The Investigation of Suspected Fracture— a Comparison of Ultrasound With Conventional Imaging
Systematic review and meta-analysis
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Background: Ultrasound imaging can be used to diagnose fractures in patients with acute trauma. Its main advantages over conventional imaging are the absence of radiation exposure and its greater availability.
Methods: A systematic search in electronic databases (Medline, Embase, Cochrane CENTRAL) was supplemented by a manual search on the Internet and in the reference lists of pertinent publications. The QUADAS-2 instrument was used to assess the quality of the individual studies retrieved. In the meta-analysis, the sensitivity and specificity of the individual studies were pooled.
Results: The available information on the diagnostic accuracy of ultrasound in the detection of fractures compared with that of conventional imaging (x-ray, CT, MRI) in patients with acute non–life-threatening trauma is summarized. The database search yielded 2153 hits, among which there were 48 studies that were suitable for inclusion in this review. The pooled sensitivity and specificity were 0.91 (95% confidence interval [0.90; 0.92]) and 0.94 [0.93; 0.95], although the analyzed studies were markedly heterogeneous (I²: sensitivity 74%, specificity 81%). The sensitivity of ultrasound was higher for the detection of fractures of the humerus, the forearm, the ankle, and the long bones in general, as well as fractures in children, and lower for fractures of the short bones of the hands and feet, and in adults.
Conclusion: Strong evidence supports the use of ultrasound imaging for certain indications in the detection of fractures.
Suspected fracture following trauma is a common reason for emergency room admission. X-ray is usually used to diagnose patients with suspected fracture and is the standard procedure. The use of ultrasound to diagnose fractures has been the subject of intense discussion over the last 20 years (1–4). Viewing alterations to bone surfaces (discontinuities, displacement, subperiosteal hematomas) has been proven to be a reliable, manageable method of fracture diagnosis. One of the main advantages of ultrasound examination is the avoidance of radiation exposure; this is particularly true in children, who are more sensitive to radiation than adults (5). Ultrasound diagnosis is also easy to teach (6, e1), cheap (2), and available in emergency rooms and many medical practices. All these are arguments in favor of the use of ultrasound in diagnostic algorithms for suspected fracture, which could reduce the number of x-ray examinations performed (7, 8).
The main aim of this systematic review is to summarize the available evidence regarding the diagnostic accuracy (sensitivity and specificity) of ultrasound versus the standard imaging procedures used to diagnose acute fractures (x-ray, CT, MRI). Subgroup analyses were also performed, in order to determine accuracy for various fracture locations and age groups. This should provide a basis for discussion of the potential inclusion of ultrasound in the diagnostic algorithms of medical practices and emergency rooms and support targeted research in the future.
This systematic review was planned and performed in line with the PRISMA (preferred reporting items for systematic reviews and meta-analyses) (e2) and MOOSE (meta-analysis of observational studies in epidemiology) (e3) recommendations. The search strategy was developed by 2 physicians (GLS, TF) and one librarian (CH).
The electronic search of the literature was performed in 3 databases (Medline, EMBASE, Cochrane CENTRAL) on March 19, 2015 (last update: September 2016). In order to take account of technical advances in ultrasound machines, only publications dating from 2000 onwards were included. The PICO Framework (e4) was used to define inclusion and exclusion criteria (eMethods 1). The full study protocol is provided in eMethods 2 and was not published in advance. The methodological quality of the included studies was evaluated using QUADAS-2 (QUADAS: quality assessment of diagnostic accuracy studies) (e5) (eMethods 3).
Meta-analysis and statistics
Percent agreement and Cohen’s kappa for the 2 raters (GLS, TF) were calculated to estimate the interrater reliability of the initial screening process. Data from the included studies was pooled using a random-effects model. Heterogeneity was evaluated by means of the chi-square test and I2, using the program MetaDiSc (version 1.4, Hospital Universitario Ramón y Cajal, Madrid, Spain) (e6).
We performed subgroup analyses for various fracture locations (humerus, forearm, ankle and foot, all long bones, short bones of the hands and feet), age groups (adults versus children and adolescents), and levels of risk of bias (low/unclear risk versus high risk) described in the studies.
Additional, detailed information on the methods can be found in eMethods 1.
The flow chart (Figure 1) illustrates the search strategy and gives the number of evaluated publications and reasons for exclusion at each step.
Substantial interrater reliability was found for the screening processes of both titles (percent agreement = 91.2%, kappa = 0.622) and abstracts (percent agreement = 89.0%, kappa = 0.685).
The 2 raters considered 78 and 94 publications respectively to be potentially relevant. In all cases in which the raters’ evaluation of an abstract differed (n = 17), discussion with a third scientist (TD) led to consensus.
At the fulltext phase, 108 studies were analyzed using a data extraction form designed and piloted by the authors (eMethods 2) and either included or excluded. The 48 articles included in the review (6, 7, 9–40, e7–e20) are summarized in eTable 1.
Characteristics of the selected studies
With the exception of one publication (16), all the studies were conducted in emergency rooms. Thirty-four studies compared ultrasound findings with conventional x-ray images, 3 used CT or MRI as the reference standard, 4 combined x-ray and CT, and 7 used clinical consensus or follow-up examinations to make a correct diagnosis.
The 48 included studies covered a total of 4427 patients and 5436 examinations. They report on the sensitivity and specificity of ultrasound compared to the respective reference imaging method used (Figures 2 and 3). Pooled sensitivity was 0.91 (95% confidence interval: [0.90; 0.92]), and pooled specificity 0.94 [0.93; 0.95]. In the pooled population of all included studies, radiation exposure would have been avoided for 56 of 100 ultrasound examinations (true negatives) (median: 48%, range: 7 to 84%), but 4 of the 100 examinations would have led to a false negative (median: 2%, range: 0 to 29%).
In 15 studies findings were calculated on the basis of the number of investigated bones rather than that of injured patients. Excluding these studies, sensitivity was the same and specificity was slightly lower, at 0.92 (0.90; 0.93). This indicates that these 15 studies slightly overestimated the accuracy of ultrasound.
Nine publications reported on pain caused by ultrasound examination. In 5 of these there were no differences between ultrasound and x-ray (15, 19–21, e12), while 4 found that ultrasound diagnosis was less painful because a pain-relieving position is permitted and the ultrasound gel is cooling (18, 36, e15, e16).
The quality of the included studies improved over the last 5 years, as illustrated by a lower risk of bias and more accurate description of study design (eMethods 3). On the basis of the funnel plots shown in eMethods 4, the risk of significant publication bias was estimated as low.
The I2 values calculated to estimate the heterogeneity of the studies included in the meta-analysis were 74% for sensitivity and 81% for specificity. This indicates that heterogeneity is substantial. Subgroups for different fracture locations, age groups, and risk of bias levels were investigated to identify possible sources of this heterogeneity.
Meta-analyses were performed for the most common fractures: those of the forearm, ankle, all long bones, humerus, and bones of the hand and foot. Studies involving only pediatric patients were also summarized. Detailed findings are shown in eTable 2.
A total of 14 studies investigated forearm fractures. Unlike an earlier review (1), we did not include the data of Moritz et al. (e21) or Sinha et al. (e22). This was due to unsuitable study design in the first case, and because the same cohort was described in a more recent publication (22) in the second.
Of the 6 studies investigating fractures of the ankle and foot, 4 used the Ottawa Foot and Ankle Rules (OFAR) as a clinical test to increase pretest probability. To generate data on common ankle injuries we excluded studies on injuries to the lower leg not explicitly described as located in the ankle region.
Eight studies investigated the potential of ultrasound to diagnose humerus fractures. Five investigated only pediatric patients. Two investigated only supracondylar fractures of the humerus, and 2 only proximal fractures of the humerus.
Some authors (6, 10, 11, 14, e12) stated that diagnosis of diaphyseal long-bone fractures was more reliable than that of short-bone fractures and fractures close to joints. We compared the findings of ultrasound imaging of long bones, including the femur, humerus, forearm, and lower leg, with those of short bones (hands, feet, patella). For long bones, sensitivity was substantially higher and specificity slightly higher.
Reduced radiation exposure is particularly important for pregnant patients and children. Meta-analysis of the 20 studies conducted only in children and adolescents yielded higher sensitivity, but lower specificity, than for studies investigating only adult patients.
To estimate the effect of bias on study findings, meta-analyses were conducted of studies with a low/unclear risk of bias versus those with a high risk of bias. Sensitivity and specificity were higher in studies with a low/unclear risk of bias.
Twelve studies (6, 10–12, 17, 23, 26, 27, 30, 33, 36, e12) yielded clearly delineated data on multiple subpopulations (e.g. some patients with suspected forearm fractures and others with ankle fractures in the same publication). These subpopulations were included separately in meta-analyses of the relevant subgroups.
This systematic review summarizes data on the accuracy of ultrasound imaging in diagnosing fractures following acute trauma. Meta-analysis of 48 suitable studies found 91% sensitivity and 94% specificity. These findings show clearly that ultrasound of bone surfaces can be used as a suitable method for initial evaluation of acute injuries.
Ultrasound could be included in a diagnostic algorithm as the first machine-based method of diagnosis, instead of x-ray, following physical examination. All patients with true negative findings (corresponding to 56% of the included examinations) benefit from reduced radiation exposure. However, suitable treatment for patients with false negative findings (corresponding to 4%) might be delayed. High sensitivity is therefore vitally important in identifying fractures correctly and in ruling them out when findings are negative.
Fractures of the humerus, forearm, ankle, and long bones in general can be diagnosed with very high sensitivity and specificity. Fractures to bones of the hands and feet are more likely to be overlooked on ultrasound and should therefore be ruled out using another imaging procedure. In addition, our analyses showed ultrasound to be of greater diagnostic value in children and adolescents than in adults.
These findings are in line with those of previously published systematic reviews. Joshi et al. (3) summarized the findings of 8 relevant studies on the diagnostic value of ultrasound for fractures to the extremities and proposed the use of ultrasound in addition to x-ray. Katzer et al. (2) reported on 8 studies that investigated forearm fractures in children only. They found ultrasound to be of comparable diagnostic value to x-ray and superior to it in terms of patient comfort, time required, and cost-efficiency. Douma-den Hamer et al. (1) included 16 studies in a meta-analysis that investigated the accuracy of ultrasound in distal forearm fractures. Their calculations found sensitivity and specificity of 97% and 95% respectively, which broadly matches our findings (eTable 2). Their findings in pediatric forearm fractures only were even better.
The potential of ultrasound to diagnose fractures of the ribs and sternum should be evaluated separately. Most publications on this subject were excluded from our review due to unsuitable study design (4, e23–e29). X-ray cannot be considered the gold standard for these fractures, as some studies found ultrasound to be superior to it in diagnosing fractures of the ribs and sternum (13, e24, e25). Future studies on the accuracy of ultrasound in diagnosing fractures of the ribs and sternum should therefore select a reference standard that can establish the outcome correctly, such as MRI or strict follow-up examinations to detect callus formation, as proposed by Rainer et al. (13).
As noted by Douma den Hamer et al., the fact that occult and other fractures that were detected on ultrasound but not on x-ray were counted as false positives may result in systematic underestimation of the accuracy of ultrasound for other fracture locations too, such as those of the forearm (1).
With one exception, all the studies examined here were conducted in emergency rooms. Although the data reported supports the use of ultrasound as part of routine diagnostic algorithms for suspected fractures, it seems unlikely that current standards in emergency rooms will be changed without further incentives. Katzer et al. (2) calculated the costs of ultrasound and conventional x-ray in diagnosing forearm fractures in children as €20.54 for ultrasound and €26.60 for conventional x-ray. They reported that the greater efficiency of working processes when using ultrasound diagnostics played a vital role; often, a physician in an emergency room can make a diagnosis on the basis of history, clinical examination, and ultrasound, without needing to involve a radiologist or other staff. This factor would also be of particular interest in outpatient care, where the use of ultrasound in diagnosing fractures when possible could save resources and costs.
Strengths and limitations
This review evaluates ultrasound imaging for a broad spectrum of fracture locations and thus provides an overview of potential uses of this method of diagnosis. We were able to include a substantial number of studies, which indicates that the amount of data on the sensitivity and specificity of ultrasound in diagnosing bone fractures has increased. Subgroup meta-analyses provide data for sophisticated discussion of the potential and limitations of this method.
Despite our best efforts, the findings of the meta-analysis must be interpreted critically, as there was substantial heterogeneity between the included studies. Although it was essentially shown that most study findings varied only slightly (Figures 2 and 3), the very high I2 values nevertheless show that the variability found is probably caused by genuine differences (e.g. different populations, fracture locations, experience of those performing examinations, etc.), not by chance alone. Unfortunately, subgroup analysis could not reveal all sources of heterogeneity. On the other hand, Rücker et al. (e30) emphasized that I2 values are susceptible to systematic error, and that ultimately the clinical relevance is more important. We therefore consider our meta-analysis valid and helpful in clinical decision-making.
The fracture locations included were limited to the limbs, ribs, sternum, clavicle, and scapula in order to focus the review on fractures that might also be treated in nonhospital settings.
The study protocol was not published before the review was performed. Language-related bias cannot be completely ruled out because the included studies were limited to publications in either English or German. However, only 6 titles that were potentially of interest after title and abstract screening were excluded, suggesting that the potential effect on the final conclusions of the review was small.
We excluded absolutely all studies in which not all patients received ultrasound imaging and a reference standard. Although it is to be expected that this decision had a positive effect on the quality of the meta-analysis, it has resulted in the exclusion of some studies that make important contributions on diagnostic accuracy, practicability, and safety.
This review shows that there is already considerable evidence that the sensitivity and specificity of ultrasound imaging in diagnosing fractures following acute trauma are high. The use of ultrasound could be of greatest benefit to patients with suspected fractures of the long bones of the limbs or of superficial bones, and children and adolescents in general. Randomized controlled trials should be performed in the future in order to evaluate the potential impact of revised diagnostic algorithms on patient safety and on direct and indirect health costs.
We would like to thank Anja Heuser, Marie-Luise Meja, and Britt Häusler for their organizational support.
Conflict of interest statement
The authors declare that no conflict of interest exists.
Manuscript received on 15 March 2017, revised version accepted
on 10 July 2017.
Translated from the original German by Caroline Shimakawa-Devitt, M.A.
Dr. med. Gordian Lukas Schmid
Independent Department for General Medicine
University of Leipzig
04103 Leipzig, Germany
For eReferences please refer to:
J Ultrasound Med 2007; 26: 1143–8 CrossRef
J Med Liban 2011; 59: 70–4.
Dr. med. Schmid, Dr. rer. pol. Lippmann, Dr. rer. med. Deutsch
Institute of General Practice and Family Medicine, Martin-Luther-University Halle-Wittenberg, Halle (Saale): Dr. med. Schmid, Prof. Dr. med. Frese
Institute for Medical Epidemiology, Biometrics and Computer Science, Martin-Luther-University Halle-Wittenberg, Halle (Saale): PD Dr. rer. nat. habil. Unverzagt
Library of Medicine, University of Leipzig: Hofmann
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