Overview
This lecture covers the detailed anatomy of the thoracic wall, including its bones, joints, muscles, nerves, vessels, and clinical relevance.
Bony Structures of the Thoracic Wall
- The sternum has three parts: manubrium (with jugular/suprasternal notch), body, and xiphoid process.
- The sternal angle (at T4) is a key rib-counting landmark where the 2nd rib articulates.
- Clavicular notch on the manubrium articulates with the clavicle, forming the sternoclavicular joint.
- Costal notches on the sternum receive costal cartilage from the ribs.
- Ribs: 12 pairs—true (1–7), false (8–10), floating (11–12); each rib has a head, neck, tubercle, shaft, and costal groove.
- Costal groove (inferior rib surface) houses the neurovascular bundle.
- Ribs articulate with thoracic vertebrae at costovertebral and costotransverse joints.
Joints of the Thoracic Wall
- Manubriosternal joint: symphysis (fibrocartilaginous).
- Xiphisternal joint: synchondrosis (hyaline cartilage).
- Sternoclavicular joint: synovial saddle joint.
- Sternocostal joints: synovial plane joints (ribs 2–7).
- Costochondral joints: synchondroses between ribs and costal cartilage.
- Costovertebral and costotransverse joints: synovial plane joints between ribs and vertebrae.
Muscles of the Thoracic Wall
- External intercostal muscles elevate ribs (inspiration).
- Internal, innermost intercostal, subcostal, and transversus thoracis muscles depress ribs (forced expiration).
- Diaphragm is the primary inspiratory muscle, with openings at T8 (caval), T10 (esophageal), and T12 (aortic).
- Muscle fiber direction helps determine function (elevation vs. depression of ribs).
Nerves of the Thoracic Wall
- Intercostal nerves (T1–T11) arise from anterior rami; run in costal grooves with artery and vein.
- Provide motor innervation to intercostal muscles and sensory innervation to thoracic wall skin via lateral and anterior cutaneous branches.
- Subcostal nerve (T12) supplies the abdominal wall and skin.
- Dermatomes: T4 (nipple), T6 (xiphoid), T10 (umbilicus), T12 (pubic region).
- Neurovascular bundle runs just inferior to each rib.
Blood Vessels of the Thoracic Wall
- Posterior intercostal arteries branch from thoracic aorta; anterior intercostal arteries from internal thoracic (mammary) artery.
- Posterior intercostal veins drain into azygos (right) or hemiazygos (left); anterior intercostal veins drain into internal thoracic vein.
- Internal thoracic artery arises from subclavian artery and runs along sternum.
- Supreme intercostal artery supplies ribs 1–2.
Clinical Relevance
- Costochondritis: inflammation of costochondral joints, causing reproducible chest pain.
- Flail chest: paradoxical chest movement due to multiple rib fractures.
- Procedures (thoracentesis, chest tube): always insert needles above the rib to avoid the neurovascular bundle.
Key Terms & Definitions
- Manubrium — upper part of sternum.
- Jugular/Suprasternal notch — notch at top of manubrium.
- Costal groove — groove on rib's inferior surface, contains neurovascular bundle.
- Costochondritis — inflammation of rib-cartilage joints.
- Flail chest — chest moves inwards during inspiration due to multiple rib fractures.
- Intercostal nerves — nerves running between ribs, supplying muscles and skin.
- Dermatome — skin area supplied by a single spinal nerve.
Action Items / Next Steps
- Review labeled diagrams of thoracic wall bones, muscles, nerves, and vessels.
- Memorize key anatomical landmarks and their clinical significance.
- Practice identifying rib and sternum parts on models or illustrations.