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Sternum X-Ray Positioning: PA, Lateral, and Oblique Views

The sternum (breastbone) is one of the most challenging structures to image in diagnostic radiography. Its superficial location on the anterior chest wall might suggest it should be easy to see — but in practice, the overlying mediastinal structures, ribs, lung markings, and the spine all conspire to obscure the sternal cortex. Getting a diagnostic sternum series requires precise positioning, a carefully executed breathing technique, and a solid understanding of the anatomy you're trying to visualize.

In this guide, you'll learn the standard projections for sternum imaging — the PA oblique (RAO/LAO), the lateral sternum, and the PA/AP non-oblique views. We'll cover Clark's centering points, the breathing technique for scatter reduction, technical factors, image evaluation criteria, and high-yield ARRT exam content that will help you ace registry questions about sternum positioning.

For related thoracic imaging guides, see our rib X-ray positioning guide and portable chest X-ray technique article.

Sternum Anatomy: What You Need to Know

The sternum is a flat, elongated bone forming the anterior midline of the thoracic cage. It consists of three parts:

• Manubrium — the broad, superior segment. It articulates with the clavicles (via the sternoclavicular joints) and the first and upper half of the second costal cartilage.
• Body (gladiolus) — the longest segment, articulating with the second through seventh costal cartilages.
• Xiphoid process — the small, cartilaginous inferior tip. It may be pointed, bifid, or perforated (a normal variant).

Key landmarks for positioning:

• Sternal angle (Angle of Louis) — the palpable ridge at the manubriosternal junction, located at the T4–T5 level. This is your primary centering landmark for all sternum projections.
• Sternal notch — the palpable depression at the superior border of the manubrium (T2–T3 level).
• Xiphoid tip — approximately at T9–T10 level. Useful for confirming you've included the full sternum in your collimation.

Understanding the three-dimensional relationship of the sternum to the thoracic spine is critical: the sternum sits anterior to the heart and great vessels, which in turn sit anterior to the thoracic spine. On a straight PA projection, the sternum is superimposed over the vertebral column, making it nearly invisible. This is why an oblique projection is essential — it rotates the thorax so the sternum is projected lateral to the spine.

The Standard Sternum Series

A complete sternum series typically consists of two or three projections:

Projection 1: PA Oblique Sternum (RAO)

The PA oblique projection is the most important view in the sternum series. It uses the patient's own body rotation to project the sternum lateral to the thoracic spine, eliminating the superimposition that makes the straight PA view non-diagnostic.

Patient Position

• Prone on the table or erect against the upright Bucky
• Raise the arm on the side away from the IR, resting it comfortably above the head
• Erect position is preferred when possible — gravity helps the lungs expand fully and the shoulders naturally fall forward, improving visualization of the upper sternum
• Rotate the patient 15–20° toward the RAO (right anterior oblique) position. The RAO projects the sternum to the left of the thoracic spine. Alternatively, a 15–20° LAO can be used to project the sternum to the right

Central Ray (Clark's)

• Perpendicular (0°) to the IR
• Centering point: Mid-sagittal plane at the level of the T4–T5 intervertebral space (approximately 3–4 cm below the jugular notch)
• The CR enters the posterior thorax and exits through the sternum anteriorly

Breathing Technique

This is the most distinctive technical feature of sternum radiography. Unlike almost every other X-ray examination where breath-holding is mandatory, the sternum view uses a slow, gentle breathing technique during a long exposure (typically 2–6 seconds). Here's why:

• The sternum itself is relatively immobile during respiration
• The overlying lungs and ribs move during breathing, creating motion blur that effectively blends their shadows into a uniform background
• This motion blur eliminates the sharp edges of ribs and lung markings that would otherwise obscure the sternal cortex
• The result is an image where the stationary sternum appears sharp against a blurred background

How to instruct the patient: "Take slow, shallow breaths — like you're blowing on a hot soup — but don't move your body. Breathe gently in and out while the machine makes its noise." Practice the breathing with the patient before you start the exposure.

Technical Factors

Parameter	Value
IR size	24 × 30 cm (10 × 12 in), portrait
SID	100–110 cm (40 in)
Grid	Yes (8:1 or 12:1)
kVp	60–70
mAs	20–40 (depending on grid factor)
Exposure time	2–6 seconds (breathing technique)
Breathing	Slow, gentle respiration during entire exposure

Evaluation Criteria

• Sternum projected lateral to the thoracic spine — the most critical check. If the sternum overlies the spine, rotation was insufficient
• Full sternum visualized — manubrium, body, and xiphoid process all included
• Cortical margins sharp despite breathing technique — the sternum should be the sharpest structure in the image
• Background lung markings and ribs blurred — if the ribs appear sharp, the breathing was too shallow or the exposure too short
• No rotation of the sternum itself — the two lateral borders should be symmetrical (the sternum is a flat bone; if it appears as a narrow ribbon, the obliquity is excessive)

Common Positioning Errors

Error	Likely Cause	Correction
Sternum overlies the spine	Insufficient rotation (<15°)	Increase rotation to 15–20°
Sternum appears narrowed/distorted	Excessive rotation (>25°)	Reduce rotation to 15–20°
Rib and lung markings sharp, not blurred	No breathing technique, exposure too short, or patient held breath	Use 2–6 s exposure with gentle breathing
Upper sternum (manubrium) cut off	Centering too low	Center at T4–T5, not at the xiphoid
Xiphoid cut off inferiorly	Collimation too tight or centering too high	Include full length; center at mid-sternum
Image underexposed	kVp too low or mAs insufficient	Increase mAs; consider higher kVp for larger patients
Motion artifact on sternum itself	Patient moved entire body instead of just breathing	Reinstruct — only the chest should move, the body stays still

Projection 2: Lateral Sternum

The lateral sternum view is the complementary projection to the PA oblique. It excels at demonstrating anterior-posterior displacement of sternal fractures, retrosternal hematoma, and step-off deformities at the fracture site. It also provides the best view of the sternal angle and manubriosternal junction.

Patient Position

• Erect or seated lateral position — the patient stands with the affected side closest to the upright Bucky
• True lateral: the mid-coronal plane is parallel to the IR
• Arms raised above the head or extended forward to pull the shoulders out of the field
• A small radiolucent cushion or pad under the patient's back can help achieve a true lateral in patients who tend to lean forward
• For trauma patients who cannot stand, a cross-table lateral (supine with horizontal beam) can be used — but image quality is generally inferior

Central Ray (Clark's)

• Perpendicular (0°)
• Centering point: Lateral chest wall at the level of the sternal angle (T4–T5), midway between the anterior and posterior chest surfaces
• For the cross-table lateral in supine patients: center at the same level, but aim the horizontal beam from the side

Technical Factors

Parameter	Value
IR size	24 × 30 cm (10 × 12 in), landscape or portrait
SID	100–110 cm (40 in)
Grid	Yes
kVp	70–80 (higher than PA oblique due to thicker tissue)
mAs	25–50
Breathing	Slow, gentle respiration during 2–6 s exposure

Evaluation Criteria

• Entire sternum in profile — the anterior cortex should appear as a single continuous white line from the manubrium to the xiphoid
• Retrosternal space clearly visible (the space between the posterior sternum and the anterior surface of the heart/great vessels)
• No rotation — the posterior ribs on both sides should be superimposed; the sternum should not have a "double border"
• Sternal angle (Angle of Louis) clearly identified — this is the key landmark for fracture localization
• Breathing technique successfully blurred the background lung markings

Projection 3: PA Non-Oblique Sternum

The PA non-oblique projection is an optional view that provides a straight-on survey of the sternum. While the sternum is superimposed over the spine in this projection, the breathing technique can still blur the overlying structures enough to make the sternal cortex visible — particularly in thin patients.

Patient Position

• Prone or erect PA facing the upright Bucky
• Arms raised above the head or resting on the hip with shoulders rolled forward
• Mid-sagittal plane centered to the midline of the grid/Bucky

Central Ray

• Perpendicular (0°) to the IR
• Centering point: T4–T5 (level of the sternal angle) at the mid-sagittal plane

Technical Factors

Parameter	Value
IR size	24 × 30 cm (10 × 12 in), portrait
SID	100–110 cm (40 in)
Grid	Yes
kVp	60–70
mAs	15–25
Breathing	Slow, gentle respiration during 2–6 s exposure

Sternum Positioning at a Glance

Projection	Patient Position	CR	Centering Point	Breathing
PA Oblique (RAO)	Prone/erect, 15–20° rotation toward right	0° perpendicular	T4–T5 at MSP	Gentle, 2–6 s
Lateral	Erect true lateral, arms up	0° perpendicular	T4–T5 at lateral chest wall	Gentle, 2–6 s
PA Non-Oblique	Prone/erect, no rotation	0° perpendicular	T4–T5 at MSP	Gentle, 2–6 s

Why the Breathing Technique Works: The Physics

The breathing technique is unique to sternum imaging and deserves a deeper look. Understanding the physics behind it helps you troubleshoot when it doesn't work and explain the technique to students and colleagues.

During respiration, the ribs move up and down (pump-handle and bucket-handle motion) and the lungs expand and contract. The sternum itself, however, is relatively fixed by its articulations with the clavicles and costal cartilages. When you use a long exposure time (2–6 seconds) during gentle breathing:

1. The moving structures (ribs, lung markings) are recorded at multiple different positions on the IR, creating motion blur
2. The stationary sternum is recorded in the same position throughout the exposure, appearing sharp
3. The blurred background effectively becomes a uniform gray fog, similar to what a grid does for scatter radiation
4. The contrast between the sharp sternum and the blurred background is what makes the sternal cortex visible

Key technical requirement: The exposure time must be long enough to allow at least two full respiratory cycles during the exposure. If the exposure is too short (e.g., < 1 second), the ribs and lung markings will be captured at a single point in the respiratory cycle and appear sharp, defeating the purpose. This is why sternum techniques typically use low mA and high mAs — to stretch the exposure time while maintaining adequate density.

For more on how grids and scatter control affect image quality, see our radiographic grids and scatter control guide. For technique chart fundamentals, see our exposure technique charts article.

Sternal Fractures: What to Look For

The most common indication for sternum X-rays is suspected sternal fracture. Here's what you need to know about the types and appearances of sternal fractures:

Mechanisms of Injury

• Direct anterior blow — most common cause (MVC steering wheel impact, direct blow in sports, fall onto an object)
• Hyperflexion injury — the sternum can fracture from extreme forward bending, often with associated thoracic spine compression fractures
• Iatrogenic — during CPR (chest compressions) or post-sternotomy (cardiac surgery)

Fracture Patterns

• Transverse fracture of the sternal body — most common pattern. Look for horizontal lucency with or without displacement
• Manubriosternal dislocation — separation at the sternal angle, often with posterior displacement of the body
• Comminuted fracture — multiple fragments, more common in high-energy trauma
• Xiphoid fracture — rare but painful; frequently missed because of the small size

Pediatric and Geriatric Considerations

Pediatric Sternum Imaging

Children present unique challenges for sternum radiography. The pediatric sternum is largely cartilaginous and does not fully ossify until the late teens. The multiple ossification centers of the sternal segments can mimic fractures — a classic source of misdiagnosis. Additionally, children cannot reliably perform the breathing technique. Strategies include:

• Use the shortest possible exposure time to reduce motion artifact from involuntary movement
• Consider ultrasound as a first-line modality for suspected pediatric sternal fracture — it avoids radiation and can distinguish normal ossification centers from fractures
• CT with low-dose protocol is the gold standard when X-ray is non-diagnostic
• For the PA oblique view, use gentle reassurance and demonstrate the breathing technique yourself before the exposure

Geriatric Sternum Imaging

Elderly patients present different challenges: the sternum may be osteoporotic (subtle fractures), the patient may have difficulty standing erect or lying prone, and the breathing technique may be harder to coordinate. Key adaptations:

• Seated lateral is often the best tolerated position — the patient sits sideways on the table with the affected side against the IR
• Higher kVp (70–80 for PA oblique, 75–85 for lateral) compensates for osteoporotic bone and reduced lung volumes
• Shorter breathing technique (2–3 seconds) if the patient cannot sustain gentle breathing for 6 seconds — any blur is better than none
• Be alert for pathological fracture — a lytic or blastic lesion at the fracture site may indicate metastatic disease (breast cancer, lung cancer, and multiple myeloma commonly involve the sternum)

Positioning Errors: Quick Reference

Error	Likely Cause	Correction
Sternum projects over spine (PA oblique)	Insufficient rotation	Rotate at least 15–20°
Sternum narrowed (PA oblique)	Excessive rotation	Reduce to 15–20°
Rib shadows sharp, not blurred	Exposure too short or patient held breath	Use 2–6 s with gentle breathing
Manubrium not included	Centering too low	Center at T4–T5 (sternal angle)
Xiphoid cut off	Collimation too tight	Open collimation inferiorly
Double border on lateral sternum	Patient not in true lateral	Check shoulders and hips alignment
Retrosternal space not visible	Overpenetration or incorrect centering	Reduce kVp, check centering
Overall underexposed	Insufficient mAs or kVp	Increase technique by 30–50%

ARRT Exam Prep: Sternum Quick Review

The ARRT registry typically includes 2–4 questions on sternum positioning, often integrated into the thorax section. Here are the highest-yield facts:

1. RAO position (15–20°) is the standard oblique projection for the sternum — it projects the sternum lateral to the spine and moves the heart away from the field
2. Breathing technique (2–6 second exposure during gentle respiration) is the defining technical feature of sternum radiography — it blurs overlying lung markings and ribs while keeping the sternum sharp
3. Centering point for all sternum views: T4–T5 at the level of the sternal angle (Angle of Louis)
4. PA is preferred over AP because the sternum is closer to the IR, reducing magnification
5. Lateral sternum is best for evaluating AP displacement, fracture step-off, and retrosternal hematoma
6. The sternal angle is at T4–T5 and marks the carina/bifurcation of the trachea and the aortic arch
7. Grid is mandatory for adult sternum views due to the tissue thickness and scatter
8. Exposure time must be long (≥ 2 seconds) — not short — for the breathing technique to work
9. Sternal fractures are associated with cardiac contusion, thoracic spine fractures, and pulmonary contusion
10. The normal xiphoid can be bifid, curved, or perforated — these are normal variants, not fractures

Clinical Pearls: Tips from Experienced Techs

• Practice the breathing with the patient first. Say, "I'm going to ask you to take slow, gentle breaths — in and out — for about 5 seconds while the X-ray is running. Let's practice together." Doing this once before the exposure dramatically improves patient cooperation.
• For the RAO, don't guess the rotation. Angle the patient exactly 15–20° by rotating the shoulders away from the table. Use the jugular notch as a centering reference — the CR should enter at the level of T4–T5 at the mid-sagittal plane.
• Higher mAs than you'd expect. The breathing technique requires a long exposure time, which means low mA and high mAs. A typical technique for an average adult with a 12:1 grid: 65 kVp, 32 mAs at 4 seconds. Don't be afraid to increase mAs for larger patients.
• If the patient can't breathe gently, try a shorter exposure. Some patients (anxious, post-surgical, in pain) simply cannot maintain gentle breathing for 6 seconds. A 2-second exposure with shallower breathing is better than a full 6-second exposure where the patient holds their breath or hyperventilates.
• For trauma patients, consider CT directly. If the mechanism is high-energy (MVC, fall from height) or the patient has multiple injuries, CT thorax is more appropriate than a sternum series. It detects sternal fractures with near-100% sensitivity and screens for associated mediastinal and great vessel injuries.

Summary

Projection	Patient Position	CR	Centering Point	Breathing	Purpose
PA Oblique (RAO)	Prone/erect, 15–20° RAO	0°	T4–T5 at MSP	2–6 s gentle	Project sternum clear of spine
Lateral	Erect true lateral, arms up	0°	T4–T5, lateral chest wall	2–6 s gentle	AP displacement, retrosternal space
PA Non-Oblique	Prone/erect, no rotation	0°	T4–T5 at MSP	2–6 s gentle	Survey (limited value)