AN21.1-11 | Thoracic cage — Summary & Reflection

REFLECT

Stand up and try these on your own body:

1. Find the sternal angle — slide your finger down from the jugular notch. The horizontal ridge you feel is the sternal angle (Angle of Louis). The 2nd rib is attached here. Now count down: 2nd, 3rd, 4th, 5th intercostal space. Place your stethoscope in the 5th intercostal space, mid-clavicular line — this is where you listen for the mitral valve.

1. Feel pump-handle vs bucket-handle — place one hand on your sternum and breathe deeply (pump-handle: sternum moves forward). Now place both hands on your lower ribs and breathe deeply (bucket-handle: lower ribs flare out).

1. Locate the triangle of safety — find your nipple level (5th intercostal space). The anterior border of latissimus dorsi is behind you, the lateral border of pectoralis major is in front. The triangle between them, at nipple level, is where a chest drain goes.

1. Count your ribs on a colleague — start at the sternal angle (2nd rib). Can you find the 7th costal cartilage? Below this, the costal margin is formed by cartilages of ribs 8, 9, and 10.

Now consider: a patient has a stab wound in the 6th intercostal space in the mid-axillary line. Which structures could be injured? (Think about both thoracic and abdominal organs — the diaphragm reaches up this high.)

KEY TAKEAWAYS

Key takeaways — your study checklist:

1. Sternum has 3 parts: manubrium, body, xiphoid. The sternal angle (Angle of Louis) marks the 2nd costal cartilage, tracheal bifurcation, aortic arch, T4/T5 disc, and superior/inferior mediastinum boundary.
2. 12 pairs of ribs: true (1–7), false (8–10), floating (11–12). Typical rib (3–9) has head with 2 facets, neck, tubercle, shaft with costal groove. Atypical: 1st (flat, single facet, subclavian grooves), 2nd (serratus anterior tuberosity), 10th-12th (single facets).
3. Thoracic vertebrae: typical (T2–T8) have demifacets on body + facet on transverse process. Atypical: T1, T9-T12.
4. Thoracic inlet: T1 + 1st ribs + manubrium. Outlet: T12 + 12th ribs + costal margin + xiphoid, closed by diaphragm.
5. Intercostal muscles: 3 layers — external (hands-in-pockets, inspiration), internal (opposite direction, expiration), innermost (deepest). VAN bundle lies between internal and innermost.
6. VAN order: Vein-Artery-Nerve from above downward. Chest drain: insert just above the lower rib in the triangle of safety.
7. Intercostal nerves: T1 (mostly to brachial plexus), T2 (intercostobrachial to medial arm), T3-6 (typical), T7-11 (thoraco-abdominal), T12 (subcostal). Dermatomes: T4=nipple, T10=umbilicus.
8. Costovertebral + costotransverse joints determine the axis of rib rotation.
9. Pump-handle (upper ribs, AP expansion) + bucket-handle (lower ribs, transverse expansion) + diaphragm descent (vertical expansion) = breathing.
10. Mediastinum: 4 subdivisions (superior, anterior, middle, posterior), divided by the plane of the sternal angle/T4-T5 disc.