Thoracic Cage and Sternum Anatomy

Thoracic Cage

• The thoracic cage/bony thorax is bordered anteriorly by the sternum and costal cartilages.
• The thoracic cage is bordered laterally by the ribs.
• The thoracic cage is bordered posteriorly by the thoracic vertebrae.
• The thoracic cage protects vital thoracic and abdominal organs from external forces.
• It resists negative internal pressures from lung recoil and inspiratory movements.
• The thoracic cage provides attachment and support for the upper limbs
• It provides an anchoring attachment for muscles of the upper limbs, abdomen, neck, back and in respiration.

Sternum

• The sternum has three parts: the manubrium, the body, and the xiphoid process.
• The manubrium articulates with the clavicle at the manubrioclavicular joint.
• The manubrium articulates with the first rib.
• It also articulates at the manubriosternal joint, also called the Angle of Louis, at vertebral level T4-T5.
• The body of the sternum articulates with costal cartilages two through seven.
• The xiphoid process articulates with the body of the sternum at the xiphisternal joint.
• The xiphisternal joint lies opposite the body of the 9th thoracic vertebra.

Ribs

• There are 12 pairs of ribs attached posteriorly to the thoracic vertebrae.
• True ribs are the upper 7 pairs.
• True Ribs attach anteriorly to the sternum via their costal cartilages.
• False ribs are the 8th, 9th, and 10th pairs.
• False ribs attach anteriorly to each other and to the 7th rib via their costal cartilages.
• Floating ribs are the 11th and 12th pairs.
• Floating ribs have no anterior attachment.

Typical Ribs

• Typical Ribs are ribs 3rd through 9th.
• These ribs are long, twisted, and flat.
• Typical ribs have a rounded, smooth superior border and a sharp, thin inferior border.
• The inferior border overhangs the costal groove where the intercostal neurovascular bundle resides.
• Features of a typical rib: head, neck, tubercle, shaft and angle

Typical Ribs: Head

• A typical rib head has two articulation facets.
• The superior facet articulates with the vertebral body immediately above.
• The inferior facet articulates with the numerically same vertebral body.
• Rib 3 has a superior articulation facet with T2 and an inferior articulation facet with T3.

Typical Ribs: Neck, Tubercle, Shaft, and Angle

• The neck of a typical rib is a constricted portion between the head and tubercle.
• The tubercle is a prominence on the outer surface of the rib at the junction of the neck with the shaft.
• Articulation facet articulates with the transverse process of the vertebrae.
• The shaft is thin and flattened, twisted on its long axis.
• The inferior border has the costal groove.
• The angle is where the rib turns anterolaterally.

Atypical Ribs

• Atypical Ribs are Ribs 1, 2, 10, 11, and 12.

Atypical Rib 1

• Rib 1 is small and flattened.
• The anterior scalene muscle attaches to its superior surface and posterior border, at the scalene tubercle.
• The subclavian vein is anterior to the scalene tubercle.
• The subclavian artery and lower trunk of the brachial plexus are posterior to the scalene tubercle.
• Rib 1 has a single facet on its head that articulates with the T1 vertebra.

Atypical Rib 2

• Rib 2 is thinner, less curved and substantially longer than Rib 1.
• The head of Rib 2 has two facets for articulation with the bodies of T1 and T2 vertebrae.
• The main atypical feature of Rib 2 is a rough area on its upper surface: the tuberosity for serratus anterior.

Atypical Ribs 10, 11, and 12

• Ribs 10-12 have only one facet on their heads, like Rib 1, and articulate with a single vertebra.
• Ribs 11 and 12 are short and have no neck or tubercle.

Joints: Costovertebral

• Costovertebral joints are articulations between the heads of ribs and the vertebral bodies.
• Typical ribs: a superior facet that articulates with the body of the vertebra above and an inferior facet which articulates with the same-numbered vertebra.
• Atypical ribs 1, 10, 11 and 12: bear a single articular facet and only articulate with their corresponding vertebral body.
• Costovertebral Joints are classified as plane synovial joints.

Joints: Costotransverse

• Costotransverse joints are articulations between the articular facet on the tubercle of the rib and the transverse costal facet on the transverse process of the vertebra of the same number.
• These joints are present in ribs 1-10.
• Ribs 11 and 12 do not articulate with transverse processes of their related vertebrae.
• Costotransverse Joints are classified as plane synovial joints.

Joints: Costochondral

• Costochondral joints are articulations between the lateral end of the costal cartilage with the sternal end of the rib.
• They are classified as primary cartilaginous joints.

Joints: Interchondral

• Interchondral joints are articulations between costal cartilages of the floating ribs.
• They are classified as synovial plane joints.

Joints: Sternocostal/Chondrosternal

• Sternocostal/Chondrosternal joints are articulations between the 1st costal cartilages with the manubrium of the sternum.
• They are classified as primary cartilaginous joint.
• Articulations between the 2nd–7th pairs of costal cartilages articulate with the sternum.
• They are classified as synovial plane joint.

Joints: Sternoclavicular

• Sternoclavicular joints are articulations between the sternal end of the clavicle with the clavicular notch of the manubrium of the sternum and the 1st costal cartilage.
• They are classified as saddle synovial joints.

Joints: Manubriosternal & Xiphisternal

• The manubriosternal joint is an articulation between the manubrium and body of the sternum.
• It is classified as a secondary cartilaginous joint.
• The xiphisternal joint is an articulation between the xiphoid process and the body of the sternum.
• This joint is a primary cartilaginous joint (synchondrosis).