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Sternum

Bony elements of the sternum.

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Transcript

There is a bone in the center of our chest right in front of the rib cage which has a shape of a sword. Can you guess what bone that is? Well, yes, it's the sternum. So, today, my friends, we are going to then dedicate this tutorial to this very important bone of the human body and learn everything about its anatomy. We will cover the overall anatomy and major features of the sternum.

So, first, we will look at the three parts of the sternum which are the manubrium, the sternal body, and the xiphoid process. Then we'll look at articulations that join these parts together which are then the sternal angle and the xiphisternal junction. Then we will look at the bony landmarks unique to the manubrium and the sternal body.

On the manubrium, we will look at the suprasternal notch. We're going to be seeing these structures called clavicular notches, also the first costal notch, the second costal notch, and the sternal body features many notches for the ribs to then connect to the sternum. Each notch is named after the number of the rib so there is a third costal notch, a fourth costal notch, a fifth, a sixth, and a seventh costal notch. And at the end of this tutorial, we will also include some clinical notes connected to the sternum. Now before we explore all those elements in great detail, let's start by looking at the sternum as a whole.

So, this is the skeleton as if we were standing in front of a person. You can see the sternum here highlighted in green which is this long, flat bone in the front part of the rib cage. These are the ribs and this is the spine. Note here that the sternum joins the right and left ribs to then complete the rib cage and provides a base for the pectoral girdle. Like I mentioned before, the sternum is made up of three parts – so there is the manubrium, the sternal body and the xiphoid process, and each of these structures have their own set of unique characteristics. Let's look at each part individually. We'll start with the most superior portion of the sternum – the manubrium.

We are now looking at an isolated sternum both from the right side which is the image on the far right, and from the front which is the image on the left. Keep in mind that manubrium is Latin for "handle or hilt". If you look at it, it somewhat resembles a triangle when viewed from the front. The tip of the triangle points down and its base is in line with the two clavicles. At the center of the base, there is a small depression and this is then the suprasternal or jugular notch. On either side of the suprasternal notch, there are two smaller notches called the clavicular notches. The clavicular notches are then the contribution of the sternum to then the sternoclavicular joints. Here, each clavicle articulates with the sternum to then support and stabilize the shoulder joint.

We've backed away to look at the sternoclavicular joint along with the thorax. The clavicle attaches to the scapula at the acromioclavicular joint but the scapula itself has no bony attachments to any other part of the axial skeleton and besides the clavicle, it is only attached by some of the muscles in your back. This means the only joint holding your arm to the rest of your body is the sternoclavicular joint. Don't worry, though, this joint is reinforced with several ligaments and a strong joint capsule to hold it together.

Now, let's isolate the sternum again to look at costal notches. Costal notches are depressions marking articulations with the ribs. This first costal notch is on the manubrium directly below the clavicular notches and it articulates with the first rib. The second costal notch is below the first costal notch near the tip of the manubrium. The second rib articulates with the sternum at the junction between the manubrium and sternal body so there is a depression on each part of the sternum to then accommodate the rib.

Now, the junction between the sternal body and manubrium has a special name. It is called the sternal angle and is sometimes also known as the manubriosternal junction or angle of Louis. Here, we can see it both from the front and from the side. The sternal angle can be palpated in the center of your chest. It feels like a small horizontal ridge usually about one or two inches long or two point five to five centimeters.

The sternal angle, if you're in the Health Sciences, is an important medical landmark. It marks an imaginary transverse line between the second sternocostal joint and the intervertebral disc between T4 and T5 vertebrae. This plane separates the superior mediastinum from the inferior mediastinum.

Now, let's move on to another part of the sternum. We're going to be talking about the body. The sternal body highlighted in green now on the image is the middle part of the sternum. It is relatively flat and rectangular in shape and is formed by the fusion of two fetal cartilage models. The majority of the true ribs articulate with the sternal body through individual costal notches – and there is lots of them. The third costal notch is the most superior notch that is completely on the sternal body. The costal cartilage of the third rib articulates here.

The costal cartilage of the fourth rib articulates with then the fourth costal notch then we're going to see that the costal cartilage of the fifth rib articulates with the fifth costal notch. A bit further down, we find that the costal cartilage of the sixth rib articulates with the sixth costal notch. And, lastly, the costal cartilage of the seventh rib articulates with the seventh costal notch.

Now that we've looked at all the notches, let's take a closer look at the sternocostal joint. Now, this is a close-up view of the joints between the ribs and sternum. The sternum does not articulate directly with the ribs. Rather, they are attached by a square or rectangle-shaped costal cartilage. This feature gives the sternocostal joints the ability to stretch slightly as the rib cage expands during breathing.

We're going to move a bit further down. It is time for us to talk about the xiphoid process of the sternum. Below the sternal body, you can see that the sternum features a small bony projection. This is then the xiphoid process. And the xiphoid process is very thin and projects inferiorly and it typically ossifies in late childhood. The junction between the sternal body and the xiphoid process is then called the xiphisternal junction. This is a delicate connection and is frequently broken during CPR.

Now that we covered the anatomy of the sternum, it is time for us to look at two conditions that make this bone significant in a clinical setting. The sternal body is formed by the fusion of multiple smaller pieces of cartilage. The pieces of cartilage join in fetal development but do not completely fuse until after birth. Sometimes, parts of the cartilage do not fuse at all and will leave a small hole in the sternum. This is what we call sternal foramen. The sternal foramen is most frequently seen in a sternal body but can sometimes be located in the manubrium. Although it usually asymptomatic, a sternal foramen can cause complications in medical procedures if the variation has not been noted beforehand.

The costal cartilages between the ribs and body of the sternum can become infected. This is referred to as costochondritis. The infection causes pain in the anterior chest wall especially during repetitive activities even breathing. This is commonly found in patients over forty years of age who go to the emergency room for chest pains. Treatments include anti-inflammatory drugs and physical therapy. Although this condition typically resolves on its own, pain can last from several months to a year.

Now that we're done with clinical notes as well, we are going to summarize what we just learned before we finish this tutorial. In this tutorial, we looked at the sternum, and the sternum is a flat, sword-shaped bone in front of the rib cage. It is made up of three parts. The manubrium is the most superior portion of the sternum, the sternal body is the middle part where most of the ribs attach, and the xiphoid process which is a small piece of bone projecting off the bottom of the sternal body.

The three parts of the sternum are then connected by special junctions. The sternal angle joins the manubrium and the sternal body. The xiphisternal junction joins the sternal body and the xiphoid process. We also saw that each part of the sternum has a unique set of bony landmarks. The manubrium features a small depression at the middle of the top margin of the manubrium called the suprasternal notch.

The clavicular notches on either side of the suprasternal notch form a joint with the clavicles. The first costal notch is the attachment site of the first rib and the second costal notch is the attachment site for then the second rib. The sternal body features many notches for the rest of the true ribs, so there is a third costal notch, fourth costal notch, a fifth one, a sixth, and, finally, a seventh costal notch.

Now we have reached the end of our tutorial on the sternum. Thank you very much for watching and I hope to see you on the next video.

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