Ribs

The ribs are long, curved bones that form the lateral walls of the thoracic cage. They articulate posteriorly with the thoracic vertebrae and anteriorly (in most cases) with the sternum via costal cartilages. The ribs serve to protect thoracic organs, support respiration, and provide attachment sites for muscles of the thorax, abdomen, and back.

Location

The ribs are located on both sides of the thoracic spine, extending from the vertebral column posteriorly to the sternum or anterior thoracic wall. They span from the level of the T1 vertebra to T12, forming the primary structural components of the thoracic cage.

Number and Classification

There are 12 pairs of ribs, numbered from superior to inferior (1 to 12). They are classified based on their anterior attachments:

1. True Ribs (Vertebrosternal) – Ribs 1 to 7

• Directly attached to the sternum via their own costal cartilages

2. False Ribs (Vertebrochondral) – Ribs 8 to 10

• Attach indirectly to the sternum via the cartilage of the rib above

3. Floating Ribs (Vertebral) – Ribs 11 and 12

• Do not connect to the sternum at all; their anterior ends are free

Structure of a Typical Rib

Ribs 3 to 9 are considered typical ribs and share common anatomical features:

• Head: Posterior end; articulates with the bodies of two adjacent thoracic vertebrae and the intervertebral disc
• Neck: Narrow region between the head and tubercle
• Tubercle: Articulates with the transverse process of the corresponding vertebra
• Angle: The point of greatest curvature
• Shaft (body): Long, flat part with a costal groove on its inferior border for neurovascular structures

Atypical Ribs

• 1st rib: Shortest and broadest; has grooves for subclavian vessels and a single facet on the head
• 2nd rib: Thinner and longer than the first; has a rough area for serratus anterior attachment
• 10th rib: Has only one facet on the head (like 11 and 12)
• 11th and 12th ribs: Floating ribs; short, no neck or tubercle; single facet on the head

Articulations

Each rib forms joints with the thoracic vertebrae:

• Costovertebral joint: Between the head of the rib and vertebral bodies
• Costotransverse joint: Between the tubercle of the rib and the transverse process of the corresponding vertebra (not present in ribs 11 and 12)

Attachments

Ribs provide attachment to muscles, ligaments, and fasciae of the thorax and abdomen:

• External intercostal muscles: Attach along the superior border of each rib
• Internal and innermost intercostals: Attach along the inferior border
• Also serve as origin/insertion for muscles like serratus anterior, pectoralis major, quadratus lumborum, and diaphragm

Function

• Protect thoracic organs (heart, lungs, great vessels)
• Assist in respiration by moving upward and outward during inspiration
• Provide mechanical support for the thoracic cavity
• Act as points of attachment for various muscles involved in posture, respiration, and movement

Blood Supply

• Arterial supply: Posterior intercostal arteries (from thoracic aorta), anterior intercostal arteries (from internal thoracic artery)
• Venous drainage: Via intercostal veins into the azygos, hemiazygos, and internal thoracic veins

Innervation

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

Clinical Relevance

• Rib fracture: Common in trauma; may cause pneumothorax or damage to underlying organs
• Cervical rib: An accessory rib arising from C7; may compress neurovascular structures and cause thoracic outlet syndrome
• Costochondritis: Inflammation of the costal cartilage, often causing anterior chest pain
• Flail chest: Multiple rib fractures in multiple places leading to a segment of thoracic wall moving paradoxically