Trunk Anatomy: The Thorax (2024-2025) PDF

TRUNK ANATOMY THE THORAX 2024-2025 THIRD YEAR / FIRST SEMESTER Assist. Prof. Dr. Rana I. Mahmood  THORAX The thorax is an irregularly shaped cylinder with a narrow opening (superior thoracic aperture) superiorly and a relatively large...

TRUNK ANATOMY THE THORAX 2024-2025 THIRD YEAR / FIRST SEMESTER Assist. Prof. Dr. Rana I. Mahmood  THORAX The thorax is an irregularly shaped cylinder with a narrow opening (superior thoracic aperture) superiorly and a relatively large opening (inferior thoracic aperture) inferiorly (Fig. 3.1). The superior thoracic aperture is open, allowing continuity with the neck; the inferior thoracic aperture is closed by the diaphragm. THORACIC WALL Includes: 1. The thoracic cage 2. Muscles that extend between its elements 3. The skin, subcutaneous tissue, muscles, and fascia covering its anterolateral aspect. Thoracic Wall: Covered on the outside by skin and by muscles attaching the shoulder girdle to the trunk. Lined with parietal pleura. is formed: 1. Posteriorly by the thoracic part of the vertebral column. 2. Anteriorly by the sternum and costal cartilages. 3. Laterally by the ribs and intercostal spaces. 4. Superiorly by the suprapleural membrane. 5. Inferiorly by the diaphragm, which separates the thoracic cavity from the abdominal cavity. Skeleton of the Thoracic Wall Is osteocartilaginous thoracic cage protects the thoracic viscera and some abdominal organs. Includes: 12 pairs of ribs and associated costal cartilages 12 thoracic vertebrae and the intervertebral (IV) discs interposed between them, Sternum. Assist. Prof. Dr. Rana I. Mahmood |Page1  RIBS (COSTAE) There are 12 pairs of ribs, curved, flat bones. All of which are attached posteriorly to the thoracic vertebrae. are divided into three categories: 1. True ribs: The upper seven pairs are attached anteriorly to the sternum by their costal cartilages. 2. False ribs: The 8th, 9th, and 10th pairs of ribs are attached anteriorly to each other and to the 7th rib by means of their costal cartilages and small synovial joints. 3. Floating ribs: The 11th and 12th pairs have no anterior attachment. Assist. Prof. Dr. Rana I. Mahmood |Page2 Typical ribs (3rd-9th) have the following components: 1. Head: Wedge-shaped, has two facets, separated by the crest  One facet for articulation with the numerically corresponding vertebra  One facet for the vertebra superior to it. 2. Neck: Connects the head with the body at the level of the tubercle. 3. Tubercle: Junction of the neck and body.  A smooth articular part, for articulating with the corresponding transverse process of the vertebra,  A rough non-articular part, for attachment of the costotransverse ligament. 4. Body (shaft): thin, flat, and curved, most markedly at the costal angle where the rib turns anterolaterally. A costal groove paralleling the inferior border (internal surface) of the rib, which provides some protection for the intercostal nerve and vessels. Assist. Prof. Dr. Rana I. Mahmood |Page3 Atypical ribs (1st, 2nd, and 10th-12th): 1. 1st rib  Is the broadest (nearly horizontal), shortest, and most sharply curved of the seven true ribs.  Has a single facet on its head for articulation with the T1 vertebra only.  A scalene tubercle on superior surface, to which anterior scalene muscle is attached.  Two transversely directed grooves crossing its superior surface for subclavian vessels; these grooves are separated by scalene tubercle. 2. 2nd rib Is more typical; its body is thinner, less curved, and longer than the 1st rib, Its head has two facets for articulation with the bodies of the T1 and T2 vertebrae; A rough area on its upper surface, the tuberosity for serratus anterior muscle. 3. 10th- 12th ribs Have only one facet on their heads Articulate with a single vertebra. 4. 11th and 12th ribs Are short No neck or tubercle. COSTAL CARTILAGES Prolong the ribs anteriorly Contribute to the elasticity of the thoracic wall Providing a flexible attachment for their anterior ends (tips). Increase in length through the first 7 and then gradually decrease. The first 7 cartilages attach directly and independently to the sternum; 8th, 9th& 10th articulate with the costal cartilages superior to them, forming a continuous, articulated, cartilaginous costal margin. 11th and 12th cartilages form caps on the anterior ends of these ribs and do not reach or attach to any other bone or cartilage. The costal cartilages of ribs 1-10 clearly anchor the anterior end (tips) of the rib to the sternum, limiting its overall movement as the posterior end rotates around the transverse axis of the rib. Assist. Prof. Dr. Rana I. Mahmood |Page4 RIB FRACTURES Single rib fractures are of little consequence, though extremely painful. After severe trauma, ribs may be broken in two or more places. If enough ribs are broken, a loose segment of chest wall, a flail segment (flail chest), is produced. When the patient takes a deep inspiration, the flail segment moves in the opposite direction to the chest wall, so preventing full lung expansion and creating a paradoxically moving segment. If a large enough segment of chest wall is affected, ventilation may be impaired and assisted ventilation may be required until the ribs have healed. Assist. Prof. Dr. Rana I. Mahmood |Page5  THORACIC VERTEBRAE A- Typical vertebrae Have bodies, vertebral arches, and seven processes for muscular and articular connections. Characteristic features include: 1. Bilateral costal facets (demifacets) on their bodies, usually occurring in inferior and superior pairs, for articulation with the heads of ribs. 2. Costal facets on their transverse processes for articulation with the tubercles of ribs, except for the inferior two or three thoracic vertebrae. 3. Long, inferiorly slanting spinous processes. Superior and inferior costal facets  Demifacets  Bilaterally paired, planar surfaces on the superior and inferior posterolateral margins of typical (T2-T9) thoracic vertebrae.  Arranged in pairs on adjacent vertebrae, flanking an interposed IV disc: an inferior (demi) facet of the superior vertebra and a superior (demi) facet of the inferior vertebra.  Typically, two demifacets paired in this manner and the posterolateral margin of the IV disc between them form a single Assist. Prof. Dr. Rana I. Mahmood |Page6  socket to receive the head of the rib that is assigned the same number as the inferior vertebra. B- Atypical thoracic vertebrae: Bear whole costal facets in place of demifacets 1. Vertebra T1 The superior costal facets are not demifacets because there are no demifacets on the C7 vertebra above, and rib 1 articulates only with vertebra T1. T1 has a typical inferior costal (demi) facet. 2. T10 Has only one bilateral pair of (whole) costal facets, located partly on its body and partly on its pedicle. 3. T11 & T12 Have only a single pair of (whole) costal facets, located on their pedicles. SPINOUS PROCESSES Projecting from vertebral arches of typical thoracic vertebrae Are long and slope inferiorly, usually overlapping the vertebra below. Cover the intervals between the laminae of adjacent vertebrae. ARTICULAR FACETS  Superior articular facets of the superior articular processes face mainly posteriorly and slightly laterally  Inferior articular facets of the inferior articular processes face mainly anteriorly and slightly medially.  Bilateral joint planes between articular facets of the adjacent vertebrae form an arc, centering on an axis of rotation within the vertebral body.  Small rotatory movements are permitted between adjacent vertebra, but they are limited by the attached rib cage. Assist. Prof. Dr. Rana I. Mahmood |Page7  STERNUM (STERNON, CHEST)  Flat, elongated bone, Forms middle of anterior part of thoracic cage.  It consists of three parts: 1. Manubrium, 2. Body, 3. Xiphoid process. Assist. Prof. Dr. Rana I. Mahmood |Page8 Manubrium (handle)  Roughly trapezoidal bone, Widest and thickest of three parts of sternum.  Jugular notch (suprasternal notch): Easily palpated concave center of superior border, is deepened by medial ends of clavicles, which are much larger than relatively small clavicular notches in manubrium that receive them, forming sternoclavicular (SC) joints.  1st rib costal cartilage is tightly attached to lateral border of manubrium (inferolateral to clavicular notch), by synchondrosis. MANUBRIUM AND BODY OF STERNUM  Lie in slightly different planes superior & inferior to their junction, manubriosternal joint.  Forms a projecting sternal angle (of Louis). Body of the sternum  Longer, narrower, and thinner than the manubrium  Located at the level of the T5-T9 vertebrae.  The sternebrae articulate with each other at primary cartilaginous joints (sternal synchondroses).  These joints begin to fuse from inferior end between puberty and age 25. Assist. Prof. Dr. Rana I. Mahmood |Page9 XIPHOID PROCESS  The smallest and most variable part of the sternum, Thin and elongated.  Lies at the level of T10 vertebra.  Often pointed,  May be blunt, bifid, curved, or deflected to one side or anteriorly.  It is cartilaginous in young people  Ossified in adults older than age 40.  In elderly people, xiphoid process may fuse with sternal body.  Its junction with sternal body at xiphisternal joint indicates:  Inferior limit of the central part of the thoracic cavity projected onto the anterior body wall  Site of the infrasternal angle (subcostal angle) of the inferior thoracic aperture.  It is a midline marker for the superior limit of the:  Liver.  The central tendon of the diaphragm.  The inferior border of the heart. Assist. Prof. Dr. Rana I. Mahmood | P a g e 10