What is the recommended radiological investigation for a patient with focal pain, warmth, tenderness, and a history of a penetrating wound in the leg?

Radiological Investigation for Suspected Osteomyelitis Following Penetrating Leg Trauma

X-ray (plain radiography) should be the initial imaging study for this patient with focal leg pain, warmth, tenderness, fever, and history of penetrating wound. 1

Clinical Context and Imaging Rationale

This patient's presentation—focal pain with increasing intensity, local warmth, tenderness, subjective fever, and history of penetrating trauma—is highly concerning for osteomyelitis (bone infection) or soft tissue infection following the penetrating injury.

Why X-ray is the Initial Study

Penetrating trauma is an explicit exclusionary criterion for clinical decision rules (like Ottawa rules), mandating radiographic evaluation regardless of other clinical findings. 1 The American College of Radiology guidelines specifically state that penetrating trauma requires radiographs as the first imaging study, even when standard clinical algorithms might otherwise suggest observation. 1

Key advantages of initial plain radiography:

• Establishes baseline bone architecture and can detect retained foreign bodies (98% sensitivity for radiopaque objects) 1
• Identifies early bony changes if osteomyelitis has progressed (though may be normal in early infection) 1
• Detects fractures or bone disruption from the penetrating injury itself 1
• Rapid, widely available, and cost-effective as a screening tool 1

When Advanced Imaging Becomes Necessary

If X-rays are negative or equivocal but clinical suspicion for osteomyelitis remains high, MRI is the next appropriate study. 1 MRI provides:

• Superior soft tissue contrast to evaluate for abscess formation 1
• High sensitivity for bone marrow edema indicating early osteomyelitis 1
• Assessment of deep soft tissue involvement and extent of infection 1

CT may be considered if:

• MRI is contraindicated or unavailable 1
• Better characterization of bony destruction is needed 1
• Surgical planning requires detailed osseous anatomy 1

Why Other Options Are Less Appropriate Initially

• Nuclear scan (bone scan): Not routinely used as initial imaging for acute trauma with penetrating injury 1. While sensitive for osteomyelitis, it lacks specificity and anatomic detail compared to MRI, and is reserved for specific clinical scenarios where other modalities are inconclusive.

• CT as initial study: Not recommended as first-line imaging for penetrating extremity trauma unless in polytrauma patients requiring rapid whole-body assessment 1. CT without contrast cannot adequately assess soft tissue infection.

• MRI as initial study: Not appropriate as the first imaging modality for acute trauma evaluation 1. Plain radiographs must be obtained first to exclude fractures, foreign bodies, and establish baseline anatomy.

Critical Clinical Pitfall

Do not delay imaging in penetrating trauma based on clinical decision rules. 1 The Ottawa rules and similar algorithms explicitly exclude penetrating injuries, skin wounds, and suspected infections from their application. 1 This patient requires immediate radiographic evaluation regardless of ability to bear weight or other clinical criteria.

Algorithmic Approach

1. Obtain plain radiographs (AP and lateral views) immediately 1
2. If radiographs show bony abnormality: Proceed with appropriate treatment; consider MRI for surgical planning if needed 1
3. If radiographs are normal but clinical suspicion remains high: Order MRI without delay to evaluate for early osteomyelitis or soft tissue abscess 1
4. If foreign body suspected and not visible on X-ray: Consider ultrasound for radiolucent objects or CT for better characterization 1

Answer: A. X-ray is the correct initial radiological investigation for this clinical scenario.