LSS Anatomy of the Thorax Alexandra Burke-Smith Topography of the Thorax Anatomy of the Thorax 1 - Dr Paul Strutton ([email protected]) Lecture – Basic Anatomical nomenclature & Anatomy of the chest wall The anatomical position  Anterior (ventral)  Posterior (dorsal)  Superior (cranial, rostral- beak of spine)  Inferior (caudal- tail of spine)  Midline (median) means the mid-sagittal o The para-sagittal plane is topography lateral to the midline  Medial (towards the midline)  Lateral (away from the midline)  Proximal (think proximity – towards the beginning)  Distal (think distance – towards the end)  Superficial (outside e.g. skin)  Deep (inside e.g. organs)  Sagittal  Frontal (coronal)  Horizontal (transverse or axial) The thoracic skeleton and its boundaries  Thoracic skeleton consists of: o 12 thoracic vertebrae o 12 pairs of ribs o 12 pairs of costal cartilages o Sternum The ribs  12 pairs, with the 1st thoracic vertebra associated with the 1st rib  1-7 form direct articulations with the sternum via costal cartilage (true)  Ribs 8-10 reach costal cartilage above, forming indirect articulations (false)  11 and 12 lack anterior attachment (floating)  Articulations (= joints) o with vertebral column – heads (inferior to anterior articulations with costal cartilage) o with costal cartilages – tubercles 1 LSS Anatomy of the Thorax Alexandra Burke-Smith The Sternum  Consists of: o Manubrium o Body o Xiphoid  1st costal cartilage forms articulation with manubrium  2nd costal cartilage forms articulation with manubriosternal joint  3rd- 7th costal cartilage forms articulations with the body of the sternum o The 7th rib forms its articulation at the body-xiphoid joint  8th-10th ribs form articulations with costal cartilage above  Ribs 11 and 12 do not form articulations with the sternum, and are known as floating ribs  The costal cartilage forms articulations with the sternum via articular facets o The attachement site for rib 1 is different than the rest, as it is a NON-sinovial joint o Superior of the sternum is the articular site for the clavicle, as well as the jugular notch The thoracic inlet  Also known as the superior thoracic aperture  Ring formed of: o T1 (first thoracic vertebra) o 1st ribs o Manubrium Contents  Great vessels heading for neck and upper limb o Common carotid artery o Internal jugular vein o Subclavian artery and vein (vein tends to be anterior to artery)  Esophagus  Trachea  Nerves and lymphatic system  Also apex of the right lung is superior to the clavicle Muscles expanding chest and lung volume  The inferior thorax is larger in size to the superior thorax  Most lung tissue and capacity for lung expansion is in the inferior thorax  The diaphragm has a flat central tendon with muscle radiating to costal margin and vertebrae. On inhalation: o Dome flattens to increase vertical diameter of chest 2 LSS Anatomy of the Thorax Alexandra Burke-Smith o Costal margin is pulled up to increase transverse (horizontal) and antero-posterior diameters  The intercostals muscles have a secondary role: they stiffen the chest wall to improve efficiency of breathing movements  The ribs move in ways to either increase or decrease chest volume. In order to increase chest volume: o The sternum moves superior and anterior o There is elevation of the lateral shaft of the ribs The intercostals muscles There are three layers of muscles:  External intercostals – form inferiorly and laterally from lower border of rib above to rib below (lateral if considering origin to be vertebral column) o Replaced by anterior external intercostal membrane at costo-chondral (rib-cartilage) junction  Internal intercostals – attachments begin anteriorly at the sternum- from lower border of rib above to rib below - fibres directed at right angles to external intercostals o Replaced by membrane posteriorly  Innermost intercostals – relatively trivial Intercostals neurovascular branches  Consist of: o Vein – most superior o Artery o Intercostals nerve – most inferior  Runs just inferior to each rib, deep to the internal intercostals superficial to the innermost intercostal (i.e. between the internal and innermost)  There are also collateral branches  INTERCOSTAL NERVES o 11 pairs (relating to thoracic vertebrae 1-11)  1 subcostal nerve which relates to T12 o May be motor and/or sensory o Consists of two main branches:  Lateral cutaneous branch – which then subdivides into the posterior and anterior branch  Anterior cutaneous branch – which then subdivides into the medial and lateral branch o Supple the intercostals spaces and muscles  VASCULAR COMPONENTS: o Each intercostals artery joins (ANASTOMOSES) with a major artery at each end of the intercostals space o Posteriorly the intercostals arteries joins the aorta o anteriorly the intercostal arteries join the thoracic artery 3 LSS Anatomy of the Thorax Alexandra Burke-Smith The internal thoracic arteries are branches of the subclavian arteries The Thoracic cavity  Filled laterally by the lungs - each lying in its pleural cavity  Space between the pleural cavities = mediastinum o Heart (lying in its pericardial sac) o Great vessels o Oesophagus o Trachea o Thymus o Thoracic duct and other major lymph trunks o Lymph nodes o Phrenic and vagus nerves 4 LSS Anatomy of the Thorax Alexandra Burke-Smith Living Anatomy - Bones & landmarks of the chest wall The axial skeleton  The bones surrounding the CNS – the skull and vertebrae, as well as some related bones in the thoracic region (ribs and sternum)  The thoracic components: o 12 thoracic vertebrae (T1-T12) o 12 pairs of ribs o Sternum Thoracic vertebrae  The vertebral column is a chain of 31 bones all based on the same general plan, with a commonly known arrangement: o 7 cervical vertebrae (neck region) o 12 thoracic vertebrae (thorax region) o 5 lumbar vertebrae (abdominal region) o 5 sacral vertebrae (pelvic region – usually fused into a single mass called the sacrum) o 4 coccygeal vertebrae (tail – very small and usually fused into 2 pairs)  General features: o Main body o Vertebral canal present (for spinal cord) surrounded by vertebral arch o The arch joins with the body at the pedicle o The arch consists of two flat regions known as lamina which join together at the posterior to form the spinous process o There are also two lateral protrusions known as the transverse processes o Vertebrae are attached to their neighbours via intervertebral discs, which are fibrous tissue consisting of:  Annulus fibrosus  Nucleus pulposus  Specific features: o CERVICAL  each transverse process has a hole in the middle through which an artery passes through (when lined up these form the vertebral foramenae)  the spinous process is small, and may split into 2  the first and second cervical vertebrae are named atlas and axis respectively o THORACIC  Only ribs that form articulations with the ribs on the transverse processes and vertebral body o LUMBAR  Very large kidney shaped body  Very large FLAT spinous process  Superior articular fascets face medially  Inferior articular fascets face laterally 5 LSS Anatomy of the Thorax Alexandra Burke-Smith Diagrammatic representation of thoracic vertebra The ribs  Consist of a posterior and anterior end; the posterior end forming articulations with the thoracic vertebrae, and the anterior end attached to the sternum via costal cartilage  The posterior end consists of: o Head with a superior and inferior articular fascet o Neck o Tubercle with 1 articular fascets o Articular fascets form synovial joints with the thoracic vertebrae  The anterior end forms a primary cartillagenous joint with costal cartilage (no movement between rib and cartilage) o The costal cartilage then forms a synovial joint with the articular fascets on the sternum  The superior surface of the rib is rounder than the inferior surface  There is a costal groove on the inferior internal surfaces  The articular fascet on the rib tubercle associates with the articular fascet on the transverse process  The inferior articular fascet on the posterior head of the rib associates with the superior demi-facet on the vertebral body  The superior articular fascet on the posterior head of the rib associates with the inferior demi-fascet on the vertebral body superior to its associated vertebra 6 LSS Anatomy of the Thorax Alexandra Burke-Smith The sternum  Consists of 3 parts: o Manubrium o Body o Xiphoid  The mambriosternal join forms the sterna angle; this is important as it can be palpated  The jugular notch is a suprasternal notch which can also be palpated  Ribs are counted from the 2nd costal cartilage downwards The Upper Limb Girdle  the clavicle forms an articulation with the sternum anterior to the first rib at the sternoclavicular joint  the scapula forms an articulation with the upper limb (arm) and the lateral end of the clavicle o however it does not form an articulation with the axial skeleton, but rather is attached via muscles Dissection – The chest wall and intercostals spaces  Skin incisions made: o Midline incision extending from the jugular notch to the xiphoid process o Incision along the lower costal margin o Incision along the clavicle from the jugular notch to the acromion process, which extends downwards to the middle of the arm 7 LSS Anatomy of the Thorax Alexandra Burke-Smith Muscles of the pectoral region Pectoralis major  On pulling back the skin flaps, the pectoralis major muscle is seen. This is the largest and most superficial of the pectoral region muscles, and covers the anterior aspect of the chest wall.  It has a broad origin with two heads: o The clavicular head which originates from the anterior surfaces of the medial half of the clavicle o The sternocostal head which originates from the sternum and its related costal cartilages  The muscle fibres converge to form a flat tendon, which inserts into the the lateral lip of the intertubular sulcus of the humerus  The origin of the muscle is the fixed point and it is the insertion that moves to allow the muscle to carry out its specific action. The pectoralis major adducts, flexes and medially rotates the arm Subclavius and pectoralis minor  On turning the pectoralis muscle laterally, the pectoralis minor can be identified. Both the pectoralis muscle and the subclavius underlie the pectoralis major: o The subclavius is small and passes laterally from the junction between rib I and the costal cartilage on the inferior surface of the middle third of the clavicle  Its function is to pull the clavicle medially to stabilise the sternoclavicular joint o The pectoralis minor passes from the anterior surface of the ribs III – V to the coracoids process of the scapula  Its function is to depress the tip of the shoulder, protecting the scapula 8 LSS Anatomy of the Thorax Alexandra Burke-Smith The intercostals muscles  Peel back the pectoralis major, and turn the pectoralis minor muscle superiorly. Palpate the ribs to feel the intercostals space between adjacent ribs.  The intercostals muscles are then arranged in 3 layers: o External – run inferiorly and anteriorly from the rib above in an oblique direction o Internal - run inferiorly and posteriorly from the rib above in an oblique direction at right angles to the external intercostals o Innermost – poorly developed but extend in the same direction as the internal intercostals Intercostals nerves and vessels  Using a saw and bone cutters, cut through the manubrium between the 1st and 2nd ribs, then cut ribs 2-6 as far posteriorly as possible on both sides. Cut the body of the sternum just above its inferior end. Cut through the muscles etc with scissors to free and remove a panel of sternum and ribs from the body. Examine the detached panel to identify the internal intercostal muscle and the intercostal nerve and vessels.  The intercostals neurovascular bundles are protected by the inferior projection of the inferior border of the rib forming the costal groove o They run between the internal and innermost intercostals muscles o There are also collateral bundles within the intercostals space, therefore when inserting a chest drain or needle into an intercostals space, it is placed in the central to lower part of the space so as to protect the nerves and vessels Intercostals nerves  The intercostals nerves are the anterior primary rami of the first 11 thoracic nerves o The posterior rami supply the deep back muscles and the skin of the posterior aspect of the thorax  The nerve then consists of: o Lateral cutaneous branch o Anterior cutaneous branch 9 LSS Anatomy of the Thorax Alexandra Burke-Smith Intercostals arteries  Arteries enter intercostal spaces both anteriorly and posteriorly and run in the eleven intercostal spaces.  Arteries supplying the posterior part of each space are known as posterior intercostal arteries, the majority of which are direct branches from the descending thoracic aorta.  The anterior part of each space is supplied by anterior intercostal arteries which are branches of the internal thoracic artery in the upper six intercostal spaces.  In the seventh to ninth intercostal spaces anteriorly, the internal thoracic arteries have divided into their end branches and it is one of these end branches that give rise to the anterior intercostal arteries in these spaces. o There are no anterior intercostal arteries in the last two intercostal spaces.  Clinical importance: Coarctation of the aorta is a congenital malformation in which the aorta is constricted. The constriction normally occurs in the region of origin of the left subclavian artery. o In coarctation the intercostal arteries enlarge to facilitate blood flow to the lower part of the body beyond the obstruction. Notching of the ribs is an important radiological sign caused by erosion of the ribs by the dilated intercostal arteries 10