Ribs and Costal Cartilages

Topic Overview

Introduction

• The thorax is an osseocartilaginous cavity that provides protection and support to vital thoracic viscera (heart, lungs, and great vessels).

• The thoracic cage is dynamic, not rigid—it moves at its joints to increase or decrease its diameters during respiration.

• Functionally:

  • Expansion = Inspiration

  • Contraction = Expiration

Bones of Thorax

• The skeleton of the thorax consists of:

  1. 12 thoracic vertebrae (posteriorly)

  2. 12 pairs of ribs and costal cartilages (laterally)

  3. Sternum (anteriorly)

Ribs (Costae)

• There are 12 ribs on each side forming the major part of the thoracic skeleton.

• Number may vary (presence of cervical or lumbar rib; absence of 12th rib).

Features:

• Ribs are bony arches, one below another, with intercostal spaces in between.

• Obliquity: Increases up to the 9th rib, then decreases toward the 12th.

• Length: Increases from 1st to 7th; decreases thereafter.

• Breadth: Decreases from above downward.

Classification:

1. According to articulation with sternum:

   • True ribs (1–7): Attach directly to sternum via costal cartilages.

   • False ribs (8–10): Join cartilage of rib above (vertebrochondral).

   • Floating ribs (11–12): Free anterior ends (vertebral ribs).

2. According to morphology:

   • Typical ribs: 3rd–9th

   • Atypical ribs: 1st, 2nd, 10th, 11th, 12th

Typical Rib – Features

• Each rib has two ends and a shaft:

  • Anterior (sternal) end: Oval and concave for costal cartilage.

  • Posterior (vertebral) end: Head, neck, and tubercle.

  • Shaft: Convex outward; costal groove along lower inner surface for intercostal vessels and nerve.

Side Determination:

• Head posterior, costal groove inferior, convexity lateral.

Ossification of a Typical Rib

• Each typical rib ossifies from three centers:

  1. One primary center for the shaft (in 2nd month of fetal life).

  2. Two secondary centers—one for the head, one for the tubercle (appear at puberty and fuse by 20 years).

11th and 12th ribs:

• Ossify from two centers — one for shaft, one for head.

Costal Cartilages

• Represent the unossified anterior parts of ribs made of hyaline cartilage.

• Provide elasticity to thoracic wall.

Attachments:

• 1st–7th ribs: Costal cartilages attach directly to sternum.

• 8th–10th ribs: Join each other forming the costal margin.

• 11th–12th ribs: Small, free ends in the abdominal wall muscles.

Muscle Attachments:

• Anterior surface:

  • 1st cartilage → Subclavius, costoclavicular ligament.

  • 2nd–6th → Pectoralis major.

  • Lower cartilages → Abdominal wall muscles.

• Posterior surface:

  • 1st → Sternothyroid.

  • 2nd–6th → Sternocostalis.

  • 7th–12th → Transversus abdominis and diaphragm.

Clinical Anatomy

• Rib fractures:

  • Common at the angle due to indirect trauma.

  • Upper two ribs protected by clavicle; lower two flexible—rarely fractured.

• Cervical rib:

  • Arises from C7, compressing brachial plexus or subclavian artery (Thoracic Outlet Syndrome).

• Rib variations:

  • Absence of 12th rib or presence of extra cervical/lumbar ribs possible.

• Costochondritis:

  • Inflammation at costochondral junction causing chest pain mimicking cardiac pain.

Summary Table