Thoracic Wall Anatomy PDF 2024

Thoracic Wall Prof. Iman Abdel Aal 1. Describe the origin, insertion, nerve supply and action (s) of the intercostal muscles. 2. Interpret the mechanics of respiration & the muscles and joints involved in this process. 3. Describe the origin, course, termination, branches, and important re...

Thoracic Wall Prof. Iman Abdel Aal 1. Describe the origin, insertion, nerve supply and action (s) of the intercostal muscles. 2. Interpret the mechanics of respiration & the muscles and joints involved in this process. 3. Describe the origin, course, termination, branches, and important relations of the intercostal arteries (anterior/ posterior, typical/atypical). 4. Describe the beginning, course and termination of the intercostal veins. 5. Describe the Azygos veins and enumerate the tributaries of these veins. 6. Define the intercostal nerves and realize their subdivision into typical and atypical. 7. Describe the course, branches and important relations of each nerve. 8. Realize the clinical importance of the existence of these nerves in cases of intercostal nerve block and in thoracocentesis.  The Thoracic Cage ❑ Skeleton of the Thorax (Thoracic cage) ▪ Thorax (or chest) is the region of the body between the neck and abdomen. ▪ The thoracic cage is the bony framework of the thorax. ▪ It protects the lungs and heart and gives attachment for the muscles of the thorax, upper limb, abdomen and back.  Thoracic Wall ❑ Muscles of the Thorax ▪ Muscles of the thorax include the following: i. Muscles connecting the ribs: Intercostal that connects adjacent ribs Subcostales that cross 2-3 ribs between their attachments ii. Muscle connecting the ribs to the sternum: Transversus thoracis (sternocostalis) iii. Muscles connecting the ribs to vertebrae (just know their names) Levatores costarum (12 pairs) Serratus posterior superior Serratus posterior inferior iv. A muscle that separates the thoracic from the abdominal cavity the diaphragm  The Intercostal Muscles ❑ Connect adjacent ribs and are arranged into 3 layers from out inward: 1. External intercostal muscles 2. Internal intercostal muscles 3. Innermost intercostal muscles External intercostal m Internal intercostal m innermost intercostal  External Intercostal Muscles ❑ Extent: from the tubercle of the ribs posteriorly to the costochondral junction anteriorly where it is replaced by an aponeurosis, the anterior (external) intercostal membrane.  External Intercostal Muscles ❑Attachments: Each muscle passes from the lower border of one rib to the upper border of the rib below. ❑Direction of fibers: downwards and forwards (as one putting his hand in his pocket).  Internal Intercostal Muscles It forms the intermediate layer. Internal intercostal ❑Extent: from the sternum muscle infront to the angle of the rib Internal intercostal behind where each is replaced membrane by internal (posterior) intercostal membrane. ❑Attachments: Each muscle descends from the floor of the costal groove of one rib to the upper border of the rib below. ❑Direction of fibers: downwards, backwards i.e. at right angles to those of the external intercostal muscle.  Innermost Intercostal Muscles It forms the deepest layer. Internal intercostal It is considered the deeper part muscle of the internal intercostal Internal intercostal muscle which is split off by the membrane intercostal vessels and nerves. ❑ Extent: occupy the middle 2/4 of the intercostal spaces. ❑ Attachments: Each muscle is attached to internal aspects of two adjoining ribs (from the upper border of the costal groove of one rib to the upper border of the rib below).  Innermost Intercostal Muscles ❑ Direction of fibers: As internal Internal intercostal intercostal; actually, it is muscle considered a part of the Internal intercostal internal intercostal which is membrane split off by the intercostal nerves and vessels. ❑ Note: The innermost intercostal muscles are related internally to the endothoracic fascia and parietal pleura and externally to intercostal nerves and vessels. Innermost Intercostal Muscles  Subcostal Muscles (Subcostalis) These muscles cross 2-3 ribs between their attachments. ❑ Extent: They are well developed only in the lower and posterior part of the thorax lying near the angles of the ribs. ❑ Attachments: Each muscle descends from the internal surface of one rib to the internal surface of the 2nd or 3rd rib below.  Subcostal Muscles (Subcostalis) ❑ Direction of fibers: like those of the internal intercostal muscles. ❑ Note: The subcostales, like innermost intercostals is related internally to fascia (endothoracic fascia) and parietal pleura and externally to the intercostal nerves and vessels.  Transversus Thoracis (Sternocostalis) This muscle connects the ribs to the sternum. ❑ Extent: The muscle is present on the internal surface of the anterior part of the thoracic wall in line with the innermost intercostal. ❑ Attachments: it arises from the lower half of the posterior surface of the body of sternum to be inserted by 5 slips into the lower border of the costal cartilages from the 2nd to the 6th. ❑ Direction of fibres: upwards and laterally. ❑ Note: The innermost intercostals, subcostales and sternocostalis muscles form together an incomplete inner layer which corresponds to transversus abdominis muscle.  Nerve Supply of Muscles of the Thorax ❑ Nerve supply: All the above-mentioned muscles are supplied by the adjacent intercostal nerves.  Action of Muscles of the Thorax ❑ Action of muscles of the thorax: ▪ The external intercostal muscles are most active in inspiration (elevators of the ribs). ▪ The internal and innermost intercostal muscles are most active in expiration (depressors of the ribs). ▪ Subcostales muscle probably depresses the ribs. ▪ Transversus thoracis draws down the costal cartilages to which it is attached.  Action of Muscles of the Thorax ❑ Note: The role of these muscles in producing movement of the ribs appears to be related mainly to forced respiration. The diaphragm is the primary muscle of inspiration. The intercostal muscles support the contents of the intercostal spaces preventing them from being drawn in during inspiration or bulged out during expiration.  Movements of Respiration ❑ Respiration consists of two phases: inspiration and expiration during which an increase and a decrease of the capacity of the thoracic cavity occur respectively. 1. Inspiration ▪ The diaphragm is the major muscle of inspiration. ▪ In Quiet inspiration: all the diameters of the thoracic cavity will increase. Vertical diameter is increased by contraction (descent) of the diaphragm. Anteroposterior diameter is increased by contraction of intercostal muscles which raise the sternal ends of the downward-sloping ribs. Also the sternum will be pushed upward and forward increasing this diameter (pump-handle movement). Transverse diameter is increased by contraction of the intercostal muscles which elevate the middle of the shaft of the 7th and false ribs which lie in a lower level than their anterior and posterior ends (bucket-handles movement). Note: During quiet inspiration, fixation of the 1st rib by contraction of the scalene muscles is important so all the ribs are drawn together and raised towards it by contraction of intercostal muscles. bucket-handles movement pump-handle movement ▪ In forced inspiration There is a maximum increase in the capacity of the thoracic cavity. Every muscle that can raise the ribs is brought into action e.g. : ❖Scalenus anterior and medius elevate the first rib. ❖Sternocleidomastoid acts directly through the manubrium sterni and indirectly through the clavicle. ❖The scapulae are fixed by the trapezius, levator scapulae and rhomboid muscles which enable the serratus anterior and pectoralis minor to pull up the ribs. ❖Quadratus lumborum fixes the 12th rib so that the diaphragm can exert a more powerful downward push on the abdominal viscera. 2. Expiration: ▪ Quiet expiration is passive and is achieved by: Elastic recoil of the lungs Relaxation of the intercostal muscles and diaphragm ▪ Forced expiration It is an active process during which the muscles of the anterior abdominal wall and latissimus dorsi contract strongly pushing the diaphragm upwards and drawing the lower ribs downwards and inwards. Intercostal Nerves  Intercostal Nerves ▪ There are 12 pairs of thoracic spinal nerves. ▪ The ventral rami of these nerves form the intercostal nerves (the upper eleven) and the subcostal nerve (the 12th). ▪ Each intercostal nerve runs in the corresponding intercostal space while the subcostal nerve runs below the last rib. ▪ The intercostal nerves are classified as a. Typical intercostal nerves which have a similar course (T3-T6). b. Atypical intercostal nerves which have different courses (T1, T2 and T7-T11).  Intercostal Nerves Atypical nerves Typical nerves (1-2) (3-6) (7-11)  Intercostal Nerves ❑Typical intercostal nerves (T3- T6): ▪ Course: Each nerve emerges from the corresponding intervertebral foramen and runs in the posterior part of the intercostal space passing between the parietal pleura and the posterior intercostal membrane. From the angle of the rib to the costo-chondral junction, the nerve runs in the costal groove below the intercostal vein and artery (VAN) passing between the innermost intercostal muscle and the internal intercostal muscle. The Neurovascular Plane  Intercostal Nerves ❑ Typical intercostal nerves (T3-T6): Branches of a typical intercostal nerve 1. Rami communicantes: The intercostal nerve gives a white ramus communicans (preganglionic) to sympathetic trunk & receives a grey ramus communicans (postganglionic) from the sympathetic trunk. The gray ramus joins the nerve medial at the point at which the white ramus leaves it. ▪ Note: Grey rami communicantes are present in all spinal nerves while the white rami communicantes are present only in the thoracic and upper 2-3 lumbar nerves.  Intercostal Nerves ❑ Typical intercostal nerves (T3-T6): Branches of a typical intercostal nerve 2. Muscular branches: to the intercostal muscles and transversus thoracis. 3. A collateral branch: runs along the upper border of the rib below. 4. Pleural sensory branches go to the parietal pleura. 5. Lateral cutaneous branch: it pierces the intercostal muscles and digitations of serratus anterior and emerges on the lateral side of the trunk dividing into an anterior and a posterior branch to supply the skin. 6. Anterior cutaneous branch: the terminal branch that appears near the sternum and divides into medial and lateral branches which supply the overlying skin.  Intercostal Nerves ❑ Atypical intercostal nerves: 1. First intercostal nerve (T1): ▪ It divides unequally into a large branch that ascends across the neck of the 1st rib to share in the brachial plexus. The smaller 1st intercostal nerve runs in the 1st intercostal space and ends as the 1st anterior cutaneous nerve of the thorax. ▪ It gives no lateral cutaneous branch. 2. Second intercostal nerve (T2): ▪ Its lateral cutaneous branch is known as intercostobrachial nerve, which runs in the axilla communicating with the medial cutaneous nerve of the arm and supplies the skin of the floor of axilla and upper part of the medial side of the arm. 3. Lower 5 intercostal nerves (T7-T11): ▪ They pass between the costal slips of diaphragm to the anterior abdominal wall to supply muscles and skin. ▪ They also supply the parietal peritoneum. ❑ Note: The ventral ramus of T12 (subcostal) nerve also supplies the muscles and the skin of the anterior abdominal wall. Arteries  Arteries Intercostal Internal Artery Thoracic Artery  Intercostal Arteries Anterior Intercostal Posterior Intercostal 9 pairs 11 pairs 1 in each space and its 2 in each space collateral artery  Intercostal Arteries ▪ The intercostal arteries course through the thoracic wall between the ribs. ▪ With the exception of the 10th and 11th intercostal spaces, each intercostal space is supplied by: A large posterior intercostal artery and its collateral branch. A small pair of anterior intercostal arteries.  Intercostal Arteries 1. The anterior intercostal arteries: ▪ They are 9 pairs for the upper 9 intercostal spaces. ▪ In the upper 6 intercostal spaces, they are branches from the internal thoracic artery. ▪ In 7th, 8th and 9th intercostal spaces, they are branches from the musculophrenic artery which is one of the terminal branches of the internal thoracic artery. ▪ The 10th and 11th intercostal spaces have NO anterior intercostal arteries because they are incomplete anteriorly.  Intercostal Arteries 1. The anterior intercostal arteries: ▪ In each space the 2 anterior intercostal arteries start from the anterior end of the space, run laterally then terminate at the costo-chondral junction by anastomosing with the posterior intercostal artery and its collateral branch of the same space. ▪ They supply the intercostal muscles and send branches to the overlying pectoral muscles, breast and skin.  Intercostal Arteries 2. The posterior intercostal arteries: ▪ The posterior intercostal arteries are 11 pairs, one in each intercostal space. ▪ Origin: In the 1st and 2nd spaces, they are branches from the superior intercostal artery which is a branch of the costo-cervical trunk (from the 2nd part of the subclavian artery). In the 3rd to 11th spaces, they are branches from the descending thoracic aorta.  Intercostal Arteries 2. The posterior intercostal arteries: ▪ Course Each artery lies at first between the pleura and internal intercostal membrane as far as the costal angle, then passes between the internal intercostal and innermost intercostal muscles (at the neurovascular plane). In the costal groove it runs below its vein and above the intercostal nerve (VAN) At the angle of the rib, it gives a collateral branch which runs along the upper border of the rib below. At the costo-chondral junction, the posterior intercostal artery and its collateral branch end by anastomosing with the anterior intercostal branches from the internal thoracic or musculophrenic artery.  Internal Thoracic Artery ▪ Origin: From the 1st part of the subclavian artery in the root of the neck. ▪ Course: It descends vertically behind the upper 6 costal cartilages one cm from the lateral border of the sternum. ▪ Termination: In the 6th intercostal space, it divides into musculophrenic and superior epigastric arteries. ▪ Branches: 1. Pericardiaco-phrenic artery: a long slender branch accompanying the phrenic nerve to the diaphragm supplying twigs to pericardium, pleura and diaphragm. 2. Pericardial branches 3. Anterior intercostal branches: two arteries for the upper 6 intercostal spaces.  Internal Thoracic Artery 4. Perforating branches: accompany the anterior cutaneous nerves. The perforating branches of the 2nd, 3rd and 4th intercostal spaces supply the mammary gland in female and enlarge during lactation. 5. Musculophrenic artery: one of the 2 terminal branches. It passes inferolaterally behind the 7th to 9th costal cartilages. It traverses the diaphragm to supply it and the abdominal muscles. It gives 2 anterior intercostal arteries for each of 7th, 8th and 9th intercostal spaces. 6. Superior epigastric artery: the 2nd terminal branch of the internal thoracic a. It descends between the costal and sternal (xiphoid) origins of the diaphragm to enter the rectus sheath. It supplies the rectus abdominis and anastomoses with the inferior epigastric artery. It also supplies the abdominal skin and the diaphragm. Veins  Thoracic veins Intercostal Internal veins thoracic vein Anterior Posterior intercostal intercostal veins veins  Intercostal Veins 1. Anterior intercostal veins: ▪ Each of the upper 9 intercostal spaces is drained by 2 anterior intercostal veins. ▪ Veins of the 7th, 8th and 9th spaces are drained into the venae comitantes of the musculophrenic artery while those of the 6th, 5th, 4th, 3rd spaces are drained into the venae comitantes of the internal thoracic artery which unite to form the internal thoracic vein at the level of the 3rd costal cartilage. ▪ The anterior intercostal veins of the upper 2 spaces drain directly into the internal thoracic vein which drains into the brachiocephalic vein.  Intercostal Veins 2. Posterior intercostal veins: ▪ They are 11 pairs; each runs posteriorly in the costal groove above its artery (VAN). ▪ They have different arrangement and mode of drainage on both sides. a. On the right side The 1st right posterior intercostal vein ends in the right brachiocephalic vein. The 2nd and 3rd right posterior intercostal veins unite to form right superior intercostal vein which ends in the arch of azygos vein. The posterior intercostal veins from the 4th to 11th space ends separately in the azygos vein.  Intercostal Veins 2. Posterior intercostal veins: b. On the left side ▪ The 1st left posterior intercostal vein ends in the left brachiocephalic vein. ▪ The 2nd and 3rd left posterior intercostal veins unite to form left superior intercostal vein which ends in the left brachiocephalic vein.  Intercostal Veins 2. Posterior intercostal veins: b. On the left side ▪ The posterior intercostal veins from 4th to 8th space ends separately in the accessory (superior) hemiazygos vein which descends, then turns to the right crossing the body of the 7th thoracic vertebra to join the vena azygos. ▪ The posterior intercostal veins from 9th to 11th space ends separately in the hemiazygos (inferior hemiazygos) vein which arises from the back of the left renal vein, pierces the left crus of diaphragm to enter the thorax then crosses the body of the 8th thoracic vertebra to join the azygos vein. ❑ Note: The accessory hemiazygos and hemiazygos veins may be joined together by venous loop before crossing to the right side.  Internal Thoracic Vein ▪ The venae comitantes of the superior epigastric and musculophrenic arteries unite at the anterior end of 6th intercostal space to form the venae comitantes of the internal thoracic artery. ▪ On each side, the 2 venae comitantes of the internal thoracic artery unite at the 3rd costal cartilage to form a single internal thoracic vein which ends in the corresponding brachiocephalic vein. Thank You