What role do X-rays (radiographs) play in the diagnosis of osteomyelitis?

Role of X-ray in the Diagnosis of Osteomyelitis

Plain radiographs should be the initial imaging modality in the workup of suspected osteomyelitis due to their wide availability, low cost, and ability to provide anatomic evaluation, though they have limited sensitivity in early disease. 1

Diagnostic Value of X-rays in Osteomyelitis

Advantages of X-rays

• Widely available, even in resource-limited settings
• Relatively low cost
• Can be interpreted by most experienced clinicians
• Easy to compare sequential radiographs over time
• Provides anatomic evaluation of the affected site
• Can detect alternative diagnoses (fractures, tumors, neuropathic changes)
• Can identify gas in soft tissues or radiopaque foreign bodies

Limitations of X-rays

• Poor sensitivity in early osteomyelitis (first 2-3 weeks of infection)
• Radiographic changes may not be visible until 30-50% of bone mineral content is lost
• Limited specificity for distinguishing infection from other conditions
• Estimated positive likelihood ratio of only 2.3 and negative likelihood ratio of 0.63 1

Characteristic Radiographic Findings in Osteomyelitis

Early Findings (often subtle or absent)

• Soft tissue swelling
• Deep soft tissue fat plane obliteration
• Periosteal thickening

Later Findings (typically after 10-14 days)

• Periosteal reaction or elevation
• Loss of bone cortex with bony erosion
• Focal loss of cortical trabecular pattern
• Marrow radiolucency
• Bone sclerosis (with or without erosion)

Advanced Findings

• Sequestrum (devitalized bone with radiodense appearance separated from normal bone)
• Involucrum (new bone growth outside previously existing bone)
• Cloacae (openings in the involucrum or cortex)
• Evidence of sinus tracts from bone to soft tissue 1

Optimal Use of X-rays in Osteomyelitis Workup

Timing Considerations

• Initial radiographs may be normal in early osteomyelitis (<14 days)
• Sequential radiographs taken 2-4 weeks apart are more valuable than a single study
• Changes seen over an interval of at least 2 weeks increase the likelihood of osteomyelitis 1

Integration with Other Diagnostic Methods

• Combining probe-to-bone test results with plain radiography improves overall diagnostic accuracy 1
• When initial radiographs are negative but clinical suspicion remains high, treat for soft tissue infection for ~2 weeks and repeat radiographs 1
• If radiographs show classic changes suggestive of osteomyelitis (cortical erosion, periosteal reaction), proceed with appropriate treatment or additional imaging 1

When to Consider Advanced Imaging

• When radiographs are negative but clinical suspicion remains high
• For surgical planning
• When there is persistent diagnostic uncertainty
• For evaluating the extent of infection

Advanced Imaging Options

• MRI: Highest sensitivity (82-100%) and specificity (75-96%) for osteomyelitis; provides superior soft tissue detail 2
• Nuclear medicine scans: Useful for identifying multifocal involvement, particularly in children 3, 4
• CT: Helpful for detecting early osseous erosion, sequestrum, foreign bodies, or gas formation 4

Common Pitfalls to Avoid

• Relying solely on initial radiographs to rule out osteomyelitis
• Failing to obtain follow-up radiographs when clinical suspicion remains high
• Not considering alternative diagnoses that may mimic osteomyelitis radiographically
• Overlooking the need for advanced imaging when radiographic findings are equivocal
• Misinterpreting periosteal reactions as definitive evidence of osteomyelitis (as seen in chronically infected ingrown toenails) 5

X-ray remains a fundamental first step in the diagnostic algorithm for osteomyelitis, providing valuable anatomic information and potentially identifying alternative diagnoses, but clinicians must recognize its limitations in early disease and appropriately integrate it with clinical findings and, when necessary, advanced imaging techniques.