I.  Introduction and Indications

Ultrasound is an excellent tool for examining even contoured superficial bony structures.  The ribs are thus appropriate for ultrasound examination.  Traditionally chest radiographs are ordered in the setting of thoracic trauma and occasionally a specific rib series.  However, plain radiographs have poor sensitivity for detecting rib fractures. 

Rib fractures are common and the sensitivity of ultrasound in detecting rib fractures has been reported to be higher than that of plain radiography.(1-5)  Studies found a sensitivity of ultrasound 80-78% and plain radiography 23-12%, clinical acumen was in the range of radiography with 26% sensitivity.(2,3) 
Diagnosing rib fractures can have an impact on gauging severity of traumatic mechanism, disposition, analgesic requirements, need for incentive spirometry, and instigating further studies such as a chest CT.  One investigator published a counterpoint to the usefulness of this exam stating that it was disproportionately time consuming, difficult for the patient, and of questionable ultimate clinical significance.(5) While these are good points, teaching this exam and technique may have benefit for those who practice in austere environments, low risk trauma patients for whom the clinician is  reluctant to expose to ionizing radiation, and so on.  More than anything, it is useful whenever the treating clinician finds the information gleaned would benefit the patient. 

II. Anatomy

There are twelve ribs bilaterally of three types.  Ribs 1-7 are true ribs, 8-10 false ribs, and 11 and 12 are termed floating ribs, meaning they have no anterior attachment to the sternum. It is of note that they slant caudally at an angle as they reach from posterior to anterior.  Remember this when orienting the transducer for a longitudinal scan.

 

Illustration 1: Overview of anatomy of ribs. (Google Body)

 Scanning Technique, Normal Findings and Common Variants

The exam is based on a focal symptom or finding, and is thus generally a limited exam of the symptomatic area rather than an exhaustive screening of the rib cage.  Place a linear transducer where the patient indicates as the point of maximum pain.  Align it perpendicular to the long axis of the rib.  This is place the transducer at an angle to the body axis as the ribs slant caudally from posterior to anterior. Use of a standoff pad or copious gel to minimize necessary pressure over this painful area is important to make the exam tolerable for the patient.  Slide the probe along the length of the rib in the area of tenderness looking for disruptions in the rib.

Pathology

Examine the superficial cortex of the rib for cortical disruptions, specifically interruptions of the hyperechoic smooth cortex that widens with respirations indicating fracture. (Figure 1, video clip 1)  Slide the probe along the length of the rib in the painful area, moving to adjacent ribs as well in the painful area. Note the presence or absence of lung sliding underneath any fractures, as it is possible to have small pneumothoraces localized around the fractures.

 

Figure 1: Subtle rib fracture seen with a high frequency linear transducer.

 

Clip 1: Rib fracture.  Note the opening and closing
of the fracture with respiration. 

 

Pearls and Pitfalls

• Remember the angle of the ribs necessitates angling of the probe.
• Keep the probe perpendicular to the rib surface.
• Use a stand off pad or copious gel to enable minimal pressure on a painful area.
• Look for multiple fractures when one is found.
• Some fractures will show a hematoma around the fracture area
  

References

1) Bulger EM, Arneson MA, Mock CN, Jurkovich GJ.
Rib fractures in the elderly. J Trauma,2000;48(6):1040-6.

2) Griffith JF, Rainer TH, Ching AS, Law KL, Cocks RA, Metreweli C.
Sonography compared with radiography in revealing acute rib fracture. AJR Am J Roentgenol,1999;173(6):1603-9.

3) Rainer TH, Griffith JF, Lam E, Lam PK, Metreweli C.
Comparison of thoracic ultrasound, clinical acumen, and radiography in patients with minor chest injury. J Trauma,2004;56(6):1211-3.

4) Kara M, Dikmen E, Erdal HH, Simsir I, Kara SA.
Disclosure o unnoticed rib fractures with the use of ultrasonography in minor blunt chest trauma. Eur J Cardiothorac Surg,2003;24(4):608-13.

5) Hurley M, Keye G, Hamilton S.
Is ultrasound really helpful in the detection of rib fractures. Injury,2004;35(6):562-6.