3D Skeletal System: Bones of the Thoracic Cage

Put your hands on your chest and take a deep breath. Feel how your chest expands? That's your thoracic cage—or rib cage, as it's more commonly known—pressing up against your hands. Without the thoracic cage, some of your body's most important organs would be unprotected, and your torso would be completely without shape. Imagine walking around with your lungs somewhere near your stomach and your shoulder girdle collapsing into itself. Not a pretty thought.

The thoracic cage, a flexible framework of bones and cartilage, is conical in shape. It is narrower at the top and broadens to fit and protect some critical organs of respiration and circulation—that is, the lungs and heart. The thoracic cage gives your upper torso structure. Women have smaller cages than men; the capacity is less, and the sternum is shorter and higher.

skeletal-system-thoracic-cage-frontImage from Human Anatomy Atlas.

Note the anterior view of the thoracic cage above: The front of the thoracic cage includes  seven pairs of vertebrosternal ribs (true ribs), which articulate with the sternum, an elongated flattened bone. There are also three pairs of vertebrochondral ribs (false ribs)—each false rib attaches to the cartilage of the rib directly above it.  

skeletal-system-thoracic-cage-backImage from Human Anatomy Atlas.

Take a posterior look at the thoracic cage and you’ll find another two pairs of ribs; these are the vertebral ribs (floating ribs).  Posteriorly, all 24 ribs articulate with vertebrae of the thoracic portion of the vertebral column.

Like anything else in the body, the ribs that make up the thoracic cage aren't blank curves of bone. The ribs are complex in their own right. Let's take a look!

Did you know?
The thoracic cage is part of the axial skeleton, which also includes the laryngeal skeleton, vertebral column, and skull. 


Anatomy of a Vertebrosternal Rib

The true ribs, false ribs, and floating ribs all have a head, neck, and shaft. All the ribs of the thoracic cage articulate with vertebrae and each has a costal groove for passage of the intercostal vessels and nerve. Looking at the 24 ribs together you might tend to think that the ribs differ only in size. But they differ in shape too. For the sake of expediency let’s look at the particular bony landmarks on the seventh vertebrosternal rib (the 7th true rib). It helps form the first section of the cage.

thoracic-cage-rib-7-landmarksRib 07 (R). Image from Human Anatomy Atlas.

Landmark

Characteristics

Shaft (orange)

The longest part of the bone; gives attachment to the intercostals, the external oblique, the iliocostalis lumborum and thoracics, levatores costarum muscles, and the serratus anterior

Tubercle (olive)

Eminence that articulates with the transverse process of T07

Neck (dark grey)

Attachment site for the anterior costotransverse ligament

Head (pink-orange)

Articulates with the bodies of T06 and T07, and acts as the attachment site for the interarticular ligament

Costal cartilage (neon green)

Cartilage that allows the ribs to move; attachment site for diaphragm, pectoralis major, rectus abdominis, and transversus thoracis

Costal groove (purple)

A groove on the inner part of the bone, through which the intercostal nerves and vessels pass

 

Thoracic Cage Anomalies

Cervical Rib

While most of us are born with 12 sets of ribs, it's not uncommon to have a normal variance or two. There is a chance, dear reader, that you may have more than the normal number of ribs.  Crazy, right? Supernumerary ribs can be a harmless variant in most cases, but in some it can cause issues.

A cervical rib is a normal variant. A cervical rib is a congenital disorder in which one extra rib arises before the first normal set of ribs (01). It is small and is often called a "neck rib" due to its location. A cervical rib is present in only 0.5% of the population and is more common in females than in males. In rarer cases, an individual can present an extra set of cervical ribs.

A cervical rib is usually asymptomatic, but in some cases it can cause thoracic outlet syndrome by compressing the brachial plexus or subclavian vessels. Symptoms include pain almost always, as well as discoloration of the hands, weakness of the hand or arm, and stiffness.

Short Rib

A short rib is not a clinically significant variant, and is thus named for when a mid-thoracic rib arch is shorter than it should be through no fault of trauma or surgery. A short rib occurs in approximately 16% of the population, and out of those instances, only 8% occur on the right side.

Funnel Chest

In contrast, pectus excavatum or funnel chest is a depression of the sternum, which causes the skin to be concave. In some cases, funnel chest is a cosmetic issue, but in others it can lead to impaired breathing, heart displacement, decreased heart density, and chest pain.

Now I want you to put your hands back on your chest and take a deep breath. Feel the 12 sets of bone expand against your fingers. If you ever get stuck on what it is your thoracic cage does, think of it as your body's police force: it shapes and protects.


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Related Posts:

3D Skeletal System: Atlas, Axis, and the Atlanto-Axial Relationship

3D Skeletal System: Function of the Sphenoid

3D Skeletal System: The Pelvic Girdle


Additional Sources:

Kurihara, Y. et al (1999). The ribs: Anatomic and radiologic considerations. Manuscript submitted for publication, Department of Radiology, St Marianna University School of Medicine, Kawasaki City, Kangawa, Japan.

Freyschmidt, J., Brossman, J., Wiens, J., & Sternberg, A. (2002). Koehler/zimmer's borderlands of normal and early pathological findings in skeletal radiography. (5th ed.). Germany: Thieme.