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Sternum X-Ray Positioning: RAO and Lateral 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.

This guide covers the common dedicated two-view routine—PA oblique (usually RAO) and lateral—while clearly labeling protocol variants. It separates the PA-oblique motion-blur technique from lateral-view instructions and distinguishes educational positioning from trauma imaging decisions. Technique charts, the examination order, equipment instructions, and the radiologist-approved local protocol always govern.

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, first costal cartilages, and the superior part of the second costal cartilages.
• Body — the longest segment; together with the manubrium and xiphoid junction it receives costal cartilages 2–7.
• Xiphoid process — the variable inferior segment. It is cartilaginous early in life and ossifies variably; bifid and foraminal configurations can be normal variants.

Key landmarks for positioning:

• Sternal angle (Angle of Louis) — the palpable manubriosternal junction, generally at the T4–T5 intervertebral level. It is an anatomy landmark, not the routine sternum centering point.
• Sternal notch — the palpable depression at the superior border of the manubrium (T2–T3 level).
• Jugular notch and xiphoid process — palpate these boundaries when appropriate; their midpoint defines the usual CR level.

On a straight PA projection the sternum is superimposed on the thoracic spine. A slight anterior oblique moves it off the vertebral column and, in the usual RAO, places it over the relatively uniform cardiac shadow.

The Standard Sternum Series

A common dedicated sternum series consists of two projections; protocols vary:

Projection 1: PA Oblique Sternum (RAO)

The PA oblique projection uses slight rotation to move the sternum off the thoracic spine. The RAO generally projects it over the heart shadow, creating a more uniform background.

Patient Position

• Prone on the table or erect against the upright Bucky
• Position the right anterior thorax nearest the IR; arrange the arms so they do not obscure the sternum and keep the shoulders in the same oblique plane
• Rotate approximately 15–20° RAO for an average adult. This is a teaching range, not an invariant value: a broad/deep chest generally needs less rotation and a narrow/shallow chest more.
• An LAO reverses the direction of displacement and is a protocol-dependent alternative, not an equivalent default; document the actual position.

Central Ray

• Perpendicular (0°) to the IR
• Centering point: midpoint of the sternum, halfway between the jugular notch and xiphoid process; commonly about 2.5 cm (1 in) left of the midline in an average RAO
• The CR enters the posterior thorax and exits through the sternum anteriorly

Breathing Technique

For the PA oblique, many teaching protocols use low mA and a several-second exposure during quiet, shallow breathing. Exact time is selected from the validated technique chart; 3–4 seconds is a common teaching target, not a universal requirement.

• The sternum itself is relatively immobile during respiration
• The overlying pulmonary and rib detail moves during breathing, reducing its conspicuity by motion blur
• This does not eliminate scatter and is not an air-gap technique
• The goal is a sufficiently sharp sternum against less conspicuous blurred background detail

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	Department-specific; classic teaching uses 76–102 cm (30–40 in), with the shorter SID deliberately magnifying the sternum over the heart shadow
Grid	Use when required by patient thickness, equipment, and the department's technique chart—not an automatic universal requirement
kVp / mAs	Use the validated chart for detector, grid status, patient thickness, and required image quality; no portable universal numeric technique is safe
Exposure time	Several seconds if the protocol uses quiet-breathing blur (commonly about 3–4 s in teaching guides)
Breathing	Quiet, shallow respiration throughout the PA-oblique exposure when using this technique

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
• Appropriate obliquity — enough to clear the spine without excessive distortion; judge against the expected appearance and local reject-analysis criteria

Common Positioning Errors

Error	Likely Cause	Correction
Sternum overlies the spine	Usually insufficient rotation	Adjust obliquity for body habitus; do not force an injured patient
Sternum appears excessively distorted	Usually excessive rotation	Reduce obliquity within the local positioning range
Rib and lung detail remains prominent	Breathing technique not used/effective	If protocol permits, use quiet breathing and the charted long-time technique
Upper sternum (manubrium) cut off	Centering too low or collimation too tight	Re-center to the midpoint between notch and xiphoid
Xiphoid cut off inferiorly	Collimation too tight or centering too high	Include full length; center at mid-sternum
Inadequate receptor exposure / excessive noise	Technique or processing issue	Use the departmental technique chart and exposure-index target; do not apply an arbitrary increase
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 shows the bone in profile and can demonstrate fracture displacement or step-off. Retrosternal soft-tissue opacity may be seen, but radiography neither excludes mediastinal injury nor determines cardiac injury.

Patient Position

• Erect lateral is preferred when safe; either side may be used according to equipment and local protocol
• True lateral: the mid-coronal plane is parallel to the IR
• Draw the shoulders and arms posteriorly (often hands clasped behind the back) to move upper-arm soft tissue away from the sternum
• Use supports only if they do not compromise alignment or trauma precautions
• A supine horizontal-beam lateral is a protocol-dependent modification. Do not sit, roll, or rotate a patient with suspected spinal or other unstable injury without clearance.

Central Ray

• Perpendicular (0°)
• Centering point: midpoint of the sternum, halfway between the jugular notch and xiphoid process
• Use a horizontal beam for the erect lateral; maintain the same midpoint for an authorized cross-table modification

Technical Factors

Parameter	Value
IR size	24 × 30 cm (10 × 12 in), landscape or portrait
SID	150–180 cm (60–72 in) in common teaching protocols, reducing magnification created by the lateral OID
Grid	According to patient thickness, equipment, and local chart
kVp / mAs	Validated departmental technique chart; do not transfer fixed values between detector/grid systems
Breathing	Commonly suspend on inspiration; a local protocol may specify another method

Evaluation Criteria

• Entire sternum in profile, including manubrium and xiphoid, without superimposition by the humeri
• Retrosternal region included with adequate penetration to assess cortical detail
• No rotation — the sternum is in profile without duplicated cortical margins
• No patient-motion blur and appropriate collimation/exposure index

Protocol Variant: Straight PA or AP

A straight PA or AP is not part of every dedicated sternum routine and the sternum remains superimposed on the spine. Use it only when the order/local protocol specifies it or when an authorized modification is needed; do not present it as an equivalent substitute for the RAO.

Patient Position

• Prone or erect PA facing the upright Bucky
• Arrange arms and shoulders according to the specified protocol without compromising patient safety
• Mid-sagittal plane centered to the midline of the grid/Bucky

Central Ray

• Perpendicular (0°) to the IR
• Centering point: midpoint between the jugular notch and xiphoid at the mid-sagittal plane

Technical Factors

Parameter	Value
IR size	24 × 30 cm (10 × 12 in), portrait
SID / grid / exposure	Use the projection-specific validated local technique; these are not universal across systems
Breathing	As specified by the local projection protocol

Sternum Positioning at a Glance

Projection	Patient Position	CR	Centering Point	Breathing
PA Oblique (RAO)	Prone/erect, commonly 15–20° RAO; adjust for habitus	0° perpendicular	Midway notch-to-xiphoid; about 2.5 cm left of MSP	Quiet breathing over several seconds when protocol specifies
Lateral	Erect true lateral, shoulders/arms back	0° horizontal	Midway notch-to-xiphoid	Usually suspend on inspiration
Straight PA/AP variant	Only if ordered/protocolled	Protocol-specific	Midway notch-to-xiphoid	Protocol-specific

Why the Breathing Technique Works: The Physics

The PA-oblique breathing technique is intentional motion unsharpness, not scatter control. It should not be confused with an air gap or grid.

During respiration, ribs and pulmonary markings change position. The sternum also participates in chest-wall motion, so it is not literally stationary; quiet shallow breathing is used to limit its movement while blurring more conspicuous overlying detail:

1. The moving structures (ribs, lung markings) are recorded at multiple different positions on the IR, creating motion blur
2. The sternum should remain sufficiently sharp only if respiration is shallow and the torso does not move
3. Blur reduces anatomic distraction; it does not remove scatter or act like a grid
4. Excessive respiratory or body motion can blur the sternum and make the image nondiagnostic

Key technical requirement: use the low-mA/long-time combination specified by the departmental chart when intentional blur is desired. There is no evidence-based requirement for “at least two respiratory cycles,” and digital receptor exposure is described by exposure index rather than film “density.” Avoid repeats by rehearsing the instruction and checking positioning before exposure.

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

Suspected fracture is a common indication for dedicated sternum radiography, although modern trauma workups often detect fractures on CT performed for the overall injury pattern.

Mechanisms of Injury

• Direct anterior compression/blow — common in motor-vehicle collisions, sports trauma, and falls
• Indirect force/hyperflexion — a less common mechanism; evaluate the whole trauma pattern rather than inferring associated injuries from mechanism alone
• Iatrogenic — during CPR (chest compressions) or post-sternotomy (cardiac surgery)

Fracture Patterns

• Transverse fracture commonly involves the body; look for cortical disruption or lucency with or without displacement
• Manubriosternal joint injury — malalignment or separation at the sternal angle may occur
• Comminuted fracture — multiple fragments can occur with substantial force
• Xiphoid injury — uncommon and difficult to assess radiographically because anatomy/ossification is variable

Pediatric and Geriatric Considerations

Pediatric Sternum Imaging

The pediatric sternum develops from multiple ossification centers, and normal developmental appearances can mimic injury. Ossification and fusion are variable and continue beyond the late teens in some individuals; avoid a single “fully ossified” age claim. Adapt the examination to age and cooperation:

• Immobilize safely and use pediatric technique charts; do not trade unnecessary motion blur for excessive exposure
• Ultrasound can depict superficial cortical disruption without ionizing radiation, but operator dependence and local expertise matter; it is not a universal first-line mandate
• CT is not automatically the “gold standard” after every nondiagnostic radiograph; the clinician/radiologist balances the complete trauma question against pediatric radiation risk
• Explain and rehearse breathing only when the child can cooperate; otherwise use the locally approved alternative technique

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 may be better tolerated when permitted; support the patient and keep the sternum in true lateral without assuming an “affected side” rule
• Do not increase kVp merely because bone is osteoporotic; choose factors from measured thickness and the validated technique chart
• If quiet breathing cannot be coordinated, use the approved short-time alternative rather than assuming “any blur is better than none”
• An atraumatic fracture or focal destructive/sclerotic change warrants radiologist assessment for pathologic fracture; do not infer a specific primary malignancy from the radiograph alone

Trauma, Pregnancy, Dose, and Scope Safeguards

• Trauma: stabilize first. Do not remove immobilization, roll, stand, or oblique a patient until the responsible clinician has cleared the movement. Use a horizontal-beam or other authorized modification when needed.
• Imaging escalation: dedicated radiographs answer a focused bony question but do not exclude intrathoracic injury. ACR major-blunt-trauma guidance supports chest radiography and/or CT according to hemodynamic status, mechanism, and suspected injury; the radiographer does not independently substitute CT for the ordered study.
• Pregnancy: verify pregnancy status under facility policy, but do not cancel or delay a medically indicated examination on your own. Optimize by tight collimation, correct positioning, the validated technique chart, and avoiding repeats. The fetus is outside the primary sternum beam when correctly collimated; risk questions or protocol changes go to the radiologist/medical physicist.
• Shielding: routine gonadal/fetal contact shielding is no longer recommended by AAPM because it provides negligible benefit outside the beam and can obscure anatomy, interfere with automatic exposure control, or cause repeats. Follow current facility policy; shielding never replaces collimation.
• Dose: no defensible universal sternum effective-dose number applies to every projection, patient, and system. Use indication-specific images only, monitor exposure index, collimate, and avoid repeats. A longer exposure time does not itself lower dose; mAs and the full technique determine receptor exposure and patient dose.
• ARRT scope: ARRT certification standards assess positioning, radiation protection, image evaluation, and patient care. They do not authorize a technologist to diagnose, order CT, clear a spine, or override the examination order/local scope-of-practice rules.

Positioning Errors: Quick Reference

Error	Likely Cause	Correction
Sternum projects over spine (PA oblique)	Usually insufficient rotation	Adjust within the habitus/local range
Excessive distortion (PA oblique)	Usually excessive rotation	Reduce obliquity
Rib detail prominent	Intentional blur not achieved	Use the approved long-time quiet-breathing technique
Manubrium not included	Centering/collimation too low	Center midway between notch and xiphoid
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 region excluded	Collimation or centering error	Re-center/collimate to include the sternum and adjacent region
Excessive noise / low exposure index	Technique or processing issue	Consult the validated chart; never apply an arbitrary percentage increase

ARRT Exam Prep: Sternum Quick Review

ARRT does not publish a guaranteed count of sternum questions. Its content specifications place sternum work within thorax positioning and broader patient-care, safety, and image-evaluation domains. High-yield, protocol-aware principles are:

1. RAO is commonly 15–20° for an average adult, adjusted for habitus; it projects the sternum off the spine and over the heart shadow
2. PA-oblique breathing technique: quiet shallow breathing during the charted several-second exposure blurs overlying detail; it is not scatter control
3. Centering: midpoint between the jugular notch and xiphoid, not the sternal angle
4. Lateral: preferably erect, shoulders/arms posterior, horizontal perpendicular CR, commonly 60–72 in SID, and usually suspended inspiration
5. PA versus AP: PA reduces sternal OID, but a straight PA/AP is a protocol variant rather than a universal routine substitute
6. The sternal angle lies near the T4–T5 disc; nearby mediastinal landmarks vary
7. Grid and exposure factors depend on thickness, equipment, and the validated chart
8. Trauma safety: do not move an uncleared patient to obtain routine positioning
9. Sternal fracture alone does not diagnose blunt cardiac injury; follow ECG/troponin and trauma protocols
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 instruction first. Match the wording and duration to the technique chart; rehearsal can identify patients who need an approved alternative before exposure.
• For the RAO, assess rather than guess. Start with the protocol's average obliquity, adjust for chest habitus, and center halfway from jugular notch to xiphoid—not at T4–T5 by rote.
• Do not copy a fixed exposure recipe. Detector response, grid, generator, patient thickness, and target exposure index differ. Use the installed chart and review exposure indicators.
• If the patient cannot follow breathing instructions, use the department's approved short-time alternative and document limitations. Avoid preventable repeats.
• For major trauma, escalate through the team. CT is highly useful for fracture and associated thoracic injury, but “near-100% sensitivity” is not universal across scan orientation/reconstruction and a technologist should not independently change the ordered test.

Summary

Projection	Patient Position	CR	Centering Point	Breathing	Purpose
PA Oblique (RAO)	Prone/erect; usually 15–20°, habitus-adjusted	0°	Midpoint notch-to-xiphoid; ~2.5 cm left MSP	Quiet breathing, charted several seconds	Move sternum off spine, over heart shadow
Lateral	Erect true lateral, shoulders/arms back	0° horizontal	Midpoint notch-to-xiphoid	Usually suspend inspiration	Profile and displacement
Straight PA/AP	Ordered/local variant only	Protocol-specific	Midpoint notch-to-xiphoid	Protocol-specific	Limited by spinal superimposition

Authoritative Sources and Protocol Boundaries

Accessed July 28, 2026. Numeric positioning values above are identified as teaching/protocol values rather than universal clinical mandates.

• University of Missouri Clinical Preceptor Reference Guide — Sternum: accredited-program procedure guide for routine RAO/lateral positioning, midpoint centering, SID, and respiration.
• ARRT Examination Content Specifications: official scope of tested radiography content; no guaranteed sternum question count.
• ACR Appropriateness Criteria — Major Blunt Trauma: chest radiography/CT selection depends on trauma scenario.
• EAST Practice Management Guideline — Blunt Cardiac Injury Screening: ECG/troponin recommendations and the limited significance of isolated sternal fracture.
• AAPM Position Statement PP 32-A: routine gonadal/fetal shielding should be discontinued.
• Khoriati et al., Sternal fractures and their management: peer-reviewed overview of diagnosis, associated injury, and management.