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Retained foreign bodies may lead to a severe inflammatory response (from wood, thorns, and spines), chronic local pain (from glass, metal, and plastic), local toxic reactions (from sea urchin spines and catfish spines), systemic toxicity (from lead), or infection. Most foreign bodies can be located during clinical examination. High risk wounds will need diagnostic imaging. Most foreign bodies should be removed in the emergency department but some may be left in place due to risk of removal.

Every wound has potential for containing a foreign body. The mechanism of injury, composition, and shape of the wounding object as well as the shape and location of the resulting wound determine the risk of a retained foreign body. Lacerating objects that splinter, shatter, or break increase the risk of a foreign body. Patient perception of the sensation of a foreign body more than doubles the likelihood of one being present. Every effort should be made to inspect all recesses of a wound. Extending the edges of the wound is often necessary for complete visualization. Wounds deeper than 5 mm and those whose depths cannot be investigated have a higher association with foreign bodies. Blind probing with a hemostat may be used if the wound is narrow and deep or if extending the wound is not desirable but is less effective.

Patients returning to the emergency department with retained foreign bodies may complain of sharp pain at the wound site with movement, a chronically irritated nonhealing wound, or a chronically infected wound.

Imaging studies should be ordered if a foreign body is suspected or if multiple foreign bodies were extracted from a wound. Most foreign bodies (80%–90%) can be seen on plain radiographs. MRI, CT, or US may be needed in certain circumstances (Table 14-1) Using an under-penetrated soft tissue technique or adjusting the contrast and brightness using a digital system may increase the likelihood of identifying a foreign body by increasing the contrast between the foreign body and the surrounding tissue. Wooden foreign bodies can mimic air bubbles on initial CT imaging. Ultrasound is sensitive for detecting foreign bodies larger than 4 to 5 mm but has a high false positive rate and is dependent upon the composition of the foreign body, proximity to echogenic structures, and operator experience. High frequency probes are used for superficial depths and low frequency probes are used to search to depths of 10 cm. MRI is more accurate than the other modalities in identifying wood, plastic, spines, and thorns, but it is less available for emergency use.

Table 14-1 Comparison of Imaging Modalities for Detection of Soft Tissue Foreign Bodies

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