Diagnostic Accuracy of Emergency Bedside Ultrasonography to Detect Cutaneous Wooden Foreign Bodies: Does Size Matter?

Abstract

Soft-tissue occult foreign bodies are a concerning cause of morbidity in the emergency department. The identification of wooden foreign bodies is a unique challenge because they are often not detectable by plain radiography. The purpose of this study was to determine the diagnostic accuracy of emergency physician-performed ultrasonography to detect wooden foreign bodies of varying sizes. We hypothesized that sonographic sensitivity would improve with increasing foreign body size. We conducted a blinded, prospective evaluation using a previously validated, chicken, soft-tissue model to simulate human tissue. We inserted wooden toothpicks of varying lengths (1mm, 2.5mm, 5mm, 7.5mm, 10mm) to a depth of 1cm in five tissue models. Five additional models were left without a foreign body to serve as controls. Fifty emergency physicians with prior ultrasonography training performed sonographic examinations of all 10 models and reported on the presence or absence of wooden foreign bodies. Subjects performed 10 ultrasonography examinations each for a total of 500 examinations. For the detection of wooden foreign bodies, overall test characteristics for sonography included sensitivity 48.4% (95% confidence interval [CI], 42.1%-54.8%) and specificity 67.6% (95% CI, 61.3%- 73.2%). Sensitivity did not change as object size increased (ρ = s.709). Emergency physician bedside ultrasonography demonstrated poor diagnostic accuracy for the detection of wooden foreign bodies. Accuracy did not improve with increasing object size up to 10mm. Providers should consider alternative diagnostic modalities if there is persistent clinical concern for a retained, radiolucent, soft-tissue foreign body.