Thoracic Wall (Skeletal Elements & Muscles) Lecture 1 Part 1 PDF

Thoracic Wall (Skeletal elements and muscles) By Dr. Mohammad Ba’ara  Thoracic cage or Rib Cage, vertebral column behind, the ribs and intercostal spaces on either side, and the sternum and costal cartilages in front. Superiorly, the thorax communicates with the neck, and infe...

Thoracic Wall (Skeletal elements and muscles) By Dr. Mohammad Ba’ara  Thoracic cage or Rib Cage, vertebral column behind, the ribs and intercostal spaces on either side, and the sternum and costal cartilages in front. Superiorly, the thorax communicates with the neck, and inferiorly it is separated from the abdomen by the diaphragm. Content and attachment to muscles.  The thoracic cavity enclosed by the thoracic wall and the diaphragm is subdivided into three major compartments: a left and a right pleural cavity, each surrounding a lung, and the mediastinum. Visceral pleura Vs. Parietal pleura.  The mediastinum is a thick, flexible soft tissue partition oriented longitudinally in a median sagittal position. It contains the heart, esophagus, trachea, major nerves, and major systemic blood vessels. The pleural cavities are completely separated from each other by the mediastinum. Therefore abnormal events in one pleural cavity do not necessarily affect the other cavity. This also means that the mediastinum can be entered surgically without opening the pleural cavities.  Function Muscle of inspiration, The thorax not only contains the lungs but also provides the machinery necessary—the diaphragm, thoracic wall, and ribs—for effectively moving air into and out of the lungs. Protection of vital organs. Conduit, The mediastinum acts as a conduit for structures that pass completely through the thorax from one body region to another. Muscle of abdominal straining Weight-lifting muscle:greatly assists the postvertebral muscles in the lifting of heavy weights. Thoracoabdominal pump: blood and lymph  The thoracic wall is covered on the outside by skin and by muscles attaching the shoulder girdle to the trunk. It is lined with parietal pleura.  The thoracic wall consists of skeletal elements and muscles: Posteriorly, it is made up of twelve thoracic vertebrae and their intervening intervertebral discs; Laterally, the wall is formed by ribs (twelve on each side) and three layers of flat muscles, which span the intercostal spaces between adjacent ribs, move the ribs, and provide support for the intercostal spaces; Anteriorly, the wall is made up of the sternum, which consists of the manubrium of sternum, body of sternum, and xiphoid process.  Sternum Flat bone, divide to manubrium sterni, body of the sternum, and xiphoid process. Upper part, articulates with the body of the sternum at the manubriosternal joint, and it also articulates with the clavicles and with the 1st costal cartilage and the upper part of the 2nd costal cartilages on each side. It lies opposite the 3rd and 4th thoracic vertebrae. The superior surface of the manubrium is expanded laterally and bears a distinct and palpable notch, the jugular notch (suprasternal notch), in the midline.  The body of the sternum articulates above with the manubrium at the manubriosternal joint and below with the xiphoid process at the xiphisternal joint. On each side, it articulates with the 2nd to the 7th costal cartilages. xiphoid process is a thin plate of cartilage that becomes ossified at its proximal end during adult life. On each side of its upper lateral margin is a demifacet for articulation with the inferior end of the seventh costal cartilage.  The sternal angle (angle of Louis), at the level of the 2nd costal cartilage, lies opposite the intervertebral disc between the 4th and 5th thoracic vertebrae. The xiphisternal joint lies opposite the body of the ninth thoracic vertebra.  Ribs 12 pairs, 3 categories. True ribs: first 7 False ribs: 8,9,10, costal cartilage to the 7th rib Floating ribs: 11 and 12, no anterior attachment.  Typical Rib Long, twisted, flat bone having a rounded, smooth superior border and a sharp, thin inferior border. The inferior border overhangs and forms the costal groove. The anterior end of each rib is attached to the corresponding costal cartilage. A rib has a head, neck, tubercle, shaft, and angle.  Head: two facets for articulation with the numerically corresponding vertebral body and that of the vertebra immediately above. Neck: portion situated between the head and the tubercle. Tubercle: prominence on the outer surface of the rib at the junction of the neck with the shaft, facet for articulation with the transverse process of the numerically corresponding vertebra, and raised nonarticular part is roughened by ligament attachments. Shaft: thin and flattened and twisted on its long axis. Its inferior border has the costal groove. The angle is where the shaft of the rib bends sharply forward.  Atypical ribs: 1st rib is close to the brachial plexus and the main vessels. This rib is small and flattened, shortest, and most sharply curved of the seven true ribs. Anterior Scalene attached to it, subclavian vein crosses anterior and subclavian artery and the lower trunk of the brachial plexus cross posterior.  It has a single facet on its head for articulation with the T1 vertebra only and two transversely directed grooves crossing its superior surface for the subclavian vessels; the grooves are separated by a scalene tubercle and ridge, to which the anterior scalene muscle is attached.  A typical thoracic vertebra has a heart-shaped vertebral body, with roughly equal dimensions in the transverse and anteroposterior directions, and a long spinous process. The vertebral foramen is generally circular and the laminae are broad and overlap with those of the vertebra below. The superior articular processes are flat, with their articular surfaces facing almost directly posteriorly, while the inferior articular processes project from the laminae and their articular facets face anteriorly. The transverse processes are club shaped and project posterolaterally.  Atypical thoracic vertebrae bear whole costal facets in place of demifacets: 1. The superior costal facets of vertebra T1 are not demifacets because there are no demifacets on the C7 vertebra above, and rib 1 articulates only with vertebra T1. 2. T1 has a typical inferior costal (demi)facet. T10 has only one bilateral pair of (whole) costal facets, located partly on its body and partly on its pedicle.  T11 and T12 also have only a single pair of (whole) costal facets, located on their pedicles.