Osmosis from Elsevier - Bones and joints of the thoracic wall: Anatomy
The thorax is the region between the neck and abdomen, consisting of the thoracic cavity, its contents, and surrounding walls. The thoracic skeleton forms a protective cage for thoracic viscera and some abdominal organs, comprising the sternum, 12 pairs of ribs, costal cartilages, and thoracic vertebrae. Ribs are categorized into true, false, and floating types based on their connection to the sternum. True ribs (1-7) attach directly to the sternum, false ribs (8-10) connect indirectly, and floating ribs (11-12) do not connect to the sternum. The sternum, a flat bone, consists of the manubrium, body, and xiphoid process, providing protection to mediastinal viscera, especially the heart. The thoracic cage facilitates respiration by changing its volume and diameter through movements like the pump handle and bucket handle, driven by the diaphragm and intercostal muscles. This dynamic structure allows for efficient air inflow and outflow during breathing.
Key Points:
- The thoracic cage protects vital organs and supports respiration.
- Ribs are classified as true, false, or floating based on their sternum connection.
- The sternum consists of the manubrium, body, and xiphoid process, crucial for protecting the heart.
- Intercostal spaces and movements like pump handle and bucket handle aid in breathing.
- The thoracic cage's structure allows for changes in volume and pressure during respiration.
Details:
1. ðĶī Anatomy of the Thoracic Skeleton
- The thoracic skeleton consists of the sternum, 12 pairs of ribs, associated costal cartilages, 12 thoracic vertebrae, and intervertebral discs. These elements form an osteocartilaginous thoracic cage that protects thoracic and some abdominal organs.
- Ribs and costal cartilages constitute the largest part of the thoracic cage, with ribs numbered 1 to 12 and costal cartilages numbered 1 to 10; ribs 11 and 12 lack costal cartilages.
- The thoracic cage serves as a protective structure, safeguarding vital organs such as the heart and lungs, and providing attachment points for muscles involved in respiration.
- The true thoracic wall includes the thoracic cage, intercostal muscles, skin, subcutaneous tissue, muscles, and fascia covering the anterolateral and posterior aspects, which collectively support respiratory mechanics.
- Mammary glands, located within the subcutaneous tissue of the thoracic wall, are also considered part of this anatomical structure.
2. ð Types and Characteristics of Ribs
- Ribs are curved, flat, lightweight, and highly resilient bones forming most of the thoracic cage.
- Each rib has a spongy interior with bone marrow or hematopoietic tissue that forms blood cells.
- There are three types of ribs based on their connection to the sternum: true, false, and floating ribs.
- True (vertebrosternal) ribs are the first seven pairs and attach directly to the sternum through their own costal cartilages.
- False (vertebrochondral) ribs are the 8th, 9th, and usually the 10th pairs, connecting indirectly to the sternum via the cartilage of the rib above them.
- Floating (vertebral or free) ribs are the 11th, 12th, and sometimes the 10th pairs, with no anterior connection to the sternum, ending in the posterior abdominal region.
3. ð Anatomy of Typical and Atypical Ribs
- Typical ribs are defined as the third through the ninth pair of ribs.
- Each typical rib has a head, neck, tubercle, and body.
- The head of a typical rib is wedge-shaped with two facets: superior and inferior, separated by the crest of the head.
- The inferior facet articulates with the vertebrae of the same number, while the superior facet articulates with the vertebrae above.
- The tubercle has a smooth articular part that connects with the transverse process of the corresponding vertebrae.
- The body of the rib is thin, flat, and curved, especially at the costal angle where it turns anterolateral.
- The internal surface of the body is concave with a costal groove parallel to the rib's inferior border.
4. ð Rib Articulations and Joints
- The first rib, the broadest and shortest of the true ribs, features a single facet for the T1 vertebra articulation, emphasizing its unique structure.
- The second rib has a tuberosity for serratus anterior and two facets for T1 and T2 articulation, highlighting its role in muscular attachment and dual articulation.
- Ribs 10-12, similar to the first rib, have one facet and articulate with a single vertebra, simplifying their articulation process.
- The 11th and 12th ribs lack a neck or tubercle, marking their distinct morphology among ribs.
- Ribs 2-9 articulate with two vertebral facets and an intervertebral disc, demonstrating a complex articulation structure.
- Rib heads articulate with thoracic vertebrae via synovial plane joints, showing the functional mechanics of rib movement.
- Ribs 2-9 feature a two-facet system involving both superior and inferior costal facets, indicating a dual articulation mechanism.
- Ribs 1, 11, 12, and sometimes 10, exclusively articulate with a single vertebral body, underscoring a simpler articulation pattern.
5. ðïļ Structure and Features of the Sternum
- The sternum is a flat, elongated bone in the front of the thoracic cage, consisting of the manubrium, body, and xiphoid process, and protecting mediastinal viscera, especially the heart.
- The manubrium, the widest and thickest part of the sternum, is trapezoidal, featuring a jugular notch that is easily palpable.
- The sternoclavicular joint, a saddle-type synovial joint, involves the clavicle and clavicular notches of the manubrium, along with the first costal cartilages.
- The primary cartilaginous joint at the first sternal costal joint connects the costal cartilage of the first rib to the manubrium.
- The manubriosternal joint forms the sternal angle, or angle of Louis, which is palpable and visible in young individuals.
- The sternal angle aligns with the T4-T5 intervertebral disc and the space between the third and fourth thoracic spinous processes.
- Rib articulation: Ribs 1-10 articulate with vertebrae at tubercles, while ribs 11 and 12 do not articulate with the transverse process of vertebrae.
6. ðŽïļ Thoracic Apertures and Diaphragm Function
- The left side of the manubrium is anterior to the arch of the aorta, and its right side overlies the merging of the brachiocephalic veins to form the superior vena cava.
- The superior vena cava passes inferiorly deep to the manubrium and manubriosternal joint but projects as much as a fingerbreadth to the right margin of the manubrium.
- The body of the sternum is located roughly at the level of T5 through T9 vertebrae, with articulation occurring at ribs 2 through 7 with synovial plane joints.
- The xiphoid process is thin, elongated, and lies at the level of the T10 vertebra, indicating the inferior limit of the central part of the thoracic cavity and serving as a midline marker for the superior limit of the liver, central tendon of the diaphragm, and inferior border of the heart.
- The diaphragm plays a crucial role in respiration by contracting and flattening to increase thoracic volume and decrease pressure, facilitating air intake.
7. ð Physiological Movements of the Thoracic Cage
7.1. Anatomy and Apertures of the Thoracic Cage
7.2. Physiological Movements: Mechanics of Breathing
8. ð Comprehensive Recap and Clinical Application
- The thoracic wall and diaphragm collaborate to modulate intrathoracic volume, crucial for air expulsion and intake via pressure changes. During expiration, muscle relaxation increases pressure to expel air, while diaphragm contraction during inspiration expands the thoracic cavity for air intake.
- Thoracic cage dynamics involve rib and intercostal muscle movements, creating 'pump handle' (upper ribs) and 'bucket handle' (lower ribs) effects, enhancing thoracic dimension changes to facilitate breathing.
- The thoracic wall consists of the thoracic cage, intercostal muscles, skin, subcutaneous tissue, and fascia, with 12 rib pairs categorized as true, false, or floating according to sternum attachment.
- The sternum, divided into the manubrium, body, and xiphoid process, features landmarks like the sternal angle (T4-T5 level) and the xiphoid process (T10).
- Intercostal spaces are identified by the rib above them, with the superior thoracic aperture connecting the thorax and neck, and the inferior thoracic aperture linking to the abdomen.
- Forced inspiration enhances thoracic cage dimensions through diaphragm contraction and rib movement, accommodating increased air intake.