The thorax is the region of the body between the neck and the abdomen. Its walls are formed by the vertebral column posteriorly, the ribs and intercostal spaces laterally and the sternum and costal cartilages anteriorly. Superiorly is the neck and inferiorly the diaphragm.

 

The function of the chest all is to protect the heart, lungs and great vessels. It also provides attachment for the muscles of the thorax, upper extremity, abdomen and back.

The thoracic wall has various bones involved in creating its protective cage. We will work our way around from front to back.

 

Sternum

The bone in the anterior midline of the chest wall is the sternum or breast bone. It is composed of three parts: manubrium, body, xiphisternum or xiphoid process (from top to bottom).

 

Manubrium - as the upper part of the sternum, it articulates with the clavicles, first costal cartilages and upper part of the second costal cartilages. Its articulation with the body of the sternum is at the manubriosternal joint which creates the sternal angle or angle of Louis.

 

Body - articulates above and below with the manubrium and xiphoid process and the manubriosternal and xiphisternal joints respectively. Along its length is also articulates with the 2nd to 7th costal cartilages.

 

Xiphoid process - this is made of cartilage, not bone.

 

Clavicle

The clavicle articulates with the manubrium of the sternum. Further details of its anatomical relations and muscle attachments can be found in its own section in this text.

 

Ribs

There are 12 pairs of ribs in total. Ribs can be described either via their attachments ie, true, false and floating, or by their appearance i.e. typical or atypical.

 

There are 7 true ribs, 3 false ribs and 2 floating ribs.

 

True ribs - these are the upper 7 ribs that are attached anteriorly to the sternum via the costal cartilages as well as posteriorly to the thoracic vertebrae.

 

False ribs - ribs 8-10 are attached anteriorly to each other and to the sternum by way of the costal cartilage of the 7th rib. They are also attached posteriorly to the thoracic vertebrae.

 

Floating ribs - Ribs 11 and 12 have no interior attachment

 

 

Typical ribs

A typical rib is a long, flat bone that twists round to form the lateral wall of the thorax.

It has a smooth superior border and a thin inferior border that over hangs to house the costal groove.The posterior end of the rib articulates with the thoracic vertebrae. It has a head, neck, tubercle, shaft and angle.

 

The head has two facets - one articulates with its numerically corresponding thoracic vertebra and one articulates with the vertebra above.

 

The neck is the portion between the head and the tubercle

 

The tubercle has a facet which articulates with the transverse process of the numerically corresponding thoracic vertebra. The tubercle also marks the transition from the neck to the shaft of the rib.

 

The shaft is thin and flattened with the twist on its long axis. Along its inferior border runs the costal groove which contains the neurovascular bundle.

 

The angle is where the rib bends sharply forwards on its spiral towards the sternum. This also marks the lateral limit of attachment of the erector spinae muscles to the ribs.

 

Atypical ribs

 

First rib

 

The first ribs difference in it appearance compared to the other 11 ribs. It is small and is flattened from above downward rather than from front to back. Its head has only one facet for articulation with the T1 vertebra.

 

It is of important clinical relevance due to its anatomical relationship with a number of important structures, namely the lower nerves of the brachial plexus and the subclavian artery and vein which all run over the rib on their way to the upper limb.

 

The scalene anterior muscle is attached to upper surface and inner border of the 1st rib - the subclavian vein cross the 1st rib anterior to this muscle.

 

The subclavian artery and brachial plexus cross the rib posterior to anterior scalene muscle attachment and then run in contact with the bone on their way to the upper limb.

 

Second rib

 

This ribs appearance is more consistent with the typical ribs. Its main atypical feature is a roughened area on its upper surface, the tuberosity for serratus anterior, from which part of that muscle originates.

 

Tenth to Twelfth ribs

 

Like the first rib, they have only one facet on their heads and articulate with their numerically corresponding thoracic vertebrae only.

 

Eleventh and Twelfth ribs

 

These are short and have no neck of tubercles for articulation with vertebral transverse processes.

 

Thoracic vertebrae

 

The thoracic vertebrae consist of vertebral bodies, vertebral arches, spinal processes and transverse process.

Their characteristic features include:

 

Bilateral costal facets (demifacets) on their bodies, which articulate with the heads of the ribs.

 

Costal facets on their transverse process for articulation with the tubercles of ribs (except for the inferior two ribs).

 

Long inferior slanting spinous processes.

 

Costal Cartilages

 

These are pieces of cartilage connecting the end of the first seven ribs to the sternum, and the eighth to tenth ribs to the costal cartilage above.

The eleventh and twelfth ribs do not have a costal cartilage, these ribs end in the abdominal musculature.

These pieces of cartilage contribute greatly to the elasticity and mobility of the chest wall.

 

 

Joints

 

Manubrium to sternal body: Manubriosternal joint

A cartilaginous joint between the manubrium and the body of the sternum. It allows and small amount of movement during respiration.

 

Sternal body to xiphoid process: Xiphisternal joint

A cartilaginous joint between the xiphoid process (cartilage) and the body of the sternum. This joint usually fuses during middle age.

 

Sternum to costal cartilage: Sternocostal joints

•   This costal cartilage of the first rib articulates with the manubrium by a cartilaginous joint that allows no movement.

•   The second to seventh costal cartilages articulate to the lateral order of the sternum via synovial joints.

•   The sixth to tenth costal cartilages also articulate with each other via synovial joints along their borders.

•   The cartilages of the eleventh and twelfth ribs are embedded in the abdominal wall musculature.

 

Costal cartilage to ribs: Costochondral joints

These are cartilaginous joints which do not permit any movement.

 

Costovertebral joints

 

Head of ribs to vertebrae

The first rib and the three lowest ribs have a single synovial joint with the corresponding thoracic vertebra. The second to ninth ribs have their heads articulating via a synovial joint to their corresponding thoracic vertebra and the one above. This joints are strengthened by an intra-articular ligament.

 

Rib tubercles to vertebrae

These are synovial joint between the tubercle of the rib and their corresponding vertebra’s transverse process. The eleventh and twelfth ribs do not have this joint.

 

 

Bones	Joints	Muscles	Neurovascular
Sternum	Manubriosternal joint (secondary cartilaginous)	External intercostal	Intercostal arteries (anterior and posterior)
Clavicle	Xiphisternal joint (primary cartilaginous)	Internal intercostal	Intercostal veins (anterior and posterior)
Ribs	Sternocostal joints (1st: primary cartilaginous, 2nd-7th: synovial)	Innermost intercostal (transverse thoracis)	Intercostal nerves (anterior rami of first 11 thoracic spinal nerves)
Thoracic vertebrae	Costochondral joints (primary cartilaginous)
	Costovertebral joints (synovial)

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The chest wall is made up of numerous joints connecting the anterior sternum, lateral ribs and posterior vertebrae. The ribs and their costal cartilages are fixed to the sternum and are immobile. The joints of the ribs to the vertebrae allow movement so that the ribs can be raised and lowered during respiration.

 

The upper ribs movement up and down in a ‘pump-handle’ fashion. The lower ribs swing outwards in a ‘bucket-handle’ type movement.

 

The intercostal muscles run in varying directions so they can mobile the thoracic cage in different axises of movements. This, along with a more detailed look at the neurovascular bundled will be covered in subsequent sections.

Snell, R. S. (2004). Clinical Anatomy by Regions. 7th ed. United States of America: Lippincott Williand & Wilkins. p46-55.

Moore, K. L., Dalley, A. F. (2006). Clinically Orientated Anatomy. 5th ed. United States of America: Lippincott Williams & Wilkins. p77-79.