Bones of the Thorax

7/27/2019 Bones of the Thorax.

1/18

ChapterI Bones of the thorax

1

Bones Of The Thorax

Thoracic Cage

Definition:

The thoracic cage is an osteocartilaginous framework

Shape:

-It is conical in shape with its upper end (inlet) narrow and its lower end (outlet) wide.

-Its posterior wall is longer than its anterior wall.

Function:

It encloses and protects the heart and its great vessels together with the lungs on both sides.

Formation:

The skeleton of the thorax is formed of

Anteriorly:

-The sternum

-The costal cartilage and

-The anterior parts of the ribs

Laterally:

The ribs.

Posteriorly

-The thoracic vertebrae-The posterior parts of the ribs.

Fig. (1) Bony framework of thorax

Inlet of the thorax:

Definition: It is the narrow upper end, which is continuous above with the root of the neck.

Direction:

- Its plane is oblique and slopes downwards and forwards.

Boundaries:

-In front: the upper border of the manubrium sterni.-Behind: the upper border of the body of the first thoracic vertebra.-On each side: first rib and its costal cartilage. Outlet of the thorax:

Definition: It is the broad lower end of the thorax and is separated from the upper part of the

abdominal cavity by the diaphragm.


2/18


2

Direction:

- Its plane is oblique and slopes downwards and backwards.

Boundaries:

- In front: the cartilages of the seventh, eighth, ninth and tenth ribs,(costal margin) which join each

other on each side.

- Behind: the lower border of the twelfth thoracic vertebra.

- On each side: eleventh and twelfth ribs.

Sternum

The sternum is a flat bone forming the median part of the anterior wall of the chest.

It is composed of 3 parts (from above downwards):

1. Manubrium sterni.

2. Body.

3. Xiphoid process.

Measurements of the sternum:

-Xiphoid process = 2.5 crn long.

-Manubrium sterni = 5 cm long.

-Body of the sternum = 10 cm long.

General features:

1. Manubrium sterni

- Is the upper quadrilateral part of the sternum.

- Lies opposite the third and fourth thoracic

vertebrae.

- Broad above and narrow below where it

articulates with the body of the sternum.

- Has two surfaces (anterior and posterior) and four

borders (superior, inferior and two lateral)

The surfaces of the manubrium sterni:

a. The anterior surface: is slightly convex from side to side.

b. The posterior surface: is slightly concave.

Fig. (2) Anterior surface of the sternum


3/18


3

The borders of the manubrium sterni:

a. The superior border:

- Is thick and rounded. It presents:

1. Jugular (suprasternal) notch: a median notch.

2. Clavicular notch: the notch on each side of the suprasternal notch for articulation with the medial

end of the clavicle to form the sternoclavicular joint (synovial, saddle variety).

b. The inferior border:

- Articulates with the upper border of the body of the sternum at manubrio-sternal joint (secondary

cartilaginous joint).

Sternal angle (angle of Louis): -

- Angle between manubrium sterni and body of the sternum, can be

felt on the surface and lies opposite the second costal cartilage.c. The lateral borders:

- Articulate with:

1. The first costal cartilage, just below the clavicular notch (primary


2. The second costal cartilage, close to the inferior border (synovial

plane).

2. Body of the sternum

- Long with its widest part present opposite the fifth costal cartilage.

- Lies opposite the fifth, sixth, seventh, eighth and ninth thoracic vertebrae.

- The body of the sternum has:

I. Two surfaces:

The anterior surface: is flat and is marked by three ill-defined transverse ridges, which indicate

the lines of fusion of the four primitive segments of the sternum.

The posterior surface: is smooth and slightly concave backwards.

II. Two ends:

The upper end: articulates with the lower border of the manubrium sterni at the sternal angle.

The lower end: articulates with the xiphoid process.

III. Two lateral borders

Each lateral border shows: costal notches for the costal cartilages from second to seventh

(synovial plane).

Fig. (3) Sternocostal articulations


4/18


4

The notch for the second costal cartilage: at the upper border of the body with a similar one on the

manubrium forms a complete notch for the second costal cartilage.

The notch for the seventh costal cartilage: lies at the junction of the body with the xiphoid process.

3. Xiphoid process

- Is the smallest part of the sternum

- Shape: It may be pointed, bifid or perforated.

- Articulation: -with the lower border of body of sternum to form xiphisternal joint (secondary


-Withthe seventh costal cartilage at its junction with the body of the sternum.

- Ossification: ossified after 40 years.

Particular features


5/18


5

1. Manubrium sterni

Muscles attached:

a) To the anterior surface:

1- Sternal head of the sternomastoid muscle (origin): from the upper part of the anterior surface.

2- Pectoralis major muscle (origin): from the sides of the anterior surface.

b) To the posterior surface:

1- Sternohyoid muscle (origin): from posterior surface opposite the clavicular notch.

2- Sternothyroid muscle (origin): from posterior surface opposite the notch of the first rib.

Ligaments attached to the manubrium sterni:

1.The interclavicular ligament: is attached to the jugular notch.2.The costoclavicular ligament: is attached to the side of the manubrium sterni below the

clavicular notch.

Vessels related to the posterior surface of the manibrum:

1. The lower half of the surface is related to the arch of the aorta.

2. The upper half of the surface is related to the left brachiocephalic vein, brachiocephalic artery,

left common carotid artery and left subclavian artery

N. B. The posterior relation of the manubrium sterni = the content of the superior mediastinum.

2. Body of the sternum:

Muscles attached to the anterior surface:Sternal head of pectoralis major muscle (origin): from the lateral half of the anterior surface.

Muscles attached to the posterior surface:

- Sternocostalis muscle (origin): from the lower part of the posterior surface of the body.

Ligaments attached to the posterior surface of the body:

1. The superior sternopericardial ligament: is attached to the upper part of the posterior surface of

the body.

2. The inferior sternopericardial ligament: is attached to the lower part of the posterior surface of

the body.

The lateral border of the body gives attachment to the followings:

1. Anterior intercostal membranes.

2. Anterior ends of the internal intercostal muscles.


6/18


6

3. Xiphoid process:

Muscles attached to the xiphoid process:

1. Rectus abdominis muscle (origin): from the anterior surface.

2. Aponeurosis of external oblique, internal oblique and transversus abdominis through the

linea alba (insertion): to the lateral borders.

3. Diaphragm (origin): the sternal origin from the posterior surface.

4. Sternocostalis muscle (origin): from the posterior surface.

The posterior surface of the xiphoid process is related to the anterior surface of the liver.

Ossification:

From 6 centers; one for the manubrium, four for the body and one for the xiphoid process.

The relation between the sternal and vertebral levels:

1. The suprasternal notch: lies opposite the disc between the second and third thoracic vertebrae.

2. The sternal angle (angle of Louis): lies opposite the disc between the fourth and fifth thoracic

vertebrae.

3. The xiphisternal joint: at the level of the lower 'border of the 9th thoracic vertebra.

Ribs General characters of the ribs:

1. The ribs are 12 pairs, forming the greater part of the thoracic cage.

2. They are separated from each other by the intercostal spaces. These spaces are wider in front than

behind and wider between the upper ribs than lower ribs.

3. The ribs increase in length from the first to the seventh rib (the longest), then gradually diminish

to the twelfth rib.

4. Each rib articulates posteriorly with the vertebral column and in front, it is continued with the

costal cartilage.

5. The upper ribs are less oblique than the lower ribs. The tenth rib is the most oblique.

Classification of the ribs:

A. According to the structure of the rib:

1. Typical: which include the ribs from third to ninth.


7/18


7

2. Atypical: which include the first two ribs and the last three ribs (have special features).

B. According to the extent (true and false):

1. True ribs (vertebrocostal):

- Represented by the first seven ribs, which known as the true ribs.

-They articulate behind with the vertebra and in front, through the costal cartilages, with the

sternum.

2. False ribs:

a. Vertebrochondral ribs:

- Include the eighth, ninth and tenth ribs.

-They join the vertebrae behind, but ventrally join the costal cartilages of the ribs above.

b. Floating ribs:

-Include the eleventh and twelfth ribs.

The ventral ends of the ribs are free.

Typical ribs

How to identify the side of the rib, right or left ?

Posteriorly: the posterior end consists of head, neck and tubercle.

Anteriorly: the anterior end is cup-shaped.

Superiorly: the superior border is thick and rounded.

Inferiorly: the inferior border is thin and

sharp.

Outer surface: convex.

Inner surface: concave and has the costal

groove near the inferior border.

General features

Each rib has two ends (anterior and

posterior) and a shaft:

I-The posterior (vertebral) end:

The posterior end includes the head, neck

and tubercle.

I-The head:

-It presents two articular facets divided by a transverse ridge known as the crest.

crest

Fig.(5) Typical rib


8/18


8

-The larger lower facet articulates with the side of the body of the thoracic vertebra having the same

number as the rib.

-The smaller upper facet articulates with the side of the body of the thoracic vertebra just above.

-The crest lies opposite the intervertebral disc.

-The head lies above the level of the anterior end.

2.The neck:

- About one inch in length.

- Lies lateral to the head and in front of the transverse process of the vertebra of the same number.

- The upper border is sharp and is called the crest of the neck.

-The lower border is rounded and is continuous with the upper border of the costal groove.- The posterior surface is rough.

- The anterior surface is smooth and is related to the pleura.

3. The tubercle:

-Lies on the outer surface of the ribs at the junction of the neck and the body.

- It is divided into:

a) Articular part: articulates with the oval facet on the tip of the transverse process of the

corresponding vertebra.

b) Non-articular part: is rough and lies lateral to the articular part.

II-The shaft:

It has two surfaces (outer and inner) and two borders (superior and inferior).

1. The surfaces:

a) The outer (external) surface: Is convex and rough.

b) The inner (internal) surface: It is concave and smooth.

It is marked along its lower border by the costal groove.

2. The borders:

a) The upper (superior) border: It is thick and rounded.

b) The lower (inferior) border: It is thin and sharp.

-Angle of the ribs: lies about 5 cm from the tubercle and it is marked on the external surface of the

rib by an oblique ridge.

III. The anterior end:

It is distinguished by the presence of small cup-shaped depression, which receives the lateral end of

the costal cartilage.


9/18


9

Particular Features

A. Ligaments attached to the typical rib:

1. To the head: it gives attachment to:

a. Radiate ligament: is attached to the anterior aspect of the head.

b. Intra-articular ligament: is attached to crest of the head.

2. To the tubercle: it gives attachment to:

Lateral costotransverse ligament

3. To the neck: it gives attachment to:

a. Superior costotransverse ligament.

b. Inferior costotransverse ligament.

B. Muscles attached to the typical rib:

1. Muscles attached to the outer surface:

a. Serratus anterior muscle (origin): from the upper 8 ribs.

b. External oblique muscle (origin): from the lower 8 ribs.

c. Latissimus dorsi muscle (origin): from the lower 4 ribs.

2. Muscles attached to the inner surface:

a. Internal intercostal muscle: from the floor of the costal groove of the rib.

b. Intercostalis intimus muscle: from the middle two-fourth of the ridge above the costal groove.

c. Diaphragm (origin): from the lower 6 ribs.

d. Subcostalis muscle: from the inner surface of the rib near the angle to the inner surface of the2nd or 3rd rib below.

3. Muscles attached to the superior border:

a. External intercostal muscle (insertion): to the outer lip of the superior border.

b. Internal intercostal muscle (insertion): to the inner lip of the superior border.

4. Muscles attached to the inferior border:

External intercostal muscle (origin): the outer lip of the inferior border.

C. Contents of the costal groove (from above downwards):

1. Posterior intercostal vein (V).

11. Posterior intercostal artery (A).

111. Intercostal nerve (N).


10/18


10

Atypical Ribs

1) First rib:

How to identify the side of first rib, right or left?

- The anterior end: is much expanded than that of the other ribs.

- The posterior end: consists of head, neck and tubercle.

- Outer border: convex.

- Inner border: concave.

- The superior surface: is rough and is characterized by the presence

of the scalene ridge and impressions for the attached structures.

General features:

A. The posterior end:

1. The head:- It is small and carries, only, one articular facet.

- Articulates with the facet on the body of the first thoracic

vertebra.

- Lies below the level of the anterior end.

2. The neck:

-It is rounded.

3. The tubercle:

-Is directed upwards.

- Coincides with the angle of the rib.

- It has an oval facet on its medial part for articulation with the transverse process of the first

thoracic vertebra.

B. The shaft:

- It has two surfaces (superior and inferior) and two borders (outer and inner).

1. The surfaces:

a) The superior surface:

I t is crossed by two shallow grooves. The two grooves are separated from each other by a ridge,

which ends at the inner border of the rib by a small projection known as the scalene tubercle.

b) The inferior surface:

Smooth and has no costal groove.

2. The borders:

a) The outer border: Is convex.

Fig. (6) First rib


11/18


11

b) The inner border: Is concave.

C. The anterior end:

- Is expanded and cup shaped.

Particular Features

A. Structures attached and related to the superior surface of the 1st rib:

a. Scalenus anterior muscle (insertion): to the ridge between the two grooves on the superior

surface and to the scalene tubercle.

b. Subclavius muscle (insertion): to the most anterior part of the superior surface.

c. Scalenus medius (insertion): to the rough area on the superior surface near the tubercle of the

rib.

d. Costoclavicular ligament: to the most anterior part of the superior surface.

e. Subclavian artery: is related to the posterior groove on the superior surface behind the scalene

tubercle.

f. Subclavian vein: is related to anterior groove on the superior surface in front of the scalene

tubercle.

Fig. (7) First rib (structures attached & related)


12/18


12

Structures related to the inferior surface of the 1st rib:

a. 1st

intercostal nerve.

b. Parietal pleura.

Structures attached to the outer border of the 1st rib:

a. 1st digitation of the serratus anterior (origin): to the outer border opposite the groove for the

subclavian artery.

b. External intercostal muscle.

Structure attached to the inner border of the 1st rib:

It gives attachment to the suprapleural membrane.

Structures in front of the neck of the 1st rib: (from medial to lateral side)

a. Sympathetic chain (stellate ganglion).

b. Superior intercostal artery and vein.

c. Ventral primary ramus of the 1st thoracic nerve.

2) Second rib:

Identification:

1. The second rib twice the length of the first rib.

2. The external surface is marked near its middle by a large rough impression.

3. The superior border in its posterior part has distinct outer and inner lips.

4. The anterior and posterior ends lie at the same horizontal level.

General features:

A. The posterior end:

i. The head:

Shows two small facets, which articulate with the adjacent facets of the bodies of the first and

second thoracic vertebrae.

ii. The non-articular area of the tubercle is

small.

iii. The angle: is ill defined and is close to the

tubercle.

B. The shaft:

The surfaces are oblique and intermediate in

direction between the first rib (superior and

inferior) and the typical rib (medial and lateral).

Fig. (8) Left 1st & 2nd ribs


13/18


13

-The external surface faces superolaterally.

-The internal surface faces inferomedially.

Particular features:

Muscles attached to the second rib:

a. The first and second digitations of serratus anterior muscle (origin): it is attached to the

rough impression near the middle of the external surface.

b. The scalenus posterior muscle (insertion): is attached to the rough outer lip in front of the

angle.

c. The serratus posterior superior (insertion): to the external surface below the scalenus

posterior.

3) Tenth rib:

Its head presents only a single facet for the articulation with the body of the tenth thoracic vertebra.

4) Eleventh and twelfth ribs:

General features:

The anterior end: is pointed.

The posterior end: has a single large facet on the head.

The inner surface: near the posterior end is directed upwards and inwards.

Particular features:

Muscles attached to the last rib:

a. The quadratus lumborum (insertion): into the lower part of the medial half of the outer

surface.

b. The internal intercostal muscle (insertion): is attached near the upper border.

c. The diaphragm (origin): takes origin from the lateral part of the inner surface close to the upper

border.


14/18


14

Table (1): Differences between 10th , 11th &12th ribs

Fig. (10) Ribs (different views)

10t

rib 11t

rib 12t

rib

Facet on the head Large & single. Large & single. Large & single.

The neck Present, but short. Absent. Absent

The tubercle Present Absent. Absent.

The anterior end Cup-shaped. Pointed Pointed.

The costal groove Present. Shallow. Absent

The length Shorter than the

typical rib

Shorter than the 10th

rib

Shorter than the

11th

rib


15/18


16/18


16

Fig. (12) Typical thoracic vertebra (side view)

Fig. (13) Typical thoracic vertebra (superior view)

Identification:

i. The body: is medium sized and is characterized by the presence of costal facets on the side of the

vertebral bodies.

ii. The transverse process: is characterized by the presence of costal facet for articulation with the

tubercle of the ribs.

iii. The spine: is long and pointed.

iv. The vertebral foramen: is small and circular in shape.

General features of the typical thoracic vertebra:

1.The body:

-Heart-shaped. Its transverse and antero-posterior diameters are nearly equal.

-On each side of the body, there are two incomplete articular facets for the articulation with the

heads of the ribs. They are called the costal demifacets.

a) Superior costal facet: is larger and is placed on the upper border near the pedicle. It articulates

with the head of the same numbered rib.

b) Inferior costal facet: is smaller and is placed on the

lower border in front of the inferior vertebral notch.

It articulates with the head of the rib below.

2. The vertebral foramen: Small and circular in outline.

3. The lamina: Thick and broad.

4. The spine: Long with a pointed tip and directed backwards and downwards.

5. The articular processes:

a) The superior articular process: Faces backwards and slightly upwards and laterally.

b) The inferior articular process: Faces forwards and slightly downwards and medially.

6. The transverse process:

- Large and directed posterolaterally

-Bears on its anterior surface near the tip a costal

facet for articulation with the facet on the tubercle of

the rib of the same number.

Atypical thoracic vertebrae: -

1. The first thoracic vertebra: It is distinguished by:

a) The upper costal facet on the body: is a complete circular facet, which articulates with the

single facet on the head of the first rib.


17/18


17

Fig. (14) Thoracic vertebrae

b) The inferior costal facet on the body: is a

demifacet, which articulates with the upper facet on the

head of the second rib.

c) The spine is thick, long and horizontal.

c) The other features of typical thoracic vertebra are

present.

2. The ninth thoracic vertebra: Is distinguished by:

a) Has a small demifacet at the upper border of its body

for the head of the ninth rib.

b) The inferior costal facets on the lower border of the

body are absent.

c) The other features of the typical thoracic vertebra are

present.

3. The tenth thoracic vertebra:

a) Has a large oval facet on the side of the body close to

the upper border.

b) The inferior costal facet on the lower border of the

body is absent.

c) The other features of the typical thoracic vertebra are present.

4. The eleventh thoracic vertebra:

a) Has a single circular facet close to the upper border of the body for the head of the eleventh rib.

b) The transverse process is small with no costal facet.

c) The spine is triangular with a blunt tip.

5. The twelfth thoracic vertebra:

a) Has a single circular facet for the head of the twelfth rib. This facet lies at some distance below

the upper border and encroaches on the pedicle.

b) The body is large and lumbar in type.

c) The spine is triangular with a blunt tip.

d) The transverse process is very small and carries no costal facet.

e) The inferior articular process is slightly convex and is directed forwards and laterally.

Fig.(12) Thoracic vertebrae


18/18


18

1st 9th 10th 11th 12th

Body & articular

facet

1 single facet

near the upper

border

Only 1

demifacet near

the upper

border

One complete

facet

One complete

facet

One complete facet

Transverse process

& costal facets

Present Present Present Small with no

facet

Small with no facet

Spines Long , thick

&horizontal

Long &

tapering

Long &

tapering

Triangular with

blunt tip

Triangular with blunt

tip

Articular processes Directed

backward &

forward

Directed

backward &

forward

Directed

backward &

forward

Directed

backward &

forward

The inferior facet is

directed forward and

laterally

Table (2A) Differences between thoracic vertebrae

Table (2B) Differences between thoracic vertebrae

Documents

Bones of the Thorax