Chapter 8

### Chest Wall and Surface Anatomy

The thoracic viscera are protected by the chest wall and sternum. The bony framework of the chest wall is composed of 12 thoracic vertebrae, intervertebral discs, 12 pairs of ribs with corresponding cartilages, and the sternum. The thoracic vertebrae and intervertebral discs are positioned in the posterior midline; the spinous processes are relatively easy to identify as landmarks. The scapula overlies a portion of the first seven pairs of ribs posteriorly. With the arm abducted, the (vertebral) medial border of the scapula is parallel to the oblique fissure of the underlying lung.1

The sternum lies in the anterior midline and has three components: manubrium, body, and xiphoid process. The sternal notch, or superior border of the manubrium, is easily located between the clavicular heads. The junction of the manubrium and body of the sternum is called the sternal angle, or angle of Louis. This is an important landmark, corresponding to the level where the second costal cartilages articulate with the sternum. Since the first rib may be partially or completely obscured by the clavicle, accurate counting of ribs may commence at the sternal angle. This landmark is also important for deeper thoracic structures, marking the level of the tracheal bifurcation (carina) as well as the aortic arch.2

The upper seven pairs of ribs are considered to be true ribs because they form a complete circle between the sternum and vertebrae. The costal cartilages connect the ribs to the sternum anteriorly. In contrast to those of the first seven pairs of ribs, the costal cartilages of the 8th, 9th, and 10th ribs attach to the cartilage of the preceding rib. The 10th costal cartilage marks the most inferior point of the costal margin.1 Aside from their vertebral attachments, the 11th and 12th ribs do not have other skeletal attachments and are considered to be "floating ribs."

The blood supply to the chest wall comes from the subclavian artery and aorta. The subclavian artery gives rise to the internal thoracic artery, also known as the internal mammary artery, as well as the first two intercostal arteries. Together, these vessels supply the anterior chest wall. The lateral and posterior areas of the chest wall are supplied by the remaining intercostal arteries, which arise as direct branches from the aorta posteriorly. Importantly, the intercostal bundle, consisting of the intercostal artery, vein and nerve, runs along the inferior aspect of each rib and is subject to injury during procedures such as thoracotomy or even thoracostomy tube placement.

The extrathoracic muscles of the chest wall provide both anatomic landmarks as well as substrate for surgical reconstruction of chest wall defects. The latissimus dorsi provides a large and versatile myocutaneous flap. Supplied by the thoracodorsal artery, nerve and vein, it is used most frequently for reconstruction of anterior and lateral chest wall defects. The pectoralis major is often used for ...

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