Abstract
Background
Pediatric elbow injuries are a common pathology in the emergency department. Radiographic imaging is the reference test for diagnosing elbow fractures. However, ultrasonography is an imaging method with growing importance that has shown to be useful in musculoskeletal pathology. The aim of this study was to evaluate the precision of point-of-care ultrasound (POCUS) performed by pediatric emergency physicians compared with radiography for the detection of elbow fractures in pediatric patients, and to compare the interobserver concordance between the performer and an independent evaluator with wide experience in POCUS.
Methods and settings
This was a prospective, observational cohort study including pediatric patients under 14 years that visited the emergency department with elbow injuries and required radiographs. Before obtaining the radiographic image, an elbow ultrasonography was performed and interpreted as positive for fracture if an elevated posterior fat pad or lipohemearthrosis was detected. All patients got an elbow radiograph and clinical follow-up.
Results
One hundred and six patients were selected, from which 91 patients were electable for the study with a mean of age of 7.8 years. Twenty eight patients of the total (30.8%) had fracture. A sensitivity for POCUS positive result of 96.4% was obtained (95% confidence interval [CI] 81.7%-99.9%), with a specificity of 84.1% (95% CI 72.7%-92.1%). The positive predictive value was 74% (95% CI 61.6-83.4) and the negative predictive value 98.1% (95% CI 88.0-99.7). The POCUS took 14.2 (standard deviation 5.2) seconds to be performed. The interobserver concordance was almost perfect (ĸ = 0.89).
Conclusion
Elbow POCUS is a useful tool for the diagnosis of elbow fracture with a high sensitivity and negative predictive value and a very good interobserver concordance. It may be a useful safe alternative to optimize the evaluation and diagnosis of elbow trauma.
Keywords: POCUS, Ultrasound, Children, Elbow trauma, Posterior fat pad, Radiography, Pediatric emergency department
Pediatric elbow injuries are a relatively common presenting complaint in the emergency department (ED).2 When an elbow fracture is suspected, some tests have to be done as elbow fractures are among the most common childhood fractures and can account for up to 15% of fractures in the pediatric population.2,12,14 These type of fractures, if not correctly diagnosed and treated, can have considerable effects on activity restriction and severely impact the activity of the child.1
To confirm or exclude a possible elbow fracture, radiographic imaging is obtained, including standard 2-way anteroposterior and lateral views, as it is the reference test for diagnosing elbow fractures.8,17
However, pediatric patients have some special characteristics that can make detecting minimally displaced elbow fractures in an X-ray image difficult.1,2,14 On the one hand, the anatomy of the elbow joint is quite complex as it is composed of 3 separate articulations (ulnohumeral, radiohumeral, and radioulnar).13,18 In addition, the nonossified epiphyses, the overlying soft-tissue structures and the varying appearance of the ossification nuclei during skeletal maturation in a minimally displaced fracture can lead to misdiagnosis of certain elbow fractures.1,8,13 Moreover, even though radiographic imaging uses low-dose radiation, studies often have to be repeated due to uncooperative children, leading to possible excess radiation exposure in a vulnerable growing bone.1,4,14
Therefore, this has led to the development of alternative imaging methods such as point-of-care ultrasound (POCUS), to enhance the diagnostic accuracy and reduce exposure to radiation.1,4,8, 9, 10, 11, 12,14,15,17,19
Ultrasonography (US) is an imaging method that can be performed by a physician not specialized in radiology. This is a technique with growing importance that has proven to be useful for routine emergency room evaluation.1,4,12,15,17,19 Recent studies have shown the utility of POCUS for the detection of elbow fractures in the pediatric ED.1,12,17 POCUS is an operator-dependent technique that with adequate training can detect or exclude quite accurately minimally displaced elbow fractures in the pediatric patient.1,8,12,17
US is an easy, fast, accessible, cost-effective, and painless imaging method that allows for real-time radiation-free assessment of the elbow joint.1,8,12,17 It can detect cortical disruption and irregularity that directly indicates fracture, but it can also detect indirect signs of fracture that are somewhat easier to identify in children because of the particularities previously mentioned.1,12
Thus, an elevation of the posterior fat pad exceeding the olecranon fossa corresponding to the presence of blood and fat in the posterior fat pad can indirectly indicate fractures often not visualized in the radiographic imaging.1,4,8,12,14
Multiple studies have shown the superiority of US compared to the actual gold standard radiographic imaging in detecting these indirect signs of elbow fracture.1,4,8,12,14
The aim of this prospective study was to evaluate the utility of POCUS performed by pediatric emergency physicians for the detection of elbow fractures in the pediatric ED and to evaluate the interobserver concordance between the performer and an independent evaluator with wide experience in POCUS.
Material and methods
Study design and patient selection
This was an observational cohort study performed in the ED of Basurto University Hospital of Bilbao (Spain), from January of 2021 to December of 2022. The study received the approval from the Local Ethics Committee of Clinical Research and all participants had to give written and verbal informed consent to be selected for the study. A convenience sample of patients with elbow trauma that attended the ED was selected, based on the inclusion criteria and their consent to participate on the study. The patients included in this study were those under 14 years that attended the ED with elbow pain after an upper-extremity trauma and had an indication for radiography to rule out fracture. Patients were excluded if they had previous or recent diagnosis of elbow fracture, deformity, neurovascular compromise or those who didn’t want to sign the consent for the study.
Research team
The performers were 5 medical first-year pediatric residents. Before the start of the study, the performers received a basic training on elbow POCUS. They were instructed on the US technique of elbow examination with a didactic lecture and a practical session of supervised ultrasound on live models.
They also received training on the management of elbow trauma, learning how to evaluate and immobilize the joint and how to administer adequate analgesia; an experienced pediatrician that works on the ED was in charge of the supervision (FS).
Procedure
This study required an additional clinical test that was part of the initial clinical evaluation. It didn’t exclude the realization of complementary exams like the radiography which, at the moment, is the gold standard for the diagnosis of fracture.
When patients that fulfilled the inclusion criteria arrived to the ED, one of the participants of the study was informed and they evaluated the patient while supervised by an attending physician. In triage, patients were evaluated using pain scales and were given the appropriate analgesia. The POCUS was integrated in the initial evaluation while also considering swelling, ecchymosis, movement restriction, painful points and other clinical information.
The US was performed using a SonoSite PX ultrasonograph (Fujifilm Sonosite Iberica S.L., Madrid, Spain), equipped with a high frequency (15-4 MHz) linear transducer in 2 dimensional mode. An abundant quantity of ultrasound gel was applied over the posterior aspect of the distal humerus to create a film that prevents direct contact of the transducer with the skin to reduce the pressure of the transducer.
With the elbow in a 90-degree position, the lineal transducer was placed longitudinally on the posterior part of the elbow over the olecranon fossa. US examination was performed after the approval of at least one parent and always in their presence.
Images and videos of the exploration of the hurt elbow were taken and the time it took for the ultrasonographic evaluation to be completed was recorded. Sometimes, images of the contralateral elbow were needed to obtain comparative images, but this was not taken into account for the time measurement.
A positive result was defined when an elevation of the posterior pad or presence of lipohemearthrosis of the posterior fat pad was visualized. Elevation of the posterior pad was defined as elevation of fat pad on the olecranon fossa over the extension of the humeral line (Fig. 1). Lipohemearthrosis was defined as a heterogeneous echodensity of the posterior fat pad. Afterward, radiographs in 2 projections were requested, anteroposterior in elbow extension and lateral on 90° flexion. If there were more painful points, other joints and bones were included on the radiographic projections. In these images not only fractures were searched for, but also indirect signs of them.
Figure 1.
Comparative bilateral ultrasonographic exploration of the olecranon fossa. (A) Elevated PFP in longitudinal view. (B) Normal PFP in longitudinal view with the PFP below the distal humeral line. PFP, posterior fat pad.
Finally, the patient was referred to the emergency traumatology department, blinded to the results of the ultrasonographic images. Patients were followed up. To provide a measure of agreement, the US images and videos were reviewed by a second examiner with large experience on US (FS) who, blinded to clinical findings, US interpretation of the first evaluator and radiographic imaging, gave an independent diagnosis.
Outcome measures
The primary outcome was to determinate the sensitivity and specificity of the elevation of posterior fat pad. The secondary objectives were to evaluate the interobserver concordance between the performer and an independent evaluator with wide experience in POCUS.
Data analysis
Statistical analysis of data was performed using IBM SPSS Statistics version 25.0 software (IBM Corp., Armonk, NY, USA). Sensitivity, specificity, positive and negative predictive values, and 95% confidence interval (CI) were described.
A descriptive statistical analysis was used for quantitative variables obtaining the mean and standard deviation (SD) as well as minimum and maximum values. Categorical variables were reported as number and percentage.
Cohen’s κ-test was used to determine the interobserver concordance for US in pediatric elbow injuries. The precision of US for the diagnosis of elbow fractures was calculated on the basis of the radiography findings, with this being considered the gold standard. A P value of less than .05 was considered to be statistically significant.
Results
One hundred and six patients were initially selected, of which 91 fulfilled the inclusion criteria. The mean age was of 7.8 (SD 3.3, range 1.2-13.9) years old with similar prevalence between sex. The aching elbow was the left one in 62.6% of the patients. The patients’ demographic and clinical information is presented in Table I.
Table I.
Demographics and clinical characteristics.
| Variables | Total: n = 91 |
|---|---|
| Age (mean (SD), y) | 7.8 (3.3) |
| Sex | |
| Male | 46 (50.6%) |
| Female | 45 (49.4%) |
| Elbow | |
| Left | 57 (62.6%) |
| Right | 34 (37.4%) |
| Physical examination | |
| Point of tenderness | 80 (87.9%) |
| Swelling | 35 (38.5%) |
| Ecchymosis | 7 (7.7%) |
| Movement restriction | 46 (50.6%) |
| US findings | |
| Elevated posterior fat | 35 (38.5%) |
| Elevated posterior fat and lipohemearthrosis | 62 (68.1%) |
SD, standard deviation; US, ultrasound.
With X-ray imaging as the gold standard, fracture was diagnosed in 28 patients (30.8% of the cases). Nearly half of these fractures were supracondylar (46.4%), with condylar or epicondylar fractures being the next most common. The distribution of the fractures is shown in Table II.
Table II.
Classification of elbow fractures.
| Type of fractures | n = 28 |
|---|---|
| Supracondylar | 13 (46.4%) |
| Humeral condyle | 7 (25.0%) |
| Radial head | 4 (14.3%) |
| Olecranon | 1 (3.6%) |
| Radial head + olecranon | 3 (10.7%) |
An elevated posterior fat pad was present in 37 patients (40.7%), representing a positive US, but there was no fracture in 10 of these patients (27.1%), which represented the false positive cases of the study. A negative or normal US was obtained in 54 patients (59.3%). Only one of these was found to have a fracture on radiographs (1.9%), a radial head fracture which was not identified on the US imaging and represents the only false negative of the study, though it was evaluated as positive by the reviewer. The study flow chart is presented in Figure 2.
Figure 2.
Study flow chart. US, ultrasound; RX, radiograph.
The duration of the US technique took 14.2 (SD 5.2) seconds to be performed.
The sensitivity for US positive result was of 96.4% (95% CI 81.7%-99.9%), the specificity of 84.1% (95% CI 72.7%-92.1%). The positive predictive value was 74.0% (95% CI 61.6-83.4) and the negative predictive value 98.1% (95% CI 88.0-99.7). The interobserver concordance between the first observer and the reviewer was very good, with a coefficient kappa of 0.89.
Discussion
Elbow trauma occurs quite frequently in pediatric patients. This study evaluates the utility of POCUS for the detection of elbow fractures in the pediatric ED.
The population of the study seems representative of the general population, with a mean age, percentage of fracture, as well as demographic and clinical information similar to other studies.1,12,17 An incidence of supracondylar fractures of 46.4% was detected, data quite alike to other publications,1,6,12,17 that makes us believe that the study population is representative of the pediatric population.
In this study, the elevation of the posterior fat pad and the presence of lipohemearthrosis were evaluated as indirect signs of elbow fracture as it has been suggested that these 2 signs could be reliable indicators of elbow fracture.1,12,17,20 Moreover, elevation of the posterior fat pad detected with an ultrasonographic image seems more sensitive than radiographic detection12,17 as the milliliters of liquid needed for ultrasonographic visualization are less than those needed for radiographic visualization (1-3 ml vs. 5-10 ml).3
This study shows that elbow US has a high sensitivity and high negative predictive value detecting elbow fractures in pediatric patients (sensitivity 96.4% and predictive negative value 98.1%).
These findings are similar to those observed recently by Rabiner et al12 and Azizkhani et al,1 who obtained a sensitivity of 98.0% and 92.9% respectively and a predictive negative value of 98.0% and 95.5% respectively.
The higher sensitivity and negative predictive value for identification of elbow fractures in the pediatric patient found in the study, proves that elbow US is more useful for ruling out, rather than ruling in, fractures.
The ultrasound was carried out using one longitudinal plane of the elbow over the olecranon fossa that, according to the literature, is more reliable than the transverse plane for detecting joint effusion.12 This also helped minimize mobilization of the extremity to reduce pain during the examination. In the study performed by Varga M et al,17 the protocol used included 5 longitudinal sonographic planes, with which a sensitivity and a negative predictive value of 100% was obtained. Evaluating just 1 plane (dorsal plane over the olecranon fossa), a sensitivity and a negative predictive value of 97.0% was obtained for elbow fracture detection.
The average time required for the elbow US to be performed was of 14 seconds, while in the work of Rabiner et al12 it took a mean of 95 seconds. This is explained because while in this study just one plane (longitudinal plane) was carried out, in the work of Rabiner et al,12 both longitudinal and transverse views of the elbow were obtained.
Moreover, in this study there was just one case with a false negative finding in the US, which is similar to the findings in the previously mentioned publications. The study performed by Rabiner et al12 reported to have missed only 1 fracture (a medial epicondyle fracture) in a 130-patient cohort. On the other hand, Azizkhani et al1 reported 2 false negative cases in a 75-patient cohort (a medial epicondyle fracture and a lateral epicondyle of humerus fracture).
The elevation of the posterior fat pad is seen when a joint effusion occurs. This happens in the majority of elbow fractures. However, some of these fractures can occur without a joint effusion and therefore, if the examination is only accomplished with elbow US, fractures that occur without joint effusion can be missed.5,7,12,16
The false negative case in the study turned out to be a radial head fracture that does not affect the olecranian fossa directly. Nevertheless, sometimes joint effusion can be seen in these type of fractures due to inflammatory changes from the strength of the trauma. This fracture was detected by the second reviewer (FS) when reviewing the US images.
In the study, the elbow POCUS showed a positive result on 2 patients who weren’t diagnosed initially on the emergency traumatology department.
In contrast to the findings in the study performed by Rabiner et al12 and Varga M et al17 where the interobserver concordance was of 0.77 and 0.81 respectively, in the study the interobserver concordance for US in pediatric elbow injuries was of 0.89.
US is a reliable, easy, fast, cost-effective, and painless imaging method that can be performed by trained pediatric physicians and detect indirect signs of fracture with a high sensitivity and negative predictive value.
US is an operator-dependent technique that requires training to be able to detect elbow fractures. Moreover, this study has been performed in a single center and the cohort is a selected convenience sample. Thus, although more patients could have been included in this study, due to the availability of the researchers, some of the patients have not been included in spite of fulfilling the inclusion criteria. Nevertheless, we believe our sample is representative of general population given the similar demographics and clinical characteristics. More studies and a bigger cohort are needed to be able to extrapolate our findings.
Conclusion
Elbow US is an easy, fast, sensitive and reproducible technique. It also has a good sensitivity and negative predictive value and a very good interobserver concordance. Despite the promising results of the study, more studies are needed to determine whether US is a helpful test for the optimization of the management of elbow trauma and a useful complementary test to the clinical evaluation and the radiography and to extract more conclusive results.
Disclaimers:
Funding: This article received a grant from the Biobizkaia Health Research Institute (Basurto University Hospital, Bilbao).
Conflicts of interest: The authors, their immediate families, and any research foundations with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.
Footnotes
The study received the approval from the Local Ethics Committee of Clinical Research (Basurto University Hospital, Bilbao, number 99.22 CEIHU).
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