Thorax and Abdomen
4 Sternum
Anatomy & Pathology
Key Anatomical Structures
- Manubrium – Superior portion of sternum articulating with clavicles and first two pairs of ribs.
- Clavicular notches – Lateral depressions on the manubrium for articulation with clavicles.
- Jugular (suprasternal) notch – Central superior indentation at level of T2–T3; key centering landmark.
- Sternal angle (angle of Louis) – Junction between manubrium and body at approximately T4–T5; landmark for rib 2 articulation.
- Body (gladiolus) – Longest portion of sternum; articulates with costal cartilages of ribs 2–7.
- Xiphoid process – Small inferior tip at level of T9–T10; variable in size and ossification.
- Costal facets – Sites of articulation between costal cartilages and sternum.
- Articulations – Sternoclavicular, manubriosternal, and xiphisternal joints; all synarthrodial (immovable) in the adult.
Landmarks & Levels
- Jugular notch → T2–T3
- Sternal angle → T4–T5
- Xiphoid process → T9–T10
Common Pathologies
- Fracture of Sternum – Usually due to blunt anterior chest trauma (e.g., steering wheel injury). May be associated with rib fractures or cardiac contusion.
Exposure adjustment: Increase mAs moderately to penetrate overlying thoracic structures when swelling or dressings are present. - Metastatic Lesions – Sternum is a common site for bone metastasis, especially from breast or prostate carcinoma.
Exposure adjustment: Increase mAs moderately for osteoblastic lesions to visualize through sclerotic bone. - Osteoporosis – Results in decreased bone density and thinning of cortical margins, producing a less distinct outline of the sternum.
Exposure adjustment: Decrease kVp slightly to improve subject contrast and visibility of bone detail.
Routine Projections
RAO Sternum
CR Location & Positioning
- SID: 40 inches or less (short distance increases magnification of sternum for contrast)
- Patient position: Upright or prone; 15–20° RAO (right anterior chest closest to IR)
- Adjustments: Rotate shoulders forward to bring sternum closer to IR
- CR: Perpendicular to IR, centered midway between jugular notch and xiphoid process, about 1 inch left of MSP
- Pt. Instructions: Suspend respiration on expiration, or use breathing technique (low mA, 2–3 sec exposure) to blur lung markings
- Exposure: On expiration or during breathing technique
Evaluation Criteria
- Coverage: Entire sternum from jugular notch through xiphoid process
- Rotation checks: Sternum projected over heart shadow, free from spine
- Motion checks: Sharp bony margins (if suspended) or blurred lung fields (if breathing technique used)
- Technique checks: Sternum visible through heart shadow without overexposure
- Clinical aim: Demonstrate the sternum free of vertebral superimposition
Lateral Sternum
CR Location & Positioning
- SID: 60–72 inches (longer distance compensates for large OID)
- Patient position: Upright preferred; left side against IR
- Adjustments: Arms drawn back with hands clasped; shoulders rotated posteriorly; MSP parallel to IR
- CR: Perpendicular to IR, centered midway between jugular notch and xiphoid process; top of IR about 1.5″ above jugular notch
- Pt. Instructions: Suspend respiration on full inspiration to move sternum laterally away from spine
- Exposure: On full inspiration
Evaluation Criteria
- Coverage: Entire sternum visualized without superimposition from ribs, humeri, or soft tissue
- Rotation checks: Posterior ribs directly superimposed (true lateral)
- Motion checks: Sharp anterior and posterior borders of sternum
- Technique checks: Adequate density and contrast; margins well defined
- Clinical aim: Demonstrate lateral sternum in profile for evaluation of displacement or deformity
Supplementary Projections
LPO Sternum (Alternative for Trauma or Limited Mobility)
CR Location & Positioning
- SID: 40 inches
- Patient position: Supine or upright in LPO (left posterior oblique)
- Adjustments: Rotate 15–20° (opposite of RAO) so sternum projects over heart shadow
- CR: Perpendicular to IR, centered midway between jugular notch and xiphoid process, about 1 inch right of MSP
- Pt. Instructions: Suspend respiration on expiration, or use slow breathing if tolerated
- Exposure: On expiration or during breathing technique
Evaluation Criteria
- Coverage: Entire sternum from jugular notch through xiphoid process
- Rotation checks: Sternum projected over heart shadow, free from spine
- Motion checks: Lung markings blurred if breathing technique used
- Technique checks: Uniform exposure across sternum and mediastinum
- Clinical aim: Substitute for RAO in trauma or nonambulatory patients
Hows & Whys of Sternum Radiography
Anatomy
- How many parts make up the sternum, and what are they?
Three — the manubrium, body, and xiphoid process. - How do the costal notches function?
They provide articulation points for the costal cartilages of the first seven ribs. - How can vertebral levels help with positioning?
They guide centering: T2–T3 (jugular notch), T4–T5 (sternal angle), T9–T10 (xiphoid process).
Positioning
- Why is the RAO position used for the sternum?
It projects the sternum over the heart shadow, avoiding superimposition with the thoracic spine. - Why might an LPO be used instead of RAO?
For trauma or limited mobility; LPO provides equivalent projection geometry. - Why is 15–20° rotation used?
Rotation varies by body habitus — larger patients require more rotation, thinner patients less — to keep the sternum clear of the spine. - Why is the breathing technique helpful for the RAO?
It blurs lung and rib detail, making the sternum margins more distinct. - Why is the lateral sternum performed on inspiration?
Inspiration expands the chest, moving the sternum away from the thoracic spine. - Why use a long SID for the lateral sternum?
To compensate for large OID and reduce magnification.
Technique & Image Evaluation
- How do you know there’s no rotation on the lateral sternum?
Posterior ribs are directly superimposed, and the sternum appears as a sharp vertical structure. - How do you verify correct density and contrast?
Sternum should be visible through heart shadow with clear cortical margins. - How do you confirm correct positioning on the RAO?
Sternum centered over the cardiac shadow, not over the spine or lateral ribs. - How do you ensure radiation safety during the exam?
Keep the tube at least 12 inches from the patient; use tight collimation and shielding when possible.
Clinical Applications
- Why perform a sternum study after blunt chest trauma?
To identify fractures and evaluate for potential cardiac or pulmonary injury. - Why include both RAO and lateral views?
RAO visualizes the sternum free of the spine, while the lateral shows displacement or depression fractures. - Why might the technologist adjust mAs for a sternum exam?
Moderate increases may be necessary for trauma patients with immobilization devices, swelling, or thick body habitus. - Why is careful rotation selection important?
Incorrect rotation either superimposes the sternum on the spine or shifts it too far laterally over the lung field, obscuring margins.
