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What is the Costal Margin?

Mary McMahon
Updated Mar 03, 2024
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The costal margin is the cartilage along the edge of the eighth through tenth ribs in the middle of the chest. It marks the lower portion of the chest and the location of the diaphragm. This cartilage allows these ribs, which do not come into contact with the sternum, to articulate rather than float in the chest cavity, protecting the heart and lungs from physical impact. People can feel the costal margin by locating the base of the sternum and moving down and to the side to find the costal cartilage.

Locating the costal margin can be important for some surgical procedures, and it is one of the points of orientation people can use to locate the positions of the bones in the torso. The cartilage marks two sides of the triangular space at the bottom of the rib cage, with the base of the triangle indicating the divide between the upper and lower chest. A related medical term some people may find useful is the costal angle, the term describing the angle between the two costal margins.

This is part of the body's medial anatomy, the structures falling roughly in the middle of the body. Doctors may need to access the costal margin for some surgical procedures, and it can provide an anchoring point for the use of surgical retractors to expose areas of interest in the chest and abdomen during open surgeries.

The ribs attached to the costal margin are known as the false ribs because they do not connect directly with the sternum; they form part of the protective network of bone known as the rib cage. The costal cartilage connects with the true ribs to reinforce the false ribs and make sure they remain in a stable position. Just below them lie the 11th and 12th ribs, the floating ribs. These ribs do not articulate at the front of the body, attaching only to the spinal column.

Medical problems with the costal margin and attached ribs can include rib fractures, deformities, and displacement. These are usually evident on an x-ray of the chest, and the approach to treatment can vary depending on the nature of the problem. Setting and casting fractures of the ribs is challenging because the ribcage needs a high degree of flexibility. Immobilizing the ribs to allow fractures to heal is not an option, as the patient would not be able to breathe.

The Health Board is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a The Health Board researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments
By croydon — On Dec 06, 2011

@browncoat - Anyone who seriously considers taking out ribs in order to look skinnier has a serious problem with body dysmorphic disorder, in my opinion.

But I can see why waist training, done within reason, could appeal. I don't think it affects the ribs or the costal margin much unless you take it to extremes.

And you really wouldn't want to take it to extremes. Fiddling with the ability of the chest and ribs to expand was the reason women were always fainting back when corsets were popular. It just completely wrecks your lungs if you don't give them the space that the rib cage usually provides.

And I can't even imagine what it would be like to get the hiccups if you couldn't fully expand your diaphragm.

By browncoat — On Dec 06, 2011

@indigomoth - That's right, I've heard that waist training can damage the rib cage as well. I've also heard rumors that certain celebrities have had surgery to remove the costal margin altogether, in order to make a smaller waist.

These rumors always turn out to be false though. I don't think people realize that you can't just take out a rib, just like that. It's a piece of bone and it's there for a reason.

And the costal margin basically adds to your entire body shape. Removing it, you could end up in serious medical trouble. Not to mention it would leave a terrible scar.

By indigomoth — On Dec 05, 2011

The costal margin is one of the areas that gets modified when you have whats called waist training. This is when you wear a properly fitted corset for hours every day, lacing it a bit tighter every now and then, in order to "train" your waist to get smaller.

It's supposed to slightly mimic what happens when you get pregnant and all your organs get pushed up by the uterus. Except they get pushed up by your smaller waist.

Of course, with the ribs and cartilage growing closer together, you end up with all kinds of problems and they say that you can more easily fracture your ribs as well.

There are people who say that its healthy if not taken too far, but personally, I'd rather stick with the waist I've got.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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