Thoracic Cage

The thoracic cage, also known as the rib cage, is a bony and cartilaginous structure that encloses the thoracic cavity. It protects vital organs such as the heart and lungs, supports the upper body, and facilitates respiration by expanding and contracting during breathing. It is composed of the thoracic vertebrae, ribs, costal cartilages, and sternum.

Location

The thoracic cage is located in the upper part of the trunk, between the neck and the abdomen. It extends from the base of the neck (superior thoracic aperture) to the diaphragm (inferior thoracic aperture). Posteriorly, it is anchored to the thoracic vertebrae; anteriorly, it connects to the sternum.

Structure

The thoracic cage is made up of 37 bones:

• 12 thoracic vertebrae (posteriorly)
• 12 pairs of ribs (24 bones in total)
• Sternum – manubrium, body, and xiphoid process (anteriorly)

Ribs

There are 12 pairs of ribs, categorized based on their anterior attachment:

• True ribs (1–7): Attach directly to the sternum via individual costal cartilages
• False ribs (8–10): Attach indirectly via the cartilage of the rib above
• Floating ribs (11–12): Do not attach to the sternum

Sternum

• Manubrium: Upper part; articulates with clavicles and first two ribs
• Body: Middle portion; articulates with ribs 2–7
• Xiphoid process: Inferior, cartilaginous in youth, often ossifies in adults

Costal Cartilages

• Bars of hyaline cartilage that prolong the ribs anteriorly and contribute to elasticity

Joints and Articulations

The thoracic cage includes several important joints:

• Costovertebral joints: Between ribs and thoracic vertebrae
• Sternocostal joints: Between costal cartilages and sternum
• Costochondral joints: Between ribs and costal cartilages
• Interchondral joints: Between adjacent costal cartilages of false ribs

Function

• Protection: Shields vital organs such as the heart, lungs, and great vessels
• Support: Provides structural support to the upper body and anchor for upper limb muscles
• Respiration: Expands and contracts with breathing to assist lung inflation
• Attachment: Serves as the origin or insertion for many muscles of the chest, back, neck, and upper limbs

Muscles Associated with the Thoracic Cage

• External intercostal muscles: Elevate ribs during inspiration
• Internal intercostal muscles: Depress ribs during forced expiration
• Innermost intercostal muscles: Assist internal intercostals
• Diaphragm: Major muscle of respiration, forming the floor of the thoracic cage
• Serratus posterior muscles: Assist in rib movement during breathing

Neurovascular Supply

Arterial Supply

• Posterior intercostal arteries: Branches of thoracic aorta
• Anterior intercostal arteries: Branches of internal thoracic artery

Venous Drainage

• Drains into the azygos and hemiazygos systems (posterior), and internal thoracic vein (anterior)

Innervation

• Intercostal nerves (anterior rami of thoracic spinal nerves T1–T11)

Apertures of the Thoracic Cage

Superior Thoracic Aperture

• Bounded by the first rib, manubrium, and T1 vertebra
• Allows passage of trachea, esophagus, major vessels, and nerves

Inferior Thoracic Aperture

• Bounded by the costal margin, xiphisternal joint, and T12 vertebra
• Closed by the diaphragm

Clinical Relevance

• Rib fractures: Common injuries, may damage underlying organs (e.g., lung, spleen)
• Thoracic outlet syndrome: Compression of neurovascular structures at the superior thoracic aperture
• Pectus excavatum: Congenital deformity where the sternum is sunken inward
• Sternal angle (Angle of Louis): Landmark for rib 2 and level of the carina