Thoracic Cage-Structure & Functions

COMPONENTS OF THORACIC CAGE:

• Sternum
• Manubrium, Body (Gladiolus), Xiphoid process
• Ribs
• 7 True Ribs
• 5 False Ribs (including 2 floating ribs)
• Clavicle
• Scapula
• Pectoral girdle

12 Thoracic Vertebrae (T1 – T12)

Thoracic Cage

• It forms a conical enclosure for the lungs and heart and

provides attachment for the pectoral girdle and upper limb.

It has a broad base and a narrower superior apex; it is rhythmically expanded by the respiratory muscles to create a vacuum that draws air into the lungs.

The inferior border of the thoracic cage is formed by a downward arc of the ribs called the costal margin.

The ribs protect the thoracic organs and spleen, most of the liver, and to some extent the kidneys.

Sternum/Breast bone

• Flat bone, with 3 parts:
• Manubrium sterni

Body/Gladiolus

Xiphoid process

PARTS OF STERNUM:

• Manubrium sterni
• Jugular/suprasternal notch
• Articulates with Clavicles
• and Ribs 1 and 2

Lies opposite to T3 and T4 vertebrae Manubriosternal joint inferiorly – called Sternal Angle/Angle of Louis – opposite articulation with 2nd rib – at the level of intervertbral disc between T4 and T5 vertebrae (imp. for counting the ribs)

PARTS OF STERNUM:

Body/Gladiolus

• Articulates with Ribs 2-7
• Xiphisternal joint inferiorly- opposite to T9 vertebra
• Xiphoid process
• Cartilaginous – calcifies through time
• Allows attachment of
• muscles

Tip of xiphoid – at level of T10

Sternocostal joints

Ribs

Typical Ribs 2-7

• Head
• Neck
• Tubercle
• Angle
• Shaft
• Subcostal groove

Atypical Ribs 1, 8 -10

• Rib 1 – short, flat and supports Subclavian vessels
• Ribs 1, 10-12 – articulate with only 1 vertebra
• Ribs 11 and 12 –

“floating ribs” – do not articulate with Transverse processes of Vertebrae or Sternum

Typical ribs: 1 – 7 pairs of ribs are attached anteriorly to the sternum by their costal cartilages.

Atypical ribs: 8th, 9th and 10th pairs of ribs are attached anteriorly to each other and to the 7th rib by means of their costal cartilages and small synovial joints.

Floating ribs :The 11th and 12th pairs have no anterior attachment. They are embedded in the abdominal muscles.

Typical Ribs (2 -7)

• Long, twisted, flat bone
• The anterior end of each rib is attached to the corresponding costal cartilage

A rib has a head, neck, tubercle, shaft, and angle Head – located posteriorly – has 2 facets for articulation – one for the numerically corresponding vertebral body and the other for the vertebral body immediately above it.

Neck is a constricted portion – between the head and the tubercle.

The Tubercle is a prominence on outer surface of the rib – at the junction of the neck with the shaft. It has a facet for articulation with the transverse process of the numerically corresponding vertebra.

The Shaft is thin, flat and twisted on its long axis.

Atypical Rib (1st Rib)

The first rib has a close relationship to the lower nerves of the Brachial plexus, Subclavian artery and vein This rib is small and flattened from above downward Scalenus anterior muscle is attached to its upper surface and inner border Anterior to the attachment of Scalenus anterior, the Subclavian vein crosses the rib Posterior to the attachment of Scalenus anterior, the Subclavian artery and the lower trunk of the Brachial plexus cross the rib and lie in contact with the bone

JOINTS OF STERNUM

• MANUBRIOSTERNAL JOINT:
• cartilaginous joint, symphysis
• between Manubrium and body of Sternum
• XIPHISTERNAL JOINT
• cartilaginous joint
• between Xiphoid process and body of Sternum

The Xiphoid process usually fuses with the body of the Sternum during middle age

JOINTS OF RIBS

• COSTOVERTEBRAL JOINTS:
• 2 joints between heads of the Ribs and bodies of

Vertebrae (corresponding and upper)- Synovial joints 1st, 10th, 11th and 12th rib has 1 synovial joint with the corresponding vertebra, the rest have 2 each; one for the corresponding vertebra and the other for the vertebra above it 1 joint between tubercle of Ribs and transverse process of Vertebra (corresponding) – Synovial joint (1st- 10th Rib) Intra articular ligament connects head of Rib to the intervertebral disc

JOINTS OF RIBS

• COSTOCHONDRAL JOINTS:
• Joints of the Ribs with costal cartilages
• Cartilaginous joints
• STERNOCOSTAL JOINTS:
• Joints between Sternum and costal cartilages
• 1st : Cartilaginous joint
• 2nd – 10th : Synovial joints=
• 2nd-7th costal cartilages with Sternum 8th-10th costal cartilages with each other

(11th and 12th costal cartilages are embedded in muscles)

MOVEMENTS

Cartilaginous joints are immobile (thus 1st rib and all costochondral joints do not move during respiration) Synovial joints are slightly mobile (due to movements in both the joints between head, tubercle and vertebrae, necks of Ribs rotate along their axis, helping in raising and lowering of ribs during respiration)