13.3 Ribs, Sternum & Soft-Tissue Neck/Airway

Rib Radiography

The bony thorax has 12 pairs of ribs. Ribs 1-7 are true (vertebrosternal) ribs that attach directly to the sternum by costal cartilage; ribs 8-10 are false (vertebrochondral) ribs whose cartilage joins the rib above; and ribs 11-12 are floating (vertebral) ribs with no anterior attachment. Because the ribs curve around the thorax, the tested principle is where the injury lies relative to the diaphragm and which surface is injured.

Breathing Phase and Centering

The diaphragm splits rib imaging into two techniques:

For upper (axillary) ribs, expose on full inspiration so the diaphragm drops and uncovers the lower posterior ribs. For lower ribs, position the patient recumbent and expose on expiration; this elevates the diaphragm and provides more uniform density over the upper abdomen so the lower ribs are seen against soft tissue rather than aerated lung.

Which Projection?

Place the site of injury closest to the image receptor and choose the projection by which surface hurts:

• AP projection — best for posterior ribs (patient supine, back against IR).
• PA projection — best for anterior ribs (patient prone/erect facing IR).
• AP oblique (RPO or LPO), 45 degrees — profiles the axillary (lateral) ribs. Rotate the patient with the affected side toward the IR to elongate that side's axillary rib curve away from the spine.

For unilateral rib pain, always turn the affected side against the IR to reduce OID and place the injured ribs closest to the receptor. Use a breathing (orthostatic) technique only for the sternum, never routinely for ribs — ribs require a suspended-respiration technique.

Worked Example

A patient reports pain over the right posterior lower ribs after a fall. Reason it out in order: Below the diaphragm? Yes (lower ribs) — so recumbent, expose on expiration. Posterior surface? Yes — so use an AP projection. Which side to the IR? The right (affected) side. If the tender area were the axillary portion, you would add a 45-degree AP oblique (RPO) with the right side toward the IR to elongate the axillary ribs. This ordered reasoning — diaphragm level, then surface, then oblique — answers most rib items correctly.

Sternum

The sternum has three parts: the manubrium superiorly, the body (gladiolus), and the xiphoid process inferiorly. The jugular (suprasternal) notch sits at the top of the manubrium (T2-3), and the sternal angle (manubriosternal junction) lies at T4-5. The sternum is a thin, flat bone directly over the spine, so imaging it AP or PA would superimpose it on the vertebrae.

RAO of the Sternum

The solution is the PA oblique (RAO) projection, rotated 15-20 degrees. The RAO is chosen (not the LAO) because it throws the sternum to the left, over the homogeneous heart shadow, giving a uniform background instead of the busy, air-filled lung. The thinner the patient, the greater the rotation needed to move the sternum off the spine. This projection classically uses an orthostatic (breathing) technique: a low mA with a long exposure time (2-3 seconds) during quiet, shallow breathing. The breathing intentionally blurs the overlying ribs and pulmonary vascular markings while the stationary sternum stays sharp.

Lateral Sternum

The lateral sternum is performed erect at a 72-inch SID (to minimize magnification of this anterior structure) with the patient's shoulders and arms drawn behind the back to project the sternum forward, free of superimposition. Expose on full inspiration. The lateral demonstrates the sternum in profile, which is essential for assessing the depth of a depressed (flail) fracture.

Sternoclavicular (SC) Joints

The SC joints are demonstrated with a PA or a shallow PA oblique (RAO/LAO of 10-15 degrees). A slight oblique rotates the spine away and demonstrates the SC joint of interest (the side nearest the IR).

Soft-Tissue Neck and Upper Airway

Soft-tissue neck imaging targets the air-filled upper airway — the pharynx, larynx, epiglottis, and trachea — rather than bone, so it uses a low kVp technique for high soft-tissue contrast.

• Lateral upper airway: performed erect at a 72-inch SID, neck slightly extended, exposed during slow inspiration to fill the airway with air. It profiles the air-filled pharynx, larynx, epiglottis, and trachea. The lateral airway is the projection that reveals the "thumb sign" of epiglottitis and enlarged adenoids.
• AP soft-tissue neck: demonstrates the trachea and larynx and the subglottic "steeple sign" (hourglass narrowing) of croup.

Because the airway must be air-filled to be visible, timing the exposure to inspiration is the key technical point. A collapsed (expiration) airway can hide a small foreign body or falsely suggest narrowing.

Clinical Scenario

A toddler arrives drooling, leaning forward, with stridor, and epiglottitis is suspected. The correct study is a lateral upper-airway image taken erect (never force the child supine, which can obstruct the airway) at 72 inches during slow inspiration; a swollen epiglottis produces the rounded "thumb sign." Contrast that with a barking-cough toddler suspected of croup, where the AP projection shows the subglottic "steeple sign." Both use a low kVp for maximum soft-tissue contrast and both depend on catching the airway while it is air-filled, which is why respiration timing — not high technique — is the examiner's focus.

Remember the sternal landmarks one more time, because they anchor thoracic centering across chapters: the jugular notch (T2-3), the sternal angle (T4-5, level of the carina), and the xiphoid tip (T9-10). Miscentering the sternum, ribs, or airway is almost always a landmark-palpation error, not an exposure error.