What is the recommended radiological diagnostic approach for a patient with suspected osteomyelitis (infection of the bone) presenting with focal pain, local warmth, tenderness, and a history of a penetrating wound?

Radiological Diagnostic Approach for Suspected Osteomyelitis

Start with plain X-ray (A) as the initial imaging modality, but proceed immediately to MRI (B) if clinical suspicion remains high, as MRI is the definitive diagnostic test for osteomyelitis and should not be delayed in this acute presentation with penetrating trauma history. 1, 2, 3

Initial Imaging Algorithm

Plain Radiographs First

• X-rays must be obtained first in all suspected osteomyelitis cases due to wide availability, low cost, and ability to exclude alternative diagnoses such as fractures or retained foreign bodies from the penetrating wound 1, 2, 3
• However, radiographs have extremely limited sensitivity in early acute osteomyelitis—they are often normal or show only mild soft tissue swelling in the first 1-2 weeks, with bone destruction not appearing until 7-10 days and requiring >30% osseous matrix destruction to be visible 3
• In this 8-year-old with acute symptoms following penetrating trauma, normal X-rays do NOT exclude osteomyelitis 3

Proceed Directly to MRI

• MRI is the imaging modality of choice for suspected bone infection with superior sensitivity for bone marrow abnormalities, excellent soft tissue contrast, and anatomic detail 1, 2, 4
• MRI has a 100% negative predictive value for excluding osteomyelitis—a normal marrow signal reliably excludes infection 2
• The American College of Radiology specifically recommends MRI as the preferred imaging study when osteomyelitis is suspected, particularly in the setting of penetrating trauma where early detection is critical 1
• Do not wait 2-4 weeks for repeat radiographs in this acute presentation with penetrating wound history—the risk of progression and complications is too high 1, 2

Key MRI Findings to Identify

MRI will demonstrate:

• Bone marrow edema (earliest finding) 1, 4
• T2-weighted image hyperintensity 5
• T1-weighted confluent signal abnormality 5
• Cortical erosion (highly specific when present) 1, 5
• Soft tissue involvement, abscesses, and extent of infection 1, 4
• Periosteal reaction and alterations in tissue perfusion 1, 4

Alternative Imaging (When MRI Unavailable or Contraindicated)

CT Scan (C)

• CT depicts cortical bone well and can detect periosteal reaction, bone destruction, sequestra, soft tissue infections, and abscesses 1, 2, 4
• CT is less sensitive than MRI for detecting early bone marrow infection 1, 6
• Consider CT only if MRI is contraindicated or unavailable 2, 4

Nuclear Scan (D)

• Three-phase bone scan is highly sensitive and can become positive as early as 1-2 days after symptom onset 2, 7
• Specificity is poor (25%) in distinguishing infection from trauma, fracture healing, or other inflammatory processes 1, 7
• Nuclear medicine studies are most appropriate when MRI is contraindicated, infection is multifocal, or hardware is present 1, 2
• In this pediatric case with acute presentation, nuclear scanning would delay definitive diagnosis 1

Critical Pitfalls to Avoid

• Never rely solely on radiographs to rule out infection in acute presentations—early osteomyelitis has normal radiographic appearance 2, 3
• Do not delay MRI waiting for radiographic changes to develop, as this can take weeks while infection progresses 3
• In penetrating trauma, foreign bodies and post-traumatic changes can complicate interpretation, making early MRI even more critical 1
• Multifocal involvement is more common in children than adults—MRI can identify all sites of involvement 2

Clinical Context Considerations

In this specific case of an 8-year-old with:

• Acute focal pain with increasing intensity
• Local warmth and tenderness (signs of active infection)
• History of penetrating wound (direct inoculation route)
• Subjective fever (systemic involvement)

The answer is B (MRI) as the definitive diagnostic test, though A (X-ray) should be obtained first as the initial screening study. 1, 2, 6 If forced to choose only one answer, MRI (B) is the correct choice as it is the most sensitive and specific modality that will definitively diagnose or exclude osteomyelitis in this acute setting. 1, 6