False Ribs

False ribs are the 8th, 9th, and 10th pairs of ribs that do not attach directly to the sternum. Instead, their anterior ends are connected to the sternum indirectly through the cartilage of the rib above. They help complete the lower thoracic cage and assist in protecting abdominal and thoracic organs.

Location

False ribs are located in the lower portion of the rib cage, inferior to the true ribs (1st to 7th ribs) and superior to the floating ribs (11th and 12th). Each extends from a thoracic vertebra posteriorly and curves anteriorly, with its costal cartilage joining that of the rib above.

Definition

Ribs are classified as "false" if they do not connect directly to the sternum via their own costal cartilage. Ribs 8 through 10 share a common cartilaginous attachment to the 7th rib, forming the costal margin.

Classification of False Ribs

• Ribs 8–10: Known as vertebrochondral ribs; they attach to the sternum indirectly through the costal cartilage of the rib above
• Ribs 11–12: Technically also false ribs, but often categorized separately as floating ribs because they do not attach to the sternum at all

Anatomical Features

False ribs, particularly ribs 8 to 10, are similar in structure to the true ribs but slightly shorter and less curved:

• Head: Articulates with thoracic vertebrae
• Neck: Connects head to tubercle
• Tubercle: Articulates with the transverse process of the same-numbered vertebra
• Shaft: Curved body with a costal groove on the inner surface
• Anterior end: Costal cartilage joins that of the rib above

Articulations

• Posterior: Articulate with thoracic vertebrae (T8–T10)
• Anterior: Do not attach directly to the sternum; costal cartilages connect to that of the rib above (ultimately attaching to the 7th rib's cartilage)

Function

• Provide protection for lower thoracic and upper abdominal organs (e.g., liver, kidneys)
• Support expansion and contraction of the thoracic cavity during respiration
• Contribute to the structure of the costal margin

Muscle Attachments

• Serve as points of origin and insertion for intercostal muscles
• Attachment sites for external oblique, internal oblique, and transversus abdominis muscles

Blood Supply

• Arterial: Posterior intercostal arteries (from thoracic aorta), anterior intercostal arteries (from internal thoracic artery via the musculophrenic branch)
• Venous: Intercostal veins draining into the azygos, hemiazygos, and internal thoracic veins

Innervation

• Intercostal nerves (anterior rami of spinal nerves T8–T10)

Clinical Relevance

• Rib fractures: Ribs 8–10 are more flexible but still prone to fractures, especially in lateral trauma
• Costal margin pain: Inflammation or strain along the lower costal margin may involve false ribs
• Surgical relevance: The costal margin formed by false ribs is used as a landmark in abdominal and thoracic surgeries