Sternal angle vertebral level: T4-T5, not T3

The sternal angle: anatomy and palpable landmark

The sternal angle (also called the angle of Louis or manubriosternal joint) is a bony ridge you can feel on the front of your chest. It marks the point where the manubrium (the upper segment of the sternum) meets the body of the sternum. This anatomic junction is one of the most important landmarks in radiography because it sits at a specific, reliable vertebral level: T4-T5.

The sternal angle is palpable. You can find it by placing your fingers on the jugular notch (the hollow at the top of the breastbone) and sliding down about an inch or two until you feel a ridge. That ridge is the sternal angle. It’s one of the few internal vertebral landmarks you can touch and use for positioning, which is why it shows up so frequently on the ARRT.

The 2nd rib articulates with the sternum precisely at the sternal angle. This is critical for rib counting. If you’re looking at a chest radiograph and need to verify a vertebral level by counting ribs, you start at the 2nd rib (which you can find by locating the sternal angle), then count up or down from there.

Why T4-T5 matters: the landmark cluster

The sternal angle is not just one landmark. It’s the midpoint of several important anatomic converging points at the T4-T5 intervertebral disc:

2nd rib articulation

The 2nd costal cartilage (the flexible cartilage at the anterior end of the 2nd rib) attaches to the sternum at the sternal angle. This is the only reliable anterior rib landmark you can palpate without imaging. All other ribs require counting from this reference point.

Tracheal bifurcation (carina)

The trachea divides into the right and left mainstem bronchi at approximately the T4-T5 level. This is the carina, and it’s visible on chest x-rays as a small ridge inside the mediastinum. It’s a key anatomic relationship: trachea above, two main bronchi below.

Aortic arch

The aortic arch (the portion of the aorta that loops from left ventricle up and over to the descending aorta) begins at approximately the T4-T5 level. The arch is a common feature on chest radiographs and a frequent positioning reference.

Azygos vein arch

The azygos vein (a major right-sided vein that drains to the superior vena cava) arches over the right mainstem bronchus at approximately T4-T5. It appears as a small rounded opacity in the right lung base on PA chest views.

All four of these structures cluster at T4-T5. This is why the ARRT tests the sternal angle location so heavily. It’s a single palpable landmark that anchors multiple vital anatomy.

Common wrong answer: T3

Some ARRT study materials, flashcards, and older review books cite T3 as the sternal angle level. This is wrong, but it’s wrong in a way that sticks because it’s close and sounds authoritative when printed on a study card.

The error likely originated from older anatomic texts or simplified positioning guides that weren’t precise enough. The canonical correct answer is T4-T5, and this is the answer the ARRT expects. If you learned T3, correct it now before exam day.

You can verify this in any anatomy textbook. Open Bontrager, Gray’s Anatomy, or the ARRT’s own content specifications. All three say T4-T5. The vertebral level of the sternal angle is as standardized as the vertebral level of the vertebra prominens (C7). There is no debate.

Practical use: chest positioning and centering

The sternal angle itself is not the centering point for a PA chest radiograph. But it’s the reference landmark that helps you find the actual centering point.

For a PA chest radiograph:

The centering point is typically 3-4 inches below the jugular notch, or approximately at the T7 vertebral level. To find it:

1. Palpate the jugular notch (the hollow at the top of the sternum). This is approximately T2-T3.
2. Move your finger down to the sternal angle. This is T4-T5.
3. Continue down another 2-3 inches (or about 2 rib spaces further down). You’re now at approximately T7.
4. This is your centering point. The central ray enters anteriorly at T7 and exits posteriorly at T7, ensuring the entire thorax is captured.

Why this matters:

If you centering too high (above T7), you miss lower lung lobes and the costophrenic angles. If you center too low, you miss apices and upper lobes. Consistent centering is a positioning fundamental the ARRT expects, and it starts with knowing the sternal angle as your reference landmark.

For lateral chest projections, you center at the same vertebral level (T7) but over the midaxillary line instead of the midsternal line.

Vertebral landmarks the ARRT loves to test

The sternal angle is one of five major vertebral landmarks that form the backbone of ARRT anatomy questions. Here’s the full reference set:

Landmark	Vertebral Level	How to Palpate	Key Anatomy	ARRT Frequency
Jugular notch	T2-T3	Top of breastbone, hollow at base of neck	Sternal reference, landmark for chest centering	High
Sternal angle (angle of Louis)	T4-T5	Ridge where manubrium meets sternal body	2nd rib, tracheal carina, aortic arch start	Very High
Xiphoid process (tip)	T9-T10	Tip of breastbone, bottom of sternum	Lower chest reference, abdominal boundary	High
Iliac crest	L4-L5	Top rim of pelvis, level with hip	Lumbar spine reference, abdominal centering	Very High
Vertebra prominens	C7	Most prominent bone at base of neck	Cervical reference, cervical counting	Very High

Memorize this table. Every single landmark will appear on your ARRT exam in some form. The vertebral levels are non-negotiable; they are the same on every exam, in every year, at every testing center.

Why sternal angle and T4-T5 appear on the ARRT

The ARRT tests landmark anatomy to verify that you can:

1. Position correctly, Knowing vertebral levels means you know where to center the central ray and what anatomy should be included in the final radiograph.
2. Count ribs and vertebrae, Given a chest radiograph with ribs visible, can you identify which ribs they are? Can you name the vertebral level of the sternal angle and work up or down from there?
3. Communicate with radiologists, If you document that a finding is “at the level of the sternal angle,” the radiologist knows immediately you mean T4-T5 and the anatomy cluster that comes with it.
4. Prevent repeats, Incorrect centering often results in repeated exposures, which means extra radiation dose to the patient and extra time in the clinic. Knowing landmarks reduces repositioning.

Quick reference: sternal angle at a glance

• Name: Sternal angle (angle of Louis, manubriosternal joint)
• Level: T4-T5 intervertebral disc
• Palpable: Yes, it’s a ridge you can feel on the front of the chest
• Rib marker: 2nd rib articulates here
• Anatomy cluster: Tracheal carina, aortic arch start, azygos vein arch
• Chest positioning: Use as reference to locate T7 centering point (3-4 inches below sternal angle)
• Why it matters: Most reliable anterior landmark for chest radiography and anatomy verification
• Common wrong answer: T3 (incorrect; the ARRT expects T4-T5)

ARRT exam tip

If you see a question asking “The sternal angle is located at what vertebral level?” the answer is T4-T5. Not T3, not T5-T6. T4-T5. This is the single most testable landmark fact in the procedures domain.

Study strategy: As you prepare for the ARRT, make flash cards for all five major landmarks (jugular notch, sternal angle, xiphoid, iliac crest, vertebra prominens) and drill them until they’re automatic. Then, when you see a positioning question on practice exams, mentally palpate the landmark, count the rib or vertebra, and verify the anatomy cluster. This is how the ARRT tests it, and this is how you’ll answer it on exam day.

For a complete walkthrough of chest radiography positioning, see our chapter on chest radiography. For detailed coverage of all axial skeleton landmarks, visit axial skeleton, spine, and thorax. And if you want to drill 20 free ARRT practice questions on procedures, procedures, and positioning, check out our free sample questions.