INTRODUCTION
Rib fractures represent a frequent condition associated with minor thoracic injury (mTI).Reference Liman, Kuzucu and Tastepe 1 Previous studies have shown that more than a third of patients with minor blunt chest trauma may be suffering from rib fractures.Reference Liman, Kuzucu and Tastepe 1 , Reference Sirmali, Turut and Topcu 2 These are associated with short- and long-term limitations such as acute pain and significant work absenteeism.Reference Kerr-Valentic, Arthur and Mullins 3 , Reference Gordy, Fabricant and Ham 4 Serious acute complications, such as pneumothorax, hemothorax, lung contusion, and flail chest, may result from rib fractures.Reference Sirmali, Turut and Topcu 2 Moreover, delayed complications, such as pneumothorax, hemothorax and pneumonia, may also following such injuries.Reference Misthos, Kakaris and Sepsas 5 - Reference Flagel, Luchette and Reed 7 These complications increase with the number of diagnosed rib fractures,Reference Sirmali, Turut and Topcu 2 , Reference Bulger, Arneson and Mock 6 , Reference Flagel, Luchette and Reed 7 as does mortality.Reference Bulger, Arneson and Mock 6 - Reference Battle, Hutchings and Evans 8 In order to identify patients at risk of complications, an early and accurate diagnosis of rib fracture may be helpful.
In patients with a blunt chest trauma, studies have shown that clinical symptoms alone do not correlate well with the presence of rib fractures.Reference DeLuca, Rhea and O’Malley 9 , Reference Dubinsky and Low 10 Chest X-ray and rib views have a limited sensitivity to identify rib fractures and vary significantly among studies, reaching at most 50%.Reference Rainer, Griffith and Lam 11 , Reference Chardoli, Hasan-Ghaliaee and Akbari 12 Computed tomography (CT) is sometimes considered as the gold standard to diagnose rib fractures, but it exposes patients to a significant amount of radiation. Furthermore, it is an imperfect imaging tool, because the axis of tomography images can miss fractures due to the particular rib cage anatomy.Reference Cho, Sung and Kim 13
Since the last decade, point-of-care ultrasound (PoCUS) has become an important part of emergency physicians’ (EP) daily practice, and its applications have become numerous. Studies have reported that ultrasound is more sensitive than X-ray to detect rib fractures.Reference Rainer, Griffith and Lam 11 , Reference Griffith, Rainer and Ching 14 , Reference Kara, Dikmen and Erdal 15 As such, there may be potential benefits over plain radiography for performing rib PoCUS in mTI. Knowing the limits of existing imaging techniques used for the diagnosis of rib fractures and the growing availability of PoCUS in emergency departments (EDs), we conducted a prospective cohort study in which we hypothesized that rib PoCUS would be a feasible technique to diagnose rib fractures in patients with mTI. Secondary objectives were to 1) evaluate patients’ pain during the PoCUS procedure, 2) identify the limitations of the PoCUS technique, and 3) compare the diagnosis obtained with PoCUS to radiography results.
METHODS
Population
This study took place in a tertiary trauma centre in the province of Quebec, Canada. Clinical suspicion of rib facture was the main inclusion criterion in patients age 18 years or older who sustained blunt thoracic trauma. A convenience sample was used. The exclusion criteria were defined as follows: delay in seeking care (more than 96 hours post-trauma), hemodynamic instability (defined as a heart rate of more than 100 beats per minute, saturation of less than 95%, systolic pressure of less than 90 mm Hg, and respiratory rate of more than 20 per minute), a score of 14 or less on the Glasgow Coma Scale (GCS), patients suffering from significant traumatic injuries requiring treatment and hospitalization (mediastinal injury, spinal fractures, flail chest, significant hemothorax, and/or pneumothorax requiring tube thoracostomy).
Ultrasound training
Participating clinicians attended a 2-hour training session before the recruitment of patients began (see Supplementary Material). Two experienced PoCUS instructors taught participating EPs. The first hour allowed them to become familiarized with the study protocol, and the ultrasound technique to diagnose rib fractures was explained. During the second hour of this session, EPs were allowed to practice the ultrasound technique.
EPs were told to locate the point of maximal tenderness with palpation of the patient thorax. Then, the operator applied a high frequency linear ultrasound probe perpendicular to the long axis of the rib. A distinct shadowing posterior to the rib helped in differentiating the pleural line from the rib cortex. After adequately locating the rib, the probe was turned ninety degrees to allow the clinician to follow the rib cortex longitudinally; this appeared as a white, hyperechoic line. The clinician was asked to start screening 10 cm before the point of maximal tenderness and to finish 10 cm beyond, to ensure that no fracture would be missed.Reference Chardoli, Hasan-Ghaliaee and Akbari 12 EPs were asked to stabilize the probe between the index and major fingers of the non-dominant hand. This made it possible to feel the intercostal spaces with the same index and major fingers, allowing the clinician to precisely screen the rib (Figure 1). The upper and lower adjacent ribs were also screened. A rib fracture was diagnosed when a discontinuity of the cortical alignment was observed, visualized as a gap through the hyperechoic cortical line of the rib.
Rib point-of-care ultrasound technique.
Data collection
Sociodemographic and clinical characteristics were collected using a standardized form during the initial ED visit. Presence or absence of rib fractures was documented. EPs were blinded to the chest X-ray findings when they performed the rib PoCUS and when they filled out the study survey materials. Subsequently, a radiologist, blinded to the PoCUS results, interpreted the X-rays, and results were compiled.
Outcome measures
The feasibility of PoCUS for the detection of rib fractures was mainly ascertained in terms of acceptability.Reference Bowen, Kreuter and Spring 16 The primary outcome was the feasibility score (FS), which was defined as a score of more than 50 measured on a visual analogue scale (VAS) completed by the EP who performed the PoCUS. This score allowed to evaluate the extent to which the technique could be performed in the context of the ED. The clinician was asked to rate the feasibility of the rib PoCUS technique, from 0 (extremely difficult) to 100 (extremely easy). There are no previous publications in the medical literature to provide a formal accepted definition of a feasibility score for rib PoCUS for fractures. A steering committee, which included five EPs experienced with PoCUS, was consequently formed in order to come to a consensus agreement for the main outcome. The threshold FS was defined by the steering committee as a score of more than 50 measured on a VAS completed by the EP who performed the PoCUS.
Furthermore, to assess acceptability, patients were asked to rate their degree of pain associated with the technique using a VAS ranging from 0 (no pain) to 100 (unbearable pain). Technical limitations were classified as present or absent. Anticipated limitations, such as obesity, technical difficulty, and patient’s pain during the technique, were available answers but clinicians could also specify any other limitations regarding the PoCUS that they performed. Further comparisons were made using a database in which formal chest X-ray interpretation and PoCUS results were compiled for each patient. Patient charts were also reviewed in order to complete the database with this information when available.
Statistical analysis
All data were described with measures of proportion, median, and dispersion with interquartile range. All analyses were conducted using the Statistical Analysis System software, version 9.4 (SAS Institute Cary, NC, USA). Cohen tagsReference Cohen 17 and Pearson correlation coefficient were used for statistical analysis purposes.
Ethics
The Research Ethics Boards of the Centre Hospitalier Universitaire (CHU) de Québec – Université Laval approved the study protocol, and written consent was obtained for all recruited patients.
RESULTS
Ninety-six patients were recruited from November 2011 to December 2013, and 11 out of 24 (46%) full-time EPs participated in this study. All recruiting clinicians had a mean experience of 9 years with bedside ultrasound, although none of the participating EPs had experience with rib PoCUS.
The majority of patients were men (69.8%). The main mechanisms for trauma were fall from height (60%), sport (12%), motor vehicle collision (8%), and direct blow (7%). Median time between trauma and ED consultation was 18.9 hours (IQR 5.6–47.3). These results and others, including vital signs on arrival, are further described in Table 1.
Baseline clinical and demographic characteristics of the study population
A majority (65%) of EPs concluded that the PoCUS technique to diagnose rib fracture was feasible (FS > 50) with a median score of 63 (Table 2). Patients’ pain related to the PoCUS examination was relatively low, with a median score of 31 (IQR 5–57). Limiting factors to the ultrasound technique were found in 33 patients (34%). These factors were mainly the following: pain during examination (13 [15%] patients), technical difficulty (10 [10%] patients), and obesity (7 [7%] patients). Other identified factors were perception of technical inexperience for rib ultrasound (4 [4%] patients), posterior localization of the suspected fracture (2 [2%] patients), and presence of voluminous breasts limiting ultrasound access (2 [2%] patients. Six patients had two factors identified. Of them, three had technical difficulty and obesity outlined as limiting factors. Correlation coefficients were obtained for each limiting factor to evaluate whether there was any relation with the degree of feasibility reported by EPs (Table 3). Feasibility categories divided patients in two groups: those with a VAS of 50 or less and those with 51 or more. We found a trend for a weak negative relationship between limiting factors and feasibility. Obesity had a moderate negative correlation,Reference Cohen 17 identified as the main factor that could make rib fracture PoCUS technique less feasible (r=−0.39).
Main and secondary outcome results
FS=feasibility score; VAS=visual analogue scale.
Correlation coefficient between limiting factors to the PoCUS examination and degree of feasibility reported by the emergency physicians
We found 27 (29%) patients who were diagnosed with rib fractures on the basis of PoCUS examination who were not diagnosed with standard radiography (Table 4). For 11 patients, a rib fracture was diagnosed with radiography but not with PoCUS (Table 5). Nine of these patients were men with a mean age of 63 years old. No limiting factor was identified for five patients. Patients’ pain was identified as a limiting factor for 2 of these 11 patients, as was technical difficulty. One patient had three fractures diagnosed with radiography that were not diagnosed with PoCUS. Three others had two fractures on radiography with a negative PoCUS examination in ED. An FS between 0 and 50 was noted for five patients, and the remaining six patients had an FS superior to 50.
Comparison between point-of-care ultrasound (PoCUS) results and X-rays blinded interpretation (n=94) by radiologists
Characteristics of the 11 patients whose ultrasound was negative and X-ray was positive
DISCUSSION
To our knowledge, no previous studies have investigated PoCUS feasibility when performed by EPs to diagnose rib fractures in patients with mTI. Considering a mean FS of 65 on our VAS, our study suggests that the use of PoCUS as technique to diagnose rib fractures in the ED is feasible. EPs reported that patients’ pain during PoCUS evaluation was the most significant limiting factor. However, this limiting factor was found in only 13 (14%) patients on the total number of recruited patients, potentially explaining the global positive evaluation of the ultrasound technique reported by patients. Indeed, the vast majority of patients reported a low score of pain during PoCUS examination. Our results suggest that PoCUS is an acceptable technique that does not seem to be unacceptably painful when rib fractures are suspected. It should be noted that the level of pain experienced during plain radiography evaluation is not zero, considering the mobilization required to obtain adequate views.
Technical difficulty, obesity, posterior location, and voluminous breasts in women were also identified as limiting factors. Obesity had a negative correlation with feasibility but was still moderate. Practice and experience with the specific PoCUS technique may compensate for technical difficulty, but obesity, posterior location, and voluminous breasts in women are identified as non-modifiable factors that could limit ultrasound evaluation for rib fractures. We suppose that the occurrence of technical difficulty might decrease as the experience of the EP grows with rib fracture PoCUS. Therefore, because our participating EPs were inexperienced with rib PoCUS at the beginning of the study, we believe that the importance of this limiting factor may have been overestimated, and, consequently, the FS results may have been underestimated.
Interestingly, we found that 27 (29%) patients had rib fractures diagnosed with PoCUS who were not diagnosed with radiography. Given the absence of gold standard in our study, it remains unclear whether these patients represent true or false positives. Nevertheless, the actual evidence on ultrasound sensitivity over radiography concerning rib fracture diagnosis suggests that they were likely to be true positives.Reference Rainer, Griffith and Lam 11 , Reference Griffith, Rainer and Ching 14 , Reference Kara, Dikmen and Erdal 15 On the other hand, rib fractures were also diagnosed on X-ray with negative PoCUS results for 11 patients, including multiple fractures in 4 patients. We noted that patients’ pain and technical difficulty were identified as the two most important limiting factors. The lack of experience of EPs for rib detection with PoCUS might explain these false-negative results. As the expertise of EPs with rib PoCUS improves, we expect the sensitivity to increase accordingly. Future studies are required to assess this issue.
Some limitations have to be considered when interpreting these results. First, we chose a convenience sample for our study. Underestimation or overestimation of particular groups within the population may have influenced our study results. For example, obese patients could have been underrepresented, leading to easier technique for most patients and fewer identified limiting factors. Second, there is no gold standard for routine rib fracture diagnosis by EP. Even though a CT might be considered in the case of diagnostic tools for rib fractures, we have to take into account the amount of radiation, cost, and accessibility. Our study does not have a gold standard as reference, which limits the interpretation of our results on the number of rib fractures diagnosed with PoCUS. Finally, we know that ultrasound is operator-dependant. EPs who performed the PoCUS examinations in our study had a mean experience of 9 years using bedside ultrasound as part of their daily practice. They are working in a tertiary trauma centre, where the opportunities to use ultrasound in blunt chest trauma patients are frequent. However, even if they had prior ultrasound exposure, none of the recruiting EPs had previous experience with rib PoCUS. Therefore, we believe that our results could be easily applicable to any clinicians using ultrasound without specific technical experience in rib sonography, making the results of our study widely applicable in the emergency medicine community.
PoCUS indications are growing in number. Within the last few years, PoCUS has become an essential diagnostic modality in our daily practice, and EPs have had numerous opportunities to improve their ability to use it more efficiently. The feasibility of the use of PoCUS for the diagnosis of rib fractures observed in our study might thus be slightly underestimated, as EPs become more experienced and skilled with PoCUS.Reference Heller and Melanson 18
CONCLUSIONS
PoCUS examination to diagnose rib fractures seems to be a feasible and reasonably comfortable technique for ED patients. Rib PoCUS has the potential to augment conventional radiography to diagnose rib fractures. Considering the number of patients diagnosed with rib fractures in the ED, further studies evaluating the potential economic and timesaving impact of using PoCUS for rib fracture diagnosis would be beneficial.
Acknowledgements: The authors want to thank all emergency physicians of the CHU de Québec-Université Laval Enfant-Jésus Hospital for patients’ recruitment and Dr. Claude Topping for teaching the training session. As well, they want to thank M. Pier-Alexandre Tardif for his valuable support in reviewing this article.
The authors assert that all procedures contributing to this work comply with the ethical standards of the relevant national and institutional committees on human experimentation and with the Helsinki Declaration of 1975, as revised in 2008. This research received no specific grant from any funding agency, commercial or not-for-profit sectors.
Competing interests: None declared.
SUPPLEMENTARY MATERIALS
For supplementary material/s referred to in this article, please visit http://dx.doi.org/10.1017/cem.2016.383
