Bones and joints of the thoracic wall

Definitions & Key takeaways

The bones and joints of the thoracic wall play a vital role in protecting the heart, lungs, and other vital organs. The ribs attach to the spine in the back and flare out to form the rib cage. Ribs attach to the sternum by costal cartilages, which help to hold the ribs in place and absorb shocks. The sternum, or breastbone, is located in the center of the chest and forms the front of the rib cage. The clavicle, or collarbone, attaches the arm to the body and also helps to support the structure of the rib cage. Some of the joints in the chest include the costovertebral joints, the sternoclavicular joint, the sternocostal joints, and the xiphisternal joint.

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Introduction0:00–1:30

The thorax is the area between the neck and abdomen and consists of the thoracic cavity, its contents, and the walls that surround it.
The thoracic skeleton forms the osteocartilaginous thoracic cage that protects the thoracic viscera and some of the abdominal organs.
This skeleton is made up of the sternum, 12 pairs of ribs and associated costal cartilages, as well as 12 thoracic vertebrae and intervertebral discs interposed between them.
The ribs and costal cartilages form the largest part of the thoracic cage and both can be identified numerically, going from 1 to 12 for the ribs, and going from 1 to 10 for the costal cartilage, as ribs 11 and 12 do not have an associated costal cartilage.
Now, the true thoracic wall includes the thoracic cage and the muscles between the ribs and the skin, as well as subcutaneous tissue, muscles and fascia that cover its anterolateral aspect.
The structures that cover its posterior aspect are considered to belong to the back. Additionally, the mammary glands of the breasts lie within the thoracic wall subcutaneous tissue, and the anterolateral axioappendicular muscles are also considered part of the thoracic wall.
Okay, let’s start talking about the ribs, which form most of the thoracic cage. They’re curved, flat, lightweight, and highly resilient bones.

Ribs1:30–7:11

Each rib has a spongy interior that contains bone marrow or hematopoietic tissue which forms blood cells. There are three types of ribs based on their connection to the sternum: true, false, and floating ribs.
The true or vertebrosternal ribs are the first 7 pairs of ribs, and they attach directly to the sternum through their own costal cartilages.
The false or vertebrochondral ribs are the 8th, 9th, and usually the 10th pair of ribs, and their cartilages are connected to the cartilage of the rib above them.
Consequently, their connection to the sternum is indirect. The floating ribs or vertebral or free ribs are the 11th, the 12th pair of ribs, and sometimes the 10th pair of ribs.
The cartilages of these ribs don’t connect anteriorly to the sternum at all; instead they end up in the posterior abdominal musculature.
Ribs can further be classified as either typical or atypical ribs. Typical ribs are the 3rd through the 9th pair of ribs and have the following components: head, neck, tubercle, and body.
On a posterior view, the head of a typical rib is wedge shaped and has two facets - superior and inferior - that are separated by the crest of the head.
The inferior facet articulates with the numerically corresponding vertebra, and the superior facet articulates with the vertebra above it.
The neck connects the head with the body at the level of the tubercle. The tubercle, located at the junction of the neck and body, has a smooth articular part that connects with the corresponding transverse process of the vertebra and a rough nonarticular part where the costotransverse ligament attaches.
The body is thin, flat, and curved, especially at the costal angle, where the rib makes an anterolateral turn. This angle also demarcates the lateral limit of attachment of the deep back muscles to the ribs.
The internal surface of the body is concave and has a costal groove that’s parallel to the inferior border of the rib, which provides protection for the intercostal nerves and vessels at that level.
Now, the 1st, 2nd, 10th through 12th rib are atypical ribs because they are unlike the typical ribs in various ways. So, the 1st rib is the broadest, shortest, and most sharply curved of the seven true ribs.
Its body is the widest and is nearly horizontal. Its head has a single facet because it only articulates with the T1 vertebra, and its body has two transverse grooves crossing its superior surface for the subclavian artery and vein.
The grooves are separated by a scalene tubercle and ridge to which the anterior scalene muscle is attached. It also has a tubercle, which articulates with the transverse process of T1.
Now, the 2nd rib has a thinner and less curved body, and it’s longer than the 1st rib. Its main atypical feature is a rough area on its upper surface called the tuberosity for serratus anterior where the serratus anterior originates.
Its head has two facets for articulation with the bodies of T1 and T2 vertebrae. The 10 through 12th ribs, like the 1st rib, only have one facet on their heads and articulate with a single vertebra.
The 11th and 12th ribs are short and don’t have a neck or tubercle.Now, the head of each rib articulates with thoracic vertebrae via costovertebral joints, which are synovial plane joints.
Regarding ribs 2 through 9, the head of each rib articulates with the superior costal facet of the vertebral body of the same number and with the inferior costal facet of the vertebral body above it and to the intervertebral disc between them.
So, for example, the head of rib 4 articulates with the superior costal facet of the vertebral body of T4 and with the inferior costal facet of the vertebral body of T3 and with the intervertebral disc between those two vertebrae.
Unlike ribs 2 through 9, the 1st, 11th, 12th, and sometimes the 10th rib only articulate with a single vertebral body at the same vertebral level as the rib.
For example, rib 11 articulates with T11. Then there are the costotransverse joints, which are also synovial plane joints.
Regarding ribs 1 through 10, the tubercle of the rib articulates with the transverse process of the vertebra of the same number.
Ribs 11th and 12th don’t articulate with the transverse process of vertebrae of the same number. Now, let’s take a deep breath and play a fun game.

Quiz7:11–7:28

Let’s see if you can identify which atypical rib we’re showing in these images and what the structures are that form a typical rib.
Moving on to the sternum, which is a flat, elongated bone that forms the middle of the anterior part of the thoracic cage.

Sternum7:28–11:42

The sternum is the protector of the mediastinal viscera, especially the heart. It consists of three parts: manubrium, body, and xiphoid process.
Let’s now identify each structure and their components one by one in both anterior and lateral views. The manubrium is a trapezoidal bone and is the widest and thickest part of the sternum.
The jugular notch - or the suprasternal notch - is the superior and concave border of the manubrium and can be easily palpated.
The notch is deepened by the medial ends of the clavicles, which are much larger than the small clavicular notches in the manubrium found laterally on either side.
Now, the sternoclavicular joint is a saddle type of synovial joint and the joints formed between the ends of the clavicles and the clavicular notches of the manubrium as well as 1st costal cartilages.
Inferior and lateral to the clavicular notch, there’s the first sternocostal joint which is the costal cartilage of the 1st rib attached to the lateral border of the manubrium of the sternum, which is classified as a primary cartilaginous joint.
Between the manubrium and body of the sternum, there’s the manubriosternal joint, which is a secondary cartilaginous joint.
Now, the manubrium and body of the sternum lie in different planes superior and inferior to their junction. Because of this, their junction forms an angle called the angle of Louis - or the sternal angle - which you can see better in a lateral view.
The sternal angle is palpable and even visible in young individuals. The sternal angle lies at the level of T4-T5 intervertebral disc and the space between the 3rd and 4th thoracic spinous processes.
The sternal angle also marks the level of the 2nd pair of costal cartilages. Now, the left side of the manubrium is anterior to the arch of the aorta and its right side overlies the merging of the brachiocephalic veins to form the superior vena cava.
The superior vena cava then passes inferiorly deep to the manubrium and manubriosternal joint but it projects as much as a fingerbreadth to the right margin of the manubrium.The body of the sternum is longer, narrower, and thinner than the manubrium and is located roughly at the level of the T5 through T9 vertebrae.
Particularly, its width varies due to the scalloping of the lateral borders by the costal notches. Finally, the body of the sternum articulates with the costal cartilages of ribs 2 through 7 through synovial plane joints to form the rest of the sternocostal joints.
The xiphoid process is the smallest and most variable part of the sternum. It’s thin and elongated and its end lies at the level of T10 vertebrae.
Between the body of the sternum and the xiphoid process, there’s the xiphisternal joint, which is a primary cartilaginous joint.
The xiphoid process is important because the xiphisternal joint indicates the inferior limit of the central part of the thoracic cavity projected onto the anterior body wall.
This joint is also the site of the infrasternal angle or subcostal angle formed by the left and right costal margins. It’s also a midline marker for the superior limit of the liver, the central tendon of the diaphragm, and the inferior border of the heart.

Intercostal spaces11:42–12:12

Now let’s look at the big picture. So, there are 11 intercostal spaces that separate the ribs and their costal cartilages from one another.
The name of each intercostal space is according to the rib that forms the superior border of the space. For example, the 6th intercostal space is between ribs 6 and 7.
The space below the 12th rib doesn’t lie between any ribs, so it’s called the subcostal space. So at the end of the day, the thoracic cage forms a complete wall peripherally, but it’s open superiorly and inferiorly.

Thoracic apertures12:12–14:13

The superior thoracic aperture - or opening - is smaller and allows communication with the neck and upper limbs, while the inferior thoracic aperture is larger and provides the ring-like origin of the diaphragm which completely closes this opening.
The superior thoracic aperture is bounded posteriorly by T1 vertebra, with its body protruding anteriorly into the opening.
Laterally, there’s the first pair of ribs and their costal cartilages. Anteriorly, there’s the superior border of the manubrium.
Structures that pass through the superior thoracic aperture include the trachea, esophagus, nerves, and vessels that supply and drain the head, neck, and upper limbs.
The inferior thoracic aperture is bounded posteriorly by the 12th thoracic vertebra, and the body of this vertebra also protrudes anteriorly into the opening.
Posterolaterally, there are the 11th and 12th pair of ribs. Anterolaterally, there are the joined costal cartilages of ribs 7 through 10 forming the costal margins.
Anteriorly, there’s the xiphisternal joint. The diaphragm closes the inferior aperture and separates the thoracic and abdominal cavities almost completely.
The structures that pass to and from the thorax to the abdomen pass through openings that traverse the diaphragm such as the esophagus and inferior vena cava; or pass posterior to the diaphragm, like the aorta.

Quiz14:13–14:28

In this image, can you identify the borders of the superior thoracic aperture? How about the inferior thoracic aperture?
Finally, the thoracic wall with all its bones and joints are essential during respiration, along with the diaphragm. They increase or decrease the intrathoracic volume and diameters of the thorax, resulting in changes of pressure.

Respiration14:28–16:21

During expiration, the diaphragm, intercostal muscles, and other muscles relax, reducing the diameter of the thoracic wall and increasing intrathoracic pressure to expel air from the lungs.
During inspiration, the vertical dimension of the thoracic cavity increases as contraction of the diaphragm causes it to descend inferiorly into the abdominal cavity.
The AP dimension of the thorax also changes considerably during inspiration as the intercostal muscles contract. During intercostal contraction, the costotransverse joints of ribs 1-7 move around an axis passing through the neck of the ribs, causing the anterior sternal ends of the ribs to rise to create a ‘pump-handle’ movement.
Additionally, the transverse dimension of the thorax also increases during inspiration as contraction of the intercostal muscles raises the middle, lateral most parts of the lateral lower ribs to create a ‘bucket-handle’ movement, made possible by the 8-10th costotransverse joints having flat articular surfaces which allow gliding.
These combinations of movements allow the thoracic cage to move anteriorly, superiorly, and laterally to accommodate air inflow during inspiration.

Review16:21–18:32

##SummaryAll right, as a quick recap, the thoracic wall includes the thoracic cage and the muscles between the ribs and the skin, as well as subcutaneous tissue, muscles, and fascia that covers its anterolateral aspect.
Of the 12 pairs of ribs, the first 7 pairs are true ribs and they attach directly to the sternum through their own costal cartilages.
The 8th, 9th, and usually the 10th rib are false and their cartilages are connected to the cartilage of the rib above them.
The 11th and 12th pair of ribs are floating ribs and they’re not connected to the sternum. The 3rd through 9th pair of ribs are typical ribs.
The 1st, 2nd, and 10 through 12th ribs are atypical. The sternum has three parts: manubrium, body, and xiphoid process.
The manubrium has a jugular notch, clavicular notches, and between the manubrium and body of the sternum is the manubriosternal joint.
At this level, there’s the sternal angle, which lies at the level of the T4-T5 intervertebral disc and marks the level of the 2nd pair of costal cartilages.
The xiphoid process lies at the level of T10 vertebrae. The ribs and their costal cartilages are separated from one another by the 11 intercostal spaces, and each space gets its name from the rib that forms the superior border of the space.
The superior thoracic aperture allows passage of structures between the thorax and the neck, while the inferior thoracic aperture is bounded inferiorly by the diaphragm and is where structures pass to and from the abdomen.
Finally, during forced inspiration, the thoracic cage increases its vertical height through diaphragmatic contraction, the antero-posterior diameter of the thoracic wall through a pump-handle movement, and the transverse diameter through