Thoracic Wall Anatomy

Structure of the Thoracic Wall

• Consists of 12 thoracic vertebrae, 12 pairs of ribs with their costal cartilages, the sternum, and intercostal muscles.

Bones of the Thoracic Cage

• The sternum consists of the manubrium, body, and xiphoid process.
• Costa is defined as the rib bone and its cartilage.
• Vertebrosternal ribs (true ribs) are ribs 1-7.
• Vertebrochondral ribs (false ribs) are ribs 8-10.
• Vertebral ribs (floating ribs) are ribs 11-12.

Manubriosternal Joint

• The manubriosternal joint is known as the sternal angle or angle of Louis.
• It is a secondary cartilaginous joint (symphysis).
• The sternal angle serves as a palpable clinical landmark.
• It is located at the level of the 2nd pair of costal cartilages and the intervertebral disc between T4 and T5.

Xiphisternal Joint

• The xiphisternal joint is a xiphisternal synchondrosis.
• This joint may persist until middle age but often ossifies, forming a synostosis between the two sternal elements.
• It aligns with the T9 vertebra.

Typical Rib

• The head has two articular facets that articulate with costal demifacets on adjacent thoracic vertebrae.
• The neck is the narrow section between the head and tubercle.
• The tubercle articulates with the transverse process of the vertebra with the same number.
• Other features of a typical rib include the shaft, sternal extremity, and angle.

Typical Rib - Costal Groove

• Contains the intercostal vein, intercostal artery, and intercostal nerve from superior to inferior.

Atypical Ribs

• The 1st, 2nd, 10th, 11th, and 12th pairs of ribs are considered atypical.
• Atypical ribs have a single facet on their posterior end.
• Atypical ribs lack a costal groove.
• Atypical ribs do not have an angle.
• The 1st rib forms a primary cartilaginous joint with the manubrium.

First Rib

• It is flattened in a horizontal (transverse) plane.
• The scalene tubercle serves as the insertion point for the scalenus anterior muscle.
• There is a shallow groove for the subclavian vein anterior to the tubercle.
• There is a shallow groove for the subclavian artery posterior to the tubercle.

Bones of the Thoracic Cage - Thoracic Vertebra

• It has a heart-shaped centrum (body).
• The centrum is notched on the left side for the descending aorta.
• Intervertebral discs make up ¼ of the total length of the thoracic vertebral region.
• Typical vertebrae (T2-T9) have superior and inferior costal demifacets.

Atypical Thoracic Vertebra

• T1 has a superior costal facet (not a demifacet).
• T10 has one pair of costal facets located partly on the body and partly on the pedicle.
• T11 and T12 have one pair of costal facets located on the pedicles.

Typical Rib Articulation

• The head articulates with demifacets of its own vertebra number and the vertebra above, as well as the intervertebral disc between them.
• The tubercle articulates with the transverse process of the vertebra with the same number.

Superior Boundary (Inlet)

• Defined by the first thoracic vertebra, first pair of ribs and costal cartilages, and the manubrium.

Inferior Boundary (Outlet)

• Defined by the twelfth thoracic vertebra, twelfth pair of ribs and costal cartilages, and the xiphisternal joint and is closed by the diaphragm.
• The diaphragm is the main muscle of respiration, a dome-shaped sheet of skeletal muscle, separating the thoracic and abdominal cavities, consisting of muscle fibres and a central tendinous portion
• It is pierced by a series of apertures to permit the passage of structures between the thorax and abdomen.

Respiratory Muscles

• The main respiratory muscles include the diaphragm, external intercostal muscle, internal intercostal muscle, and innermost intercostal muscle.

Three Large Openings of the Diaphragm

• The Vena Caval Foramen is at level T8 and contains the inferior vena cava and some branches of the right phrenic nerve.
• The Esophageal Hiatus is at level T10 and contains the esophagus, the anterior and posterior vagal trunks, and some small esophageal arteries.
• The Aortic Hiatus is at level T12 and contains the aorta, the azygos vein, and the thoracic duct.

Intercostal Muscles

• External intercostals aid in inspiration.
• Internal intercostals aid in expiration.

Intercostal Muscles - Innermost Intercostal

• Represent the deepest layer of the intercostal muscles, separated from other layers by a neurovascular bundle.
• The innermost intercostal muscle consists of the transversus thoracis muscle, innermost intercostal (intercostales intimi), and subcostalis muscle.

Neurovascular Bundle of Intercostals

• VAN (vein, artery, nerve).
• Includes intercostal vein, intercostal artery, and intercostal nerve.
• Located in the subcostal groove between the internal intercostal and innermost intercostal muscles.