How is a wooden foreign body diagnosed in a finger?

Diagnosis of Wooden Foreign Bodies in the Finger

Ultrasound is the most effective imaging modality for detecting wooden foreign bodies in the finger when radiographs are negative, with a reported sensitivity of 95% for foreign body detection. 1, 2

Initial Diagnostic Approach

• Radiographs of the area of interest should be the first imaging study for suspected foreign bodies in the finger, with multiple views to maximize detection 1, 2
• Wood is radiolucent (not visible) on radiographs, unlike metal, stone, and glass which are radiodense and more easily detected 1
• If initial radiographs are negative but a wooden foreign body is still suspected based on history and examination, further imaging is necessary 1

Imaging Modalities for Wooden Foreign Body Detection

Ultrasound

• Ultrasound is the imaging modality of choice for detecting wooden foreign bodies when radiographs are negative 1, 2
• All foreign bodies appear hyperechoic on ultrasound with some degree of posterior acoustic shadowing 2
• Ultrasound allows for characterization of foreign body morphology, depth, and relationship to adjacent structures 2
• Ultrasound can provide real-time guidance during removal procedures 3
• Limitations include reduced effectiveness for foreign bodies deeper than 4cm from skin and difficult visualization if air is present in adjacent soft tissues 2

CT Scanning

• CT has high sensitivity for detection of foreign bodies and is 5-15 times more sensitive than radiography 1
• CT is superior to MRI in identifying water-rich fresh wood 1
• CT can precisely localize foreign bodies and determine their relationship to surrounding structures 1
• For comparable studies regarding foreign bodies in the feet, CT has 63% sensitivity and 98% specificity 1
• Thin slice thickness (1 mm) is recommended as small foreign bodies may be missed on CT if thicker slices are obtained 1

MRI

• MRI has lower sensitivity compared to CT and ultrasound for foreign body detection 1, 2
• For foreign bodies in the feet, MRI has 58% sensitivity and 100% specificity 1
• On MRI, wooden foreign bodies are usually low signal on all sequences and demonstrate non-anatomic morphology (linear or polygonal shape) 1
• MRI may be useful in detecting complications such as surrounding edema, inflammation, or abscess formation 1
• MRI is not recommended as the initial study for wooden foreign body detection 2, 4

Clinical Pitfalls and Considerations

• Wood foreign bodies can cause granulomatous reactions and superimposed soft tissue infections including cellulitis, abscess, myositis, or sinus tract formation 1
• Hand surgeons should be consulted due to the risk of damage to tendons, nerves, and blood vessels during removal 2
• Chronic pain, inflammation, and infection can develop even months after the initial injury if wooden foreign bodies are not completely removed 2, 5
• When removing wooden foreign bodies, adequate wound visualization and patient cooperation are essential for success 5
• Wound irrigation with normal saline or tap water is recommended after foreign body removal, while antiseptic solutions should be avoided as they may impair healing 5