Can ultrasound be used to detect a small glass fragment in the foot?

Ultrasound for Detecting Small Glass Foreign Bodies in the Foot

Yes, ultrasound is highly effective for detecting small glass fragments in the foot and should be used as the primary imaging modality after initial radiographs, with sensitivity approaching 100% for glass detection and the added benefit of real-time guidance for removal. 1, 2

Initial Imaging Algorithm

Step 1: Plain Radiographs First

• Obtain standard three-view foot radiographs (anteroposterior, lateral, and oblique) as the initial imaging study for any suspected foreign body. 3, 1
• Glass is radiodense and detectable on X-rays in approximately 98% of cases, making radiographs an excellent first-line study. 3, 1
• If an unembedded glass fragment is available from the injury scene, image it alongside the foot to provide additional information about the morphology and density of the retained foreign body. 3, 1

Step 2: Ultrasound When Radiographs Are Negative or for Precise Localization

• When radiographs are negative but clinical suspicion remains high (persistent pain, visible entry wound, palpable foreign body sensation), proceed immediately to high-resolution ultrasound. 1, 2
• Ultrasound can detect glass fragments as small as 2.5 mm in length and provides precise depth localization from the skin surface. 2
• In the original validation study, ultrasound successfully detected glass and metal wire foreign bodies in the foot that were clinically suspected, with 100% accuracy in identifying which patients were truly free of foreign bodies. 2

Why Ultrasound Excels for Glass Detection

Superior Soft Tissue Visualization

• Glass appears as a hyperechoic (bright) linear or curvilinear structure with posterior acoustic shadowing on ultrasound, making it readily distinguishable from surrounding soft tissue. 2
• Ultrasound pinpoints the exact surface beneath which the foreign body lies and localizes it precisely as to depth, which is crucial to avoid miscalculation during removal surgery. 2

Real-Time Guidance Capability

• Ultrasound enables real-time needle or instrument guidance for foreign body removal, increasing success rates and minimizing tissue damage, blood loss, and complications. 1, 4
• The ability to visualize the fragment dynamically during the procedure is a major advantage over static imaging modalities. 4

Assessment of Complications

• Ultrasound simultaneously evaluates surrounding soft tissues for fluid collections, abscess formation, or developing infection around retained fragments—complications that plain radiographs cannot detect. 1, 5

Technical Considerations

Optimal Ultrasound Technique

• Use a high-frequency linear-array transducer (10 MHz or higher) for maximum resolution of superficial structures in the foot. 2, 6
• Scan in at least two orthogonal planes to accurately localize the fragment in three-dimensional space. 1
• Apply copious gel and minimal transducer pressure to avoid displacing small mobile fragments. 2

Limitations to Recognize

• Ultrasound is operator-dependent and requires experience in musculoskeletal imaging; the quality of the examination varies significantly with operator skill. 3
• Very deep fragments (>4-5 cm) or those adjacent to bone may be obscured and harder to visualize. 1

When to Consider CT

• Reserve CT without IV contrast for cases where the fragment is suspected to be very deep within tissues, near bone, or when multiple fragments are suspected from high-energy trauma. 1, 7
• However, CT has only 63% sensitivity for foreign body detection overall, making it less reliable than both radiographs and ultrasound for glass detection. 1
• CT is most useful for surgical planning when precise anatomic relationships to bone, tendons, or neurovascular structures must be defined before removal. 1

Critical Clinical Pitfalls to Avoid

• Never skip the initial plain radiographs—they remain essential for detecting radiopaque foreign bodies and excluding associated fractures or gas-forming infections. 3, 7
• Do not assume a negative radiograph rules out a glass foreign body; up to 2% of glass fragments may be missed on X-ray due to small size or obscuration by adjacent bone. 1
• Always document neurovascular status before and after any intervention, as penetrating glass trauma can cause nerve or vascular injury. 1
• Obtain culture of any surrounding fluid or tissue if infection is suspected; imaging guides the procedure, but microbiologic diagnosis is essential for targeted antibiotic therapy. 7

Consequences of Missed Glass Foreign Bodies

• Retained glass fragments cause chronic inflammation, persistent pain, recurrent infection, and delayed wound healing. 1
• Early detection and removal prevent these complications and improve patient outcomes. 1, 2