In a patient with a nail‑bed infection of the finger that is not improving despite antibiotics and aspiration, are plain radiographs (AP and lateral views) useful for detecting a retained foreign body?

X-rays Are Helpful as Initial Imaging but Have Significant Limitations for Foreign Body Detection in Refractory Nail-Bed Infections

Yes, obtain plain radiographs (AP and lateral views) as the initial imaging study, but recognize that if clinical suspicion for a retained foreign body remains high and x-rays are negative, you must proceed directly to ultrasound or CT for definitive evaluation. 1, 2

Algorithmic Approach to Imaging

Step 1: Initial Plain Radiographs

• Always start with x-rays when foreign body is suspected, even though they have major limitations 1, 2
• Order AP and lateral views at minimum
• X-rays will detect:
  • Radiodense materials: metal, graphite, stone (100% sensitivity) 1, 3
  • Glass: 96% visible, but small fragments or those obscured by bone may be missed 1, 3
  • Wood: Only 15% visible—essentially useless for organic material 3
  • Plastic, rubber: Not visible (radiolucent) 2

Step 2: If X-rays Are Negative but Clinical Suspicion Persists

Do NOT stop at negative x-rays. The ACR guidelines explicitly address this scenario as "Variant 3" 1, 2:

Next Step: Ultrasound (Preferred for Acute Setting)

• 95% sensitivity for foreign body detection 2
• Advantages:
  • Excellent for radiolucent materials (wood, plastic) that x-rays miss
  • Can characterize depth, location relative to tendons/nerves/vessels
  • Shows inflammatory changes (hyperechoic rim with increased vascularity develops within 24 hours) 2
  • Can guide real-time removal 2
• Limitations:
  • Difficult for objects >4 cm deep 2
  • Air in adjacent tissues degrades images 2
  • Cannot detect foreign bodies within bone 2

Alternative: CT with Thin Slices

• 5-15 times more sensitive than radiography 2
• Use 1mm slice thickness to avoid missing small foreign bodies 2
• Advantages:
  • Detects glass and wood (both appear moderately hyperdense despite being radiolucent on x-ray) 2
  • Precise localization for surgical planning
  • Evaluates complications: abscess, osteomyelitis, sinus tracts 2
• Choose CT over ultrasound when:
  • Suspected deep penetration
  • Concern for bone involvement
  • Need for precise surgical planning 4

Step 3: Consider MRI for Infection Complications (Not for Foreign Body Detection)

• MRI is NOT sensitive for detecting foreign bodies 2
• Small foreign bodies are frequently missed 2
• However, MRI excels at:
  • Detecting surrounding inflammatory changes (edema, enhancement)
  • Diagnosing osteomyelitis if bone involvement suspected 1
  • Evaluating abscess, fasciitis, tenosynovitis 1, 2
• Caution: Screen for metallic foreign bodies before MRI due to heating/movement risk 2

Critical Clinical Pitfalls

Common Diagnostic Errors

1. Stopping at negative x-rays: 38% of foreign bodies are missed by initial physicians, often because radiographs weren't obtained or were falsely negative 3
2. Assuming all glass is visible: Small fragments or those obscured by bone may not appear 1
3. Relying on x-rays for organic material: Wood is only 15% visible radiographically 3

Why This Infection Isn't Improving

A retained foreign body triggers a granulomatous reaction that perpetuates infection regardless of antibiotics 1, 2. The foreign body must be physically removed—antibiotics alone will fail 5, 6.

Red Flags Requiring Advanced Imaging

• Persistent infection despite appropriate antibiotics and drainage
• History of puncture wound or penetrating trauma
• Palpable mass or localized tenderness
• Chronic drainage or sinus tract formation 5, 6

Practical Workflow Summary

1. Obtain x-rays first (AP/lateral minimum)—quick, inexpensive, detects radiodense materials
2. If negative but suspicion remains: Order ultrasound (first-line for superficial foreign bodies) or CT with 1mm cuts (for deep/complex cases)
3. Reserve MRI for evaluating infection extent and osteomyelitis, not foreign body detection
4. Plan surgical exploration if imaging confirms foreign body or if clinical suspicion remains very high despite negative advanced imaging

The 2022 ACR guidelines are unequivocal: in puncture wounds with suspected foreign bodies and negative radiographs, ultrasound or CT must be performed 2. Do not allow negative x-rays to provide false reassurance in this clinical scenario.