Thoracic Wall Anatomy

Thoracic Wall - Learning Objectives

• Define the boundaries, spaces, and contents of the thorax
• Describe the osteology of the thoracic wall
• Describe the intercostal muscles of the chest wall
• Understand the blood supply to the chest wall
• Understand the intercostal neurovascular structures

Anatomy of the Thorax

• Thorax (Chest):
  • Boundaries: Chest wall (bony structures), superior/inferior outlets
  • Spaces: Right and left pleural cavities, mediastinum
  • Contents: Heart, lungs, and others

Definition of the Thorax

• Thoracic Inlet: Superior border, bounded by T1 vertebra, rib 1, and manubrium
• Thoracic Diaphragm and Costal Margin: Inferior border

Surface Anatomy

• Surface Anatomy Landmarks: Jugular notch, clavicle, anterior axillary fold, manubrium, sternal angle and manubriosternal joint, body of sternum, intermammary cleft, xiphisternal joint, epigastric fossa, costal margin, midclavicular line, xiphisternal angle, ribs, and costal arch

Anatomical Planes

• Anterior view
• Lateral view
• Posterior view

Anatomy of the Thorax - Thoracic Inlet

• Superior thoracic aperture (Thoracic inlet):
  • Boundaries: Posteriorly – first thoracic vertebra (T1), Laterally – first pair of ribs & costal cartilages, Anteriorly – superior border of the manubrium
  • Contents: Esophagus, brachial plexus, subclavian artery and vein, trachea

Anatomy of the Thorax - Inferior Thoracic Aperture

• Inferior thoracic aperture (Thoracic outlet):
  • Boundaries: Posteriorly – 12th thoracic vertebra, Laterally – 11th and 12th pairs of ribs, Anteriorly – costal cartilages of ribs 7-10, xiphisternal joint.
  • Closure: Closed by the diaphragm

Anatomy of the Thorax - Inferior Thoracic Aperture - Musculature of the Diaphragm

• T8: Inferior vena cava
• T10: Esophagus
• T12: Aorta

Thorax/Abdomen Relationship

• Nipples: Level of the 4th rib, diaphragm elevation upon full expiration (4th intercostal space)

Osteology of the Thorax

• Components: Thoracic vertebrae (12), Ribs (12 pairs), Sternum

Osteology of the Thorax - Ribs

• Typical Ribs: Long, twisted, and flat bone with a rounded superior border and a sharp inferior border. Consists of a head, neck, tubercle, shaft, and angle. The head articulates with the vertebral body and the vertebra immediately above.
• The Neck: A constricted portion between the head and the tubercle.
• The Tubercle: A prominence on the outer surface, articulates with the transverse process of the corresponding vertebra.
• The Shaft: Thin, flat, and curved. The inferior border forms the costal groove, housing intercostal vessels and nerves.
• Angle: The anterior end of each rib is attached to the corresponding costal cartilage. Ribs 3rd-9th are typical ribs.
• Atypical Ribs:
  • 1st rib: Broadest, most curved, shortest, flattened from above downward, articulates only with T1, clinically important for brachial plexus and subclavian vessels.
  • 2nd rib: Prominent tuberosity for serratus anterior muscle, similar curvature to 1st rib.
  • 10th, 11th, 12th ribs: Short, lack a neck or tubercle, 12th rib lacks a costal groove or angle, 10th rib articulates only with T10.

Rib Articulations

• The spinous processes of T5-T8 are nearly vertical, T1, T2, T11, and T12 are horizontal, and T3, T4, T9, and T10 slope inferiorly

Costal Cartilages

• Hyaline cartilage bars: More rounded, extends from the anterior ends of the ribs
• Costal margins: 7th to 10th costal cartilages join to form cartilaginous costal margins.
• Infrasternal angle: Formed by the right and left costal margins

Sternum

• Components: Manubrium, body, xiphoid process
• Landmarks: Jugular notch, sternal angle, transverse ridges, articular facets

Sternocostal Joints

• 1st to 7th costal cartilages: With the sternum (1st pair - primary cartilaginous (synchondrosis); 2nd to 7th - Synovial.
• Costochondral joints: Between costal cartilage and anterior end of the rib (primary cartilaginous joint - synchondrosis)
• Interchondral joints: Between adjacent borders of ribs (synovial)
• Manubriosternal joint: Between manubrium and body of sternum (secondary cartilaginous joint - symphysis)
• Xiphisternal joint: Between xiphoid process and body of sternum (primary cartilaginous joint - synchondrosis)

Muscles of the Anterior Thoracic Wall

• Intercostal muscles: External, internal, and innermost intercostal muscles.
  • Pectoralis major
  • Pectoralis minor
  • Deltoid (part superficial)
  • Cephalic Vein

Superficial Thorax: The Breast

• Breast components: breast, nipple, areola, suspensory ligaments (Cooper's), gland lobule, lactiferous duct, and fat.
• Axillary tail (of Spence): Found along superior edge of the axilla

Intercostal Muscles

• External intercostal muscle
• Internal intercostal muscle
• Innermost intercostal muscle
• Collateral branches

Layer of the Thoracic Wall

• Superficial and deep fasciae
• External intercostal muscle
• Internal intercostal muscle
• Innermost intercostal muscle (or transversus thoracis muscle)
• Endothoracic fascia
• Pleura (not seen)
• Intercostal nerve

Blood Supply to the Thoracic Wall

• Posterior intercostal artery
• Internal thoracic (mammary) artery
• Site of anastomosis (allows collateral flow)
• Anterior intercostal artery

Diaphragm

• Dome-shaped musculotendinous partition between thorax and abdomen
• Principal muscle of respiration
• Pierced by structures passing between thorax and abdomen
• Descends during contraction, ascends during relaxation. Only the dome moves.
• Openings:
  • Caval opening (T8): Inferior vena cava and terminal branch of right phrenic nerve
  • Esophageal opening (T10): Esophagus, vage nerve parts, vessels, lymph
  • Aortic opening (T12): Aorta, thoracic duct, azygos vein
  • Other minor openings: Sympathetic trunk, superior epigastric vessels, left phrenic nerve, neurovascular bundles of lower sixth intercostal spaces

This quiz covers the anatomy of the thoracic wall, including its boundaries, osteology, intercostal muscles, and neurovascular structures. Understanding these components is essential for comprehending the thorax's role in respiratory function. Test your knowledge on the key features and functions of this vital region!