To test our first hypothesis, data were analyzed with use of the McNemar test. Odds ratios (ORs) with corresponding 95% confidence intervals (CIs) were calculated along with an exact p value to test for systematic differences. To test our second hypothesis, the sensitivity and the specificity as well as the positive and negative predictive values were calculated.
A total of 91 patients (55% men; mean age, 43 years) were included in the study (Table I). The prevalence of an extremity fracture was 27%. We tested for systematic differences between the results of ultrasound and conventional radiographic examination. There were 4 false-positive and 2 false-negative results (Table II). There were no systematic differences between the results of ultrasound and those of conventional radiography (p = 0.69). The 6 conflicting results were equally distributed with regard to patient age and anatomical region (Table III). A wide spectrum of bones were represented (Table IV). There was no displacement (<1 mm) of the fracture in 16 patients and displacement (≥1 mm) in 9 patients.
We hypothesized that the use of ultrasonography as a diagnostic tool would have a minimum sensitivity of 90% and a minimum specificity of 85% when conventional radiography was the gold standard for identifying fractures. We found that ultrasonography had a sensitivity of 92% (95%; CI, 74% to 100%), a specificity of 94% (95% CI, 85% to 100%), a positive predictive value of 85% (95%, CI, 66% to 96%), a negative predictive value of 97% (95% CI, 89% to 100%), a positive likelihood ratio of 15.33, and a negative likelihood ratio of 0.085. Thus, the probability of having a fracture if the ultrasound examination was positive was 85% and the probability of not having a fracture if the ultrasound examination was negative was 97%.
The purpose of the present study was to investigate whether ultrasonography can be used as a diagnostic tool to exclude extremity fractures in adults. We found that ultrasonography, when performed and interpreted by experienced ultrasonographers, had high accuracy as a diagnostic modality for the evaluation of suspected extremity fractures. There were no systematic differences between the results of ultrasound and those of conventional radiography, and ultrasound had a high sensitivity and specificity. This finding indicates that ultrasonography can be used as a diagnostic tool to exclude extremity fractures in adults.
The design of the present study differs from those of previous investigations. Our patients were referred directly from their general practitioner to the Department of Radiology at Viborg Regional Hospital, and no clinical examination by the investigators was performed prior to ultrasound examination. Therefore, we performed a fair comparison between ultrasonography and conventional radiography without additional clinical information that might have helped the investigator to diagnose or rule out a fracture. All patients who were diagnosed with a fracture on the basis of conventional radiography were referred for additional treatment. In the present study, ultrasound was associated with 2 false-negative results (missing 1 minimally displaced fracture of the base of the fifth metacarpal and 1 fracture in which a small piece of bone had been stripped from the clavicle) and 4 false-positive results (incorrectly identifying fractures in 1 finger, 1 wrist, and 2 ankles). All of the false-positive results were caused by irregularities in the bones.
When an examination method is compared with a gold standard, the agreement or systematic differences between the results of the 2 methods can be investigated. In the present study, the McNemar test demonstrated no systematic differences between the results of the 2 modalities. To our knowledge, no other studies have used the McNemar test and therefore comparison of our results is not possible.
There seemed to be no association between the conflicting results and the age of the patient or the specific anatomical region of the fracture. We performed no statistical tests because there were only 6 conflicting results—too few to test statistically. Some studies have indicated that it is particularly difficult to identify a fracture in the hand and in the metatarsals4-7, whereas other studies evaluating specific bones have shown good results8-10. Age did not seem to have an impact on whether a patient with a suspected fracture had a fracture or not11.
Only a few studies have examined the interrater agreement of ultrasound examinations to identify fractures. Barata et al. reported substantial agreement, with a kappa value of 0.742. Bolandparvaz et al. reported much lower kappa values of between 0.25 and 0.58, depending on the scanned limb3; however, their study population involved patients with multiple trauma and was not fully comparable with our study population.
We acknowledge that the present study had some limitations. The prevalence of fractures that were verified with radiography was fairly low (27%) and there were few cases of disagreement between the 2 modalities (6.6%). The present study included a small, but representative, sample of a selected group of patients who were seen during the daytime. A larger study population would have enabled us to examine whether the accuracy of ultrasonography depends on which extremity is examined. Moreover, if conventional radiography did not provide true results of the examination, then the present study might be biased. Theoretically, the 4 patients in whom a fracture was identified with ultrasound but not verified with conventional radiographs might actually have had a fracture, in which case the results of those examinations were misclassified and the discriminative ability of ultrasonography has been underestimated. Furthermore, the specificity of ultrasound may be overestimated because scaphoid fractures were included in the study and conventional radiography is not the gold standard for the diagnosis of scaphoid fractures. We did not follow up with the patients after the ultrasound and conventional radiographic examinations and thus do not know if any of the patients sought medical assistance after the initial referral to the hospital, nor do we have any cost data.
In conclusion, the present study indicates that ultrasonography, when performed and interpreted by experienced ultrasonographers, has high accuracy as a diagnostic modality for the evaluation of suspected extremity fractures. No systematic differences were found between the results of the 2 modalities, and ultrasonography showed a high sensitivity and specificity and most notably a high negative predictive value.
Investigation performed at the Orthopaedic Department, Viborg Regional Hospital, Denmark
Disclosure: No external funds were received in support of this study. The Disclosure of Potential Conflicts of Interest forms are provided with the online version of the article (http://links.lww.com/JBJSOA/A18).
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© 2017 The Authors. Published by Wolters Kluwer Health, Inc. on behalf of The Journal of Bone and Joint Surgery, Incorporated.
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