Thoracic Wall Anatomy Quiz

Thoracic Wall Anatomy

• The thoracic wall is bordered by 12 vertebrae, 12 pairs of ribs with their costal cartilages, the sternum, suprapleural membrane, and the diaphragm.
• True ribs (1-7) attach directly to the sternum.
• False ribs (8-10) attach indirectly to the sternum via the cartilage of the rib above.
• Floating ribs (11-12) are free and do not attach to the sternum.
• Costosternal joints are cartilaginous in the first rib and synovial in ribs 2-7.
• Ribs 1, 11, and 12 articulate with their corresponding vertebrae.
• Ribs 2-10 articulate with their own and the vertebra above.

Rib Characteristics

• A typical rib has a head with two articular facets, a neck, a tubercle (articulates with the transverse process and the lateral costotransverse ligament), an angle (point where the shaft bends forward), a shaft with a costal groove, and a sharp lower border lodging the neurovascular bundle.
• The first rib is atypical, being the shortest, flattest, broadest, and most curved. It has one articular facet, a groove for the subclavian artery and vein, and little movement during respiration. It connects to the manubrium via a cartilaginous joint.

Sternum

• The sternum is composed of the manubrium, body, and xiphoid process.
• Like the ribs, it's made of cancellous bone with hematopoietic tissue.
• The manubrium has a jugular notch, a concavity for the sterno-clavicular joints (synovial), the first costal cartilages at its lateral border, and sternohyoid and sternothyroid attachments posteriorly.
• The sternum body has articular facets along its lateral border for costal cartilages 2-7, which are synovial joints.
• The xiphisternum projects downward to attach to the linea alba and typically ossifies in middle age.

Costosternal Joints

• The upper seven costal cartilages connect to the sternum at the sternocostal joints (true ribs).
• Ribs 8-10 articulate via interchondral joints.
• Ribs 11 and 12 are floating ribs, meaning their costal cartilages do not attach to the sternum.

Pectoral Region

• Pectoralis major covers the chest wall, forming the anterior wall of the axilla. Its origin is from the clavicle, sternum, and ribs 1-6. The tendon inserts into the humerus.
• Pectoralis minor lies beneath the pectoralis major, taking its origin from ribs 3-5. It inserts to the coracoid process of the scapula.
• Both are accessory muscles of respiration.

Muscles from Abdomen to Thorax

• Rectus abdominus originates from the xiphoid process and costal cartilages 5-7.
• External oblique attaches to the external surface of the lower eight ribs.
• Serratus anterior inserts into ribs 1-8 from the scapula.

The Diaphragm

• The diaphragm is a dome-shaped, fibro-muscular sheet separating the thorax from the abdomen.
• It is primarily responsible for inspiration through contraction.
• Its anterior attachments are at the level of the xiphoid process, with posterior attachments below the 12th thoracic vertebra.
• Its profile is inverted J-shaped, with crura posteriorly and xiphisternal attachment anteriorly. It has two domes, with the right higher than the left.

Origins of the Diaphragm

• Crura (right and left)
• Median arcuate ligament
• Medial arcuate ligament
• Lateral arcuate ligament
• Inner surface of lower 6 ribs and their costal cartilages
• Posterior surfaces of the xiphisternum

Diaphragm Innervation

• The diaphragm is innervated by the left and right phrenic nerves (C3, C4, C5). Patients with damage above C3 require mechanical respiration.

Thoracic Vertebrae

• Thoracic vertebrae possess a body, superior and inferior demifacets, pedicle, superior and inferior articular processes, transverse process, lamina, spinous process, superior and inferior notches, vertebral canal.

Neurovascular Bundles

• Neurovascular bundles travel in the costal groove of the ribs between the internal and innermost intercostals, superior to the ribs.

Intercostal Muscles

• External intercostal muscles: fibers directed superior-lateral to inferior-medial. Anteriorly they become a transparent membrane.
• Internal intercostal muscles: fibers perpendicular to the external intercostals. Posteriorly they become the internal intercostal membrane from the rib angles.
• Innermost intercostal muscles: are the deepest and thinnest.
• All three intercostal muscles are accessory muscles of respiration.