SURFACE ANATOMY & MARKINGS OF THE THORAX G.LUFUKUJA

Bony Landmarks of the thorax The thorax (or chest) is the region of the body between the neck and the abdomen. The jugular notch is in the same horizontal plane as the lower border of the body of the second thoracic vertebra (T2) G.LUFUKUJA

Bony Landmarks… The sternal angle corresponding to the second costal cartilage, is at the level opposite the intervertebral disc between the fourth and fifth thoracic vertebrae is so readily found that it is used as a starting-point from which to count the ribs. G.LUFUKUJA

The sternal angle (angle of Louis) The angle is formed by the articulation of the manubrium with the body of the sternum, can be recognized by the presence of a transverse ridge on the anterior aspect of the sternum. The transverse ridge lies at the level of the second costal cartilage, the point from which all costal cartilages and ribs are counted. The sternal angle lies opposite the intervertebral disc between the fourth and fifth thoracic vertebrae G.LUFUKUJA

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Landmarks… Lungs The apex of the lung is situated in the neck above the medial third of the clavicle. The height to which it rises above the clavicle varies very considerably, but is generally about 2.5 cm. G.LUFUKUJA

Landmarks… G.LUFUKUJA

Landmarks… Trachea. This may be marked out on the back by a line from the spinous process of the sixth cervical to that of the fourth thoracic vertebra (C6-T4). In front, the point of bifurcation corresponds to the sternal angle. It’s a point where trachea bifurcates. G.LUFUKUJA

Landmarks… Esophagus.—The extent of the esophagus may be indicated on the back by a line from the sixth cervical to the level of the ninth thoracic spinous process (C6-T9), 2.5 cm. to the left of the middle line. G.LUFUKUJA

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Landmarks… Heart:-The apex of the heart is first determined, either by its pulsation or as a point in the fifth interspace, 9 cm. The position of the various orifices is as follows: The pulmonary orifice is situated in the upper angle of the third left sternocostal articulation; the aortic orifice is a little below and medial to this, close to the articulation. The left atrioventricular opening is opposite the fourth costal cartilage, and rather to the left of the midsternal line; the right atrioventricular opening is a little lower, opposite the fourth interspace of the right side. G.LUFUKUJA

G.LUFUKUJA

Structure of the Thoracic Wall 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. G.LUFUKUJA

Thoracic vertebra: Classification: They are 12 in number Typical thoracic vertebra: Second to Eight Atypical thoracic vertebra: First, Nine to Twelve G.LUFUKUJA

Features of typical thoracic vertebra: Body: It is heart shaped; Presence of two costal demifacets The transverse process: Tips bear oval costal facets Spinous process: Long and slopes downward G.LUFUKUJA

Features of typical thoracic vertebra… G.LUFUKUJA

Features of typical thoracic vertebra… G.LUFUKUJA

Atypical thoracic vertebra: First, Nine to Twelve have only a single pair of costal facets Atypical typical G.LUFUKUJA

Thorax… The framework of the walls of the thorax, which is referred to as the thoracic cage, is formed posteriory by the vertebral column, the ribs and intercostal spaces on either side, and the sternum and costal cartilages in front G.LUFUKUJA

Structure of the Thoracic Wall The thoracic wall is formed posteriorly by the thoracic part of the vertebral column; anteriorly by the sternum and costal cartilages; laterally by the ribs and intercostal spaces; superiorly by the suprapleural membrane; and inferiorly by the diaphragm, which separates the thoracic cavity from the abdominal cavity G.LUFUKUJA

Skeleton of the Thoracic Wall The thoracic skeleton includes 12 pairs of ribs and associated costal cartilages, 12 thoracic vertebrae and the intervertebral discs interposed between them, and the sternum. G.LUFUKUJA

Sternum The sternum lies in the midline of the anterior chest wall. It is a flat bone that can be divided into three parts: manubrium sterni, body of the sternum, and xiphoid process. G.LUFUKUJA

The manubrium The manubrium is the upper part of the sternum. It articulates with the body of the sternum at the manubriosternal joint, and it also articulates with the clavicles and with the first costal cartilage and the upper part of the second costal cartilages on each side. It lies opposite the third and fourth thoracic vertebrae G.LUFUKUJA

Applied anatomy Sternum and Marrow Biopsy Since the sternum possesses red hematopoietic marrow throughout life, it is a common site for marrow biopsy. Under a local anesthetic, a wide-bore needle is introduced into the marrow cavity through the anterior surface of the bone. The sternum may also be split at operation to allow the surgeon to gain easy access to the heart, great vessels, and thymus. G.LUFUKUJA

Ribs Ribs (L. costae) are the long curved, flat bones that form most of the thoracic cage G.LUFUKUJA

Ribs… There are three types of rib: True (vertebrocostal) ribs (1st to 7th ribs): They attach directly to the sternum through their own costal cartilages. False (vertebrochondral) ribs (8th, 9th, and usually 10th ribs): Their cartilages are connected to the cartilage of the rib above them; thus their connection with the sternum is indirect. Floating (vertebral, free) ribs (11th, 12th, and sometimes 10th ribs): The rudimentary cartilages of these ribs do not connect even indirectly with the sternum; instead they end in the posterior abdominal musculature. G.LUFUKUJA

Ribs… G.LUFUKUJA

Ribs… Typical ribs (3rd to 9th) have the following components: Head: wedge-shaped and has two facets Neck: connects the head with the body at the level of the tubercle Tubercle: at the junction of the neck and body and has a smooth articular part, for articulating with the corresponding transverse process of the vertebra Body (shaft): thin, flat, and curved, most markedly at the costal angle where the rib turns anterolaterally, the concave internal surface of the body has a costal groove paralleling the inferior border of the rib G.LUFUKUJA

Typical ribs (3rd to 9th) G.LUFUKUJA

Intercostal spaces Intercostal spaces separate the ribs and their costal cartilages from one another. There are 11 intercostal spaces and 11 intercostal nerves. Intercostal spaces are occupied by intercostal muscles and membranes, and two sets (main and collateral) of intercostal blood vessels and nerves, identified by the same number assigned to the space. The space below the 12th rib does not lie between ribs and thus is referred to as the subcostal space, and the anterior ramus of spinal nerve T12 is the subcostal nerve. G.LUFUKUJA

G.LUFUKUJA

Intercostal spaces The spaces between the ribs contain three muscles of respiration: the external intercostal, the internal intercostal, and the innermost intercostal muscle. The innermost intercostal muscle is lined internally by the endothoracic fascia, which is lined internally by the parietal pleura. The intercostal nerves and blood vessels run between the intermediate and deepest layers of muscles G.LUFUKUJA

Applied anatomy: Pleural effusion is excess fluid that accumulates between the two pleural layers, the fluid-filled space that surrounds the lungs. Excessive amounts of such fluid can impair breathing by limiting the expansion of the lungs during ventilation. Pleural tap G.LUFUKUJA

Applied Anatomy: Thoracentesis Sometimes it is necessary to insert a hypodermic needle through an intercostal space into the pleural cavity (thoracentesis) to obtain a sample of fluid or to remove blood or pus Inserting the needle into the 9th intercostal space in the midaxillary line during expiration will avoid the inferior border of the lung. G.LUFUKUJA

Intercostal muscles Action When the intercostal muscles contract, they all tend to pull the ribs nearer to one another. If the 1st rib is fixed by the contraction of the muscles in the root of the neck, namely, the scaleni muscles, the intercostal muscles raise the 2nd to the 12th ribs toward the first rib, as in inspiration. If, conversely, the 12th rib is fixed by the quadratus lumborum muscle and the oblique muscles of the abdomen, the 1st to the 11th ribs will be lowered by the contraction of the intercostal muscles, as in expiration. Nerve Supply The intercostal muscles are supplied by the corresponding intercostal nerves. G.LUFUKUJA

G.LUFUKUJA

Vasculature of the Thoracic Wall Arteries of the Thoracic Wall The arterial supply to the thoracic wall derives from the: Thoracic aorta, through the posterior intercostal and subcostal arteries. The internal thoracic arteries. Axillary artery, through the superior and lateral thoracic arteries G.LUFUKUJA

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Applied anatomy: Referred Pain An intercostal nerve not only supplies areas of skin, but also supplies the ribs, costal cartilages, intercostal muscles, and parietal pleura lining the intercostal space. Furthermore, the 7th to 11th intercostal nerves leave the thoracic wall and enter the anterior abdominal wall so that they, in addition, supply dermatomes on the anterior abdominal wall, muscles of the anterior abdominal wall, and parietal peritoneum. This latter fact is of great clinical importance because it means that disease in the thoracic wall may be revealed as pain in a dermatome that extends across the costal margin into the anterior abdominal wall. G.LUFUKUJA

Applied anatomy: Referred Pain For example, a pulmonary thromboembolism or a pneumonia with pleurisy involving the costal parietal pleura could give rise to abdominal pain and tenderness and rigidity of the abdominal musculature. The abdominal pain in these instances is called referred pain. Irritation of the mediastinal and central diaphragmatic areas of the parietal pleura results in pain that is referred to the root of the neck and over the shoulder G.LUFUKUJA

Lymph Drainage of the Thoracic Wall G.LUFUKUJA

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