early diagnosis of rib fractures can rapidly indicate the source of thoracic pain and be helpful in pain management of trauma patients .
other than pain , rib fractures have been reported to be associated with morbidity and mortality in elderly patients ( 3 - 5 ) . in most emergency departments ,
ultrasonography is considered as one of the most useful screening tools for rapid evaluation of trauma patients ( 6 ) .
application of ultrasonography for assessment of chest wall injuries has been reported from 1980s ( 7 ) . since then the technology of ultrasound devices
has significantly improved so that images with higher resolutions are obtained . in light of these improvements ,
the diagnostic value of this modality has been considerably enhanced ( 9 ) . in this
regard , studies have illustrated a considerably high diagnostic value of ultrasonography in detection of thoracic fractures , even higher than that of chest radiography ( 8 , 10 - 12 ) .
for instance in his narrative review , chan referred to ultrasonography as a reliable diagnostic tool for detection of thoracic bone fractures ( 13 ) .
nevertheless , still no comprehensive review has been carried out comparing the diagnostic values of chest ultrasonography and radiography in detection of thoracic fractures .
one solution is to perform a meta - analysis on the available evidence ( 15 , 16 ) .
accordingly , the present systematic review and meta - analysis aimed to determine the diagnostic values of chest ultrasonography and radiography in detection of thoracic bone fractures .

 search strategy and selection criteria 
  the study protocol was established based on the guidelines of meta - analysis of observational studies in epidemiology statement ( moose ) ( 19 ) . after selection of keywords from medical subject heading ( mesh ) terms and emtree ,
two reviewers ( m.y , p.g ) independently carried out an extended systematic search in databases of medline ( via pubmed ) , embase ( via ovidsp ) , isi web of knowledge , scopus , cochrane library , and proquest without any time or language limitations .
sonography  or  ultrasound  or  radiography  or  chest film  or  chest radiograph  combined with  rib fractures  or  chest wall fracture  or 
additionally , the bibliographies of original and review articles as well as google scholar were also searched .
all the studies evaluating the diagnostic accuracy of ultrasonography or chest radiography in detection of chest wall fractures were assessed .
review and editorial articles , case reports and studies with sample populations of less than 10 patients were excluded .
two reviewers ( m.y , p.g ) independently worked on summarizing the data regarding assessing quality of studies , baseline characteristics of patients ( age , gender , the number of patients with and without hemothorax , the etiology of hemothorax ) , the characteristics of ultrasonography device ( transducer , frequency ) , physicians in charge of imaging interpretation , blinding status , sampling method ( consecutive , convenience ) , study design ( retrospective , prospective ) .
finally the number of true positive ( tp ) , true negative ( tn ) , false positive ( fp ) , and false negative ( fn ) cases were extracteded .
disagreements were discussed with the third reviewer ( m.h ) and a solution was proposed . in cases of data inaccessibility ,
data presented as charts were extracted via the method proposed by sistrom and mergo ( 28 ) . in cases where only the sensitivity and specificity were presented , reliable web - based programs were used to calculate the number of tp , tn , fp , and fn cases .  
charecteristics of included studies 1 , ( + / - ) : number of patient with fracture / number of patient without fracture ; 2 , number are presented as mean  standard deviation or ( range ) .
ct : computed tomography ; cxr : chest radiography ; ep : emergency physician ; na : not applicable ; nr : not reported ; us : ultrasonography 
 quality assessment 
  quality of the studies were assessed based on the guidelines of 14-item quality assessment of diagnostic accuracy studies ( quadas2 ) tool ( 29 ) .
the quality assessment were performed based on following items : acceptable reference tests , accounting for indeterminate results , avoiding differential verification bias , disease progression bias , incorporation bias and verification bias , blind index test interpretation , blind interpretation of reference test , explained withdrawal , relevant clinical data available , and representative spectrum .
a total grading of poor , fair , and good was attributed to each survey and only the fair and good studies were included in the meta - analysis . 

statistical analysis 
  analysis was performed using stata 11.0 statistical software via midas module . to evaluate the screening performance characteristics of ultrasonography and radiography in detection of chest wall fractures , summary receiver operative curves ( srocs ) were drawn and pooled sensitivity , specificity , positive likelihood ratio and negative likelihood ratio with 95% confidence interval ( 95% ci ) were calculated .
due the high heterogeneity between the included studies , mixed - effects binary regression model was used .
heterogeneity was evaluated through calculations of i2 and 2 tests and a p value of less than 0.1 together with an i2 greater than 50% were considered as positive heterogeneity ( 30 ) .
deek s asymmetry funnel plot was used to search for publication bias . in all the analyses , p value of less than 0.05

 study characteristics 
  17 out of 3894 studies found in the comprehensive search were included in the systematic review and meta - analysis ( 1 , 2 , 8 , 10 - 12 , 14 , 17 , 18 , 20 - 27 ) . 5 studies had assessed the diagnostic accuracy of ultrasonography in detection of thoracic bone fractures ( 1 , 2 , 18 , 20 , 21 ) , 8 diagnostic value of chest radiography ( 14 , 17 , 22 - 27 ) , and 4 diagnostic values of ultrasonography and radiography simultaneously ( 8 , 10 - 12 ) .
1667 cases ( 807 with and 860 without fractures ) were extracted from the 17 mentioned articles , whose age ranged from 0 to 92 years old .
figure 1 shows the inclusion process of articles and table 1 summarizes the characteristics of included studies .
the results of the analyses are presented as srocs and funnel plots in figures 3 to 5 .
the area under the curve of sroc for ultrasonography and radiography in detection of chest wall fractures were found to be 0.99 ( 95% ci : 0.97 - 0.99 ) and 0.97 ( 95% ci : 0.96 - 0.99 ) , respectively ( figure 3 ) .
pooled sensitivity and specificity of ultrasonography in detection of thoracic bone fractures were 0.97 ( 95% ci : 0.90 - 0.99 ; i2= 88.88 , p<0.001 ) and 0.94 ( 95% ci : 0.86 - 0.97 ; i2= 71.97 , p<0.001 ) , respectively ( figure 4-a ) .
these characteristics for radiography were found to be 0.77 ( 95% ci : 0.56 - 0.90 ; i2= 97.76 , p<0.001 ) and 1.0 ( 95% ci : 0.91 - 1.00 ; i2= 97.24 , p<0.001 ) , respectively ( figure 5-a ) .
in addition , pooled positive and negative likelihood ratios of ultrasonography were 16.26 ( 95% ci : 6.26 - 38.87 ; i2= 59.14 , p<0.001 ) and 0.03 ( 95% ci : 0.01 - 0.11 ; i2= 86.76 , p<0.001 ) , respectively ( figure 4-b ) , while these measures for radiography were reported to be 774.63 ( 95% ci : 7.0 - 8573.0 ; i2= 96.62 , p<0.001 ) and 0.23 ( 95% ci : 0.11 - 0.48 ; i2= 96.94 , p<0.001 ) , respectively ( figure 5-b ) . there were significant heterogeneity between the articles ( figure 4 and 5 ) .
specificity of ultrasonography in detection of thoracic bone fractures was directly correlated with frequency of transducer ( 90% vs. 95% ) .
the sensitivity of this modality was found to be higher in detection of rib fractures rather than fractures of clavicle or sternum ( 97% vs. 91% ) .
moreover it was found that the sensitivity would be higher if the procedure is performed by a radiologist ( 96% ) compared to an emergency medicine specialist ( 90% ) .
studies with sample sizes of greater than 100 patients reported higher diagnostic accuracies for ultrasonography in detection of thoracic bone fractures ( 97% vs. 91% ) .
as can be seen in table 2 , the most important factor affecting sensitivity of chest radiography is the interpreting physician .
the sensitivity was found to be 66% when the radiogram was interpreted by an emergency medicine specialist while it was 80% when interpreted by a radiologist .
furthermore , consecutive sampling method compared with convenience ( 80% vs. 73% ) and sample size of more than 100 patients ( 82% vs. 73% ) were also found to be sources of heterogeneity .
base on the results of the present meta - analysis sensitivity of chest ultrasonography in detection of thoracic bone fractures following trauma was prominently higher than radiography ( 97% vs. 77% ) .
yet , the specificity of radiography was found to be significantly higher than ultrasonography in this regard ( 100% vs. 94% ) . on this basis and according to calculated likelihood ratios , a negative result of ultrasonography in detection of thoracic fracture is more reliable than radiography ( negative likelihood ratio=0.03 ) , while a positive result of chest radiography is more reliable than ultrasonography ( positive likelihood ratio=774.63 ) .  
subgroup analysis of diagnostic accuracy for chest radiography and ultrasonography in detection of thoracic bone fractures , p value < 0.1 was considered as significant for heterogeneity ; ci : confidence interval .  
ultrasonography had a higher sensitivity in diagnosis of rib fractures rather than other chest wall bones , while the type of fracture had no effect on diagnostic value of radiography .
this finding can be ascribed to the higher attention that physicians pay to rib fractures rather than other chest wall bones such as scapula and sternum .  
fractures are diagnosed via ultrasonography based on observation of cortical bone disruption . in cases of small fractures , detection of this sign in sonogram and distinguishing it from other findings is highly dependent on the skills of the operator .
the role of operator s skills in detection of injuries via ultrasonography was verified in the present study as well ( 31 - 34 ) .
the present study found that the specificity of this modality increased with frequencies of higher than 10mhz which might be due to the higher resolution obtained with higher frequencies ( 35 ) , making it easier to detect the signs of fracture .  
some narrative review articles and qualitative systematic reviews are indicative of the potential benefit of ultrasonography in detection of chest wall fractures . in this
regard , chan , in his systematic review conducted on studies indexed in medline , declares that ultrasonography has a higher sensitivity in detection of thoracic bone fractures compared to radiography ( 13 ) . finding the diagnostic accuracy of ultrasonography to be two times the ability of radiography in fracture diagnosis , dietrich et al
. also referred to ultrasonography as a useful diagnostic tool for detection of rib fractures ( 36 ) .
presence of considerable heterogeneity between the included articles and simultaneous inclusion of retrospective and prospective studies in the meta - analysis were major limitations of this study .
ess : effective sample sizes summary receiver operative curves ( sroc ) for ultrasound ( a ) and chest radiography ( b ) in detection of thoracic bone fractures .
auc : area under the curve ; sens : sensitivity ; spec : specificity forest plot of screening performance characteristics of chest ultrasonography in detection of thoracic bone fractures .
sensitivity and specificity ( a ) ; diagnostic likelihood ratio ( dlr ) ( b ) .
ci : confidence interval forest plot of screening performance characteristics of chest radiography in detection of thoracic bone fractures .
sensitivity and specificity ( a ) ; diagnostic likelihood ratio ( dlr ) ( b ) .
base on the findings of the present meta - analysis , screening performance characteristic of ultrasonography in detection of thoracic bone fractures was found to be higher than radiography .
however , these characteristics were more prominent in detection of rib fractures and in cases where was performed by a radiologist .
this research has been supported by tehran university of medical sciences & health services grant number : 93 - 02 - 38 - 25618 .
all authors passed four criteria for authorship contribution based on recommendations of the international committee of medical journal editors .
 introduction : the potential benefit of ultrasonography for detection of thoracic bone fractures has been proven in various surveys but no comprehensive conclusion has been drawn yet ; therefore , the present study aimed to conduct a thorough meta - analytic systematic review on this subject . 
 methods : two reviewers independently carried out a comprehensive systematic search in medline , embase , isi web of knowledge , scopus , cochrane library , and proquest databases . 
 data were summarized as true positive , false positive , true negative and false negative and were analyzed via stata 11.0 software using a mixed - effects binary regression model . 
 sources of heterogeneity were further assessed through subgroup analysis . 
 results : data on 1667 patients ( 807 subjects with and 860 cases without thoracic fractures ) , whose age ranged from 0 to 92 years , were extracted from 17 surveys . 
 pooled sensitivity and specificity of ultrasonography in detection of thoracic bone fractures were 0.97 ( 95% ci : 0.90 - 0.99 ; i2= 88.88 , p<0.001 ) and 0.94 ( 95% ci : 0.86 - 0.97 ; i2= 71.97 , p<0.001 ) , respectively . 
 the same measures for chest radiography were found to be 0.77 ( 95% ci : 0.56 - 0.90 ; i2= 97.76 , p<0.001 ) and 1.0 ( 95% ci : 0.91 - 1.00 ; i2= 97.24 , p<0.001 ) , respectively . 
 the sensitivity of ultrasonography was higher in detection of rib fractures , compared to fractures of sternum or clavicle ( 97% vs. 91% ) . 
 moreover , the sensitivity was found to be higher when the procedure was carried out by a radiologist in comparison to an emergency medicine specialist ( 96% vs. 90% ) . 
 conclusion : base on the findings of the present meta - analysis , screening performance characteristic of ultrasonography in detection of thoracic bone fractures was found to be higher than radiography . 
 however , these characteristics were more prominent in detection of rib fractures and in cases where was performed by a radiologist . 
Introduction:
Methods:
Results:
Discussion:
Conclusion:
Conflict of interest:
Funding support:
Authors contributions: