THORAX

Introduction; Thoracic Wall; Thoracic Cage

(Skeleton); Intercostal spaces; Thoracic
Apertures

Ismail Mk ABDULLAHI
Introduction
• Lies between the neck and the abdomen, flattened in front and behind but
curved at the sides.

• The thoracic cage (framework of the walls of the thorax): Formation

the vertebral column (behind) the ribs and intercostal spaces
(on either sides) and the sternum and costal cartilages (in front)

• The Thorax
Superiorly: the thorax communicates with the neck
Inferiorly: it is separated from the abdomen by the diaphragm.

• The thoracic cage protects vital organs such as the lungs and heart and
affords attachment for the muscles of the thorax, upper extremity,
abdomen, and back.
Intro Cont’d
• The thoracic cavity can be divided into a median partition, called the
mediastinum, and the laterally placed pleurae and lungs.

• The pleura has two membranes: the visceral pleura, which covers the
lungs and passes from each lung at its root to the inner surface of the
chest wall, where it is called the parietal pleura.

• This arrangement give two membranous sacs called the pleural

cavities, one on each side of the thorax, between the lungs and the
thoracic walls
Thoracic Wall
• This includes: the thoracic cage and the muscles that extend between
the ribs as well as the skin, subcutaneous tissue, muscles, and fascia
covering its anterolateral aspect.

• Back: similar structures covering its posterior aspect.

• The mammary glands of the breasts lie within the subcutaneous

tissue of the thoracic wall.

• The anterolateral axioappendicular muscles: are distinctly upper limb

muscles based on function and innervation.
Thoracic Cage
Boundaries
• Posterior: Thoracic part of the vertebral column
• Anterior: Sternum and costal cartilages
• Lateral: Ribs and intercostal spaces
• Superior: Suprapleural membrane
• Inferior: Diaphragm
Thoracic Cage: Functions

• Protection
• Resistance to negative pressure
• Support and Attachment:
Bones of upper limb
Muscles: upper limb, neck, back, respiration
Thoracic Skeleton
The thoracic skeleton includes

• The sternum
• The 12 pairs of ribs and associated costal cartilages
• The 12 thoracic vertebrae and the intervertebral (IV) discs

The ribs and costal cartilages form the largest part of the thoracic cage.
The Sternum
The sternum is a ‘T’ shape flat bone located at the anterior aspect of
the thorax and lies in the midline of the chest.

Parts of the Sternum

Manubrium,
Body
Xiphoid process

In children, these elements are joined by cartilage. The cartilage

ossifies to bone during adulthood.
Manubrium
 The most superior portion of the sternum, trapezoid in shape.
 The superior aspect of the manubrium is concave, producing a
depression known as the jugular notch
 Either side of the jugular notch has a large fossa lined with
cartilage which articulate with the medial ends of the clavicles,
forming the sternoclavicular joints.
 On the lateral edges: there is a facet and demifacet for
articulation with the costal cartilage of the 1st rib and the 2nd rib
respectively.
 Inferiorly: sternal angle where manubrium articulates with the
body of the sternum.
Body
 Flat and elongated.
 Superiorly: manubriosternal joint
 Inferiorly: xiphisternal joint
 The lateral edges: marked by numerous articular facets (for costal
cartilages of ribs 3-6.
 Also contains demifacets for 2nd and 7th .
Xiphoid Process
 The most inferior and smallest part of the sternum.
 It is variable in shape and size the tip of which is located at the level
of the T10 vertebrae.
 Largely cartilaginous in structure and completely ossifies late in life
(around the age of 40).
 In some individuals, the xiphoid process articulates with part of the
costal cartilage of the seventh rib
The Ribs
• The ribs are a set of twelve paired bones which form the protective
cage of the thorax.

• The ribs:
Articulate with the vertebral column posteriorly
Terminate anteriorly as cartilage (costal cartilage)

• As part of the bony thorax, the ribs:

Protect the internal thoracic organs.
They also have a role in ventilation; moving during chest
expansion to enable lung inflation.
Types of Ribs
The ribs are divided into three types based on their attachment:

True ribs:
The upper seven pairs.
Attached anteriorly to the sternum by their costal cartilages.

False ribs:
The 8th, 9th, and 10th pairs of ribs.
Attached anteriorly to each other and to the 7th rib by means of their
costal cartilages.

Floating ribs: The 11th and 12th pairs have no anterior attachment.
Rib Structure
Based on structure there are two classifications of ribs:

 Typical: generalised structure

 Atypical: varied structures.

Typical Ribs

The typical rib consists of a head, neck and body

 The head
Wedge shaped with two articular facets separated by a wedge of bone.

 The neck
No bony prominences but simply connects the head with the body.
Roughed tubercle with a facet for articulation with the transverse process
of the corresponding vertebra.

 The body (shaft)

Flat and curved
The internal surface of the shaft has a groove for the neurovascular supply
of the thorax, protecting the vessels and nerves from damage.
Atypical Ribs

1st, 2nd, 10th, 11th and 12th

Rib 1
Shorter and wider than the other ribs.
Only has one facet on its head for articulation with its corresponding
vertebra.
The superior surface is marked by two grooves making a way for
the subclavian vessels.
Rib 2
Thinner and longer than rib 1
Two articular facets on the head as normal.
It has a roughened area on its upper surface giving origin to serratus
anterior muscle.
Rib 10
One facet for articulation with its numerically corresponding
vertebra.

Ribs 11 and 12
No neck
One facet for articulation with their corresponding
vertebra.
Articulations
The majority of the ribs have an anterior and posterior articulation.
Posterior
Costotransverse joint: tubercle of the rib and the transverse
costal facet of the corresponding vertebra.
Costovertebral joint: head of the rib and (i) superior costal facet
of the corresponding vertebra and (ii) the inferior costal facet of
the vertebra above.
Anterior
Ribs 1-7: the sternum (True)
Ribs 8 – 10: costal cartilages superior to them (False)
Ribs 11 and 12: No anterior attachment (floating ribs)
Costal cartilages
• Connect the upper seven ribs to the lateral edge of the sternum and
the 8th, 9th, and 10th ribs to the cartilage immediately above.

• The cartilages of the 11th and 12th ribs end in the abdominal
musculature.

• The costal cartilages contribute significantly to the elasticity and

mobility of the thoracic walls.
Thoracic Vertebrae
Thoracic Vertebrae can be classified as:
• Typical: T2 – T9
• Atypical: T1; T10 – T12

Characteristic features
• Bilateral costal facets (on the vertebral bodies): usually occurring in inferior
and superior pairs, for articulation with the heads of ribs.

• Costal facets (on the transverse processes): for articulation with the
tubercles of ribs, except for the inferior two or three thoracic vertebrae.

• Spinous processes: Long inferior and slanting

Atypical thoracic

T1
The superior costal facets of vertebra T1 are not demifacets.
T1 has a typical inferior costal (demi) facet.

T10
T10 has only one bilateral pair of costal facets, located partly on
its body and partly on its pedicle.

T11 and T12

T11 and T12 also have only a single pair of costal facets, located
on their pedicles.
Intercostal Spaces
The spaces between the ribs contain:
1. Muscles: Three muscles of respiration:
External intercostal
Internal intercostal
Innermost intercostal

2. Neurovascular Bundles: The intercostal nerves and blood vessels run

between the intermediate and deepest layers of muscles. They are
arranged from above downward: intercostal vein, intercostal artery,
and intercostal nerve (i.e. VAN).
Intercostal Muscles
• External Intercostals: There are 11 pairs of external intercostal muscles. They
run inferoanteriorly from the rib above to the rib below, and are continuous
with the external oblique of the abdomen.

• Internal Intercostals: Like the external intercostals, they run from the rib
above to the one below, but in an opposite direction i.e. inferoposteriorly.
They are continuous with the internal oblique muscle of the abdominal wall.

• Innermost Intercostals: Similar in structure to the internal intercostals.

They are separated from the internal intercostals by the intercostal
neurovascular bundle and are found in the most lateral portion of the
intercostal spaces.
 Muscle Origin Insertion Nerve Supply Actions
External Lower border of the Elevates the ribs, increasing
Intercostals rib the thoracic volume

Superior border of the rib below

Intercostal nerves (T1-T11)

Internal Lateral edge of the  The interosseous part
Intercostals costal groove reduces the thoracic
volume by depressing the
ribcage

 The interchondral part

elevates the ribs
Innermost Medial edge of the
Intercostals costal groove
Intercostal Vessels
The vessels comprise the posterior and anterior intercostals.
The posterior intercostal arteries:
Lower nine spaces: branches of the thoracic aorta
First two: derived from the superior intercostal branch of the costocervical trunk
 Each runs forward in the subcostal groove to anastomose with the anterior
intercostal artery and has a number of branches to adjacent muscles, to the skin
and to the spinal cord.
 The corresponding veins: mostly tributaries of the azygos and hemiazygos veins.
 The first posterior intercostal vein drains into the brachiocephalic or vertebral
vein
• On the left, the 2nd and 3rd veins often join to form a superior intercostal vein
which crosses the aortic arch to drain into the left brachiocephalic vein.
The anterior intercostal arteries

• Branches of the internal thoracic artery (1st–6th space) or of its

musculophrenic branch (7th–9th spaces).

• The lowest two spaces have only posterior arteries.

• Perforating branches pierce the upper five or six intercostal spaces;

those of the 2nd–4th spaces are large in the female and supply the
breast.
Intercostal Nerves
The intercostal nerves are the anterior primary rami of the thoracic
nerves, each of which gives off:
Collateral muscular branch
Lateral and anterior cutaneous branches

For the innervation of the thoracic and abdominal walls

Thoracic Apertures
• While the thoracic cage provides a complete wall peripherally, it is
open superiorly and inferiorly.

• The much smaller superior opening is a passageway that allows

communication with the neck and upper limbs.

• The larger inferior opening provides the ring-like origin of the

diaphragm, which completely occludes the opening.

• Movements of the diaphragm primarily control the internal pressure

of the thoracic cavity.
Superior thoracic aperture
The anatomical thoracic inlet refers to the opening at the top of the thoracic cavity

Boundaries

• Posterior: Vertebra T1, the body of which protrudes anteriorly into the opening.

• Lateral: 1st pair of ribs and their costal cartilages.

• Anterior: Superior border of the manubrium.

Dimensions
• The adult thoracic outlet is around 6.5cm anteroposteriorly and 11cm
transversely.
• Because of the obliquity of the first pair of ribs, the aperture slopes
anteroinferiorly.
Relations

• Anterior: Clavicle and manubrium

• Superior: root of the neck

• Inferior: Superior mediastinum

• Superolateral: brachial plexus

Structures that pass through the thoracic inlet include:
• Trachea
• Oesophagus
• Thoracic duct
• Apices of the lungs
• Nerves: phrenic nerve, vagus nerve, recurrent laryngeal nerves,
sympathetic trunks
• Vessels:
• Arteries: left and right common carotid arteries, left subclavian
arteries
• Veins: internal jugular veins, brachiocephalic veins, subclavian
veins
• Lymph nodes and lymphatic vessels
Inferior Thoracic Aperture
The anatomical thoracic outlet
• Encompasses the abdominal cavity.
• The thoracic cavity and the abdominal cavity is divided by the large
musculoaponeurotic diaphragm connected to the margins of thoracic
outlet.
Boundaries
• Posterior: Body of the 12th thoracic vertebra.
• Posterolateral: 11th and 12th pairs of ribs.
• Anterolateral: Joined costal cartilages of ribs 7–10, forming the costal
margins.
• Anterior: Xiphisternal joint.
Clinical and Applied Anatomy
Sternum and Marrow Biopsy

 Since the sternum possesses red hematopoietic marrow throughout

life, it is a common site for marrow biopsy.

 Under a local anesthetic, a wide-bore needle is introduced into the

marrow cavity through the anterior surface of the
bone.

 The sternum may also be split at operation to allow the surgeon to

gain easy access to the heart, great vessels, and thymus.
Cervical rib
• Rib arising from the anterior
tubercle of the transverse process
of the 7th cervical vertebra
• Usually occurs in about 0.5% of
humans

Significance
• Pressure on the lower trunk of the
brachial plexus
• It can also exert pressure on the
overlying subclavian artery
The Thoracic Outlet Syndrome

 The brachial plexus of nerves and the subclavian artery and vein are closely
related to the upper surface of the 1st rib and the clavicle as they enter the
upper limb.

 It is here that the nerves or blood vessels may be compressed between the
bones.

 Most of the symptoms are caused by pressure on the lower trunk of the
plexus.

 Pressure on the blood vessels may compromise the circulation of the upper
limb
Thoracic Cage Distortion

 The shape of the thorax can be distorted by congenital anomalies of

the vertebral column or by the ribs.

 Destructive disease of the vertebral column that produces lateral

flexion or scoliosis results in marked distortion of the thoracic cage