Abstract
In an out-of-hospital setting, evaluation for soft-tissue foreign bodies after impalement with a sea urchin spine can be challenging, with management options consisting of nonsurgical management or local surgical exploration. However, when an intra-articular foreign body is suspected, transfer to a hospital setting is often required for radiographic evaluation and surgical removal. Ultrasound (US) evaluation may allow for determining in the field if joint involvement is present, possibly eliminating patient transport to a health care facility. Our objective is to evaluate the effectiveness of bedside US in accurately determining the absence of an intra-articular foreign body in comparison to fluoroscopy and computed tomography (CT).
This was a prospective blinded study to determine the utility of US and fluoroscopy to detect an intra-articular foreign body. The largest joint in a skin-on chicken thigh was the target for the foreign body insertion. A single spine from a freshly harvested Uni sea urchin was introduced through the skin of the chicken, directed towards the joint. The spines were very fragile, and introduction caused the spine to break leaving no evidence of the location of insertion. As a result, the investigator was unable to determine the final position of the spinous tip. Each chicken quarter was evaluated for the presence of an intra-articular foreign body by 3 methods: bedside US, fluoroscopy, and CT. A separate investigator performed each modality and was blinded to the other's results. US evaluation was performed by an emergency medicine physician (EMP) with hospital credentials for emergency US using a SonoSite MicroMaxx US machine with a linear probe. Fluoroscopy was performed by a second EMP using a GE series 9600 fluoroscopy system. There was no time limit for the evaluation of the quarter by either fluoroscopy or US. Using a GE Lightspeed VCT2 CT scanner, 0.625-mm slices (joint protocol) were acquired to evaluate the location of the foreign body. If the foreign body violated the joint capsule, then the interpreting radiologist classified the foreign body as intra-articular. Descriptive statistics were used to report the accuracy of each modality for the detection of intra-articular foreign bodies. All values are reported with a 95% confidence interval (CI).
Six of the 10 trials resulted in the spine penetrating the joint capsule. Ultrasound detected 9 of the 10 foreign bodies. There was one false positive result for joint penetration, yielding a sensitivity and specificity for detecting the intra-articular foreign body of 100% (95% CI: 46.3%–100%) and 75.0% (95% CI: 21.9%–98.7%), respectively. Fluoroscopy detected all 10 foreign bodies but had one false positive result for joint penetration, yielding a sensitivity of 100% (95% CI: 51.7%–100%) and specificity of 75.0% (95% CI: 21.9%–98.7%). The false positive result of both US and fluoroscopy occurred with the same foreign body.
CT remains the gold standard for detecting foreign body joint penetration. However, US may prove to be a valuable tool in identifying out-of-hospital joint penetration, thereby reducing unnecessary delay in treatment or hospital transfer.