Anatomy of the Thoracic Wall PDF

Anatomy of the Thoracic Wall Sheila Nunn Professor of Anatomy Email: [email protected] Please email me any questions or to set up a 1:1 TEAMS meeting  Objectives: On completion of this session, and any further necessary study...

Anatomy of the Thoracic Wall Sheila Nunn Professor of Anatomy Email: [email protected] Please email me any questions or to set up a 1:1 TEAMS meeting  Objectives: On completion of this session, and any further necessary study you should be able to: Describe the general morphology of the thoracic wall Name the location of the major surface anatomical landmarks and the anatomical reference planes Translate the location of the major surface anatomical landmarks and the anatomical reference planes to the underlying structures and their use in clinical procedures. Describe the boundaries and features of the superior & inferior thoracic apertures Categorize the different types of ribs (i.e., true, false and floating ribs) Locate the three parts of the sternum and the articulation sites for the costal cartilages Arrange the muscles of the thoracic wall from superficial to deep State the different movements associated with the thoracic wall. Describe the role of muscles in movements of the thoracic wall Summarize the neurovasculature of the thoracic wall Identify the neurovasculature of the thoracic wall in situ Explain the segmental innervation of the thoracic wall.  Objectives Continued Describe the endothoracic fascia layer Explain the surgical significance of the endothoracic fascial layer Relate the anatomical details to these clinical conditions: congenital thoracic wall deformities, supernumerary ribs, rib fractures and flail chest, sternal fractures, Relate the anatomical details to these clinical conditions: thoracentesis/thoracocentesis/pleural tap, & chest tube procedures  Thoracic Cavity The thoracic cavity is divided into three compartments: Cavity Structures Two Lateral Pleural cavities Lungs (respiratory module) One Central Mediastinum Many, including thymus, heart, pericardium, great vessels, trachea, esophagus, thoracic duct, azygos venous system Anterior Transverse coronal Section. section Superior view.  Thoracic Wall Reference Planes Based on palpable (superficial) anatomical landmarks Facilitate anatomical & clinical description of structures & procedures (see later in thorax lectures for examples) Link to information and procedures carried out in your clinical skills lab (physical examination of MSK, respiratory and cardiovascular systems (sem 1)  V Thoracic Wall Skeleton S 1. 12 pairs of ribs and their costal cartilages (CC) CC 2. Sternum (S) S 3. 12 Thoracic vertebrae (V) CC 4. Joints of the thoracic wall S Link to your Osteology Directed Self-Learning  Thoracic Apertures Superior Thoracic Aperture (STA): STA Anatomically → thoracic inlet manubrium Clinically → thoracic outlet Boundaries: T1 vertebra 1st rib & costal cartilages Superior border of the manubrium. Inferior Thoracic Aperture (ITA): Xiphisternal joint ITA 7th-10th costal cartilage 11th & 12th ribs T12 vertebra Inferior thoracic aperture is covered by the diaphragm and is mobile Typical Thoracic Vertebrae Heart-shaped vertebral body, long spinous process Typical vertebrae has three facets on each side for articulation with the ribs; two demi-facets and transverse costal facet Note not all vertebrae articulate with ribs in the same fashion Articulation Between a Rib and Typical Vertebrae The tubercle of a rib articulates with the transverse process of the vertebra of the same number. At the costotransverse joint The head of the rib is the part of the rib that articulates with the demifacets of two adjacent vertebral bodies. So, the head of rib 5 should articulate with the 4th vertebra at inferior costal facet superiorly and the 5th vertebra inferiorly at superior costal facet. These occur at the Costovertebral joint Note students tend to do poorly on this concept in lab and MCQ assessments! Make sure you practice this in lab I. Three Types of Ribs Based on their articulation with the sternum True ribs 1st - 7th → Connect to the sternum via costal cartilages Costal False ribs 8th- 10th → Connect to the costal cartilage cartilages of the ribs directly above them Floating ribs No connection with 11th and 12th → sternum; terminate in the posterior abdominal muscles Important landmarks: 2nd rib articulates with the sternum at the sternal angle (of Louis) 7th rib articulates with the sternum at the xiphisternal joint  Can be Further Classed as Typical or Atypical Left Typical Rib TYPICAL RIBS: Ribs 3 – 9 Head. Wedge-shaped with two facets that articulate with corresponding vertebral bodies. Neck. Connects the head with the body near the tubercle. Tubercle. Smooth articular portion that articulates with the transverse process of the corresponding vertebra. the costotransverse joint. Body or shaft of the rib is flat, thin and curved.  Typical Rib The curved portion of the body of the rib is most evident at the costal angle. The weakest point of the rib is just anterior to the costal angle, and this serves as the most common site for rib fractures The costal groove is located on the inferior border of the rib, and it is where the intercostal neurovasculature runs Costal cartilages. Anterior extensions of the ribs and contribute to the elasticity of the thoracic wall  Atypical Rib One way to remember which ribs are atypical are that they have the digits "1" or "2" in them. Thus, ribs "1, 2, 10 ,11, 12" are atypical. The 1st rib is the shortest, broadest and has the sharpest curve of the true ribs. It has a groove on its superior surface for both the subclavian vein and artery. The grooves are separated by the scalene tubercle, which is the attachment site for the anterior scalene muscle.  Atypical Rib The 2nd rib is thinner and less curved but much longer than the 1st rib. The tuberosity of the serratus anterior muscle is located approximately in the middle of the body region and acts as an attachment site for this muscle. The 11th and 12th ribs only have one facet at the head region and thus only articulate with the 11th and 12th vertebrae individually and respectively. The 11th and 12th ribs are also short and have no neck or tubercles.  Clinical Relevance: Supernumerary Ribs 1. Cervical Ribs: About 0.5 - 2% of population have a cervical rib Can be unilateral or bilateral Associated with Thoracic Outlet Syndrome which can result in compression of the neurovascular structures exiting or entering the Superior Thoracic Aperture (covered in more detail in head and neck lectures in semester 5) Can lead to confusion of the vertebral levels in diagnostic images  2. Lumbar Ribs Found in < 1% of population Rudimentary rib articulating with the transverse process of the first lumbar vertebra Can also be called the 13th ribs; Can be unilateral or bilateral Not usually associated with any problems  Clinical Relevance: Flail chest A life-threatening unstable injury of the thoracic wall Multiple ribs fractures detach part of the thoracic wall from the rib cage. The detached part is subjected to unopposed intra-pleural pressure Segment is sucked in by negative pressure resulting in paradoxical motion seen during the breathing cycle. https://www.youtube.com/watch?v=5Qi Qj8cBsAA Segment pushed out by positive pressure  Sternum: Forms the anterior part of the thoracic cage Protects the Superior Mediastinal structures Three parts: Costal notches 1. Manubrium Anter Broad quadrangular superior part of the sternum Articulates with clavicle at the sternoclavicular joint Manubriosternal joint ( Sternal angle or Angle of Louis) =140)° Anterior view 2. Body Lateral costal notches (attachments for 2nd –7th ribs) 3. Xiphoid Process Costal Corresponds to T10 vertebral body notches Xiphisternal joint: marks the inferior Anter limit of the heart, central thoracic cavity, superior limit of the liver & the anterior attachment of the diaphragm Anterior view Right Lateral view  Congenital Thoracic Wall Deformities Link to Clinical Skills Lab: Physical Examination Respiratory System (Sem 1) I. Pectus excavatum: Concave depression. Causes: Intrauterine pressure on the chest wall during development. Complications: Compression of heart & lungs Treatment: surgical II. Pectus carinatum: Protrusion of the sternum and costal cartilages Causes: A disorder of the cartilage that joins the ribs to the sternum Complications: May include scoliosis and congenital heart disease. Treatment: Brace worn around the chest and provides pressure from both the front and back to move the breastbone back to its usual position. The individual wears the brace for up to 24 hours a day, for a period of months to years. Surgery is an alternative..  Clinical Relevance: Sternum I. Sternal fracture: The majority of sternal fractures result from blunt trauma Most common location of the fracture is in the manubrium or body In many cases, there is an underlying organ injury. Heart and lung contusion, damage to superior mediastinal structures as well as rib fractures, are not uncommon with sternal fractures  II. Xiphoid process fracture: Damage can occur from incorrect cardiopulmonary resuscitation (CPR) or resuscitation with too much force Also, from contact sports Potentially leading to punctures or lacerations of the diaphragm: because xiphisternal joint forms the anterior attachment of diaphragm Broken pieces can puncture the heart or liver Thoracic Wall Musculature 1) Extrinsic muscles: Stabilizes and moves the pectoral girdle, upper limbs and neck e.g., pectorals, rhomboids, scalene muscles p.minor These were covered in back sessions in semester 2. Can be tested again in this course! 2) Intrinsic muscles (Intercostal Muscles: → between the ribs) Three groups of muscles 1. External intercostal mm. 2. Internal intercostal mm. 3. Innermost intercostal mm. As described previously, the neurovascular bundle runs between internal & innermost intercostal muscles Intercostal muscles are served by the corresponding intercostal nerves and vessels  Intercostal Muscles i. External intercostal muscles: Span from the rib tubercles to the costochondral junction Muscle fibers run inferoanteriorly from rib above to the Lateral view. rib below (“hands in pocket” orientation) Thorax Right hand side ii. Internal intercostal muscles: Span from the sternum to the angle of ribs Muscle fibers run inferiorposteriorly Run deep and right angled to the external intercostal m. fibers iii. Innermost intercostal muscles Lateral view. Thorax Right hand side Occupy lateral most part of the intercostal spaces Muscle fibers run inferiorposteriorly Separated by the intercostal neurovascular structures  Intercostal Muscles Muscle fibers eim External intercostal muscle fibers are replaced by a membrane anteriorly where membrane is located Internal intercostal muscle where membrane is located Internal intercostal muscle fibers are replaced by a membrane posteriorly In this image on the right side the external Intercostal membrane (eim) has been removed so you can see the underlying Internal Intercostal muscle Muscle fibers On the left-hand side, the external Intercostal membrane is still intact  Lateral Thoracic view muscles in Rib Intercostal nerve transverse section Costal angle Location of intercostal neurovascular bundle internal intercostal External intercostal membrane Innermost Internal intercostal intercostal Thoracic Wall Movements During Breathing Thoracic wall movements causes changes in intrathoracic volume and pressure Lungs move with the thoracic wall This allows air to get in and out of the lungs  Three Main Movements in Quiet Inspiration to Increase Thoracic Volume: I. Anteroposterior dimension: Primarily involves 2nd – 6th ribs II. Lateral dimension: Primarily involves 7th – 10th ribs III.Superior-inferior (vertical) dimension: As the diaphragm contracts its dome flattens. Note In quiet expiration the diaphragm relaxes and lung tissue recoils resulting in the expulsion of air  Accessory Muscles of Respiration During Forced Respiration when there is an increased demand for oxygen, e.g., in exercise or disease, accessory muscles of respiration are used During forced inspiration, muscles of the neck, including the scalenes, contract and lift the thoracic wall, increasing lung volume. During forced expiration, accessory muscles of the abdomen, including the obliques, contract, forcing abdominal organs upward against the diaphragm These muscles can be seen hard at work in patients with respiratory distress e.g., acute asthma, C.O.P.D. or in athletes at the end of a hard race  Intercostal Arteries and Veins The intercostal arteries are arranged in two groups, anterior and posterior. The anterior intercostal arteries are branches of the internal thoracic (upper six spaces) and musculophrenic (seventh to ninth spaces) arteries. Musculophrenic & Superior epigastric arteries are terminal branches of the internal thoracic artery. There are no 10th or 11th anterior intercostal arteries. Only posterior intercostal arteries  The posterior intercostal arteries are branches of the superior (also known as supreme)intercostal artery (upper two spaces) and the descending aorta (lower nine spaces). This is relevant in the collateral circulation associated with coarctation of the aorta (see superior and posterior mediastinum lecture) They supply the chest wall, parietal pleura, and, through their dorsal branches, the skin and muscles of the back and the spine and its contents  The anterior and posterior intercostal arteries anastomose around the midclavicular line. However, the anterior and posterior intercostal veins anastomose as they approach the vertebral column LOCATION OF ANASTOMOSIS OF ANT AND POST INTERCOSTAL ARTERIES LOCATION OF ANASTOMOSIS OF ANT AND POST INTERCOSTAL ARTERIES  Please note in some textbooks and images you may read about or see the smaller (collateral) branches of the anterior intercostal arteries descends into the lower aspect of their respective intercostal space and courses laterally. Here they are not offered protection by the rib above  Subclavian v. Intercostal Veins Brachiocephalic v. Internal thoracic vein. Intercostal veins accompany the H arteries and nerves Azygos system. A Lie immediately & superiorly along the H costal grooves) (VAN) 11 posterior on each side Most posterior intercostal veins (4 - 11) drain into the azygos/hemiazygos system and then into the SVC Anterior intercostal veins drain into the internal thoracic vein Thoracic cage with organs removed  Intercostal Nerves Intercostal nerves are the anterior (ventral) rami of the first 11 thoracic spinal nerves; the anterior ramus of the twelfth thoracic nerve lies in the abdomen as the subcostal nerve Each intercostal nerve enters the corresponding intercostal space between the posterior intercostal membrane and the parietal pleura.  Thoracic Wall Dermatomes T4 Nipple area T6 T8 T10 Strip-like segmental innervation of thoracic wall by the intercostal nerves.  Intercostal Nerve Block (ICNB) As shown in previous slide, the intercostal nerves (ICNs) innervate the major parts of the skin and musculature of the chest and abdominal wall ICNB provides excellent analgesia in patients with rib fractures and for postsurgical pain after chest and upper abdominal surgery such as thoracotomy, thoracostomy, mastectomy, gastrostomy, and cholecystectomy An intercostal nerve block is an injection of an anesthetic and/or steroid into this nerve to help relieve pain Injection is made proximal to the midaxillary line before the origin of lateral cutaneous branches  Layers of the Thoracic Wall (superficial to deep): 1 Skin 2 Superficial fascia 3 Intercostal muscles: i) External mm Superior edge ii) Internal mm iii) Innermost mm 4 Endothoracic fascia 5 Parietal pleura 6 Pleural space * *Visceral pleura which covers the lungs is not part of the thoracic wall layers Endothoracic fascia Inferior edge  Endothoracic fascia A loose connective tissue that separates the inner surface of the thoracic wall and the parietal pleura (acts like glue between the parietal pleura and thoracic wall) Sibson’s fascia: thickened endothoracic fascia above the 1st rib to C7 transverse process (covers the apex of lung, which is prone to injuries). Clinical Relevance: Extrapleural Intrathoracic Surgical Access Endothoracic fascia forms an important natural cleavage plane for surgical separation of parietal pleura from thoracic wall  Thoracentesis /Thoracocentesis /Pleural tap/Pleural Fluid Analysis Inserting a needle into the pleural cavity to obtain samples of fluids Needle inserted midway within the intercostal spaces to avoid damaging the nerves (intercostals & collateral branches) The needle is angled upward to avoid injuring the diaphragmatic pleura and the diaphragm When patient is in the upright position, fluid accumulates in the costodiaphragmatic recess. Inserting the needle into the 8th/9th intercostal space midaxillary line during expiration will the avoid inferior border of lung  Clinical Relevance: Chest tube / Chest drain Function to REMOVE EXCESS fluid, blood, fluid, pus or air Ideal sites 5th or 6th intercostal space (at nipple line) along the midaxillary line (below this level can potentially damage the diaphragm) Fluid removal: tube directed inferiorly towards the costodiaphragmatic recess. Air removal: tube directed superiorly towards the cervical pleura. Ideal site: 5th or 6th intercostal space within the “safe triangle”