Thorax

• Introduction to the Thorax:

  • The thorax refers to the region of the body between the neck and the abdomen
  • The thoracic cavity is enclosed by the musculoskeletal walls of the thorax and the diaphragm
  • Anteriorly, the thoracic wall consists of the sternum
  • Posteriorly, it consists of the 12 thoracic vertebrae and their intervening intervertebral discs
  • Laterally, it consists of the ribs, each rib’s associated costal cartilages, and muscles that span the space between adjacent ribs/costal cartilages
• • Inferiorly, the diaphragm forms the physical boundary between the thoracic cavity and the abdominal cavity
• Bones of the Thorax:

  • The bones of the thorax include the Sternum, Ribs, and Thoracic Spine
  • The sternum is a flat bone located at the anterior aspect of the thorax with a ‘T’ shape
  • The sternum can be divided into three parts: manubrium, body, and xiphoid process
  • The manubrium articulates with the body of the sternum, forming the sternal angle
  • The body articulates with the manubrium superiorly and the xiphoid process inferiorly
  • The xiphoid process is the most inferior and smallest part of the sternum, largely cartilaginous in structure
• Clinical Relevance of Sternum:

  • Sternal fractures are associated with severe blunt trauma to the chest, such as in a vehicular accident
  • Sternal fractures have a high mortality rate (25-45%)
  • It is crucial to check patients with sternal fractures for visceral injury using X-ray, CT, and ultrasound
• The Ribs:

  • The ribs are a set of twelve paired bones forming the protective ‘cage’ of the thorax
  • There are two classifications of ribs: atypical and typical
  • Typical ribs consist of a head, neck, and body
  • Atypical ribs include ribs 1, 2, 10, 11, and 12 with variations in structure
• Rib Articulations:

  • Posteriorly, all twelve ribs articulate with the vertebrae of the spine
  • Anteriorly, ribs 1-7 attach independently to the sternum
  • Ribs 8-10 attach to the costal cartilages superior to them
  • Ribs 11 and 12 do not have an anterior attachment and end in the abdominal musculature
• Clinical Relevance of Rib Fractures:

  • Rib fractures commonly occur in the middle ribs due to crushing injuries or direct trauma
  • Complications of rib fractures include soft tissue injury to structures like the lungs, spleen, or diaphragm
  • Flail chest can occur with two or more fractures in adjacent ribs, impairing lung inflation and treated by fixing the affected ribs
• The Thoracic Spine:

  • The thoracic spine consists of twelve vertebrae separated by intervertebral discs
  • The thoracic spine, along with the sternum and ribs, forms part of the thoracic cage
  • Thoracic vertebrae have characteristic features including heart-shaped vertebral bodies and long, slanting spinous processes
• Thoracic Spine Joints:

  • Joints present throughout the vertebral column include intervertebral discs and articulation of superior and inferior articular processes
  • Unique to the thoracic spine are costovertebral and costotransverse joints for articulation with the ribs
  • Costovertebral joints consist of the head of the rib articulating with the superior and inferior costal facets of the corresponding vertebrae
• Atypical Vertebrae:

  • T1 articulates with the 1st rib and has a unique superior facet
  • T10 has a single pair of whole facets articulating with the 10th rib
  • T11 and T12 each have a single pair of entire costal facets located on the pedicles
• The thoracic spine is strengthened by numerous ligaments
• Ligaments present throughout Vertebral Column:

  • Anterior and posterior longitudinal ligaments: Long ligaments that run the length of the vertebral column, covering the vertebral bodies and intervertebral discs
  • Ligamentum flavum: Connects the laminae of adjacent vertebrae
  • Interspinous ligament: Connects the spinous processes of adjacent vertebrae
  • Supraspinous ligament: Connects the tips of adjacent spinous processes
• Ligaments unique to the Thoracic Spine:

  • Radiate ligament of head of rib: Fans outwards from the head of the rib to the bodies of the two vertebrae and intervertebral disc
  • Costotransverse ligament: Connects the neck of the rib and the transverse process
  • Lateral costotransverse ligament: Extends from the transverse process to the tubercle of the rib
  • Superior costotransverse ligament: Passes from the upper border of the neck of the rib to the transverse process of the vertebra superior to it
• Various diseases can lead to kyphosis in adults, with osteoporosis being the most common cause
• Thoracic Cavity Apertures:

  • Superior thoracic aperture (Thoracic inlet)
  • Inferior thoracic aperture (thoracic outlet)
• Superior thoracic aperture:

  • Bounded anteriorly by the superior surface of the manubrium, posteriorly by the internal margins of the T1 vertebra, and laterally by the first pair of ribs
• Inferior thoracic aperture:

  • Anterolateral border formed by the costal arch (margin) from ribs 7-10 attaching to each side of the sternum
  • Posteriorly by the inferior surface of the body of the twelfth thoracic vertebra
  • Diaphragm encloses the inferior thoracic aperture
• The mediastinum is the central compartment of the thoracic cavity, divided into superior and inferior parts
• Superior mediastinum:

  • Borders include thoracic inlet, continuous with inferior mediastinum at sternal angle, anteriorly by manubrium, posteriorly by vertebral bodies of T1-T4, and laterally by pleurae of the lungs
  • Contains great vessels of the heart, including arch of aorta, brachiocephalic artery, left common carotid artery, left subclavian artery, superior vena cava, and various veins and nerves
• Middle mediastinum:

  • Borders include anterior and posterior margins of the pericardium, mediastinal pleura of the lungs, superiorly by sternal angle, and inferiorly by superior surface of the diaphragm
  • Contains heart, pericardium, tracheal bifurcation, left and right main bronchi, ascending aorta, pulmonary trunk, and superior vena cava
• Posterior mediastinum:

  • Borders include lateral mediastinal pleura, anterior pericardium, posterior T5-T12 vertebrae, roof extending from sternal angle to T4 vertebrae, and floor by diaphragm
  • Contains thoracic aorta, oesophagus, thoracic duct, and various organs, blood vessels, and nerves