Anatomy of Thoracic Wall and Diaphragm PDF

ANATOMY OF THORACIC WALL AND DIAPHRAGM DR. SAIMA TASNEEM Thorax Thorax (Latin) chest or breastplate Upper part of trunk of body. Supported by skeletal framework, thoracic cage. Thoracic cavity contains ❑Principal organs of respiration lungs ❑Principle organ of circulation, heart B...

ANATOMY OF THORACIC WALL AND DIAPHRAGM DR. SAIMA TASNEEM Thorax Thorax (Latin) chest or breastplate Upper part of trunk of body. Supported by skeletal framework, thoracic cage. Thoracic cavity contains ❑Principal organs of respiration lungs ❑Principle organ of circulation, heart Bony landmarks Suprasternal/jugular notch ❑Superior border of manubrium between sternal ends of clavicles. ❑Lies at level of lower border of body of T2. Trachea can be palpated here. Sternal angle/angle of Louis: ❑Transverse ridge approx. 5 cm below suprasternal notch. ❑Marks manubriosternal joint ❑Lies at level of 2nd costal cartilage ant., and the disc between T4 & T5 post. Bony landmarks Xiphisternal joint: Costal margin on each side is formed by 7th to 10th costal cartilages. Between these lies subcostal or infrasternal angle. Joint lies at level of upper border of T9. Ribs: Scapula overlies 2-7 ribs on posterolat. aspect of chest wall. 10th rib the lowest point, lies at 3rd lumbar vertebra level. 11th and 12th ribs are not seen from the front SIG. OF ANGLE OF LOUIS ✓Counting of ribs. 2nd costal cartilage and 2nd rib located at this level. ✓Separates sup mediastinum from inf mediastinum ✓Ascending aorta ends here, arch begins and ends here and descending aorta begins. ✓Trachea divides into 2 principle bronchi ✓Upper limit of base of heart. Soft Tissue Landmarks Nipple: Variable in females, in males in 4th IC space about 10 cm from midsternal line Apex beat: Visible & palpable cardiac impulse in left 5th IC space, 9 cm from the midsternal line/medial to midclavicular line. Trachea: Palpable in suprasternal notch midway between 2 clavicles. Midaxillary line: Passes vertically between 2 folds of axilla Scapular line: Passes vertically along inferior angle of scapula. Skeleton Of Thorax Osseocartilaginous elastic cage; increases and decreases intrathoracic pressure FORMATION OF THORACIC SKELETON Ant: sternum Post: 12 thoracic vertebrae and intervening intervertebral discs On each side by 12 ribs with their cartilages. Each rib articulates post. with vertebral column. Ribs (L. costae) Curved, flat bones, form most of the thoracic cage Light in weight & resilient. Spongy interior contains hematopoietic tissue Types of Ribs True (vertebrosternal) (1st–7th ribs): Attach directly to sternum through own costal cartilages. False (vertebrochondral) (8th, 9th, & 10th ribs): Cartilages are connected to the cartilage of the rib above, indirectly connected with sternum. Floating (vertebral, free) (11th, 12th ribs): Rudimentary cartilages do not connect even indirectly with the sternum  Features of Typical Ribs Head; wedge shaped, has 2 facets, separated by crest; 1 for articulation with corresponding vertebra other for superior vertebra Neck: connects head with body at level of tubercle. Tubercle: 2 parts Smooth articular part, at junction of neck and body (articulates with transverse process of corresponding vertebra); Rough non-articular part for attachment of costotransverse ligament Body (shaft): thin, flat, and curved, esp. at costal angle where the rib turns anterolat. Angle marks lat. limit of attachment of deep back muscles to ribs. Concave internal surface has costal groove along the inf. border and provides protection for the intercostal nerve and vessels. Features of Atypical Ribs 1st rib: body is widest horizontal, shortest, and most sharply curved. Single facet for articulation with T1 2 transverse grooves on sup. surface for subclavian vessels separated by a scalene tubercle and ridge (anterior scalene muscle is attached). Features of Atypical Ribs 2nd rib: ✓thinner, less curved ✓body, longer than 1st. ✓2 facets for articulation with T1 and T2; ✓rough area on upper surface, (tuberosity for serratus anterior, part of muscle originates). 10th–12th ribs: 1 facet on head. 11th and 12th ribs: short; no neck or tubercle. Costal cartilages Prolong ribs ant.; provide elasticity to thoracic wall, Cartilages in length through first 7 and then gradually. 1st 7 cartilages attach to sternum directly; 8th, 9th, and 10th articulate with cartilages sup. to them, forming a cont., cartilaginous costal margin 11th & 12th cartilages form caps on ant. ends of corresponding ribs and do not attach to any other bone or cartilage. Cartilages of 1–10 anchor the anterior end of the rib to the sternum, limiting its overall movement. Intercostal spaces Separate ribs & their costal cartilages. Named as per rib forming superior border of space, e.g., 4th intercostal space is b/w 4 and 5 ribs. 11 intercostal spaces and 11 intercostal nerves, occupied by intercostal muscles and membranes, and two sets (main and collateral) of intercostal blood vessels and nerves, (same no. as no. of space). Space below 12th rib isn’t between ribs; known as subcostal space, & ant. branch of T12 nerve is subcostal nerve. Spaces are widest anterolat. Spaces widen with inspiration and on contralateral extension and/or lateral flexion of the thoracic vertebral column. Thoracic Vertebrae Typical thoracic vertebrae; have bodies, vertebral arches, and seven processes for muscular and articular connections. Characteristic features include: Bilateral demifacets on bodies, in inferior and superior pairs, for articulation with ribs’ heads. Costal facets on transverse processes for articulation with ribs’ tubercles, except for the inferior 2 or 3 vertebrae. Spinous processes; long & inferiorly slanting. Thoracic Vertebrae Atypical thoracic vertebrae have whole facets instead of demi facets. Superior costal facets of T1 for head of 1st rib & inferior demi facet for cranial part of 2nd rib. T10 has one costal facet, located on body and its pedicle. T11 and T12 also have only 1 costal facet, located on pedicles. Sternum G. sternon, chest Flat, elongated bone that forms middle of ant. part of thoracic cage. Overlies and protects mediastinal viscera and much of the heart. Consists of three parts: Manubrium Body Xiphoid process Parts are connected together by cartilaginous joints (synchondroses) in young adults; ossify during middle to late adulthood.  Sternum Manubrium (L. handle) Trapezoidal shape. Widest and thickest Concave center (suprasternal notch), sternal ends of clavicles articulate with clavicular notches. Inferolat. to notch, cartilage of 1st rib is attached Manubrium and body lie in different planes superior and inferior to manubriosternal joint Sternum Body Long, narrow & thin Located at T5–T9 level 4 sternebrae (primordial segments) in young people articulating with each other at sternal synchondroses. In adults body has 3 transverse ridges representing lines of fusion (synostosis) of 4 originally separate sternebrae. Sternum Xiphoid process Smallest part; thin and elongated. Inf. end lies at T10 level. Cartilaginous in young people, ossified in adults older than 40. In elderly it may fuse with body. Landmark in the median plane, xiphisternal joint indicates inf. limit of central part of thoracic cavity; Joint is site of the infrasternal angle (subcostal angle) formed by the right and left costal margins Midline marker for the superior limit of the liver, the central tendon of the diaphragm, and the inferior border of the heart. Thoracic Apertures Thoracic cage is a complete wall peripherally but is open superiorly and inferiorly. Cone shaped. Smaller superior opening (aperture) allows communication with the neck and upper limbs. Larger inferior opening provides ring-like origin of diaphragm, which completely occludes the opening. Movements of the diaphragm control the volume/internal pressure of the thoracic cavity helping with air exchange. Sup Thoracic Aperture Post.: T1, the body of which protrudes anteriorly into the opening. Lat.: 1st pair of ribs and their costal cartilages. Ant.: sup. border of manubrium. Structures passing through Sup Thoracic Aperture Trachea Esophagus Nerves, and vessels supplying & draining the head, neck, and upper limbs. Adult aperture measures approx. 6.5 cm anteropost. and 11 cm transversely. Aperture slopes antero-inf. due to obliquity of the 1st pair of ribs. Inferior Thoracic Aperture Post.: by T12, the body of which protrudes anteriorly into the opening. Posterolat.: by 11th and 12th ribs. Anterolat.: joined costal cartilages of ribs 7–10, forming the costal margins. Ant: xiphisternal joint. Inferior Thoracic Aperture Diaphragm separates thoracic and abdominal cavities almost completely. Structures passing from the thorax to the abdomen, or vice versa, pass through openings that traverse the diaphragm (e.g., the esophagus and inferior vena cava) or pass posterior to it (e.g., the aorta). Diaphragm Thin muscular and tendinous septum that separates thorax & abdominal cavities. Pierced by structures that pass between the chest and the abdomen. Most important muscle of respiration. Dome shaped and consists of a peripheral muscular part, which arises from the margins of the thoracic opening, and a centrally placed tendon.  Origin of the diaphragm A sternal part arising from the posterior surface of the xiphoid process A costal part arising from the deep surfaces of the lower six ribs and their costal cartilages & forms the right & left domes A vertebral/lumbar part arising from upper three lumbar vertebrae; forms the right & left crura & the arcuate ligaments Shape of the Diaphragm It is studied as (a)Central tendon (b)Right & left crus (c)Right & left dome Insertion of the Diaphragm Inserted into a central tendon. Superior surface of tendon partially fused with inferior surface of fibrous pericardium. Some of fibers of right crus pass up to the left and surround the esophageal orifice in a slinglike loop. These fibers act as a sphincter and assist in the prevention of regurgitation of the stomach contents into the thoracic part of the esophagus.  Crura & Arcuate Ligaments Right Crus arises from the sides of the bodies of the L 1-3 & IV discs; Left crus arises from the sides of the bodies of the L 1-2 & IV disc. Lateral to the crura the diaphragm arises from the medial & lateral arcuate ligament. Medial arcuate ligament extends from the side of the body of L2 to the tip of the transverse process of L1. Lateral arcuate ligament extends from the tip of the transverse process of L1 to the lower border of the 12th rib. Medial borders of 2 crura are connected by a median arcuate ligament which crosses over the anterior surface of the aorta Functions of the Diaphragm Muscle of inspiration: On contraction the diaphragm pulls its central tendon down and increases the vertical diameter of the thorax. The diaphragm is the most important muscle used in inspiration. Muscle of abdominal straining: The contraction of the diaphragm assists the contraction of the muscles of the anterior abdominal wall in raising the intra- abdominal pressure for micturition, defecation, and parturition. Weight lifting muscle: In a person taking a deep breath and holding it (fixing the diaphragm), the diaphragm assists the muscles of the anterior abdominal wall in raising the intra-abdominal pressure. Before doing this make sure that a person have adequate sphincteric control of the bladder and anal canal under these circumstances. Thoracoaabdominal pump: The descent of the diaphragm decreases the intrathoracic pressure & increases the intra-abdominal pressure. This compresses the blood in the inferior vena cava and forces it upward into the right atrium of the heart. Within the abdomin lymph in vessels is also compressed, and its passage upward within the thoracic duct is aided by the negative intrathoracic pressure. The presence of valves within the thoracic duct prevents backflow. Openings in the Diaphragm The diaphragm has three main openings: The caval opening lies at the level of the T 8 vertebra in the central tendon. Inferior vena cava & branches of the right phrenic nerve. The esophageal opening lies at the level of the T 10 vertebra in a sling of muscle fibers derived from the right crus at the left of median plane. Esophagus, the right and left vagus nerves, the esophageal branches of the left gastric vessels, & the lymph vessels. The aortic opening lies anterior to the body of the T 12 vertebra between the crura. Aorta, thoracic duct, & azygos vein. Nerve Supply of the Diaphragm Motor nerve supply: The right and left phrenic nerves (C3, 4, 5) Sensory nerve supply: The parietal pleura and peritoneum covering the central surfaces of the diaphragm are from the phrenic nerve and the periphery of the diaphragm is from the lower six intercostal nerves.  Clinical Notes Hiccup Involuntary spasmodic contraction of diaphragm accompanied by approximation of vocal folds and closure of glottis of larynx. It is a common condition in normal individuals and occurs after eating or drinking as a result of gastric irritation of the vagus nerve endings. It may, however, be a symptom of disease such as pleurisy, peritonitis, pericarditis, or uremia. Paralysis of the Diaphragm A single dome of the diaphragm may be paralyzed by crushing or sectioning of the phrenic nerve in the neck. Occasionally, the contribution from the fifth cervical spinal nerve joins the phrenic nerve late as a branch from the nerve to the subclavius muscle. This is known as the accessory phrenic nerve. To obtain complete paralysis under these circumstances, the nerve to the subclavius muscle must also be sectioned. Penetrating Injuries of the Diaphragm Any penetrating wound to the chest below the level of the nipples should be suspected of causing damage to the diaphragm until proved otherwise. The arching domes of the diaphragm can reach the level of the fifth rib (the right dome can reach a higher level). Clinical Cervical rib: Rib attached to C7. Seen in about 0.5% of subjects Exerts traction on lower trunk of brachial plexus which arches over a cervical rib. Pt complains of paraesthesia or abnormal sensations along the ulnar border of the forearm, and wasting of the small muscles of the hand supplied by segment T1. Clinical In coarctation or narrowing of the aorta, the posterior intercostal arteries get enlarged greatly to provide a collateral circulation. Pressure of the enlarged arteries produces characteristic notching Clinical Thoracic cage injuries result from trauma and often involve rib fractures. Ribs 1, 11, and 12 are the least fractured ribs. Rib fractures may occur in a transverse plane or an oblique plane or at multiple sites on the same rib, resulting in a free floating segment (stove-in, or flail chest, injury). Pain is intense because of the continued expansion and contraction of the rib cage necessary during respiration Clinical Intercostals assist the diaphragm and, along with other accessory muscles of respiration (e.g., the scalene muscles), can become hypertrophied if a respiratory pathologic process occurs (e.g., in a chronic obstructive pulmonary disease such as emphysema). Chest trauma can lead to very painful breathing. Injection of a local anesthetic agent into the intercostal space (intercostal nerve block) can relieve this pain. Clinical Thoracic ventral rami (intercostal nerves) run in the costal groove at the inferior margin of each rib; physicians must be aware of this positioning when entering the intercostal space (for injections or chest tube placements) Thoracic outlet syndrome Caused by cervical rib or abnormal scalene muscle or first rib form Neurogenic Venous Arterial