Human Anatomy
Thoracic Cage
Thoracic cage anatomy for MBBS: ribs, sternum, sternal angle, intercostal spaces and chest drain anatomy, mapped to NMC codes AN21.1 to AN21.11.
MedNext Academy | 3 min read
Thoracic Cage
Thoracic cage anatomy for MBBS: ribs, sternum, sternal angle, intercostal spaces and chest drain anatomy, mapped to NMC codes AN21.1 to AN21.11.
This chapter covers the bony and muscular thoracic cage that protects the heart and lungs and moves in breathing. It details the ribs and their groove, the sternum and the sternal angle as a landmark, the intercostal spaces and their neurovascular bundle, and clinical points such as chest drains and cervical ribs.
High-yield: Thoracic Cage
- The thoracic cage is formed by twelve thoracic vertebrae, twelve pairs of ribs and their cartilages, and the sternum.
- The upper seven ribs are true ribs joining the sternum directly; ribs eight to ten are false ribs; ribs eleven and twelve are floating.
- A typical rib has a head, neck, tubercle, angle and shaft, with a costal groove sheltering the neurovascular bundle.
- The intercostal nerve and vessels run in the costal groove in the order vein, artery, nerve from above downward.
- A chest drain or aspiration needle is passed just above the lower rib to avoid the main neurovascular bundle.
- The first rib is short, flat and sharply curved and grooved by the subclavian vessels and the lower trunk of the brachial plexus.
- The sternum has a manubrium, body and xiphoid process joined at the manubriosternal and xiphisternal joints.
- The sternal angle of Louis marks the second costal cartilage and the level of the T4 to T5 disc.
- The sternal angle also marks the start and end of the aortic arch and the bifurcation of the trachea.
- The external intercostals elevate the ribs in inspiration and the internal intercostals mainly depress them.
- The typical intercostal space contains three muscle layers, the neurovascular bundle running between the inner two.
- Cervical ribs arise from the seventh cervical vertebra and can compress the lower brachial plexus or subclavian artery.
- The thoracic inlet is bounded by the first thoracic vertebra, the first ribs and the upper border of the manubrium.
- The intercostal nerves are the ventral rami of the thoracic spinal nerves and supply the chest and abdominal walls.
Intercostal space essentials
- **Neurovascular order:** In the costal groove from above down: vein, artery, nerve. The bundle runs between the inner two muscle layers.
- **Safe drain site:** Pass a needle or drain just above the lower rib to avoid the main bundle in the groove of the upper rib.
- **Sternal angle:** Marks the second costal cartilage, the T4 to T5 disc, the aortic arch and the tracheal bifurcation.
- **Rib types:** True ribs 1 to 7, false ribs 8 to 10, floating ribs 11 and 12.
NMC competencies in this chapter
- **AN21.1:** Bones of the thoracic cage: ribs, costal cartilages and sternum
- **AN21.2:** Features of a typical rib
- **AN21.3:** Features of atypical ribs
- **AN21.4:** Features and joints of the sternum
- **AN21.5:** Intercostal muscles and their action
- **AN21.6:** Intercostal nerves and their distribution
- **AN21.7:** Intercostal vessels
- **AN21.8:** Movements of the thoracic cage in respiration
- **AN21.9:** Boundaries of the thoracic inlet and outlet
- **AN21.10:** Diaphragm attachments and openings in outline
- **AN21.11:** Applied anatomy including chest drain and cervical rib
Frequently Asked Questions
Why is a chest drain inserted just above a rib?
The main intercostal neurovascular bundle runs in the costal groove along the lower border of each rib. Passing the drain just above the rib below keeps it clear of these vessels and the nerve.
What does the sternal angle mark?
The sternal angle of Louis lies at the level of the second costal cartilage and the T4 to T5 disc. It marks the beginning and end of the aortic arch and the bifurcation of the trachea.
What is a cervical rib and why does it matter?
A cervical rib is an extra rib arising from the seventh cervical vertebra. It can press on the lower trunk of the brachial plexus or the subclavian artery, causing thoracic outlet symptoms.
What is the order of the intercostal neurovascular bundle?
In the costal groove, from above downward, lie the intercostal vein, artery and nerve. Knowing this order guides safe placement of needles and drains in the chest wall.
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