Accuracy of radiography, computed tomography and magnetic resonance imaging in diagnosing foreign bodies in the foot.

PURPOSE: The purpose of this study was to determine the accuracy of conventional radiography, computed tomography (CT) and magnetic resonance imaging (MRI) in detecting foreign bodies by using cadaver feet. MATERIALS AND METHODS: One hundred and sixty foreign bodies consisting of 5 × 2-mm fresh wood, dry wood, glass, porcelain and plastic fragments were randomly placed in the plantar soft tissue of the forefoot and sole. An additional 160 incisions were made without the insertion of foreign bodies. Radiographs, CT and MRI scans were assessed in a blinded fashion for the presence of a foreign body. RESULTS: Overall sensitivity and specificity for foreign body detection was 29% and 100% for radiographs, 63% and 98% for CT and 58% and 100% for MRI. The sensitivity of radiography was lower in the forefoot. CT and MRI detection rates depended on the attenuation values of the foreign bodies and on the susceptibility artefact, respectively. CT was superior to MRI in identifying water-rich fresh wood. CONCLUSIONS: Radiography, CT and MRI are highly specific in detecting foreign bodies but sensitivity is poor. The detection rate depends on the type of foreign body for all techniques and on location for radiography. To identify foreign bodies with MRI, pulse sequences should be used to enhance the susceptibility artefact. In water-rich wood, as in chronically retained wood, CT is more accurate than MRI.