Blunt Trauma Prediction Rule: Aortic Injury

Probability of Aortic Rupture in Blunt Chest Trauma  
Traumatic rupture is a rare and lethal injury in patients sustaining blunt chest trauma. The chest radiograph remains a useful means to screen the thorax for aortic injury. A normal chest radiograph virtually excludes aortic rupture. In the past, an abnormal chest radiograph was investigated with an aortogram to exclude rupture. However, the yield was low. CT has been used as a means to better select those requiring angiography. Most recently, spiral CT has been investigated as a means for primary diagnosis, with promising results.

The chest radiograph is important to screen for a variety of injuries which occur in the blunt trauma victim. The ABC's approach is a useful pneumonic to survey for these injuries.
ABC's Blunt Chest Trauma
A: Aortic Transection
B: Bronchial Fracture
C: Cord Contusion
D: Diaphragmatic Rupture
E: Esophageal Fracture
F: Flail Chest
G: Gas (subtle pneumothorax, pneumomediastinum)
H: Heart (cardiac injury)
I: Iatrogenic injury (misplaced tubes and catheters)
Determining Risk of Traumatic Aortic Injury: Prediction Rule

Derived from a 2-year case-control study of 31 cases of traumatic aortic injury. Logistic regression was used to determine injury predictors. Clinically similar predictors were combined into composite predictors. These predictors were combined into a seven-point injury index clinical prediction rule using multivariate logistic regression. Probability of injury was determined through Bayes' theorem. All injured patients had at least one predictor. (
from Blackmore et al
Lecture ABC's Blunt Chest Trauma reviews the role of the chest radiograph in the blunt trauma victim.
Injury Prediction Rule
Age > 50
Thoracic injury
Abdominopelvic injury
Extremity fracture
Head injury
The Probability of Aortic Rupture:
Prevalence of Aortic transection in blunt chest trauma 4 studies (n=8772 pts), prevalence 1.4% (0.3 - 3.5%) from Hunink.

no vehicle occupant restrain device used, or unknown

Any systolic blood pressure < 90 mm Hg while in emergency department

Thoracic Injury
Rib fracture, pneumothorax, lung contusion, or laceration

Abdominal Injury
lumbar spine fracture, pelvic fracture, or injury requiring laparotomy

Extremity Fracture
Fracture of humerus, radius, ulna, femur, tibia, or fibula

Head Injury
Skull fracture, intracranial or intraparenchymal hemorrhage, or unconsciousness at evaluation

Data Used
Predictors Likelihood ratios
Characteristic Odds Ratio (95% CI)
Age > 50 12.1
1.8 - 84
Unrestrained 5.9
1.1 - 31
Hypotension 9.9
1.8 - 54
Thoracic Injury 12.1
2.7 - 54
Abdominopelvic Injury 4.5
1.1 - 19
Extremity Fracture 8.4
1.3 - 55
Head Injury 4.9
1.2 - 20
Likelihood Ratios:

Likelihood ratios are intuitive measures of the diagnostic information provided by a test result or clinical finding. The likelihood ratio varies from zero to infinity, depending on the degree of strength of the test result. A test strongly suggestive of aortic rupture has a likelihood ratio much greater than one, a test that suggests no rupture has a likelihood ratio close to zero, and a test that contains no diagnostic information has a likelihood ratio of one. In the odds-likelihood ratio form of Bayes theorem, the odds that the aorta is ruptured is the product of the likelihood ratios favoring aortic rupture multiplied by the prior odds of aortic rupture.


Bayes Theorem:
Posterior odds = prior odds x likelihood ratios

Likelihood Ratios:

= Prob in subjects with aortic rupture / Prob in subjects without aortic rupture
= Sensitivity / (1 - Specificity)
= True positive fraction / False positive fraction


Probability = Odds / (Odds + 1)
Odds = Prob / (1 - Prob)
Odds Ratio:

When the likelihood of developing disease (or in this case, rupturing the aorta) is low, then the case-control study if often used to study risk factors. The odds ratio is an approximation of relative risk and when the prevalence of the disorder is small. Odds ratio is computed from a 2x2 table as AD/BC.

Risk Factor present
Risk Factor absent
Blackmore CC, Zweibel A , Mann FA. Determining risk of traumatic aortic injury: how to optimize imaging strategy. AJR 2000; 174:343-347.
Hunink MG , Bos JJ. Triage of patients to angiography for detection of aortic rupture after blunt chest trauma: cost-effectiveness analysis of using CT. AJR 1995; 165:27-36.
Black WC , Armstrong P. Communicating the significance of radiologic test results: the likelihood ratio. AJR 1986; 147:1313-1318. [Related Records]


Information provided is not intended to be medical or technical advice. The information given at this site is for educational purposes only and is not sufficient for medical decisions. I disclaim any liability for the acts of any physicians or any other individual who receives any information on any medical procedure through this web site. I accept no legal responsibility for any injury and/or damage to persons or property from any of the suggestions or material discussed herein.