Thorax: Thoracic Cage, Wall, Boundaries, and Surface Anatomy PDF

Thorax: thoracic cage, wall, boundaries and surface anatomy Dr. Malak Alghamdi Assistant Professor of Anatomy [email protected] 20/8/2024  Lecture Objectives Describe structures forming the thoracic wall and their organization (bo...

Thorax: thoracic cage, wall, boundaries and surface anatomy Dr. Malak Alghamdi Assistant Professor of Anatomy [email protected] 20/8/2024  Lecture Objectives Describe structures forming the thoracic wall and their organization (bones + muscles) Describe relevance of structure of the thorax to the mechanism of gas exchange Describe the blood supply and innervation of the structures of the thoracic wall Describe the diaphragm (structure, attachments, openings, blood supply, lymphatic, and innervation) List some common clinical problems relevant to the structures of the thoracic cavity Overview  Overview Thoracic cavity enclosed by thoracic wall Subdivided into 3 major compartments: – Lt & Rt pleural cavities à each surrounding lung – Mediastinum à heart, esophagus, trachea, major nerves, and major systemic blood vessels Functions: – Breathing – Protection of vital organs – Conduit – Support for bones of ULs Thoracic wall  Thoracic wall Consists of skeletal elements and muscles Skeletal cage is flattened from front to back and rounded at sides Formed by – Posteriorly: 12 thoracic vertebrae and their intervening intervertebral discs – Laterally: ribs (twelve on each side) and three layers of flat muscles – Anteriorly: costal cartilages and sternum Skeleton of thoracic wall Thoracic vertebrae Thoracic vertebrae  Thoracic vertebrae Thoracic vertebrae consist of vertebral body, vertebral arch, and 7 processes Vertebral body: anterior, increases in size from vertebra T1 – T12, fibrocartilaginous intervertebral discs separate vertebral bodies of adjacent vertebrae Vertebral arch: posterior to vertebral body, consists of two (right and left) pedicles and laminae – Pedicles: short cylindrical processes that project posteriorly from vertebral body – Laminae: two broad, flat plates of bone that meet pedicles & unite in midline Seven processes arise from vertebral arch of typical vertebra – 1 median spinous process projects posteriorly and inferiorly from at the junction of laminae – 2 transverse processes project posterolaterally from the junctions of the pedicles and laminae – 4 articular processes: two superior and two inferior arise from the junctions of the pedicles and laminae  Typical thoracic vertebrae Costal facets: Two demifacets located on superior and inferior aspects of the body à articulate with heads of adjacent ribs superior costal facet articulates with part of head of its own rib inferior costal facet T4 articulates with part of the head of the rib below. 5 T5 An oval facet (transverse costal facet) at the end of the transverse process articulates with the tubercle of its own rib Atypical thoracic vertebrae T1 T9 T10 T11 T12  Atypical thoracic vertebrae TI T1 – Has a long, almost horizontal spinous process – Complete superior costal facets on the body TIX – Lack inferior demifacets on the body TX, TXI and TXII T9 – Have a single complete facet on each side T10 of their bodies T11 – Lack inferior demifacets on their bodies T12 – TXI & TXII lack transverse costal facets  Ribs 12 pairs of ribs attached posteriorly to thoracic vertebrae 1. True ribs: 1-7 attached anteriorly to sternum by their costal cartilages 2. False ribs: 8-10 attached anteriorly to costal cartilage of 7th rib 3. Floating ribs: 11 & 12 have no anterior attachment The length of ribs Increase from ribs 1-7, thereafter decreasing The Intercostal spaces contain intercostal muscles Typical Ribs  Typical Ribs Consists of curved shaft with anterior and posterior ends. Anterior end is continuous with its corresponding costal cartilage. Posterior end articulates with vertebral column and characterized by: Head which presents two articular surfaces separated by crest Neck is short flat region of bone that separates head from tubercle Tubercle projects posteriorly between neck and shaft and consists of two regions: Articular part: medial, has oval facet for articulation with corresponding transverse costal facet Nonarticular part: roughened by ligament attachments Shaft: thin and flat, with internal and external surfaces. It bends forward at a site termed angle Its inferior margin marked by costal groove, which accommodates intercostal vessels and nerve  Atypical Ribs (first two + last three) Rib 1 shorter and wider than other ribs. has one facet on its head for articulation with its T1 Rib 2 has roughened area on its upper surface (tuberosity for serratus anterior) Rib 10 has only one facet for articulation with T10 Ribs 11&12 short and have no neck or tubercles, contain one facet for articulation with their corresponding vertebrae (T11 & 12) Sternum  Sternum Manubrium – Jugular (suprasternal) notch (T2-T3) – Fossa for articulation with clavicle – Facet for articulation with 1st costal cartilage – Demifacet for articulation with 2nd costal cartilage Body – Sternal angle (T4&T5) – Demifacet for articulation with 2nd costal cartilage – Facets for articulation with 3rd -6th costal cartilages – Demifacet for articulation with 7th costal cartilage Xiphoid – Demifacet for articulation with 7th costal cartilage  Intercostal Spaces Between successive ribs Contain 3 intercostal mm.: external, internal, innermost Neurovascular bundle runs superficial to innermost intercostal m., and arranged from superior to inferior as vein, artery, and nerve (VAN) Intercostal Muscles  Superior Muscle Inferior attachment Innervation Function attachment Most active during inspiration; Inferior margin of Superior margin of Intercostal nerves; External intercostal supports intercostal rib above rib below T1–T11 space; moves ribs superiorly Superior margin of Most active during Lateral edge of rib below deep to Intercostal nerves; expiration; supports Internal intercostal costal groove of rib the attachment of T1–T11 intercostal space; above the related external moves ribs inferiorly intercostal Medial edge of Internal aspect of Innermost Intercostal nerves; Acts with internal costal groove of rib superior margin of intercostal T1–T11 intercostal muscles above rib below Internal surface Internal surface of Related intercostal Subcostales (near angle) of second or third rib May depress ribs nerves lower ribs below Inferior aspect of Inferior margins and deep surface of Related internal surfaces of body of sternum, Depresses costal Transversus thoracis intercostal costal cartilages of xiphoid process, cartilages second to sixth ribs and costal cartilages nerves of ribs IV–VII Mechanism of gas exchange  Arteries of Thoracic Wall Posterior intercostal aa. § 1st & 2nd posterior intercostal aa.: o from 2nd part of supclavian a. à costocervical trunk à superior intercostal a. à § 3rd – 12th posterior intercostal aa.: o Descending thoracic aorta à § Aa. on right side longer than those on left side  Arteries of Thoracic Wall Anterior intercostal aa. Subclavian § 1st – 6th anterior intercostal aa.: Internal thoracic o 1st part of subclavian a. à internal thoracic a § 7th – 12th anterior intercostal aa.: Musculophrenic o Internal thoracic a. à musculophrenic a. à  Veins of Thoracic Wall Posterior intercostal veins – Drain into the azygos, hemiazygos, & accessory T5-T6 hemiazygos veins Anterior intercostal T7-T8 veins – Follow the corresponding aa. (internal intercostal and musculophrenic vv.)  Nerves of Thoracic Wall Anterior rami of thoracic spinal nerves – 1-11 intercostal nerves 1-6 supply only thoracic wall 7-11 supply abdomen and peritoneum – 12 subcostal nerve abdominal wall  Branches of the intercostal nerves Lateral cutaneous branch Anterior cutaneous branch Rami communicants Collateral branch Muscular branches Pleural sensory branches Peritoneal sensory branches (6-11)  Diaphragm Large, dome-shaped muscle consists of peripheral muscular part and centrally placed tendon separates thoracic cavity from abdominal cavity From front, it curves up into right (higher) and left domes Attachment of diaphragm Sternal: posterior surface of xiphoid process Costal: lower six ribs and their costal cartilages Vertebral: – Right crus: bodies of L1-L3 – Left crus: bodies of L1-L2 Arcuate ligaments – Median: connects crura anterior to aorta – Medial: L2 body to transverse process of L1 – Lateral: transverse process of L1 to 12th rib Openings in the Diaphragm Aortic opening- T12 – Between crura – Content Aorta, thoracic duct, & azygos vein Esophageal opening- T10 – In sling of muscle fibers derived from right crus – Content Esophagus, vagi, BVs & lymphatic vessels Caval opening- T8 – Content IVC, branches of right phrenic nerve Other structures pass the diaphragm – Splanchnic nerves – through crura – Sympathetic trunk – medial arcuate lig. – Superior epigastric vessels – between sternal & costal origins – Subcostal nerve – lateral arcuate lig.  Diaphragm Innervation Motor – right and left phrenic nerves (C3-C5) Sensory – Centrally – phrenic nerves – Peripherally – intercostal nerves (T7-T12) Diaphragm: Blood Supply  Clinical problems Dislocation of Sternocostal and Interchondral Joints displacement of costal cartilage from sternum Usually unilaterally and involves ribs 8-10 Trauma sufficient to displace these joints often injures underlying structures such as diaphragm and/or liver, causing severe pain, particularly during deep inspiratory movements Rib dislocations are common in body contact sports, and complications may result from pressure on or damage to nearby nerves, blood vessels, and muscles  Clinical problems Flail Chest Multiple rib fractures may allow segment of the anterior and/or lateral thoracic wall to move freely but paradoxically (inward on inspiration and outward on expiration) extremely painful injury and impairs ventilation thereby affecting oxygenation of blood  Clinical problems Sternal Fracture Can occur after traumatic compression of thoracic wall, e.g. in automobile accidents Displacement of bone fragments is uncommon – sternum is invested by deep fascia – sternal attachments of pectoralis major muscles Sternal angle is most common site of sternal fracture in elderly people Sternal injuries might accompany heart injury and/or lung injury Mortality associated with sternal fractures is 25–45%, largely owing to these underlying injuries  Clinical problems Ossified Xiphoid Processes Many people in their early 40s suddenly become aware of their partly ossified xiphoid process and consult their physician about the hard lump in the “pit of their stomach” (epigastric fossa). Never having been aware of their xiphoid process before, they fear they have developed a tumor  Clinical problems Paralysis of Diaphragm Paralysis of one half because of injury to its motor supply from the phrenic nerve does not affect the other half One can detect the paralysis of the diaphragm by noting its paradoxical movement – It ascend during inspiration and descend in expiration  References Richard Drake, A. Wayne Vogl, and Adam W. M. Mitchell (2019). Gray’s anatomy for students 4th edition. Elsevier. Keith L. Moore, Arthur F. Dalley, Anne M. Agur, Clinically Oriented Anatomy, Lippincott Williams & Wilkins Richard S Snell, Clinical Anatomy by Systems, Lippincott Williams & Wilkins