The thoracic cage is your body's protective shield for vital organs. It's made up of the sternum, ribs, and thoracic vertebrae, working together to safeguard your heart and lungs while allowing you to breathe.

This bony structure isn't just a rigid box. It's a flexible framework that expands and contracts with each breath, thanks to the costal cartilages and intercostal muscles. Understanding its components helps you grasp how your body protects and functions.

The Thoracic Cage

Components of thoracic cage

• Sternum serves as an attachment point for ribs and costal cartilages (manubrium, body, xiphoid process)
• 12 pairs of curved, flat ribs form lateral walls of thoracic cage (also known as the rib cage)
  • Attach posteriorly to thoracic vertebrae and anteriorly to sternum via costal cartilages
  • Protect vital organs (heart, lungs) and assist in respiration
• 12 thoracic vertebrae (T1 to T12) in upper back provide attachment points for ribs and support thoracic cage
  • Form thoracic curvature of spine
• Intercostal muscles between ribs aid in respiration by assisting in rib cage expansion and contraction
  • Consist of external intercostal muscles, internal intercostal muscles, and innermost intercostal muscles
• Costal cartilages connect ribs to sternum
  • Hyaline cartilage provides flexibility to thoracic cage, allowing for chest expansion during respiration

Structure and significance of sternum

• Manubrium is most superior and widest part of sternum
  • Articulates with clavicles and first pair of ribs
• Sternal angle (angle of Louis) is junction between manubrium and body of sternum
  • Important anatomical landmark corresponds to level of second rib attachment
  • Indicates location of tracheal bifurcation, aortic arch, and azygos vein arch
• Body is longest part of sternum, located inferior to manubrium
  • Provides attachment points for ribs 2-7 via costal cartilages
• Xiphoid process is smallest and most inferior part of sternum
  • Consists of hyaline cartilage in young individuals, may ossify in adults
  • Serves as attachment point for diaphragm and rectus abdominis muscles

Types and features of ribs

• True ribs (1-7) attach directly to sternum via their own costal cartilages
  • Provide stability to thoracic cage
• False ribs (8-12) have indirect or no attachment to sternum
  • Ribs 8-10 attach indirectly to sternum via common costal cartilage
  • Floating ribs (11 and 12) have no anterior attachment to sternum, allowing for greater flexibility
• Atypical ribs have unique features
  • First rib is shortest, flattest, and most curved with unique attachment to manubrium
  • Second rib attaches to sternum at sternal angle, serving as key anatomical landmark
• Typical ribs (3-10) share common features and attachments
  • Consist of head, neck, tubercle, angle, body, and costal groove
  • Head articulates with facets of thoracic vertebrae
  • Tubercle articulates with transverse process of corresponding thoracic vertebra

Thoracic Openings and Clinical Significance

• Thoracic inlet: superior opening of the thoracic cage, formed by first thoracic vertebra, first pair of ribs, and superior border of manubrium
  • Allows passage of important structures between neck and thorax
• Thoracic outlet: inferior opening of the thoracic cage, bordered by the costal margin, formed by the inferior edges of the rib cage and xiphoid process
  • Separates thoracic and abdominal cavities
• Thoracic outlet syndrome: compression of neurovascular structures passing through the thoracic outlet, causing pain, numbness, or weakness in the upper extremity