing a potentially limb-threatening infection that will only worsen with delay. 1, 2, 3