Thorax

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8 Thorax

Chapter contents

Costal cartilages

Sternum (Figs 8.1 and 8.2)

Type

Fig. 8.1 Sternum (anterior aspect).

A–Jugular notch (suprasternal notch)

B–Clavicular notch

C–Manubrium sterni

D–Facet for 1st costal cartilage

E–Sternal angle

G–Xiphisternal angle

H–Xiphoid process

I–Facet for 7th costal cartilage

J–Facet for 6th costal cartilage

K–Facet for 5th costal cartilage

L–Facet for 4th costal cartilage

M–Facet for 3rd costal cartilage

N – Facet for 2nd costal cartilage.

Fig. 8.2 Sternum (lateral aspect).

1 – Clavicular facet

2 – Facet for 1st costal cartilage

3 – Sternal angle

4 – Xiphisternal angle

5 – Xiphoid process

6 – Facet for 7th costal cartilage

7 – Facet for 6th costal cartilage

8 – Facet for 5th costal cartilage

9 – Facet for 4th costal cartilage

10 – Facet for 3rd costal cartilage

11 – Facet for 2nd costal cartilage.

Position

Lies on the anterior aspect of the thorax in the midline.

Articulations

The clavicular notch with the sternal end of the clavicle to form the sternoclavicular joint.

Notches on the lateral aspect of the sternum articulate with the first 7 costal cartilages to form the sternocostal joints.

Main parts

Manubrium sterni

Jugular (suprasternal) notch on the superior border; lies at the level of the 2nd–3rd thoracic vertebrae.

Clavicular notches on either side of the jugular notch; articulate with the clavicles to form the sternoclavicular joints.

Facet for the 1st costal cartilage, at the upper end of the lateral border.

Demi-facet for the 2nd costal cartilage, at the lower end of the lateral border.

Inferior border articulates with the body to form the sternal angle, which lies at the level of the 4th–5th thoracic vertebrae and can be easily palpated.

Body

4 segments –

form the long, thin body.

3 ridges –

connect the segments.

4 notches –

on each lateral aspect for the 3rd–6th costal cartilages.

2 demi-facets –

on each lateral aspect for the 2nd and 7th costal cartilages.

Xiphoid process

Superior angle –

completes the notch for the 7th costal cartilage.

Xiphisternal joint –

at the junction of the body and the xiphoid process at the level of the 9th–10th thoracic vertebrae.

Radiographic appearances of the sternum (Figs 8.3 and 8.4)

Fig. 8.3 Sternum: anterior oblique projection.

A–Right sternoclavicular joint

D–Sternal angle

E–Body of sternum

F–Xiphisternal joint

G–Xiphoid process

I–Thoracic vertebra

J–Left sternoclavicular joint

K–Suprasternal notch.

(From Bryan 1996.)

Fig. 8.4 Sternum: lateral projection of a child.

1 – Sternoclavicular joints

2 – Manubrium

3 – Sternal angle Segments of the body of the sternum:

8 – Xiphoid process

9 – Diaphragm

11 – Thoracic vertebra.

(From Bryan 1996.)

RIBS (Fig. 8.5)

There are 12 pairs of ribs.

Fig. 8.5 A ‘typical’ left rib (inferior aspect).

B–Facet of the head

D–Articular part of tubercle

E–Non-articular part of tubercle

G–Costal groove

I–Anterior end.

1–7 are true ribs as they are directly attached to the sternum by the costal cartilage.

8–12 are false ribs; 8–10 are indirectly attached to the sternum by their costal cartilages; 11 and 12 are floating ribs as they are not attached to the sternum.

3rd–9th ribs are considered to be ‘typical’.

The ribs increase in size from 1–7 and then decrease in size.

In vivo the ribs are inclined downwards and forwards. Therefore the posterior ends are at a higher level than the anterior ends.

Type

Position

Form the thoracic cage.

Articulations

The anterior end is connected to the sternum by the costal cartilage to form the sternocostal joint.

The head with the demi-facets of the vertebral bodies to form the costovertebral joint.

The articular part of the tubercle with the transverse process of the vertebra to form the costotransverse joint.

Ossification

Primary centre

Shaft –

8th week intrauterine life.

Secondary centres

head appears at puberty;

articular part of the tubercle appears at puberty;

non-articular part of the tubercle appears at puberty.

Fuse with shaft age 20.

Atypical ribs

10th rib

Has only one facet –

for articulation with the 10th thoracic vertebra.

Ossification

As for a typical rib.

12th rib

Shorter than the 11th rib.

Has only one facet –

for articulation with the 12th thoracic vertebra.

Tubercle –

Neck –

Ossification

Primary centre

Shaft –

8th week intrauterine life.

Secondary centre

head appears at puberty.

Fuses with shaft age 20.

Radiographic appearances of the ribs (Figs 8.8, 8.9 and 8.10, Plate 5)

Costal cartilages (Fig. 8.11)

Formed by hyaline cartilage.

Fig. 8.8 Upper ribs: posterior projection.

B–Posterior borders of 4th, 5th and 6th ribs

D–Anterior end of 6th rib

L–Anterior borders of 1st, 2nd and 3rd ribs.

(From Bryan 1996.)

Fig. 8.9 Lower ribs: anteroposterior projection.

1 – Lung tissues

2 – Diaphragm

3 – Diaphragm

(From Bryan 1996.)

Fig. 8.10 Ribs: oblique projection.

A–Thoracic vertebrae

C–Posterior mediastinum

H–Glenoid cavity

(From Bryan 1996.)

Fig. 8.11 The bony thorax – demon- strating the position of the costal cartilages.

Base is attached to the anterior end of the ribs.

Costal cartilages of the:

1st–7th ribs articulate with the sternum

8th–10th ribs articulate with the costal cartilage of the rib above

11th and 12th ribs end in the muscles of the abdominal wall.

The costal cartilages:

increase in length from the 1st to the 7th

decrease in length from the 8th to the 12th

decrease in width from the 1st to the 12th.

Related

Bones and Joints A Guide for Students