Sonography Compared with Radiography in Revealing Acute Rib Fracture
Abstract & Commentary
Synopsis: In comparison to radiographic evaluation for detecting rib fractures, sonographic evaluation was 10 times as effective.
Source: Griffith JF, et al. Sonography compared with radiography in revealing acute rib fracture. AJR Am J Roentgenol 1999;173:1603-1609.
In patients suspected clinically of having a rib fracture, chest radiographs are often done to confirm the diagnosis. Despite dubious sensitivity for visualizing the fractured rib per se, this approach has been defended on the basis that it may detect complications such as pneumothorax, hemothorax, and pulmonary contusion.
The purpose of the current study was to compare the sensitivity of sonography and radiography for rib fracture detection. To do their analysis, Griffith and colleagues examined 50 patients with acute chest injury, excluding unconscious, uncooperative, or significantly injured patients. Initially, a posteroanterior chest film and a single low-voltage oblique rib film were obtained over the area of clinical concern. Within the next 24-48 hours (in all cases within 72 hours), a comparative ultrasound examination was done, using either a 9- or 12-MHz linear array transducer. The sonographic technique consisted of doing scans parallel to the long axis of the rib, not only over the area of clinical concern, but also imaging the entire rib from the costosternal to the costovertebral junction. Using an identical technique, additional scans were performed over contiguous superior and inferior ribs. Fractures, degree of displacement, and associated hematomas were recorded. An effort was also made to detect a pneumothorax or a hemothorax.
At initial presentation, radiographs detected eight rib fractures in six (12%) of 50 patients, while sonography detected 83 rib fractures in 39 (78%) subjects. In 46% of cases, an accompanying soft tissue hematoma was also visible by sonography, and in no case was a hematoma present without a fracture. Of 19 patients with two to seven rib fractures visible by sonographic imaging, in only a single patient were multiple fractures detected by radiographic examination (in the remaining 18 patients, no fracture was identified). A single patient had a hemothorax visible by both imaging modalities; in no case was a pneumothorax detected.
Repeat sonography of 37 patients, done three weeks later, not only confirmed healing for each initially visible fracture, but also detected 12 additional rib fractures. Combining fractures detected initially, as well as those identified on the subsequent sonographic examination, revealed a total of 95 fractures in 44 (88%) patients.
Comment by Faye C. Laing, MD
The major strength of this study is to confirm lack of radiographic sensitivity to detect rib fractures. Indeed, the results of this well-executed investigation revealed sensitivities of 12% vs. 90%, respectively, for radiographic vs. sonographic imaging. Stated differently, in comparison to radiography, sonography was able to detect 10 times as many rib fractures in six times as many subjects. An additional and (to me) surprising outcome was that 88% of patients did, indeed, have at least one rib fracture.
Before we each begin to use ultrasound imaging in our effort to detect rib fractures, several things should be considered. As pointed out by Griffith et al, sonographic mimickers that can be misinterpreted for fractures include the irregularly contoured pleural surface, partial voluming of the rib/intercostal space, costal cartilage calcification, and the costochondral/posterior rib junction. In addition, because they are anatomically inaccessible to the sonographic transducer, retroscapular ribs and the infraclavicular portion of the first rib cannot be imaged. Obesity or large breasts may also limit sonographic access. The fact that sonographic evaluation is relatively time consuming, requires considerable technical expertise, and requires a superior-quality, high-frequency transducer must also be considered.
In my mind, however, the ultimate question regarding rib fractures is—"Is it necessary to detect them in the first place?" Unfortunately, no good treatment regimen exists for uncomplicated fractures, and the usual therapeutic rule is, "tincture of time." Nonetheless, sonographic rib imaging may be useful in certain clinical situations. These include evaluating patients: 1) with significant chest trauma in whom the radiographic examination is either negative or reveals only a single fracture; 2) to look for a pathologic or insufficiency fracture in an individual with minimal or no trauma, a negative x-ray, and unexplained focal pain or; 3) with a fracture, to help target injection of therapeutic intercostal analgesia.
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