Ch 10: Bony Thorax - Sternum and Ribs Notes

Bony Thorax

Function:
- Expandable chamber for respiration
- protects vital organs
Composition:
- sternum (anterior)
  - often used for marrow biopsy b/c cancellous (spongy) tissue.
- thoracic vertebrae (posterior)
- 12 pairs of ribs

Components of Bony Thorax

Sternum
- Structure: flat bone approx 7 inches long, consisting of:
  - Manubrium: ~2 inches
  - Body: ~4 inches
  - Xiphoid Process: Cartilaginous in youth, ossifies by ~40 years.
- Key Landmarks:
  - Jugular/Suprasternal/Manubrial Notch: Located at T2-T3.
  - Sternal Angle: At T4-T5, also used to locate the ribs.
  - Xiphoid Process: Corresponds to T9-T10.
  - Sternoclavicular Joint: Only connect of shoulder girdle to thorax.
Ribs
- Numbering: Corresponds with thoracic vertebrae.
- True Ribs (1-7): Attach directly to sternum via costal cartilage.
- False Ribs (8-12): Connect indirectly or do not connect at all (11-12 are floating ribs).
- Inferior Rib View:
  - vertebral end - head, neck w/ tubercle close for transverse process articulation
  - anterior/sternal end - body curves around; angle = anterior part
- Posterior Rib View:
  - inferior view + inferior internal margin/costal groove
    - protects arteries, veins, nerves
      - cause of extreme pain & hemorrhage w/ injury
- Counting Ribs:
  - count posterior ribs
  - superior end located posterior/nearest vertebrae side
  - inferior end is anterior
- Rib Cage:
  - 1st ribs = most vertical
  - from 1st ribs, cage width ↑ to 7th rib, then cage ↓ again
  - bony thorax widest @8th or 9th rib

Positioning for the Sternum

RAO Position: Rotate pt 15° to 20° to
- visualize sternum w/o T-sp superimposition
- superimpose sternum over heart for better visibility
Exposure Factors:
- 65-75 kV
- breathing/orthostatic technique
- low mA
- long exposure 3-4sec
- SID 40”min to NOT ↑ pt. dose
- collimation = tight/small = ↓ pt. dose

Positioning for Ribs

Above Diaphragm: Erect preferred, exposure on full inspiration.
- SID: min 40 inches, ideally 72 inches to min magnification.
- Technical Factors: 65-75 kV for upper ribs.
Below Diaphragm: Supine w/ exposure on expiration.
- Technical Factors: 70-80 kV

Sterile Positions: RAO or Lateral for sternum; Posterior and Anterior
Clinical Indications: Trauma, fractures, or pathological conditions such as neoplasia.

Fractures: Common in ribs, leading to potential injuries of adjacent organs.
Congenital Anomalies: Pectus carinatum (pigeon breast) & Pectus excavatum (funnel chest).
Metastatic Diseases: Ribs often involved in metastatic processes, visible changes include osteolytic (destruction/less dense) & osteoblastic (overgrowth/more dense) lesions.