ANATOMY OF THE THORAX THORACIC CAGE, THORACIC WALL & SURFACE ANATOMY DR. A.O.AJELETI OUTLINE • THORACIC CAGE • SKELETAL ARTICULATION • THE THORACIC VERTEBRAE • THE STERNUM • THE RIBS • MUSCELES OF THORACIC WALLS • THE THORACIC WALL VESSELS Learning objective • By the end of this lecture, students should be able to: • Know the types and apertures of thoracic skeleton • Know the thoracic skeletal arrangement and articulation • Have the knowledge of manubrium and clinical importance • Know the types of ribs and coastal joints. • Understand the thoracic wall muscles and vessels • Describe the clinical correlates. THORACIC CAGE • Thoracic skeleton consists of consists of 12 thoracic vertebrae, 12 pairs of ribs and coastal cartilages and the sternum • Upper Aperture is formed by the body of the 1st thoracic vertebrae, 1st rib, 1st cartilage and the upper sternum margin. • The lower aperture is formed by the lower 6 coastal cartilages and the 12th ribs, the xiphoid process in front and the body of the 12th thoracic vertebra behind. • The 11th rib is longer than the 12th rib even close to the iliac crest. THORACIC WALL & CAVITY • Thoracic cavity is kidney shaped on T/S because the ribs are carried backward beyond the vertebral bodies. • Diaphragm dome rises to 5th or 6th rib level so bony thorax protects the heart and lungs also the upper abdominal viscera: liver, stomach and spleen. TYPICAL THORAX SKELETAL ARTICULATION • The costovertebral articulations include the joints of the head of the rib with two adjacent vertebral bodies and the tubercle of the rib with the transverse process of a vertebra. • There are two articular facets on the head of the rib: a larger, inferior costal facet for articulation with the vertebral body of its own number, and a smaller, superior costal facet for articulation with the vertebral body of the vertebra superior to the rib. • The crest of the head of the rib separates the superior and inferior costal facets. • The smooth articular part of the tubercle of the rib, the transverse costal facet, articulates with the transverse process of the same numbered vertebra at the costotransverse joint. THORACIC VERTEBRAE – TYPICAL FEATURES THE BODY • The body has an upper and lower demifacet on each side for articulation with the head of ribs.(some bodies has only one). • Middle thoracic bodies are heart-shaped making thoracic portion of the vertebral column concave forward. TRANSVERSE PROCESSES • Act as buttress. • They are stout and conform with the backward sweep of the ribs, having on their tips facets for the tubercles of the ribs. • The transverse process become progressively shorter from 1st to the 12th. SPINOUS PROCESS (SPINES) • Intermediate four (5,6,7and 8) are long and vertical. • Those above and below are progressively more horizontal. ARTICULAR PROCESSES • They are set almost vertically on the arc of a circle. • They cause rotary movement between adjacent thoracic vertebrae. • Superior articular facets faces posterolaterally and inferior is anteromedially. VERTEBRAL FORAMEN • Small and circular. INFERIOR VERTEBRL NOTCHES • They are large. • The superior ones are absent. TRANSITION • Thoracic vertebrae from the middle up and down assume characteristics of cervical and lumbar vertebrae. • Th. 1 is very much like C7 and Th. 12 is like L. 1. STERNUM • A breast bone, likened to a broad sword. • It is composed of 3 parts: • Manubrium • Corpus sterni or body • Xiphoid process. STERNUM MANUBRIUM • Very thick concave border called jugular notch. • Much deepened by the proximal sternal ends of the clavicles. • Below the clavicle is the 1st costal cartilage joining the manubrium to the rib by synochondrosis. • Manubrium is 5cm long. • Upper border lies at the level of Th.2 lower border. • Its lower border articulates with the body at sternal angle. MANUBRIUM • Very thick concave border called jugular notch, readily palpated at the root of the neck. • Has a clavicular notch on each side for articulation with the clavicle. • Manubrium is 5cm long. • Also articulates with the cartilage of the first rib, the upper half of the second rib, and the body of the sternum at the manubriosternal joint, or sternal angle. Sternal Angle (Angle of Louis) • This is the junction between the manubrium and the body of the sternum. • It’s located at the level where: • The second ribs articulate with the sternum. • The aortic arch begins and ends. • The trachea bifurcates into the right and left bronchi at the carina. • The inferior border of the superior mediastinum is demarcated. • A transverse plane can pass through the intervertebral disk between T4 and T5. BODY OF THE STERNUM • It is composed of 4 fused pieces or sternebrae. • It is slightly more than twice the length of the manubrium. • Articulates with the second to seventh costal cartilages. • The 2nd rib cartilage articulates in a notch on the side of the sternal angle. • The 7th cartilage articulate with the angle between the body and the front of the xiphoid. • The symphysis joint type of the manubriosternal joint affords hinge-like movements of the body of the sternum forward and backward. • Xiphisternal joint is at level with the ninth thoracic vertebra. THE XIPHOID PROCESS. • Is a flat, cartilaginous process at birth that ossifies slowly from the central core and unites with the body of the sternum after middle age. • Lies at the level of T10 vertebra, and the xiphisternal joint lies at the level of the T9 vertebral body, which marks the lower limit of the thoracic cavity in front, the upper surface of the liver, diaphragm, and lower border of the heart. • It descends a variable distance downward to the posterior wall of the sheath of the rectus abdominis. • Its half as thick the body of the sternum and posteriorly flush with the posterior surface of the body. STERNUM –CLINICAL CORRELATES • Bone marrow biopsy • Sternotomy. USEFUL LANDMARKS • Vertebral level of: • Jugular notch – 2nd thoracic • Sternal angle – 4th thoracic • Xiphisternal joint – 8th+ thoracic POSTERIOR MUSCLES ATTACHMENT & RELATIONS • MANUBRIUM: Sternothyroid Sternohyoid - Neck muscles • BODY: Transversus Thoracis • XIPHOID PROCESS: Diaphragm POSTERIOR RELATIONS: • Pleura and lungs, heart and great vessels, thymus. ANOMALY THE RIBS • A rib bone and its cartilages constitute a costa. • There are 12 pairs of costae. • Every rib articulates posteriorly with the vertebral column. • They are in 3 classes: • True or Vertebrosternal ribs: The cartilages of the upper 7 pairs of ribs articulate directly with the sternum. • Vertebrochondral ribs: the cartilages of 8th, 9thand 10th articulate each with the costal cartilage above it. • Floating or Vertebral ribs: The cartilaginous end of the last pairs- 11th & 12th are free. • Classes 2 & 3 are also called false ribs. • Ribs are flattened ,a very thin outer compact layer and highly resilient. • The 1st rib is the highest , strongest, flattest and most curved ribs. RIBS TYPICAL COMPARING TYPICAL WITH ATYPICAL CHEST WALL SKELETAL STRUCTURE WOMAN MAN THE RIBS (CONTD) • Typical rib consists of: • BODY: Internal and external surfaces, superior or inferior borders; an angle and a costal groove. • The body posterior ¼ is cylindrical and anterior ¾ is compressed. • VERTEBRAL END: Head, neck and tubercle. • STERNAL END: Pit for costal cartilage. COSTAL JOINTS – HEAD OF A RIB • The head of a rib articulates with the sides of the bodies of the 2 vertebrae. • The tubercle of a rib articulates with tip of a transverse process. • The costal cartilage articulate with the sides of 2 sternebrae. ANOMALIES • BIFID • BICIPITAL COSTAL JOINTS- Costovertebral articulation: • Joint of the head of the rib. • Joint of the tubercle of a rib. • The head of each typical rib (2nd – 10th) articulates with the demifacet of 2 adjacent vertebrae and with the intervertebral disc between them. • Attachment to the intervertebral disc is by the intra-articular ligament. • Ribs 1, (10), 11 and 12 heads are confined to single vertebrae, are rounded and have no intra- articular ligament. • Sternocostal articulation: Each joint cavity is divided into 2 by intra-articular ligarment, it is closed ventrally by a ligament that radiates from the perichondrium to the sternum. • Interchondral articulation: Except for the 12th cartilage, the lower cartilages form joint – synovial or fibrous, or complete union with each other. TUBERCLE OF A RIB • The tubercle of a rib articulates with the facet at the tip of the transverse process of its own vertebra (except 11 and 12) to form a synovial joint called a costotransverse joint. • The ligamentous fibers are divided into medial and lateral group. • Medial costotransverse ligament for ligament of the neck and lateral costotransverse ligament for the ligament of the tubercle. • Another band of superior costotransverse descend from a transverse process to the upper border of the of the rib next below, producing a sharp crest of the neck. ANGLE OF THE RIB • Vertical insertion of the iliocostalis are at most backwardly projecting part of the outer surface of the ribs. • Anterior to this, the ribs are twisted downward, forward, and medially. MUSCLES OF THORACIC WALL ABDOMINAL THORACIC • External Oblique External Intercostal • Internal Oblique Internal Intercostal Nerves and Vessels in the Interval Innermost Intercostal • Transversus abdominis Subcostals Transversus thoracics Intercostal Nerves • Anterior primary rami of the first 11 thoracic spinal nerves. • Subcostal nerve: This is the anterior primary ramus of the 12th thoracic spinal nerve which runs beneath the 12th rib. • Run between the internal and innermost layers of muscles, with the intercostal veins and arteries above (veins, arteries, nerves [VAN]). • Give rise to lateral and anterior cutaneous branches and muscular branches. • Lateral cutaneous branch is the largest of the branches is the which pierces the lateral thoracic wall and divides into an anterior branch and a posterior branch that innervate the overlying skin. THORACIC WALL ARTERIES . THE INTERNAL THORACIC ARTERY (INTERNAL MAMMARY A.) • It is a branch of the Subclavian artery, descend from the sternum behind the upper 6 costal cartilages.