Sternal Angle Landmarks

Mnemonic

The angle of Louis, at T4/T5, is the single busiest landmark in the thorax:

• Junction of the manubrium and body of the sternum
• Attachment of the second costal cartilage, the starting point for counting ribs
• Bifurcation of the trachea (carina)
• Bifurcation of the pulmonary trunk
• Beginning and end of the aortic arch
• Azygos vein enters the superior vena cava
• Thoracic duct crosses to the left
• Divides superior from inferior mediastinum
• Ligamentum arteriosum, and the left recurrent laryngeal nerve hooking round it

“Everything happens at T4/5.”

Other thoracic levels worth pairing with it: T8 caval opening, T10 oesophageal hiatus, T12 aortic hiatus (the “I ate ten eggs at twelve” rule), and C6 for the start of the trachea and oesophagus.

Expansion

The sternal angle (angle of Louis) is the palpable ridge where the manubrium meets the body of the sternum. At this level:

• The second costal cartilage articulates - the starting point for counting ribs
• The plane passes back to the T4/T5 intervertebral disc
• The trachea bifurcates at the carina
• The aortic arch begins and ends
• The azygos vein arches over the right main bronchus to join the superior vena cava
• The thoracic duct crosses the midline from right to left
• The superior and inferior mediastinum are divided

Almost every important thoracic landmark question resolves to this one plane, which is why it is worth learning as a single list rather than piecemeal.