Anterior Thoracic Wall

What composes the bony thorax?

Sternum + 12 pairs of costae + 12 thoracic vertebrae forming a tubular space.

What bones make up the upper aperture (thoracic inlet)?

Body of the first thoracic vertebra, first ribs, first costal cartilages, and the manubrium sterni.

What bones make up the lower aperture (thoracic outlet)?

Xiphoid process, lower four costal cartilages (7th–10th), 10th–12th ribs, and the body of the 12th thoracic vertebra.

What are the parts of the sternum?

Manubrium, body, and xiphoid process.

What are the characteristics of the manubrium?

It is wider than the body, contains a suprasternal notch, and three notches:

• Clavicular notch

• First costal notch

• Second costal notch

What are the features of the body of the sternum?

Derived from four segmental precursors called sternebrae; has notches for the 2nd–7th costal cartilages.

What is the xiphoid process and its junction called?

The xiphoid process forms the lower part of the sternum and meets the body at the xiphisternal junction.

What is the Angle of Louis?

Also called the manubriosternal joint; located at the level of the 2nd costal cartilage and the 4th thoracic vertebra.

How are ribs classified according to structure?

1⃣ By structure → Typical vs Atypical
2⃣ By attachment → True (1–7, vertebrosternal), False (8–10, vertebrochondral), Floating (11–12, vertebral)

How are ribs classified according to attachment?

• True (vertebrosternal) ribs: 1st–7th; attach directly to sternum via costal cartilage.

• False (vertebrochondral) ribs: 8th–10th; attach indirectly through the cartilage above.

• Floating (vertebral) ribs: 11th–12th; have no anterior attachment.

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What are the parts of a rib?

Head, neck, tubercle, body, sternal end.

What makes a rib typical?

• Head with 2 facets separated by a crest

• Neck ≈ 1 inch long medial to tubercle

• Tubercle rough superiorly (for ligaments/muscles) and smooth inferiorly (for transverse process)

• Body with costal groove on inferior border

• Sternal end pitted for costal cartilage (7th is last to articulate directly with sternum)

Which ribs are typical and atypical?

• Typical: 2–9

• Atypical: 1, 10, 11, 12

What features make the 1st rib atypical?

Shortest, widest; head with one facet; large tubercle; has scalene tubercle (for scalene anterior m.); grooves for subclavian vein and artery.

Why is the 10th rib atypical?

Head has one facet; 9th vertebra lacks lower demifacet; 10th vertebra has complete costal facet; tubercle has facet.

What makes 11th and 12th ribs atypical?

Each head with single facet; no facet on tubercle; no costal pit.

Name the parts of a typical vertebra.

Body, pedicle/lamina, transverse process, spinous process, articular process, vertebral foramen, notches.

What are the distinguishing features of thoracic vertebrae?

• Body: Upper and lower demifacets for ribs; posterior deeper.

• Transverse process: T1–T7 → concave facets in front of process; T8–T10 → flat facets above tip; T11–T12 → no facets.

• Spinous process: T5–T8 → long and vertical.

• Articular process: plane of joint along arc center anterior to body.

• Foramen: small and circular.

• Notches: large inferior, absent superior.

List the major joints of the thoracic cage.

• Costovertebral (head of rib)

• Costotransverse

• Sternocostal

• Interchondral

• Costochondral

• Sternal joints

What layers are present in an intercostal space?

External intercostal, internal intercostal, inner complex (transversus thoracis, intercostalis intimi, subcostalis).

Describe the external intercostal layer.

Fibers run anteromedially from tubercle → costochondral junction; continue as external intercostal membrane.

Describe the internal intercostal layer.

Fibers run inferoposteriorly from parasternal region → midaxillary line; continue as internal intercostal membrane.

Components of the inner complex?

• Transversus thoracis: xiphisternum → 2nd–6th costal cartilages

• Intercostalis intimi: parallel to internal intercostals, midaxillary line → rib angles

• Subcostalis: posterior thorax near rib angles, spans two intercostal spaces

What defines a typical thoracic nerve?

T3–T6; emerge from intervertebral foramen; run between parietal pleura and internal intercostal membrane; give collateral branch at rib angle; course with costal groove; give lateral and anterior cutaneous branches.

Which thoracic nerves are atypical and why?

• T1 → joins brachial plexus

• T2 → lateral cutaneous branch = intercostobrachial nerve

• T7–T12 → continue into anterior abdominal wall

Describe the posterior intercostal arteries.

• T1–T2 from costocervical trunk (subclavian)

• Remaining from thoracic aorta

• Course with intercostal nerve

• Anastomose with anterior intercostal arteries (T3–T6 via internal mammary; T7–T9 via musculophrenic)

Describe the internal thoracic artery and its branches.

• Origin = subclavian artery

• Runs with vein and nerve in same plane

• Branches: anterior intercostal, anterior cutaneous, musculophrenic, pericardiophrenic, mediastinal, superior epigastric

How is venous drainage of the thoracic wall organized?

• Upper 3–4 left intercostal veins → supreme intercostal → brachiocephalic vein

• Remaining intercostals → azygos system