Osteology: Thorax

• Location: Inferior to the neck, superior to the abdomen

• Contains:

  • 12 Thoracic vertebrae, intervertebral discs, and ribs (which connect to the sternum anteriorly)

  • Costal cartilages

  • Sternum

  • Unique to thoracic spine:

    • Spinous processes are long, slender, and slant inferiorly

    • Facets face anterior/posterior and allow for rotation and some lateral flexion (restricted by ribs)

• Role:

  • Cage-like to protect viscera

  • Provides frame for muscles of respiration

• Thorax and Ribs

  • Ribs articulate with two thoracic vertebrae, one above and one below.

    • The name of the rib correlates with the inferior vertebrae

  • The thoracic vertebrae have costal facets on the vertebral body and transverse process to articulate with the rib

  • Costal cartilages are medial, hyaline cartilage, creating sternocostal, synovial joints.

  • Ribs 1-7 are true ribs

  • Ribs 8-10 are false ribs

    • Connect via costal cartilage but not to sternum

    • Costal margin located at ribs 7-10

  • Ribs 11 and 12 are floating ribs

    • No attachment to sternum or costal cartilages’

  • “The type of rib is determined by how it attaches to the sternum, not how it attaches to the thoracic spine”

• Ribs: Atypical Ribs

  • Rib one

    • Flat, short, and tightly curved

    • Two grooves present for subclavian artery and vein

  • Rib 11 and Rib 12

    • Floating ribs

    • Do not have articulation with costal cartilage or sternum

• Thorax: Sternum

  • Location of articulation of ribs anteriorly and medially

  • Three sections

    • Manubrium

    • Jugular notch

    • Clavicular notch. Makes up sternoclavicular joint (SC)

    • Manubrium and body meet at the sternal angle (at rib 2)

      • Lines up with T4/T5 posteriorly

  • Body

    • Articulation for ribs 2-7

  • Xiphoid process

    • Level of T10

    • Ossifies at 40 years old

    • Attachment for diaphragm

    • Xiphisternal joint marks inferior limit of thoracic cavity and inferior border of heart

• Thoracic Wall: Movement

  • Inspiration

    • Sternum moves anteriorly

    • Increases anterior to posterior dimension

    • Ribs move laterally and superiorly

    • Increases transverse area of thoracic wall

    • Thoracic pressure less than atmospheric

    • If forceful: Performed by pectoralis major, pectoralis minor, scalenes, and diaphragm

  • Exhalation: Reverses

    • Thoracic pressure greater than atmospheric

    • Diaphragm relaxes

    • If forceful: Obliques and rectus abdominus

Muscles of the Thoracic Wall

• Thoracic Muscles

  • Anteriorly:

    • Pectoralis Major

      • Innervation: Medial and Lateral Pectoral nerve

      • Action:

        • FYI: When the muscle works together: Adduct and internal rotate humerus (at glenohumeral joint)

        • ACTION TO KNOW: Assist with forceful inhalation

        • If could isolate: One part flexes, one part extends

    • Pectoralis Minor

      • Innervation: Medial Pectoral nerve

      • Action (FYI): Pulls scapula anteriorly (anterior tilts)

      • ACTION TO KNOW: Assist with forceful inhalation

    • Transverse thoracis

      • Innervation: Intercostal nerves

      • Action: Depresses ribs

  • Posteriorly

    • Serratus Anterior

      • Innervation: Long thoracic nerve

      • Action: Abducts and protracts scapula

• Muscles of Thoracic Wall: Intercostals

  • Stabilize intercostal spaces during respiration

  • Innervated by intercostal nerves

  • Layers

    • External: Elevate ribs during forceful inspiration

    • Internal: Depress ribs during forced expiration

    • Innermost: Depress ribs while supporting integrity of rib cage during expiration (stabilization)

  • Neurovascular bundle: Between Internal and innermost layers:

    • Vein

    • Artery

    • Nerve

Nerve Anatomy

• Intercostal Nerves

  • Arise from ventral rami of T1-T11

  • T12 is termed subcostal nerve

  • Intercostal nerve fibers supply:

    • Motor: Intercostal muscles

    • Sensory: Skin of thoracic wall

    • Sympathetic fibers:

      • Sweat glands

      • Arrector pili muscles

      • Blood vessels in skin

• Thoracic Dermatomes

  • Thoracic spinal nerve roots: Correlate with region they receive sensory information from

  • Termed “dermatomes”

  • Important for testing for interventions such as intercostal nerve blocks

Arterial System

• Thoracic Wall: Blood Supply

  • Thoracic aorta arises from aortic arch

    • Posterior intercostal arteries arise from thoracic aorta

    • Posterior intercostal arteries supply the thoracic wall, running with an intercostal nerve and vein

    • They anastomose with the anterior intercostal arteries

  • Subclavian arteries give rise to internal thoracic arteries

    • Internal thoracic arteries give rise to anterior intercostal arteries

    • Two anterior intercostal arteries present per intercostal space

Venous System

• Intercostal Venous System

  • Posterior intercostal veins

    • Drain into azygos system

    • Azygos system drains into superior vena cava (SVC)

  • Anterior intercostal veins

    • Drain into internal thoracic veins

    • Drain into brachiocephalic veins

    • Brachiocephalic veins drain into superior vena cava (SVC)

Thoracic Cavity

• Thoracic Cavity: Pluera

  • Superficial sacs surrounding the lungs

    • Parietal pleura: Lines walls of thoracic cavity (along the ribcage)

    • Visceral pleura: Lines surface of lungs (external to lung)

  • Innervation:

    • Parietal pleura:

      • Sensitive to pain/temperature/touch via intercostal nerves and phrenic nerve → somatic sensory

    • Visceral pleura:

      • Visceral sensory: Stretch and ischemia → visceral sensory

  • Potential space is present between visceral and parietal pleura

    • Contains serous fluid for lubrication during lung inflation and deflation

  • Can become inflamed, termed pleuritis. Causes sharp chest pain during breathing

• Application: Pluera

  • Pneumothorax: Air in pleural cavity

  • Hydrothorax: Fluid in the pleural cavity

  • Hemothorax: Blood in the pleural cavity

  • Atelectasis: Lung collapse

    • Trachea shifts towards side of collapse

    • Appears whiter and more surrounded by black air on radiograph

• Movement: Costodiaphragmatic Recesses

  • Recesses decrease in area during inspiration (lungs inflated)

  • Maximal recesses seen during expiration (lungs deflated)

• Application: Thoracentesis

  • Removal of accumulated fluid in the pleural cavity

  • An intercostal nerve block is done first

  • Performed between 7-9th rib

    • Least chance of hitting the lung

  • Enters the costodiaphragmatic recess

• Thoracic Cavity: Lungs

  • Found within the visceral pleura

  • Location of gas exchange (Respiration)

  • Visually:

    • Normally light and elastic → can adjust to change sin pressure

    • Pollutants darken over time

    • Disease can make them fibrous and rigid

• Lungs: Superficial Anatomy

  • Right Lung: Middle

    • 3 lobes

      • Superior

        • Horizontal fissure separates superior from middle lobe

      • Middle

        • Oblique fissure separates middle from inferior lobe

      • Inferior

  • Left Lung:

    • Two lobes (only two because there needs to be room for the heart)

      • Superior

        • Lingula present at inferior anterior aspect of superior lobe → only on LEFT lung

        • Oblique fissure separates superior and inferior lobes

      • Inferior

      • Cardiac notch present on left lung only

• Lungs: Medial Superficial Anatomy

  • Right lung:

    • Apex

    • Indentions:

      • Esophagus

      • Azygos groove

      • Right brachiocephalic groove

    • Root

    • Base

  • Left lung:

    • Indentions:

      • Thoracic duct groove

      • L common carotid groove

      • Aortic groove

  • Root

• Pathway into the lung

  • Trachea

    • Cartilage supported airway with C-shaped hyaline rings

    • Palpable at jugular notch

    • Bifurcates into left and right main bronchi at carina (behind the sternal angle)

      • Bronchi are extrapulmonary

      • Right is wider, shorter, and more vertical → increased risk of aspiration

      • Carina in line with sternal angle and T4/T5 posteriorly

  • Bronchial tree continues into:

    • Lobar bronchi (arrows)

      • Three right

      • Two left

    • Segmental bronchi (colors)

  • Each bronchopulmonary segments have:

    • Segmental bronchus

    • Segmental branch of pulmonary artery

  • Functionally the bronchopulmonary segments are functionally independent (since they each have a segmental branch of pulmonary artery), separated by connective tissue septa. Pulmonary veins are present within the septa

  • Right side has 10 (3 superior, 2 middle, 5 inferior)

  • Left side has 8-9 (4-5 in each lobe)

• Lung: Vasculature

  • Arteries and veins are present for system circulation as well as supply for the lung tissue.

    • Two different systems

  • Systemic circulation (for the full body): Pulmonary arteries and veins

    • Pulmonary arteries: Oxygen poor blood from the heart to the lungs for oxygenation

    • Pulmonary veins: Oxygen rich blood from the lungs to the heart to be distributed to the body

  • Bronchial circulation (for the lungs): Specific to the bronchi of the lungs

    • Bronchial arteries: Bring oxygen to the bronchi for oxygenation

    • Bronchial veins: Bring deoxygenated blood away from the bronchi to the azygos system/intercostal veins

    • These vessels are found within the connective tissue of the lungs

• Lung: Innervation

  • Parasympathetic:

    • Result: Bronchoconstriction of smooth muscle of bronchial tree

    • Pathway: Cranial Nerve X (Vagus Nerve)

      • Preganglonic cell bodies are in the brain, preganglionic fiber is Vagus Nerve → Postganglionic fiber and cell bodies are in the walls of the lung

  • Sympathetic:

    • Result: Bronchodilation of smooth muscle of bronchial tree

    • Pathway: Sympathetic System

      • Preganglionic cell bodies are in the lateral horn of the spinal cord in the thoracic spine.

      • The preganglionic fiber travels from the spinal cord → ventral root → spinal nerve → ventral rami → white rami communicans → paravertebral ganglion (part of sympathetic trunk)

      • Postganglionic cell bodies are the thoracic paravertebral (above the diaphragm) ganglia and the post-ganglionic fibers are the pulmonary nerves (which go to the lung to

        • Anything AFTER the postganglionic cell body is considered the pulmonary nerve

  • Preganglionic section:

    • Cell bodies: Lateral horn of the spinal cord

    • Preganglionic fiber:

      • Ventral root → spinal nerve → ventral rami → white rami communicanes → paravertebral ganglia

  • Synapse occurs

    • Postganglionic section:

    • Post ganglionic cell body: Paravertebral ganglia (above the diaphragm)

    • Postganglionic fiber:

      • Pulmonary nerves

• Sympathetic Trunk

  • Paravertebral ganglia in sequence are called the sympathetic trunk/sympathetic chain

  • Reminder: You enter T1-L3

  • It travels superiorly and inferiorly to the other areas to provide sympathetic input to other areas

• Diaphragm

  • Separates thoracic and abdominal cavities

  • The central tendon of the diaphragm is central and assists with maintaining shape

    • Attaches to the pericardium of the heart

  • Two domes are present superiorly with the right dome sitting more superior due to presence of the liver

  • Central tendon attaches to fibrous pericardium of the heart

    • Results in heart moving during respiration

  • Insertions:

    • Xiphoid process

    • Costal margin

    • Ribs 11-12

    • Anterior aspect of lumbar vertebrae (crus attaches)

• Diaphragm Openings

  • Caval Opening

    • T8

    • Contents: Inferior vena cava

  • Esophageal hiatus

    • T10

    • Contents: Vagus nerve, Esophagus

  • Aortic Hiatus

    • T12

    • Contents: Aorta, Thoracic duct, Azygos vein

• Diaphragm Innervation

  • Phrenic nerve (C3-C5) innervates the diaphragm

    • C3, C4, C5 keep the diaphragm alive

  • Intercostal nerves provide peripheral innervation to the diaphragm

  • Left and Right domes have independent innervation

  • The diaphragm is a primary muscle of inspiration.

  • As a result, one lobe of the diaphragm can be paralyzed in a situation of a phrenic nerve lesion

    • Left: Diaphragm with unilateral paralysis (L)

    • Middle: Diaphragm relax (after an exhale)

    • Right: Diaphragm contracted (after an inhale)

• Diaphragm: Blood Supply

  • The internal thoracic artery branches off the proximal portion of the subclavian artery. It follows the inner chest wall inferiorly near the sternum

    • Several branches occur from the internal thoracic artery including the musculophrenic and pericardiacophrenic arteries, suppling the superior surface of the diaphragm

      • Comes in from anterior side

  • The thoracic aorta is descending from the heart, just to the left of midline

    • The superior phrenic artery branches from the thoracic aorta and supplies the superior surface of the diaphragm

      • Comes in from posterior side

  • The inferior phrenic artery branches from the abdominal aorta and supplies the inferior surface of the diaphragm

  • **Anything ending in -phrenic is blood supply for the diaphragm!!

Systemic Circulation

• Blood flow for Systemic Oxygenation

  • Pulmonary arteries:

    • Oxygen poor blood leaves the right ventricle →

    • Pulmonary trunk →

    • Right and left pulmonary arteries →

    • Lobar arteries →

    • Segmental arteries

  • Same branching pattern as the bronchial tree

  • Oxygen exchanges occurs within the lungs

  • Pulmonary Veins:

    • Bring oxygen rich blood from the lungs (right and left) →

    • Pulmonary veins (two on each side) →

    • Left atrium of the heart

Application

• Incisions

  • Thoracotomy: Incision through thoracic wall to enter pleural cavity

    • Lateral Approach: Typical approach

    • Rib retraction: Allows procedures to be performed via single intercostal space

  • Median Sternotomy:

    • Wide access to thoracic cavity

    • Often for cardiac surgeries

  • Sternal Biopsy

    • Bone needle biopsy